WO2003074560A2 - Critical hypoxia-inducible factor-1alpha residues, products and methods related thereto - Google Patents

Abstract

A modified HIF-1alpha protein is capable of avoiding degradation by failing to bind or failing to bind properly to pVHL. This modified HIF-1alpha protein can be used in research regarding hypoxic response as well as in treatments for hypoxicrelated conditions. The amino acids at residues (568, 570, 571, and 573) of HIF-1alpha play a critical role in mediating degradation at normoxia. Further, the pairs of residues at (560 and 561), and at (566 and 567) are critical as well. Resistance to pVHL-mediated degradation can be imparted using specific alterations at these residues. At least one amino acid residue selected from the group consisting of positions (390 through 531) may also be altered. Active fragments of the HIF-1alpha N-TAD may also be used as treatments for hypoxic-related conditions.

Description

TITLE OF THE INVENTION

CRITICAL HYPOXIA-INDUCIBLE FACTOR- 1 alpha RESIDUES, PRODUCTS AND METHODS RELATED THERETO

FIELD OF THE INVENTION

The present invention relates to the field of molecular biology. More specifically, the present invention relates to hypoxia- inducible factors.

BACKGROUND OF THE INVENTION Mammalian organisms are able to adapt to low oxygen levels by activating a network of genes encoding erythropoietin, vascular endothelial growth factor (VEGF), glycolytic enzymes and other factors (1). Hypoxia-dependent activation of transcription is mediated by the heterodimeric complex of the hypoxia-inducible factor- 1 alpha (HIF-lalpha) and the structurally related partner factor aryl hydrocar- bon receptor nuclear translocator (Arnt). In contrast to Arnt, HIF-lalpha protein expression is regulated in response to alterations in cellular oxygen levels. At nor- moxia, HIF-lalpha is degraded by the ubiquitin-proteosomal pathway (2-4, 29). At hypoxia, HIF-lalpha is stabilized, it translocates to the nucleus and activates transcription of target genes (5). HIF-lalpha contains two distinct transactivation domains that mediate hypoxia-dependent activation of transcription, the N-terminal transactivation domain (N-TAD, residues 531-584 of mHIF-1 alpha) and C-terminal transactivation domain (C-TAD, residues 772-_822 of mHIF-1 alpha corresponding to residues 776-826 in human HIF-alpha) (6-9, 30). The transactivation function mediated by the N-TAD and C-TAD motifs has been shown to be enhanced by cofactors such as CREB binding protein (where CREB stands for cyclic-AMP response element, also called CBP), steroid receptor coactivator 1 (Src-1), and Redox Factor- 1 (Ref-1) (8,9). Although they are domains within the same protein, the regulation mechanisms of these two TADs are quite distinct since N-TAD protein stability is strictly regulated by oxygen levels while the C-TAD is constitutively stable (8, 10). C-TAD has been recently shown to be hydroxylated at Asn803 (of hHIF-1 alpha) by a Fe(II)-2- oxoglutarate-dependent dioxygenase (31-33) and this modification has been proposed to inhibit the bonding to the CHI domain of CBP at normoxia.

HIF-lalpha is targeted for normoxia-dependent ubiquitylation by the von- Hippel Lindau tumor supressor gene product (pVHL) (1 1-15). The binding of pVHL to HIF-lalpha is regulated by hydroxylation of Pro402 and Pro564 which is mediated by members of the FE(II)-2-oxoglutarate-dependent dioxygenase family of enzymes (23, 24, 34-37).

The VHL tumor suppressor gene was first identified as the gene responsible for a rare inherited autosomal dominant cancer syndrome characterized by the development of clear-cell renal carcinoma, hemangioblastoma and pheochromocytoma (16). The VHL gene is also inactivated in sporadic clear cell renal carcinoma. VHL-negative neoplasms are characterized by being hypervascularized and by expressing constitutively hypoxia-inducible mRNAs such as VEGF (17,18). pVHL has been shown to harbor an E3 ubiquitin-protein ligase activity in vitro (19,20) and shows structural similarity to the SKPl-CUL-1-F-box E3 ubiquitin ligase complex (21). HIF-lalpha and its paralogues HIF-2alpha and HIF-3alpha are so far the only known substrates recognized by the pVHL E3 ubiquitin ligase complex (14).

The beta domain of pVHL has been shown to interact with the N-TAD of HIF-lalpha, resulting in ubiquitylation and proteosome-dependent degradation of HIF-lalpha at normoxia (12-15,22). The crystal structure of a N-TAD peptide with the pVHL-ElonginB-ElonginC (pVHL-BC) complex has been solved by two independent groups (38, 39). These groups observed that the hydroxyproline is buried in a hydrophobic pocket of pVHL and has a central role in the complex formation. Researchers have previously identified a central PYI563-566 motif within the N- TAD that is critical for binding of pVHL and conditional degradation of the N- TAD.

Despite these advances, there remains a need in the art to particularly identify additional critical residues within the N-TAD for pVHL binding. Researchers could benefit from compounds or treatments that regulate HIF-lalpha and pVHL interac- tion. There is a need for means to artificially regulate HIF-lalpha degradation. Further, there is a need in the art for additional methods that evaluate molecules for an effect on hypoxic responses, HIF-lalpha, or conditions related to the over- or un- derexpression of HIF-lalpha. Presently, a gap in working knowledge exists in these areas.

SUMMARY OF THE INVENTION

According to the present invention, residues within the N-TAD that are important for binding pVHL are identified. Amino acid mutations that inhibit interac- tion with pVHL and subsequent degradation at normoxia include P563A, Y564G, I565G, D568A/D569A/D570A, F571A and L573A. Moreover, reporter gene assays demonstrated that the P563A mutation generates a more potent and constitutively active transactivation domain, as compared to the wild type N-TAD. It has also been determined that both N-TAD and the P563A mutant are able to interact with CBP, and mutations that decrease N-TAD transactivation affect the activation of transcription mediated by the full-length HIF-lalpha.

The present invention relates to HIF-lalpha, the sequence of which is known in the art and is disclosed at, inter alia, Wang, G.L. et al, Hypoxia-Inducible Factor- 1 alpha is a Basic helix-loop-helix-PAS Heterodimer Regulated by Cellular 02 Ten- sion, Proc. Natl. Acad. Sci. USA 92, 5510-5514, discussing the human sequence, and Wenger, R. H., et al, Nucleotide Sequence, Chromosomal Assignment and mRNA Expression of Mouse Hypoxia-Inducible Factor- 1 alpha, Biochem. Biophys. Res. Commun. 223:54-59, discussing the murine sequence.

Abbreviations are commonly used in the present application to refer to spe- cific amino acid residues in the HIF-lalpha sequence. For example, P563 is an abbreviation used to denote a proline at residue 563 of HIF-lalpha. Where a mutation at a particular residue is abbreviated, for example P563A, the initial letter represents the original residue, the number represents the position in the HIF-lalpha sequence where the residue is located, and the terminal letter represents the residue used for replacement. Capital letters represent the commonly known abbreviations for amino acids, e.g., P for proline.

Unless otherwise noted, references to amino acid residue locations are based on the murine HIF-lalpha sequence, however, it is understood that the HIF-lalpha of other mammalian species, including, but not limited to, humans, is within the scope of the present invention. Adjustment of residue location based on slight differences in HIF sequences between species can be easily effected using information known to one of skill in the art. For example, the P563 of the murine HIF-lalpha sequence corresponds to the P564 of the human HIF-lalpha sequence. Where used herein, the terms native, natural, or naturally occurring refer to the form of a protein or polypeptide endogenous to a mammalian host or host cell.

Where used herein, the terms carrier and adjuvant refer to materials that may be utilized in the preparation of pharmaceuticals. Examples include, but are not limited to, water, salt solutions, alcohols, polyethylene glycols, oils, acacia, stearic acid or lower alkyl ethers of cellulose, fatty acids, hydroxymethylcellulose, or mixtures thereof. Further, they may include sustained release material, wetting agents, emulsifying and suspending agents, preserving agents, surfactants, and agents to maintain sterility of preparation mixtures. Carriers and/or adjuvants may be selected for properties including quick, sustained or delayed release, ability to alter smell, taste, or color. Suitable carriers or adjuvants may be an encapsulator such as a capsule or other container. They may be solid, semi-solid or liquid materials which act as a vehicle, excipient, or medium for the active compound. Routes of administration and appropriate amounts of pharmaceuticals according to the present invention can be determined by a skilled worker and may rely upon any available art in rele- vant fields.

Where used herein, the term improved stability refers to a molecule that is more stable than the native molecule under normal conditions. The stability increase may be a result of modification to the molecule and/or alteration of the conditions surrounding the molecule, or other reasons. According to a first embodiment of the present invention, an HIF-lalpha protein is provided having an altered transactivation capacity and at least one first mutated residue at a position corresponding to a position selected from the group consisting of positions 563, 564, 565, 570, 571, 572 and 573 of murine HIF-lalpha and at least one second mutated residue at a position selected from the group consisting of positions 390 through 531 of murine HIF-lalpha. Optionally, the first mutated residue can be an alanine at position 563, 570, 572 or 573. Other options for the first mutated residμe are a glycine at position 564, a glycine at position 564 plus a glycine at position 565, or a hydrophilic amino acid at position 564. The em- bodiment also includes an isolated polynucleotide sequence encoding the protein, and functional fragments thereof.

According to a further embodiment of the present invention, a pharmaceutical composition is provided, comprising a pharmaceutically active amount of a protein according to the first embodiment and at least one carrier or adjuvant. According to further embodiments of the invention, methods are provided which comprise administering an HIF-lalpha protein according to the first embodiment to a cell, group of cells, or organism. Methods accomplished with this administration include a method of interfering with pVHL binding to HIF1 -alpha in a cell, a group of cells, or an organism, a method of decreasing HIF-lalpha degradation in a cell, a group of cells, or an organism, a method of increasing HIF-lalpha transactivation capacity in a cell, a group of cells, or an organism, and a method of increasing angiogenesis in a cell, a group of cells, or an organism. Optionally, the cell, group of cells, or organism can be at normoxia or hypoxia.

According to further embodiments of the present invention, additional meth- ods are provided with comprise administering an HIF-lalpha protein according to the first embodiment to a cell, group of cells, or organism. Methods accomplished with this administration include a method of interfering with a normal response to reoxygenation following hypoxia in a cell, a group of cells, or an organism, a method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, and a method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism.

According to a further embodiment of the present invention, a vector is provided, comprising a polynucleotide according to the present invention in operative association with at least one promoter. Optionally, the vector may be a plasmid, viral vector, or retroviral vector.

According to a further embodiment of the present invention, a host cell is provided that is transformed or transfected with a vector according to the previous example. Optionally, the host cell may be a prokaryotic cell, bacterial cell, a eukaryotic cell, or a mammalian cell.

According to a further embodiment of the present invention, a method of interfering with pVHL binding to HIF1 -alpha in a cell, a group of cells, or an organism is provided, comprising introducing a vector according to the present invention to the cell, group of cells, or organism. Optionally, the cell, group of cells, or or- ganism can be at normoxia or hypoxia.

According to further embodiments of the present invention, methods are provided which comprise introducing a vector according to the present invention to a cell, group of cells, or organism. Methods accomplished with this procedure include a method of decreasing HIF-lalpha degradation in a cell, a group of cells, or an or- ganism, a method of increasing HIF-lalpha transactivation capacity in a cell, a group of cells, or an organism, and a method of increasing angiogenesis in a cell, a group of cells, or an organism. Optionally, the cell, group of cells, or organism can be at normoxia or hypoxia.

According to further embodiments of the present invention, additional meth- ods are provided which comprise introducing a vector according to the present invention to a cell, group of cells, or organism. Methods accomplished with this procedure include a method of interfering with a normal response to reoxygenation following hypoxia in a cell, a group of cells, or an organism, a method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, and a method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism.

According to a further embodiment of the present invention, a method of determining whether an HIF-lalpha sequence encodes an HIF-lalpha protein capable of resisting degradation at normoxia is provided, comprising evaluating the HIF- lalpha sequence for a first alteration to at least one residue at a position selected from the group consisting of positions 563, 564, 565, 570, 571, 572 and 573, and evaluating the HIF-lalpha sequence for a second alteration to any one of residues 390 through 531, wherein an HIF-lalpha sequence having a first alteration and a second alteration encodes an HIF-lalpha protein capable of resisting degradation at normoxia.

According to a further embodiment of the present invention, an isolated amino acid according to SEQ ID NO:s 1-19 or its encoding polynucleotide sequence is provided. Optionally, a pharmaceutical composition may be formed with a phar- maceutically active amount of the amino acid or polynucleotide and at least one carrier or adjuvant.

According to a further embodiment of the present invention, methods are provided which interfere with pVHL binding to native HIF1 -alpha in a cell, a group of cells, or an organism; or decrease native HIF-lalpha degradation in a cell, a group of cells, or an organism; or increase angiogenesis in a cell, a group of cells, or an organism; or treat a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism; or sustain HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism; or treat ischemia in a group of cells or an organism, the methods comprising administering a pharmaceutical composition ac- cording to the preceding paragraph to the cell, group of cells, or organism.

According to a further embodiment of the present invention, a HIF-lalpha protein is provided having improved stability at normoxia and comprising at least one mutated residue at a position corresponding to a position selected from the group consisting of positions 568, 570, 571, and 573 of murine HIF-lalpha. The mutated residue can be an alanine at position 568, an alanine at position 570, an ala- nine at position 571, and/or an alanine at position 573. The protein may further comprise at least one mutated residue at a position corresponding to a position selected from the group consisting of positions 390 through 531 of murine HIF- lalpha. According to a further embodiment of the present invention, a HIF-lalpha protein is provided having improved stability at normoxia, comprising at least two mutated residues at positions 560 and 561 or 566 and 567 of murine HIF-lalpha. The mutated residues can be alanines at positions 560 and 561, and/or glutamic acids at positions 566 and 567. The protein may further comprise at least one mutated residue at a position corresponding to a position selected from the group consisting of positions 390 through 531 of murine HIF-lalpha.

According to a further embodiment of the present invention, an isolated polynucleotide sequence encoding a protein according to either one of the previous examples, and functional fragments thereof are provided. The embodiment also en- compasses a vector which comprises such a polynucleotide in operative association with at least one promoter and a host cell transformed or transfected with the vector. The vector may be a plasmid, a viral vector, or retroviral vector. The host cell may be a prokaryotic cell, a bacterial cell, a eukaryotic cell, or a mammalian cell. The vector may be introduced to a cell, group of cells, or organism to interfere with pVHL binding to HIFl-alpha.or to decrease HIF-lalpha degradation, to increase angiogenesis, to treat a condition characterized by HIF-lalpha underexpression, or sustain HIF-lalpha expression at normoxia.

According to a further embodiment of the present invention, a pharmaceutical composition, comprising a pharmaceutically active amount of a protein accord- ing to any of the previous three examples and at least one carrier or adjuvant is provided.

According to a further embodiment of the present invention, methods of interfering with pVHL binding to HIF1 -alpha, methods of decreasing HIF-lalpha degradation, methods of increasing angiogenesis, methods of treating conditions char- acterized by HIF-lalpha underexpression, and methods of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism are provided which comprise administering an HIF-lalpha protein according to any one of the previous four examples to the cell, group of cells, or organism. Optionally, the cell, group of cells, or organism is at normoxia or hypoxia. According to a further embodiment of the present invention, a method of determining whether an HIF-lalpha sequence encodes an HIF-lalpha protein capable of resisting degradation at normoxia is provided, which comprises evaluating the HIF-lalpha sequence for an alteration to at least one residue at a position selected from the group consisting of positions 568, 570, 571, and 573, wherein an HIF- 1 alpha sequence having an alteration encodes an HIF-lalpha protein capable of resisting degradation at normoxia.

According to a further embodiment of the present invention, a method of determining whether an HIF-lalpha sequence encodes an HIF-lalpha protein capable of resisting degradation at normoxia is provided, which comprises evaluating the HIF-lalpha sequence for an alteration to at least one pair of residues at positions selected from the group consisting of positions 560 and 561, and positions 566 and 567, wherein an HIF-lalpha sequence having an alteration encodes an HIF-lalpha protein capable of resisting degradation at normoxia.

According to a further embodiment of the present invention, methods of in- terfering with pVHL binding to native HIF1 -alpha, methods of decreasing native HIF-lalpha degradation, methods of increasing angiogenesis, methods of treating a condition characterized by HIF-lalpha underexpression, methods of sustaining HIF- lalpha expression at normoxia, and methods of treating ischemia in a group of cells or an organism are provided, which comprise administering a pharmaceutical com- position according to the invention to the cell, group of cells or organism.

According to a further embodiment of the present invention, methods of mimicking the hypoxic response and methods of artificially inducing a hypoxic response in a cell, group of cells, or organism comprise administering an altered HIF- lalpha protein according to the present invention to the cell, group of cells, or or- ganism. The cell, group of cells, or organism may be at normoxia. According to a further embodiment of the present invention, a method of enhancing activity of wild type or mutant HIF-lalpha N-TAD in a cell, group of cells, or organism is provided, which comprises coexpressing CBP in the cell, group of cells, or organism. According to a further embodiment of the present invention, a method of screening molecules for potential regulators of the HIF-lalpha pathway is provided, comprising expressing the molecule in a non endothelial cell or cellular system, detecting a presence or an absence of functional activity of the molecule in the non endothelial cell or cellular system, expressing the molecule in an endothelial cell or cellular system, and detecting a presence or an absence of functional activity of the molecule in the endothelial cell or cellular system, wherein the molecule is a potential regulator of the HIF-lalpha pathway when a presence of functional activity of the molecule is detected in the non endothelial cell system and an absence of functional activity of the molecule is detected in the endothelial cell system. The mole- cule can be a fragment of HIF-lalpha. The invention also encompasses potential regulators identified according to the novel method.

According to a further embodiment of the present invention, a pharmaceutical composition is provided which comprises a pharmaceutically active amount of at least one peptide selected from the group consisting of SEQ ID NO:s 1, 4, 5, 7, 13, 14, 15, 16, and 17 and at least one carrier or adjuvant. A further pharmaceutical composition is provided which comprises a pharmaceutically active amount of at least one polynucleotide encoding a peptide selected from the group consisting of

SEQ ID NO:s 1, 4, 5, 7, 13, 14, 15, 16, and 17 and at least one carrier or adjuvant.

According to a further embodiment of the present invention, a method of in- creasing angiogenesis in a cell, a group of cells, or an organism is provided, comprising administering a pharmaceutical composition according to the previous paragraph to the cell, group of cells, or organism. Optionally, the cell, group of cells, or organism may be at hypoxia or normoxia. The pharmaceutical composition may also be administered to a cell or group of cells in a method of inducing at least one of vascular formation or vascular development in the cell or group of cells. Again, the cells may be at any conditions, including hypoxia and normoxia. The cells may be endothelial cells. The pharmaceutical composition may also be administered to a cell, a group of cells, or an organism to increase angiogenesis or to induce vascular formation or vascular development. According to a further embodiment of the present invention, a method of activating HIF-lalpha in an endothelial cell is provided, which comprises adding a peptide to or expressing a peptide in the cell, wherein the peptide is a fragment of HIF-lalpha measuring no more than 17 amino acids. Optionally, the fragment may come from the 546-573 or 380-416 region of HIF-lalpha. According to a further embodiment of the present invention, a method of identifying an agent which modulates the HIF-lalpha pathway is provided, comprising expressing a molecule in a non endothelial cell or cellular system, detecting a presence or an absence of functional activity of the molecule in the non endothelial cell or cellular system, expressing the molecule in an endothelial cell or cellular system, and detecting a presence or an absence of functional activity of the molecule in the endothelial cell or cellular system, wherein the molecule is an agent which modulates the HIF-lalpha pathway when a presence of functional activity of the molecule is detected in the non endothelial cell system and an absence of functional activity of the molecule is detected in the endothelial cell system. The molecule used can be a fragment of HIF-lalpha, the agent can be a portion of the HIF-lalpha fragment. The invention further encompasses agents that modulate the

HIF-lalpha pathway and are identified according to this method.

According to a further embodiment of the present invention, a pharmaceutical composition is provided, comprising a pharmaceutically active amount of at least one peptide selected from the group consisting of SEQ ID NO:s 1, 4, 5, 7, 13, 14, 15, 16, and 17 and at least one carrier or adjuvant. The invention further provides pharmaceutical compositions comprising a pharmaceutically active amount of at least one polynucleotide encoding a peptide selected from the group consisting of SEQ ID NO:s 1, 4, 5, 7, 13, 14, 15, 16, and 17 and at least one carrier or adjuvant.

According to a further embodiment of the present invention, method of in- creasing angiogenesis and/or inducing at least one of vascular formation or vascular development in a cell, a group of cells, or an organism is provided, comprising administering a pharmaceutical composition according to the preceding example to the cell, group of cells, or organism. Optionally, the cell, group of cells, or organism may be at hypoxia or normoxia. The cells may be endothelial cells.

According to a further embodiment of the present invention, method of increasing angiogenetic activity in a cell is provided, comprising adding a peptide to or expressing a peptide in the cell, wherein the peptide is a fragment of HIF-lalpha and the peptide comprises no more than 17 amino acids. The cell may be an endothelial cell, and the peptide may correspond to a fragment between positions 546- 573 or 380-416 of HIF-lalpha.

According to a further embodiment of the present invention, a method of in- fluencing erythropoietin production in a cell, a group of cells, or an organism is provided, comprising administering a protein according to the present invention to the cell, group of cells, or organism. The method may also be accomplished by administering a pharmaceutically effective amount of a pharmaceutical composition according to the present invention to the cell, group of cells, or organism. Either ap- proach may be practiced to increase erythropoietin production.

According to a further embodiment of the present invention, a method of influencing metabolism in a cell, a group of cells, or an organism is provided, which may comprise administering a protein according to the present invention to the cell, group of cells, or organism. The method may alternately comprise administering a pharmaceutical composi- tion according to the present invention to the cell, group of cells, or organism. These methods may relate to glycolytic metabolism.

According to a further embodiment of the present invention, a method of influencing an inflammatory response in a cell, a group of cells, or an organism is provided, which may comprise administering a protein according to the present invention to the cell, group of cells, or organism. The method may alternately comprise administering a pharmaceutical composition according to the present invention to the cell, group of cells, or organism. These methods may relate to glycolytic metabolism.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic representation of a reoxygenation procedure; Figure 2 shows immunoblot results analyzing the binding of pVHL to HIF- 1 alpha N-TAD at normoxia (N) and at various levels of reoxygenation (R);

Figure 3 depicts immunoprecipitation results demonstrating the specificity of pVHL binding to HIF-lalpha N-TAD; Figure 4 is a schematic representation of the functional architecture of mHIF-

1 alpha showing the predicted alpha-helical (H) structure of the N-TAD, the figure also depicts specific point mutations generated within the N-TAD;

Figure 5 shows in vivo interaction between pVHL and proteins of wild-type or mutant N-TAD HIF-lalpha; Figure 6 shows the degradation of HIF-lalpha N-TAD mutants under nor- moxic conditions in the presence of increasing levels of p VHL, where + and ++ represent 500 ng and 1000 ng of pVHL, respectively;

Figure 7 shows the degradation of additional HIF-lalpha N-TAD mutants under conditions as in Figure 6; Figure 8 shows pVHL mediation of N-TAD degradation under reoxygenation conditions, where +, ++, and +++ represent 250 ng, 500 ng, and 1000 ng of pVHL, respectively;

Figure 9 depicts different transactivation functions, expressed as luciferase activity, between HEK 293 cells transfected with a control, a wild-type or a mutant HIF-lalpha N-TAD expression plasmid and exposed to normoxia or hypoxia following culture;

Figure 10 shows a comparison of HIF-lalpha and HIF-lalpha (P563A) protein levels, where the arrow indicates bands of HIF-lalpha detection and the asterisk represents non-specific immunoreactivity; Figure 11 shows transactivation activity of HEK 293 cells expressing HIF- lalpha or HIF-lalpha (P653A) under normoxia or hypoxia;

Figure 12 shows transactivation activity of MBEC cells expressing HIF- lalpha or HIF-lalpha (P653A) under normoxia or hypoxia;

Figure 13 is a schematic representation of HIF-lalpha deletion mutants; Figure 14 shows HIF-lalpha (532-583) protein levels in cells transfected with 700 ng (left two columns) or 1 μg (right two columns) of expression plasmid;

Figure 15 shows protein expression in cells transfected with lesser (left two columns for each plasmid type) or greater (right two columns for each plasmid type) amounts of expression plasmids at both normoxia and hypoxia;

Figure 16 shows mediation of hypoxia-inducible transactivation by fusion proteins;

Figure 17 depicts mediation of HIF-lalpha degradation by overexpressed pVHL, where -, +, and ++ represent the absence, presence of 500 ng, or presence of 1000 ng of p VHL expression vector, respectively;

Figure 18 shows stabilization of HIF-lalpha by overexpression of N-TAD at normoxia;

Figure 19 is a schematic representation of mutant HIF-lalpha constructs;

Figure 20 is a table showing relative luciferase activity of normoxic cells ex- pressing the mutant constructs depicted in Figure 19;

Figure 21 is a table depicting the relative luciferase activity of the FLAG control at normoxia and hypoxia;

Figure 22 is a schematic representation of short N-TAD constructs;

Figure 23 is a table depicting relative luciferase activity measured in nor- moxic cells expressing the mutated N-TAD fragments depicted in Figure 22;

Figure 24 is a table depicting the relative luciferase activity of the FLAG control at normoxia and hypoxia;

Figure 25 is a table depicting the effects of short N-TAD fragments;

Figure 26 is a table depicting the effects of mutant HIF-lalpha constructs; Figure 27 depicts experimental results identifying mHIF-1 N-TAD residues critical for pVHL interaction in vitro and in vivo;

Figure 27A is a schematic representation of the functional architecture of mHIF-1 alpha and generated N-TAD mutants, where asterisks indicate mutated residues; Figure 27B shows in vitro interaction of N-TAD mutants with pVHL; Figure 27C depicts an analysis of the binding of pVHL to the N-TAD at normoxia (N) or under conditions of reoxygenation (R);

Figure 27D shows in vivo interaction of wild type or mutant N-TAD proteins with pVHL; Figure 28 shows results of a normoxia-dependent degradation of wild type or mutant forms of N-TAD by pVHL;

Figures 28A and 28B show degradation of mHIF-1 alpha N-TAD mutants under normoxic conditions in the presence of increasing levels of pVHL;

Figure 28C shows degradation of the N-TAD motif under conditions of re- oxygenation is mediated by pVHL;

Figure 29 shows the identification of critical residues for pVHL interaction located in the C-terminal region of the N-TAD;

Figure 29A shows in vitro binding of pVHL to residues 546 to 574 of wild type or point-mutated forms of N-TAD; Figure 29B shows pVHL-dependent degradation at normoxia of mutants of the residue 546-574-fragment of the N-TAD;

Figure 30 depicts an analysis of the transactivation function of N-TAD mutant proteins;

Figure 30A demonstrates how mutation of residue P563 to alanine generates a constitutively active and potent transactivation domain;

Figure 30B shows that CBP potentiates transactivation activity mediated by the NTAD or the P563A mutant;

Figure 30C shows how CBP interacts with either the wild type N-TAD or the P563A mutant; Figure 31 shows mutation of N-TAD residues decreasing the transactivation activity of full-length mHIF-1 ;

Figure 31A shows relative luciferase activity of mHIF-lalpha mutants;

Figure 3 IB shows expression levels of wild type or mutated forms of mHIF- lalpha; Figure 32 depicts the constructs of three experimental peptides; Figure 33 depicts immunoprecipitation results of experimentation with the peptides of Figure 32;

Figures 34A, 34B, and 34C show corneas of mice treated with peptides 1, 2, and 3, respectively, of Figure 32; Figure 35 is a table showing measured vessel area in each of the corneas depicted in Figures 34A, 34B, and 34C;

Figure 36 is a schematic representation of five fragments of the second N- TAD degradation box of HIF-lalpha;

Figure 37 depicts the results of analysis of increasing amounts of peptide un- der normoxic and hypoxic conditions;

Figure 38 represents the measured luciferase activity of, inter alia, MBE cells expressing the fragments of Figure 36; and

Figure 39 represents the measured luciferase activity of, inter alia, the HepG2 cells expressing the fragments of Figure 36.

DETAILED DESCRIPTION

The HIF-lalpha N-TAD mediates both pVHL-dependent degradation at normoxia and transcriptional activation at hypoxia. Under normoxic conditions, the HIF-lalpha protein is targeted for degradation by pVHL acting as an E3 ubiquitin ligase. Binding of pVHL to HIF-lalpha is dependent upon hydroxylation of specific proline residues by oxygen-dependent prolyl-4-hydroxylases: upon exposure to hypoxia the hydroxylase activity is inhibited. This inhibition results in stabilization of HIF-lalpha protein levels and activation of transcription of target genes. By interfering with critical residues, artificially stabilized HIF-lalpha proteins can be pre- pared and used directly or as components of screening methods. Mutation analysis was conducted to ascertain which residues are critical for either one or both of the interdigitated and conditionally regulated degradation and transactivation functions. The mutant forms of HIF-lalpha were evaluated for functionality and critical residues were thereby elucidated. Binding of p VHL to the N-TAD has been shown to be dependent on the hy- droxylation status of P563 (23,24,34). This modification is oxygen-dependent and is mediated by prolyl-4-hydroxylases (36, 37). Two additional N-TAD residues (Y564 and 1565) have now been identified which, in addition to P563, are critical for pVHL-mediated degradation at normoxia. Further, the present analysis has identified D568A/D569A/D570A, F571A and L573A as mutations of the N-TAD that both abrogate binding to pVHL in vitro and in vivo, and constitutively stabilize N- TAD against degradation at normoxia. Moreover, the mutations Y564G, L556A/L558A, and F571A/L573A drastically reduce the transactivation function of either the isolated N-TAD or full-length HIF-lalpha in hypoxic cells. The P563A mutant has been found to exhibit a constitutively active and potent transactivation function that is enhanced by functional interaction with the transcriptional coacti- vator protein CBP. Using proteins expressed in rabbit reticulocyte lysate, M556- L558 and D570 have also been identified as critical for in vitro binding of pVHL. Two independently elucidated crystal structures of the pVΗL-BC complex with a peptide spanning the PYI core of the N-TAD (38, 39) have been prepared. Experiments with these structures demonstrated that hydroxyproline 563 of the N- TAD is the residue that establishes contact with pVHL in a site frequently found to have tumorigenic mutations. As expected (23,24,25) the P563A mutation com- pletely disrupted binding of pVHL both in vitro and in vivo. In addition, the results of the present invention demonstrate that the P563A mutation generated a constitutively active and more potent transactivation domain as compared to the wild type N-TAD. Thus, in contrast to the C-TAD (31), there is no requirement of any additional hypoxic signal in order for the constitutively stabilized N-TAD to transacti- vate. All the other N-TAD mutations that abrogate pVHL binding negatively affected the transactivation function mediated by the N-TAD. This reveals overlapping structural requirements for both pVHL binding and functional interaction with the transcription machinery, and establishes P563A as the only mutation that conferred a conformation favorable for the transactivation function. N-TAD-mediated activation of transcription is potentiated by coactivators such as CBP/p300 (8,9). It has been demonstrated that inactivation of the C-TAD in the full-length HIF-lalpha by deletion or point mutation does not abrogate functional interaction with CBP (40). However, in contrast to the C-TAD motif which interacts with the CHI domain of CBP (41-43) the N-TAD does not interact with this region of CBP (41).

Research leading to the present invention improves the state of the art by showing that the N-TAD is able to interact in vitro with full-length CBP and that the P563A mutant retains the ability to interact with this coactivator. Two mutants, L556A/L558A and M560A/L561A, have been identified that impair transactivation mediated by N-TAD without affecting pVHL binding in vivo. The residue L559 in hHIF-1 alpha (corresponding to L558 in mHIF-lalpha) has previously been mutated alone (44) or in the context of a double mutant together with a mutation of D558 (34) and shown not to affect the binding of pVHL. Moreover, the mutations L556A/L558A in the N-TAD did not affect pVHL binding in vitro or in vivo. However, in contrast to mutants such as Y564F and P566E/M567E that bind pVHL and transactivate as well as the wild type N-TAD, the L556A/L558A mutations impaired the transactivation activity of the N-TAD and significantly reduced the transactivation potency of full-length mHIF-lalpha. L562 in hHIF-1 alpha (L561 in mHIF- 1 alpha) was also previously mutated in several reports with apparently contradictory results (24,34,44).

In the assays described herein, mutation of M560A/L561A resulted in abrogation of the binding of pVHL in vitro but not in vivo. The use of rabbit reticulocyte lysate or cell extracts could explain the different results described in the previous reports (24,34,44). The invention lies therefore not only in the novel mutants and their uses, but in the approach to evaluating or assaying for other prospective agents useful in the HIF-lalpha pathway. In the co-crystals of the N-TAD peptide and pVHL-BC complex both M560 and L561 have direct contacts with pVHL residues (38, 39). Results according to the present invention demonstrate that, even when the two residues are mutated, pVHL can bind and degrade N-TAD at normoxia. The major effect of the M560A/L561A mutation was observed in gene reporter assays where a drastic reduction in transactivation activity was measured, indicating a critical role for transcriptional activation.

In addition to the P563A mutation, two other point mutants of the PYI motif (Y564G and I565G) are critical for pVHL binding and pVHL-mediated degradation. In transactivation assays these two mutants generate a weak and constitutively active transactivation response. The introduction of the Y564G mutation into the full- length mHIF-lalpha resulted in a drastic reduction in transactivation potential, revealing an important role for this residue in the N-TAD mediated transactivation function.

Previous studies using in vitro assays of the effect of the mutation Y565A in hHIF-1 alpha (Y564 in mHIF-lalpha) yielded contradictory results with regard to the importance of this residue for binding of pVHL (23,24). Structural studies (38, 39) have shown that residue Y565 interacts with HI 10 of pVHL, and the integrity of this tyrosine has been suggested to be important for the hydroxylation of P564 by two of the prolyl-4-hydroxylases (37). The results discussed herein regarding the Y564G mutant demonstrate that this residue is critical both for the degradation function mediated by pVHL at normoxia and the transactivation function of the N- TAD. The residue 1566 in hHIF-1 alpha (1565 in mHIF-lalpha) has previously been mutated to alanine and shown not to affect the interaction with pVHL (24,34). One of the studies of the cocrystal of an NT AD peptide and the pVHL-BC complex showed 1565 to interact through hydrogen bonds with two residues, P99 and 1109, of pVHL (38). However, the mutation of 1565 to glycine showed, in both in vitro and in vivo assays, that this residue is critical for pVHL binding. Thus, 1565 constitutes the residue in the vicinity of P564 that makes the most contact with pVHL. This information can be used for further developments in the art.

Several residues located in the C-terminus of the PYI motif were also mutated. The mutants D568A/D569A/D570A, F571A and L573A were shown to be critical for the in vivo interaction with the pVHL. The mutations F571A and L573A stabilized the NTAD against degradation by pVHL at normoxia, the integrity of both F571 and L573 has been found to be critical for N-TAD-pVHL interaction. The D568A/D569A/D570A triple mutant was also resistant to pVHL-mediated degradation. However, in the subsequent analysis of single amino acid point mutants only the mutation D570A resulted in disruption of the binding in vitro, whereas it was still degraded in vivo at normoxia. This residue has been shown to interact with R107 of p VHL (38). Data of the present invention surprisingly suggest that this interaction may not be critical for function in vivo.

The following examples describe specific experimentation, however, the in- vention is not limited to these specific methods. References may be used to provide supplemental or alternative approaches. Materials used in the experiments are generally commercially available. Sources are known to one skilled in the art, in some cases sources are specified.

Example 1 : Technical Methods A. Plasmid Constructs

A PCR fragment from mHIF-lalpha (25, 26) spanning amino acids 1-244 (Exxon 1.2) and carrying EcoKL and Sail ends was cloned into pFLAG-CMV-2 (Kodak) generating pFLAG-mHIF-1 alpha (1-244), followed by the cloning of a re- striction fragment SatllBpu 11021 from pmcH into SaWBamrll restriction sites. A PCR fragment spanning HIF-lalpha amino acids 698-822 and carrying a Bsu36l site in the 5' end and Kpnl/Nhel/STOΫ codon/Xhol/Pvull sites in the 3' end was then inserted into the Bsu36l and Smal sites in order to generate pFLAG-mHlF-1 alpha.

A PCR fragment spanning amino acids 244-390, with Sail and BamHl sites was cloned into pFLAG-mHIF-1 alpha (1-244), creating a pFLAG-mHIF-1 alpha (1- 390) plasmid. pFLAG-mHIF-1 alpha (1-531) was constructed using a PCR insert corresponding to amino acids 462-531, with a BstBl site in the 5' end and an Kpnl/Nhel/STO? codon/XhoVPvull sites in the 3' end. pFLAG-mHIF-1 alpha (532- 583) was generated in two steps by cloning a first PCR product corresponding to amino acids 462-531 with BstBl in the 5' end and Swal/Kpnl/Nhel/STOP co- don/Xhol/Pvuϊl sites in the 3' end, where the Swal fragment encoded amino acids 531-584, and then cloning a second PCR product containing amino acids 584-822, with Swal/ Kpnl ends. pFLAG-mHIF-1 alpha (391-628) was generated by cloning a PCR insert containing amino acids 629-822 with an Afl l site in the 5' end and Kpnl/Nhel/STOP codon/Xhol/Pvull sites in the 3 ' end, with the Aflll base sequence encoding amino acids 391-628. pFLAG-mHlF-lalpha-VP16, pFLAG-mHIF-1 alpha (1-531)-VP16 and pFLAG-mHlF-1 alpha (l-390)-VP16 were constructed by cloning a PCR fragment containing the VP16 transactivation domain with Nhel ends and inserting it into the Nhel site of the corresponding constructs. pFLAG-GAL4 was generated by PCR amplification of the GAL4 DNA binding domain using primer pairs carrying Hindlll ends, followed by insertion of the PCR product into the Hindlll site of pFLAG-CMV-2. pFLAG-AL4/mHIF-l alpha (531-584) and pFLAG-GAL4/mHIF- 1 alpha (546-574) were constructed with PCR fragments generated with primer pairs carrying EcoRI and BamHl ends. The PCR fragments were inserted in frame into EcoRl- BamRl-ϊQstήcted pFLAG-GAL4 (40). pSP72-FLAG-GAL4/mHIF-lalpha-(531- 584) and pSP72-FLAG-GAL4/mHIF-lalρha-(546-574) were generated by inserting Sacl-Smal fragments from the corresponding pFLAG-GAL4 construct into Sacl- EcoRV-digested pSP72 (Promega). pGEX-4T3/mHIF-lalpha-(531-584) was constructed by inserting the EcoRl-Sall fragment from the pFLAG-GAL4/mHIF- lalpha-(531-584) in frame in front of the GST cDNA of the pGEX-4T3 digested with the same restriction enzymes. Constructs for pRc/RSV-CBP-HA and pBS- CBP-HA (expressing full-length mouse CBP) were obtained rather than constructed, they are commercially available.

All the inserts generated by PCR were completely sequenced using the Dyen- amic sequencing kit (Amersham-Pharmacia). Amino acid mutations were introduced using the QuickChange site-directed mutagenesis kit (Stratagene) according to the instructions of the manufacturer. Positive mutants were screened by se- quencing. B: Cell Culture and Transient Transfection

Human embryonic kidney 293 (HEK 293) cells were maintained in Dul- becco's Modified Eagle Medium (DMEM) and F-12 (HAM) medium in a 1 : 1 ratio containing 10% of fetal calf serum, 50 IU/ml penicillin and 50 μg/ml streptomycin sulphate. Mouse brain endothelial (MBE) cells were grown in HAM medium with 10% fetal calf serum, 50 IU/ml penicillin and 50 μg/ml streptomycin sulfate (media and cell culture products, Life Technologies). HEK 293 cells were transfected using Lipofectamine, and the MBE cells were transfected using FuGene6 (Boehringer Mannheim) following the instructions of the manufacturer. Unless otherwise specified, cells were cultured 24 hours before transfection in six-well plates and after transfection were cultured at normoxia (20% 0₂) or hypoxia (1% 0₂) for time periods specified. MBE cells were treated with the hypoxia-mimicking agent CoCl₂ at a final concentration of 100 uM. For reporter gene assays, the cells were harvested after 36 hours of transfection and the luciferase activity determined. Total protein concentration was analyzed in whole cell extracts using the Bradford method (Bio- Rad).

C: in vitro Immunoprecipitation Assays Immunoprecipitation assays were performed with proteins translated in rabbit reticulocyte lysate (Promega) either in the presence or absence of ³⁵S methionine.

Translated proteins were incubated for 1 hour at room temperature in 100 ml of lysis buffer and added to 20 ml of Protein G sepharose (AmershamPharmacia) preincu- bated with anti-FLAG-M2 (Sigma) antibodies. After a further incubation for 1.5 hours at room temperature under rotation the Sepharose pellet was washed three times with lysis buffer and the precipitated proteins were analysed by SDS-PAGE followed by autoradiography.

D: in vivo Immunoprecipitation Assays

Transfected cells were used to prepare whole cell extracts by two sonications of the cells, each for 5 seconds, in lysis buffer. Whole cell extracts (800 μg -1 mg of total protein) were incubated at 4°C for 16 hours with anti-FLAG-M2 antibodies- bound to Protein G-Sepharose as described previously (40). The Sepharose pellet was washed three times with TBS buffer (150 mM NaCl and 50 mM Tris-HCL, pH4.0), and precipitated proteins were eluted from Sepharose by incubation under rotation with 0.5 mg/ml FLAG peptide (Sigma) in TBS for 1.5 hours at room temperature.

E: Immunoblotting Assays

Immunoprecipitated proteins or 50 μg of whole cell extract protein were separated by SDS-PAGE and blotted onto nitrocellulose filters. Blotting was performed in TBS with 5% non-fat milk, followed by incubation for 1 hour at room temperature with anti-FLAG or anti- VHL (PharMingen) antibodies diluted 1 :500 and 1 :250, respectively, in TBS with 1% non-fat milk. After several washes with TBS containing 0.5% Tween-20, the filters were incubated with 1 : 1000 dilutions of anti-mouse IgG-horseradish peroxidase conjugate (Amersham-Pharmacia) in TBS with 1% non-fat milk and washed several times with TBS containing 0.5% Tween- 20. Proteins were visualized using enhanced chemiluminescence (Amersham- Pharmacia).

F: GST Precipitation Assays

GST fusion proteins were expressed in BL-21 cells as previously described (40). In vitro translated CBP (pBS-CBPHA) was precipitated by incubating 20 ml of gluthatione- Sepharose previously bound to bacterially-expressed GST fusion proteins with CBP in the presence of whole cell extracts of HEK293 cells. The incuba- tion occurred under rotation for 16 hours at 4°C. Sepharose pellets were washed three times with lysis buffer. The precipitated CBP was analysed by SDS-PAGE followed by autoradiography. Example 2: The Integrity of the PYI Motif and its' Surrounding Residues determines the in vitro binding of pVHL to N-TAD

The PYI motif (563-565 in mHIF-lalpha) is known to be essential for N- TAD - pVHL interaction. To further evaluate this phenomena, point mutants of each residue of the PYI motif were generated. Double and triple mutants of the residues located N- or C-terminally of this motif were also constructed, see Figure 27A. Interaction of N-TAD (FLAG-GAL4/mHIF-lalpha-(531-584)) and mutants with pVHL was investigated using proteins in vitro translated in rabbit reticulocyte lysate. In these assays equal concentrations of the in vitro translated proteins were incubated with in vitro translated pVHL that had been [35S] methionine-labeled, Precipitation was done with FLAGGAL4/mHIF- 1 alpha fusion proteins and analyzed by SDS-PAGE and autoradiography. As shown in Figure 27B, two of the N- TAD mutants, L556A/L558A (lane 4) and Q572A/R574A (lane 13) maintained wild type levels of pVHL binding activity, whereas P566E/M567E (lane 10) demonstrated reduced but detectable levels of pVHL binding activity. In contrast, all the point mutants of the PYI motif, P463A (lane 7), Y564G (lane 8) and I565G (lane 9) did not show any in vitro interaction with pVHL. Three additional N-TAD mutations, M560A/L561A (lane 5), D568A/D569A/D570A (lane 11) and F571A/L573A (lane 12) also completely abrogated binding of the N-TAD to pVHL.

Example 3: pVHL Interacts with mHIF-lalpha N-TAD under Reoxygenation Conditions pVHL is able to interact with hHIF-1 alpha in assays using whole cell extracts from cells expressing both proteins (hereafter referred to as in vivo interaction) under conditions where proteosome-mediated degradation has been inhibited (12,14,34). This interaction is inhibited when cells are exposed to hypoxia or hypoxia mimicking agents (23,24,34). In order to determine the critical residues according to the present invention, an examination was conducted to see if pVHL binding to the N-TAD could be observed without the use of proteosome inhibitors. Experimental conditions were selected to allow overexpression of HIF-lalpha N- TAD to saturate the endogenous degradation machinery, see Figure 27C (12).

HEK 293 or COS7 cells were transfected with 800 ng of pFLAG- GAL4/mHIF-l alpha N-TAD (531-584) and 200 ng of pCMX-VHL, a VHL expres- sion plasmid, according to Example IB. After transfection the cells were allowed to grow for 24 hours. The cells were then exposed to normoxia (20% 02) or hypoxia (1% 02) for 12 hours followed by varying reoxygenation durations (Rl, 1 minute; R10, 10 minutes; R60, 60 minutes). As indicated by a '+' in Figure 2, some cells were treated with 1 uM MG132 during the last 12 hours of incubation. Immunoprecipitation assays were performed using the anti-FLAG antibodies

(alp a-FLAG-IP) and precipitated proteins were detected by immunoblotting with anti-FLAG or anti- VHL antibodies (alp a-FLAG, alpha- VHL). Input material was analyzed by SDS polyacrylamide gel electrophoresis (SDS-PAGE) of 50 μg of whole cell extract protein and immunoblotting. As shown in Figure 2, strong bind- ing of VHL to the N-TAD of HIF- 1 alpha can be observed in the absence of MG132 treatment both in HEK 293 and COS7 cells after 1 minute or 9 minutes of reoxygenation. Significantly lower levels of HIF- 1 alpha - pVHL interaction were observed either at normoxia or following 1 hour of reoxygenation.

In the version of the experiment shown in Figure 27C, HEK293 cells were transfected with 800 ng of pFLAG-GAL4/mHIF-lalpha-(531-584) and 200 ng of pCMX-VHL (VHL expression plasmid). The cells were exposed to normoxia (21% O2) or hypoxia (1% 02) for 16 hours. Cells exposed to hypoxia were harvested after different times of reoxygenation (1 minutes, Rl; 10 minutes; RIO; 60 minutes, R60). In indicated cases the cells were treated with 1 mM MG132 (MG) during the last 12 hours of incubation.

Immunoprecipitation assays were performed using the anti-FLAG antibodies (α-FLAGIP) and precipitated proteins were detected by immunoblotting with anti- FLAG or anti- VHL antibodies ( -FLAG, -VHL). Input material was analyzed by SDS-PAGE of 50 mg of whole cell extract protein and immunoblotting. As also seen in Figure 27C, strong binding of VHL to the N-TAD is observed in the absence of MG132 treatment after 1 minute (lane 2) and 10 minutes (lane 3) of reoxygenation. In contrast, much lower levels of N-TAD - pVHL interaction were observed either at normoxia (lane 1) or following 1 hour (lane 4) of reoxygenation.

Treatment of the cells with the proteosome inhibitor MG132 increased the levels of expressed pVHL (lanes 5-8) and inhibited the decrease in pVHL binding observed after 1 hour of reoxygenation (lane 8). Surprisingly, binding of VHL to the N-TAD also increased in cells treated with MG132 under hypoxic conditions.

The data described herein demonstrates that some modification occurs during hypoxia which allows a more efficient recruitment of p VHL when the cells return to normoxia. These observations could be explained by an increase in prolyl-4- hydroxylase activity during reoxygenation since some of these prolyl-4-hydroxylase enzymes have been shown to be induced at the mRNA levels by hypoxia (36). This would be consistent with the proposed model that an important factor for HIF- lalpha degradation, one other than pVHL, is up-regulated by hypoxia (26). Fol- lowing these results, in vivo VHL binding assays were performed using cells not treated with MG132 and exposed to 1 minute of reoxygenation. The binding of VHL to mHIF-lalpha N-TAD proved to be specific since no binding was observed when the GAL4 DNA binding domain was expressed alone (Fig. 3).

Example 4: pVHL Binding to mHIF-lalpha N-TAD Depends Upon Four Critical Residues

The N-TAD is the HIF-lalpha interaction interface with pVHL. Furthermore, the PYI motif (residues 563-565 in mHIF-lalpha) is an essential motif for interaction with pVHL (12). The investigation described in this Example determined the effect of point mutations on either the PYI motif or on hydrophobic amino acids present in the predicted alpha-helices of the N-TAD. The analysis was based on the secondary HIF-lalpha structure predicted with the program PREDATOR (27,28).

In the HIF-lalpha N-TAD, three alpha-helices are predicted with the PYI motif located in a loop between helices 2 and 3. Since the constructs used in the foregoing work span only the minimal N-TAD region (residues 531-584), the pre- dieted helix 1 is disrupted (Fig. 4). Immunoprecipitation experiments using different N-TAD point mutants further characterized the pVHL - N-TAD interface.

HEK 293 cells were transfected with 800 ng of pFLAG_-GAL4/mHIF- lalpha (531-584) (N-TAD) containing the wild-type sequence (N-TAD) or muta- tions pFLAG-GAL4/mHIF-l alpha (546-574), pFLAG-GAL4/mHIF-l alpha (772- 822) (C-TAD), as well as 200 ng of pVHL expression plasmid. Immunoprecipita- tions were performed as described in Example lC. pVHL and HIF-lalpha NTAD protein levels were analyzed by immunoblotting using either anti-pVHL or FLAG antibodies, respectively. The cells were exposed to normoxia (N) or hypoxia for 12 hours and 10 minutes of reoxygenation (R) before harvesting, results are shown in Figure 5.

Abrogation of the interaction between the N-TAD and pVHL was observed not only in the case of the mutant P563D/Y564D/I565D but also in the case of the single amino acid point mutants P563A and Y564G, and in the case of the double mutants Y564G/I565G and F571A/L573A. Mutation of L556A/L558A in the putative helix 2 did not affect binding of pVHL to the N-TAD. The double mutant P566E/M567E interacted with pVHL. A weak interaction of pVHL with HIF- lalpha N-TAD was observed with the mutant I565G, indicating that 1565 is not important for binding of p VHL. The hydrophobicity of Y564 was found to play an essential role in generating an interface with pVHL. The mutation Y564G completely disrupted binding of pVHL, while phosphorylation of Y564 did not seem to be relevant. The mutant Y564F did not affect pVHL binding. Interaction of pVHL was also observed with a shorter protein fragment of the HIF-la NTAD spanning residues 546-574, whereas no binding was observed with the HIF-lalpha C-TAD that has previously been shown to be a constitutively expressed transactivation domain of HIF-lalpha (Fig. 5). Thus, in addition to the importance of P563 and Y564, the hydrophobic amino acids present in the predicted helix 3 are important for binding of pVHL. This knowledge, that the integrity of P563, the hydrophobicity of the residue at 564, and the integrity of F571 and L573 are critical, has therapeutic applicability, see Example 5.

Example 5: Critical Residues for in vivo Interaction between N-TAD and pVHL To determine whether the mutants that disrupt the interaction between the N-

TAD and pVHL in vitro are also critical for the binding in vivo, immunoprecipitation assays were performed using transfected HEK 293 cells expressing FLAG- GAL4-(531-584) mutants and pVHL. Transfections and immunoprecipitations were performed as described in Example 3 regarding Figure 27C. The cells were exposed to normoxia (N) or hypoxia for 12 hours and 10 minutes of reoxygenation (R) before harvesting. Abbreviations used in the Figures are as follows: LL-A is L556A/L558A; ML-A is M559A/L570A; PYI-D is P563D/Y564D/I565D; PM-E is P566E/M567E; DDD-A is D568A/D569A/D570A; FL-A is F571A/L573A; and QR- A is Q572A/R574A. As evident in Figure 27D, abrogation of the interaction between the N-TAD and pVHL was observed in the case of the mutant P563D/Y564D/I565G (lanes 5 and 6) and the corresponding point mutants P563A (lanes 23 and 24) and Y564G (lanes 13 and 14). The hydrophobicity of Y564 was shown to play an essential role in binding to pVHL. The mutant Y564G completely disrupted binding of pVHL, see Figure 27D.

Phosphorylation of Y564 is not, however, relevant for pVHL interaction since the mutant Y564F did not affect pVHL binding activity. Mutation of 1565 drastically reduced interaction with pVHL but did not completely inhibit binding activity (lanes 15 and 16). Moreover, the two HIF-lalpha N-TAD mutants, D568A/D569A/D570A and F571A/L573A, did not interact with pVHL and also failed to bind pVHL in vivo, see Figure 27D, lanes 9-12.

In contrast to the in vitro results shown in Figure 27B, mutation M560 and L561 did not inhibit pVHL binding in vivo, see Figure 27D, lanes 3 and 4, possibly due to the absence in reticulocyte lysate of appropriate modifying enzymes (i.e., prolyl-4-hydroxylases) required for binding of p VHL to these mutants. The mutant P566E/M567E demonstrated significantly stronger pVHL binding activity than the wild type N-TAD (see Figure 27D, lanes 7 and 8). Interaction of pVHL was also observed with a shorter protein fragment of the N-TAD spanning residues 546-574 (lanes 17 and 18), whereas no binding was observed with the C-TAD (see Figure 27D, lanes 19 and 20).

This, in vivo binding of pVHL depends on the PYI motif and the integrity of residues D568-D569-D570 and F571-L573. This knowledge, combined with the information provided in Example 4, has therapeutic applicability. It can form the foundation of treatment methods as well as compositions, including altered HIF- 1 alpha sequences, that can be used both in test models and in the treatment or prevention of a variety of conditions and diseases. For example, a mutated HIF-lalpha sequence can be generated that is capable of transcription activation during normoxic conditions and in the presence of sufficient, functional pVHL. This mutated sequence could be used to induce a hypoxic response in a cell for testing purposes, or for therapeutic benefit. Fields of hypoxia-related conditions or diseases that may benefit from this sort of inventive application include, but are not limited to, angiogenesis, diabetic retinopathy, erythropoiesis, inflammation, ischemia, ischemic heart disease, coronary heart disease, peripheral vascular disease, rheumatoid arthritis, stroke, tumorogenesis and wound healing. Any or all of these conditions, among others, could be affected by manipulation of the HIF-lalpha pathway. One example would be to administer a protein of the present invention to influence the production of erythropoietin. A further example would be the administration of a pharmaceutical according to the present invention to create, alter, or prevent an inflammatory response.

Example 6: HIF-lalpha N-TAD Mutants that do not bind pVHL are Resistant to pVHL-Mediated Protein Degradation

To evaluate the effect of different point mutations introduced into the N- TAD on the ability of p VHL to mediate protein degradation at normoxia (21% 02), pFLAG-GAL4-mHIF-lalpha-(531-584) was transiently expressed in HEK 293 cells in the absence or presence of increasing concentrations of pVHL. Specifically, the HEK 293 cells were transfected with pFLAG-GAL4/mHIF-l alpha (531-584) encoding either the wild-type or point-mutated forms of the N-TAD motif, pFLAG- GAL4/mHIF-l alpha (546-574), or pFLAG-GAL4/mHIF- 1 alpha (772-822) (C- TAD) at concentrations (750 ng) allowing detection of the protein at normoxia. Where indicated, cells were also transfected with increasing concentrations of pCMX-VHL (500 ng, +; 1000 ng, ++). The cells were incubated for 36 hours between transfection and harvest. These data are shown in Figure 28A.

As shown in Figure 28A, NTAD-(531-584) and N-TAD-(546-574), as well as the mutants L556A/L558A, M560A/L561A and P565E/M566E were degraded by pVHL in a dose-dependent manner at normoxia. The mutant M560A/L561A was more resistant to degradation than the other expressed GAL4-fusion proteins. In contrast, mutants P563D/Y564D/I565D, P563A, Y564G, I565G, D568A/D569A/D570A, F571A/L573A and the C-TAD (see Figures 6, 7, 28A, 28B) were not degraded, even following exposure to the highest tested levels of pVHL tested. With exception of I565G, binding of pVHL to the various N-TAD mutants correlated with its ability to mediate degradation of these protein fragments.

Although pVHL was able to interact with N-TAD I565G as assessed by immunoprecipitation assays, no pVHL-dependent degradation was observed of this mutant. This result is explained by conformational changes introduced by the mutation that do not affect pVHL binding but do impair subsequent ubiquitylation of this protein fragment and thus inhibit proteosome-mediated degradation. Further data on specific point mutations within the N-TAD is shown in Figures 19-21 and SEQ ID NO:s 1-10. As previously stated, the present invention presents opportunities to realize new therapeutic and scientific advances. The invention makes use of new findings by, inter alia, forming mutated HIF-lalpha proteins that do not bind to pVHL but are otherwise functional. These data demonstrate that in vivo binding of pVHL to the various N-TAD mutants correlated with its ability to mediate degradation of these protein fragments. The data present opportunities to realize new therapeutic and scientific advances. The invention makes use of this data by, inter alia, forming mutated HIF-lalpha proteins that do not bind to pVHL but are otherwise functional. The unique mutant I565G, for example, may be exploited for its' ability to bind pVHL yet resist degradation. Mutant HIF-lalpha proteins of the present invention can provide researchers with new routes of mimicking the hypoxic response or artificially inducing a hypoxia response in a cell or group of cells that are not under hypoxic conditions.

Example 7: Degradation of mHIF-lalpha (1-531) is Mediated by pVHL pVHL mediation of mHIF-lalpha (1-531) degradation at normoxia was investigated. As described below, mHIF-lalpha (1-531) expression plasmid was transiently expressed in HEK 293 cells at a concentration that allowed detection of the protein at normoxia. The endogenous degradation machinery of the cells was saturated to allow monitoring of the effects of expression of increasing pVHL concen- tration at normoxia. As shown in Figure 17, pVHL induced degradation of mHIF- lalpha (1-531) at normoxia in a dose-dependent manner. In contrast, mHIF-lalpha (1-390) did not show any differences in protein levels in the absence or presence of pVHL, demonstrating resistance to pVHL-mediated protein degradation (Fig. 17).

Specifically, HEK 293 cells were transfected with 250 ng of pFLAG-mHIF- lalpha (1-531) in the absence of pVHL expression vector (-) or in the presence of 500 (+) or 1000 (++) ng of pVHL expression vector (left panel of Fig. 17). As shown in the right panel of Figure 17, HEK 293 cells were transfected with 500 ng pFLAG-mHIF- lalpha (1-390) in the absence (-) or presence of 1000 ng (+) of pCMX-VHL. The cells were incubated for 12 hours at normoxia (N) or hypoxia (H). Expression of the proteins was analysed by immunoblotting using anti-FLAG (-FLAG) or anti-VHL (--VHL) antibodies.

Competition of the minimal pVHL target domain N-TAD (546-574) for degradation of the mHIF-lalpha (1-531) protein at normoxia was observed. This further confirmed the pVHL role in mediating degradation of mHIF-lalpha (1-531). Overexpression of N-TAD (546-574) resulted in stabilization of mHIF-lalpha (1- 531) protein levels at normoxia, demonstrating that both domains compete for the same degradation mechanism. Therefore, pVHL mediates degradation of both N- TAD (546-574) and mHIF-lalpha (1-531). Results are shown in Figure 18, where HEK 293 cells were transfected with 150 ng of pFLAG-mHIF- lalpha (1 -531) and 1000 ng of pFLAG-GAL4/mHIF- lalpha (545-574). The cells were treated and analyzed as described above in this Example. Combined with the teachings of the other Examples, this presents stronger evidence of the importance of addressing each region of HIF-lalpha that can interact with pVHL when designing HIF-lalpha mutants. Properly designed mutants can offer clinical and therapeutical advances in the art. There is a need for both the point mutants, for example, N-TAD mutants, and mutated fragments or proteins that contain targeted mutations in more than one region.

Example 8: N-TAD Fragments Having Transactivation Capacity Fragments within the N-TAD region of HIF-lalpha were evaluated for transactivation capacity when fused to GAL4. The fragments are depicted in Figure 22, form SEQ ID NO:s 11-19, and lie between residues 546-573. Luciferase reporter assays were used to measure activity (Figs. 23, 25). As shown, some fragments are functional transactivators in cellular assays and can therefore be used to stabilize the endogenous HIF-lalpha protein. This stabilization occurs through the prevention of VHL/HIF-alpha interaction and subsequent degradation of HIF-lalpha.

One of the contributions of the present invention is the analysis of the activity of these fragments in HepG2 cells as compared to MBE cells. Certain of the fragments, for example, SEQ ID NO: 15, had minimal activity in the HepG2 or non- endothelial cell line, whereas they had significant activity in the MBE or endothelial cell line. This activity gradient enables the creation of new screening and treatment methods that exploit the difference in activity between cell lines. Molecules of interest may be evaluated to determine their activity levels in both types of cells. Where there is a difference in activity between the target cell type and an unrelated cell type, potential functions of the molecule can be ascertained. In addition, differ- ent responses indicate a potential mechanism within one type of cell to block or enhance function of the molecule. Not only does this allow for investigation of novel treatments, it may unmask molecules that would be cell-type specific in their activity and therefore could be used to selectively target certain cell lines. This could be useful, for example, for drug delivery where unrelated cell types would be protected from toxic effects.

Taken in addition with the teachings of, inter alia, Example 7, the showing that the same fragment has different reactions in different cell types has practical relevance. Alteration or inactivation in more than one domain may be necessary to achieve functionality in the cell type of interest. Further, it may be one region, perhaps as small as one residue, of the fragment that interacts with the endogenous machinery and creates the varied effect as compared to a neighboring mutant. Use of the present invention to identify those sites of activity and interest can result in commercially relevant treatments and materials. For example, those sites may be used as models for the creation of pharmaceutical treatments. Not only could pharmaceuticals be modeled as mimics of the relevant portion of the fragment, they could be formed as antagonists of that portion. Further, characterization of the select portion of the fragment could help identify the active agent (for example, an enzyme) in the specific cell type that interacts with the portion of the fragment. This could lead to further routes of manipulation and treatment.

With the relevance and activity of these specific fragments now shown, they can be incorporated into treatment methods. These fragments may be as small as 17 amino acids. Further, the present invention also discloses the ability to use even smaller fragments, such as fragments 16, 15, 14, or 13 residues in size, or smaller. Similarly sized fragments from the second degradation box, lying between 380-416, can also be employed according to the present invention, separately or in conjunction with N-TAD fragments. One use of fragments is administration to cells for pVHL binding, allowing some native HIF- 1 alpha to avoid degradation at normoxia. This stabilization of HIF-lalpha could be useful to offset conditions where there is an overabundance of pVHL or a shortage of HIF-lalpha. One of the many other treatments with fragments disclosed herein could be to affect an increase in angiogenic activity, for example, to resolve ischemia.

Example 9: Reoxygenation-Dependent Degradation of the N- TAD Is Mediated by pVHL

To provide further support for the above-described in vivo binding assays, the efficiency of pVHL-mediated degradation was evaluated under normoxia and conditions of reoxygenation, see Figure 28C. Specifically, HEK 293 cells were transfected with 750 ng of pFLAG-GAL4/mHIF- lalpha (531-584) (N-TAD), or pFLAG- GAL4/mHIF- lalpha (531-584) P563A (P-A) in the absence or presence of 250 ng (+), 500 ng (++), or 1000 ng (+++) pCMX-VHL. Following transfection the cells were incubated for 24 hours at normoxia (N), for 12 hours at hypoxia (H), or for 12 hours of hypoxia followed by 2 hours of reoxygenation (R). 25 mg of whole cell extract proteins was analyzed by SDS PAGE and immunoblotting using anti-FLAG {-FLA G) or anti- VHL (- VHL) antibodies .

Degradation of the wild type N-TAD motif was observed both at normoxia and in reoxygenated cells in a manner that was strictly dependent on the pVHL concentration. In contrast, the N-TAD P563A mutant did not show any differences in protein levels between cells exposed to 21% or 1% oxygen in the presence of in- creasing concentrations of pVHL (Fig. 8). For the wild type N-TAD motif, pVHL was significantly more potent in mediating protein degradation under conditions of reoxygenation as compared to normoxic cells. This is consistent with the proposition that pVHL may have a higher affinity for the N-TAD in the reoxygenated cells (36). These test results support another inventive application, to interfere with nor- mal cellular responses during and following reoxygenation by replacing HIF-lalpha with one of the novel HIF-lalpha mutants herein described.

Example 10: Identification of Residues Important for pVHL Binding Located at the C-terminus of the PYI motif The mutants D568A/D569A/D570A and F571A/L573A failed to interact with pVHL in vitro and in vivo and were resistant to pVHL mediated degradation at normoxia (Figures 27B, 27C, and 28A). Since these are triple and double mutants, single amino acid point mutants were also generated for all these residues in a shorter protein fragment of the NTAD spanning residues 546-574 (pFLAG-GAL4- mHIF-lalpha-(546-574)).

HEK 293 cells were transfected with pFLAG-GAL4/mHIF-lalpha(531-584) encoding either the wild type or point-mutated forms of the N-TAD motif, pFLAG- GAL4/mHIF-lalpha(546-574), or pFLAG-GAL4/mHIF-lalpha(772-822) at con- centrations (750 ng) allowing detection of the protein at normoxia. In indicated cases (see Fig. 28A) the cells were also transfected with increasing concentrations of pCMX-VHL (+, 500 ng; ++, 1000 ng). Following transfection the cells were incubated for 36 hours. Whole cell extract proteins (25 mg) were analyzed by SDS PAGE and immunoblotting using anti- FLAG or anti- VHL antibodies (-FLAG, - VHL).

The mutants D568A, D569A and Q572A were able to interact with pVHL in an in vitro binding assay, as shown in Figure 29 A, lanes 5, 6, and 9, respectively. The mutant D568A, shown in lane 5, consistently demonstrated weaker binding to pVHL. In contrast to these results, mutation of residues D570, F571 and L573 completely abrogate pVHL-NTAD interaction, see Figure 29A, lanes 7, 8 and 10, respectively. In the in vivo pVHL-mediated degradation assay, the shorter fragment of the N-TAD spanning residues 546-574 and the mutant D570A were degraded by pVHL in a dose dependent manner. D570A was more resistant to pVHL-mediated degradation than the wild type. These results indicate the presence in HEK 293 cells of enzymes (notably one or several prolyl-4-hydroxylases) that facilitate binding of pVHL in vivo. The other two mutants F571A and L573A, which failed to bind pVHL in vitro were resistant to pVHL-mediated degradation even at the highest doses of pVHL tested. These data demonstrate that, in addition to the PYI motif, residues F571 and L573 are critical for the physical interaction with pVHL and pVHL-mediated degradation of the N-TAD. This allows for inventive application of the new information, such as research models and treatments that will be effective for hypoxia-related conditions.

Example 11 : The P563A Mutant of HIF-lalpha N-TAD Functions as a Constitu- tively Active Transactivation Domain

The HIF-lalpha N-TAD motif has previously been shown to function as a bi- functional domain both constituting a hypoxia-regulated degradation box as well as a hypoxia-dependent transactivation domain that can be potentiated by coactivators such as p300/CBP (6-9). The effect of the different mutations within the N-TAD on the ability of this domain to mediate the hypoxia-dependent transactivation response was evaluated. Transient transfection experiments were performed in HEK 293 cells using a GAL4-driven luciferase reporter gene and pFLAG-GAL4-mHIF- lalpha-(531-584) or different mutants of this motif.

HEK 293 cells were transfected with 500 ng of a GAL4-responsive reporter gene plasmid, 20 ng of wild-type or mutant GAL4-N-TAD expression plasmids and carrier DNA pFLAG to keep a constant DNA concentration of 1 gg. The cells were cultured for 12 hours after transfection and exposed to 24 hours of normoxia or hypoxia. Data in Figure 9 are presented as luciferase activity relative to normoxic cells transfected with pFLAG-GAL4 alone. At normoxia, the wild type N-TAD construct mediated about 2.4-fold activation of transcription when compared with the activity observed following expression of the GAL4 DNA binding domain (DBD) alone. However, in cells treated with hypoxia for 24 hours, 9-fold activation of transcription was observed over the values produced by the GAL4 DBD at normoxia. This resulted in an approximately 4-fold hypoxia-dependent activation response, see Figure 30 A. See also Figure 9, where values shown are the mean ± SD of three independent experiments performed in duplicate.

In contrast to the wild type N-TAD, most of the N-TAD mutants tested did not mediate any significant levels of hypoxia-inducible transactivation. For exam- pie, the mutants L556A/L558A and M560A/L561A produced only very modest transactivation responses as compared to the wild type chimeric protein. These mutants both show interaction with pVHL and pVHL-dependent degradation, suggesting that the low transactivation capacity is because residues L556, L558, M560 and L561 are important for the interaction with factors involved in the transactiva- tion response.

The mutants P563D/Y564D/I565D (4.8- and 5-fold activation at normoxia and hypoxia, respectively), Y564G (3- and 3.5-fold activation), I565G (6.9- and 6.4- fold activation), D570A (5.6- and 6.8- fold activation) and F571A/573A (4.3- and 4.1 -fold activation) all showed similarly low values of transactivation both at nor- moxia and hypoxia. In contrast to the Y564G mutant, the Y564F mutant resulted in transactivation levels similar to those produced by the wild type HIF-lalpha N-TAD motif (2.7- and 9.2-fold activation over background values at normoxia and hypoxia, respectively).

The P566E/M567E mutant transactivates as efficiently as the wild type N- TAD. The short protein fragment of the N-TAD spanning residues 546-576 was able to mediate a 2.6-fold hypoxia-dependent transactivation response, indicating a reduced ability to transactivate although it maintained all properties of conditionally regulated protein degradation observed with the larger NTAD fragment. The transactivation results obtained with the Y564G and Y564F mutants (see Fig. 5) are commensurate with the pVHL binding experiments shown in Figure 27B.

The Y564F mutant affected neither pVHL binding nor the transactivation function of the N-TAD, suggesting that phosphorylation of the Y564 may not be required for interaction with pVHL or the ability to transactivate. Alternatively, hydrophobicity of this residue plays an important role in regulation of N-TAD function since the Y564G mutant abrogated pVHL binding (see Figure 27) and generated a weak, constitutively active transactivation domain (see Figure 30).

The P563A mutant also generated a constitutively active transactivation domain that was much more potent than the wild type N-TAD. N-TAD P563A was able to mediate 28- and 25-fold activation responses over the background values at normoxia or hypoxia, respectively (Figs. 9, 30A). Although all three mutants of the PYI motif abrogated pVHL-mediated degradation of the N-TAD, only the P563A generated a more potent, constitutively active transactivation function. The P563A mutation therefore not only inhibits binding of p VHL and subsequent degradation of the N-TAD but also confers a conformational change onto the N-TAD that im- proved the transactivation potency of this domain.

Example 12: Introduction of the P563A Mutation into Full-Length mHIF-lalpha Fails to Stabilize the Protein at Normoxia

After characterization of the degradation box present in the isolated N-TAD of mHIF-lalpha (see Example 11), the effect of introduction of the P563A mutation into full-length mHIF-lalpha was examined. As detailed below, although the P563A mutation stabilized isolated N-TAD against pVHL-mediated protein degradation, both wild-type and P563A full-length mHIF-lalpha proteins were degraded at normoxia and showed hypoxia-dependent protein stabilization upon transient ex- pression in HEK 293 cells.

As shown in Figure 10, 50 μg of whole cell extract protein was analyzed by immunoblot using anti-FLAG antibodies (--FLAG). MBE cells were transfected with 2000 ng of wild-type or P563A mutant mHIF-lalpha expression vector. The cells were treated with CoC12 for 12 hours. Protein expression was monitored by immunoprecipitation and immunoblotting using anti-FLAG antibodies. Similar results were obtained following expression of either protein in MBE cells at normoxia or following treatment of the cells with the hypoxia-mimicking chemical CoC12. These results indicate that, in addition to the N-TAD, at least one more functional degradation box is present in full-length mHIF-lalpha. This additional box medi- ates degradation at normoxia independently of P563 regulating binding of pVHL.

The effect of the P563A mutation on the transactivation potential of full- length HIF-lalpha was also investigated. HEK 293 and MBE cells were transfected with the reporter gene pT81/HRE- lalpha and with pFLAG-mHIF- lalpha or pFLAG-mHIF- lalpha (P563A). Specifically, HEK 293 or MBE cells were trans- fected with 500 ng of an hypoxia response element (HRE) driven reporter gene vector and 50 ng of wild-type or P563A mHIF-lalpha expression vectors. The total DNA concentration was kept at 1 μg with pFLAG-CMV-2.

The cells were incubated at normoxia, hypoxia or with CoC12 for 36 hours. Results are presented in Figures 11 and 12 as luciferase activity relative to cells transfected with the HRE-driven reporter gene and pFLAG-CMV-2 at normoxia. In HEK 293 cells, transcription mediated by wild-type mHIF-lalpha produced a 4.7- fold hypoxia-dependent activation response (2.5- and 11.4-fold activation at normoxia and hypoxia, respectively), over the control values obtained by expression of the empty vector pFLAG-CMV-2 at normoxia. Data represent the mean ± SD of three independent experiments performed in duplicate.

The mHIF-lalpha P563A mutant mediated about 2-fold higher levels of transactivation function both at normoxia and hypoxia as compared to wild-type HIF-lalpha (4.0-and 20.1 -fold activation over background values, respectively). The mHIF-lalpha P563A mutant also maintained an approximately 5-fold hypoxia- dependent induction response that was very similar to the response mediated by the wild-type protein. Similar results were obtained in MBE cells treated with the hy- poxia-mimicking agent CoC12.

In cells transfected only with the empty expression vector pFLAG-CMV-2, endogenous HIF-lalpha mediated 12-fold hypoxia-dependent activation of the re- porter gene. Overexpression of either wild-type mHIF-lalpha or mHIF-lalpha P563A produced very similar (5.7- and 5.8-fold) hypoxia-dependent activation responses. The insertion of the P563A mutation did not stabilize the mHIF-lalpha protein in HEK 293 or MBE cells cultured at normoxia. The P563A mutation insertion maintained hypoxia-dependent regulation of the transactivation function of the protein. The approximately 2-fold increase in transactivation potency observed in the case of the mHIF-lalpha P563A reflects the previously observed (Fig. 9) increase in transactivation potential of the isolated N-TAD P563A.

The finding that the P563A mutation cannot, alone, protect HIF-lalpha from degradation at normoxia presents useful information. Approaches to generate a mutant HIF-lalpha that is stable at normoxia must factor in this critical finding. For example, by combining the findings in the various Examples, full length as well as fragmented mutated HIF-lalpha sequences can be prepared and used that are sufficiently conserved to be functional, yet contain mutations that allow the sequence or fragment to resist degradation at normoxia.

Example 13: Activation of P563A-Mediated Transcription is Enhanced by Coexpression of CBP and Correlates with the Ability of P563A to Bind CBP

The P563A mutant generated a constitutive transactivation domain that was significantly more potent in activation of transcription than the wild type N-TAD in hypoxia. In addition, in contrast to the wild type N-TAD fragment, this mutant showed constitutive functional activity. Transactivation mediated by the N-TAD P563A mutant was evaluated to see if it could still be potentiated by coexpression of CBP in a manner similar to that of the wild type N-TAD. As shown in Figure 30B, transient cotransfection of CBP moderately (about 1.7-fold) potentiated transactiva- tion mediated by the N-TAD both at normoxia and hypoxia. CBP enhanced to a similar degree transcription activation mediated by the P563A mutant of N-TAD, indicating that CBP is able to interact functionally with both the N-TAD and P563A mutant.

To determine whether it was possible to detect interaction between CBP and wild type N-TAD and between CBP and the P563 A mutant, bacterially expressed N- TAD and P563A were tested to see if they were able to precipitate ³⁵S-labelled CBP. pGEX-4T3/mHIF-lalpha-(531-584) and the P563A mutant were bacterially expressed and bound to glutathione-Sepharose beads (Fig. 30C). ³⁵S-labeled CBP was incubated with the GST-fusion proteins bound to glutathione-Sepharose. Precipi- tated CBP was analyzed by SDS PAGE and autoradiography.

As expected, GST alone was not able to precipitate CBP while both N-TAD and P563A could efficiently interact with CBP. No differences were observed between incubations performed in the presence of whole cell extracts of cells at normoxia or those treated with CoC12. Accordingly, N-TAD and the P563A mutant are able to interact with full-length CBP. The finding that the P563A mutation can interact with full-length CBP presents useful clinical information.

Example 14: Mutations that Negatively Affect Activation of Transcription Medi- ated by the N-TAD Decrease Transactivation Mediated by full-length HIF- 1

In addition to the N-TAD, HIF-lalpha contains a second hypoxia-responsive transactivation domain termed the C-TAD. As described above, mutations were identified that affected the activation of transcription mediated by the N-TAD (see Figure 30A). Mutations were examined for their ability to interfere with the trans- activation function of full-length HIF-lalpha. Several of the relevant N-TAD mutations were inserted into the context of the full-length mHIF-lalpha (pFLAG- mHIF- lalpha). These mutants were tested in transactivation assays by transfecting HEK 293 cells together with an HRE-driven luciferase reporter gene. Expression levels of the different mHIF-lalpha mutants (see Figure 20) were monitored using the same DNA preparations tested in the luciferase reporter assays. Activation of transcription mediated by wild type HIF-lalpha produced 8.8-fold and 27.4-fold activation at normoxia and hypoxia, respectively, over the value of the expression of pFLAG at normoxia (see Figure 21).

Three of the mutants tested, mHIF-lalpha(P563A), mHIF-lalpha(I565G), and mHIF-lalpha(P402A/P563A), generated a transactivation response similar to that of the wild type protein, whereas the other mutants showed a significant reduction of the transactivation function both at normoxia and hypoxia (Figure 19). The mutant mHIF-lalpha (P563A) trans activated as efficiently as the wild type protein but was expressed at lower levels. This mutation alone could have increased the transactivation efficiency of mHIF- 1 alpha.

Mutation of both P402 and P563 generated a mutant that showed elevated levels of expression and transactivated 2-fold more potently at normoxia than the wild type mHIF-lalpha. This mutant was still responsive to hypoxia (2-fold hypoxia-dependent activation response). The results obtained with mHIF- lalpha(P563A) and mHIF-lalpha(P402A/P563A) are in contrast with a previous study using RCC4 cells stably transfected with pVHL (35), where mutation of Pro564 in hHIF- lalpha increased transactivation in normoxia and protein expression in non treated cells.

The present results show the mutant mHIF-lalpha(P563A) is as well de- graded as the wild type protein. The double mutant P402A/P564G in hHIF- lalpha is presented as a constitutive transactivator in a previous report (35), while according to the present invention this protein presents a higher transactivation at normoxia but is still responsive to hypoxia. The three mutants that showed reduced transactivation activity are expressed at levels similar to the wild type. The Y564G mutant generates a much weaker transactivator with a 60% reduction of transcription activation at normoxia and hypoxia while mHIF- lalpha(L556A/L558A) and mHIF-lalpha(F571A/L573A) demonstrated a transactivation capacity that was reduced at hypoxia to 40% and 50%, respectively, of the wild type levels. Given the fact that these mutants have wild type hypoxia-regulated expression levels, these results show that some of the mutations which decreased transactivation potential of the N-TAD in GAL4-fusion protein experiments also decreased total transactivation activity of full-length mHIF-lalpha.

Combined with the teachings of the previous Examples, this data presents further evidence of the importance of addressing each region of HIF-lalpha that can interact with pVHL when designing HIF-lalpha mutants. Properly designed mutants can offer clinical and therapeutical advances in the art.

Example 15: Identification of a Second Degradation Box of HIF-lalpha Located between Residues 390 and 531 To further corroborate the inventive results described above with mHIF- lalpha P563A, experiments were performed in HEK 293 cells with the deletion mutant mHIF-lalpha (532) 583) lacking the entire N-TAD. HEK 293 cells were transfected with two increasing concentrations of pFLAG-mHIF- lalpha (532 583) (700 ng or 1 μg plasmid) and exposed to normoxia (N) or hypoxia (H) for 12 hours. This mutant is schematically represented in Figure 13. Consistent with the proper- ties of mHIF-lalpha P536A, the N-TAD deletion mutant was degraded at normoxia and showed hypoxia-dependent protein stabilization (Fig. 14). This indicates additional functional domains within HIF-lalpha mediate conditionally regulated protein degradation. To identify such additional domains, immunoblot analysis was used to monitor the protein levels of a series of mHIF-lalpha deletion mutants upon transient expression in HEK 293 cells at normoxia and hypoxia. HEK 293 cells were transfected with two increasing concentrations of pFLAG-mHIF- lalpha (1-531) (150 and 200 ng), pFLAG-mHIF- lalpha (1-390) (300 and 500 ng) and pFLAG- mHIF-lalpha (391-628) (500 and 700 ng). Protein expression was analyzed by immunoblotting using 50 μg of whole cell extract protein. While mHIF-lalpha (1- 531) showed degradation at normoxia, both mHIF-lalpha (1-390) and mHIF-lalpha (390-628, lacking the large oxygen-dependent degradation domain (3), generated similar protein levels both at normoxia and hypoxia (Fig. 15). Therefore, in addition to the N-TAD the ODD domain contains a second domain located between residues 390 and 531 that can mediate degradation of mHIF- 1 alpha at normoxia.

This finding was further substantiated by performing reporter gene assays with VP16 fusion proteins spanning either full-length mHIF-lalpha or the deletion mutants mHIF-lalpha (1-531) and mHIF-lalpha (1-390). Since the two C-terminal deletion mutants (1-531) and (1-390) do not contain any endogenous transactivation domains, any observed hypoxia-inducible transactivation potential in the gene reporter assays would necessarily be the result of differences in protein expression levels.

As shown in Figure 16, VP16 fusion proteins spanning mHIF-lalpha (1-531) mediate hypoxia-inducible transactivation. Reporter gene assays were performed in HEK 293 cells transfected with 500 ng of an HRE-driven reporter gene and 50 ng of pFLAG-mHIF-lalpha-VP16, pFLAG-mHIF- lalpha (1-531)-VP16, or pFLAG- mHIF-lalpha (1-531)-VP16. The cells were incubated for 36 hours at normoxia or hypoxia. Full-length mHIF-lalpha VP16 fusion protein produced about 5.6-fold hypoxia-dependent activation of reporter gene activity when compared to normoxia values. mHIF-lalpha (1-531)-VP16 mediated about a 3-fold increase in transactivation function in hypoxic cells, whereas mHIF-lalpha (l-390)-VP16 mediated very similar activation responses under either normoxic or hypoxic conditions (21.6- and 17-fold activation when compared to the values observed in the presence of the empty expression vector alone at normoxia). The domain located between residues 390-531 mediates protein degradation at normoxia and confers hypoxia-dependent regulation on a heterologous transactivation domain, i.e., VP16.

Specific locations within the domain between residues 390-531 that may be targeted for mutation can be determined by a skilled worker conducting routine ex- perimentation. The present description provides methods and materials that may be used to perform a mutation analysis and create mutations to the domain between residues 390-531 that have the desired effect. Further methods known in the art may be utilized.

Example 16: Detailed Analysis of Target Peptide Fragments

In order to analyze the in vivo and in vitro effects of SEQ ID NO: 15, a peptide was created which combined a fluorescein label linked to the cellular uptake signal HIV-TAT, see Figure 32. This peptide, peptide 1, was modified with the addition of the fragment of SEQ ID NO: 15 to create peptide 2. Peptide 1 was also combined with a hydroxylated version of the sequence to create peptide 3.

Peptides 1, 2, and 3 were added in vitro at various concentrations and their expression was analyzed using immunoprecipitation, see Figure 33. Methods described in previous Examples may be utilized in this evaluation, or any appropriate technique known in the art may be substituted. Peptides 1, 2, and 3 were also evaluated in an in vivo cornea assay, as shown in Figures 34A, 34B, and 34C. The mouse cornea, normally devoid of vasculariza- tion, remains so after treatment with peptide 1 or peptide 2 (Figs. 34A and 34B, respectively). In contrast, addition of peptide 3 to the normally avascular cornea results in visible vessel generation. The vessel-containing area of each cornea was measured, results are depicted in Figure 35. As shown, the total vessel area in cor- neas treated with peptide 1 or 2 remained at zero, whereas 0.8 mm² of vessel area was observed in the corneas treated with peptide 3.

Analysis of the in vivo and in vitro effects of the fragment demonstrates the remarkable utility of small molecules according to the present invention. Fragments with similar in vitro activity (see Fig. 25) are also potential in vivo vasculature generators. They provide the basis for compounds and treatments that increase vessel formation or growth. Further, they can be useful in analysis of cellular responses to hypoxia and reoxygenation.

To further confirm these findings a second assay was conducted essentially as disclosed by Passaniti et al, Lab Invest, 1992, 67:4, 519-528. 48 μl of 1.0 mg/ml HIF-lalpha Peptide 2 was added to 4750 μl Matrigel (Becton-Dickinson) to prepare Peptide 2 material at a concentration of 10 μg/ml. 40 μl of 1.2 mg/ml HIF-lalpha Peptide 3 and 8 μl PBS were added to 4750 μl Matrigel to prepare Peptide 3 material at a concentration of 10 μg/ml. Based on previous results, the Peptide 2 prepa- ration served as control.

Two 350 μl doses of either Peptide 2 material or Peptide 3 material were injected into mice and allowed to form a plug. Five days later, the plugs were removed then processed and analyzed using a Drabkin's reagent 525 kit (Sigma). The hemoglobin content of each plug was determined by measuring absorbance at 540 nm, normalized against the weight of the plug. Plugs from mice injected with Peptide 2 material had an average absorbance of less than 0.1, whereas plugs from mice injected with Peptide 3 material had an average absorbance of 0.2. Hemoglobin amounts correlate with the degree of vascularization in the plug. Therefore, in addition to the results of the cornea assay showing Peptide 3 can induce vasculariza- tion in an avascular area, it has also been demonstrated that Peptide 3 can induce greater vascularization than the control Peptide 2. The difference in hemoglobin content is statistically significant and provides further evidence of the practical applications of Peptide 3, for example, increasing vascular development.

Example 17: Evaluation of Degradation Box Fragments Fragments of the second degradation box of HIF-lalpha were analyzed to' lo- cate and evaluate active fragments. Figure 36 shows the analyzed constructs. These fragments were also analyzed for functionality in MBE and HepG2 cell lines (Figs. 38, 39). Of particular relevance may be fragments such as 391-416, which exhibit activity in one cell line but not in another. These fragments may form templates for molecules that interact with the HIF-lalpha pathway. Further, they can be utilized in a variety of screening methods to evaluate potential cell specific regulation mechanisms.

Example 18: Gene Therapy Approaches

Certain embodiments of the present invention can be effectuated through the use of gene therapy. Gene therapy provides one means for inserting a desired polynucleotide sequence into a target cell to achieve some function in the cell, e.g., production of a protein. For example, U.S. Patent Nos. 5,399,346 and 5,585,362, in addition to other references such as journal articles, detail specific techniques and experimental successes in all mammalian species relevant to the present invention.

Ex vivo gene therapy techniques require removal of cells from an organism, introduction of a polynucleotide into the cells, optionally culturing and selecting cells that have incorporated and express the polynucleotide, then re-introducing the (selected) cells into the organism or introducing them in to a second organism. In vivo gene therapy techniques are also known, and allow direct introduction of the desired polynucleotide into an organism. This may be accomplished systematically or by direct injection. Preferably, the polynucleotide is in a composition or state that facilitates direct uptake of the polynucleotide by cells in vivo. The polynucleotide may be DNA or RNA, alone, in a complex, or in a vector.

The polynucleotide may include a promoter region, enhancer, or other control function to help encourage cellular expression of the polynucleotide. One of the most utilized methods of gene therapy is the use of vectors, for example, plasmid and viral vectors. Based on the polypeptide, route of administration, and target cell or cells, certain vectors may be more preferable. Further details on the practical use of gene therapy are known in the art. Additional techniques developed in the future will be useful and are within the scope of the present invention.

An HIF-lalpha sequence according to the present invention may be administered to an organism, for example, to treat a condition caused or related to under- expression of HIF-lalpha. A desired route of administration would be determined, such as a direct in vivo injection of the presently invented mutated HIF-lalpha sequence. The site for injection would be chosen to maximize the delivery of the polynucleotide to the cell or cells of interest. Naked polypeptide, enhanced polypeptide, polypeptide in a vector, or other desired composition would be prepared and administered to an organism. The target cells would take up and incorporate the mutated HIF-lalpha sequence of the present invention. Production of a mutated HIF-lalpha sequence of the present invention by the cells would follow, providing the direct intracellular treatment that is the hallmark of gene therapy.

While the data presented above refers to mouse HIF-lalpha, it is understood that the present invention can be performed in or on other mammalian systems, and the scope of the following claims includes additional mammalian systems, including, but not limited to, humans.

The foregoing description and examples have been set forth merely to illustrate the invention and are not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed broadly to include all variations falling within the scope of the appended claims and equivalents thereof. REFERENCES

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Claims

WHAT IS CLAIMED IS:

1. An HIF-lalpha protein having an altered transactivation capacity and at least one first mutated residue at a position corresponding to a position selected from the group consisting of positions 563, 564, 565, 570, 571, 572 and 573 of murine HIF- lalpha and at least one second mutated residue at a position selected from the group consisting of positions 390 through 531 of murine HIF-lalpha.

2. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is an alanine at position 563.

3. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is a glycine at position 564.

4. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is a hydrophilic amino acid at position 564.

5. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is a glycine at position 564 and a glycine at position 565.

6. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is an alanine at position 570.

7. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is an alanine at position 572.

8. An HIF-lalpha protein according to Claim 1, wherein said at least one first mutated residue is an alanine at position 573.

9. An isolated polynucleotide sequence encoding a protein as in any one of the preceding claims, and functional fragments thereof.

10. A pharmaceutical composition comprising a pharmaceutically active amount of a protein according to Claim 1 and at least one carrier or adjuvant.

11. A method of interfering with pVHL binding to HIF 1 -alpha in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to Claim 1 to the cell, group of cells, or organism.

12. A method of decreasing HIF-lalpha degradation in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to Claim 1 to the cell, group of cells, or organism.

13. A method of increasing HIF-lalpha transactivation capacity in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to Claim 1 to the cell, group of cells, or organism.

14. A method of increasing angiogenesis in a cell, a group of cells, or an organ- ism, comprising administering an HIF-lalpha protein according to Claim 1 to the cell, group of cells, or organism.

15. A method according to any one of Claims 1 1-14, wherein the cell, group of cells, or organism is at normoxia.

16. A method according to any one of Claims 11-14, wherein the cell, group of cells, or organism is at hypoxia.

17. A method of interfering with a normal response to reoxygenation following hypoxia in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to Claim 1 to the cell, group of cells, or organism.

18. A method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, comprising administering an HIF- lalpha protein according to Claim 1 to the cell, group of cells, or organism.

19. A method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to Claim 1 to the cell, group of cells, or organism.

20. A vector comprising a polynucleotide according to Claim 9 in operative association with at least one promoter.

21. A vector according to Claim 20, wherein the vector is a plasmid.

22. A vector according to Claim 20, wherein the vector is a viral vector.

23. A vector according to Claim 20, wherein the vector is a retroviral vector.

24. A host cell transformed or transfected with a vector according to Claim 20.

25. A host cell according to Claim 24, wherein the host cell is a prokaryotic cell.

26. A host cell according to Claim 24, wherein the host cell is a bacterial cell.

27. A host cell according to Claim 24, wherein the host cell is a eukaryotic cell.

28. A host cell according to Claim 24, wherein the host cell is a mammalian cell.

29. A method of interfering with pVHL binding to HIF 1 -alpha in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 20 to the cell, group of cells, or organism.

30. A method of decreasing HIF-lalpha degradation in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 20 to the cell, group of cells, or organism.

31. A method of increasing HIF-lalpha transactivation capacity in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 20 to the cell, group of cells, or organism.

32. A method of increasing angiogenesis in a cell, a group of cells, or an organ- ism, comprising introducing a vector according to Claim 20 to the cell, group of cells, or organism.

33. A method according to any one of Claims 29-32, wherein the cell, group of cells, or organism is at normoxia.

34. A method according to any one of Claims 29-32, wherein the cell, group of cells, or organism is at hypoxia.

35. A method of interfering with a normal response to reoxygenation following hypoxia in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 20 to the cell, group of cells, or organism.

36. A method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, comprising introducing a vector ac- cording to Claim 20 to the cell, group of cells, or organism.

37. A method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 20 to the cell, group of cells, or organism.

38. A method of determining whether an HIF-lalpha sequence encodes an HIF- lalpha protein capable of resisting degradation at normoxia, comprising: evaluating the HIF-lalpha sequence for a first alteration to at least one residue at a position selected from the group consisting of positions 563, 564, 565, 570, 571, 572 and 573; and evaluating the HIF-lalpha sequence for a second alteration to any one of residues 390 through 531, wherein an HIF-lalpha sequence having a first alteration and a second alteration encodes an HIF-lalpha protein capable of resisting degradation at nor- moxia.

39. An isolated amino acid comprising a sequence selected from the group consisting of SEQ ID NO:s 1-19.

40. An isolated polynucleotide sequence encoding an amino acid according to Claim 39.

41. A pharmaceutical composition, comprising a pharmaceutically active amount of an amino acid according to Claim 39 and at least one carrier or adjuvant.

42. A pharmaceutical composition, comprising a pharmaceutically active amount of an polynucleotide according to Claim 40 and at least one carrier or adjuvant.

43. A pharmaceutical composition, comprising a pharmaceutically active amount of an amino acid according to any one of SEQ ID NO:s 11-19 and at least one carrier or adjuvant.

44. A method of interfering with pVHL binding to native HIFl-alpha in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 43 to the cell, group of cells, or organism.

45. A method of decreasing native HIF-lalpha degradation in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 43 to the cell, group of cells, or organism.

46. A method of increasing angiogenesis in a cell, a group of cells, or an organ- ism, comprising administering a pharmaceutical composition according to Claim 43 to the cell, group of cells, or organism.

47. A method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, comprising administering a pharma- ceutical composition according to Claim 43 to the cell, group of cells, or organism.

48. A method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 43 to the cell, group of cells, or organism.

49. A method of treating ischemia in a group of cells or an organism, comprising administering a pharmaceutical composition according to Claim 43 to the group of cells or organism.

50. A HIF-lalpha protein having improved stability at normoxia, comprising at least one mutated residue at a position corresponding to a position selected from the group consisting of positions 568, 570, 571, and 573 of murine HIF-lalpha.

51. An HIF-lalpha protein according to Claim 50, wherein said at least one mutated residue is an alanine at position 568.

52. An HIF-lalpha protein according to Claim 50, wherein said at least one mutated residue is an alanine at position 570.

53. An HIF-lalpha protein according to Claim 50, wherein said at least one mutated residue is an alanine at position 571.

54. An HIF-lalpha protein according to Claim 50, wherein said at least one mu- tated residue is an alanine at position 573.

55. A HIF-1 alpha protein having improved stability at normoxia, comprising at least two mutated residues at positions 560 and 561 or 566 and 567 of murine HIF-1alpha.

56. An HIF-lalpha protein according to Claim 55, wherein said at least two mutated residues are alanines at positions 560 and 561.

57. An HIF-lalpha protein according to Claim 55, wherein said at least two mu- tated residues are glutamic acids at positions 566 and 567.

58. A HIF-lalpha protein according to either one of Claims 50 and 55, further comprising at least one mutated residue at a position corresponding to a position selected from the group consisting of positions 390 through 531 of murine HIF- lalpha.

59. An isolated polynucleotide sequence encoding a protein as in any one of Claims 50-58, and functional fragments thereof.

60. A pharmaceutical composition comprising a pharmaceutically active amount of a protein according to any one of Claims 50-58 and at least one carrier or adjuvant.

61. A method of interfering with pVHL binding to HIFl-alpha in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism.

62. A method of decreasing HIF-lalpha degradation in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism.

63. A method of increasing angiogenesis in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism.

64. A method according to any one of Claims 61-63, wherein the cell, group of cells, or organism is at normoxia.

65. A method according to any one of Claims 61-63, wherein the cell, group of cells, or organism is at hypoxia.

66. A method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, comprising administering an HIF- lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism.

67. A method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism, comprising administering an HIF-lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism.

68. A vector comprising a polynucleotide according to Claim 59 in operative association with at least one promoter.

69. A vector according to Claim 68, wherein the vector is a plasmid.

70. A vector according to Claim 68, wherein the vector is a viral vector.

71. A vector according to Claim 68, wherein the vector is a retroviral vector.

72. A host cell transformed or transfected with a vector according to Claim 68.

73. A host cell according to Claim 72, wherein the host cell is a prokaryotic cell.

74. A host cell according to Claim 72, wherein the host cell is a bacterial cell.

75. A host cell according to Claim 72, wherein the host cell is a eukaryotic cell.

76. A host cell according to Claim 72, wherein the host cell is a mammalian cell.

77. A method of interfering with pVHL binding to HIFl-alpha in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 68 to the cell, group of cells, or organism.

78. A method of decreasing HIF-lalpha degradation in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 68 to the cell, group of cells, or organism.

79. A method of increasing angiogenesis in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 68 to the cell, group of cells, or organism.

80. A method according to any one of Claims 77-79, wherein the cell, group of cells, or organism is at normoxia.

81. A method according to any one of Claims 77-79, wherein the cell, group of cells, or organism is at hypoxia.

82. A method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 68 to the cell, group of cells, or organism.

83. A method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism, comprising introducing a vector according to Claim 68 to the cell, group of cells, or organism.

84. A method of determining whether an HIF-lalpha sequence encodes an HIF- lalpha protein with improved stability at normoxia, comprising evaluating the HIF-lalpha sequence for an alteration to at least one residue at a position selected from the group consisting of positions 568, 570, 571, and 573, wherein an HIF-lalpha sequence having an alteration to at least one of said positions encodes an HIF-lalpha protein capable of resisting degradation at normoxia.

85. A method of determining whether an HIF-lalpha sequence encodes an HIF- lalpha protein with improved stability at normoxia, comprising evaluating the HIF-lalpha sequence for an alteration to at least one pair of residues at positions selected from the group consisting of positions 560 and 561, and positions 566 and 567, wherein an HIF-lalpha sequence having an alteration to at least one of said positions encodes an HIF-lalpha protein capable of resisting degradation at normoxia.

86. A method of interfering with pVHL binding to native HIFl-alpha in a cell, a group of cells, or an organism, comprising administering a pharmaceutical compo- sition according to Claim 60 to the cell, group of cells, or organism.

87. A method of decreasing native HIF-lalpha degradation in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 60 to the cell, group of cells, or organism.

88. A method of increasing angiogenesis in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 60 to the cell, group of cells, or organism.

89. A method of treating a condition characterized by HIF-lalpha underexpression in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 60 to the cell, group of cells, or organism.

90. A method of sustaining HIF-lalpha expression at normoxia in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 60 to the cell, group of cells, or organism.

91. A method of treating ischemia in a group of cells or an organism, comprising administering a pharmaceutical composition according to Claim 60 to the group of cells or organism.

92. A method of mimicking the hypoxic response in a cell, group of cells, or organism, comprising administering an HIF-lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism.

93. A method of artificially inducing a hypoxic response in a cell, group of cells, or organism, comprising: administering an HIF-lalpha protein according to any one of Claims 50-58 to the cell, group of cells, or organism, wherein the cell, group of cells, or organism is not at hypoxia.

94. A method according to Claim 93, wherein the cell, group of cells, or organism is at normoxia.

95. A method of enhancing activity of wild type or mutant HIF- 1 alpha N-TAD in a cell, a group of cells, or an organism, comprising coexpressing CBP in the cell, group of cells, or organism.

96. A method of identifying an agent which modulates the HIF-lalpha pathway, comprising: expressing a molecule in a non endothelial cell or cellular system; detecting a presence or an absence of functional activity of the molecule in the non endothelial cell or cellular system; expressing the molecule in an endothelial cell or cellular system; and detecting a presence or an absence of functional activity of the molecule in the endothelial cell or cellular system, wherein the molecule is an agent which modulates the HIF-lalpha pathway when a presence of functional activity of the molecule is detected in the non endothelial cell system and an absence of functional activity of the molecule is detected in the endothelial cell system.

97. A method according to Claim 96, wherein the molecule is a fragment of HIF- 1 alpha.

98. A method according to Claim 97, wherein the agent which modulates the

HIF-lalpha pathway is a portion of the fragment of HIF-lalpha.

99. An agent which modulates the HIF-lalpha pathway identified according to the method of Claim 96.

100. A pharmaceutical composition, comprising a pharmaceutically active amount of at least one peptide selected from the group consisting of SEQ ID NO:s 1, 4, 5, 7, 13, 14, 15, 16, and 17 and at least one carrier or adjuvant.

101. A pharmaceutical composition, comprising a pharmaceutically active amount of at least one polynucleotide encoding a peptide selected from the group consisting of SEQ ID NO:s 1, 4, 5, 7, 13, 14, 15, 16, and 17 and at least one carrier or adjuvant.

102. A method of increasing angiogenesis in a cell, a group of cells, or an organism, comprising administering a pharmaceutical composition according to Claim 100 or Claim 101 to the cell, group of cells, or organism.

103. A method according to Claim 102, wherein the cell, group of cells, or organ- ism is at hypoxia.

104. A method according to Claim 102, wherein the cell, group of cells, or organism is at normoxia.

105. A method of inducing at least one of vascular formation or vascular development in a cell or a group of cells, comprising administering a pharmaceutical composition according to Claim 100 or Claim 101 to the cell or group of cells.

106. A method according to Claim 105, wherein the cell or group of cells is at hypoxia.

107. A method according to Claim 105, wherein the cell or group of cells is at normoxia.

108. A method according to Claim 105, wherein the cell or group of cells are endothelial cells.

109. A method of increasing angiogenetic activity in a cell, comprising adding a peptide to or expressing a peptide in the cell, wherein the peptide is a fragment of HIF-lalpha; and wherein the peptide comprises no more than 17 amino acids.

110. A method of increasing angiogenic activity according to Claim 109, wherein the cell is an endothelial cell.

111. A method of increasing angiogenic activity according to Claim 109, wherein the peptide corresponds to a fragment between positions 546 and 573 of HIF- lalpha.

112. A method of increasing angiogenic activity according to Claim 109, wherein the peptide corresponds to a fragment between positions 380 and 416 of HIF- lalpha.

113. A method of influencing erythropoietin production in a cell, a group of cells, or an organism, comprising: administering a protein according to any one of Claims 1, 50, and 55 to the cell, group of cells, or organism.

114. A method according to Claim 113 wherein erythropoietin production is increased.

115. A method of influencing erythropoietin production in a cell, a group of cells, or an organism, comprising: administering a pharmaceutically effective amount of a pharmaceutical composition according to any one of Claims 10, 41, 43, and 60 to the cell, group of cells, or organism.

116. A method according to Claim 115 wherein erythropoietin production is in- creased.

117. A method of influencing metabolism in a cell, a group of cells, or an organism, comprising: administering a protein according to any one of Claims 1, 50, and 55 to the cell, group of cells, or organism.

118. A method according to Claim 117 wherein the metabolism is glycolytic metabolism.

119. A method of influencing metabolism in a cell, a group of cells, or an organism, comprising: administering a pharmaceutical composition according to any one of Claims 10, 41, 43, and 60 to the cell, group of cells, or organism.

120. A method according to Claim 119 wherein the metabolism is glycolytic metabolism.

121. A method of influencing an inflammatory response in a cell, a group of cells, or an organism, comprising: administering a protein according to any one of Claims 1, 50, and 55 to the cell, group of cells, or organism.

122. A method of influencing an inflammatory response in a cell, a group of cells, or an organism, comprising: administering a pharmaceutical composition according to any one of Claims 10, 41, 43, and 60 to the cell, group of cells, or organism.