WO2002034781A1

WO2002034781A1 - Human g-protein coupled diadenosine tetraphosphate receptor (ap4ar)

Info

Publication number: WO2002034781A1
Application number: PCT/EP2001/011953
Authority: WO
Inventors: Claudia Berger; Martin Th. M. Tulp; Randen Jan Van
Original assignee: Solvay Pharmaceuticals Gmbh
Priority date: 2000-10-20
Filing date: 2001-10-16
Publication date: 2002-05-02
Also published as: AU2002221685A1

Abstract

The present invention relates to the identification of the first specific diadenosine tetraphosphate receptor (hereinafter referred to as AP4A-receptor; AP4AR) which is a G-protein coupled receptor, and in particular the invention relates to the use of this receptor in drug discovery with respect to certain dysfunctions or diseases, and furthermore to the drugs that play a role in preventing, ameliorating or correcting said dysfunctions or diseases. In this context also described are AP4AR-polynucleotides, AP4AR-polypeptides encoded by them, and the use of such polynucleotides and polypeptides, and their production. The invention also relates to inhibiting or activating the action of such polynucleotides and polypeptides, to a vector containing said polynucleotides, a host cell containing such vector and transgenic animals where the AP4ARgene is either overexpressed, misexpressed, underexpressed or suppressed (knock-out animals). The invention further relates to a method for screening compounds capable to act as an antagonist of said G-protein coupled receptor AP4AR or which modulate the activity of said G-protein coupled receptor AP4AR, and to the cognate ligand of AP4AR. Furthermore, the invention relates to the treatment and/or prophylaxis of a dysfunction or disorder associated with the cardiovascular system, the central nervous system and/or the glucose or insulin metabolism, preferably to the treatment and/or prophylaxis of a dysfunction or disorder associated with the cardiovascular system, including the heart, in the nervous system, including the central nervous system, and also in glucose and insulin metabolism, and furthermore in immunological diseases and disorders of the genitourinary system. Dysfunctions or disorders associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

Description

Human G-protein Coupled Diadenosine Tetraphosphate Receptor (AP4AR)

Description

The present invention relates to the identification of the first specific diadenosine tetraphosphate receptor (hereinafter referred to as AP4A-receptor; AP4AR) which is a G-protein coupled receptor, and in particular the invention relates to the use of this receptor in drug discovery, preferably with respect to certain dysfunctions or diseases, and furthermore to the drugs that play a role in preventing, ameliorating or correcting said dysfunctions or diseases, in this context also described are AP4AR-polynucleotides, AP4AR-polypeptides encoded by them, and the use of such polynucleotides and polypeptides, and their production. The invention also relates to inhibiting or activating the action of such polynucleotides and polypeptides, to a vector containing said polynucleotides, a host cell containing such vector and transgenic animals where the AP4AR-gene is either overexpressed, misexpressed, underexpressed or suppressed (knockout animals). The invention further relates to a method for screening compounds capable to act as an agonist or an antagonist of said G-protein coupled receptor AP4AR, or which modulate the activity of said G-protein coupled receptor AP4AR, and to the cognate or endogenous ligands of AP4AR, and to the use of these ligands in treating, preventing, ameliorating or correcting said dysfunctions or diseases related to the activities of IGS2 in relation to their specific endogenous ligands.

BACKGROUND OF THE INVENTION

Diadenosine tetraphosphate is a known endogenous substance or ligand which plays a major role in several dysfunctions or diseases, but for which the natural receptor has not yet been identified, heretofore. Such endogenous substances which qualify as a potential receptor ligand, but for which the specific receptor is yet unknown, are called "orphan ligands". The orphan ligand diadenosine tetraphosphate, hereinafter referred to as AP4A, is known to be in particular involved in the cardiovascular system, including the heart, in the nervous system, including the central nervous system, and also in glucose and insulin metabolism, and furthermore in immunological diseases and disorders of the genitourinary system.

With regard to diadenosine tetraphosphate a number of publications exist, some of which are referenced as representative literature below, and which are incorporated by reference herein.

Diadenosine polyphosphates, including diadenosine tetraphosphate (AP4A), are members of a group of dinucleoside polyphosphates that are ubiquitous, naturally occurring molecules. They form a recently identified class of compounds derived from ATP and consist of two adenosine molecules bridged by up to six phosphate groups. These compounds are stored in high concentrations in platelet dense granules and are released when platelets become activated. Some of the compounds promote platelet aggregation, while others are inhibitory. Possible roles as neurotransmitters, extracellular signalling molecules or 'alarmones' secreted by cells in response to physiologically stressful stimuli have been postulated. Recent studies suggest a role for these compounds in atrial and synaptic neurotransmission. Studies using isolated mesenteric arteries indicate an important role of phosphate chain length in determining whether diadenosine polyphosphates produce vasodilation or vasoconstriction, but in the coronary circulation, diadenosine polyphosphates generally produce vasodilation via mechanisms thought to involve release of NO or prostacyclin (PGI2). They produce cardiac electrophysioiogical effects by altering ventricular refractoriness at submicromoiar concentrations and reduce heart rate. Mechanisms involving KATP channels have been proposed in addition to the involvement of P1- and P2- purinergic receptors and the specific diadenosine polyphosphate receptor identified on isolated cardiac myocytes. Clinical evidence suggests a role for diadenosine polyphosphates in hypertensive patients and those with the Chediak-Higashi syndrome.

The particular effects of diadenosine polyphosphates on the cardiovascular system were reported in a review by Flores, N.A., et al. (Cardiovasc. Res. 1999 Apr.;42(1): 15-26) which outlines the effects of diadenosine polyphosphates on the cardiovascular system and considers their potential involvement in mediating the pathophysiological effects associated with platelet activation during myocardial ischaemia. Clinical application of diadenosine tetraphosphate (Ap4A:F-1500) for controlled hypotension were reported by Kikuta, Y., et al. (Acta Anaesthesiol. Scand. 1999 Jan;43(1):82-6). The authors revealed in an animal study that diadenosine tetraphosphate (AP4A) has a dose-dependent hypotension effect of up to 60% decrease in mean arterial pressure compared to control value. Furthermore, in healthy male volunteers, the safety of AP4A up to 4 mg.min-1 was confirmed. In patients who require surgical procedures under general anesthesia together with controlled hypotension, hypotension was induced by AP4A in order to examine its hypotensive effect and modulating action on the blood pressure. As it produces an excellent hypotensive effect together with a modulating action on blood pressure, AP4A was assessed as useful in producing controlled hypotension.

The cardioprotective effect and mechanism of diadenosine tetraphosphate (AP4A) and ischemic preconditioning in rat hearts was reported also previously, as well as the applicability of AP4A administration to cardiac surgery was tested by using a canine cardiopulmonary bypass model (Ahmet, I., et al., Ann. Thorac. Surg. 2000 Sep, 70(3):901-5; and Ahmet, I., et al., Basic Res. Cardiol. 2000 Jun;95(3):235-42)). Administration of AP4A was shown to be cardioprotective without apparent adverse effects. Because the cardioprotective mechanism may be similar to that of ischemic preconditioning, the addition of AP4A into cardioplegia may be a novel safe' method for clinical application of preconditioning cardioprotection. Preischemic administration of diadenosine tetraphosphate (AP4A) has also been shown to be cardioprotective, when used as a cardioplegic adjuvant in isolated rat hearts (Ahmet, I., et al., Heart Vessels 2000;15(1):30-4). The contributions of the ATP-sensitive potassium channel (K ATP channel), adenosine receptor (AR), and purine 2y receptor (P2yR) to the effect of AP4A were also tested. The addition of AP4A into the cardioplegia solution led to an added cardioprotective effect, either by opening the K ATP channel or by activating P2yR.

Furthermore it is known that diadenosine polyphosphates can cause contraction and relaxation in isolated rat resistance arteries (Steinmetz, M., et al., J. Pharmacol. Exp. Ther. 2000 Sep;294(3): 1175-81). Investigations on the influence of purinoceptor antagonism on diadenosine pentaphosphate-induced hypotension in anesthetized rats (Steinmetz, M., et al., J. Pharmacol. Exp. Ther. 2000 Sep;294(3):963-8) have proven diadenosine polyphosphates (APnA) as potent vasoactive agents in isolated vessels. Information on effects of APnA in vivo is still limited despite the fact that these compounds are starting to be used in humans, and studies showed the effects of APnA and their possible metabolites on blood pressure in vivo and the functional involvment of purinoceptors in their action. In summary, the systemic cardiovascular effects of APnA, including AP4A, are hypotensive, also making them candidates for blood pressure reduction in humans. These effects are fast in onset and easily reversible.

Effects of diadenosine tetraphosphate (AP4A) and other related diadenosine polyphosphates on smooth muscle cells from porcine aorta were examined (Schlatter, E., Ceil Physiol Biochem 2000; 10(3): 125-34). From experimental results it was concluded that diadenosine polyphosphates activate predominantly a Ca(2+)-dependent K(+)-conductance in smooth muscle cells obtained from porcine aorta most likely mediated via P2Y-purinoceptors and possibly partially also by AP4A receptors.

Further publications of interest in the context of the present invention are Schlϋter, H., et al., pertaining to diadenosine phosphates and the physiological control of blood pressure (Nature, Vol. 367, 1994, 186-188); Knapp, J., et al., pertaining to inositol-1 ,4,5-trisphosphate increase by diadenosine tetraphosphate in preparations from failing human myocardium (Naunyn- Schmiedeberg's Arch. Pharmacol. (1999) 360: 354-357) in which the increased force of contractions by administering AP4A is described, as well as other effects of AP4A on the myocardium.

Diadenosine tetraphosphate (AP4A), amongst others, is stored in and released from rat brain synaptic terminals (Emanuelli, T., et al., Braz. J. Med. Biol. Res. 1998 Dec;31 (12): 1529-32). This shows that AP4A may also play an important role in central nervous system (CNS).

Diadenosine polyphosphates, such diadenosine tetraphosphate (AP4A), were recently also proposed to participate in the stimulus-secretion coupling for nutrient-stimulated insulin release. Since NaF, an inhibitor of inorganic pyrophosphatase, was reported to lower A2P4 content in glucose-stimulated pancreatic islets, its effects upon metabolic, cationic, biosynthetic and secretory variables in rat pancreatic islets were investigated (Courtois, P., et al., Int. J. Mol. Med. 2000 May;5(5):493-503). Stimulatory effect of exogenous diadenosine tetraphosphate on insulin and glucagon secretion in the perfused rat pancreas were investigated by Silvestre, R.A., et al. (Br. J. Pharmacol. 1999 Oct;128(3):795-801). Diadenosine tetraphosphate (AP4A) is released by various cells (e.g. platelets and chromaffin cells), and may act as extracellular messengers. In pancreatic B-cells AP4A is an inhibitor of the ATP-regulated K+ channels, and glucose increases intracellular levels of AP4A. Therefore the effect of exogenous AP4A was studied on insulin and glucagon secretion by the perfused rat pancreas. AP4A induced a prompt, short-lived insulin response (approximately 4 fold higher than basal value; P<0.05) in pancreases perfused at different glucose concentrations (3.2, 5.5 or 9 mM). AP4A-induced insulin release was abolished by somatostatin and by diazoxide. Therefore AP4A shows capacity to activate ATP-dependent K+ channels, suggesting that these channels are a potential target for AP4A in the B-cell. Further results (AP4A stimulated glucagon release at both 3.2 and 5.5 mM glucose; this effect was abolished by somatostatin) suggest that extracellular AP4A may play a physiological role in the control of insulin and glucagon secretion.

In particular in view of the highly interestin physiological and potential pharmacological properties of adenosine tetraphosphate (AP4A) there is a strong objective to identify the corresponding specific AP4A-receptor, in particular in order to enable the drug discovery process for screening lead compounds and for designing also non-diadenosine polyphosphate synthetic organic drugs with AP4A-activity.

Although a number of receptor classes exist in humans, by far the most abundant and therapeutically relevant is represented by the G protein-coupled receptor (GPR or GPCR) class. Within the human genome, about 2,000 genes are estimated to code for GPCRs. Receptors, including GPCRs, for which the endogenous ligand has been identified are referred to as "known" receptors, while receptors for which the endogenous ligand has not been identified are referred to as "orphan" receptors. GPCRs represent an important area for the development of pharmaceutical products.

It is well established that many medically significant biological processes are mediated by proteins participating in signal transduction pathways that involve G-proteins and/or second messengers; e.g., cAMP (Lefkowitz, Nature, 1991, 351:353-354). Herein these proteins are referred to as proteins participating in pathways with G-proteins. Some examples of these proteins include the GPC receptors, such as those for adrenergic agents and dopamine (Kobilka, B.K., et al., Proc. Natl. Acad. Sci., USA, 1987, 84:46-50; Kobilka, B.K., et al., Science, 1987, 238:650-656; Bunzow, J.R., et al., Nature, 1988, 336:783-787), G-proteins themselves, effector proteins, e.g., phospholipase C, adenyl cyclase, and phosphodiesterase, and actuator proteins, e.g., protein kinase A and protein kinase C (Simon, M.I., et al., Science, 1991, 252:802-8). For example, in one form of signal transduction, upon hormone binding to a GPCR the receptor interacts with the heterotrimeric G-protein and induces the dissociation of GDP from the guanine nucleotide-binding site. At normal cellular concentrations of guanine nucleotides, GTP fills the site immediately. Binding of GTP to the α subunit of the G-protein causes the dissociation of the G-protein from the receptor and the dissociation of the G-protein into α and βγ subunits. The GTP-carrying form then binds to activated adenylate cyclase. Hydrolysis of GTP to GDP, catalyzed by the G-protein itself (α subunit possesses an intrinsic GTPase activity), returns the G- protein to its basal, inactive form. The GTPase activity of the α subunit is, in essence, an internal clock that controls an on/off switch. The GDP bound form of the α subunit has high affinity for βγ and subsequent reassociation of αGDP with βγ returns the system to the basal state. Thus, the G- protein serves a dual role, as an intermediate that relays the signal from receptor to effector (in this example adenylate cyclase), and as a clock that controls the duration of the signal.

The membrane bound superfamily of G-protein coupled receptors has been characterized as having seven putative transmembrane domains. The domains are believed to represent transmembrane α-helices connected by extracellular or cytoplasmic loops. G-protein coupled receptors include a wide range of biologically active receptors, such as hormone, viral, growth factor and neuroreceptors.

The G-protein coupled receptor family includes dopamine receptors which bind to neuroleptic drugs used for treating CNS disorders. Other examples of members of this family include, but are not limited to calcitonin, adrenergic, neuropeptide Y, somastotatin, neurotensin, neurokinin, capsaicin, VIP, CGRP, CRF, CCK, bradykinin, galanin.-motiiin, nociceptin, endothelin, cAMP, adenosine, muscarinic, acetylcholine, serotonin, histamine, thrombin, kinin, follicle stimulating hormone, opsin, endothelial differentiation gene-1, rhodopsin, odorant, and cytomegalovirus receptors.

G-protein coupled receptors share a common structural motif. All these receptors have seven sequences of between 22 to 24 hydrophobic amino acids that form seven alpha helices, each of which spans the membrane (each span is identified by number, i.e. transmembrane-1 (TM1), transmembrane-2 (TM2), etc.). The transmembrane helices are joined by strands of amino acids between TM2 and TM3, TM4 and TM5, and TM6 and TM7 on the exterior, or "extracellular" side, of the cell membrane (these are referred to as "extracellular" regions 1 , 2 and 3 (EC1 , EC2 and EC3), respectively). The transmembrane helices are also joined by strands of amino acids between TM1 and TM2, TM3 and TM4, and TM5 and TM6 on the interior, or "intracellular" side, of the cell membrane (these are referred to as "intracellular" regions 1, 2 and 3 (IC1, IC2 and IC3), respectively). The "carboxy" ("C") terminus of the receptor lies in the intracellular space within the cell, and the "amino" ("N") terminus of the receptor lies in the extracellular space outside of the cell. Most G-protein coupled receptors have single conserved cysteine residues in each of the first two extracellular loops which form disulfide bonds that are believed to stabilize functional protein structures. The 7 transmembrane regions are designated as TM1 , TM2, TM3, TM4, TM5, TM6 and TM7. The cytoplasmic loop which connects TM5 and TM6 may be a major component of the G- protein binding domain.

Most G-protein coupled receptors contain potential phosphoryiation sites within the third cytoplasmic loop and/or the carboxy terminus. For several G-protein coupled receptors, such as the β-adrenoreceptor, phosphoryiation by protein kinase A and/or specific receptor kinases mediates receptor desensitization.

Recently, it was discovered that certain GPCRs, like the calcitonin-receptor like receptor, might interact with small single pass membrane proteins called receptor activity modifying proteins (RAMP's). This interaction of the GPCR with a certain RAMP is determining which natural ligands have relevant affinity for the GPCR-RAMP combination and regulate the functional signaling activity of the complex (McLathie, L.M. et al., Nature (1998) 393:333-339).

For some receptors, the ligand binding sites of G-protein coupled receptors are believed to comprise hydrophilic sockets formed by several G-protein coupled receptor transmembrane domains, said sockets being surrounded by hydrophobic residues of the G-protein coupled receptors. The hydrophilic side of each G-protein coupled receptor transmembrane helix is postulated to face inward and form a polar ligand-binding site. TM3 has been implicated in several G-protein coupled receptors as having a ligand-binding site, such as the TM3 aspartate residue. TM5 serines, a TM6 asparagine and TM6 or TM7 phenylalanines or tyrosines are also implicated in ligand binding.

G-protein coupled receptors can be intracellularly coupled by heterotrimeric G-proteins to various intracellular enzymes, ion channels and transporters (see, Johnson et al., Endoc. Rev., 1989, 10:317-331). Different G-protein -subunits preferentially stimulate particular effectors to modulate various biological functions in a cell. Phosphoryiation of cytoplasmic residues of G- protein coupled receptors has been identified as an important mechanism for the regulation of G- protein coupling of some G-protein coupled receptors. G-protein coupled receptors are found in numerous sites within a mammalian host.

Receptors - primarily the GPCR class - have led to more than half of the currently known drugs (Drews, Nature Biotechnology, 1996, 14: 1516). This indicates that these receptors have an established, proven history as therapeutic targets. The AP4A GPCR described in the context of this invention below clearly satisfies a need in the art for identification and characterization of further receptors that can play a role in diagnosing, preventing, ameliorating or correcting a broad range of dysfunctions, disorders, or diseases.

As already described above, diadenosine tetraphosphate is an endogenous orphan ligand that may play an important physiological role. However, the progressively accumulated knowledge on diadenosine tetraphosphate (AP4A) has so far resulted in only rather modest contribution in the field of therapeutic applications, as the relation of AP4A orphan ligand to its particular receptor was not yet known hitherto. It can be anticipated that there is a need to further develop novel classes of therapeutic agents with potential applications in dysfunctions, disorders, or diseases to which reference is made herein in the context of the relation of the AP4A ligand to the AP4A receptor, and to provide such compounds that will be useful to alleviate said dysfunctions, disorders or diseases in the foreseeable future.

From the above it is clearly evident that there is not only a need for identification of further receptors, in particular of further G-protein coupled receptors, but in particular also for characterization of receptors which can play a role in preventing, ameliorating or correcting dysfunctions or diseases. One of the most important characteristics to be elucidated for a receptor, in particular for an "orphan" receptor, that is a receptor for which the cognate or endogenous ligand is unknown, pertains to the identification of the respective endogenous ligand. Thus, as on the one hand the receptor, on the other hand the endogenous ligand of a receptor also plays a major physiological role. Knowledge of the endogenous ligand of a specific receptor therefore is a valuable characteristic of such a receptor, including but not limited for further enabling research for agonists, antagonists or modulators of said receptor.

Generally, when an endogenous ligand binds with the receptor (often referred to as "activation" of the receptor), there is a change in the conformation of the intracellular region that allows for coupling between the intracellular region and an intracellular "G-protein". It has been reported that GPCRs are "promiscuous" with respect to G proteins, i.e., that a GPCR can interact with more than one G protein (see, Kenakin, T., 43 Life Sciences 1095 (1988)). Although other G- proteins exist, currently, Gq, Gs, Gi, Gz and Go are G-proteins that have been identified. Endogenous ligand-activated GPCR coupling with the G-protein begins a signalling cascade process (referred to as "signal transduction"). Under normal conditions, signal transduction ultimately results in cellular activation or cellular inhibition. It is thought that the third intracellular (1C3) loop as well as the carboxy terminus of the receptor interact with the G protein.

Under physiological conditions, GPCRs exist in the cell membrane in equilibrium between two different conformations: an "inactive" state and an "active" state. A receptor in an inactive state is unable to link to the intracellular signalling transduction pathway to produce a biological response. Changing the receptor conformation to the active state allows linkage to the transduction pathway (via the G-protein) and produces a biological response. A receptor may be stabilized in an active state by an endogenous ligand or a compound such as a drug.

SUMMARY OF THE INVENTION

Particular aspects of the invention are defined in the claims. Furthermore the various aspects of the invention described hereiafter are particularly exemplified by the examples and figures for further understanding.

In a first aspect the invention relates to the identification of the G-protein coupled receptor which specifically binds the endogenous ligand diadenosine tetraphosphate (AP4A), in particular with substantial affinity. The receptor which according to the present invention for the first time is found to specifically bind the endogenous ligand AP4A, and thus is named herein AP4A-receptor (AP4AR), was formerly described and designated as orphan receptor GPR56. But no specific pharmacological properties or specific therapeutic applications were described for this orphan receptor in the state of the art, due lack of knowledge of the endogenous ligand. Thus, according to the experimental work of the present invention, for the first time the orphan receptor GPR56 is identified to bind the endogenous ligand diadenosine tetraphosphate (AP4A), and these findings are further elucidated. The AP4A GPCR and the finding of its endogenous ligand described in the context of this invention below, therefore clearly satisfy a need in the art for identification and characterization of valuable receptors that can play a role in diagnosing, preventing, ameliorating or correcting a broad range of specific dys unctions, disorders or diseases.

Based on the specific findings of the present inventions, e.g. the specific pharmacological properties or specific applications for the AP4A receptor and the knowledge of the newly identified endogenous ligand diadenosine tetraphosphate (AP4A), or analogues thereof, the invention particularly relates also to the use of this AP4A-receptor and the ligand AP4A in drug discovery with respect to certain dysfunctions or diseases related to any interaction of said ligand with AP4A- receptor, and furthermore to the drugs that play a role in preventing, ameliorating or correcting said dysfunctions or diseases as indicated herein. Therefore, in the context the invention reference is made also to AP4AR-polynucleotides, AP4AR-polypeptides encoded by them and to the use of such polynucleotides and polypeptides, and to their production.

Furthermore, the invention relates to the treatment and/or prophylaxis of a dysfunction or disorder associated with or being implicated by pathophysiological conditions related to the activities of AP4AR, and its possible interrelation with the AP4A ligand. Preferably, for example but without limitation, such pathophysiological conditions may evoke dysfunctions, disorders or diseases related to the cardiovascular system, the central nervous system and/or the glucose or insulin metabolism, immunological diseases and disorders of the genitourinary system. Preferably the invention relates to the treatment and/or prophylaxis of a dysfunction or disorder associated with the cardiovascular system, including the heart, in the nervous system, including the central nervous system, and also in glucose and insulin metabolism. Dysfunctions or disorders associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

Thus, the various aspects of the invention pertain to methods for using such AP4AR polypeptides and polynucleotides in the context of certain AP4AR-related dysfunctions, disorders or diseases related to any interaction of the AP4A ligand with AP4A-receptor polypeptides, preferably in the fields of drug discovery (lead screening and/or lead structure design and optimization), diagnosis and treatment and /or prophylaxis of further specific AP4AR-related dysfunctions, disorders or diseases. Such specific AP4AR-related uses include dysfunctions, disorders or diseases related to pathophysiological conditions subjected to the activities of the AP4A-receptor in connection with its interrelation with the AP4A ligand; these dysfunctions, disorders or diseases may include those as indicated supra. In a broader aspect of the present invention it may also be related to dysfunctions, disorders or diseases of the cardiovascular system including myocardial ischemia, heart failure, angina pectoris, arrhythmias, myocardial infarction, hypotension; hypertension, thrombosis; local regulation of blood flow, hypertrophy of the heart, development of congestive heart failure, preconditioning, and related diseases such as symptoms of syndrome X. Such specific AP4AR-related uses include dysfunctions or disorders related to nervous system including schizophrenia, episodic paroxysmal anxiety (EPA) disorders such as obsessive compulsive disorder (OCD), post traumatic stress disorder (PTSD), phobia and panic, major depressive disorder, bipolar disorder, Parkinson's disease, general anxiety disorder, autism, delirium, Alzheimer disease/dementia, severe mental retardation and dyskinesias, such as Huntington's disease or Gilles dela Tourett's syndrome, anorexia, bulimia, stroke, addiction/dependency/craving, sleep disorder, epilepsy, migraine; attention deficit/hyperactivity disorder (ADHD). Such specific AP4AR-related uses include dysfunctions or disorders related to genitourinary system including renal failure, urinary retention and benign prostatic hypertrophy, among others. Further specific AP4AR-related uses may include dysfunctions or disorders related to dyslipidemias; obesity; emesis; IBS; IBD; GERD; conditions of delayed gastric emptying, such as postoperative or diabetic gastroparesis; NIDDM, IDDM, insulin resistance, glucose intolerance; cystic fibrosis; Chediak-Higashi syndrome; shock; inflammation, cancer, e.g. oligodendroglioma, melanoma and neuroblastoma; and in endocrinology: hormon deficiency, hyposecretion diseases, hormone excess and/or hypersecretion diseases related to thyroid hormones.

In one aspect, the invention also relates to methods to identify agonists, antagonists or modulators using the materials provided by the invention, and treating conditions associated with AP4AR imbalance with the identified compounds. In this respect the invention also relates to drug candidate compounds themselves, which are identified by means of the present invention for the first time, said candidate compounds being easily to synthesize and to characterize by conventional synthetic and analytical methods, and which may be developed to a drug. Another aspect of the invention relates to diagnostic assays for detecting diseases associated with inappropriate AP4AR activity or levels. A further aspect of the invention relates to animal-based systems which act as models for dysfunctions, disorders or diseases arising from aberrant expression or activity of AP4AR. Preferred novel agonists, novel antagonists or novel modulators identified according to the present invention are those which are suited for the for treating, preventing, ameliorating or correcting the said dysfunctions, disorders or diseases as mentioned before to be related to the specific activities of AP4A-receptor in connection with its specific interrelation with the AP4A ligand.

In still another aspect the invention relates to the use of (isolated) AP4AR/ligand-complexes, e.g. AP4AR/AP4A-complexes in the identification and optimization of lead structures which are synthetic novel organic molecules (e.g. "candidate compounds"), other than adenosine polyphosphates, e.g. novel organic substances with non-adenosine-polyphosphate-structure.

In still a further aspect the invention relates to the use of novel AP4AR activators, inhibitors or modulators for the preparation of a pharmaceutical composition for the treatment and/or prophylaxis of AP4AR-related dysfunctions, disorders or diseases as indicated above. Preferably those dysfunctions, disorders or diseases are related to the cardiovascular system, including the heart, to the nervous system, including the central nervous system, and also to glucose and insulin metabolism, and furthermore to immunological diseases and to disorders of the genitourinary system. Dysfunctions, disorders or diseases associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases. In particular those AP4AR activators, inhibitors or modulators are organic molecules other than adenosine polyphosphates, e.g. organic substances with non-adenosine- polyphosphate-structure.

In another aspect the invention relates to the use of AP4AR-polynucleotides, AP4AR- polypeptides, AP4A-receptor ligands and/or AP4A in the diagnosis of AP4AR-related dysfunctions, disorders or diseases as indicated supra. Table 1: AP4AR-DNA of SEQ ID NO: 1

5 ' -

ATGACTCCCCAGTCGCTGCTGCAGACGACACTGTTCCTGCTGAGTCTGCTCTTCCTGGTCCAAG GTGCCCACGGCAGGGGCCACAGGGAAGACTTTCGCTTCTGCAGCCAGCGGAACCAGACACACAG GAGCAGCCTCCACTACAAACCCACACCAGACCTGCGCATCTCCATCGAGAACTCCGAAGAGGCC CTCACAGTCCATGCCCCTTTCCCTGCAGCCCACCCTGCTTCCCGATCCTTCCCTGACCCCAGGG GCCTCTACCACTTCTGCCTCTACTGGAACCGACATGCTGGGAGATTACATCTTCTCTATGGCAA GCGTGACTTCTTGCTGAGTGACAAAGCCTCTAGCCTCCTCTGCTTCCAGCACCAGGAGGAGAGC CTGGCTCAGGGCCCCCCGCTGTTAGCCACTTCTGTCACCTCCTGGTGGAGCCCTCAGAACATCA GCCTGCCCAGTGCCGCCAGCTTCACCTTCTCCTTCCACAGTCCTCCCCACACGGCCGCTCACAA TGCCTCGGTGGACATGTGCGAGCTCAAAAGGGACCTCCAGCTGCTCAGCCAGTTCCTGAAGCAT CCCCAGAAGGCCTCAAGGAGGCCCTCGGCTGCCCCCGCCAGCCAGCAGTTGCAGAGCCTGGAGT CGAAACTGACCTCTGTGAGATTCATGGGGGACATGGTGTCCTTCGAGGAGGACCGGATCAACGC CACGGTATGGAAGCTCCAGCCCACAGCCGGCCTCCAGGACCTGCACATCCACTCCCGGCAGGAG GAGGAGCAGAGCGAGATCATGGAGTACTCGGTGCTGCTGCCTCGAACACTCTTCCAGAGGACGA AAGGCCGGAGCGGGGAGGCTGAGAAGAGACTCCTCCTGGTGGACTTCAGCAGCCAAGCCCTGTT CCAGGACAAGAATTCCAGCCAAGTCCTGGGTGAGAAGGTCTTGGGGATTGTGGTACAGAACACC AAAGTAGCCAACCTCACGGAGCCCGTGGTGCTCACTTTCCAGCACCAGCTACAGCCGAAGAATG TGACTCTGCAATGTGTGTTCTGGGTTGAAGACCCCACATTGAGCAGCCCGGGGCATTGGAGCAG TGCTGGGTGTGAGACCGTCAGGAGAGAAACCCAAACATCCTGCTTCTGCAACCACTTGACCTAC TTTGCAGTGCTGATGGTCTCCTCGGTGGAGGTGGACGCCGTGCACAAGCACTACCTGAGCCTCC TCTCCTACGTGGGCTGTGTCGTCTCTGCCCTGGCCTGCCTTGTCACCATTGCCGCCTACCTCTG CTCCAGGGTGCCCCTGCCGTGCAGGAGGAAACCTCGGGACTACACCATCAAGGTGCACATGAAC CTGCTGCTGGCCGTCTTCCTGCTGGACACGAGCTTCCTGCTCAGCGAGCCGGTGGCCCTGACAG GCTCTGAGGCTGGCTGCCGAGCCAGTGCCATCTTCCTGCACTTCTCCCTGCTCACCTGCCTTTC CTGGATGGGCCTCGAGGGGTACAACCTCTACCGACTCGTGGTGGAGGTCTTTGGCACCTATGTC CCTGGCTACCTACTCAAGCTGAGCGCCATGGGCTGGGGCTTCCCCATCTTTCTGGTGACGCTGG TGGCCCTGGTGGATGTGGACAACTATGGCCCCATCATCTTGGCTGTGCATAGGACTCCAGAGGG CGTCATCTACCCTTCCATGTGCTGGATCCGGGACTCCCTGGTCAGCTACATCACCAACCTGGGC CTCTTCAGCCTGGTGTTTCTGTTCAACATGGCCATGCTAGCCACCATGGTGGTGCAGATCCTGC GGCTGCGCCCCCACACCCAAAAGTGGTCACATGTGCTGACACTGCTGGGCCTCAGCCTGGTCCT TGGCCTGCCCTGGGCCTTGATCTTCTTCTCCTTTGCTTCTGGCACCTTCCAGCTTGTCGTCCTC TACCTTTTCAGCATCATCACCTCCTTCCAAGGCTTCCTCATCTTCATCTGGTACTGGTCCATGC GGCTGCAGGCCCGGGGTGGCCCCTCCCCTCTGAAGAGCAACTCAGACTGCGCCAGGCTCCCCAT CAGCTCGGGCAGCACCTCGTCCAGCCGCATCTAG-3 ' Table 2: AP4AR-protein ofSEQ ID NO: 2

MTPQSLLQTT FLLSLLFLVQGAHGRGHREDFRFCSQRNQTHRSSLHYKPTPDLRI SIENSEEALTVHAPFPAAHPASRSFPDPRGLYHFCLYWNRHAGRLHLLYGKRDFLL SDKASSLLCFQHQEESLA GPPLLATSVTSW SPQNISLPSAASFTFSFHSPPHTA AH ASVDMCELKRDLQLLSQFLKHPQKASRRPSAAPASQQLQSLESK TSVRF GD MVSFEEDRINATV KLQPTAGLQDLHIHSRQEEEQSEIMEYSVLLPRTLFQRTKGR SGEAEKRLLLVDFSSQALFQDK SSQVLGE V GIVVQNTKVA LTEPVVLTFQHQ LQPKISTVTLQCVF VEDPTLSSPGH SSAGCETVRRETQTSCFC HLTYFAVL VSS VEVDAVHKHYLSLLSYVGCWSALACLVTIAAYLCSRVPLPCRRKPRDYTI VHM LLLAVFLLDTSFLLSEPVALTGSEAGCRASAIFLHFSLLTCLSW GLEGYNLYRLV VEVFGTYVPGYLLKLSA GWGFPIFLVTLVALVDVDNYGPIILAVHRTPEGVIYPS MCWIRDSLVSYITN GLFSLVFLF MAMLATMVVQILRLRPHTQK SHVLTLLGLS LVLGLP ALIFFSFASGTFQ VV Y FSIITSFQGFLIFIWYWSMRLQARGGPSPL SNSDCARLPISSGSTSSSRI

BRIEF DESCRIPTION OF THE FIGURES

Fig.1 AP4A-induced intracellular Ca²⁺ mobilisation in CHOGα16-cells expressing the AP4A-receptor. Application of 3μM diadenosine tetraphosphate to the cell line CHOGα16- AP4AR and eight CHOGαlδ cell lines transfected with other orphan GPCRs. Cells were cultured in 96-well plates overnight and loaded with Fluo-4AM. Receptor mediated intracellular Ca²⁺ changes were measured with FLIPR (Molecular Devices), depicted in counts detected by the CCD camera. ,

Fig.2 The AP4A-dose response curve shows concentration dependent AP4AR activation.

Concentration is indicated as log c [μM] with n=5; error bars indicate SEM. CHOGα16- cells (triangle) and CHOGα16-cells (square) expressing the AP4A-receptor were cultured in 96-well plates overnight and loaded with Fluo-4AM. The receptor mediated Ca²⁺ changes were measured with FLIPR (Molecular Devices). Maxima of the fluorescence change detected by the CCD camera are depicted as counts.

Fig.3 Comparison of diadenosine polyphosphates, ATP and adenosine derivatives.

Concentration is indicated as log c [μM] with n=5; error bars indicate SEM. CHOGαlδ- cells (a) and CHOGα16-cells expressing the AP4A-receptor (b) were cultured in 96-well plates overnight and loaded with Fluo-4AM. The receptor mediated Ca ⁺ changes were measured with FLIPR (Molecular Devices). Maxima of the fluorescence change detected by the CCD camera are depicted as counts. DESCRIPTION OF THE INVENTION

Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art to which this invention belongs. Although any methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, the preferred methods, devices, and materials are now described. All publications including, but not limited to, patents and patent applications, cited in this specification are herein incorporated by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein as though fully set forth.

Definitions

The following definitions are provided to facilitate understanding of certain terms used frequently herein. The explanations are provided as a convenience and are not meant to limit the invention.

"AP4AR" or "GPR56" refers to a polypeptide comprising the amino acid sequence set forth in SEQ ID NO: 2 (AP4AR), or a variant thereof, including polypeptides essentially similar thereto, e.g. polypeptides showing at least 80% identity or any higher degree of identity as indicated below in the description of the invention.

"Receptor Activity" or "Biological Activity of the Receptor" refers to the metabolic or physiologic function of said AP4AR/GPR56 including similar activities or improved activities or these activities with decreased undesirable side effects. Also included are antigenic and immunogenic activities of said AP4AR/GPR56.

"Modulator" shall mean materials (e.g. ligands, partial agonists, antagonists, inverse agonists, candidate compounds) that in any way "modulate" the natural or original activity of a receptor e.g. a material that measurably influences the receptor's activity by e.g. evoking a total, partial or graded change or modification, preferably by evoking a partial or graded change or modification, of the natural or original activity of the receptor.

"Agonists" shall mean materials (e.g., ligands, candidate compounds) that activate an intracellular response when they bind to the receptor, or enhance GTP binding to membranes. "Partial agonist" shall mean materials (e.g., ligands, candidate compounds) that activate an intracellular response when they bind to the receptor to a lesser degree/extent than do agonists, or enhance GTP binding to membranes to a lesser degree/extent than do agonists.

"Antagonist" shall mean materials (e.g., ligands, candidate compounds) that competitively bind to the receptor at the same site as the agonists but which do not activate the intracellular response initiated by the active form of the receptor, and can thereby inhibit the intracellular response in the presence of an agonist or partial agonist.

"Substance" shall mean an organic chemical molecule, for example, and without limitation, an organic chemical compound, preferably a candidate compound.

"Candidate compound" shall mean a "novel" organic molecule.for example, and without limitation, an organic chemical compound, that is amenable to a screening technique. In this context the term "novel" means that said molecule or compound was not comprised in the state of the art prior to the filing date or preferably to the priority date of the present invention. Thus, preferably, the phrase "candidate compound" does not include compounds which were publicly known prior to the filing date or preferably to the priority date of the present invention to be compounds selected from the group consisting of inverse agonist, agonist or antagonist to a receptor, as previously determined by an indirect identification process ("indirectly identified compound"); more preferably, not including an indirectly identified compound which has previously been determined to have therapeutic efficacy in at least one mammal; and, most preferably, not including an indirectly identified compound which has previously been determined to have therapeutic utility in humans.

"Compound efficacy" shall mean a measurement of the ability of a compound to stimulate or inhibit receptor functionality, as opposed to receptor binding affinity. Exemplary means of detecting compound efficacy are disclosed in the Example section of this patent specification.

"Endogenous" shall mean a material that a mammal naturally produces. "Endogenous" in reference to, for example, and without limitation, the term "receptor", shall mean that which is naturally produced by a mammal (for example, and without limitation, a human) or a virus. By contrast, the term "non-endogenous" in this context shall mean that which is not naturally produced by a mammal (for example, and without limitation, a human) or a virus. Both terms can be utilized to describe both "in vivo" and "in vitro" systems. For example, and without limitation, in a screening approach, the endogenous or non-endogenous receptor may be in reference to an in vitro screening system. As a further example and without limitation, where the genome of a mammal has been manipulated to include a non-endogenous activated receptor, screening of a candidate compound by means of an in vivo system is feasible. "Inhibit" or "inhibiting", in relationship to the term "response" shall mean that a response is decreased or prevented in the presence of a compound as opposed to in the absence of the compound.

"Inverse agonists" shall mean materials (e.g., ligands, candidate compounds) which bind to either the endogenous form of the receptor and which inhibit the baseline intracellular response initiated by the active form of the receptor below the normal base level of activity which is observed in the absence of agonists or partial agonists, or decrease GTP binding to membranes. Preferably, the baseline intracellular response is inhibited in the presence of the inverse agonist by at least 30 %, more preferably by at least 50 %, and most preferably by at least 75 %, as compared with the baseline response in the absence of the inverse agonist.

"Known receptor" (e.g. non-orphan receptor) shall mean an endogenous receptor for which the endogenous ligand specific for that receptor has been identified.

"Ligand" shall mean an endogenous, naturally occurring molecule specific for an endogenous, naturally occurring receptor.

Orphan receptor" shall mean an endogenous receptor for which the endogenous ligand specific for that receptor has not been identified or is not known.

"AP4AR-gene" refers to a polynucleotide comprising the nucleotide sequence set forth in SEQ ID NO: 1 (AP4AR-1) or SEQ ID NO: 3 (AP4AR-2), or respective variants, e.g. allelic variants, thereof and/or their complements.

"Antibodies" as used herein includes polyclonal and monoclonal antibodies, chimeric, single chain, and humanized antibodies, as well as Fab fragments, including the products of a Fab or other immunoglobulin expression library.

"Isolated" means altered "by the hand of man" from the natural state and/or separated from the natural environment. Thus, if an "isolated" composition or substance that occurs in nature has been "isolated", it has been changed or removed from its original environment, or both. For example, a polynucleotide or a polypeptide naturally present in a living animal is not "isolated", but the same polynucleotide or polypeptide separated from the coexisting materials of its natural state is "isolated", as the term is employed herein.

"Polynucleotide" generally refers to any polyribonucleotide or polydeoxribonucleotide, which may be unmodified RNA or DNA or modified RNA or DNA. "Polynucleotides" include, without limitation single- and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions, single- and double-stranded RNA, and RNA that is a mixture of single-and double- stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded or a mixture of single- and double-stranded regions. In addition, "polynucleotide" may also include triple-stranded regions comprising RNA or DNA or both RNA and DNA. The term polynucleotide also includes DNAs or RNAs containing one or more modified bases and DNAs or RNAs with backbones modified for stability or for other reasons. "Modified" bases include, for example, tritylated bases and unusual bases such as inosine. A variety of modifications has been made to DNA and RNA; thus, "polynucleotide" embraces chemically, enzymatically or metabolically modified forms of polynucleotides as typically found in nature, as well as the chemical forms of DNA and RNA characteristic of viruses and cells. "Polynucleotide" also embraces relatively short polynucleotides, often referred to as oligonucleotides.

"Polypeptide" refers to any peptide or protein comprising two or more amino acids joined to each other by peptide bonds or modified peptide bonds, i.e., peptide isosteres. "Polypeptide" refers to short chains, commonly referred to as peptides, oligopeptides or oligomers, and to longer chains, generally referred to as proteins, and/or to combinations thereof. Polypeptides may contain amino acids other than the 20 gene-encoded amino acids. "Polypeptides" include amino acid sequences modified either by natural processes, such as posttranslational processing, or by chemical modification techniques which are well known in the art. Such modifications are well- described in basic texts and in more detailed monographs, as well as in a voluminous research literature. Modifications can occur anywhere in a polypeptide, including the peptide backbone, the amino acid side-chains and the amino or carboxyl termini. It will be appreciated that the same type of modification may be present in the same or varying degrees at several sites in a given polypeptide. Also, a given polypeptide may contain many types of modifications. Polypeptides may be branched as a result of ubiquitination, and they may be cyclic, with or without branching. Cyclic, branched and branched cyclic polypeptides may result from posttranslation natural processes or may be made by synthetic methods. Modifications include acetylation, acylation, ADP-ribosylation, amidation, covalent attachment of flavin, covalent attachment of a heme moiety, covalent attachment of a nucleotide or nucleotide derivative, covalent attachment of a lipid or lipid derivative, covalent attachment of phosphotidylinositol; cross-linking, cyclization, disulfide bond formation, demethylation, formation of covalent cross-links, formation of cystine, formation of pyroglutamate, formylation, gamma-carboxylation, glycosylation, GPI anchor formation, hydroxylation, iodination, methylation, myristoylation, oxidation, proteolytic processing, phosphoryiation, prenylation, racemization, selenoylation, sulfation, transfer-RNA mediated addition of amino acids to proteins such as arginylation, and ubiquitination. See, for instance, PROTEINS - STRUCTURE AND MOLECULAR PROPERTIES, 2nd Ed., T. E. Creighton, W. H. Freeman and Company, New York, 1993 and Wold, F., Posttranslational Protein Modifications: Perspectives and Prospects, pgs. 1-12 in POSTTRANSLATIONAL COVALENT MODIFICATION OF PROTEINS, B. C. Johnson, Ed., Academic Press, New York, 1983; Seifter et al., "Analysis for protein modifications and nonprotein cofactors", Meth. Enzymol. (1990) 182:626-646 and Rattan et al., "Protein Synthesis: Posttranslational Modifications and Aging", Ann. NY Acad. Sci. (1992) 663:48-62.

"Variant" as the term is used herein, is a polynucleotide or polypeptide that differs from a reference polynucleotide or polypeptide respectively, but retains essential properties such as essential biological, structural, regulatory or biochemical properties. A typical variant of a polynucleotide differs in nucleotide sequence from another, reference polynucleotide. Changes in the nucleotide sequence of the variant may or may not alter the amino acid sequence of a polypeptide encoded by the reference polynucleotide. Nucleotide changes may result in amino acid substitutions, additions, deletions, fusions and truncations in the polypeptide encoded by the reference sequence, as discussed below. A typical variant of a polypeptide differs in amino acid sequence from another, reference polypeptide. Generally, differences are limited so that the sequences of the reference polypeptide and the variant are closely similar overall and, in many regions, identical. A variant and reference polypeptide may differ in amino acid sequence by one or more substitutions, additions, and deletions in any combination. A substituted or inserted amino acid residue may or may not be one encoded by the genetic code. A variant of a polynucleotide or polypeptide may be a naturally occurring such as an allelic variant, or it may be a variant that is not known to occur naturally. Non-naturally occurring variants of polynucleotides and polypeptides may be made by mutagenesis techniques or by direct synthesis.

"Identity" is a measure of the identity of nucleotide sequences or amino acid sequences. In general, the sequences are aligned so that the highest order match is obtained. "Identity" per se has an art-recognized meaning and can be calculated using published techniques. See, e.g.: (COMPUTATIONAL MOLECULAR BIOLOGY, Lesk, A.M., ed., Oxford University Press, New York, 1988; BIOCOMPUTING: INFORMATICS AND GENOME PROJECTS, Smith, D.W., ed.; Academic Press, New York, 1993; COMPUTER ANALYSIS OF SEQUENCE DATA, PART I, Griffin, A.M., and Griffin, H.G., eds., Humana Press, New Jersey, 1994; SEQUENCE ANALYSIS IN MOLECULAR BIOLOGY, von Heinje, G., Academic Press, 1987; and SEQUENCE ANALYSIS PRIMER, Gribskov, M. and Devereux, J., eds., M Stockton Press, New York, 1991). While there exist a number of methods to measure identity between two polynucleotide or polypeptide sequences, the term "identity" is well known to skilled artisans (Carillo, H., and Upton, D., SIAM J. Applied Math. (1988) 48:1073). Methods commonly employed to determine identity or similarity between two sequences include, but are not limited to, those disclosed in Guide to Huge Computers, Martin J. Bishop, ed., Academic Press, San Diego, 1994, and Carillo, H., and Upton, D., SIAM J. Applied Math. (1988) 48:1073. Methods to determine identity and similarity are codified in computer programs. Preferred computer program methods to determine identity and similarity between two sequences include, but are not limited to, GCG program package (Devereux, J., et al., Nucleic Acids Research (1984) 12(1):387), BLASTP, BLASTN, FASTA (Atschul, S.F. et al., J. Molec. Biol. (1990) 215:403). The word "homology" may substitute for the word "identity". As an illustration, by a polynucleotide having a nucleotide sequence having at least, for example, 95% "identity" to a reference nucleotide sequence of SEQ ID NO: 1 is intended that the nucleotide sequence of the polynucleotide is identical to the reference sequence except that the polynucleotide sequence may include up to five nucleotide diffences per each 100 nucleotides of the reference nucleotide sequence of SEQ ID NO: 1. In other words, to obtain a polynucleotide having a nucleotide sequence at least 95% identical to a reference nucleotide sequence, up to 5% of the nucleotides in the reference sequence may be deleted or substituted with another nucleotide, or a number of nucleotides up to 5% of the total nucleotides in the reference sequence may be inserted into the reference sequence, or in a number of nucleotides of up to 5% of the total nucleotides in the reference sequence there may be a combination of deletion, insertion and substitution. These mutations of the reference sequence may occur at the 5 or 3 terminal positions of the reference nucleotide sequence or anywhere between those terminal positions, interspersed either individually among nucleotides in the reference sequence or in one or more contiguous groups within the reference sequence.

Similarly, by a polypeptide having an amino acid sequence having at least, for example, 95% "identity" to a reference amino acid sequence of SEQ ID NO: 2 is intended that the amino acid sequence of the polypeptide is identical to the reference sequence except that the polypeptide sequence may include up to five amino acid alterations per each 100 amino acids of the reference amino acid of SEQ ID NO: 2. In other words, to obtain a polypeptide having an amino acid sequence at least 95% identical to a reference amino acid sequence, up to 5% of the amino acid residues in the reference sequence may be deleted or substituted, with another amino acid, or a number of amino acids up to 5% of the total amino acid residues in the reference sequence may be inserted into the reference sequence. These alterations of the reference sequence may occur at the amino or carboxy terminal positions of the reference amino acid sequence or anywhere between those terminal positions, interspersed either individually among residues in the reference sequence or in one or more contiguous groups within the reference sequence.

Polypeptides in the Context of the Invention

With regard to the AP4AR polypeptides or GPR56 polypeptides, respectively, dealt with in the context of the present invention it was found that they show a high affinity binding for diadenosine tetraphosphate (AP4A).

In the context of the present invention the term "high affinity" is understood as to describe a ligand binding showing log EC50 values of at least those found for the AP4A itself with regard to the AP4AR; more details about the affinity binding of AP4A is given in the experimental part and the Figures. Furthermore the most important characteristics of diadenosine tetraphosphate are described above in the Background section supra. Furthermore with regard to AP4A the following may be noted:

a) with regard to synthesis and localisation:

- secretory granules of adrenomedullar chromaffin cells;

- dense secretory granules of platelets; released by activated platelets, e.g. during platelet aggregation (μM range);

- CNS: cholinergic synaptic vesicles, midbrain synaptosomes, caudate putamen, neostriatum (rat);

- cardiac tissue;

- AP4A uptake in tumor cells.

b) with regard to intracellular and extracellular concentration of AP4A:

- concentrations of AP3A and AP4A in the circulating blood of an adult following platelet stimulation have been estimated to be of the order of 1μM;

- platelet aggregation results in the release of almost all of the intrapiatelet store of diadenosine polyphosphates from an individual platelet;

- thrombus: initial concentration could be 100μM (no conirmation), but seem to be much higher than 1μM;

- concentration within platelt granula ATP/ADP : AP4A is 24-40:1 ;

- in normal growing cells the intracellular AP4A concentration is about 0.03-1.2μM;

- differentiation between local and systemic effects: up to 100μM: only local effects; 0.1 nM-1 μM: systemic effects.

c) with regard to effects of AP4A:

- human ventricular trabeculae carneae: increased force of contraction (prob. via GPCR);

- vasoconstriction: endothelium-denuded arteries, but vasodilatation by AP3A;

- vasodilatation: endothelium-intact arteries vasodilatation: AP3A 50% more effective than AP4A - different mechanisms;

- negative inotrophic effects in ventricular preparations from guinea pig heart;

- positive inotrophic effects in ventricular preparations from human heart (prob. via GPCR); - AP4A may induce hypertrophy (like angiotensin 2, endothelin 1) via GPCR;

- mediates as second messenger the glucose-induced blockade of the ATP-regulated K+ channel in pancreatic B-cells; second messenger, important: stable molecule! can act as long-range signalling molecule

- inhibitory effects on platelet aggregation (at 5μM) (AP3A promotes platelet aggregation)

- rat kidney: contraction at physiologically

The AP4AR or GPR56 polypeptides of the present invention have been identified as a G- protein coupled receptor responsive to diadenosine tetraphosphate. Thus, the responsiveness of the AP4A- or GPR56-receptor to diadenosine tetraphosphate (AP4A) will greatly facilitate the understanding of the physiological mechanisms of AP4A and e.g. other ligands, e.g. of non- polyphosphate organic molecules, with sufficiently similar binding thereto, as well as of related diseases.

With regard to the tissue distribution of the polypeptides considered under the present invention it was found that the AP4AR polypeptides of the present invention particularly are brought to expression particularly in:

- Northern Blot (see Liu et al. (1999) Genomics 55, 296-305)):thyroid gland (highest level of expression); specific brain areas; heart; kidney; testis; pancreas; skeletal muscle; neuroblastoma cell lines; p53 negative breast cancer cell lines

- In situ hybridisation (see Liu et al. (1999) Genomics 55, 296-305)): human: thyroid tissue (selectively expressed within the monolayer of cubical epithelial cells of the smaller, more active secreting follicles); rat: heart: myocardial cells; coronal sections of rat forebrain: wide distribution: CA layers of hippocampus; thalamus, anterodorsal thalamic nucleus, lower in other thalamic regions; hypothalamus, particularly strong within paraventricular nucleus; amygdala; cortex.

Thus, the finding of the present invention suggests that AP4AR polypeptides preferably play a role in dysfunctions, disorders or diseases as indicated supra; in particular dysfunctions, disorders or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also in glucose and insulin metabolism, and-furthermore of immunological diseases and disorders of the genitourinary system. Dysfunctions, disorders or diseases associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases. The AP4AR polypeptides referred to in the context of the present invention comprise any AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1. AP4AR polypeptides, preferably mammalian AP4AR polypeptides, showing at least 90% identity are particularly preferred within the context of the invention, and those with at least 95% identity are especially preferred. Furthermore, those with at least 97% identity are highly preferred and those with at least 98-99% identity are most highly preferred, with at least 99% identity being the most preferred identity.

The AP4AR polypeptides of the invention can be prepared in any suitable manner. Such polypeptides include isolated naturally occurring polypeptides, recombinantly produced polypeptides, synthetically produced polypeptides, or polypeptides produced by a combination of these methods. Methods for preparing such polypeptides are well known in the art.

Polynucleotides in the Context of the Invention

A further aspect the invention is based on AP4AR polynucleotides. AP4AR polynucleotides include isolated polynucleotides which encode the AP4AR polypeptides, including fragments, and polynucleotides closely related thereto. More specifically, the AP4AR polynucleotide includes a polynucleotide comprising the nucleotide sequence contained in SEQ ID NO: 1 or a sequence encoding a AP4AR polypeptide of SEQ ID NO: 2. The polynucleotides having the particular sequence of SEQ ID NO: 1 or a sequence that essentially correspond to the DNA in NCBl databank referenced under access no NM005682 or no. AF106858 (definition: Homo sapiens G- protein-coupled receptor (GPR56); 2822 bases). AP4A-receptor sequences are also published by Liu, M., et al. under the title "GPR56, a novel secretin-like human G-protein-coupled receptor gene" (Genomics 55 (3), 296-305 (1999)) and in an international patent application under publication no. W0 99/15551. Both, the scientific publication of Liu and the WO 99/15551 are incorporated by reference herein. The AP4AR sequence shown in SEQ ID NO: 1 which was derived by cloning is almost identical to those GPR56 sequences described by Liu and in WO 99/15551, except that the AP4AR sequence shown in SEQ ID NO: 1 shows two mutations (1) GTA to GTG in position 711 (silent mutation) and (2) TGC to AGC in position 2032 which causes an amino acid exchange Cys to Ser in the AP4AR receptor protein, compared to the published GPR56 sequences. The published sequences AF106858 and NM005682 are 100%^' identical to each other.

AP4AR polynucleotides further include a polynucleotide comprising a nucleotide sequence that has at least 80% identity over its entire length to a nucleotide sequence encoding the AP4AR polypeptide of SEQ ID NO: 2, a polynucleotide comprising a nucleotide sequence that is at least 80% identical to that of SEQ ID NO: 1 over its entire length and a polynucleotide. In this regard, polynucleotides with at least 90% identity are particularly preferred within the context of the invention, and those with at least 95% identity are especially preferred. Furthermore, those with at least 97% identity are highly preferred and those with at least 98-99% identity are most highly preferred, with at least 99% identity being the most preferred.

Other G-protein coupled receptors structurally related to AP4AR proteins which may be of interest in the context of the present invention may be identified by the skilled artisan e.g. by BLAST searches (using BLAST, Altschul S.F. et al. [1997], Nucleic Acids Res. 25:3389-3402) in the public databases. Thus, polypeptides and polynucleotides sufficiently similar to the AP4AR polypeptides and AP4AR polynucleotides considered in the present invention are expected to have, inter alia, similar biological functions/properties to their homologous polypeptides and polynucleotides, and their utility is obvious to anyone skilled in the art.

Polynucleotides in the context of the invention can be obtained from natural sources such as genomic DNA. In particular, degenerated PCR primers can be designed that encode conserved regions within a particular GPCR gene subfamily. PCR amplification reactions on genomic DNA or cDNA using the degenerate primers will result in the amplification of several members (both known and novel) of the gene family under consideration (the degenerated primers must be located within the same exon, when a genomic template is used). (Libert et al., Science, 1989, 244: 569-572). Polynucleotides of the invention can also be synthesized using well-known and commercially available techniques.

When the polynucleotides in the context of the invention are used for the recombinant production of the AP4AR polypeptide, the polynucleotide may include the coding sequence for the mature polypeptide or a fragment thereof, by itself; the coding sequence for the mature polypeptide or fragment in reading frame with other coding sequences, such as those encoding a leader or secretory sequence, a pre-, or pro- or prepro- protein sequence, or other fusion peptide portions. For example, a marker sequence which facilitates purification of the fused polypeptide can be encoded. In certain preferred embodiments of this aspect of the invention, the marker sequence is a hexa-histidine peptide, as provided in the pQE vector (Qiagen, Inc.) and described in Gentz et al., Proc^' Natl. Acad. Sci USA (1989) 86:821-824, or is an HA tag. The polynucleotide may also contain non-coding 5' and 3' sequences, such as transcribed, non-translated sequences, splicing and polyadenylation signals, ribosome binding sites and sequences that stabilize mRNA.

Further preferred embodiments are polynucleotides encoding AP4AR variants comprising the amino acid sequence of the AP4AR polypeptide of SEQ ID NO: 2 in which several, 5-10, 1-5, 1-3, 1-2 or 1 amino acid residues are substituted, deleted or added, in any combination. The present invention further may involve polynucleotides that hybridize to the herein above- described sequences. In this regard, the present invention especially relates to polynucleotides which hybridize under stringent conditions to the herein above-described polynucleotides. As herein used, the term "stringent conditions" means hybridization will occur only if there is at least 80%, and preferably at least 90%, and more preferably at least 95%, yet even more preferably 97, in particular at least 99% identity between the sequences.

Polynucleotides described in the context of the invention, which are identical or sufficiently identical to a nucleotide sequence contained in SEQ ID NO: 1, or a fragment thereof, may be used as hybridization probes for cDNA and genomic DNA, to isolate full-length cDNAs and genomic clones encoding AP4AR and to isolate cDNA and genomic clones of other genes (including genes encoding homologs and orthologs from species other than human) that have a high sequence similarity to the AP4AR gene. People skilled in the art are well aware of such hybridization techniques. Typically these nucleotide sequences are 80% identical, preferably 90% identical, more preferably 95% identical to that of the referent. The probes generally will comprise at least 15 nucleotides. Preferably, such probes will have at least 30 nucleotides and may have at least 50 nucleotides. Particularly preferred probes will range between 30 and 50 nucleotides.

A procedure to obtain a polynucleotide encoding the AP4AR polypeptide, including homologs and orthologs from species other than human, comprises the steps of screening an appropriate library under stringent hybridization conditions with a labeled probe having the SEQ ID NO: 1, or a fragment thereof, and isolating full-length cDNA and genomic clones containing said polynucleotide sequence. Such hybridization techniques are well known to those of skill in the art. Stringent hybridization conditions are as defined above or alternatively conditions under overnight incubation at 42 oC in a solution comprising: 50% formamide, 5xSSC (150mM NaCl, 15mM trisodium citrate), 50 mM sodium phosphate (pH7.6), 5x Denhardt's solution, 10 % dextran sulfate, and 20 microgram/ml denatured, sheared salmon sperm DNA, followed by washing the filters in O.lxSSC at about 65oC.

The polynucleotides and polypeptides of the present invention may be used as research reagents and materials for discovery of treatments and diagnostics to animal and human dysfunctions or diseases such as in particular of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also in glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system. Dysfunctions or disorders associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related ^■ diseases. Vectors, Host Cells, Expression, Membranes and Tissues

In the context of the present invention it may be necessary to involve vectors which comprise a AP4AR polynucleotide or AP4AR polynucleotides, and host cells which are genetically engineered with said vectors and to the production of AP4AR polypeptides by recombinant techniques. Cell-free translation systems can also be used to produce such proteins using RNAs derived from the DNA constructs described in the context of the present invention. For recombinant production, host cells can be genetically engineered to incorporate expression systems or portions thereof for said polynucleotides. Introduction of polynucleotides into host cells can be effected by methods described in many standard laboratory manuals, such as Davis et al., BASIC METHODS IN MOLECULAR BIOLOGY (1986) and Sambrook et al., MOLECULAR CLONING: A LABORATORY MANUAL, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (1989) such as calcium phosphate transfection, DEAE-dextran mediated transfection, transvection, microinjection, cationic lipid-mediated transfection, electroporation, transduction, scrape loading, ballistic introduction or infection.

Representative examples of appropriate hosts include bacterial cells, such as streptococci, staphylococci, E. coli, Streptomyces and Bacillus subtilis cells; fungal cells, such as yeast cells and Aspergillus cells; insect cells such as Drosophila S2 and Spodoptera Sf9 cells; animal cells such as CHO, COS, HeLa, C127, 3T3, BHK, HEK 293, HL60, U937, Jurkat, mouse VMRO, MM39 human trachea! gland cells, rat mesangial cells, endothelia cells, Xenopus oocytes and Bowes melanoma cells; and plant cells.

A great variety of expression systems can be used. Such systems include, among others, chromosomal, episomal and virus-derived systems, e.g., vectors derived from bacterial plasmids, from bacteriophage, from transposons, from yeast episomes, from insertion elements, from yeast chromosomal elements, from viruses such as baculoviruses, papova viruses, such as SV40, vaccinia viruses, adenoviruses, fowl pox viruses, pseudorabies viruses and retroviruses, and vectors derived from combinations thereof, such as those derived from plasmid and bacteriophage genetic elements, such as cosmids and phagemids. The expression systems may contain control regions that regulate as well as engender expression. Generally, any system or vector suitable to maintain, propagate or express polynucleotides to produce a polypeptide in a host may be used. The appropriate nucleotide sequence may be inserted into an expression system by any of a variety of well-known and routine techniques, such as, for example, those set forth in Sambrook et al., MOLECULAR CLONING, A LABORATORY MANUAL (supra).

For secretion of the translated protein into the lumen of the endoplasmic reticulum, into the periplasmic space or into the extracellular environment, appropriate secretion signals may be incorporated into the desired polypeptide. These signals may be endogenous to the polypeptide or they may be heterologous signals. If the AP4AR/GPR56 polypeptide is to be expressed for use in screening assays, generally, it is preferred that the polypeptide be produced at the surface of the cell. In this event, the cells may be harvested prior to use in the screening assay. In case the affinity or functional activity of the AP4AR/GPR56 polypeptide is modified by receptor activity modifying proteins (RAMP), coexpression of the relevant RAMP most likely at the surface of the cell is preferred and often required. Also in this event harvesting of cells expressing the AP4AR/GPR56 polypeptide and the relevant RAMP prior to use in screening assays is required. If the AP4AR/GPR56 polypeptide is secreted into the medium, the medium can be recovered in order to recover and purify the polypeptide; if produced intracellularly, the cells must first be lysed before the polypeptide is recovered.

AP4AR/GPR56 polypeptides can be recovered and purified from recombinant cell cultures by well-known methods including ammonium sulfate or ethanol precipitation, acid extraction, anion or cation exchange chromatography, phosphocellulose chromatography, hydrophobic interaction chromatography, affinity chromatography, hydroxylapatite chromatography and lectin chromatography. Most preferably, high performance liquid chromatography is employed for purification. Well-known techniques for refolding proteins may be employed to regenerate active conformation when the polypeptide is denatured during isolation and or purification.

It is also possible to work screenings with isolated membranes comprising said AP4AR which membranes may be derived from transfected cells, or it is also possible to work on tissue cultures comprising said AP4AR. Furthermore, also isolated organs comprising said AP4AR may be suitable in screenings.

Diagnostic Assays

This invention also relates to the use of AP4AR GPR56 polynucleotides for use as diagnostic reagents. Detection of a mutated form of the AP4AR/GPR56 gene associated with a dysfunction will provide a diagnostic tool that can add to or define a diagnosis of a disease or susceptibility to a disease which results from under-expression, over-expression or altered expression of AP4AR/GPR56. Also in this event co-expression of relevant receptor activity modifying proteins can be required to obtain diagnostic assays of desired quality. Individuals carrying mutations in the AP4AR/GPR56 gene may be detected at the DNA level by a variety of techniques.

Nucleic acids for diagnosis may be obtained from a subject's cells, such as from blood, urine, saliva, tissue biopsy or autopsy material. The genomic DNA may be used directly for detection or may be amplified enzymatically by using PCR or other amplification techniques prior to analysis. RNA or cDNA may also be used in similar fashion. Deletions and insertions can be detected by a change in size of the amplified product in comparison to the normal genotype. Point mutations can be identified by hybridizing amplified DNA to labeled AP4AR/GPR56 nucleotide sequences. Perfectly matched sequences can be distinguished from mismatched duplexes by RNase digestion or by differences in melting temperatures. DNA sequence differences may also be detected by alterations in electrophoretic mobility of DNA fragments in gels, with or without denaturing agents, or by direct DNA sequencing. See, e.g., Myers et al., Science (1985) 230:1242. Sequence changes at specific locations may also be revealed by nuclease protection assays, such as RNase and S1 protection or the chemical cleavage method. See Cotton et al., Proc. Natl. Acad. Sci. USA (1985) 85: 4397-4401. In another embodiment, an array of oligonucleotide probes comprising the AP4AR/GPR56 nucleotide sequence or fragments thereof can be constructed to conduct efficient screening of e.g., genetic mutations. Array technology methods are well known and have general applicability and can be used to address a variety of questions in molecular genetics including gene expression, genetic linkage, and genetic variability. (See for example: M. Chee et al., Science, Vol. 274, pp. 610-613 (1996)).

The diagnostic assays offer a process for diagnosing or determining a susceptibility to in particular AP4A-receptor related and/or AP4AR related dysfunctions or diseases as stated before, preferably such as dysfunctions or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also in glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system. Dysfunctions or disorders associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases, through detection of mutation in the AP4AR gene by the. methods described. According to the present invention, the diagnostic assays offer in particular a process for diagnosing or determining a susceptibility to said dysfunctions and disorders.

In addition, said disorders, in particular the preferred ones, can be diagnosed by methods comprising determining from a sample derived from a subject an abnormally decreased or increased level of the AP4AR polypeptide or AP4AR mRNA. Decreased or increased expression can be measured at the RNA level using any of the methods well known in the art for the quantitation of polynucleotides, such as, for example, PCR, RT-PCR, RNase protection, Northern blotting and other hybridization methods. Assay techniques that can be used to determine levels of a protein, such as an AP4AR, in a sample derived from a host are well known to those of skill in the art. Such assay methods include radioimmunoassays, competitive-binding assays, Western Blot analysis and ELISA assays.

In another aspect, the present invention relates to a diagonostic kit for a dysfunction, disorder or disease or susceptibility to a AP4AR-related dysfunction, disorder or disease, particularly dysfunctions, disorders or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also in glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system. Dysfunctions or disorders associated with the cardiovascular system may preferably include blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases. The diagonostic kit comprises:

(a) an AP4AR polynucleotide, preferably the nucleotide sequence of SEQ ID NO: 1 , or a fragment thereof;

(b) a nucleotide sequence complementary to that of (a);

(c) an AP4AR polypeptide, preferably the polypeptide of SEQ ID NO: 2, or a fragment thereof; or

(d) an antibody to an AP4AR polypeptide, preferably to the polypeptide of SEQ ID NO: 2;

(e) a RAMP polypeptide required for the relevant biological or antigenic properties of an AP4AR polypeptide

It will be appreciated that in any such kit, (a), (b), (c) (d) or (e) may comprise a substantial component. Preferably the present invention relates to a diagnostic kit for diagnosing or determining an AP4A-related disease or a susceptibility to said AP4AR-related dysfunctions or diseases.

Chromosome Assays

The AP4AR nucleotide sequences are also valuable for chromosome identification. The sequence is specifically targeted to and can hybridize with a particular location on an individual human chromosome. The mapping of relevant sequences to chromosomes according to the present invention is an important first step in correlating those sequences with gene associated disease. Once a sequence has been mapped to a precise chromosomal location, the physical position of the sequence on the chromosome can be correlated with genetic map data. Such data are found, for example, in V. McKusick, Mendelian Inheritance in Man (available on line through Johns Hopkins University Welch Medical Library). The relationship between genes and diseases that have been mapped to the same chromosomal region are then identified through linkage analysis (coinheritance of physically adjacent genes).

The differences in the cDNA or genomic sequence between affected and unaffected individuals can also be determined. If a mutation is observed in some or all of the affected individuals but not in any normal individuals, then the mutation is likely to be the causative agent of the disease. Antibodies

The AP4AR polypeptides or their fragments or analogs thereof, or cells expressing them if required together with relevant RAMP's, may also be used as immunogens to produce antibodies immunospecific for the AP4AR polypeptides. The term "immunospecific" means that the antibodies have substantially greater affinity for said AP4AR polypeptides than their affinity for other related polypeptides in the prior art.

Antibodies generated against the AP4AR polypeptides may be obtained by administering the polypeptides or epitope-bearing fragments, analogs or cells to an animal, preferably a nonhuman, using routine protocols. For preparation of monoclonal antibodies, any technique, which provides antibodies produced by continuous cell line cultures, may be used. Examples include the hybridoma technique (Kohler, G. and Milstein, C, Naure (1975) 256:495-497), the trioma technique, the human B-cell hybridoma technique (Kozbor et al., Immunology Today (1983) 4:72) and the EBV-hybridoma technique (Cole et al., MONOCLONAL ANTIBODIES AND CANCER THERAPY, pp. 77-96, Alan R. Liss, Inc., 1985).

The above-described antibodies may be employed to isolate or to identify clones expressing the polypeptide or to purify the polypeptides by affinity chromatography. The antibodies may also be used to identify the presence of the AP4A-receptor in membrane preparations, tissue cultures or isolated organs, which are e.g. foreseen for use in drug screening or drug design or drug profiling.

Antibodies against AP4AR polypeptides as such or against AP4AR polypeptide-RAMP complexes, may also be employed to treat the AP4AR-related dysfunctions or disorders as indicated supra.

Animals

Another aspect of the invention relates to a animal-based systems which act as models for disorders arising from aberrant expression or activity of AP4AR. Animal based model systems may also be used to further characterize the activity of the AP4AR gene. Such assays may be utilized as part of screening strategies designed to identify compounds which are capable to treat AP4AR based disorders such as the AP4AR-related dysfunctions or disorders as indicated supra.ln this way the animal-based models may be used to identify pharmaceutical compounds, therapies and interventions which may be effective in treating disorders aberrant expression or activity of AP4AR. In addition such animal models may be used to determine the LD50 and the ED50 in animal subjects. These data may be used to determine the in vivo efficacy of potential AP4AR disorder treatments.

Animal-based mode! systems of AP4AR based disorders, based on aberrant AP4AR expression or activity, may include both non-recombinant animals as well as recombinantly engineered transgenic animals.

Animal models for AP4AR disorders may include, for example, genetic models. Animal models exhibiting AP4AR based disorder-like symptoms may be engineered by utilizing, for example, AP4AR sequences such as those described, above, in conjunction with techniques for producing transgenic animals that are well known to persons skilled in the art. For example, AP4AR sequences may be introduced into, and overexpressed and/or misexpressed in, the genome of the animal of interest, or, if endogenous AP4AR sequences are present, they may either be overexpressed, misexpressed, or, alternatively, may be disrupted in order to underexpress or inactivate AP4AR gene expression.

In order to overexpress or misexpress a AP4AR gene sequence, the coding portion of the AP4AR gene sequence may be ligated to a regulatory sequence which is capable of driving high level gene expression or expression in a cell type in which the gene is not normally expressed in the animal type of interest. Such regulatory regions will be well known to those skilled in the art, and may be utilized in the absence of undue experimentation.

For underexpression of an endogenous AP4AR gene sequence, such a sequence may be isolated and engineered such that when reintroduced into the genome of the animal of interest, the endogenous AP4AR gene alleles will be inactivated, or "knocked-out". Preferably, the engineered AP4AR gene sequence is introduced via gene targeting such that the endogenous AP4AR sequence is disrupted upon integration of the engineered AP4AR gene sequence into the animal's genome.

Gene targeting is discussed, below, in this section.

Animals of any species, including, but not limited to, mice, rats, rabbits, guinea pigs, pigs, micro-pigs, goats, and non-human primates, e.g., baboons, squirrels, monkeys, and chimpanzees may be used to generate animal models of AP4AR related disorders.

Any technique known in the art may be used to introduce a AP4AR transgene into animals to produce the founder lines of transgenic animals. Such techniques include, but are not limited to pronuclear microinjection (Hoppe, P.C. and Wagner, T.E., 1989, U.S. Pat. No. 4,873,191); retrovirus mediated gene transfer into germ lines (van der Putten et al., Proc. Natl. Acad. Sci., USA 82:6148-6152, 1985); gene targeting in embryonic stem cells (Thompson et al., Cell 56:313- 321, 1989,); electroporation of embryos (Lo, Mol. Cell. Biol. 3:1803-1 B14, 1983); and sperm- mediated gene transfer (Lavitrano et al., Cell 57:717-723, 1989); etc. For a review of such techniques, see Gordon, Transgenic Animals, Intl. Rev. Cytol.115:171-229, 1989, which is incorporated by reference herein in its entirety.

The present invention provides for transgenic animals that carry the AP4AR transgene in all their cells, as well as animals which carry the transgene in some, but not all their cells, i.e., mosaic animals. (See, for example, techniques described by Jakobovits, Curr. Biol. 4:761-763, 1994) The transgene may be integrated as a single transgene or in concatamers, e.g., head-to-head tandems or head-to-tail tandems. The transgene may also be selectively introduced into and activated in a particular cell type by following, for example, the teaching of Lasko et al. (Lasko, M. et al., Proc. Natl. Acad. Sci. USA 89:6232-6236, 1992).

The regulatory sequences required for such a cell-type specific activation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art.

When it is desired that the AP4AR transgene be integrated into the chromosomal site of the endogenous AP4AR gene, gene targeting is preferred. Briefly, when such a technique is to be utilized, vectors containing some nucleotide sequences homologous to the endogenous AP4AR gene of interest (e.g., nucleotide sequences of the mouse AP4AR gene) are designed for the purpose of integrating, via homologous recombination with chromosomal sequences, into and disrupting the function of, the nucleotide sequence of the endogenous AP4AR gene. The transgene may also be selectively introduced into a particular cell type, thus inactivating the endogenous gene of interest in only that cell type, by following, for example, the teaching of Gu et al. (Gu, H. et al., Science 265:103-106, 1994). The regulatory sequences required for such a cell- type specific inactivation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art.

Once transgenic animals have been generated, the expression of the recombinant AP4AR gene and protein may be assayed utilizing standard techniques. Initial screening may be accomplished by Southern blot analysis or PCR techniques to analyze animal tissues to assay whether integration of the transgene has taken place. The level of MRNA expression of the AP4AR transgene in the tissues of the transgenic animals may also be assessed using techniques which include but are not limited to Northern blot analysis of tissue samples obtained from the animal, in situ hybridization analysis, and RT-PCR. Samples of target gene-expressing tissue, may also be evaluated immunocytochemically using antibodies specific specific for the target gene transagene product of interest. The AP4AR transgenic animals that express AP4AR gene mRNA or AP4AR transgene peptide (detected immunocytochemically, using antibodies directed against target gene product epitopes) at easily detectable levels may then be further evaluated to identify those animals which display characteristic AP4AR based disorder symptoms. Once AP4AR transgenic founder animals are produced (i.e., those animals which express AP4AR proteins in cells or tissues of interest, and which, preferably, exhibit symptoms of AP4AR based disorders), they may be bred, inbred, outbred, or crossbred to produce colonies of the particular animal. Examples of such breeding strategies include but are not limited to: outbreeding of founder animals with more than one integration site in order to establish separate lines; inbreeding of separate lines in order to produce compound AP4AR transgenics that express the AP4AR transgene of interest at higher levels because of the effects of additive expression of each AP4AR transgene; crossing of heterozygous transgenic animals to produce animals homozygous for a given integration site in order to both augment expression and eliminate the possible need for screening of animals by DNA analysis; crossing of separate homozygous lines to produce compound heterozygous or homozygous lines; breeding animals to different inbred genetic backgrounds so as to examine effects of modifying alleles on expression of the AP4AR transgene and the development of AP4AR-like symptoms, one such approach is to cross the AP4AR transgenic founder animals with a wild type strain to produce an F1 generation that exhibits AP4AR related disorder-like symptoms, such as those described above. The F1 generation may then be inbred in order to develop a homozygous line, if it is found that homozygous target gene transgenic animals are viable.

Vaccines

Another aspect of the invention relates to a method for inducing an immunological response in a mammal which comprises inoculating the mammal with the AP4AR polypeptide, or a fragment thereof, if required together with a RAMP polypeptide, adequate to produce antibody and/or T cell immune response to protect said animal from said AP4AR-related dysfunctions or disorders as indicated supra.

Yet another aspect of the invention relates to a method of inducing immunological response in a mammal which comprises delivering the AP4AR polypeptide via a vector directing expression of the AP4AR polynucleotide in vivo in order to induce such an immunological response to produce antibody to protect said animal from diseases. In particular the invention relates to a method for inducing an immunological response in a mammal which comprises inoculating the mammal with the AP4AR polypeptide, or a fragment thereof, if required together with a RAMP polypeptide, adequate to produce antibody and or T cell immune response to protect said animal from the AP4AR-related dysfunctions or disorders as indicated supra.

A further aspect of the invention relates to an immunological/vaccine formulation (composition) which, when introduced into a mammalian host, induces an immunological response in that mammal to an AP4AR polypeptide wherein the composition comprises an AP4AR polypeptide or AP4AR gene. The vaccine formulation may further comprise a suitable carrier. Since the AP4AR polypeptide may be broken down in the stomach, it is preferably administered parenterally (including subcutaneous, intramuscular, intravenous, intradermal etc. injection). Formulations suitable for parenteral administration include aqueous and non-aqueous sterile injection solutions which may contain anti-oxidants, buffers, bacteriostats and solutes which render the formulation isotonic with the blood of the recipient; and aqueous and non-aqueous sterile suspensions which may include suspending agents or thickening agents. The formulations may be presented in unit-dose or multi-dose containers, for example, sealed ampoules and vials and may be stored in a freeze-dried condition requiring only the addition of the sterile liquid carrier immediately prior to use. The vaccine formulation may also include adjuvant systems for enhancing the immunogenicity of the formulation, such as oil-in water systems and other systems known in the art. The dosage will depend on the specific activity of the vaccine and can be readily determined by routine experimentation.

Screening Assays and methods for determining or identifying substances

The invention also pertains to methods for determining or identifying whether a substance, preferably a candidate compound, other than diadenosine tetraphosphate (AP4A) or analogues thereof, is a potential AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist of an AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1. The AP4AR polypeptide in the context of the present invention may be employed in a screening process for compounds which bind the receptor and which activate (agonists) or inhibit activation of (antagonists), or modulate the receptor polypeptide of the present invention. Thus, polypeptides of the invention may also be used to assess the binding of small molecule substrates and ligands in, for example, cells, cell-free preparations, chemical libraries; and natural product mixtures. These substrates and ligands may be natural substrates and ligands or may be structural or functional mimetics.

AP4AR polypeptides are responsible for biological functions, including pathologies. Accordingly, it is desirable to find compounds and drugs which stimulate AP4AR on the one hand and which can inhibit the function of AP4AR on the other hand, or modulate the AP4AR-activity. In general, agonists are employed for therapeutic and prophylactic purposes for such conditions as the AP4AR-related dysfunctions, disorders or diseases as indicated supra.

Particularly, the present invention may be employed in a screening process for compounds which bind the receptor and which activate (agonists) or inhibit activation of (antagonists) or modulate the activity of the AP4AR receptor protein. These screening assays are particularly suitable for screening novel substances, in particular candidate compounds, which are effective with regard to the AP4AR-related dysfunctions, disorders or diseases as indicated supra.

In general, such screening procedures involve producing appropriate cells, which express the receptor polypeptide of the present invention on the surface thereof and, if essential co- expression of RAMP's at the surface thereof. Such cells include cells from mammals, yeast, Drosophila or E. coli. Cells expressing the receptor (or cell membrane containing the expressed receptor) are then contacted with a test compound (e.g. a candidate compound) to observe binding, or stimulation or inhibition or modulation of a functional response.

One screening technique includes the use of cells which express the receptor of this invention (for example, transfected CHO cells) in a system which measures extracellular pH or intracellular calcium changes caused by receptor activation. In this technique, compounds may be contacted with cells expressing the receptor polypeptide of the present invention. A second messenger response, e.g., signal transduction, pH changes, or changes in calcium level, is then measured to determine whether the potential compound activates or inhibits the receptor.

Another method involves screening for receptor inhibitors by determining inhibition or simulation of receptor-mediated cAMP and/or adenylate cyclase accumulation. Such a method involves transfecting an eukaryotic cell with the receptor of this invention to express the receptor on the cell surface. The cell is then exposed to potential antagonists in the presence of the receptor of this invention. The amount of cAMP accumulation is then measured. If the potential antagonist binds the receptor, and thus inhibits receptor binding, the levels of receptor-mediated cAMP, or adenylate cyclase, activity will be reduced or increased.

Another method for detecting agonists or antagonists for the receptor of the present invention is the yeast-based technology as described in U.S. Patent 5,482,835, incorporated by reference herein.

The assays may simply test binding of a candidate compound wherein adherence to the cells bearing the receptor is detected by means of a label directly or indirectly associated with the candidate compound or in an assay involving competition with a labeled competitor. Further, these assays may test whether the candidate compound results in a signal generated by activation of the receptor, using detection systems appropriate to the cells bearing the receptor at their surfaces. Inhibitors of activation are generally assayed in the presence of a known agonist and the effect on activation by the agonist by the presence of the candidate compound is observed.

Thus, candidate compounds may be screened which show ligand binding to the AP4AR receptors of the present invention. In the context of the present invention the term "ligand binding" is understood as to describe compounds with affinity to the AP4AR receptors showing log EC50 values at least in the range of those found for AP4A itself or even better ones.

The assays may simply comprise the steps of mixing a candidate compound with a solution containing an AP4AR polypeptide to form a mixture, measuring the AP4AR activity in the mixture, and comparing the AP4AR activity of the mixture to a standard.

Thus, in one aspect the invention concerns a method for determining or identifying whether a substance, preferably a candidate compound, is a potential ligand of an AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(a) contacting cells expressing the AP4A-receptor polypeptide, or contacting a receptor membrane preparation comprising said AP4A-receptor polypeptide with labeled diadenosine tetraphosphate (AP4A) or analogues thereof in the presence and in the absence of the substance; and

(b) measuring the binding of diadenosine tetraphosphate or said analogues thereof to the AP4A- receptor polypeptide.

In another aspect the invention concerns a method for determining or identifying whether a substance, preferably a candidate compound, modulates the interaction of diadenosine tetraphosphate (AP4A) or analogues thereof with an AP4A-receptor polypeptide (AP4AR polypeptide), preferably with a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to an AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(a) contacting cells expressing on the surface thereof an AP4A-receptor polypeptide, said receptor being associated with a second component capable of providing a detectable signal in response to the binding of a compound to said receptor, with a substance, preferably with a candidate compound, to be screened under conditions to permit binding to the receptor; and

(b) determining whether the substance, preferably the candidate compound, modulates the interaction of AP4A or said analogues and the AP4A-receptor polypeptide by detecting an increase or decrease in the signal normally generated by the interaction of AP4A or said analogues with the receptor after interaction of AP4A or said analogues with the receptor.

In still another aspect the invention concerns a method for determining or identifying whether a substance, preferably a candidate compound, inhibits or antagonizes the interaction of diadenosine tetraphosphate (AP4A) or analogues thereof with an AP4A-receptor polypeptide (AP4AR polypeptide), preferably with a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to an AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises: 3b

(b) determining whether the substance, preferably the candidate compound, inhibits or antagonizes the interaction of AP4A or said analogues and the AP4A-receptor polypeptide by detecting an increase or decrease in the signal normally generated by the interaction of AP4A or said analogues with the receptor after interaction of AP4A or said analogues with the receptor.

In a further aspect the invention concerns a method for determining or identifying whether a substance, preferably a candidate compound, is an agonists to an AP4A-receptor polypeptide (AP4AR polypeptide), preferably to a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to an AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(a) contacting cells expressing on the surface thereof an AP4A-receptor polypeptide with a substance, preferably a candidate compound; and

(b) determining whether the substance, preferably the candidate compound, effects a signal generated by activation of the AP4A-receptor polypeptide, using diadenosine tetraphosphate (AP4A) or analogues thereof as a positive control for the generation of a signal.

In particular variants of the methods according to the before described aspects of the present invention the AP4A-receptor polypeptide (AP4AR polypeptide), preferably the mammalian AP4AR polypeptide, exhibits high affinity binding for diadenosine tetraphosphate (AP4A).

In further particular variants of the methods according to the before described aspects of the present invention the substance, preferably the candidate compound, is effective with regard to dysfunctions, disorders or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also of glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system. In very preferred embodiments of the present invention the substance, preferably the candidate compound, is effective with regard to dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

The AP4AR cDNA, protein and antibodies to the protein may also be used to configure assays for detecting the effect of added compounds on the production of AP4AR mRNA and protein in cells. For example, an ELISA may be constructed for measuring secreted or ceil associated levels of AP4AR protein using monoclonal and polyclonal antibodies by standard methods known in the art, and this can be used to discover agents which may inhibit or enhance the production of AP4AR (also called antagonist or agonist, respectively) from suitably manipulated cells or tissues. Standard methods for conducting screening assays are well known in the art.

Examples of potential AP4AR antagonists include antibodies or, in some cases, oligonucleotides or proteins which are closely related to the ligand of the AP4AR, e.g., a fragment of the ligand, or small molecules which bind to the receptor but do not elicit a response, so that the activity of the receptor is prevented.

Thus, in another aspect, the present invention relates to a screening kit for identifying agonists, antagonists, ligands, receptors, substrates, enzymes, etc. for AP4AR polypeptides; or compounds which decrease or enhance the production of AP4AR polypeptides, which comprises:

(a) an AP4AR polypeptide, preferably that of SEQ ID NO: 2;

(b) a recombinant cell expressing an AP4AR polypeptide, preferably that of SEQ ID NO: 2;

(c) a cell membrane expressing an AP4AR polypeptide; preferably that of SEQ ID NO: 2; or

(d) antibody to an AP4AR polypeptide, preferably that of SEQ ID NO: 2.

It will be appreciated that in any such kit, (a), (b), (c) or (d) may comprise a substantial component.

Compounds Identified and/or Designed by the Use of the Invention

The present invention enables the person skilled in the art to identify novel substances or compounds, e.g. candidate compounds, by means of screening methods involving the findings of the present invention, said novel substances or compounds preferably are novel organic chemical molecules, other than diadenosine tetraphosphate or analogues thereof, and may reveal as prospective drug candidates in particular with respect to dysfunctions, disorders or diseases related to, in particular to human, dysfuctions, disorders or diseases such as stated supra and being related to the activities of the AP4A-receptor polypeptides, in particular of human AP4A- receptor polypeptide, in connection with its interrelation with the AP4A ligand or analogues thereof. Thus, the invention also relates to candidate compounds that bind to the AP4A-receptor polypeptides, modulate the interaction of AP4A or analogues thereof with an AP4A-receptor polypeptide, and to antagonistic candidate compounds that inhibit the interaction of AP4A or analogues thereof with an AP4A-receptor polypeptides, or to agonistic candidate compounds that activate the AP4A-receptor polypeptides.

Today, medicinal chemists are well aware of modern strategies for planning and performing organic synthesis in order to generate new substances or compounds that are worth to be investigated for potential physiological or pharmacological properties, and which compounds therefore promise to prove as prospective new drug candidates for the treatment and/or prophylaxis of specific dysfunctions, disorders or diseases. Furthermore, today it is common to provide compound libraries by means of combinatorial chemistry, e.g. in particular of general and of "directed" chemical or compound libraries, in which the structure and the variations of pharmacophore groups and the residues or substituents are known to the concerned artisan. If chemical libraries or compound libraries with still unknown structure of the compounds are investigated in screening assays, potential prospective compounds, e.g. candidate compounds, nevertheless, may easily be analyzed for their structure and chemical properties by today's well- established analytical means such as e.g. mass spectroscopy, nuclear magnetic resonance, infrared spectra, melting points, optical rotation if chiral compounds are involved, and elemental analysis.

Thus the invention also pertains to a process for preparing a novel substance, preferably a candidate compound, with a defined chemical structure capable of binding to, of activating, modulating or inhibiting the interaction of AP4A or of an analog thereof with an AP4A-receptor polypeptide, said process is comprising the manufacture of a compound or of a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said substance by means of chemical synthesis, provided that the activity of the substance or candidate compound to bind to, to activate, to modulate or to inhibit the interaction of AP4A or of an analog thereof with an AP4A- receptor polypeptide is determinable or identifiable by a screening method according to the present invention (see supra).

For details of e.g. chemical organic synthesis, and e.g. chemical, analytical and physical methods see the Handbook "Houben-Weyl" (Houben-Weyl, "Methoden der organischen Chemie", Georg Thieme Verlag, Stuttgart, New York) in its most recent version.

Therefore, the invention in a further embodiment pertains also to a novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a screening method of the present invention as described above to be an AP4A-receptor ligand, an AP4A- receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, or of pharmaceutically acceptable salts, hydrates, solvates or biolabile esters of said substance. Particularly, these novel substances according to the invention are effective with regard to dysfunctions, disorders or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also of glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system; and preferably is effective with regard to dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases. Protein-Ligand-Complexes in Drug Design and Lead Structure Optimization

In another aspect the invention relates to protein-ligand-complex comprising an AP4A- receptor polypeptide (AP4AR polypeptide), preferably a mammalian AP4AR polypeptide, showing at least 80% identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, and further comprising a substance, preferably a candidate compound, which qualifies in a method of one of the screening methods described supra to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, wherein said substance, preferably candidate compound, shows AP4AR-binding affinity of at least that of diadenosine tetraphosphate itself. Such protein-ligand- complexes are particularly useful in drug design methods, lead structure finding, lead structure optimization and modulation methods. The methods are well known in the state of the art. For exemplary reference see literature concerning e.g. combinatorial synthesis and multidimensional NMR-spectroscopy and its contribution to the understanding of protein-ligand-interactions (Kessler, Angew. Chem. 1997, 109, 857-859; James K. Chen et al., Angew. Chem. 107 (1995), S. 1041- 1058). Furthermore see Fesik (Journal of Medicinal Chemistry, 34 (1991), S. 2937-2945) who describes NMR studies of molecular complexes as a tool in drug design; and . Fesik et al. (Biochemical Pharmacology 40 (1990), S. 161-167) who describe NMR methods for determining the structures of enzyme/inhibitor complexes as an aid in drug design. A very recent report of Ross et al. (Journal of Biomolecular NMR, 16: 139-146 (2000)) describes the automation of NMR measurements and data evaluation for systemically screening interactions of small molecules with target proteins, e.g. receptors.

Thus, the invention also pertains to the use of a protein-ligand-complex comprising an AP4A-receptor polypeptide (AP4AR polypeptide), preferably a mammalian AP4AR polypeptide, showing at least 80% identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, and further comprising a substance, preferably a candidate compound, which qualifies in a method of one of the screening methods described supra to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, in the design, modulation or optimization of lead structures with AP4A-receptor ligand activity, AP4A-receptor modulator activity, AP4A-receptor antagonist activity or AP4A-receptor agonist activity. 3y Prophylactic and Therapeutic Methods

This invention provides methods of treating abnormal conditions related to both an excess of and insufficient amounts of AP4AR activity.

If the activity of AP4AR is in excess, several approaches are available. One approach comprises administering to a subject an inhibitor compound (antagonist) as herein above described along with a pharmaceutically acceptable carrier in an amount effective to inhibit activation by blocking binding of ligands to the AP4AR, or by inhibiting interaction with a RAMP polypeptide or a second signal, and thereby alleviating the abnormal condition.

In another approach, soluble forms of AP4AR polypeptides still capable of binding the ligand in competition with endogenous AP4AR may be administered. Typical embodiments of such competitors comprise fragments of the AP4AR polypeptide.

In still another approach, expression of the gene encoding endogenous AP4AR can be inhibited using expression-blocking techniques. Known such techniques involve the use of antisense sequences, either internally generated or separately administered. See, for example, O'Connor, J Neurochem (1991) 56:560 in Oligodeoxynucleotides as Antisense Inhibitors of Gene Expression, CRC Press, Boca Raton, Florida USA (1988). Alternatively, oligonucleotides, which form triple helices with the gene, can be supplied. See, for example, Lee et al., Nucleic Acids Res (1979) 6:3073; Cooney et al., Science (1988) 241:456; Dervan et al, Science (1991) 251:1360. These oligomers can be administered per se or the relevant oligomers can be expressed in vivo.

For treating abnormal conditions related to an under-expression of AP4AR and its activity, several approaches are also available. One approach comprises administering to a subject a therapeutical ly effective amount of a compound which activates AP4AR, i.e., an agonist as described above, in combination with a pharmaceutically acceptable carrier, to thereby alleviate the abnormal condition. Alternatively, gene therapy may be employed to effect the endogenous production of AP4AR by the relevant cells in the subject. For example, a polynucleotide of the invention may be engineered for expression in a replication defective retroviral vector, as discussed above. The retroviral expression construct may then be isolated and introduced into a packaging cell transduced with a retroviral plasmid vector containing RNA encoding a polypeptide of the present invention such that the packaging cell now produces infectious viral particles containing the gene of interest. These producer cells may be administered to a subject for engineering cells in vivo and expression of the polypeptide in vivo. For overview of gene therapy, see Chapter 20, Gene Therapy and other Molecular Genetic-based Therapeutic Approaches, (and references cited therein) in Human Molecular Genetics, Strachan T. and Read A. P., BIOS Scientific Publishers Ltd (1996). In the context of this embodiment the invention particularly pertains to method for the treatment of a subject in need of enhanced activity or expression of AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(a) administering to the subject a therapeutically effective amount of an AP4A-receptor agonist according to claim 8 or of a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said agonist; and/or

(b) providing to the subject an isolated polynucleotide comprising a nucleotide sequence that has at least 80% identity to a nucleotide sequence encoding the AP4AR polypeptide of SEQ ID NO: 2, or a nucleotide sequence complementary to one of said nucleotide sequences in a form so as to effect production of said receptor activity in vivo.

(c) providing to the subject an isolated polynucleotide comprising a nucleotide sequence that encodes an AP4A-receptor polypeptide, preferably a mammalian AP4AR-receptor polypeptide, said polypeptide exhibiting high affinity binding for diadenosine tetraphosphate (AP4A).

A further embodiment of the invention in this context particularly pertains to a method for the treatment of a subject having need to inhibit activity or expression of AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(a) administering to the subject a therapeutically effective amount of an AP4A-receptor antagonist according to claim 8 or of a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said antagonist; and/or

(b) administering to the subject a nucleic acid molecule that inhibits the expression of the nucleotide sequence encoding said AP4A-receptor; and/or

(c) administering to the subject a therapeutically effective amount of a polypeptide that competes with said AP4A-receptor for its ligand.

Formulation and Administration

Peptides, such as the soluble form of AP4AR polypeptides, and agonists and antagonist peptides or small molecules, may be formulated in combination with a suitable pharmaceutical carrier. Such formulations comprise a therapeutically effective amount of the polypeptide or compound, and a pharmaceutically acceptable carrier or excipient. Formulation should suit the mode of administration, and is well within the skill of the art. The invention further relates to pharmaceutical packs and kits comprising one or more containers filled with one or more of the ingredients of the aforementioned compositions of the invention. Polypeptides and other compounds of the present invention may be employed alone or in conjunction with other compounds, such as therapeutic compounds.

Preferred forms of systemic administration of the pharmaceutical compositions include injection, typically by intravenous injection. Other injection routes, such as subcutaneous, intramuscular, or intraperitoneal, can be used. Alternative means for systemic administration include transmucosal and transdermal administration using penetrants such as bile salts or fusidic acids or other detergents. In addition, if properly formulated in enteric or encapsulated formulations, oral administration may also be possible.

The dosage range required depends on the choice of peptide, the route of administration, the nature of the formulation, the nature of the subject's condition, and the judgment of the attending practitioner. Suitable dosages, however, are in the range of 0.1-100 μg/kg of subject. Wide variations in the needed dosage, however, are to be expected in view of the variety of compounds available and the differing efficiencies of various routes of administration. For example, oral administration would be expected to require higher dosages than administration by intravenous injection. Variations in these dosage levels can be adjusted using standard empirical routines for optimization, as is well understood in the art.

Polypeptides used in treatment can also be generated endogenously in the subject, in treatment modalities often referred to as "gene therapy" as described above. Thus, for example, cells from a subject may be engineered with a polynucleotide, such as a DNA or RNA, to encode a polypeptide ex vivo, and for example, by the use of a retroviral plasmid vector. The cells are then introduced into the subject.

In this context the invention also pertains to a method for the production of a pharmaceutical composition comprising mixing a novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a screening method of the invention as described above to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, or a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said substance with pharmaceutically acceptable carriers, excipients and/or other galenical auxiliary agents. In particular, the pharmaceutical composition is prepared for the treatment, alleviation and/or prophylaxis of an AP4AR-related dysfunction, disorder or disease; preferably those including the heart, of the nervous system, including the central nervous system, and also of glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system. Preferably the pharmaceutical composition is prepared for the treatment, alleviation and/or prophylaxis of dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

In the context of these embodiments the invention furthermore pertains to an article of manufacture (packaged pharmaceutical composition) comprising a packaging material and a novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a screening method of the invention as described above to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, or a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said substance contained in said packaging material, wherein said packaging material furthermore comprises a label or package insert or other instructions indicating that said substance or the pharmaceutically acceptable salt, hydrate, solvate or biolabile ester thereof can be administered to a mammal for the treatment, alleviation and/or prophylaxis of an AP4AR-related dysfunction, disorder or disease, preferably those associated with the cardiovascular system, including the heart, with the nervous system, including the central nervous system, and also with glucose and insulin metabolism, and furthermore with immunological diseases and disorders of the genitourinary system. More preferred articles of manufacture (packaged pharmaceutical composition) according to the invention are those, wherein said packaging material comprises a label or package insert or other instructions indicating that the substance or the pharmaceutically acceptable salt, hydrate, solvate or biolabile ester thereof can be administered to a mammal with regard to dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

Examples

EXAMPLE 1. THE CLONING OF CDNA ENCODING GPR56

In this example PCR cloning of the G-protein coupled receptor GPR56 (AP4AR) is outlined.

The details of cloning the orphan receptor GPR56 are described by Liu, M., et al. (Genomics 55,

296-305 (1999) and in WO 99/15551 which are incorporated by reference herein.

The cDNA (2081 bp) has been amplified in single stage RT-PCR using the human brain total RNA and the following primers :

5'-ACG TAA GCT TAT GAC TCC CCA GTC GCT GC-3'

5'-ACG TGC GGC CGC CTA GAT GCG GCT GGA CGA G-3'

The RT-PCR was performed following the recommended conditions from "Thermoscript Kit"

(GIBCO BRL). The used annealing temperature was 58°C.

After cloning into pCR2.1, the positive clones have been sequenced. Two mutations are present in the eleven sequenced clones when compared to the published GPR56 sequence:

GTA into GTG at position 711 (silent mutation),

TGC into AGC at position 2032 (Cys678Ser).

This GPR56 construct has been cloned into the expression vector pcDNA3.1.

Further data concerning the GPRS6 receptor:

1. Homology to other orphan receptors (as compared to the amino acid sequences):

HE6 (32%), EMR1 (27%), CD97 (226%), BAH (26%) und alpha-latrotoxin-binding protein (30%). Due to the secondary structure the receptor was not classified - as most of the GPCRs - in "class A (rhodopsin.like)" GPCRs, but classified in "Class B (secretin-like)" GPCRs

2. Expression of the receptor:

2.1 Northern Blot (see Liu et al. (1999) Genomics 55, 296-305)): thyroid gland (highest level of expression); specific brain areas; heart; kidney; testis; pancreas; skeletal muscle; neuroblastoma cell lines; p53 negative breast cancer cell lines.

2.2 In situ hybridisation (see Liu et al. (1999) Genomics 55, 296-305)): human: thyroid tissue (selectively expressed within the monolayer of cubical epithelial cells of the smaller, more active secreting follicles); rat: heart: myocardial cells; coronal sections of rat forebrain: wide distribution: CA layers of hippocampus; thalamus, anterodorsal thalamic nucleus, lower in other thalamic regions; hypothalamus, particularly strong within paraventricular nucleus; amygdala; cortex.

2.3 EST search (see Liu et al. (1999) Genomics 55, 296-305)): retina; uterus. 2.4 Electronic Northern: human: placenta, brain anaplastic oligodendroglioma, infant brain, adultbreast, cerebellum, uterus, eye-retina, oligodenroglioma, placenta, testis; Mus m.: medulla, brain, heart; Gallus g.: cerebellum.

2.5 Chromosomal localisation (see Liu et al. (1999) Genomics 55, 296-305)): human: Chr. 8 16q13 (up to now no mutations yet are known that might affect the phenotype); Chr. 8, distal (but shows homologies with Chr. 19p where many GPCRs are located).

EXAMPLE 2. SPECIFIC CHANGES IN INTRACELLULAR CALCIUM CONCENTRATIONS INDUCED IN CHOG α 16- AP4AR/GPR56 CELLS BY DIADENOSINE TETRAPHOSPHATE (AP4A).

Example 2a. Experimental Procedures: Method and Materials.

A. Method and Materials for AP4AR/GPR56 transfected CHOGα16-cells.

The following materials were used in the experiments: Vector containing AP4AR/GPR56-DNA sequence (AP4AR/GPR56 -pcDNA3.1); SuperFect Transfection Reagent (Qiagen); Nut-Mix F12 (Gibco) with 10% FCS, 0.028mg/ml Gentamycin (Gibco); 0.22mg/ml Hygromycin (Gibco). Materials used for clone selection: Nut-Mix F12 with 10% FCS; 0.028mg/ml Gentamycin; 0.22mg/ml Hygromycin and 0.55mg/ml Geneticin (Gibco).

The following method was applied: Transfection with SuperFect Transfection Reagent was carried out as described by the manufacturer (Qiagen). Cells were plated in 24-well plates to 50% confluence. Per well 0.6μg/μl plasmid-DNA with 1μl SuperFect Transfection Reagent was added. After 24 hours the medium was changed and transfected cell clones were selected by Geneticin- containing selection-medium. AP4AR/GPR56 expressing cell clones were characterized by RT- PCR (using the internal primer pair 5'-GCA GGG GCC ACA GGG AAG ACT-3' and 5'-AGC GGC CGT GTG GGG AGG ACT-3').

B. Method and Materials for FLIPR-Assay.

Cell Preparation:

For cell preparation the following materials were employed: plates: clear, flat-bottom, black well 96-well plates (Costar); Media: growth medium: Nut-Mix F-12 (HAM) with Glutamax (Gibco) supplemented with 10% fetal calf serum (Gibco); Incubator: 5% C02, 37°C (Nuaire). The method was worked as follows: Cells were seeded 24 hours or 48 hours prior to the experiment into black wall microplates. The cell density was 0.4x10^"4 cells/well for 48 hour incubation and 1.5x10^"4 cells/well for 24 hour incubation. All steps were done under sterile conditions.

Dye loading:

In order to observe changes in intracellular calcium levels, cells must be 'loaded' with a calcium- sensitive fluorescent dye. This dye, called FLUO-4 (Molecular Probes) excite at 488nm, and emit in the 500-560nm range, only if a complex with calcium is formed. The dye was used at 4μM final concentration. Pluronic acid was added to increase dye solubility and dye uptake into the cells. Probenicid, an anion exchange protein inhibitor, was added to the dye medium to increase dye retention in the cells.

The following materials were used:

• 2m M dye stock: 1mg Fluo-4 (Molecular Probes) solubilized in 443μl low-water DMSO (Sigma). Aliquots stored at -20.

• 20% pluronic acid solution: 400mg pluronic acid (Sigma) solubilized in 2ml low-water DMSO (Sigma) at 37°C-. Stored at room temperature.

• Dye/pluronic acid mixture: Immediately before use, equal volumes of the dye stock and 20% pluronic acid were mixed. The dye and pluronic acid had a final concentration of 1mM and 10%, respectively.

• Probenicid. 250mM stock solution: 710mg probenicid (Sigma) solubilized in 5ml 1 N NaOH and mixed with 5ml Hank^'s BSS without phenol red (Gibco) supplemented with 20mM HEPES.

• Loading-Buffer: 10.5ml Hank's BSS without phenol red (Gibco) supplemented with 20mM HEPES, 105μl probenicid, 210μl 1M HEPES.

• Wash-Buffer: Hank^'s BSS without phenol red (Gibco) supplemented with 20mM HEPES (Gibco) and 2.5mM probenicid.

The method was worked as follows: The 2mM stock of dye was mixed with an equal volume of 20% (w/v) pluronic acid immediately before adding to the loading-Buffer. The growth-medium was aspirated out of the well without disturbing the confluent cell layer. 100μl loading medium was dispensed into each well using a Multidrop (Labsystems). Cell were incubated in a 5% C0₂, 37°C incubator for 30 minutes. In order to calculate the background fluorescence, some wells were not dye loaded. The background fluorescence in these wells results from autofluorescence of the cells. After dye loading, cell were washed three times with Wash-Buffer (automated Denley cell washer) to reduce the basal fluorescence to 20.000-25.000 counts above background. 100 μl buffer was added and cell were incubated at 37°C till start of the experiment. C. Preparation of compound plates.

The compounds were prepared at 10μM (3x the final concentration) for initial screening. All compounds were disolved in ddH₂Oat 10mM and diluted with buffer. For concentration response curves solutions were prepared in concentration ranges from 33μM to 0.04μM.

The following materials were used: P1,P2-Di(Adenosine-5')Pyrophosphate (Sigma), P1,P3- Di(Adenosine-5')Triphosphate (Sigma), P1,P4-Di(Adenosine-5^')Tetraphosphate (Sigma), P1,P5- Di(Adenosine-5')Pentaphosphate (Sigma), P1,P6-Di(Adenosine-5^')Hexaphosphate (Sigma), α,β- Methyleneadenosine-5'-Triphosphate (Sigma), β,γ-Methyleneadenosine-5'-Tri phosphate (Sigma), ATP (Roche); Buffer: Hank's BSS without phenol red (Gibco) supplemented with 20mM HEPES (Gibco); plates: clear, flat-bottom, 96-well plates (Costar).

D. Assay.

The FLIPR setup parameters were set to 0.4 sec exposure length, filter 1 , 50μl fluid addition, pipettor height at 125μl, Dispense Speed 40μl/sec without mixing.

Example 2b. Results.

To identify the endogenous ligand for the orphan G protein coupled receptor (GPCR) GPR56, it was stable transfected in Chinese Hamster Ovary (CHO) cells. Since the G protein coupling mechanism of GPR56 was unknown, a specific CHO-cell strain was used. These CHO-cells stable express the G-protein Gα16 (CHOGα16, Molecular Devices), which is known as "universal adapter" for GPCRs (Milligan G., Marshall F. and Rees S. (1996), G16 as a universal G protein adapter: implications for agonist screening strategies. TIPS 17: 2354137).

The resulting CHOGα16-GPR56 cells were functionally screened on a Fluorometric Imaging Plate Reader (FLIPR) to measure mobilisation of intracellular calcium in response to putative endogenous ligands.

At the concentration of 3μM AP4A induced a large, transient and robust calcium-response. In contrast, CHOGα16 cells and CHOGαlδ cells expressing other, unrelated orphan GPCRs, did not respond to AP4A. The results of these experiments are shown in Fig. 1.

As by the present invention the orphan receptor GPR56 was identified as the specific diadenosine tetraphosphate receptor, accordingly this receptor was redesignated to AP4AR (AP4A-receptor).

Furthermore, the concentration dependence of AP4AR/GPR56 activation by AP4A was investigated. AP4A induced specific AP4A-mediated calcium mobilisation in the FLIPR assay with an EC-50 value of 470nM. Suggesting that AP4A is the natural agonist for this receptor. The results of these experiments are shown in Fig. 2. The calcium mobilisation response seen following activation of AP4AR/GPR56 by AP4A suggests further that this receptor is coupled to G proteins of the Gq/11 subfamily.

Since diadenosine tetraphosphate is a member of a group of dinucieoside poyphosphates, we further tested the specificity of the receptor. P1,P3-Di(Adenosine-5')Triphosphate, P1.P4- Di(Adenosine-5')Tetraphosphate, P1,P5-Di(Adenosine-5^')Pentaphosphate, and P1,P6- Di(Adenosine-5^')Hexaphosphate occur naturally, while the synthetic compound P1.P2- Di(Adenosine-5')Pyrophosphate completes the sequence. Many physiological effects were measured by these polyphosphates and other adenine nucleotides (e.g. α,β-Methyleneadenosine- 5'-Triphosphate and ATP).

The experiments (Fig. 3) show that the AP4R-receptor is highly specific for diadenosine tetraphosphate. Other tested dinucieoside poyphosphates or adenine nucleotides did not activate this receptor. Due to the endogenous expression of P2Y-purinergic receptors in CHO cells we measured intracellular Ca²⁺ release by ATP in AP4AR-transfected and non-transfected CHOGα16 cells. The experiments further show, that there is a low-affinity binding of P1,P5-Di(Adenosine- 5')Pentaphosphate, and P1,P6-Di(Adenosine-5')Hexaphosphate to the endogenous expressed of P2-purinergic receptor (Fig.3).

Thus, the findings of the present invention provide the possibility to distinguish between the effects of different dinucieoside poyphosphates and to analyse the physiological effects of AP4A and its receptor in detail, in particular in the context of drug discovery.

All publications, including but not limited to patents and patent applications, cited in this specification are herein incorporated by reference as if each individual publication were specifically and individually indicated to be incorporated by reference herein as though fully set forth.

Claims

1. A method for determining or identifying whether a substance, preferably a candidate compound, is a potential ligand of an AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(b) measuring the binding of diadenosine tetraphosphate or said analogues thereof to the AP4A-receptor polypeptide.

2. A method for determining or identifying whether a substance, preferably a candidate compound, modulates the interaction of diadenosine tetraphosphate (AP4A) or analogues thereof with an AP4A-receptor polypeptide (AP4AR polypeptide), preferably with a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to an AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

3. A method for determining or identifying whether a substance, preferably a candidate compound, inhibits or antagonizes the interaction of diadenosine tetraphosphate (AP4A) or analogues thereof with an AP4A-receptor polypeptide (AP4AR polypeptide), preferably with a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to an AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(a) contacting cells expressing on the surface thereof an AP4A-receptor polypeptide, said receptor being associated with a second component capable of providing a detectable signal in response to the binding of a compound to said receptor, with a substance, preferably with a candidate compound, to be screened under conditions to permit binding to the receptor; and (b) determining whether the substance, preferably the candidate compound, inhibits or antagonizes the interaction of AP4A or said analogues and the AP4A-receptor polypeptide by detecting an increase or decrease in the signal normally generated by the interaction of AP4A or said analogues with the receptor after interaction of AP4A or said analogues with the receptor.

4. A method for determining or identifying whether a substance, preferably a candidate compound, is an agonists to an AP4A-receptor polypeptide (AP4AR polypeptide), preferably to a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to an AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

5. A method according to one of the claims 1 to 4, wherein the AP4A-receptor polypeptide (AP4AR polypeptide), preferably the mammalian AP4AR polypeptide, exhibits high affinity binding for diadenosine tetraphosphate (AP4A).

6. A method according to one of the claims 1 to 5, wherein the substance, preferably the candidate compound, is effective with regard to dysfunctions, disorders or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also of glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system.

7. A method according to claim 6, wherein the substance, preferably the candidate compound, is effective with regard to dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

8. Novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a method of one of the claims 1 to 7 to be an AP4A-receptor ligand, an AP4A- receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, or of pharmaceutically acceptable salts, hydrates, solvates or biolabile esters of said substance.

9. Novel substance according to claim 8, characterized in that the substance is effective with regard to dysfunctions, disorders or diseases of the cardiovascular system, including the heart, of the nervous system, including the central nervous system, and also of glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system; and preferably is effective with regard to dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

10. Use of a novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a method of one of the claims 1 to 7 to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A- receptor antagonist or an AP4A-receptor agonist, or of pharmaceutically acceptable salts, hydrates, solvates or biolabile esters of said substance for the preparation of a pharmaceutical composition for the treatment, alleviation and/or prophylaxis of an AP4AR-related dysfunction, disorder or disease, preferably those associated with the cardiovascular system, including the heart, with the nervous system, including the central nervous system, and also with glucose and insulin metabolism, and furthermore with immunological diseases and disorders of the genitourinary system.

11. Use according to claim 10, characterized in that the novel substance, which qualifies to be AP4A-receptor ligand, modulator, antagonist or agonist, or the pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said substance is particularly used for the preparation of a pharmaceutical composition for the treatment, alleviation and/or prophylaxis of a dysfunction, disorder or disease associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

12. Method for the production of a pharmaceutical composition comprising mixing a novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a method of one of the claims 1 to 7 to be an AP4A-receptor ligand, an AP4A- receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, or a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said substance with pharmaceutically acceptable carriers, excipients and/or other galenical auxiliary agents.

13. Method for the production of a pharmaceutical composition according to claim 12, wherein the pharmaceutical composition is prepared for the treatment, alleviation and/or prophylaxis of an AP4AR-related dysfunction, disorder or disease, preferably those including the heart, of the nervous system, including the central nervous system, and also of glucose and insulin metabolism, and furthermore of immunological diseases and disorders of the genitourinary system;

14. Method for the production of a pharmaceutical composition according to claim 13, wherein the pharmaceutical composition is prepared for the treatment, alleviation and/or prophylaxis of dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

15. A method for the treatment of a subject in need of enhanced activity or expression of AP4A- receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(d) administering to the subject a therapeutically effective amount of an AP4A-receptor agonist according to claim 8 or of a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said agonist; and/or

(e) providing to the subject an isolated polynucleotide comprising a nucleotide sequence that has at least 80% identity to a nucleotide sequence encoding the AP4AR polypeptide of SEQ ID NO: 2, or a nucleotide sequence complementary to one of said nucleotide sequences in a form so as to effect production of said receptor activity in vivo.

(f) providing to the subject an isolated polynucleotide comprising a nucleotide sequence that encodes an AP4A-receptor polypeptide, preferably a mammalian AP4AR-receptor polypeptide, said polypeptide exhibiting high affinity binding for diadenosine tetraphosphate (AP4A).

16. A method for the treatment of a subject having need to inhibit activity or expression of AP4A- receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said method comprises:

(d) administering to the subject a therapeutically effective amount of an AP4A-receptor antagonist according to claim 8 or of a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said antagonist; and/or

(e) administering to the subject a nucleic acid molecule that inhibits the expression of the nucleotide sequence encoding said AP4A-receptor; and or

(f) administering to the subject a therapeutically effective amount of a polypeptide that competes with said AP4A-receptor for its ligand.

17. A process for diagnosing a dysfunction, disorder or disease or a susceptibility to a dysfunction, disorder or disease in a subject related to expression or activity of a AP4A-receptor polypeptide (AP4AR polypeptide) in a subject, preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, wherein said process comprises:

(a) determining the presence or absence of a mutation in the nucleotide sequence encoding said AP4AR polypeptide in the genome of said subject; and/or

(b) analyzing for the presence or amount of the AP4AR polypeptide expression in a sample derived from said subject.

18. Article of manufacture (packaged pharmaceutical composition) comprising a packaging material and a novel substance, other than diadenosine tetraphosphate (AP4A) or analogues thereof, which qualifies in a method of one of the claims 1 to 7 to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, or a pharmaceutically acceptable salt, hydrate, solvate or biolabile ester of said substance contained in said packaging material, wherein said packaging material furthermore comprises a label or package insert or other instructions indicating that said substance or the pharmaceutically acceptable salt, hydrate, solvate or biolabile ester thereof can be administered to a mammal for the treatment, alleviation and/or prophylaxis of an AP4AR- related dysfunction, disorder or disease, preferably those associated with the cardiovascular system, including the heart, with the nervous system, including the central nervous system, and also with glucose and insulin metabolism, and furthermore with immunological diseases and disorders of the genitourinary system.

19. Article of manufacture (packaged pharmaceutical composition) according to claim 18, wherein said packaging material comprises a label or package insert or other instructions indicating that the substance or the pharmaceutically acceptable salt, hydrate, solvate or biolabile ester thereof can be administered to a mammal with regard to dysfunctions, disorders or diseases associated with the cardiovascular system, preferably including blood pressure control, e.g. hypertension or vasodilatation, regulation of hemostasis, myocardial ischaemia, ischaemic preconditioning, cardioprotective activity, or other heart related diseases.

20. A method of creating a genetically modified non-human animal comprising the steps of:

(a) ligating the coding portion of a nucleic acid molecule, consisting essentially of a nucleic acid sequence encoding a protein having the amino acid sequence SEQ ID NO: 2, or a biologically active portion of one of said sequence, to a regulatory sequence which is capable of driving high level gene expression or expression in a cell type in which the gene is not normally expressed in said animal; or

(b) isolation and engineering the coding portion of a nucleic acid molecule, consisting essentially of a nucleic acid sequence encoding a protein having the amino acid sequence SEQ ID NO: 2, or a biologically active portion of one of said sequence, and reintroducing said sequence in the genome of said animal in such a way that the endogenous gene alleles, encoding a protein having the amino acid sequence SEQ ID NO: 2, or a biologically active portion of one of said sequence, are fully or partially inactivated.

21. Protein-ligand-complex comprising an AP4A-receptor polypeptide (AP4AR polypeptide), preferably a mammalian AP4AR polypeptide, showing at least 80% identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, and further comprising a substance, preferably a candidate compound, which qualifies in a method of one of the claims 1 to 7 to be an AP4A-receptor ligand, an AP4A- receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, wherein said substance, preferably candidate compound, shows AP4AR-binding affinity of at least that of diadenosine tetraphosphate itself.

22. Use of a protein-ligand-complex comprising an AP4A-receptor polypeptide (AP4AR polypeptide), preferably a mammalian AP4AR polypeptide, showing at least 80% identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1, and further comprising a substance, preferably a candidate compound, which qualifies in a method of one of the claims 1 to 7 to be an AP4A-receptor ligand, an AP4A-receptor modulator, an AP4A-receptor antagonist or an AP4A-receptor agonist, in the design, modulation or optimization of lead structures with AP4A-receptor ligand activity, AP4A-receptor modulator activity, AP4A-receptor antagonist activity or AP4A-receptor agonist activity.

23. An antibody against the interaction of diadenosine tetraphosphate (AP4A) or analogues thereof and an AP4A-receptor polypeptide (AP4AR polypeptide), preferably of a mammalian AP4AR polypeptide, showing at least 80 % identity to the AP4AR polypeptide of SEQ ID NO: 2 or to the AP4AR polypeptide encoded by the polynucleotide of SEQ ID NO: 1.