WO2002077229A2 - Cofactors of the liver x receptor alpha and methods of use - Google Patents

Abstract

The present invention relates to novel cofactors of the liver X receptor alpha which are designated CF21, CF22, and CF33a and in particular to the isolated nucleic acid sequences encoding these cofactors and the isolated polypeptides thereof. The invention further relates to processes for isolating and/or producing the nucleic acids or the polypeptides as well as methods of use of these cofactors, such as in inhibiting or activating the binding of the cofactors to the liver X receptor alpha.

Description

NOVEL COFACTORS OF THE LIVER X RECEPTOR ALPHA AND METHODS OF

USE

BACKGROUND OF THE INVENTION

Multicellular organisms are dependent on advanced mechanisms of information transfer between cells and body compartments. The information that is transmitted can be highly complex and can result in the alteration of genetic programs involved in cellular differentiation, proliferation, or reproduction. The signals such as hormones, are often simple molecules, such as peptides, fatty acid, or cholesterol derivatives.

Many of these signals produce their effects by ultimately changing the transcription of specific genes. One well-studied group of polypeptides that mediate a cell's response to a variety of signals is a family of transcription factors known as nuclear receptors, hereinafter referred to frequently as "NR". Members of this group include receptors for steroid hormones (for example, estrogens and glucocorticoids and other cholesterol-derivatives), vitamin D, ecdysone, cis and trans retinoic acid, thyroid hormone, bile acids, fatty acids (and other peroxisomal proliferators), as well as so-called orphan receptors, proteins that are structurally similar to other members of this group, but for which no ligands are known (Escriva, H. et al., Ligand binding was acquired during evolution of nuclear receptors, PNAS, 94, 6803 - 6808, 1997). Orphan receptors may be indicative of unknown signaling pathways in the cell or may be nuclear receptors that function without ligand activation. The activation of transcription by some of these orphan receptors may occur in the absence of an exogenous ligand and/or through signal transduction pathways originating from the cell surface (Mangelsdorf, D. J. et al., The nuclear receptor superfamily: the second decade, Cell 83, 835-839, 1995).

In general, three functional domains have been defined in NRs. An amino terminal domain is believed to have some regulatory function. A DNA-binding domain hereinafter referred to as "DBD" usually comprises two zinc finger elements and recognizes a specific Hormone Responsive Element hereinafter referred to as "HRE" within the promoters of responsive genes. Specific amino acid residues in the "DBD" have been shown to confer DNA sequence binding specificity (Schena, M. & Yamamoto, K.R., Mammalian Glucocorticoid Receptor Derivatives Enhance Transcription in Yeast, Science, 241:965-967, 1988). A Ligand-binding-domain hereinafter referred to as "LBD" is at the carboxy-terminal region of known NRs. In the absence of hormone, the LBD appears to interfere with the interaction of the DBD with its HRE. Hormone binding seems to result in a conformational change in the NR and thus opens this interference (Brzozowski et al., Molecular basis of agonism and antagonism in the oestogen receptor, Nature, 389, 753 - 758, 1997; Wagner et al, A structural role for hormone in the thyroid hormone receptor, Nature, 378, 690 - 697. 1995). A NR without the LBD constitu- tively activates transcription but at a low level.

Both the amino-terminal domain and the LBD of the NR appear to have transcription activation functions hereinafter referred to as "TAF". Acidic residues in the amino-terminal domains of some nuclear receptors may be important for these transcription factors to interact with RNA polymerase. TAF activity may be dependent on interactions with other protein factors or nuclear components (Diamond et al., Transcription Factor Interactions: Selectors of Positive or Negative Regulation from a Single DNA Element, Science, 249:1266-1272 , 1990). Certain oncoproteins (e.g., c-Jun and c-Fos) can show synergistic or antagonistic activity with glucocorticoid receptors (GR) in transfected cells. Furthermore, the receptors for estrogen, vitamins A and D, and fatty acids have been shown to interact, either physically or functionally, with the Jun and Fos components of AP-1 in the transactivation of steroid- or AP-1 regulated genes.

Coactivators of transcription are proposed to bridge between sequence specific transcription factors, the basal transcription machinery and in addition to influence the chromatin structure of a target cell. Several proteins like SRC-1, ACTR, and Gripl, which are also cofactors of NRs similar to those disclosed in this invention, interact with NRs in a ligand enhanced manner (Heery et al., A signature motif in transcriptional coactivators mediates binding to nuclear receptors, Nature, 387, 733 - 736; Heinzel et al., A complex containing N-CoR, mSin3 and histone deacetylase mediates transcriptional repression, Nature 387, 43 - 47, 1997). Furthermore, the physical interaction with negative receptor-interacting proteins or corepressors has been demonstrated (Xu et al., Coactivator and Corepressor complexes in nuclear receptor function, Curr Opin Genet Dev, 9 (2), 140 - 147, 1999).

Nuclear receptor ligands like steroid hormones affect the growth and function of specific cells by binding to intracellular receptors and forming nuclear receptor-ligand complexes. Nuclear receptor-hormone complexes then interact with a hormone response element (HRE) in the control region of specific genes and alter specific gene expression.

The present invention relates to the identification of novel interacting polypeptides of the liver X receptor alpha (hereinafter referred to as LXR alpha).

LXR alpha was cloned in 1995 as an orphan nuclear receptor that acts as a heterodimeric partner of the retinoid X receptor, RXR (Willy et al, Genes Dev 9, 1033-45, 1995). Interestingly, it was recognised that the heterodimeric complex was activated not only in the presence of the LXR ligand but also in the sole presence of an RXR ligand. Both ligands together have a synergistic effect on transactivation of LXR alpha target genes. In this respect, LXR can be grouped together with the peroxisome proliferator activated receptors (PPARs) and with the farnesoid X receptor (FXR), which share this kind of dual-ligand activation. Other non-steroid receptors, which form heterodimers with RXR, like the vitamin D receptor (VDR) or the thyroid hormone receptor (TR) are not activated if only the RXR ligand is present. For LXR alpha, it is proposed that binding of the RXR ligand induces a conformational change of LXR alpha within this heterodimer promoting a transcriptional activation activity.

LXR alpha expression is highest in liver, but the receptor is also found in other tissues such as kidney, small intestine, spleen, adipose tissue, the pituitary gland and the adrenals (Apfel et al., Mol Cell Biol 14, 7025-7035 (1994); Willy et al., Genes Dev 9, 1033-45 (1995) and Au- beuf et al., Diabetes 46, 1319-27 (1997)).

First insight into the physiological role of LXR alpha came with the finding that a group of mono-oxidised derivatives of cholesterol (oxysterols such as 24(S)-hydroxycholesterol, 22(R)-hydroxycholesterol and 24(S),25-epoxycholesterol) were the most potent ligands for the receptor (Janowski et al., Nature 383, 728-731 (1996); Lehmann et al., J Biol Chem 272, 3137-40 (1997). With the generation of LXR alpha deficient mice and the identification of cholesterol 7 alpha-hydroxylase (Cyp7A) as the first target gene for LXR alpha it became clear that LXR alpha represents a major player in the regulation of cholesterol homoestasis (Peet et al, Cell 93, 693-704 (1998): mice lacking the LXR alpha receptor appear normal when kept on a low-cholesterol diet but when fed a high cholesterol diet they accumulate enormous amounts of cholesterol esters in their livers which eventually leads to hepatomegaly and liver malfunction. It seems clear that the fatal consequences are due to a failure to upregulate the transcription of Cyp7A, the enzyme catalysing the rate limiting step in the conversion of cholesterol to bile acids. Thus, wild-type LXR alpha functions as a key sensor for dietary cholesterol and it regulates the elimination of cholesterol from the body through the stimulation of its catabolism into bile acids in a feed forward mechanism. Not only Cyp7A expression is upregulated by LXR alpha function, but also a number of other genes whose products play crucial roles in the hepatic lipid metabolism are controlled by LXR alpha. Importantly, it was shown that the RXR/LXR alpha heterodimer binds to an RXR LXR resonse element in the promotor of the sterol response element binding protein- lc (SREBP-lc) in a ligand-dependent manner and upregulates its transcription (Repa et al., Genes Dev 14, 2819- 2830 (2000). SREBP-lc is a transcription factor that regulates the expression of lipogenic enzymes, such as acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD-1) and others (Shimano et al., J Biol Chem 274, 35832-35839 (1999)) leading to an activation of the fatty acid, triglyceride and phospholipid synthetic pathways. Indeed, Schultz et al., Genes Dev 14, 2831-38 (2000) demonstrated that when a potent LXR agonist was orally administered to wild type mice, the levels of plasma VLDL-triglyceride and HDL-phospholipid increased significantly. In LXR null mice, this effect was not observed suggesting that the elevated levels of triglyceride/phospholipid were a consequence of LXR activation. The upregulation of SCD-1 leads to increased amounts of oleoyl-CoA, the major substrate for cholesterol esterification, within the cell, thereby promoting storage of cholesterol esters and their transport to other tissues. Thus, if cholesterol levels are high, LXR alpha indirectly promotes esterification of free cholesterol within the cell thereby protecting the cell from its haraiful effects. An increase in fatty acid biosynthesis, e.g. as a consequence of an increased transcription of ACC, FAS and other enzymes, would contribute to a more appropriate ratio of cholesterol and other lipids, which would be of importance for instance to maintain membrane integrity.

Another way in which LXR alpha promotes the removal of free cholesterol from the cell (and from the body) is via transactivation of the ATP-binding cassette (cholesterol) transporter gene ABC1 in enterocytes and macrophages, hence promoting the efflux of cholesterol into the intestinal lumen and the reverse transport from the peripheral tissues back into the liver where it becomes catabolised into bile acids for excretion (Repa et al., Science 289, 1524-29 (2000); Costet et al., J Biol Chem 275, 28240-45 (2000)). In summary, the liver X receptor alpha works as a key regulator of cholesterol homeostasis and lipogenesis by i) promoting the removal of excessive dietary cholesterol from the body via stimulation of bile acid synthesis in the liver ii) stimulating reverse cholesterol transport from peripheral tissues back to the liver and iii) inducing transcription of a number of target genes, whose products are crucial players in lipogenesis.

The present invention relates to the identification of novel interacting polypeptides of the liver X receptor. The identification and characterisation of protein factors which modulate LXR alpha function could be of great benefit for the treatment of disorders in lipid metabolism and cholesterol homeostasis including hypercholesteroemia and as a consequence atherosclerosis or Tangier disease, a condition characterised by low levels of high density lipoprotein and cholesterol accumulation in macrophages. Such protein factors could furthermore be used in screening assays in order to identify chemical compounds which directly influence LXR alpha function and which could in turn be useful for the treatment of these diseases.

The present invention provides novel polypeptides, nucleic acids, and methods useful for developing and identifying compounds for the treatment of these disorders. It also contains methods to test if a certain compound promotes or disrupts the interaction of these polypeptides with the LXR alpha receptor, allowing conclusions on the effects of the compound on LXR alpha regulated cellular processes. These novel polypeptides interact, presumably also in vivo, with the LXR alpha receptor and shall hereinafter collectively be referred to as "cofactors" or "CF", although some of them in fact do belong to the nuclear receptor family of polypeptides.

The importance of this invention is manifested in the effects of the CFs to modulate genes involved in cellular functions like regulation of metabolism and cell homeostasis, cell proliferation and differentiation, pathological cellular aberrations, or cellular defense mechanisms.

The CF polypeptides are useful for screening for LXR alpha agonists or antagonists thereby providing for agents which may influence the activity of LXR alpha.

In one aspect of the present invention, the present invention provides isolated nucleic acid sequences for novel CFs. In particular, the present invention provides the cDNA sequences encoding human CFs. These nucleic acid sequences have a variety of uses. For example, they are useful for making vectors and for transforming cells, both of which are ultimately useful for production of the CF polypeptides. They are also useful as scientific research tools for developing nucleic acid probes for determining expression levels of the cofactor genes, e.g., to identify diseased or otherwise abnormal states. They are useful for developing analytical tools such as anti sense oligonucleotides for selectively inhibiting expression of the cofactor genes to determine physiological responses.

In another aspect of the present invention, a homogenous composition comprising the cofactor proteins is provided. The protein is useful for screening drugs for agonist and antagonist activity, and, therefore, for screening for drugs useful in regulating physiological responses associated with the cofactors according to the invention. Specifically, antagonists to the CFs could be used to treat metabolic disorders, immunological indications, hormonal dysfunctions, neurosystemic diseases. The polypeptides are also useful for developing antibodies for detection of the proteins.

Flowing from the foregoing are a number of other aspects of the invention, including (a) vectors, such as plasmids, comprising the cofactor nucleic acid sequences that may further comprise additional regulatory elements, e.g., promoters, (b) transformed cells that express the cofactors, (c) nucleic acid probes, (d) antisense oligonucleotides, (e) agonists, (f) antagonists, and (g) transgenic mammals and non-mammalian animals. Further aspects of the invention comprise methods for making and using the foregoing compounds and compositions.

The problem underlying the present invention is thus solved by the independent claims of the attached set of claims. Embodiments thereof can be taken from the subclaims.

The foregoing merely summarizes certain aspects of the present invention and is not intended, nor should it be construed, to limit the invention in any manner. All patents and other publications recited herein are hereby incorporated by reference in their entirety. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

THE CF21, CF22, AND CF33A POLYPEPTIDES AND THEIR RESPECTIVE NUCLEIC ACIDS:

The present invention comprises, in part, three novel cofactors (CF21, CF22, and CF33a) of LXR alpha. Particularly preferred embodiments of these cofactors are those having an amino acid sequence substantially identical to any of SEQ ID NOs 3, 6, and 9.

As used herein, if reference to the "cofactor" is made, it is meant as a reference to any protein having an amino acid sequence substantially identical to any of SEQ ID NOs 3, 6, and 9.

As used herein, if reference to "the cofactor" or reference to "the cofactor "X"", wherein "X" stands for the number designating the cofactor is made, it is meant as a reference to any protein having an amino acid sequence substantially the same as SEQ ID NO. 3 for CF21, SEQ ID NO. 6 for CF22, and SEQ ID NO. 9 for CF33a.

The present invention also comprises the nucleic acid sequences encoding the cofactors 21 to 33a which nucleic acid sequences are substantially the same as SEQ ID NO. 1 for CF21, SEQ ID NO. 4 for CF22, and SEQ ID NO. 7 for CF33a, all encoding human cofactors as preferred embodiments and/or the complements thereof as shown in SEQ ID NO. 2 for CF21, SEQ ID NO. 5 for CF22, and SEQ ID NO. 8 for CF33a.

Herein the "complement" refers to the complementary strand of the nucleic acid according to the invention, thus the strand that would hybridize to the nucleic acid according to the invention. In accordance with standard biological terminology all DNA sequences herein are however written in 5 '-3' orientation, thus the complements depicted are actually "reverse" complements. For simplification purposes they are however some times referred to simply as "complements".

As used herein, a protein "having an amino acid sequence substantially the same as SEQ ID NO x" (where "x" is the number of one of the protein sequences recited in the Sequence Listing) means a protein whose amino acid sequence is the same as SEQ ID NO x or differs only in a way such that at least 50% of the residues compared in a sequence alignment with SEQ ID NO. x are identical, preferably 75% of the residues are identical, even more preferably 95% of the residues are identical and most preferably at least 98% of the residues are identical

Those skilled in the art will appreciate that conservative substitutions of amino acids can be made without significantly diminishing the protein's affinity for interacting proteins, DNA binding sites, cofactor modulators, e.g. small molecular hydrophobic compounds, or RNA.

Other substitutions may be made that increase the proteins' affinity for these compounds. Making and identifying such proteins is a routine matter given the teachings herein, and can be accomplished, for example, by altering the nucleic acid sequence encoding the protein (as disclosed herein), inserting it into a vector, transforming a cell, expressing the nucleic acid sequence, and measuring the binding affinity of the resulting protein, all as taught herein.

As used herein the term "a molecule having a nucleotide sequence substantially the same as SEQ ID NO y" (wherein "y" is the number of one of the protein-encoding nucleotide sequences listed in the Sequence Listing) means a nucleic acid encoding a protein "having an amino acid sequence substantially the same as SEQ ID NO y+1" (wherein "y+1" is the number of the amino acid sequence for which nucleotide sequence "y" codes) as defined above. This definition is intended to encompass natural allelic variations in the CF sequences. Cloned nucleic acid provided by the present invention may encode CF polypeptides of any species of origin, including (but not limited to), for example, mouse, rat, rabbit, hamster, cat, dog, pig, primate, and human.

Preferably the nucleic acids provided by the invention encode CFs of mammalian, preferably mouse and most preferably human origin.

IDENTIFICATION OF VARIANTS AND HOMOLOGUES AS WELL AS USE OF PROBES:

Nucleic acid hybridization probes provided by the invention are nucleic acids consisting essentially of the nucleotide sequences complementary to any sequence depicted in SEQ ID NO. 1 for CF21, SEQ ID NO. 4 for CF22, and SEQ ID NO. 7 for CF33a, and/or the complements thereof as shown in SEQ ID NO. 2 for CF21, SEQ ID NO. 5 for CF22, and SEQ ID NO. 8 for CF33a or parts thereof which are effective in nucleic acid hybridization. Nucleic acid hybridization probes provided by the invention are nucleic acids capable of detecting i.e. hybridizing to the gene encoding the polypeptides according to SEQ ID NOs 3, 6, and 9.

Nucleic acid probes are useful for detecting CF gene expression in cells and tissues using techniques well-known in the art, including, but not limited to, Northern blot hybridization, in situ hybridization, and Southern hybridization to reverse transcriptase - polymerase chain reaction product DNAs. The probes provided by the present invention, including oligonucleotide probes derived therefrom, are also useful for Southern hybridization of mammalian, preferably human, genomic DNA for screening for restriction fragment length polymorphism (RFLP) associated with certain genetic disorders. As used herein, the term complementary means a nucleic acid having a sequence that is sufficiently complementary in the Watson- Crick sense to a target nucleic acid to bind to the target under physiological conditions or experimental conditions those skilled in the art routinely use when employing probes.

It is understood in the art that a nucleic acid sequence will hybridize with a complementary nucleic acid sequence under highly stringent conditions as defined herein, even though some mismatches may be present. Such closely matched, but not perfectly complementary sequences are also encompassed by the present invention. For example, differences may occur through genetic code degeneracy, or by naturally occurring or man made mutations and such mismatched sequences would still be encompassed by the present claimed invention.

Preferably, the nucleotide sequences of the nuclear cofactors SEQ ID NOs:l, 4, and 7 and/or their complements SEQ ID Nos: 2, 5, and 8 can be used to derive oligonucleotide fragments (probes) of various length. Stretches of 17 to 30 nucleotides are used frequently but depending on the screening parameters longer sequences as 40, 50, 100, 150 up to the full length of the sequence may be used. Those probes can be synthesized chemically and are obtained readily from commercial oligonucleotide providers. Chemical synthesis has improved over the years and chemical synthesis of oligonucleotides as long as 100-200 bases is possible. The field might advance further to allow chemical synthesis of even longer fragments. Alternatively, probes can also be obtained by biochemical de novo synthesis of single stranded DNA. In this case the nucleotide sequence of the nuclear receptors or their complements serve as a template and the corresponding complementary strand is synthesized. A variety of standard techniques such as nick translation or primer extension from specific primers or short random oligonucleotides can be used to synthesize the probe (Sambrook, J., Fritsch, E.F. & Maniatis , T. Molecular cloning: a laboratory manual. Cold Spring Harbor Press, Cold Spring Harbor, 1989)). Nucleic acid reproduction technologies exemplified by the polymerase chain reaction (Saiki, R.K. et al. Primer-directed enzymatic amplification of DNA with a thermostable DNA polymerase. Science 239, 487-491 (1988)) are commonly applied to synthesize probes. In the case of techniques using specific primers the nucleic acid sequences of the nuclear receptors or their complements are not only used as a template in the biochemical reaction but also to derive the specific primers which are needed to prime the reaction.

In some cases one might also consider to use the nucleic acid sequence of the cofactors or their complements as a template to synthesize an RNA probe. A promoter sequence for a DNA-dependent RNA polymerase has to be introduced at the 5'-end of sequence. As an example this can be done by cloning the sequence in a vector which carries the respective promoter sequence. It is also possible to introduce the needed sequence by synthesizing a primer with the needed promoter in the form of a 5' "tail". The chemical synthesis of a RNA probe is another option.

Appropriate means are available to detect the event of a hybridization. There is a wide variety of labels and detection systems, e.g. radioactive isotopes, fluorescent, or chemiluminescent molecules which can be linked to the probe. Furthermore, there are methods of introducing haptens which can be detected by antibodies or other ligands such as the avidin/biotin high affinity binding system.

Hybridization can take place in solution or on solid phase or in combinations of the two, e.g. hybridization in solution and subsequent capture of the hybridization product onto a solid phase by immobilized antibodies or by ligand coated magnetic beads.

Hybridization probes act by forming selectively duplex molecules with complementary stretches of a sequence of a gene or a cDNA. The selectivity of the process can be controlled by varying the conditions of hybridization. To select sequences which are identical or highly homologous to the sequence of interest stringent conditions for the hybridization will be used, e.g. low salt in the range of 0.02 M to 0.15 M salt and/or high temperatures in the range from 50°C degrees centigrade to 70°C degrees centigrade. Stringency can be further improved by - li the addition of formamide to the hybridization solution. The use of stringent conditions which means that only little mismatch or a complete match will lead to a hybridization product would be used to isolate closely related members of the same gene family. Thus, as used herein stringent hybridization conditions are those where between 0.02 M to 0.15 M salt and/or high temperatures in the range from 50°C degrees centigrade to 70°C degrees centigrade are applied.

The use of highly stringent conditions or conditions of "high stringency" means that only very little mismatch or a complete match which lead to a hybridization product would be used to isolate very closely related members of the same gene family. Thus, as used herein highly stringent hybridization conditions are those where between 0.02 - 0.3 M salt and 65°C degrees centigrade are applied for about 5 to 18 hours of hybridization time and additionally, the sample filters are washed twice for about 15 minutes each at between 60°C - 65°C degrees centigrade, wherein the first washing fluid contains about 0.1 M salt (NaCl and/or Sodium Citrate) and the second contains only about 0.02 M salt (NaCl and/or Sodium Citrate). In a preferred embodiment the following conditions are considered to be highly stringent:

Hybridization in a buffer containing 2 x SSC (0.03 M Sodium Citrate, 0.3 M NaCl) at 65°C - 68°C degrees centigrade for 12 hours, followed by a washing step for 15 minutes in 0.5 x SSC, 0.1% SDS, and a washing step for 15 minutes at 65°C degrees centigrade in 0.1 x SSC, 0.1% SDS.

Less stringent hybridization conditions, e.g. 0.15 M salt - 1 M salt and/or temperatures from 22°C degrees centigrade to 56°C degrees centigrade are applied in order to detect functionally equivalent genes in the same species or for orthologous sequences from other species.

Unspecific hybridization products are removed by washing the reaction products repeatedly in 2 x SSC solution and increasing the temperature.

DEGENERATE PCR AND CLONING OF HOMOLOGUES

The nucleotide sequences of the cofactors CF21 to CF32 or their complements can be used to design primers for a polymerase chain reaction. Due to the degeneracy of the genetic code the respective amino acid sequence is used to design oligonucleotides in which varying bases coding for the same amino acid are included. Numerous design rules for degenerate primers have been published (Compton et al, 1990). As in hybridization there are a number of factors known to vary the stringency of the PCR. The most important parameter is the annealing temperature. To allow annealing of primers with imperfect matches annealing temperatures are often much lower than the standard annealing temperature of 55°C, e.g. 35°C to 52°C degrees can be chosen. PCR reaction products can be cloned. Either the PCR product is cloned directly, with reagents and protocols from commercial manufacturers (e.g. from Invitrogen, San Diego, USA). Alternatively, restriction sites can be introduced intro the PCR product via a 5'- tail of the PCR primers and used for cloning.

GENETIC VARIANTS

Fragments from the nucleotide sequence of the cofactors or their complements can be used to cover the whole sequence with overlapping sets of PCR primers. These primers are used to produce PCR products using genomic DNA from a human diversity panel of healthy individuals or genomic DNA from individuals which are phenotypically conspicuous. The PCR products can be screened for polymorphisms, for example by denaturing gradient gel electrophoresis, binding to proteins detecting mismatches or cleaving heteroduplices or by denaturing high-performance liquid chromatography. Products which display mutations need to be sequenced to identify the nature of the mutation. Alternatively, PCR products can be se- quenced directly omitting the mutation screening step to identify genetic polymorphisms. If genetic variants are identified and are associated with a discrete phenotype, these genetic variations can be included in diagnostic assays. The normal variation of the human population is of interest in designing screening assays as some variants might interact better or worse with a respective lead, i.e. therapeutic or potentially therapeutic substance (a pharmacody- namic application). Polymorphisms or mutations which can be correlated to phenotypic outcome are a tool to extend the knowledge and the commercial applicability of the nucleotide sequences of the cofactors CF21 to CF33a or their complements or their gene products, as variants might have a slightly different molecular behavior or desired properties. Disease- causing mutations or polymorphisms allow the replacement of this disease inducing gene copy with a wild-type copy by means of gene therapy approaches and/or the modulation of the activity of the gene product by drugs. PREPARATION OF POLYNUCLEOTIDES:

DNA which encodes cofactor CF21 to CF33a may be obtained, in view of the instant disclosure, by chemical synthesis, by screening reverse transcripts of mRNA from appropriate cells or cell line cultures, by screening genomic libraries from appropriate cells, or by combinations of these procedures, as illustrated below.

Screening of mRNA or genomic DNA may be carried out with oligonucleotide probes generated from the CF nucleotide sequences information provided herein. These oligonucleotides are in addition useful to isolate a full length cDNA from an appropriate cDNA library.

Probes may be labeled with a detectable group such as a fluorescent group, a radioactive atom or a chemiluminescent group in accordance with known procedures and used in conventional hybridization assays, as described in greater detail in the Examples below. Alternatively, the CF nucleotide sequences may be obtained by use of the polymerase chain reaction (PCR) procedure, with the PCR oligonucleotide primers being produced from the CF nucleotide sequences provided herein, according to SEQ ID NOs:l, 4, and 7 and/or the complements thereof as shown in SEQ ID NOs: 2, 5, and 8, or parts thereof.

Upon purification or synthesis, the nucleic acid according to the invention may be labeled, e.g. for use as a probe.

As single and differential labeling agents and methods, any agents and methods which are known in the art can be used provided that they do not significantly altering the stability or function of said primer in the DNA sequencing method of the present invention. For example, single and differential labels may consist of the group comprising enzymes such as β- galactosidase, alkaline phosphatase and peroxidase, enzyme substrates, coenzymes, dyes, chromophores, fluorescent, chemiluminescent and bioluminescent labels such as FITC, Cy5, Cy5.5, Cy7, Texas-Red and IRD40(Chen et al. (1993), J. Chromatog. A 652: 355-360 and Kambara et al. (1992), Electrophoresis 13: 542-546), ligands or haptens such as biotin, and radioactive isotopes such as ³H, ³⁵S, ³²P ¹²⁵I and ¹⁴C. EXPRESSION OF THE CF21 TO CF33a PROTEINS/POLYPETIDES: The CF nucleic acids or polypeptides may be synthesized in host cells transformed with a recombinant expression construct comprising a nucleic acid encoding any of the cofactors according to the invention, namely CF21 to CF33A. Such a recombinant expression construct can also be comprised of a vector that is a replicable DNA construct.

Amplification vectors do not require expression control domains. All that is needed is the ability to replicate in a host, usually conferred by an origin of replication, and a selection gene to facilitate recognition of transformants. See, Sambrook et al., Molecular Cloning: A Laboratory Manual (2nd Edition, Cold Spring Harbor Press, New York, 1989).

An expression vector comprises a polynucleotide operatively linked to a prokaryotic promoter. Alternatively, an expression vector is a polynucleotide operatively linked to an enhancer-promoter that is a eukaryotic promoter, and the expression vector further has a polyade- nylation signal that is positioned 3' of the carboxy-terminal amino acid and within a transcriptional unit of the encoded polypeptide. A promoter is a region of a DNA molecule typically within about 500 nucleotide pairs in front of (upstream of) the point at which transcription begins (i.e., a transcription start site). In general, a vector contains a replicon and control sequences which are derived from species compatible with the host cell. The vector ordinarily carries a replication site, as well as marking sequences which are capable of providing phe- notypic selection in transformed cells.

Another type of discrete transcription regulatory sequence element is an enhancer. An enhancer provides specificity of time, location and expression level for a particular encoding region (e.g., gene). A major function of an enhancer is to increase the level of transcription of a coding sequence in a cell.

As used herein, the phrase "enhancer-promoter" means a composite unit that contains both enhancer and promoter elements. An enhancer-promoter is operatively linked to a coding sequence that encodes at least one gene product.

An enhancer-promoter used in a vector construct of the present invention may be any enhancer-promoter that drives expression in a prokaryotic or eukaryotic cell to be trans- formed/transfected. A coding sequence of an expression vector is operatively linked to a transcription terminating region. RNA polymerase transcribes an encoding DNA sequence through a site where poly- adenylation occurs.

An expression vector that comprises a polynucleotide that encodes one of the the polypeptides of the cofactors CF21 to CF33a is meant to include a sequence of nucleotides encoding a CF polypeptide sufficient in length to distinguish said segment from a polynucleotide segment encoding a non-cofactor polypeptide.

A polypeptide of the invention may also encode biologically functional polypeptides or peptides which have variant amino acid sequences, such as with changes selected based on considerations such as the relative hydropathic score of the amino acids being exchanged.

These variant sequences are those isolated from natural sources or induced in the sequences disclosed herein using a mutagenic procedure such as site-directed mutagenesis.

Furthermore, an expression vector of the present invention may contain regulatory elements for optimized translation of the polypeptide in prokaryotic or eukaryotic systems. These sequences are operatively located around the transcription start site and are most likely similar to ribosome recognition sites like prokaryotic ribosome binding sites (RBS) or eukaryotic Kozak sequences as known in the art (Kozak M., Initiation of translation in prokaryotes and eukaryotes. Gene 234, 187-208 (1999)).

An expression vector of the present invention is useful both as a means for preparing quantities of the CFs' polypeptide-encoding DNA itself, and as a means for preparing the encoded CFs' polypeptide and peptides. It is contemplated that where cofactor polypeptides of the invention are made by recombinant means, one may employ either prokaryotic or eukaryotic expression vectors as shuttle systems.

Where expression of recombinant CF21 to CF33a polypeptide is desired and a eukaryotic host is contemplated, it is most desirable to employ a vector such as a plasmid, that incorporates a eukaryotic origin of replication. Additionally, for the purposes of expression in eukaryotic systems, one desires to position the cofactor encoding sequence or if desired parts thereof adjacent to and under the control of an effective eukaryotic promoter. To bring a coding sequence under control of a promoter, whether it is eukaryotic or prokaryotic, what is generally needed is to position the 5' end of the translation initiation side of the proper translational reading frame of the polypeptide between about 1 and about 2000 nucleotides 3' of or downstream with respect to the promoter chosen.

Furthermore, where eukaryotic expression is anticipated, one would typically desire to incorporate into the transcriptional unit which includes the CF polypeptide, an appropriate poly- adenylation side.

The invention provides homogeneous compositions of mammalian cofactor polypeptides produced by transformed prokaryotic or eukaryotic cells as provided herein. Such homogeneous compositions are intended to be comprised of mammalian cofactor protein that comprises at least 90%o of the protein in such homogenous composition. The invention also provides membrane preparation from cells expressing the mammalian cofactors polypeptides as the result of transformation with a recombinant expression construct, as described here.

Within the scope of the present invention the terms "recombinant protein" or "coding sequence" both also include tagged versions of the polypeptides depicted in SEQ ID Nos: 3, 6, and 9 and/or and fusion proteins of said proteins with any other recombinant protein. Tagged versions here means that small epitopes of 3-20 amino acids are added to the original protein by extending the coding sequence either at the 5 'or the 3 'terminus leading to N-terminal or C- terminal extended polypeptides respectively, or that such small epitopes are included elsewhere in the protein. The same applies for fusion proteins where the added sequences are coding for longer polypeptides, varying between 2 and 100 kDa. Tags and fusion proteins are usually used to facilitate purification of recombinant proteins by specific antibodies or affinity matrices or to increase solubility of recombinant proteins within the expression host. Fusion proteins are also of major use as essential parts of yeast two hybrid screens for interaction partners of recombinant proteins.

Tags used in the scope of the present invention may include but are not limited to the following: EEF (alpha Tubulin), B-tag (QYPALT), E tag (GAPVPYPDPLEPR) c-myc Tag (EQKLISEEDL), Flag epitope (DYKDDDDK), HA tag (YPYDVPDYA), 6 or 10 x His Tag, HSV (QPELAPEDPED), Pk-Tag (GKPIPNPLLGLDST), protein C (EDQVDPRLIDGK), T7 (MASMTGGQQMG), VSV-G (YTDIEMNRLGK), Fusion proteines may include Thiore- doxin, Glutathiontransferase (GST), Maltose binding Protein (MBP), Cellulose Binding protein, calmodulin binding protein, chitin binding protein, ubiquitin, the Fc part of Immuno- globulins, and the IgG binding domain of Staphylococcus aureus protein A. These examples of course are illustrative and not limiting.

For expression of recombinant polypeptides in living cells or organisms, vector constructs harboring recombinant cofactors as set forth in SEQ ID NOs. 1, 4, and/or 7 and/or the complements thereof SEQ ID NOs. 2, 5, and/or 8 transformed or transfected into appropriate host cells. Preferably, a recombinant host cell of the present invention is transfected with a polynucleotide of SEQ ID NOs. 1, 4, or 7.

Means of ttansforming or transfecting cells with exogenous polynucleotide such as DNA molecules are well known in the art and include techniques such as calcium-phosphate- or DEAE-dextran-mediated transfection, protoplast fusion, electroporation, liposome mediated transfection, direct microinjection and virus infection (Sambrook et al., 1989).

The most frequently applied technique for transformation of prokaryotic cells is transformation of bacterial cells after treatment with calcium chloride to increase permeability (Dagert & Ehrlich, 1979), but a variety of other methods is also available for one skilled in the art.

The most widely used method for transfection of eukaryotic cells is transfection mediated by either calcium phosphate or DEAE-dextran. Although the mechanism remains obscure, it is believed that the transfected DNA enters the cytoplasm of the cell by endocytosis and is transported to the nucleus. Depending on the cell type, up to 90% of a population of cultured cells may be transfected at any one time. Because of its high efficiency, transfection mediated by calcium phosphate or DEAE-dextran is the method of choice for studies requiring transient expression of the foreign nucleic acid in large numbers of cells. Calcium phosphate-mediated transfection is also used to establish cell lines that integrate copies of the foreign DNA, which are usually arranged in head-to-tail tandem arrays into the host cell genome.

In the protoplast fusion method, protoplasts derived from bacteria carrying high numbers of copies of a plasmid of interest are mixed directly with cultured mammalian cells. After fusion of the cell membranes (usually with polyethylene glycol), the contents of the bacterium are delivered into the cytoplasm of the mammalian cells and the plasmid DNA is transported to the nucleus. Protoplast fusion is not as efficient as transfection for many of the cell lines that are commonly used for transient expression assays, but it is useful for cell lines in which en- docytosis of DNA occurs inefficiently. Protoplast fusion frequently yields multiple copies of the plasmid DNA tandemly integrated into the host chromosome.

The application of brief, high- voltage electric pulses to a variety of mammalian and plant cells leads to the formation of nanometer-sized pores in the plasma membrane. DNA is taken directly into the cell cytoplasm either through these pores or as a consequence of the redistribution of membrane components that accompanies closure of the pores. Electroporation may be extremely efficient and may be used both for transient expression of cloned genes and for establishment of cell lines that carry integrated copies of the gene of interest. Electroporation, in contrast to calcium phosphate-mediated transfection and protoplast fusion, frequently gives rise to cell lines that carry one, or at most a few, integrated copies of the foreign DNA.

Liposome transfection involves encapsulation of DNA and RNA within liposomes, followed by fusion of the liposomes with the cell membrane. The mechanism of how DNA is delivered into the cell is unclear but transfection efficiencies may be as high as 90%.

Direct microinjection of a DNA molecule into nuclei has the advantage of not exposing DNA to cellular compartments such as low-pH endosomes. Microinjection is therefore used primarily as a method to establish lines of cells that carry integrated copies of the DNA of interest.

The use of adenovirus as a vector for cell transfection is well known in the art. Adenovirus vector-mediated cell transfection has been reported for various cells (Stratford-Perricaudet et al., 1992).

Furthermore, the possibility exists, to perform the gene transfer in vivo, either by preferential stereotactic injection of the infectious particle or by direct application of virus-producing cells (Oldfield, et al. Hum. Gen. Ther., 1993, 4:39-69).

The commonly used viral vectors for the transfer of genes according to the current state of the art are mainly retroviral, lentiviral, adenoviral and adeno-associated viral vectors. These are circular nucleotide sequences derived from natural viruses in which at least the viral structural protein encoding genes are replaced by the construct to be transferred.

Retroviral vector systems provide the prerequisite for a long-lasting expression of the transgene by the stable, but non-directed integration into the genome of the host. Vectors of the younger generation possess no irrelevant and potentially immunogenic proteins, furthermore, there is no pre-existing immunity of the recipient in view of the vector. Retroviruses contain an RNA-genome, that is packed into a lipid coating, which consists out of parts of the host cell membrane and viral proteins. For the expression of viral genes the RNA-genome is rever- sly transcribed and integrated into the target-cell DNA using the enzyme integrase. This can subsequently be transcribed and translated by the infected cell, thereby viral compounds are produced which then form retrovirus particles. RNA will then be exclusively included in the newly produced viruses. The genome of retroviruses contains three essential genes: gag, which codes for viral structural proteins, so-called group-specific antigenes, pol for Enzyme like reverse transcriptase and integrase and env for the „envelope" protein, which is responsible for the binding of the host specific receptor. The production of the replication incompetent viruses occurs after transfection in so-called packaging-celllines which are in addition provided with gag/pol-encoding genes and express those „in trans" and thereby complement the formation of replication incompetent (i.e. gag/pol-deletet) transgene virus particles. An alternative is cotransfection of the essential virus genes, wherein only the transgene containing vector carries the packaging signal.

Novel, non- viral vectors consist out of autonomically and self-integrating DNA sequences, the transposons, which are introduced into the host cell by, e.g. liposomal transfection and were for the first time successfully used for the expression of human transgenes in mammalian cells (Yant et al., 2000).

A transfected cell may be prokaryotic or eukaryotic, transfection may be transient or stable. Where it is of interest to produce a full length human CF21 to CF 33a protein, cultured mammalian or human cells are of particular interest.

In another aspect, the recombinant host cells of the present invention are prokaryotic host cells. In addition to prokaryotes, eukaryotic microbes, such as yeast may also be used illustrative examples for suitable cells and organisms for expression of recombinant polypeptides are belonging to but not limited to the following examples: Insect cells, such as Drosophila Sf21, SF9 cells or others, Expression strains of Escherichia coli, such as XL1 blue, BRL21, Ml 5, Saccharomyces cerevisiae, Schizosaccharomyces pombe, Hansenula polymorpha and Pichia pastoris strains, immortalized mammalian cell lines such as AtT-20, VERO and HeLa cells, Chinese hamster ovary (CHO) cell lines, and W138, BHK, COSM6, COS-7, 293 and MDCK cells, BHK-21 cells, Att 20HeLa cells, HeK 294, T47 D cells and others.

Expression of recombinant polypeptides within the scope of this invention can also be performed in vitro. This may occur by a two step procedure, thereby producing first mRNA by in vitro transcription of an apt polynucleotide construct followed by in vitro translation with convenient cellular extracts. These cellular extracts may be reticulocyte ly sates but are not limited to this type. In vitro transcription may be performed by T7 or SP6 DNA polymerase or any other RNA polymerase which can recognize per se or with the help of accessory factors the promoter sequence contained in the recombinant DNA construct of choice. Alternatively one of the recently made available one step coupled transcription/translation systems may be used for in vitro translation of DNA coding for the polypeptides of this invention. One illustrative but not limiting example for such a system is the TNT® T7 Quick System by Promega.

Expression of recombinant polypeptides in transfected cells may occur constitutively or upon induction. Procedures depend on the Cell/vector combination used and are well known in the art.

In all cases, transfected cells are maintained for a period of time sufficient for expression of the recombinant cofactor proteins according to the invention. A suitable maintenance time depends strongly on the cell type and organism used and is easily ascertainable by one skilled in the art. Typically, maintenance time is from about 2 hours to about 14 days. For the same reasons and for sake of protein stability and solubility incubation temperatures during maintenance time may vary from 20°C to 42 °C.

Recombinant polypeptides are recovered or collected either from the transfected cells or the medium in which those cells are cultured. Recovery comprises cell disruption, isolation and purification of the recombinant protein. Isolation and purification techniques for polypeptides are well-known in the art and include such procedures as precipitation, filtration, chromatography, electrophoresis and the like.

In a preferred embodiment, purification includes but is not limited to affinity purification of tagged or nontagged recombinant polypeptides. This is a well established robust technique easily adapted to any tagged protein by one skilled in the art. For affinity purification of tagged proteines, small molecules such as gluthathione, maltose or chitin, specific proteins such as the IgG binding domain of Staphylococcus aureus protein A, antibodies or specific chelates which bind with high affinity to the tag of the recombinant protein are employed. For affinity purification of non-tagged proteins specific monoclonal or polyclonal antibodies, which were raised against said protein, can be used. Alternatively immobilized specific inter- actors of said protein may be employed for affinity purification. Interactors include native or recombinant polypeptides as well as native or artificial specific low molecular weight ligands.

CHEMICAL SYNTHESIS OF THE POLYPEPTIDES ACCORDING TO THE INVENTION:

Alternatively, the protein itself may be produced using chemical methods to synthesize any of the amino acid sequences according to the invention (SEQ ID NOs: 3, 6, and/or 9) or that is encoded by the nucleotide sequences according to the invention and/or the complements thereof or a portion thereof. For example, peptide synthesis can be performed using conventional Merrifield solid phase f-Moc or t-Boc chemistry or various solid-phase techniques (Roberge, J. Y. et al. (1995) Science 269: 202-204) and automated synthesis may be achieved, for example, using the ABI 431 A Peptide Synthesizer (Perkin Elmer). The newly synthesized peptide(s) may be substantially purified by preparative high performance liquid chromatography (e.g., Creighton, T. (1983) Proteins, Structures and Molecular Principles, WH Freeman and Co., New York, N.Y.). The composition of the synthetic peptides may be confirmed by amino acid analysis or sequencing (e.g., the Edman degradation procedure; Creighton, supra). Additionally, the amino acid sequences according to the invention, i.e. SEQ ID NO: 3, 6, or 9 or the sequence that is encoded by SEQ ID NOs. 1, 4, and 7 or any part thereof, may be altered during direct synthesis and/or combined using chemical methods with sequences from other proteins, or any part thereof, to produce a variant polypeptide. COMPLEXES OF THE COFACTORS ACCORDING TO THE INVENTION WITH OTHER POLYPETIDES

As outlined above, CF21 to CF33a all bind LXR alpha, presumably also in vivo. In a preferred embodiment of the invention the CFs are complexed with this polypeptide or a portion thereof as disclosed in SEQ ID NO. 12 and/or 15. Such complexes are particular suited for all forms of binding or screening assays (see also below). Thus, in a preferred embodiment of the invention test and/or screening assays are performed with complexes of the associated with any of CF21 to CF33a or combinations thereof.

In one embodiment of the invention a trimeric complex is present consisting of a heterodimer of RXR (in one of the included isoforms) and LXR alpha bound to one of the CFs. In another embodiment of the invention LXR alpha could bind in monomeric form to one of the CFs. It is not excluded here that additional proteins, can be found within the above described complexes. Such complexes may be used in binding and screening assays as outlined below.

In one embodiment of the invention, the at least one of the CF21 to CF33a polypeptide is not entirely part of the complex but only a portion, e.g. a truncated fragment of the other polypeptide (LXR alpha) is part of the complex.

Furthermore, all CFs can bind to complexes which are formed with additional factors which are known to bind LXR alpha or a fragment thereof in order to form heterodimers or other oligomeric protein complexes. Such factors can be, for example, RXR alpha as disclosed in SEQ ID NO. 18, RXR beta as disclosed in SEQ ID NO. 21, and RXR gamma as disclosed in SEQ ID NO. 24 as well as combinations thereof.

SCREENING ASSAYS

In still a further embodiment, the present invention concerns a method for identifying new inhibitory or stimulatory substances of the cofactors according to the invention, these substances may be termed as "candidate substances". It is contemplated that this screening technique proves useful in the general identification of compounds that serve the purpose of inhibiting or stimulating cofactor activity.

Mono-oxidised derivatives of cholesterol (oxysterols such as 24(S)-hydroxycholesterol, 22(R)-hydroxycholesterol and 24(S),25-epoxycholesterol) are known to be the most potent ligands for the LXR receptor (Janowski et al, Nature 383, 728-731 (1996); Lelimann et al., J Biol Chem 272, 3137-40 (1997). In addittion, polyunsaturated fatty acids such as arachidonic acid, eicosapentaenoic acid, docosahexaenoic acid and linoleic acid have been described to inhibit LXR alpha transcriptional activity by binding to the receptor (Yoshikawa et al., J Biol Chem 277,1705-1711 (2002).

Other substances that were identified as interacting with LXR alpha and/or cofactor complexes thereof, accordmg to the invention, are:

T0314407 (Tularik) Schultz et al, Gen Dev 14, 2831-2838 (2000), and T0901317 (Tularik) Schultz et al., Gen Dev 14, 2831-2838 (2000).

One may use the screening method to identify such substances which activate or repress the transactivation function of LXR alpha, and thus lead to elevated or decreased expression of LXR alpha target genes. In turn, this will alter the responsiveness of a person to estrogens when treated with the substance, and therefore the substance might be used to treat medical indications such as cancer, osteoporosis, bone disease, cardiovascular disorders and Alzheimer's disease or the compound could be used in a hormone replacement therapy.

Accordingly, in screening assays for identifying pharmaceutical agents which affect cofactor acitivity, it is proposed that compounds isolated from natural sources, such as fungal extracts, plant extracts, bacterial extracts, higher eukaryotic cell extracts, or even extracts from animal sources, or marine, forest or soil samples, may be assayed for the presence of potentially useful pharmaceutical agents.

It will be understood that that the pharmaceutical agents to be screened can also be derived from chemical compositions or man-made compounds. The candidate substances could also include monoclonal or polyclonal antibodies, peptides or proteins, such as those derived from recombinant DNA technology or by other means, including chemical peptide synthesis. The active compounds may include fragments or parts or derivatives of naturally-occurring compounds or may be only found as active combinations of known compounds which are otherwise inactive. We anticipate that such screens will in some cases lead to the isolation of agonists of nuclear receptors or cofactors, in other cases to the isolation of antagonists. In other instances, substances will be identified that have mixed agonistic and antagonistic effects, or affect nuclear receptors or cofactors in any other way.

In another embodiment, the invention concerns the isolation of substance inhibiting the interaction of the cofactor protein and LXR alpha. Such substances are useful for the development of drugs against diseases as listed above. Substances disrupting the interactions may be isolated by a variety of screening methods including the two hybrid system or the reverse two hybrid system (Lenna CA. and Hannink, M. 1996, Nucl. Acids Res. 24: 3341-3347), or any variation of cellular or cell free assays as described in this invention, as is obvious to anyone skilled in the art.

In an important embodiment of the invention, the binding of the cofactor protein and LXR alpha can be used to monitor the binding of a substance to one of the binding partners. The substance, which can be a small molecule such as a ligand to a nuclear receptor, will lead to a change in the allosteric conformation of the binding protein which in consequence leads to a loss of the interaction of the two proteins. Using this effect of ligand-dependent protein- protein interactions one can design assays where the protein-protein interaction serves as a surrogate read-out for the binding of one of the proteins to small molecule ligand. Any assay method which is useful for the measurement of protein-protein interactions can be used for such an indirect assay. Such assay methods are well known in the art and include the methods described in this patent under "Cell free assays" and "Cell based assays". In a preferred embodiment, this assay will measure the binding of substances to LXR alpha, resulting in an effect on the interaction of LXR alpha with the cofactor.

CELL BASED ASSAYS

To identify a candidate substance capable of influencing the cofactor protein activity, one first obtains a recombinant cell line. One designs the cell line in such a way that the activity of the cofactor leads to the expression of a protein which has an easily detectable phenotype (a reporter), such as luciferase, fluorescent proteins such as green or red fluorescent protein, beta- galactosidase, alpha-galactosidase, beta-lactamase, chloramphenicol-acetyl-transferase, beta- glucuronidase, or any protein which can be detected by a secondary reagent such as an antibody. Methods for detecting proteins using antibodies, such as ELISA assays, are well known to those skilled in the art.

Here, the amount of reporter protein present reflects the activity of the cofactor. This recombinant cell line is then screened for the effect of substances on the expression of the reporters, thus measuring the effect of these substances on the activity of the cofactor. These substances can be derived from natural sources, such as fungal extracts, plant extracts, bacterial extracts, higher eukaryotic cell extracts, or even extracts from animal sources, or marine, forest or soil samples, may be assayed for the presence of potentially useful pharmaceutical agents. It will be understood that that the pharmaceutical agents to be screened may be derived from chemical compositions or man-made compounds.

The candidate substances can also include monoclonal or polyclonal antibodies, peptides or proteins, such as those derived from recombinant DNA technology or by other means, including chemical peptide synthesis. The active compounds may include fragments or parts or derivatives of naturally-occurring compounds or may be only found as active combinations of known compounds which are otherwise inactive.

In general the assay can be performed by firstly bringing a suitable cell containing a reporter gene which transcription is influenced by the cofactors activity in contact with a compound and secondly monitoring the expression of the reporter gene to evaluate the effect of the compound on the activity of the cofactor.

In other embodiments of the invention assays are included where measuring the activity of di- or multimeric complexes of the cofactor and other proteins such as LXR alpha. Further included are assays aiming at the identification of compounds which specifically influence only the monomeric, homodimeric or homomultimeric form of the cofactor, or influencing only multimeric forms of the cofactor. Such assays include measuring the effect of a compound on the cofactor in the absence of a binding partner, and measuring the effect of a compound on the cofactor in the presence of a binding partner, such as LXR alpha. One skilled in the art will find numerous more assays which are equally covered by the invention.

A cell line where the activity of LXR alpha or any other nuclear receptor determines the expression of a reporter can be obtained by generating an artificial promoter upstream of the reporter gene, which contains preferably multiple copies of HREs to which LXR alpha or any other nuclear receptor binds.

Furthermore, transgenic animals described in the invention can be used to derive cell lines useful for cellular screening assays.

Cell lines useful for such an assay include many different kinds of cells, including prokaryotic, animal, fungal, plant and human cells. Yeast cells can be used in this assay, including Saccharomyces cerevisiae and Schizosaccharomyces pombe cells.

One way of building cellular assays is by measuring the effect of compounds is the use of the two hybrid system (see for example, U.S. Pat. No. 5,283,317; Zervos et al. (1993) Cell 72:223-232; Madura et al. (1993) J. Biol. Chem. 268:12046-12054; Bartel et al. (1993) Biotechniques 14:920-924; Iwabuchi et al. (1993) Oncogene 8:1693-1696; PCT Publication No. WO 94/10300, and U.S. Pat. No. 5,667,973), or possible variants of the basic two hybrid system as discussed e.g in Vidal M, Legrain P, Nucleic Acids Res 1999 Feb 15;27(4):919-29. Briefly, the two hybrid assay relies on reconstituting in vivo a functional transcriptional activator protein from two separate fusion proteins. In particular, the method makes use of chimeric genes which express hybrid proteins. To illustrate, a first hybrid gene comprises the coding sequence for a DNA-binding domain of a transcriptional activator fused in frame to the coding sequence for a cofactor. The second hybrid protein encodes a transcriptional activation domain fused in frame to another gene, for example LXR alpha. If the cofactor and LXR alpha proteins are able to interact, they bring into close proximity the two domains of the transcriptional activator. This proximity is sufficient to cause transcription of a reporter gene which is operably linked to a transcriptional regulatory site responsive to the transcriptional activator, and expression of the reporter gene can be detected and used to score for the interaction of the cofactor and LXR alpha protems. Suitable host cells for such assays include yeast cells, but also mammalian cells or bacterial cells.

In such assays, one primarily measures the effect of a compound on a given interaction involving one of the CF21 to CF33a cofactors, optionally additional cofactors, like RXR alpha, beta and/or gamma and a binding protein. In a preferred embodiment of the invention systems using other hosts such as prokaryotes as E. coli, or eukaryotic mammalian cells are described. Two hybrid systems using hybrid protein fusions with other proteins than transcription factors, including enzymes such as beta-galactosidase or dϊhydrofolate reductase may also be applied. These assays are useful both to monitor the effect of a compound, including peptides, proteins or nucleic acids on an interaction of a cofactor with a given binding partner, as well as to identify novel proteins or nucleic acids interacting with the cofactor.

CELL-FREE ASSAYS

Recombinant forms of the polypeptides according to SEQ ID NOs. 3, 6, or 9 can be used in cell-free screening assays aiming at the isolation of compounds affecting the activity of co- factors. In such an assay, the cofactor polypeptides are brought into contact with a substance to test if the substance has an effect on the activity of the cofactor.

The detection of an interaction between an agent and a cofactor may be accomplished through techniques well-known in the art. These techniques include but are not limited to centrifuga- tion, chromatography, electrophoresis and spectroscopy. The use of isotopically labeled reagents in conjunction with these techniques or alone is also contemplated. Commonly used radioactive isotopes include ³H, ¹⁴C, ²²Na, ³²P, ³³P, ³⁵S, ⁴⁵Ca, ⁶⁰Co, ¹²⁵I, and ¹³¹I. Commonly used stable isotopes include ²H, ,¹³ C, ¹⁵N, ¹⁸O.

For example, if an agent binds to any of the cofactors of the present invention, the binding may be detected by using radiolabeled agent or radiolabeled cofactor. Briefly, if radiolabeled agent or radiolabeled cofactor is utilized, the agent-cofactor complex may be detected by liquid scintillation or by exposure to x-ray film or phosho-imaging devices.

One way to screen for substances affecting cofactor activity is to measure the effect of the substance on the binding affinity of the cofactor to other proteins or molecules, such as activators or repressors, DNA, RNA, other proteins, antibodies peptides or other substances, including chemical compounds known to affect receptor activity or to a nuclear receptor itself. Assays measuring the binding of a protein to a ligand are well known in the art, such as ELISA assays, FRET assays, bandshift assays, plasmon-resonance based assays, scintilUation proximity assays, fluorescence polarization assays, alpha screen assays.

In one example, a mixture containing a cofactor polypeptide, effector and candidate substance is allowed to incubate. The unbound effector is separable from any effector/cofactor complex so formed. One then simply measures the amount of each (e.g., versus a control to which no candidate substance has been added). This measurement may be made at various time points where velocity data is desired. From this, one determines the ability of the candidate substance to alter or modify the function of the cofactor.

Numerous techniques are known for separating the effector from effector/cofactor complex, and all such methods are intended to fall within the scope of the invention. This includes the use of thin layer chromatographic methods (TLC), HPLC, spectrophotometric, gas chroma- tographic/mass spectrophotometric or NMR analyses. Another method of separation is to immobilize one of the binding partners on a solid support, and to wash away any unbound material. It is contemplated that any such teclinique may be employed so long as it is capable of differentiating between the effector and complex, and may be used to determine enzymatic function such as by identifying or quantifying the substrate and product.

A screening assay in which candidate agent binding of cofactors is analysed can include a number of conditions. These conditions include but are not limited to pH, temperature, tonic- ity, the presence of relevant other proteins, and relevant modifications to the polypeptide such as glycosylation or lipidation. It is contemplated that the cofactors can be expressed and utilized in a prokaryotic or eukaryotic cell. The host cell expressing the cofactors can be used whole or the cofactor can be isolated from the host cell. The cofactor can be membrane bound in the membrane of the host cell or it can be free in the cytosol of the host cell. The host cell can also be fractionated into sub-cellular fractions where the cofactor can be found. For example, cells expressing the cofactor can be fractionated into the nuclei, the endoplasmic re- ticulum, vesicles, or the membrane surfaces of the cell.

pH is preferably from about a value of 6.0 to a value of about 8.0, more preferably from about a value of about 6.8 to a value of about 7.8, and most preferably, about 7.4. In a preferred embodiment, temperature is from about 20°C degrees to about 50°C degrees more preferably, from about 30°C degrees to about 40°C degrees and even more preferably about 37°C degrees. Osmolality is preferably from about 5 milliosmols per liter (mosm/1) to about 400 mosm/1, and more preferably, from about 200 milliosmols per liter to about 400 mosm/1 and, even more preferably from about 290 mosm/1 to about 310 mosm/1. The presence of further cofactors or other proteins can be required for the proper functioning of the cofactors according to the invention. Typical chemical cofactors include sodium, potassium, calcium, magne- sium, and chloride. In addition, small, non-peptide molecules, known as prosthetic groups may also be required. Other biological conditions needed for cofactor function are well- known in the art.

It is well-known in the art that proteins can be reconstituted in artificial membranes, vesicles or liposomes. (Danboldt et al.,1990). The present invention contemplates that the cofactor can be incorporated into artificial membranes, vesicles or liposomes. The reconstituted cofactor can be utilized in screening assays.

It is further contemplated that a cofactor of the present invention can be coupled to a solid support, e.g., to agarose beads, polyacrylamide beads, polyacrylic, sepharose beads or other solid matrices capable of being coupled to polypeptides. Well-known coupling agents include cyanogen bromide (CNBr), carbonyldiimidazole, tosyl chloride, diaminopimelimidate, and glutar aldehyde.

In a typical screening assay for identifying candidate substances, one employs the same recombinant expression host as the starting source for obtaining the cofactor polypeptide, generally prepared in the form of a crude homogenate. Recombinant cells expressing the cofactor are washed and homogenized to prepare a crude polypeptide homogenate in a desirable buffer such as disclosed herein. In a typical assay, an amount of polypeptide from the cell homogenate, is placed into a small volume of an appropriate assay buffer at an appropriate pH. Candidate substances, such as agonists and antagonists, are added to the admixture in convenient concentrations and the interaction between the candidate substance and the cofactor polypeptide is monitored.

Where one uses an appropriate known substrate for the cofactors, one can, in the foregoing manner, obtain a baseline activity for the recombinantly produced cofactors. Then, to test for inhibitors or modifiers of the cofactor function, one can incorporate into the admixture a candidate substance whose effect on the cofactor is unknown. By comparing reactions which are carried out in the presence or absence of the candidate substance, one can then obtain information regarding the effect of the candidate substance on the normal function of the cofactor. Accordingly, this aspect of the present invention will provide those of skill in the art with methodology that allows for the identification of candidate substances having the ability to modify the action of cofactor polypeptides in one or more manners.

Additionally, screening assays for the testing of candidate substances are designed to allow the determination of structure-activity relationships of agonists or antagonists with the cofactors, e.g., comparisons of binding between naturally-occurring hormones or other substances capable of interacting with or otherwise modulating the cofactor; or comparison of the activity caused by the binding of such molecules to the cofactor.

In certain aspects, the polypeptides of the invention are crystallized in order to carry out x-ray crystallographic studies as a means of evaluating interactions with candidate substances or other molecules with the cofactor polypeptide. For instance, the purified recombinant polypeptides of the invention, i.e. of the cofactors according to the invention, when crystallized in a suitable form, are amenable to detection of intra-molecular interactions by x-ray crystallography. In another aspect, the structure of the polypeptides can be determined using nuclear magnetic resonance.

PHARMACEUTICAL COMPOSITION:

This invention provides a pharmaceutical composition comprising an effective amount of an agonist or antagonist drug identified by the method described herein and a pharmaceutically acceptable carrier. Such drugs and carrier can be administered by various routes, for example oral, subcutaneous, intramuscular, intravenous or intracerebral. The preferred route of administration would be oral at daily doses of about 0.01 -100 mg/kg.

This invention provides a method of treating diseases such as cancer, cardiovascular diseases, bone diseases, hormonal dysfunctions and others by altering the activity of the cofactor thereby influencing the binding affinity of the cofactor to LXR alpha.

TRANSFORMATION OF CELLS AND DRUG SCREENING :

The recombinant expression constructs of the present invention are useful in molecular biology to transform cells which do not ordinarily express the CF21 to CF33a polypeptides to express these cofactors upon transformation. Such cells are useful as intermediates for making cellular preparations useful for cofactor binding assays, which are in turn useful for drug screening.

The recombinant expression constructs of the present invention are also useful in gene therapy. Cloned genes of the present invention, or fragments thereof, may also be used in gene therapy carried out by homologous recombination or site-directed mutagenesis. See generally Thomas & Capecchi, Cell 51, 503-512 (1987); Bertling, Bioscience Reports 7, 107-112 (1987); Smithies et al., Nature 317, 230-234 (1985).

Oligonucleotides of the present invention are useful as diagnostic tools for probing cofactor gene expression in tissues. For example, tissues are probed in situ with oligonucleotide probes carrying detectable groups by conventional autoradiographic techniques, as explained in greater detail in the examples below, to investigate native expression of this cofactor or pathological conditions relating thereto. Further, chromosomes can be probed to investigate the presence or absence of the CF genes, and potential pathological conditions related thereto, as also illustrated by the Examples below. Probes according to the invention should generally be at least about 15 nucleotides in length to prevent binding to random sequences, but, under the appropriate circumstances may be smaller.

ANTIBODIES AGAINST THE CF21, CF22, AND/OR CF33a COFACTOR PROTEIN OR POLYPEPTIDE

Another aspect of the invention includes antibodies specifically reactive with the polypeptides or any parts of the polypeptides according to the invention and or polypeptides encoded by the nucleotide sequences of the cofactors. The term „antibody" refers to intact molecules as well as fragments thereof, such as Fa, F(ab).sub.2, and Fv, which are capable of binding the epitopic determinant. By using immunogens derived from the polypeptide according to the invention and/or encoded by the nucleic acids according to the mvention, anti-protein/anti- peptide antiserum or monoclonal antibodies can be made by standard protocols (E. Howell & D. Lane. Antibodies: A Laboratory Manual. Cold Spring Harbor Laboratory (1988)).

A polyclonal antibody is prepared by immunizing a mammal, such as a mouse, a hamster or rabbit with an immunogenic form of the cofactors according to the invention depending on which of these are desired) of the present invention, and collecting antisera from that immu- nized animal. Because of the relatively large blood volume of rabbits, a rabbit is a preferred choice for production of polyclonal antibodies.

As an immunizing antigen, fusion proteins, intact polypeptides or fragments containing small peptides of interest can be used. They can be derived by expression from a cDNA transfected in a host cell with subsequent recovering of the protein/peptide or peptides can be synthesized chemically (e.g. oligopeptides with 10-15 residues in length). Important tools for monitoring the function of the cofactor gene according to the present invention, i.e. encoded by a sequence according to SEQ ID NOs. 1, 4 or 7 are antibodies against various domains of the polypeptides according to the invention.

A given polypeptide or polynucleotide may vary in its immunogenicity. It is often necessary to couple the immunogen (e.g. the polypeptide) with a carrier. Commonly used carriers that are chemically coupled to peptides include bovine serum albumin (BSA) and keyhole limpet hemocyanin (KLH). The coupled peptide is then used to immunize the animal in the presence of an adjuvant, a non-specific stimulator of the immune response in order to enhance immunogenicity. The production of polyclonal antibodies is monitored by detection of antibody titers in plasma or serum at various time points following immunization. Standard ELISA or other immunoassays can be used with the immunogen as antigen to assess the levels of antibodies. When a desired level of immunogenicity is obtained, the immunized animal may be bled and the serum isolated, stored and purified.

To produce monoclonal antibodies, antibody-producing cells (e.g. spleen cells) from an immunized animal (preferably mouse or rat) are fused by standard somatic cell fusion procedures with immortalizing cells such as myeloma cells to yield hybridoma cells. Where the immunized animal is a mouse, a preferred myeloma cell is the murine NS-1 myeloma cell. Such techniques are well known in the art, and include, for example, the hybridoma technique (originally developed by Kohler & Milstein. Nature 256: 495-497 (1975)), the human B cell hybridoma technique (Kozbar et al. Immunology Today 4:72 (1983)), and the EBV- hybridoma technique to produce human monoclonal antibodies (Cole et al. Monoclonal Antibodies and Cancer Therapy. Alan R. Liss, Inc. pp. 77-96 (1985)).

The fused spleen/myeloma cells are cultured in a selective medium to select fused spleen/myeloma cells from the parental cells. Fused cells are separated from the mixture of non-fused parental cells, for example, by the addition of agents that block the de novo synthesis of nucleotides in the tissue culture media. This culturing provides a population of hybridomas from which specific hybridomas are selected. Typically, selection of hybridomas is performed by culturing the cells by single-clone dilution in microtiter plates, followed by testing the individual clonal supernatants for reactivity with an antigen-polypeptide. The selected clones may then be propagated indefinitely to provide the monoclonal antibody in convenient quantity.

The creation of antibodies which specifically bind the polypeptides according to the invention and/or encoded by the nucleotide sequences of the cofactors or their complements provides an important utility in immunolocalization studies, and may play an important role in the diagnosis and treatment of such diseases and disorders as metabolic disorders, immunological indications, hormonal dysfunctions and/or neurosystemic diseases. The antibodies may be employed to identify tissues, organs, and cells which express the cofactors. Antibodies can be used diagnostically in immuno-precipitation and immuno-blotting to detect and evaluate co- factor protein levels in tissue or from cells in bodily fluid as part of a clinical testing procedure.

Monoclonal antibodies provided by the present invention are also produced by recombinant genetic methods well known to those of skill in the art, and the present invention encompasses antibodies made by such methods that are immunologically reactive with an epitope of a mammalian cofactor protein or peptide according to the invention.

The present invention encompasses fragments of the antibody that are immunologically reactive with an epitope of a cofactor protein or peptide. Such fragments are produced by any number of methods, including but not limited to proteolytic cleavage, chemical synthesis or preparation of such fragments by means of genetic engineering technology. The present invention also encompasses single-chain antibodies that are immunologically reactive with an epitope of a cofactor protein or peptide made by methods known to those of skill in the art.

CHIMERIC ANTIBODIES AND OTHER TYPES OF ANTIBODIES: The invention also includes chimeric antibodies, comprised of light chain and heavy chain peptides immunologically reactive to an epitope that is a cofactor protein or peptide according to the invention. The chimeric antibodies embodied in the present invention include those that are derived from naturally occurring antibodies as well as chimeric antibodies made by means of genetic engineering technology well known to those of skill in the art as, for example, humanized antibodies. Furthermore, the antibodies can also be chemically and/or enzymatically modified, for example carry a glycosylation and/or a label, like a fluorescent or radioactive label.

Also included are methods for the generation of antibodies against any of the group comprising the peptides according to SEQ ID NOs 3, 6, and/or 9, which rely on the use of phage display systems and related systems, such as described in Hoogenboom HR, de Bruine AP, Hufton SE, Hoet RM, Arends JW, Roovers RC, Immunotechnology 1998 Jun;4(l):l-20, and references therein.

EPITOPES OF THE CF21 to CF33a COFACTORS

The present invention also encompasses one or more epitopes of a cofactor protein or peptide that is comprised of sequences and/or a conformation of sequences present in the cofactor polypeptides or peptide molecule. These epitopes may be naturally occurring, or may be the result of proteolytic cleavage of the cofactor proteins or peptides and isolation of an epitope- containing peptide or may be obtained by synthesis of an epitope-containing peptide using a method of genetic engineering technology and synthesized by genetically engineered prokaryotic or eukaryotic cells.

ANTISENSE OLIGONUCLEOTIDES AGAINST CF21 to CF33a GENE TRANSCRIPTS

Antisense oligonucleotides are short single stranded DNA or RNA molecules which may be used to block the availability of the cofactor messenger(s). Synthetic derivatives of ribonu- cleotides or desoxyribonucleotides and/or PNAs (see above) are equally possible. These are potential candidate agents which may interact with the cofactor according to the invention.

The sequence of an antisense oligonucleotide is at least partially complementary to the sequence of the cofactor of interest. The complementarity of the sequence is in any case high enough to enable the antisense oligonucleotide to bind to the nucleic acid according to the invention or parts thereof in which the binding of oligonucleotides to the target sequence interfere with the biological function of the targeted sequence (Brysch W, Schlingensiepen KH, Design and application of antisense oligonucleotides in cell culture, in vivo, and as therapeu- tic agents, Cell Mol Neurobiol 1994 Oct;14(5):557-68; Wagner RW, Gene inhibition using antisense oligodeoxynucleotides, Nature 1994 Nov 24;372(6504):333-5 or Brysch W, Magal E, Louis JC, Kunst M, Klinger I, Schlingensiepen R, Schlingensiepen KH Inhibition of pl85c-erbB-2 proto-oncogene expression by antisense oligodeoxynucleotides down-regulates pl85-associated tyrosine-kinase activity and strongly inhibits mammary tumor-cell proliferation, Cancer Gene Ther 1994 Jun;l(2):99-105 or Monia BP, Johnston JF, Ecker DJ, Zounes MA, Lima WF, Freier SM Selective inhibition of mutant Ha-ras mRNA expression by antisense oligonucleotides, J Biol Chem 1992 Oct 5;267(28): 19954-62 or Bertram J, Palfner K, Killian M, Brysch W, Schlingensiepen KH, Hiddemann W, Kneba M, Reversal of multiple drug resistance in vitro by phosphorothioate oligonucleotides and ribozymes, Anticancer Drugs 1995 Feb;6(l): 124-34).

This interference occurs in most instances at the level of translation, i.e. through the inhibition of the translational machinery by oligonucleotides that bind to mRNA, however, two other mechanisms of interference with a given gene's function by oligonucleotides can also be envisioned, (i) the functional interference with the transcription of a gene through formation of a triple helix at the level of genomic DNA and the interference of oligonucleotides with the function of RNA molecules that are executing at least part of their biological function in the untranslated form (Kochetkova M, Shannon MF, Triplex-forming oligonucleotides and their use in the analysis of gene transcription. Methods Mol Biol 2000;130:189-201 Rainer B. Lanzl, Neil J. McKennal, Sergio A. Onatel, Urs Albrecht2, Jiemin Wongl, Sophia Y. Tsail, Ming-Jer Tsail, and Bert W. O'Malley A Steroid Receptor Coactivator, SRA, Functions as an RNA and Is Present in an SRC-1 Complex Cell, Vol. 97, 17-27, April, 1999).

Antisense oligonucleotides can be conjugated to different other molecules in order to deliver them to the cell or tissue expressing any of the cofactor genes. For instance the antisense oligonucleotide can be conjugated to a carrier protein (e.g. ferritin) in order to direct the oligonucleotide towards the desired target tissue, i.e. in case of ferritin predominantly to the liver.

Antisense expression constructs are expression vector systems that allow the expression - either inducible or uninducible - of a complementary sequence to the CF21 TO CF33A co- factor sequences according to the invention. The potential possibility of such an approach has been demonstrated in many different model systems (von Ruden T, Gilboa E, Inhibition of human T-cell leukemia virus type I replication in primary human T cells that express an- tisense RNA, J Virol 1989 Feb;63(2):677-82; Nemir M, Bhattacharyya D, Li X, Singh K, Mukherjee AB, Mukherjee BB, Targeted inhibition of osteopontin expression in the mammary gland causes abnormal morphogenesis and lactation deficiency, J Biol Chem 2000 Jan 14;275(2):969-76; Ma L, Gauville C, Berthois Y, Millot G, Johnson GR, Calvo F Antisense expression for amphiregulin suppresses tumorigenicity of a transformed human breast epithelial cell line, Oncogene 1999 Nov l l;18(47):6513-20; Refolo LM, Eckman C, Prada CM, Yager D, Sambamurti K, Mehta N, Hardy J, Younkin SG, Antisense-induced reduction of presenilin 1 expression selectively increases the production of amyloid beta42 in transfected cells, J Neurochem 1999 Dec;73(6):2383-8; Buckley NJ, Abogadie FC, Brown DA, Dayrell M, Caulfield MP, Delmas P, Haley JE, Use of antisense expression plasmids to attenuate G- protein expression in primary neurons, Methods Enzymol 2000;314:136-48).

According to the invention an antisense expression construct can be constructed with virtually any expression vector capable of fulfilling at least the basic requirements known to those skilled in the art.

In one embodiment of the invention retroviral expression systems or tissue specific gene expression systems are preferred.

Current standard technologies for delivering antisense constructs are performed through a conjugation of constructs with liposomes and related, complex-forming compounds, which are transferred via electroporation techniques or via particle-mediated "gene gun" technologies into the cell. Other techniques may be envisioned by one skilled in the art.

Microinjection still plays a major role in most gene transfer techniques for the generation of germ-line mutants expressing foreign DNA (including antisense RNA constructs) and is preferred embodiment of the present invention.

RIBOZYMES DIRECTED COFACTOR 21 TO 33a GENE TRANSCRIPT.

Ribozymes are either RNA molecules (Gibson SA, Pellenz C, Hutchison RE, Davey FR, Shillitoe EJ, Induction of apoptosis in oral cancer cells by an anti-bcl-2 ribozyme delivered by an adenovirus vector, Clin Cancer Res 2000 Jan;6(l):213-22; Folini M, Colella G, Villa R, Lualdi S, Daidone MG, Zaffaroni N, Inhibition of Telomerase Activity by a Hammerhead Ribozyme Targeting the RNA Component of Telomerase in Human Melanoma Cells, J Invest Dermatol 2000 Feb;114(2):259-267; Halatsch ME, Schmidt U, Botefur IC, Holland JF, Oh- numa T, Marked inhibition of glioblastoma target cell tumorigenicity in vitro by retrovirus- mediated transfer of a hairpin ribozyme against deletion-mutant epidermal growth factor receptor messenger RNA, J Neurosurg 2000 Feb;92(2):297-305; Ohmichi T, Kool ET, The virtues of self-binding: high sequence specificity for RNA cleavage by self-processed hammerhead ribozymes, Nucleic Acids Res 2000 Feb l;28(3):776-783) or DNA molecules (Li J, Zheng W, Kwon AH, Lu Y, In vitro selection and characterization of a highly efficient Zn(II)- dependent RNA-cleaving deoxyribozyme; Nucleic Acids Res 2000 Jan 15 ;28(2) :481 -488) that have catalytic activity. The catalytic activity located in one part of the RNA (or DNA) molecule can be "targeted" to a specific sequence of interest by fusing the enzymatically active RNA molecule sequence with a short stretch of RNA (or DNA) sequence that is complementary to the cofactor gene transcript of interest. Such a construct will, when introduced into a cell either physically or via gene transfer of a ribozyme expression construct find the corresponding cofactor sequence (our sequence of interest or also targeted in RNA) and bind via its sequence-specific part to said sequence. The catalytic activity attached to the construct, usually associated with a special nucleic acid structure (people distinguish so called "hammerhead" structures and "hairpin" structures), will then cleave the targeted RNA. The targeted mRNA will be destroyed and cannot be translated efficiently, thus the protein encoded by the mRNA derived from cofactor will not be expressed or at least will be expressed at significantly reduced amounts.

These are potential candidate agents which may interact with the cofactor according to the invention.

In a preferred embodiment the invention covers inducible ribozyme constructs (Koizumi M, Soukup GA, Kerr JN, Breaker RR, Allosteric selection of ribozymes that respond to the second messengers cGMP and cAMP, Nat Struct Biol 1999 Nov;6(l 1):1062-1071).

In a further preferred embodiment the invention concerns the use of "bivalent" ribozymes (multimers of catalytically active nucleic acids) as described in (Hamada M, Kuwabara T, Warashina M, Nakayama A, Taira K, Specificity of novel allosterically trans- and cis- activated connected maxizymes that are designed to suppress BCR-ABL expression FEBS Lett 1999 Nov l2;461(l-2):77-85). TRANSGENIC ANIMALS CARRYING THE CF21 to CF33a COFACTOR GENE

Also provided by the present invention are non-human transgenic animals grown from germ cells transformed with at least one CF21 to CF33A nucleic acid sequence according to the invention and that express the cofactor accordmg to the invention and offspring and descendants thereof. Also provided are transgenic non-human mammals comprising a homologous recombination knockout of the native cofactors, as well as transgenic non-human mammals grown from germ cells transformed with nucleic acid antisense to the nucleic acids of the invention and offspring and descendants thereof. Further included as part of the present invention are non-human transgenic animals in which the native cofactor has been replaced with the human ortholog. Of course, offspring and descendants of all of the foregoing transgenic animals are also encompassed by the invention.

Transgenic animals according to the invention can be made using well known techniques with the nucleic acids disclosed herein. E.g., Leder et al., U.S. Patent Nos.4,736,866 and 5,175,383; Hogan et al., Manipulating the Mouse Embryo, A Laboratory Manual (Cold Spring Harbor Laboratory (1986)); Capecchi, Science 244, 1288 (1989); Zimmer and Grass, Nature 338, 150 (1989); Kuhn et al., Science 269, 1427 (1995); Katsuki et al., Science 241, 593 (1988); Hasty et al, Nature 350, 243 (1991); Stacey et al, Mol. Cell Biol. 14, 1009 (1994); Hanks et al, Science 269, 679 (1995); and Marx, Science 269, 636 (1995). Such transgenic animals are useful for screening for and determining the physiological effects of the cofactor agonists and antagonist.

Consequently, such transgenic animals are useful for developing drugs to regulate physiological activities in which the cofactors participate.

MODELLING OF THE STRUCTURE OF ANY OF CF21 TO CF33a

In one embodiment of the invention the amino acid sequences of the present invention can be used for structural drug design. Aim is to produce structural analogs of biologically active polypeptides of interest or of small molecules with which they interact (e.g. agonists, antagonists or inhibitors) in order to design drags which are, for example, more active or stable forms of the polypeptide, or which, for example, enhance or interfere with the function of a polypeptide in vivo. In one approach one first determines the three-dimensional structure of a protein of interest, i.e. the cofactor, by computer-modeling, x-ray crystallography or a combi- nation of both approaches. Additional useful information with respect to the stracture of a polypeptide could also be gained from comparison of the protein sequence of the protein of interest with the sequence of related proteins where the structure is known. From the three- dimensional stracture, binding sites of potential inhibitors or activators can be predicted. It can further be predicted which kinds of molecule might bind there. The predicted substances can then be screened to test their effect on the activity of the protein and its biological function.

The invention is further illustrated by the following sequence description and examples from which further features, advantages and embodiments can be taken. The following Examples are provided for illustrative purposes only and are not intended, nor should they be construed, as limiting the invention in any manner.

SEQUENCE DESCRIPTIONS:

SEQ ID No 1 to 3 show CF21 (AK000429 (found with LXR alpha full length)) sequences, in particular the cDNA Sequence (Seq ID No 1) the Reverse Complement of the cDNA Sequence (Seq ID No 2) and the amino acid sequence (Seq ID No 3),

SEQ ID No 4 to 6 show CF22 (AK023923 (found with LXR alpha full length)) sequences, in particular the cDNA Sequence (Seq ID No 4) the Reverse Complement of the cDNA Sequence (Seq ID No 5) and the amino acid sequence (Seq ID No 6),

SEQ ID No 7 to 9 show CF33a (AY007790.1; p47ING3 (found with LXR alpha full length)) sequences, in particular the c DNA Sequence (Seq ID No 7) the Reverse Complement of the cDNA Sequence (Seq ID No 8) and the amino acid sequence (Seq ID No 9),

SEQ ID No 10 to 12 show LXR alpha (Bait) sequences, in particular the cDNA Sequence (Seq ID No 10) the Reverse Complement of the cDNA Sequence (Seq ID No 11) and the amino acid sequence (Seq ID No 12),

SEQ ID No 13 to 15 show LXR alpha (LBD) (Bait) sequences, in particular the cDNA Sequence (Seq ID No 13) the Reverse Complement of the cDNA Sequence (Seq ID No 14) and the amino acid sequence (Seq ID No 15), SEQ ID No 16 to 18 show RXR alpha (known to form complex with LXR) sequences, in particular the cDNA Sequence (Seq ID No 16) the Reverse Complement of the cDNA Sequence (Seq ID No 17) and the amino acid sequence (Seq ID No 18),

SEQ ID No 19 to 21 show RXR beta (known to form complex with LXR sequences, in particular the cDNA Sequence (Seq ID No 19) the Reverse Complement of the cDNA Sequence (Seq ID No 20) and the amino acid sequence (Seq ID No 21), and

SEQ ID No 22 to 23 show RXR gamma (known to form complex with LXR) sequences, in particular the cDNA Sequence (Seq ID No 22) the Reverse Complement of the cDNA Sequence (Seq ID No 23) and the amino acid sequence (Seq ID No 24).

EXAMPLES

EXAMPLE 1: CLONING AND EXPRESSION OF THE CF-GENES ACCORDING TO THE INVENTION

Construction of suitable vectors containing the desired coding and control sequences employs standard ligation and restriction techniques that are well understood in the art. Isolated plas- mids, DNA sequences, or synthesized oligonucleotides are cleaved, tailored, and religated in the form desired.

Site-specific DNA cleavage is performed by treatment with the suitable restriction enzyme (or enzymes) under conditions that are generally understood in the art, and the particulars of which are specified by the manufacturer of these commercially available restriction enzymes.

See, e.g., New England Biolabs, Product Catalog. In general, about 1 μg of plasmid and/or DNA sequence is cleaved by one unit of enzyme in about 20 μl of buffer solution. Often excess of restriction enzyme is used to ensure complete digestion of the DNA substrate. Incubation times of about one hour to two hours at about 37°C are workable, although variations are tolerable.

After each incubation, protein is removed by extraction with phenol/chloroform, and may be followed by ether extraction. The nucleic acid may be recovered from aqueous fractions by precipitation with ethanol. If desired, size separation of the cleaved fragments may be per- formed by polyacrylamide gel or agarose gel electrophoresis using standard techniques. A general description of size separations is found in Methods in Enzymology 65, 499-560 (1980).

Transformed host cells are cells which have been transformed or transfected with recombinant expression constructs made using recombinant DNA techniques and comprising cofactor encoding sequences. Preferred host cells for transient transfection are COS-7 cells. Transformed host cells may ordinarily express one of the CF21 to CF33a cofactors but host cells transformed for purposes of cloning or amplifying nucleic acid hybridization probe DNA need not express the cofactors. When expressed, the cofactor proteins will typically be located in the host cell membrane.

Cultures of cells derived from multicellular organisms are desirable hosts for recombinant nuclear receptor protein synthesis. In principal, any higher eukaryotic cell culture is workable, whether from vertebrate or invertebrate culture. However, mammalian cells are preferred. Propagation of such cells in cell culture has become a routine procedure. See Tissue Culture (Academic Press, Kruse & Patterson, Eds., 1973). Examples of useful host cell lines are bacteria cells, insect cells, yeast cells, human 293 cells, VERO and HeLa cells, LMTK- cells, and WI138, BHK, COS-7, CV, and MDCK cell lines. Human 293 cells are preferred.

EXAMPLE 2: COFACTOR TISSUE LOCALIZATION:

A multiple tissue northern blot (Clontech, Palo Alto) is hybridized to a labeled probe. The blot contains about 0.3 to 3 μg of poly A RNA derived from various tissues. Hybridization may be carried out in a hybridization solution such as one containing SSC (see Maniatis et al, ibid) at an optimized temperature between 50°c and 70°C, preferably 65°C. The filter may be washed and a film exposed for signal detection (see also: Maniatis et al., Molecular Cloning: A laboratory Manual, Cold Spring Harbor Laboratory Press, N.Y.(1989)).

EXAMPLE 3: COFACTOR cDNA ISOLATION FROM HUMAN AND OTHER ORGANISMS:

A cloning strategy is used to clone the desired CF21 to CF33a cofactor cDNA from specific cDNA libraries (Clontech, Palo Alto) or alternatively, RNA is obtained from various tissues and used to prepare cDNA expression libraries by using for example an Invitrogen kit. (Invi- trogen Corporation, San Diego). For the isolation of the CF cDNA clones the chosen library may be screened under stringent condition (see definitions above) by using CF21, CF22 or CF33a specific probes. The cDNA insert of positive clones is subsequently sequenced and cloned in a suitable expression vector.

Additionally, full length cofactor clones from various species are obtained by using RACE PCR technology. In brief, suitable cDNA libraries are constructed or purchased. Following reverse transcription, the first strand cDNA is used directly in RACE PCR reactions using a RACE cDNA amplification kit according to the manufactures protocol (Clontech, Palo Alto). Amplified fragments are purified, cloned and subsequently used for sequence analysis.

To obtain information about the genomic organization of the cofactor gene, genomic libraries (Clontech, Palo Alto) are screened with a receptor specific probe under stringent conditions. Positive clones are isolated and the complete DNA sequence of the putative receptor is determined by sequence analysis (Maniatis et al., Molecular Cloning: A laboratory Manual, Cold Spring Harbor Laboratory Press, N.Y.(1989)).

EXAMPLE 4: ISOLATION OF THE COFACTOR POLYPEPTIDES BY USE OF THE YEAST TWO-HYBRID SYSTEM

A yeast two-hybrid assay was performed using methods such as described by Fields and Song Nature 340, pp245 (1989), Bartel et al., Biotechniques 14, pp920 (1993) and Lee et al. Nature 374 pp91-4 (1995). A sequence encoding amino acids (aa) 1-447 of LXR alpha (full length protein) or alternatively a sequence encoding aa 155-447 of LXR alpha (containing the ligand binding domain; LBD) was cloned into the vector pGBT9 (Clontech) in such way that, after transformation of the haploid yeast strain CGI 945 (Clontech), a hybrid protein is expressed consisting of the DNA-binding domain (BD) of the Gal4 transcription factor fused N- terminally to full length LXR alpha or alternatively fused to a fragment consisting of aa 155- 447 of LXR alpha.

CG1945 cells expressing the Gal4BD::LXR alpha (aa 1-447) or Gal4BD::LXR alpha (aall5- 447) fusion proteins, respectively, were mated to cells of strain Y187 (Clontech) containing a library of Gal4 transcription activation domain (AD) fusion plasmids with human cDNA generated from a range of tissues inserted into the vector pACT2 (Clontech). All libraries were purchased from Clontech Laboratories (MATCHMAKER human cDNA libraries) and in- cluded Cat. numbers HL4040AH (aorta), HL4041AH (chondrocytes), HY4004AH (brain), HY4035AH (testis), HY4024AH (liver), HY4042AH (heart), HY4053AH (bone marrow), HY4028AH (fetal brain), HY4043AH (kidney), HY4051AH (ovary), HY4047AH (skeletal muscle) and HY4000AA (hela). The two-hybrid screens were essentially performed following the Clontech "Pretransformed Matchmaker Libraries User Manual" (PT3183-1): Transformed CG1945 and Y187 cells were mated in order to coexpress one of the Gal4BD::LXR alpha fusion proteins and the Gal4AD fusion proteins encoded on the library plasmids within one cell. Interaction of the two hybrid proteins led to activation of reporter gene transcription. Cells were selected for interactions of LXR alpha with library proteins in medium lacking tryptophan, leucine and histidine and containing 2 mM 3-aminotriazol and 250 nM 22(R)- hydroxycholesterol and were further assayed for expression of D-galactosidase, encoded by the MEL1 reporter gene. Colonies which were positive for reporter gene activation were chosen for further analysis. The DNA inserts of the library plasmids contained in these colonies were amplified by use of the polymerase chain reaction directly on the yeast colonies using oligonucleotide primers which hybridize on vector sequences flanking both sides of the insert. The identity of the insert was determined by standard DNA sequencing techniques.

Three novel cofactors (CF21 (AK000429), CF22 (AK023923) and CF33a (AY007790.1;p47ING3)) interacting with LXR alpha full length protein were isolated using this approach: CF21 (AK000429) was isolated from the skeletal muscle, ovary and liver cDNA libraries, CF22 (AK023923) from the chondrocytes, heart and testis libraries and CF33a (AY007790.1) from the skeletal muscle cDNA library.

EXAMPLE 5: DETECTION OF MUTANT ALLELES OF THE GENE(S) ACCORDING TO THE INVENTION AND THEIR UTILISATION FOR DIAGNOSTIC PURPOSES.

According to the diagnostic and prognostic method of the present invention, alteration of the wild-type cofactor gene is detected. In addition, the method can be performed by detecting the wild-type cofactor gene and confirming the lack of cause of the disease as a result of the locus.

"Alteration of the wild-type gene" encompasses all forms of mutations including deletions, insertions and point mutations in the coding and non-coding regions. Deletions may be of the entire gene or of only a portion. Point mutations may result in stop codons, frameshift mutations or amino acid substitutions. Somatic mutations are those which occur only in certain tissues and are not inherited in the germline. Germline mutations can be found in any of a body's tissue and are mostly inherited. Point mutational events may occur in regulatory regions, such as the promotor of the gene, leading to loss or dimunition of expression of the mRNA. Point mutations may also abolish proper RNA processing, leading to loss of expression of the cofactor gene product or to a decrease in mRNA stability or translation efficiency.

Applicable diagnostic techniques include, but are not limited to fluorescent in situ hybridization (FISH), direct DNA sequencing, PFGE analysis, Southern blot analysis, single stranded conformation analysis (SSCA), RNAse protection assay, allele-specific oligonucleotide (ASO), dot blot analysis, hybridization using nucleic acid modified with gold nanoparticles and PCR-SSCP, as discussed in detail further below. Furthermore, DNA microchip technology can be applied.

The presence of a disease due to a germline mutation of a cofactor can be ascertained by testing any tissue of the diseased human for mutations of the cofactor gene. For instance, a person who has inherited a germline mutation in the cofactor gene, especially one that will alter the interaction of the cofactor with the LXR alpha protein, will be prone to develop a disease, such as cancer, bone diseases or defects in reproductive organs. The presence of such a mutation can be determined by extracting DNA from any tissue of the body. For example, blood can be drawn and DNA extracted from blood cells and analyzed. Moreover, prenatal diagnosis of the disease will be possible by testing fetal cells, placental cells or amniotic cells for mutations in the cofactor gene. There are several methods that allow the detection of alterations of the wild-type cofactor gene, including for instance point mutations as well as deletions in the DNA sequence and these methods are discussed here:

Direct genomic DNA sequencing, either manually or by automated means can detect sequence variations of cofactor genes (Nucleic Acids Res 1997 May 15;25(10):2032-2034 Direct DNA sequence determination from total genomic DNA. Kilger C, Paabo S, Biol. Chem. 1997 Feb; 378(2):99-105, Direct exponential amplification and sequencing (DEXAS) of genomic DNA. Kilger C, Paabo S, DE 19653439.9 and DE 19653494.1). Another way is to make use of the single-stranded conformation polymorphism assay (SSCP; Orita et al., PNAS 86, 2766 (1989)). Variations in the DNA sequence of the cofactor gene from the wild-type sequence will be detected due to a shifted mobility of the corresponding DNA-fragments in SSCP gels. Other approaches are based on the detection of mismatches between the two complementary DNA strands. These methods, which will not allow the detection of large deletions, duplications or insertions nor the detection of a regulatory mutation affecting transcription or translation of the cofactor gene include the clamped denaturing gel electrophoresis (CDGE; Sheffield et al.,1991), heteroduplex analysis (HA; White et al., Genomics 4, 560 (1992)) and chemical mismatch cleavage (CMC; Grompe et al., 1989). Other methods detect specific types of mutations such as deletions, duplications or insertions, for instance a protein truncation assay or the asymmetric assay. These assay however, will not detect missense mutations. A review of currently available methods of detecting DNA sequence variation can be found in a review by Grompe, Nature Genetics 5, 111 (1993). Once a mutation is known, an allele specific detection approach such as allele specific oligonucleotide (ASO) hybridisation will allow the rapid screening of a large number of other sample for that mutation. Such a technique may involve the utilisation of probes which are labeled with gold nanoparticles to yield a visual color result (Elghanian et al. Science 277, 1078 (1997)).

In another embodiment of the present invention large scale genetic studies might be applied to investigate the association of a disease-phenotype with the gene of interest. The availability of the human genome allows an easy definition of genetic markers for most genes for a particular disease physiology. More importantly, single nucleotide polymorphisms (SNPs) are amenable markers for large genetic studies. SNPs in coding or regulatory regions of genes which are thought to contribute to a disease physiology can have a direct impact on the phenotype, e.g. change a quantitative readout of disease physiology, for example the age of onset of heart attack. Association and linkage studies with related individuals, therefore provide an excellent means to test or verify a hypothesis on the functional impact of the gene of interest on disease physiology in vivo, in humans.

The LXR alpha protein is known to represent a major player in the regulation of cholesterol homeostasis (Peet et al, Cell 93, 693-704 (1998). Further, wild-type LXR alpha functions as a key sensor for dietary cholesterol and it regulates the elimination of cholesterol from the body through the stimulation of its catabolism into bile acids in a feed forward mechanism. Not only Cyp7A expression is upregulated by LXR alpha function, but also a number of other genes whose products play crucial roles in the hepatic lipid metabolism are controlled by LXR alpha. Proteins interacting with LXR alpha and or the cofactors according to the invention are involved in the function of LXR alpha. Therefore, alterations in the cofactors are use- ful for determining the genetic state of a person with respect to its capability to respond to and/or to metabolize cholesterol.

In order to detect polymorphisms in DNA sequences, DNA samples can be prepared from normal individuals and from persons being affected by the disease and these samples can be cut by one or more restriction enzymes and applied to Southern analysis. Southern blots displaying hybridizing fragments differing in length from the control DNA when probed with sequences near or including the cofactor locus could indicate a possible mutation. If large DNA fragments are used it is appropriate to separate these fragments by pulsed field gel electrophoresis (PFGE).

Detection of point mutations may be accomplished by amplification, for instance by PCR, from genomic or cDNA and sequencing of the amplified nucleic or by molecular cloning of the cofactor allele and sequencing the allele using techniques well known in the art.

There are six well known methods for a more complete, yet still indirect, test for confirming the presence of a susceptibility allele: 1) single stranded conformation analysis (SSCP) (Orita et al., PNAS, 86, 2766 (1989)); 2) denaturing gradient gel electrophoresis (DGGE) (Wartell et al, NAR 18, 2699, (1990); Sheffield et al., PNAS 86 , 232 (1989)); 3) RNase protection assays (Finkelstein et al., Genomics 7, 167 (1990); Kinszler et al, Science 251, 1366 (1991)); 4) allele specific oligonucleotides (ASOs, Conner et al., PNAS, 80, 278 (1983)); 5) the use of proteins which recognise nucleotide mismatches, such as the E. coli mutS protein (Modrich, Ann. Rev. Genetics, 25, 229 (1991)) and 6) allele-specific PCR (Ruano and Kidd, NAR 17, 8392 (1989)). For allele-specific PCR, primers are used which hybridise at their 3' ends to a particular cofacto mutation. Without the mutation, no PCR product is observed. Amplification Refractory Mutation System could also be used, as disclosed in European Patent Application Publication No. 0332435 and in Newton et al., NAR 17, 2503 (1989). Insertions and deletions of genes can also be detected by molecular cloning, amplification and sequencing. Moreover, restriction fragment length polymorphism (RFLP) probes for the gene or surrounding marker genes can be used to score for alteration of an allele or an insertion in a polymorphic fragment. Such a method would be particularly useful for screening relatives of an affected person for the presence of the mutation found in that person. Other approaches for detecting insertions and deletions as known for those trained in the art can be used. SSCP detects a band which migrates differently because the variation causes a difference in single strand, intramolecular base pairing. The RNAse protection assay involves cleavage of the mutant fragment into two or more smaller fragments. By using DGGE variations in the DNA can be detected by differences in the migration rates of mutant compared to normal al- leles in a denaturing gradient gel. In the mutS assay, the protein binds only to sequences that contain a nucleotide mismatch in a hetero duplex between mutant and wild-type sequences.

Mismatches, according to the present invention, are hybridised nucleic acid duplexes in which the two strands are not 100% complementary. Lack of total homology may be due to deletions, insertions, inversions or substitutions. Mismatch detection can be used to detect point mutations in the gene or the corresponding mRNA product. While these techniques are less sensitive than sequencing, they can preferably be used when a large number of samples shall be tested. An example of a mismatch cleavage method is the RNAse protection assay. In the practice of the present invention , the method involves the use of a labeled ribonucleotide probe which is complementary to the wild-type sequence of the cofactor gene coding se- quence.The riboprobe and either mRNA or DNA isolated from the person are hybridised together and subsequently digested with the enzyme RNase A which is able to detect some mismatches in a duplex RNA stracture. If a mismatch is detected by the enzyme, it cleaves at the site of the mismatch. Consequently, when the annealed RNA preparation is separated on an electrophoretic gel matrix, if a mismatch has been detected and cleaved by RNAse A, an RNA product will be seen which is smaller than the full length duplex RNA for the riboprobe and the mRNA or DNA. If the riboprobe comprises only a fragment of the mRNA or the gene, it is advantageous to use a number of probes to screen the whole mRNA sequence for mismatches.

Similarly, DNA probes can be used to detect mismatch mutations through enzymatic or chemical cleavage (Cotton et al., PNAS 85, 4397 (1988); Shenk et al., PNAS 72, 989 (1975); Novack et al, PNAS 83, 586 (1986)). Alternatively, mismatches can be detected by shifts in the electrophoretic mobility of mismatched duplexes relative to match duplexes (Cariello, Human Genetics 42, 726 (1988)). With either riboprobes or DNA probes, the cellular mRNA or DNA which might contain a mutation can be amplified using PCR (see below) before hybridisation. Variations in DNA of the cofactor) gene can also be detected using Southern hybridisation, especially if the changes are major rearrangements, such as deletions or insertions. DNA sequences of the cofactor gene which have been amplified by PCR may also be screened using allele specific probes. These probes are nucleic acid oligomers, each of which contains a region of the gene sequence harboring a known mutation. For instance, one oli- gomer could be about 25 nucleotides in length corresponding to a portion of the gene sequence. By using a number of such allele-specific probes, PCR amplification products can be screened to identify the presence of a previously discovered mutation in the gene. Hybridisation of allele-specific probes with amplified cofactor sequences can be performed, for example, on a nylon filter. Under high stringency hybridisation conditions, the hybridisation of a particular probe should indicate the presence of the same mutation in the tissue as in the allele-specific probe.

The newly developed technique of nucleic acid analysis via microchip technology is also applicable to the present invention. In this technique, thousands of distinct nucleotide probes are built up in an array on a silicon chip. Nucleic acid to be analysed is fluorescently labeled and hybridised to the probes on the chip. It is also possible to study nucleic acid-protein interactions using these nucleic acid microchips. Using this technique one can determine the presence of mutations or even sequence the nucleic acid being analysed or one can measure expression of a gene of interest. This method is one of parallel processing of thousands of probes at once and can tremendously accelerate the analysis. In several publications the use of this method is described (Hacia et al, Nature Genetics 14, 441 (1996); Shoemaker et al., Nature Genetics 14, 450 (1996); Chee et al, Science 274, 610 (1996); DeRisi et al, Nature Genetics 14, 457 (1996)). This new technology has also been reviewed in Borman et al., Chemical and Engineering News 9, 42 (1996) and has been subject of an editorial in Nature Genetics (1996).

The most definite test for mutations in a candidate locus is to directly compare genomic co- factor sequences from patients with those from normal individuals. Alternatively one could sequence mRNA after amplification (for example by PCR) thereby eliminating the necessity of determining the exon structure of the respective gene.

Mutations from patients falling outside the coding region of the cofactor gene can be detected by examining the non-coding regions, such as introns and regulatory sequences within or near the genes. Early indications of mutations in non-coding regions could be for example the abundance or abnormal size of mRNA products in patients as compared to control individuals as detected by northern blot analysis. Alteration of cofactor expression can be detected by any technique known in the art. These include northern blot analysis, PCR amplification and RNAse protection. Diminished mRNA expression indicates an alteration in the wild-type gene sequence. Alterations of wild-type genes can also be detected by screening for alteration of cofactor protein. For example, monoclonal antibodies against cofactor protein can be used to screen a tissue. Lack of cognate antigen would indicate a mutation. Antibodies specific for products of mutant alleles could also be used to detect mutant gene product. These kind of immunological assays could be done in any convenient format known in the art. These include western blots, immunohistochemical assays and ELISA assays. Any means for detecting an altered cofactor protein can be used to detect alteration of the wild-type cofactor gene. Functional assays such as protein binding determinations can be used. Moreover, assays can be used which detect the cofactors' biochemical function. Finding a mutant cofactor gene product indicates an alteration of the co- factor wild-type gene. One such binding assay tests the binding of cofactor protein with wild- type LXR alpha protein. Conversely, wild-type LXR alpha protein or the domain interacting with the cofactor protein can be used in a protein binding assay or biochemical function assay to detect normal or mutant proteins.

A mutant cofactor gene or gene product or a mutant LXR alpha protein can also be detected in other human body samples, such as serum, stool, urine and sputum. The same techniques discussed above for detection of mutant genes or gene products in tissues can be applied to other body samples. By screening such body samples, a simple early diagnosis can be achieved for the disease) resulting from a mutation in the cofactor gene.

EXAMPLE 6: A CELL BASED ASSAY FOR MEASURING THE BINDING OF THE COFACTOR(S) CF21, CF22, OR CF33A, RESPECTIVELY, TO LXR ALPHA.

The DNA sequence encoding the open reading frame of the respective cofactor is transferred into the vector pVP16 (Clontech) to allow the expression of a fusion protein of the cofactor with the strong transactivation domain of the VP16 protein (of herpex simplex virus) in mammalian cells under the control of the strong CMV promoter. On another vector (the reporter), the luciferase gene is cloned under the control of a minimal promoter containing a LXR alpha-responsive DNA element. This vector also expresses a second enzyme, e.g. beta- galactosidase, under the control of a constitutive promoter, to allow normalisation for trans- fection efficiency between experiments. A third vector contains the LXR alpha gene under the control of the strong CMV promoter.

CV-1 cells are then transiently transfected with different combinations of the three plasmids. Transfection is done by standard methods, e.g. by use of the CalPhos Maximizer (Clontech, #8021-1,-2). Interaction of the cofactor protein with LXR alpha will lead to a strong transactivation due to the attached VP16 domain of the cofactor fusion protein. Thus, interaction of the cofactor with LXR alpha will result in increased luciferase activity. Inclusion of the co- factor VP16 will result in increased luciferase activity as compared to transfection of the LXR alpha and the reporter alone. To measure this effect, extracts are prepared of the transfected cells 48 to 72 hours after transfection, and luciferase activity is determined. To normalise for transfection efficiency, beta-galactosidase activity is also determined.

Addition of substances known or suspected to influence the binding of LXR alpha to the co- factor are added to the medium of the transfected cells. These substances are added at different timepoints prior to cell lysis, typically ranging between 18 hours to a five minutes before cell lysis. Luciferase activity is taken as a measure of the effect of these substances on the binding of the cofactor to LXR alpha. To avoid activation of LXR alpha by substances contained in the serum of the medium, charcoal stripped serum has to be used for these experiments.

In an alternative setting of the experiment, the DNA-binding domain of LXR alpha is replaced with the DNA-binding domain of the yeast GAL4 transcription factor. On the reporter plasmid, the luciferase is expressed under the control of GAL4-responsive upstream activating sequences. Expression of luciferase again is an indication for binding of the cofactor CF21 to CF33a-VP16 fusion to the GAL4-LXR alpha fusion. This setting is also referred to as the mammalian two hybrid system. A description of the experiment is found in the manual to the Mammalian MATCHMAKER Two-Hybrid Assay Kit from Clontech, #PT3002-1, catalogue #K1602-1)

Substances activating nuclear receptors cause an exchange of the proteins bound to the receptors, thus effecting the dissociation of some proteins and promoting the binding of other proteins. Thus, in the experiments as described above, one can test for LXR alpha-activating compounds and LXR alpha-inactivating compounds by monitoring the binding of the cofactor to LXR alpha.

In an alternative setting, stably transfected cell lines are used which contain copies of the two different expression constructs for LXR alpha and the respective cofactor as well as the reporter construct stably integrated into the chromosomes of the cells.

EXAMPLE 7: A FRET ASSAY USING COFACTOR POLYPEPTIDES

DNA sequences encoding the open reading frame of the cofactor and the LXR alpha gene are each transferred separately into the vector pENTRY (Life Technologies) to allow efficient construction of a diverse set of expression constructs. The open reading frame is then recom- bined into the vector pDEST17 for expression in E. coli strain BL21 as a fusion protein to a six-histidine tag induced by IPTG, as well as into the pDEST15 for expression as a fusion protein with glutathione S-transferase (GST). The plasmids pDEST15, pDEST17and pENTRY are purchased from LIFE TECHNOLOGIES. Alternatively, the open reading frame is introduced into the vector pLV-CBDgw for expression as a fusion protein with the calmodu- lin binding protein using recombinant baculoviruses as specified by the manufacturer (Becton Dickinson). pLV-CBDgw is a derivative of the vector pLV1392 (Becton Dickinson) which is modified by the insertion of a calmodulin binding protein fragment, followed by the sequence required for recombinational cloning via the Gateway system (Life Technologies). Protein expression is induced and recombinant protein is purified by passage over a Ni-NTA-column, or a glutathione column or a calmodulin column, respectively.

To measure the interaction of the two proteins, a biotinylated (Biotintag Micro biotinylation Kit, Sigma) His-tagged LXR alpha protein and the GST fusion of the cofactor are mixed at 0.2-5 μM. Antibody to the GST protein is added which is labelled by the europium chelate at a concentration of 1-3 (typical 2.5) nM. Streptavidin which is fluorescently labeled by covalent attachment of allophycocyanin is added at a concentration of 5-30 μg/ml (typical lOμg/ml). The europium chelate is stimulated by a flash of light (320nm) and, the emitted light is measured in a delayed (50-200 μs) time window for 300 to 450 μs after the flash at 615 nm (fluorescence of europium chelate) and 655nm (fluorescence of APC). Since APC is only excited by the light emitted by the europium chelate, a close proximity of the two different fluorophores is required for excitation. The strength of the APC signal, as well as the ratio of the signals from the two fluorophores (i.e. the ratio of the intensities of light emitted at 655 and 615nm) serves as a measure for the interaction of the two proteins. Reaction buffers contain 20mM TrisHCl pH 7.9, 60mM KCl, 4mM MgCl₂. Reaction volume is 25 μl. The Wallac VictorV fluorimeter is used for the fluorimetric measurements.

In an alternative setting, the cofactor is used as a biotinylated His-tagged protein, and the LXR alpha protein is used as fusion to GST. In yet another setting, the His-tagged proteins are replaced by the same proteins fused to the calmodulin binding protein. In the latter case, the detection of the interaction is via biotinylated calmodulin, which is in turn binding to APC- coupled streptavidin. Calcium has to be included in the buffer in the form of 4mM CaCl₂, to allow complex formation between calmodulin and the calmodulin binding protein.

Claims

CLAIMS:

1. An isolated nucleic acid molecule coding for a cofactor (CF) of the liver X receptor alpha which is selected from the group consisting of:

a) the nucleotide sequences set forth in SEQ ID NOs: 1, 4, and/or 7;

b) or complements thereof as set forth in SEQ ID NOs: 2, 5, and/or 8;

c) a nucleic acid which hybridizes to a nucleic acid having a nucleotide sequence which is the complement of the nucleotide sequence of SEQ ID NOs: 1, 4, and/or 7, under conditions of high stringency, and

d) a nucleic acid which hybridizes to a nucleic acid having a nucleotide sequence which is the complement of the nucleotide sequence of SEQ ID NOs: 2, 5, and/or 8, under conditions of high stringency.

2. The isolated nucleic acid molecule of claim 1 which is genomic DNA.

3. The isolated nucleic acid molecule of claim 1 which is cDNA.

4. The isolated nucleic acid molecule of claim 1 which is RNA.

5. An isolated nucleic acid molecule comprising the nucleic acid molecule of any of claims 1 to 4 and a label attached thereto.

6. A vector comprising the nucleic acid molecule of claim 1.

7. The vector of claim 6, which is an expression vector.

8. A host cell transfected with the vector of claim 6 or 7.

9. A host cell transfected with the expression vector of claim 7.

10. A method of producing a polypeptide comprising the step of culturing the host cell of claim 9 in an appropriate culture medium to thereby produce the polypeptide.

11. An isolated polypeptide encoded by any portion of a nucleic acid of claim 1.

12. An isolated polypeptide selected from the group consisting of the amino acid sequences set forth in SEQ ID NOs.: 3, 6 and/or 9.

13. Proteinous complex, comprising a cofactor polypeptide according to any of SEQ ID NOs.: 3, 6 and/or 9 or a portion thereof together with a liver X receptor alpha polypeptide according to any of SEQ ID NOs. 12 or 15 or a portion thereof.

14. Complex according to claim 13, further comprising at least one RXR polypeptide according to any of SEQ ID NOs. 18, 21 or 24 or a portion thereof.

15. Complex according to claim 13 or 14, further comprising at least one non-protein cofactor.

16. A method for screening for compounds which are capable of inhibiting the cellular function of at least one of the cofactors CF21, CF22 and/or CF33a, in particular binding of said cofactors to liver X receptor alpha polypeptide according to any of SEQ ID NOs. 12 or 15 or a portion thereof comprising the steps of:

a) contacting one or more candidate compounds with a polypeptide according to claims 11, 12 or a complex according to any of claims 13 to 15, b) removing unbound compound(s), c) detecting whether the compounds(s) interact with the polypeptide of the cofactor.

17. A method for screening for compounds which are capable of inhibiting or activating the cellular function of liver X receptor alpha polypeptide according to any of SEQ ID NOs. 12 or 15 or a portion thereof, in particular binding of said liver X receptor alpha polypeptide to at least one of the cofactors CF21, CF22 and/or CF33a, comprising the steps of: a) contacting one or more candidate compounds which are capable of binding with a complex according to any of claims 13 to 15, b) removing unbound compound(s), c) detecting the amount of the polypeptide of the CF according to any of claims 11 or 12 of that remained bound within the complex and d) identifying such compounds capable of either: i) releasing a large amount of the polypeptide of the CF according to any of claims 11 or 12 from the complex, or ii) promoting the association of CF polypeptides according to any of claims 11 or 12 from the complex.

18. Compound or mixture of compounds, identified by the method according to claim 17.

19. A method for inhibiting or activating the cellular function of the cofactor CF21, CF22, and/or CF33a, comprising the steps of:

a) contacting a cell with a binding agent that binds the polypeptide according to claim 11, 12 or the complex according to any of claims 13 to 15, b) whereby the cellular function of CF21 , CF22 and/or CF33a is inhibited or activated.

20. A method for inhibiting or activating the binding of the cofactor CF21, CF22 and/or CF33a to an liver X receptor alpha polypeptide according to any of SEQ ID NOs. 12 or 15 or a portion thereof comprising the steps of:

a) contacting the polypeptide according to claim 11, 12 or the complex according to any of claims 13 to 15 with a binding agent, b) whereby the binding of CF21 , CF22 and/or CF33a to the liver X receptor alpha polypeptide is inhibited or activated.

21. A method according to claim 19 or 20, characterized in that the binding agent is an antibody.

22. A method according to claim 19 or 20, characterized in that the binding agent is RNA.

23. A method according to claim 19 or 20, characterized in that the binding agent is an anti- sense oligonucleotide.

24. A method according to claim 19 or 20, characterized in that the binding agent is a ribozyme.

25. A method according to claim 19 or 20, characterized in that the binding agent is a steroid molecule.

26. A method according to claim 19 or 20, characterized in that the cell is in a body.

27. A method for predicting the ability of a human to metabolise xenobiotic substances or drugs, comprising the steps of

Screening the genes coding for CF21, CF22 and/or Cf33a for genetic polymorphisms or other aberrations, wherein the existence of genetic polymorphisms or other aberrations will predict an altered ability of the human to metabolise xenobiotic substances or drugs.