CYTOKINE-, STRESS-, AND ONCOPROTEIN-ACTIVATED HUMAN PROTEIN KINASE KINASES

Abstract: Disclosed are human mitogen-activated (MAP) kinase kinase isoforms (MKKs). MKKs mediate unique signal transduction pathways that activate human MAP kinases p38 and JNK, which result in activation of other factors, including activating transcription factor-2 (ATF2) and c-Jun. The pathways are activated by a number of factors, including cytokines and environmental stress. Methods are provided for identifying reagents that modulate MKK function or activity and for the use of such reagents in the treatment of MKK-mediated disorders.

Description: CYTOKINE-, STRESS-, AND ONCOPROTEIN-ACTIVATED HUMAN PROTEIN KINASE KINASES Background of the Invention This invention relates to protein kinases . Mitogen-activated protein (MAP) kinases are important mediators of signal transduction from the cell surface to the nucleus. Multiple MAP kinases have been described in yeasc including SMK1 , HOG1 , MPK1 , FUS3 , and KSS1. In mammals, the MAP kinases identified are extracellular signal -regulated MAP kinase (ΞRK) , c-Jun amino-terminal kinase (JNK) , and p38 kinase (Davis (1994) Trends Biochem. Sci. 19:470). These MAP kinase isoforms are activated by dual phosphorylation on threonine and tyrosine . Activating Transcription Factor-2 (ATF2 ) , ATFa, and cAMP Response Element Binding Protein (CRE-B?a) are related transcription factors that bind to similar sequences located in the promoters of many genes (Ziff (1990) Trends in Genet . 5:69). The binding of these transcription factors leads to increased transcriptional activity. ATF2 binds to several viral proteins, including the oπcoprotem Ξla (Liu and Green (1994) Nature 368:520), the hepatitis B virus X protein (Maguire et al . (1991) Science 252:842), and the human T cell leukemia virus 1 tax protein (Wagner and Green (1993) Science 262:395). ATF2 also interacts with the tumor suppressor gene product Rb (Kim et al . (1992) Nature 358:331), the high mobility group protein HMG(I)Y (Du et al. (1993) Cell 74:887), and the transcription factors nuclear NF-KB (Du et al . (1993) Cell 74:887) and c-Jun (Benbrook and Jones (1990) Oncogene 5:295). Summary of the Invention The invention is based cn the identification and isolation of a new group of human mitogen-activated protein kinase kinases (MKKs) . The MKK isoforms described herein, MKK3 , MKK6 , MKK4 (including MKK4-C., -β , and -γ) , MKK7 (including murine MKK7, human MKK7, MKK7b, MKK7c, MKK7d, and MKK7e) have serine, threonine, and tyrosine kinase activity. MKK3 , MKK , and MKK6 specifically phosphorylate the human MAP kinase p38 at Thr 130 and Tyr 182 . The MKK4 isoforms also phosphorylate the human MAP kinases JNK (including JNK1 , JNK2 , and JNK5) at Thr 133 and Tyr 133 . The MKK7 isoforms phosphorylate JNK at Thr 133 and Tyr 135 . Accordingly, the invention features a substantially pure human MKK polypeptide having serine, threonine, and tyrosine kinase activity that specifically phosphorylates human p38 MAP kinase. MKK3 has the amino acid sequence of SEQ ID NO : 2. The invention further includes MKK6 having the amino acid sequence of SEQ ID NO : 4 and having serine, threonine, and tyrosine kinase activity that specifically phosphorylates human p38 MAP kinase . The invention further features a substantially pure human MKK polypeptide having serine, threonine, and tyrosine kinase activity that specifically phosphorylates human p38 MAP kinase and JNK. MKK4 isoform MKK4-α? has the amino acid sequence of SEQ ID NO: 6. MKK4 isoform MKK4- J 0 has the amino acid sequence of SEQ ID NO:8. MKK4 isoform MKK4-γ has the amino acid sequence of SEQ ID NO: 10. The invention also features a substantially pure MKK polypeptide (MKK7) having serine, threonine, and tyrosine kinase activity that specifically phosphorylates mitogen-activated protein kinase JNK. MKK isoforms MKK7 (murine) and MKK7 (human) have the amino acid sequences of SEQ ID NOS: 18 and 26, respectively. The MKK7 isoforms MKK7b, MKK7c, MKK7d, and MKK7e have the amino acid sequences of SEQ ID NO: 20, SEQ ID NO: 28, SEQ ID NO: 30, and SEQ ID NO: 32, respectively. As used herein, the term "mitogen-activating protein kinase kinase" or "MKK" means a protein kinase which possesses the characteristic activity of phosphorylating and activating a human mitogen-activating protein kinase. Examples of MKKs include MKK3 and MKK6, which specifically phosphorylate and activate p38 MAP kinase at Thr 130 and Tyr 182 , MKK4 isoforms which specifically phosphorylate and activate p38 MAP kinase at Thr 130 and Tyr 132 , and JNK at Thr 133 and Tyr 135 , and MKK7 isoforms which specifically phosphorylate JNK at Thr 183 and Tyr 185 . An "MKK7" is a mammalian isoform of mitogen- activated protein kinase kinase (MKK) polypeptide having serine, threonine, and tyrosine kinase activity, and phosphorylating mitogen-activated protein (MAP) kinase JNK but not p38. The invention includes the specific p38 and JNK MKKs disclosed, as well as closely related MKKs which are identified and isolated by the use of probes or antibodies prepared from the polynucleotide and amino acid sequences disclosed for the MKKs of the invention. This can be done using standard techniques, e.g., by screening a genomic, cDNA, or combinatorial chemical library with a probe having all or a part of the nucleic acid sequences of the disclosed MKKs. The invention further includes synthetic polynucleotides having all or part of the amino acid sequence of the MKKs herein described. The term "polypeptide" means any chain of amino acids, regardless of length or post-translational modification (e.g., glycosylation or phosphorylation), and includes natural proteins as well as synthetic or recombinant polypeptides and peptides. The term "substantially pure, " when referring to a polypeptide, means a polypeptide that is at least 60%, by weight, free from the proteins and naturally-occurring organic molecules with wnich it is naturally associated. A suostantially pure MKK polypeptide (e.g., human) is at least 75%, more preferably at least 90%, and most preferably at least 99%, by weight, MKK polypeptide. A substantially pure MKK can oe obtained, for example, cy extraction from a natural source; by expression of a recomninant nucleic acid encoding a MKK polypeptide, or by cnemically synthesizing the protein. Purity can be measured by any appropriate method, e.g., column chromatography, polyacrylamide gel electrophoresis, or HPLC analysis. In one aspect, the invention features isolated polynucleotides wnich encode the MKKs of the invention. In one embodiment, the polynucleotide is the nucleotide sequence of SEQ ID NO : 1. In other embodiments, the polynucleotide is the nucleotide sequence of SEQ ID NO: 3, SEQ ID NO: 5, SEQ ID NO : 7 , SEQ ID NO : 9 , SEQ ID NO:l^, SEQ ID NO: 19, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, or SEQ ID NO:31, respectively. As used herein, "polynucleotide" refers to a nucleic acid sequence of deoxyriDonucleotides or ribonucleotides in the form of a separate fragment or a component of a larger construct. DNA encoding portions or all of the polypeptides of the invention can be assembled from cDNA fragments or from oligonucleotides that provide a synthetic gene which can be expressed m a recombinant transcriptional unit. Polynucleotide sequences of the invention include DNA, RNA, and cDNA sequences, and can be derived from natural sources or synthetic sequences synthesized by methods known to the art. An "isolated" polynucleotide is a nucleic acid molecule that s separated m some way from sequences m the naturally occurring genome cf an organism. Thus, the term "isolated polynucleotide" includes any nucleic acid molecules that are not naturally occuπng. The term therefore includes, for example, a recombinant polynucleotide wnich is incorporated into a vector, into an autonomously replicating plasmid or virus, or into the genomic DNA of a prokaryote or eukaryote, or which exists as a separate molecule independent of other sequences. It also includes a recomoinant DNA wiicn is part of a hybrid gene encoding additional polypeptide sequences. The isolated polynucleotide sequences of the invention also include polynucleotide sequences that hybridize under stringent conditions to the polynucleotide sequences specified herein. The term "stringent conditions" means hybridization conditions that guarantee specificity between hybridizing polynucleotide sequences, such as those described herein, or more stringent conditions. One skilled m tr.e art can select posthyoridizaticn washing conditions, including temperature and salt concentrations, which reduce the number of nonspecific hybridizations such that cnly highly complementary sequences are identified (Samorook et al. (1989) m Molecular Cloning, 2d ed. ; Cold Spring Harbor Laboratory Press, Cold Spring Harbor, NY. The isolated polynucleotide sequences of the invention also include sequences complementary to the polynucleotides encoding MKK (antisense sequences) . Antisense nucleic acids are DNA or RNA molecules that are complementary to at least a portion of a specific mRNA molecule ( emtraub (1990) Scientific American 262:40). The invention includes all antisense polynucleotides that inhibit production of MKK polypeptides. In the cell, the antisense nucleic acids hybridize to the corresponding mRNA, forming a double-stranded molecule. Antisense oligomers of about 15 nucleotides are preferred, since they are easily synthesized and introduced into a target MKK-producing cell. The use of antisense methods to inhibit the translation of genes is known in the art, and is described, e.g., in Marcus-Sakura Anal. Biochem., 172:289 (1988) . In addition, ribozyme nucleotide sequences for MKK are included in the invention. Ribozymes are RNA molecules possessing the ability to specifically cleave other single- stranded RNA m a manner analogous to DNA restriction endonucleases. Through the modification of nucleotide sequences encoding these RNAs, molecules can be engineered to recognize specific nucleotide sequences in an RNA molecule and cleave it (Cech (1988) J. Amer. Med. Assn. 260:3030). A major advantage of this approach is that, because they are sequence-specific, only mRNAs with particular sequences are inactivated. There are two basic types of ribozymes, tetrah mena-type (Hasselhoff (1988) Nature 334:555) and "hammerhead" -type . Tetrahymena- ype ribozymes recognize sequences which are four bases in length, while "hammerhead" -type ribozymes recognize base sequences Ills bases in length. The longer the sequence, the greater the likelihood that the sequence will occur exclusively in the target mRNA species. Consequently, hammerhead- type ribozymes are preferable to tetra.hy7r.ena-type ribozymes for inactivating a specific mRNA species, and 18 -base recognition sequences are preferable to shorter recognition sequences . The MKK polypeptides can also be used to produce antibodies that are immunoreactive or bind epitcpes of the MKK polypeptides. Accordingly, one aspect of the invention features antibodies to the MKK polypeptides of the invention. The antibodies of the invention include polyclonal antibodies which include pooled monoclonal antibodies with different epitopic specificities, as well as distinct monoclonal antibody preparations. Monoclonal antibodies are made from antigen-containing fragments of the MKK polypeptide by methods known m the art see, for example, Kohler et al . (1975) Nature 256:495). The term "antibody" as used herein includes intact molecules as well as fragments thereof, such as Fa, F(ab') 2 / an <3 Fv, which are capable of binding an epitopic determinant. Antibodies that specifically bind MKK polypeptides can be prepared using intact polypeptides or fragments containing small peptides of interest as the immunizing antigen. The polypeptide or peptide used to immunize an animal can be derived from translated cDNA or chemically synthesized, and can be conjugated to a carrier protein, if desired. Commonly used carriers that are chemically coupled to peptides include bovine serum albumin and thyroglobulin . The coupled peptide s then used to immunize the animal (e.g., a mouse, a rat, or a rabbit) . A molecule (e.g., antibody) that "specif cally binds" is one that binds to a particular polypeptide, e.g., MKK7, but that does not suostantially recogmze or bind to other molecules in a sample, e.g., a biological sample which includes MKK7. References to constructs made of an antibody (or fragment thereof) coupled to a compound comprising a detectable marker include constructs made by any technique, including chemical means and recombinant techniques. The invention also features methods of identifying subjects at risk for MKK-mediated disorders by measuring activation of the MKK signal transduction pathway. Activation of the MKK signal transduction pathway can be determined by measuring MKK synthesis; activation of MKK isoforms; activation of MKK substrates p38 or JNK isoforms; or activation of p38 and JNK substrates such as ATF2, ATFa, CRE-BPa, and c-Jun. The term "JNK" or "JNK isoforms" includes JNK1 , JNK2 , and JNK3. The term "MKK substrate" as used herein includes MKK substrates, as well as MKK substrate substrates, e.g., p38, JNK, ATF2 , and c-Jun. In one embodiment, activation of the MKK signal transduction pathway is determined by measuring activation of the appropriate MKK signal transduction pathway substrates (for example, selected from p38, JNK isoforms, ATF2 , ATFa, CRE-BPa, cr c-Jun). MKK activity is measured by the rate of substrate phosphorylation as determined by quantitation of the rate of labelled phosphorus (e.g., [ 32 ] P or [ 33 ]P) incorporation. This can also be measured using phosphorylation-specific reagents, such as antibodies . The specificity of MKK substrate phosphorylation can be tested by measuring p38 activation, JNK activation, or both, or by employing mutated p38 or JNK molecules that lack the sites for MKK phosphorylations . Altered phosphorylation of the substrate relative to control values indicates alteration of the MKK signal transduction pathway, and increased risk in a subject of an MKK-mediated disorder. MKK activation of p38 and JNK can be detected in a coupled assay with the MKK signal transduction substrate ATF2 , or related compounds such as ATFa and CRE-BPa. Activation can also be detected with the substrate c-Jun. When ATF2 is included in the assay, it is present as an intact protein or as a fragment of the intact protein, e.g., the activation domain (residues 1-109, or a portion thereof) . ATF2 is incubated with a test sample in which MKK activity is to be measured and [γ- 3 P]ATP, under conditions sufficient to allow the phosphorylation of ATF2. ATF2 is then isolated ana the amount of phosphorylation quantitated. In a specific embodiment, ATF2 is isolated by lmmunoprecipitation, resolved by SDS- PAGE, and detected by autoradicgraphy. In another embodiment, activation of the MKK signal transduction pathway is determined by measuring the level of MKK expression in a test sample. In a specific embodiment, the level of MKK expression is measured by Western blot analysis. The proteins present in a sample are fractionated by gel electrophoresis, transferred to a membrane, and probed with labeled antibodies to MKK In another specific emoodiment , the level of MKK expression is measured by Northern plot analysis. Total cellular or polyadenylated [poly (A)"] mRNA is isolated from a test sample. The RNA is fractionated by electrophoresis and transferred to a membrane. The emprane is probed with labeled MKK cDNA. In another embodiment, MKK expression is measured by quantitative PCR applied to expressed mRNA. The MKKs of the invention are useful for screening reagents that modulate MKK activity. MKKs are activated by phosphorylation. Accordingly, in one aspect the invention features metnods for identifying a reagent whicn modulates MKK activity, py incubating MKK with the test reagent and measuring the effect of the test reagent on MKK synthesis, phosphorylation, function, or activity. In one embodiment, the test reagent is incubatea with MKK and [ 3 ]P-ATP, and the rate of MKK phosphorylation determined, as described above. In another embodiment, the test reagent is incubated with a cell transfected with an MKK polynucleotide expression vector, and the effect of the test reagent on MKK transcription is measured by Northern blot analysis, as described above. In a further embodiment, the effect of the test reagent on MKK synthesis is measured by Western blot analysis using an antibody to MKK. In still another embodiment, the effect of a reagent on MKK activity is measured by incubating MKK with the test reagent, [ 32 ]P-ATP, and a substrate in the MKK signal transduction pathway, including one or more of p38, JNK, and ATF2. The rate of substrate phosphorylation is determined as described above . The term "modulation of MKK activity" includes inhibitory or stimulatory effects. The invention is particularly useful for screening reagents that inhibit MKK activity. Such reagents are useful for the treatment or prevention of MKK-mediated disorders, for example, inflammation and oxidative damage . The invention further features a method of treating a MKK-mediated disorder by administering to a subject in need thereof, an effective dose of a therapeutic reagent that inhibits the activity of MKK. An "MKK-mediated disorder" is a pathological condition resulting, at least in part, from excessive activation of an MKK signal transduction pathway. The MKK signal transduction pathways are activated by several factors, including inflammation and stress. MKK-mediated disorders include, for example, lschemic heart disease, burns due to heat or radiation (UV, X-ray, γ, β , etc.), kidney failure, liver damage due to oxidative stress or alcohol, respiratory distress syndrome, septic shock, rheumatoid arthritis, autoimmune disorders, and other types of inflammatory diseases. A "therapeutic reagent" any compound or molecule that achieves the desired effect on an MKK-mediated disorder when administered to a subject in need thereof. MKK-mediated disorders further include proliferative disorders, particularly disorders that are stress-related. Examples of stress-related MKK-mediated proliferative disorders are psoriasis, acquired immune deficiency syndrome, malignancies of various tissues of the body, including malignancies of the skin, bone marrow, lung, liver, breast, gastrointestinal system, and genito-uπnary tract. Preferably, therapeutic reagents inhibit the activity or expression of MKK inhibit cell growth or cause apoptosis. A therapeutic reagent that "inhibits MKK activity" interferes with a MKK-mediated signal transduction pathway. For example, a therapeutic reagent can alter the protein kinase activity of MKK, decrease the level of MKK transcription or translation, e.g., an antisense polynucleotide able to bind MKK mRNA, or suppress MKK phosphorylation of p38, JNK, or ATF2 , thus disrupting the MKK-mediated signal transduction pathway. Examples of such reagents include antibodies that bind specifically to MKK polypeptides, and fragments of MKK polypeptides that competitively inhibit MKK polypeptide activity. A therapeutic reagent that "enhances MKK activity" supplements a MKK-mediated signal transduction pathway. Examples of such reagents include the MKK polypeptides themselves, which can be administered in instances where the MKK-mediated disorder is caused by under expression of the MKK polypeptide, or expression of a mutant MKK polypeptide. In addition, portions of DNA encoding an MKK polypeptide can be introduced into cells that under express an MKK polypeptide. A "therapeutically effective amount" is an amount of a reagent sufficient to decrease or prevent the symptoms associated with the MKK-mediated disorder. Therapeutic reagents for treatment of MKK-mediated disorders identified by the methods of the invention are administered to a subject in a number of ways known to the art, including parenterally by injection, infusion, sustained-release injection or implant, intravenously, intraperitoneally, intramuscularly, subcutaneously, or transdermally. Epidermal disorders and disorders of the epithelial tissues are treated by topical application of the reagent. The reagent is mixed with other compounds to improve stability and efficiency of delivery (e.g., liposomes, preservatives, or dimethyl sulfoxide (DMSO)). Polynucleotide sequences, including antisense sequences, can be therapeutically administered by techniques known to the art resulting in introduction into the cells of a subject suffering from the MKK-mediated disorder. These methods include tne use of viral vectors (e.g., retrovirus, adenovirus, vaccinia virus, or herpes virus), colloid dispersions, and liposomes. The materials of the invention are ideally suited for the preparation of a kit for the detection of the level or activity of MKK. Accordingly, the invention features a kit comprising an antibody that binds MKK, or a nucleic acid probe that hybridizes to a MKK polynucleotide, and suitable buffers. The probe or monoclonal antibody can be labeled to detect binding to a MKK polynucleotide or protein. In a preferred embodiment, the kit features a labeled antibody to MKK. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. All publications, patent applications, patents, and other references mentioned herein are incorporated by reference in their entirety. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting. Other features and advantages of the invention will be apparent from the detailed description, and from the claims. Detailed Description The drawings will first be described. Drawings Fig. 1 is a comparison of the amino acid sequences of MKK3 (SEQ ID NO : 2 ) , MKK4-α (SEQ ID NO:6), the human MAP kinase kinases MEK1 (SEQ ID NO: 11) and MEK2 (SEQ ID NO.12), and the yeast HOGl MAP kinase kinase PBS2 (SEQ ID NO:13). Sequences were compared using the PILE-UP program (version 7.2; Wisconsin Genetics Computer Group). The protein sequences are presented in single letter code (A, Ala; C, Cys; D, Asp; E, Glu; F, Phe; G, Gly; H, His; I, lie; K, Lys; L, Leu; M, Met; N, Asn; P, Pro; Q, Gin; R, Arg; S, Ser; T, Thr; V, Val; W, Trp, and Y, Tyr) . The PBS2 sequence is truncated at both the NH 2 - (<) and COOH- (>) termini. Gaps introduced into the sequences to optimize the alignment are illustrated by a dash. Identical residues are indicated by a period. The sites of activating phospnoryiation ιr_ MEK are indicated by asterisks . Fig. 2A is a dendrogram showing the relationship between members of the human and yeast MAP kinase kinases. The dendrogram was created by the unweighted pair-group method with the use of arithmetic averages (PILE-UP program) . The human t,hu) MAP kinase kinases MEK1, MEK2, MKK3, and MKK4 ; the Saccharomyces cβrevisiae (sc) MAP kinase kinases PBS2 , MKK1 , and STE7 ; and the Saccharomyces pombe (sp) MAP kinase kinases WISl and BYRl are presented. Fig. 2B is a dendrogram showing the relationship between MKKs . The dendrogram was created as described for Fig. 2A. Fig. 3 is a schematic representation of the ERK, p38, and JNK signal transduction pathways. MEK1 and MEK2 are activators of the ERK subgroup of MAP kinase. MKK3 and MKK4 are activators of the p38 MAP kinase. MKK4 is identified as an activator of bcth the p38 and JNK subgroups of MAP kinase. Figs. 4A-4D are a representation of the nucleic acid (SEQ ID NO:l) and amino acid sequences (SEQ ID NO: 2) for MKK . Figs. 5A-5C are a representation of the nucleic acid (SEQ ID NO: 3) and amino acid sequences (SEQ ID NO: 4) for MKK6. Figs. 6A-6F are a representation of the nucleic acid (SEQ ID NO: 5) and amino acid sequences (SEQ ID NO: 6) Figs. 7A-7F are a representation of the nucleic acid (SEQ ID NO: 7) and amino acid sequences (SEQ ID NO: 8) for MKK43. Figs. 8A-8F are a representation of the nucleic acid (SEQ ID NO: 9) and amino acid sequences (SEQ ID NO: 10) for MKK47- Fig. 9 is a representation of the deduced primary structure cf MKK7 (SEQ ID NO: 18) compared with hep (SEQ ID NO:21) , the MAP kinase kinases MEK1 (MKK1; SΞQ ID NO: 11), MEK2 (MKK2 ; SEQ ID N0.12), MKK3 (SEQ ID O:2), MKK4γ (SEQ ID NO:10), MKK5 (SEQ ID NO:22), and MKK6 (SEQ ID NO:4) using the PILE-UP program (version 7,2; Wisconsin Genetics Computer Group) . Gaps introduced into the sequences to optimize the alignment are illustrated with a dash (-) . Identity is indicated with a dot (.) . The sites of activating phosphorylation of MAP kinase kinases (2, 27, 37, and 38) are indicated with asterisks (*) • Figs. 10A-10D are a representation of the nucleic acid (SEQ ID NO: 17) and amino acid (SEQ ID NO: IS) sequences for MKK7. Figs. 11A-11D are a representation of the nucleic acid (SEQ ID NO: 19) and ammo acid (SEQ ID NO:2C* sequences of MKK7b. Figs. 12A-12B are a representation of the nucleic acid (SEQ ID NO: 25) and ammo acid (SEQ ID NO: 26) sequences of human MKK7. Figs. 13A-13D are a representation of the nucleic acid (SEQ ID NO:27) and ammo acid (SEQ ID NO:28) sequences of murine MKK7c . Figs. 14A-14D are a representation of the nucleic acid (SEQ ID NO: 29) and ammo acid (SEQ ID NO: 30) sequences of murine MKK7d. Figs. 15A-15D are a representation of the nucleic acid (SEQ ID NO:31) and ammo acid (SEQ ID NO:32) sequences of murine MKK7e. Fig. 16A is a graph of data from a transfection assay in which cells were co-transfected with AP-1 reporter plasmid pTRE-Luciferase with expression vectors for MKK4, MKK7, JNK1, JNK1 (APF) , or control vector. Fig. 16B is a graph of a transfection assay in which cells were co-transfected witn a GAL4-ATF2 fusion vector and an expression vector for MKK4 , MKK7 , JNK1 , JNK1 (APF) , or control vector. Human Mitogen-Activated Protein Kinase Kinases The numan MAP kinase kinases MKK3 and MKK4 (MKK3/4) , and MKK7 , described herein mediate the transduction of specific signals from the cell surface to the nucleus along specific pathways. These signal transduction pathways are initiated by factors such as cytok es, UV radiation, osmotic shock, and oxidative stress. Activation of MKK3/4, MKK6 , and MKK7 results in activation of the MAP kinases. p38 is activated by MKK3 and MKK4. JNK is activated by MKK4 and MKK7. p38 and JNK in turn activate a group of related transcription factors such as ATF2 , ATFa, and CRE-BPa. These transcription factors in turn activate expression of specific genes. For example, ATF2 in known to activate expression of human T cell leukemia virus 1 (Wagner and Green ,1993) Science 262:395), transforming growth factor-b2 (Kim et al. (1992) supra) , terferon-0 (Du et al . (1993) Cell 74:887), and E-seiectin (DeLuca et al . (1994) J. Biol. Chem. 269:19193). In addition, ATF2 is implicated in the function of a T ceil -speci ic ennancer (Georgopculos et al. 1992) Mol. Cell. Biol. 12:747) . The JNK group of MAP kinases is activated by exposure of cells to environmental stress or by treatment of cells with pro- inflammatory cytokmes (Gupta et al . (1994) EMBO J. 15:2760-2770; Derijard et al . (1991) Cell 76:1025-1037; Kyπakis et al . (1994) Nature 369:156-160; Sluss et al. (1994) Mol. Cell. Biol . 14:8376-8384; Kallunki et al . (1994) Genes & Dev. 8:2996-3007). Targets of the JNK signal transduction pathway include the transcription factors ATF2 and c-jun (Whitmarsh & Davis (1996) J. Mol. Med. "4 : 589-607) . These transcription factors are members of the bZIP group that bind as homo- and hetero-dimeric complexes to AP-1 and AP-1-like sites the promoters of many genes (Curran & Franza (1988) Cell 55:395-397) . JNK binds to an NH 2 - termmal region of ATF2 and c-Jun and phosphorylates two sites within the activation domain of each transcription factor (Derijard et al . (1994) Cell 76:1025-1037; van Dam et al. (1995) EMBO J. 14:1798-1811; Livingstone et al . (1995) EMBO J. 14:1785-1797). This phosphorylation leads to increased transcriptional activity (Whitmarsh, supra) . Together, these biochemical studies indicate that the JNK signal transduction pathway contributes to the regulation of AP-1 transcriptional activity in response to cytok es and environmental stress (Whitmarsh, supra) . Strong support for this r.ypothesis is provided by genetic evidence indicating that the JNK signaling pathway is required for the normal regulation of AP-1 transcriptional activity (Yang et al . (1997) Proc. Natl. Acad. Sci. USA, 94:3004-3009). JNK is activated by dual pnosphorylation on Thr- 183 and Tyr-185 (Derijard, supra) . MKK4 (also known as SEKI) was the first MAP kinase Kinase identified as a component of the JNK signal transduction pathway (Derijard et a__ . 1995; Science 267:682-685; Lin et al . (1995) Science 268:286-290; Sancnez et al . (1994) Nature 372:794-798). 3ιocnemιcal studies demonstrate that MKK4 phosphorylates and activates JNK (Derijard et al . (1995) Science 267:682-685; L et al . (1995) Science 268:286- 290; Sanchez et al . (1994) Nature 372:794-798). However, the function of MKK4 may not be restricted to the JNK signal transduction pathway because MKK4 also phosphorylates ana activates p38 MAP kinase (Derijard et al . (1995) Science 267:682-685; Lin et al . (1995) Science 268:286-290). This specificity of MKK4 to activate ooth JNK and p38 MAP Kinase provides a mechanism that may account for the co-orαinate activation of tnese MAP Kinases in cells treated with cytoKines or environmental stress (Davis (1994) Trends Biocnem. Sci. 19:470-473). However, this co-ordinate activation is not always observed. For example, JNK activation in the liver correlates with decreased p38 MAP kinase activity (Mendelson et al. '1996) Proc. Natl. Acad. Sci. USA 93:12908-12913). These data suggest that the properties of MKK4 are insufficient to account for the regulation of The isolation of human MKKs is described in Example 1, Example 22, Derijard et al . ((1995) Science 267:682-685, hereby specifically incorporated by reference), and Raingeaud et al. ((1995) Mol. Cell. Biol. 16:1247-1255). Distinctive regions of the yeast PBS2 sequence were used to design polymerase chain reaction (PCR) primers. Amplification of human brain mRNA with these primers resulted in the formation of specific products which were cloned into a plasmid vector and sequenced. Two different complementary DNAs (cDNAs) that encoded human protein kinases were identified: one encoding a 36 kD protein (MKK3), and one encoding a 44 kD protein (MKK4) . MKK4 includes 3 isoforms that vary sligntly at the NH 2 - terminal , identified as a , β , and γ. The am o acid sequences of MKK3 (SEQ ID NO:2), MKK4-α (SEQ ID NO.-6), MKK4-3 (SEQ ID NO:8), and MKK4-γ (SEQ ID NO: 10) are shown in Fig. 1. The nucleic acid and ammo acid sequences of MKK3 (Fig. 4), MKK6 (Fig. 5), MKK4-α (Fig. 6), MKK4-S (Fig. 7), and MKK4-γ (Fig. 8) are also provided. MKK6 was isolated from a human skeletal muscle library by cross-hybridization with MKK3. Except for differences at the N-termmus, MKK6 is highly homologous to MKK3. Other human MKK3 and MKK4 isoforms that exist can be identified by the method described in Example 1. The expression of tnese numan MKK isoforms was examined by Northern (RNA) plot analysis of mRNA isolated from eight adult human tissues (Example 2) . Botn protein kinases were found to be widely expressed human tissues, with the highest expression seen in skeletal muscle tissue. The substrate specificity of MKK3 was investigated in an in vi tro phosphorylation assay with recombinant epitope-tagged MAP kinases (JNK1, p38, and ERK2) as substrates (Example 3). MKK3 phosphorylated p38, but did not phosphorylate JNK1 or ERK2. Phosphoammoacid analysis of p38 demonstrated the presence of a phosphothreonme and phosphotyrosme. Mutational analysis of p38 demonstrated that replacement of phosphorylation sites Thr 180 and Tyr 132 with Ala and Phe, respectively, blocked p38 phosphorylation. These results establish that MKK3 functions in vi tro as a p38 MAP kinase kinase. Studies of the in vi tro substrate specificity of MKK4 are described in Example 4. MKK4 incubated with [γ- 32 P]ATP, and JNK1 , p38, or ERK2 was found to phosphorylate both p38 and JNK1. MKK4 activation of JNK and p38 was also studied by incubating MKK4 with wild-type or mutated JNK1 or p38. The p38 substrate ATF2 was included in each assay. MKK4 was found to exhibit less autophosphorylation than MKK3. MKK4 was also found to be a substrate for activated MAP kinase. Unlike MKK3 , MKK4 was also found to activate JNK1. MKK4 incubated with wild-type JNK1 , but not mutated JNK1 , resulted in increased phosphorylation of ATF2. These results establish that MKK4 is a p38 MAP kinase kinase that also phosphorylates the JNK subgroup of MAP kinases . In vivo activation of p38 by UV-stimulated MKK3 is described in Example 5. Cells expressing MKK3 were exposed in the presence or absence of UV radiation. MKK3 v/as isolated by lmmunoprecipitation and used fcr protein kinase assays with the substrates p38 or JNK. ATF2 was included in some assays as a substrate for p38 and JNK. MKK3 from non-activated cultured COS cells caused a small amount of phosphorylation of p38 MAP kinase, resulting from basal activity of MKK3. MKK3 from UV- irradiated cells caused increased phosphorylation of p38 MAP kinase, but not of JNK1. An increase in p38 activity was also detected in assays in which ATF2 was included as a substrate. These results establish that MKK3 is activated by UV radiation. The effect of expression of MKK3 and MKK4 on p38 activity was examined in COS-1 cells (Example 6) . Cells were transfected with a vector encoding p38 and a MEK1, MKK3 , or MKK4. Some of the cells were also exposed to EGF or UV radiation. p38 was isolated by immunoprecipitation and assayed for activity with [γ- 32 P]ATP and ATF2. The expression of the ERK activator MEK1 did not alter p38 pnosphorylation of ATF2. In contrast, expression of MKK3 or MKK4 caused increased activity of p38 MAP kinase. The activation of p38 caused by MKK3 and MKK4 was similar to that observed UV- irradiated cells, and was much greater than that detected in EGF- reated cells. These m vi tro results provide evidence that MKK3 and MKK4 activate p38 m vivc . A series of experiments was conducted to examine the potential regulation of ATF2 by JNK1. These experiments are described in Gupta et al . (1995) Science 267:389-393, herepy specifically incorporated by reference. The effect of UV radiation on ATF2 phosphorylation was investigated COS-1 cells transfected with and without epitope-tagged JNK1 (Example 7) . Cells were exposed to UV radiation, and JNK1 and JNK2 visualized by -gel protein kinase assay with the substrate ATF2. JNK1 and JNK2 //ere detected in transfected and non-transfected cells exposed tc UV radiation; nowever, JNK1 levels were higher in tne transfected cells. These results demonstrate that ATF2 is a substrate for the JNK1 and JNK2 protein kinases, and that these protein kinases are activated in cells exposed to UV light. The site of JNK1 phosphorylation of ATF2 was examined by deletion analysis (Example 8) . Progressive NH 2 - terminal domain deletion GST-ATF2 fusion proteins were generated, and phosphorylation by JNK1 isolated from UV- lrradiated cells was examined. The results showed that JNK1 requires the presence of ATF2 residues 1-60 for phosphorylation of the NH 2 -terminal domain of ATF2. The ATF2 residues required for binding of JNK1 were similarly examined. JNK1 was incubated with immobilized ATF2 , unbound JNK1 was removed by extensive washing, and bound JNK1 was detected by incubation with [γ- 32 p]ATP. Results indicate that residues 20 to 60 of ATF2 are required for binding and phosphorylation by JNK1. A similar binding interaction between ATF2 and the 55 kD JNK2 protein kinase has also been observed. Phosphorylation by JNK1 was shown to reduce the electrophoretic mobility of ATF2 (Example 9) . Phosphoamino acid analysis of the full-length ATF2 molecule (residues 1-505) demonstrated that JNK phosphorylated both Thr and Ser residues. The major sites of Thr and Ser phosphorylation were located in the NH 2 and COOH terminal domains, respectively. The NH 2 - terminal sites of phosphorylation were identified as Thr 69 and Thr 71 by phosphopeptide mapping and mutational analysis. These sites of Thr phosphorylation are located in a region of ATF2 that is distinct from the sub-domain required for JNK binding (residues 20 to 60) . The reduced electrophoretic mobility seen with phosphorylation of ATF2 was investigated further (Example 10) . JNK1 was activated m CHO cells expressing JNK1 by treatment with UV radiation, pro- inflammatory cytokine mterleukin-1 (IL-1), or serum. A decreased electrophoretic mobility of JNK1-activated ATF2 was observed in cells treated with UV radiation and IL-1. Smaller effects were seen after treatment of cells with serum. These results indicate that ATF2 is an in vivo substrate for JNK1. The effect of UV radiation on the properties of wild-type (Thr 63 ' 71 ) and phosphorylation-defective (Ala 69 ' 71 ) ATF2 molecules was investigated (Example 11) . Exposure to UV caused a decrease in the electrophoretic mobility of both endogenous and over-expressed wild-type ATF2. This change in electrophoretic mobility was associated with increased ATF2 phosphorylation. Both the electrophoretic mobility shift and increased phosphorylation were blocked by the replacement of Thr 69 Ξ and Thr 71 with Ala ATF2. This mutation also blocked the phosphorylation of ATF2 on Thr residues in vivo . Transcriptional activities of fusion proteins consisting of the GAL4 DNA binding domain and wild-type or mutant ATF2 were examined (Example 12) . Point 0 mutations at Thr 69 and/or Thr 71 of ATF2 significantly decreased the transcriptional activity of ATF2 relative to the wild- type molecule, indicating the physiological relevance cf phospnorylation at these sites for activity. The binding of JNK1 to the NH 2 -terminal activation domain of ATF2 [described in Example 8) suggested that a catalytically inactive JNK1 molecule could function as a dominant inhibitor of the wild-type JNK1 molecule. This hypothesis was investigated by examining the effect of a catalytically inactive JNK1 molecule on ATF2 function (Example 13) . A catalytically- inactive JNK1 mutant was constructed by replacing the sites of activating Thr 133 and Tyr 185 phospnorylation with Ala and Phe, respectively (Ala 1S3 , Phe :5S , termed " dominant -negative" ) . Expression of wild-type JNK1 caused a small increase in serum- stimulated ATF2 transcriptional activity. In contrast, dominant -negative JNK1 inhibited both control and serum- stimulated ATF2 activity. This inhibitory effect results from the non-productive binding of the JNK1 mutant to the ATF2 activation domain, effectively blocking ATF2 phosphorylation. The tumor suppressor gene product Rb binds to ATF2 and increases ATF2-stimulated gene expression (Kim et al . (1992) Nature 358:331). Similarly, the adenovirus oncoprotein ElA associates with the DNA binding domain of ATF2 and increases ATF2 -stimulated gene expression by a mechanism that requires the NH 2 -terminal activation domain of ATF2 (Liu and Green (1994) Nature 368:520). ATF2 transcriptional activity was investigated with the luciferase reporter gene system in control, Rb-treated, and ElA-treated cells expressing wild-type or mutant ATF2 molecules (Example 14) . Rb and ElA were found to increase ATF2 -stimulated gene expression of both wild- type and mutant ATF2. However, mutant ATF2 caused a lower level of reporter gene expression than did wild- type ATF2. Together, these results indicate a requirement for ATF2 phosphorylation (on Thr 69 and Thr 71 ) plus either Rb or ElA for maximal transcriptional activity. Thus, Rb and ElA act in concert with ATF2 phosphorylation to control transcriptional activity. A series of experiments were conducted to examine the action of p38 activation and to establish the relationship of the p38 MAP kinase pathway to the ERK and JNK signal transduction pathways (Raingeaud et al . (1995) J. Biol. Chem. 270:7420, hereby specifically incorporated by reference) . Initially, the substrate specificity of p38 was investigated by incubating p38 with proteins that have been demonstrated to be substrates for the ERK and/or JNK groups of MAP kinases (Example 15) . We examined the phosphorylation of MBP (Erickson et al . (1990) J. Biol. Chem. 265:19728), EGF-R (Northwood et al . (1991) J. Biol. Chem. 266:15266), cytoplasmic phospholipase A, (cPLA 2 ) (Lin et al . (1993) Cell 72:269), c-Myc (Alvarez et al . (1991) J. Biol. Chem. 266:15277), I/_B, c-Jun, and wild-type (Thr 69 ' 71 ) or mutated (Ala 69 - 71 ) ATF2. p38 phosphorylated MBP and EGF-R, and to a lesser extent I κB , but not the other ERK substrates, demonstrating that the substrate specificity of p38 differs from both the ERK and JNK groups of MAP kinases. Wild-type ATF2 , but not mutated ATF2 (Ala 69,71 ), was found to be an excellent p38 substrate. The phosphorylation of ATF2 by p38 was associated with an electrophoretic mobility shift of ATF2 during polyacrylamide gel electrophoresis. We tested the hypothesis that p38 pnosphorylates ATF2 at the same sites as JNK1 by replacing Thr 69 and Thr" with Ala (Ala 69 ' 71 ) . It was found that p38 did not phospnorylate mutated ATF2 , which demonstrates that p38 phosphorylates ATF2 within the NH 2 -terminal activation domain on Thr 69 and Thr 71 . A comparison of the binding of JNK and p38 to ATF2 was conducted by incubating extracts of cells expressing JNK1 or p38 with epitope alone (GST) or GST-ATF2 (residues 1-109 containing the activation domain) (Example 16) . Bound protein kinases were detected by Western blot analysis. The results demonstrate that both p38 and JNK bind to the ATF2 activation domain. EGF and phorbol ester are potent activators of the ERK signal transduction pathway (Egan and Wemberg (1993) Nature 365:781), causing maximal activation of tr.e ERK sub-group of MAP kinases. These treatments, however, cause only a small increase in JNK protein kinase activity (Derijard et al . (1994) supra ; Hibi et al . (1993) supra) . The effects of EGF or phorbol esters, as well UV radiation, osmotic snocκ, mterleukιn-1 , tumor necrosis factor, and LPS , on p38 activity were ail tested (Example 17) . Significantly, EGF and phorbol ester caused only a modest increase m p38 protein kinase activity, whereas environmental stress (UV radiation and osmotic shock) caused a marked increase in the activity of both p38 and JNK. Both p38 and JNK were activated in cells treated with pro- inflammatory cytokines (TNF and IL-1) or endotoxic LPS. Together, these results indicate that p38, like JNK, is activated by a stress-induced signal transduction pathway. ERKs and JNKs are activated by dual phosphorylation within the motifs Thr-Glu-Tyr and Thr- Pro-Tyr, respectively. In contrast, p38 contains the related sequence Thr-Gly-Tyr. To test whether t is motif is relevant to the activation of p38, the effect of the replacement of Thr-Gly-Tyr with Ala-Gly-Phe was examined (Example 18) . The effect of UV radiation on cells expressing wild-type (Thr 130 , Tyr 132 ) or mutant p38 (Ala 180 , Phe 182 ) was studied. Western blot analysis using an anti-phosphotyrosme antibody demonstrated that exposure to UV radiation caused an increase in the Tyr phospnorylation of p38. The increased Tyr phosphorylation was confirmed by phosphoammo acid analysis of p38 isolated from [γ- 32 P] phospnate-labeled cells. This analysis also demonstrated that UV radiation caused increased Thr phospnorylation of p38. Significantly, the increased phosphorylation on Thr 180 and Tyr 132 was blocked by the Ala 180 /Phe 182 mutation. This result demonstrates that UV radiation causes increased activation of p38 by dual phospnorylation. It has recently been demonstrated that ERK activity is regulated by the mitogen-induced dual specificity phospnatases MKP1 and PAC1 (Ward et al . (1994) Nature 367:651). The activation of p38 by dual phospnorylation (Example 18) raises the possibility that p38 may also be regulated by dual specificity pnosphatases . We examined the effect of MKP1 and PAC1 on p38 MAP kinase activation (Example 19) . Cells expressing human MKP1 and PAC1 were treated with and without UV radiation, and p38 activity measured. The expression of PAC1 or MKP1 was found to inhibit p38 activity. The inhibitory effect of MKP1 was greater than PAC1. In contrast, cells transfected with a catalytically inactive mutant phosphatase (mutant PAC1 Cys 257 /Ser) did not inhibit p38 MAP kinase. These results demonstrate that p38 can be regulated by dual specificity phosphatases PAC1 and MKP1. The sub-cellular distribution of p38 MAP kinase was examined by indirect mmunofluorescence microscopy (Example 20) . Epitope-tagged p38 MAP kinase was detected using the M2 monoclonal antibody. Specific staining of cells transfected with epitope-tagged p38 MAP kinase was observed at the cell surface, m the cytoplasm, and in the nucleus. Marked changes in cell surface and nuclear p38 MAP kinase were not observed following UV irradiation, but an increase in the localization of cytoplasmic p38 MAP kinase to the permuclear region was detected. A series of experiments were conducted to study the activation of JNK by hyper-csmotic media (Example 21) . These experiments were reported by Galcheva-Gargova et al . (1994) Science 265:806, hereby specifically incorporated by reference. CHO cells expressing epitope- tagged JNK1 were incubated with 0 - 1000 mM sorbitol, and JNK1 activity measured in an immune complex kinase assay with the substrate c-Jun. Increased JNK1 activity was observed m cells incubated for 1 hour with 100 mM sorbitol. Increased JNK1 activity was observed within 5 minutes of exposure to 300 mM sorbitol. Maximal activity was observed 15 to 30 minutes after osmotic shocκ with a progressive decline m JNK1 activity at later times. The activation of JNK by osmotic shock was studied m cells expressing wild-type (Thr 183 , Tyr *35 ) or mutated (Ala 133 , Phe 135 ) JNK1. JNK1 activity was measured after incubation for 15 minutes with or without 300 mM sorbitol. Cells expressing wild-type JNK1 showed increased JNK1 activity, while cells expressing mutated JNK1 did not. These results demonstrate that the JNK signal transduction pathway is activated in cultured mammalian cells exposed to hyper-osmotic media. The results of the above-described experiments are illustrated in Fig. 3, which diagrams the ERK, p38, and JNK MAP kinase signal transduction pathways. ERKs are potently activated by treatment of cells with EGF or phorbol esters. In contrast, p38 is only slightly activated under these conditions (Example 15) . However, UV radiation, osmotic stress, and inflammatory cytokines cause a marked increase in p38 activity. This difference in the pattern of activation of ERK and p38 suggests that these MAP kinases are regulated by different signal transduction pathways. The molecular basis for the separate identity of these signal transduction pathways is established by the demonstration that the MAP kinase kinases that activate ERK (MEK1 and MEK2 ) and p38 (MKK3 , MKK4, and MKK6) are distinct. The isolation of murine and human MKK7 s described in Example 22. Distinctive regions of the Drosophila MAP kinase kinase hep sequence were used to design polymerase chain reaction (PCR) primers. Amplification of murine testis mRNA with these primers resulted in the formation of specific products which were cloned into a plasmid vector and sequenced. One sequence related to hep was identified and used to screen a murine testis library. Five DNAs (cDNAs) that encoded protein kinases were identified: one encoding a MAP protein kinase kinase (MKK7) . The others encoded various splice variants: MKK7b (a partial sequence appears in Fig. 11), MKK7c (Fig. 13), MKK7d (Fig. 14), MKK7e (Fig. 15). The deduced amino acid sequences of MKK7 (SEQ ID NO: 18) and hep (SEQ ID NO: 21) are shown in Fig. 9, and compared to the MAP kinase kinases MEK1 (SEQ ID NO: 11), MEK2 (SEQ ID NO:12), MKK3 (SEQ ID NO : 2 ) , MKK4 (SEQ ID NO:10), MKK5 (SEQ ID NO: 22) , and MKK6 (SEQ ID NO: 4) . A human MKK7 was identified by screening a human cDNA library with a full- length (mouse) MKK7 cDNA probe. The identified partial sequence (lacking the 3 'end) is homologous to mouse MKK7c . The expression of MKK7 and MKK4 isoforms was examined by Northern (RNA) blot analysis of poly A+ mRNA isolated from eight murine tissues (Example 23) . Both protein kinases were found to be widely expressed. The substrate specificity of MKK7 was investigated in an in vi tro phosphorylation assay with recombinant, epitope-tagged MAP kinases (JNK1, p38, and ERK2) as substrates (Example 24) . MKK7 phosphorylated JNK, but did not phosphorylate p38 or ERK2. MKK7 was phosphorylated by p38 and JNK1. MKK7 was found to specifically activate JNK protein kinase in vivo (Example 25) . CHO cells were co- transfected with an epitope-tagged MAP kinase (JNK1, p38, or ERK2 ) together with an empty expression vector or an expression vector encoding MKKl, MKK4 , MKK6, or MKK7 and the product of the phosphorylation reaction analyzed. MKK7 activated only JNK1 , and did so to a greater extent than did MKK . To test whether MKK7 could cause increased AP-1 transcriptional activity, a co-transfection assay was employed (Example 26) . Co-expression of MKK7 with JNK caused an increase in AP-1 reporter gene expression that was greater than the increase seen with MKK4 and JNK. A similar result was seen when ATF2 was used as the reporter gene. In addition, MKK7 alone was able to increase expression of ATF2 (Fig. 16) . MKK isoforms are useful for screening reagents which modulate MKK activity. Described in the Use section following the Examples are methods for identifying reagents capable of inhibiting or activating MKK activity. The discovery of human MKK isoforms and MKK- mediated signal transduction pathways is clinically significant for the treatment of MKK-mediated disorders. One use of the MKK isoforms is in a method for screening reagents able to inhibit or prevent the activation of the MKK-MAP kinase- ATF2 pathways. EXAMPLES The following examples are meant to illustrate, not limit, the invention. Example 1. MKK Protein Kinases The primary sequences of MKK3 and MKK4 were deduced from the sequence of cDNA clones isolated from a human fetal brain library. The primers TTYTAYGGNGCNTTYTTYATHGA (SEQ ID NO: 14) and ATBCTYTCNGG GCCATKTA (SEQ ID NO: 15) were designed based on the sequence of PBS2 (Brewster et al . (1993) Science 259:1760; Maeda et al . ;1994) Nature 369:242). The primers were used in a PCR reaction with human brain mRNA as template. Two sequences that encoded fragments of PBS2 -related protein kinases were identified. Full- length human cDNA clones were isolated by screening of a human fetal brain library (Derijard et al . (1995) Science 267:682-685) . The cDNA clones were examined by sequencing with an Applied Biosystems model 373A machine. The largest clones obtained for MKK3 (2030 base pairs (bp) ) and MKK4 3576 bp) contained the entire coding region of these protein kinases. The primary structures of MKK3 (SEQ ID NO : 2 ) and MKK4-C. (SEQ ID NO : 6 ) are shown in Fig. 1. An in-frame termination codon is located in the 5' untranslated region of the MKK3 cDNA, but not in the 5' region of the MKK4 cDNA. The MKK4 protein sequence presented starts at the second in-frame initiation codon. These sequences were compared to those of the human MAP kinase kinases MEK1 (SEQ ID NO: 11) and MEK2 (SEQ ID NO: 12) (Zheng and Guan (1993) J. Biol. Chem 268:11435) and of the yeast MAP kinase kinase PBS2 (SEQ ID NO: 13) (Boguslawaski and Polazzi (1987) Proc. Natl. Acad. Sci. USA 84:5848) (Fig. 1). The identity and similarity of the kinases with human MKK3 (between subdomains I and XI) were calculated with the BΞSTFIT program (version 7.2; Wisconsin Genetics Computer Group) (percent of identity to percent of similarity) : MEK1, 41%/63%; MEK2, 41%/62%; MKK4α, 52%/73%; and PBS2 , 40%/59%) . The identity and similarity of the kinases with human MKK4α. were calculated to be as follows (percent of identity to percent of similarity) : MEK1, 44%/63%; MEK2 , 45%/61%; MKK3 , 52%/73%; and PBS2 , 44%/58%. The cDNA sequences of MKK3 and MKK4γ have been deposited in GenBank with accession numbers L36719 and L36870, respectively. The MKK4γ cDNA sequence contains both the cDNA sequences of MKK4α and MKK4/3, which are generated in vivo from alternate splicing sites. One of ordinary skill in the art can readily determine the amino acid sequences of MKK3 and MKK4 isoforms from the deposited cDNA sequences. Example 2. Expression of MKK3 and MKK4 mRNA in Adult Human Tissue Northern blot analysis was performed with polyadenylated [poly (A) * ] mRNA [ 2 μg) isolated from human heart, brain, placenta, lung, liver, muscle, kidney, and pancreas tissues. The mRNA was fractionated by denaturing agarose gel electrophoresis and was transferred to a nylon membrane. The blot was probed with the MKK3 and MKK4 cDNA labeled by random priming with [c.- 32 P]ATP (deoxyadenosine triphosphate) (Amersham International PLC) . MKK3 and MKK4 were expressed in all tissues examined; the highest expression of MKK3 and MKK4 was found in skeletal muscle tissue. The relation between members of the human and yeast MAP kinase kinase group is presented as a dendrogram (Fig. 2) . MKK3/4 form a unique subgroup of human MAP kinase kinases . Example 3. In Vi tro Phosphorylation of P38 MAP kinase by MKK3 GST-JNK1, and GST-ERK2 have been described (Derijard et al. (1994) supra ; Gupta et al . (1995) Science 267:389; Wartmann and Davis (1994) J. Biol. Chem. 269:6695, each herein specifically incorporated by reference) . GST-p38 MAP kinase was prepared from the expression vector pGSTag (Dressier et al . (1992) Biotechniques 13:866) and a PCR fragment containing the coding region of the p38 MAP kinase cDNA. GST-MKK3 and MKK4 were prepared with pGEX3X (Pharmacia-LKB Biotechnology) and PCR fragments containing the coding region of the MKK3 and MKK4 cDNAs . The GST fusion proteins were purified by affinity chromatography with the use of GSH-agarose (Smith and Johnson (1988) Gene 67:31) . The expression vectors pCMV-Flag-JNKl and pCMV- MEK1 have been described (Derijard et al . (1994) supra ; Wartmann and Davis (1994) supra) . The plasmid pCMV-Flag- p38 MAP kinase was prepared with the expression vector pCMVS (Andersson et al . (1989) J. Biol. Chem. 264:8222) and the p38 MAP kinase cDNA. The expression vectors for MKK3 and MKK4 were prepared by subclon g of the cDNAs into the polylmker of pCDNA3 (Invitrogen) . The Flag epitope (Asp-Tyr-Lys-Asp-Asp-Asp-Asp-Lys (SEQ ID NO:16); Immunex, Seattle, WA) was inserted between codons 1 and 2 of the kinases by msertional overlapping PCR (Ho et al . (1989) Gene 77:51) . Protein kinase assays were performed in kinase buffer (25 mM 4- (2 -hydroxyethyl) -1- piperazmeethansulfonic acid, pH 7.4 , 25 m /.- glycerophosphate, 25 mM MgCl 2 , 2 mM dithiothreitol , and 0.1 mM orthovanadate) . Recombinant GST-MKK3 was incubated with [γ- 32 P]ATP and buffer, GST-JNKl, -3T-p38 MAP kinase, or GST-ERK2. The assays were initiated by the addition of 1 μg of substrate proteins and 53 μM [γ- 32 P]ATP (10 Ci/mmol) a final volume of 25 μl . The reactions were terminated after 30 minutes at 25°C by addition of Laemmli sample buffer. The phosphorylation of the substrate proteins was examined after SDS- polyacrylamide gel electrophoresis (SDS-PAGE) by autoradiography. Phospnoammoacid analysis was performed by partial acid hydrolysis and thm- layer chromatography (Derijard et al . (1994) supra ; Alvarez et al . (1991) J. Biol. Chem. 266:15277) Autopnosphorylation of KK3 was observed m all groups. MKK3 pnosphorylated p38 MAP kinase, but not JNK1 or ERK2. A similar sertional overlapping PCR procedure was used to replace Thr 180 and Tyr 182 of p38, with Ala and Phe, respectively. The sequence of all plasmids was confirmed by automated sequencing on an Applied Biosystems model 373A machine. GST-MKK3 was incubated with [γ- 32 P]ATP and buffer, wild-type GST-p38 MAP kinase (TGY) , or mutated GST-p38 MAP kinase (AGF) . The phosphorylated proteins were resolved by SDS-PAGE and detected by autoradiography. Only phospnorylaticn of wild-type p38 was observed. Example 4. In Vi tro Phospnorylation and Activation of JNK and P38 MAP Kinase by MKK4 Protein kinase assays were conducted as described in Example 3. Recombinant GST-MKK4 was incubated with [γ- 32 P]ATP and buffer, GST-JNKl, GST-p38 MAP kinase, or GST-ERK2. JNK1 and p38 were phosphorylated, as was MKK4 incubated with JNK1 and p38. GST-MKK4 was incubated with [γ- 32 P]ATP and buffer, wild-type JNK1 (Thr 183 , Tyr 185 ) , or mutated GST-JNKl (Ala 183 , Phe 185 ). The JNK1 substrate ATF2 (Gupta et al . (1995) supra) was included in each incubation. ATF2 was phosphorylated m the presence of MKK4 and wild-type JNK1. The results establish that MKK4 phosphorylates and activates both p38 and JNK1. Example 5. Phosphorylation and Activation of P38 MAP Kinase by UV-stimulated MKK3 Epitope-tagged MKK3 was expressed in COS-1 cells maintained in Dulbecco's modified Eagle's medium supplemented with fetal bovine serum (5%) (Gibco-3RL) . The cells were transfected with the lipofectamme reagent according to the manufacturer's recommendations Gibco- BRL) and treated with UV radiation or EGF as described (Derijard et al . (1994) supra) . The cells were exposed the absence and presence of UV-C (40 J/m 2 ) . The cells were solubilized with lysis buffer (20 mM tris, pH 7.4, 1% TRITON ® X-100, 10% glycerol, 137 mM NaCl, 2 mM EDTA, 25 mM β- glycerophosphate, 1 mM Na orthovanadate, 1 mM phenylmethylsulfonyl fluoride, and leupeptm (10 μg/mi)) and centrifuged at 100,000 x g for 15 minutes at 4°c. MKK3 was isolated by lmmunoprecipitation. The epitope- tagged protem Kinases were mcuoated for 1 hour at 4°C with the M2 antibody to the Flag epitope (IBI -Kodak) bound to protein G-Sepharose ( Pharmacia-LKB Biotechnology) . The immunoprecipitates were wasned twice with lysis buffer and twice with kinase buffer. Protem kinase assays were conducted with the substrate GST-p38 MAP kinase or JNK1. ATF2 was included in some assays. Basal levels of MKK3 phosphorylation of p38 MAP kinase were observed. UV- irradiation resulted in increased phosphorylation of p38 MAP kinase, but not of JNK1. The increased p38 MAP kinase activity resulted in increased phosphorylation of ATF2. Example 6. Activation of p38 MAP Kinase m Cells Expressing MKK3 and MKK4 COS-1 ceils were transfected with epitope-tagged p38 MAP kinase, together with an empty expression vector or an expression vector encoding MEK1 , MKK3 , or MKK4α. Some of the cultures were exposed to UV radiation (40 J/m 2 ) or treated with 10 nM EGF. p38 MAP kinase was isolated by immunoprecipitation with M2 monoclonal antibody, and tr.e prote kinase activity was measured m the immunecomplex with [γ- 32 P]ATP and ATF2 as substrates. The product of tne phosphorylation reaction was visualized after SDS-PAGE by autoradiography. ATF2 was not pnospnorylated in the control MEK1, or EGF- reated groups, but was phospnorylated in the MKK3 , MKK4 , and UV- irradiated groups. MKK3 and MKK4 pnosphorylation of ATF2 was similar to that seen with p38 MAP kinase isolated from UV- irradiated cells. Example 7. Phosphorylation of ATF2 by JNKl and JNK2 COS-1 cells were maintained m Dulbecco's modified Eagle's medium supplemented with bovine serum albumin (5%) (Gibco-BRL) . Metabolic labeling with [ 32 ] P was performed by mcuoaticn of cells for 3 hours m phosphate- free modified Eagle's medium (Flow Laboratories Inc.) supplemented with [ 32 P] orthopnosphate (2 mCi/ml) (Dupont-NEN) . COS-1 cells were transfected without (Mock) and with epitope-tagged JNKl (JNKl) . Plasmid expression vectors encoding the JNKl cDNA have previously been described (Derijard et al . (1994) Cell 76:1025, herein specifically incorporated by reference) . Plasmid DNA was transfected into COS-1 cells by the lipofectamme method (Gibco-BRL) . After 48 hours of incubation, some cultures were exposed to 40 J/m 2 UV radiation and incubated for 1 hour at 37oc. Cells were lysed m 20 mM Tris, pH 7.5 , 25 mM β- glycerophosphate, 10% glycerol, 1% Triton ® X-100, 0.5% (w/v) deoxycholate, 0.1% (w/v) SDS, 0.137 M NaCl, 2 mM pyropnosphate, 1 mM orthovanadate , 2 mM EDTA, 10 μg/ml leupeptm, 1 mM PMSF. Soluble extracts were prepared by centrifugation in a microfuge for 20 minutes at 4oc. JNKl lmmunoprecipitates were also prepared by reaction with a rabbit antiserum prepared with recombinant JNKl as an antigen. In-gel protem kinase assays were performed with cell lysates and JNKl lmmunoprecipitates after SDS-PAGE by renaturation of protem kinases, polymerization of the substrate (GST-ATF2, residues 1-505) in the gel, and incubation with [γ- 32 P]ATP (Derijard et al . (1994) supra). The incorporation of [ 32 P] phosphate was visualized by autoradiography and quantitated with a Phosphorimager and ImageQuant software (Molecular Dynamics Inc., Sunnyvale, CA) . The cell lysates demonstrate the presence of 46 kD and 55 kD protem kinases that phosphorylate ATF2 m extracts prepared from UV-irradiated cells. The 46 kD and 55 kD protem kinases were identified as JNKl and JNK2 , respectively. Example 8. Binding of JNKl to ATF2 and Phosphorylation of the NH, -Terminal Activation Domain The site of JNKl phosphorylation of ATF2 was investigated by generation of progressive NH 2 - erminal domain deletions of ATF2. Plasmid expression vectors encoding ATF2 (pECE-ATF2) (Liu and Green (1994) and (1990)), have been described. Bacterial expression vectors for GST-ATF2 fusion proteins were constructed by sub-cloning ATF2 cDNA fragments from a polymerase chain reaction (PCR) into pGEX-3X (Pharmacia-LKB Biotechnology Inc.). The sequence of all constructed plasmids was confirmed by automated sequencing with an Applied Biosystems model 373A machine. The GST-ATF2 proteins were purified as described (Smith and Johnson (1988) Gene 67:31), resolved by SDS-PAGE and stained with Coomassie blue. GST-ATF2 fusion proteins contained residues 1-505, 1-349, 350-505, 1-109, 20-109, 40-109, and 60-109. The phosphorylation of GST-ATF2 fusion proteins by JNKl isolated from UV- irradiated cells was examined in an immunocomplex kinase assay. Immunecomplex kinase assays were performed with Flag epitope-tagged JNKl and the monoclonal antibody M2 (IBI-Kodak) as described by Derijard et al . (1994) supra) . Immunecomplex protein kinase assays were also performed with a rabbit antiserum prepared with recombinant JNKl as an antigen. The cells were solubilized with 20 mM Tris, pH 7.5, 10% glycerol, 1% Triton ® X-100, 0.137 M NaCl, 25 mM /?-glycerophosphate, 2 mM EDTA, 1 mM orthovanadate, 2 mM pyrophosphate, 10 μg/ml leupeptin, and 1 mM PMSF. JNKl was immunoprecipitated with protein G-Sepharose bound to a rabbit polyclonal antibody to JNK or the M2 monoclonal antibody to the Flag epitope. The beads were washed three times with lysis buffer and once with kinase buffer (20 mM Hepes, pH 7.6 , 20 mM MgCl 2 , 25 mM β- glycerophosphate, 100 μM Na orthovanadate, 2 mM dithiothreitol) . The kinase assays were performed at 25oC for 10 minutes with 1 μg of substrate, 20 μM adenosine triphosphate and 10 μCi of [γ- 32 P]ATP in 30μl of kinase buffer. The reactions were terminated with Laemmli sample buffer and the products were resolved by SDS-PAGE (10% gel) . JNKl phosphorylates GST-ATF2 fusion proteins containing residues 1-505, 1-349, 1-109, 20-109, and 40-109, but not 60-109. These results indicate that the presence of ATF2 residues 1-60 are required for phosphorylation by JNK. The binding of immobilized GST-ATF2 fusion proteins was examined in a solid-phase kinase assay as described by Hibi et al . ((1993) Genes Dev. 7:2135, herein specifically incorporated by reference) . JNKl from UV-irradiated cells was incubated with GST-ATF2 fusion proteins bound to GSH-agarose. The agarose beads were washed extensively to remove the unbound JNKl. Phosphorylation of the GST-ATF2 fusion proteins by the bound JNKl protem kinase was examined by addition of [γ- 32 P]ATP. JNKl bound GST-ATF2 fusion proteins containing residues 1-505, 1-349, 1-109, 20-109, and 40-109, indicating that the presence of residues 20-60 were required for binding of JNKl to ATF2. Example 9. Phospnorylation of the NH-,- terminal Activation Domain of ATF2 on Thr 69 and Thr 71 by JNKl The effect of UV radiation on the properties of wild-type (Thr 6571 ) and phosphorylation-defective (Ala 69,71 ) ATF2 molecules was examined. Mock- transfected and JNK1- transfected COS cells were treated without and with 40 J/m 2 UV radiation. The epitope-tagged JNKl was isolated by immunoprecipitation with the M2 monoclonal antibody. The phosphorylation of GST-ATF2 (residues 1 to 109) was examined in an immunocomplex kinase assay as described above. The GST-ATF2 was resolved from other proteins by SDS-PAGE and stained with Coomassie blue. The phosphorylation of GΞT-ATF2 was detected by autoradiography. JNKl -transfected cells, but not mock- transfected cells, phosphorylated ATF2. JNKl phosphorylation of ATF2 was greater in cells exposed to UV radiation. Phosphorylation of ATF2 by JNKl was associated with a decreased electrophoretic mobility. In a separate experiment, GST fusion proteins containing full-length ATF2 (residues 1 to 505) , an NH 2 - termmal fragment (residues 1 to 109) , and a COOH- term al fragment (residues 95 to 505) were phosphorylated with JNKl and the sites of phosphorylation analyzed by phosphoamino acid analysis. The methods used for phosphopeptide mapping and phosphoamino acid analysis have been described (Alvarez et al . (1991) J. Biol. Chem. 266:15277) . The horizontal dimension of the peptide maps was electrophoresis and the vertical dimension was chromatography. The NH 2 -terminal sites of phosphorylation were identified as Thr 69 and Thr 71 by phosphopeptide mapping and mutational analysis. Site-directed mutagenesis was performed as described above, replacing Thr 69 and Thr 71 with Ala. Phosphorylation of mutated ATF2 was not observed. Example 10. Reduced Electrophoretic Mobility of JNK- Activated ATF2 CHO cells were maintained in Ham' s F12 medium supplemented with 5% bovine serum albumin (Gibco-BRL) . Cells were labeled and transfected with JNKl as described above. CHO cells were treated with UV-C (40 J/πr) , IL-lα (10 ng/ml) (Genzyme) , or fetal bovine serum (20%) (Gibco- BRL) . The cells were incubated for 30 minutes at 37oc prior to harvesting. The electrophoretic mobility of ATF2 after SDS-PAGE was examined by protein immuno-blct analysis. A shift in ATF2 electrophoretic mobility was observed in cells treated with UV, IL-1, and serum. These results indicate that JNKl activation is associated with an electrophoretic mobility shift of ATF2 , further suggesting that ATF2 is an in vivo substrate for JNKl. Example 11. Increased ATF2 Phosphorylation After Activation of JNK COS-1 cells were transfected without (control) and with an ATF2 expression vector (ATF2) , as described above (Hai et al . (1989) supra) . The effect of exposure of the cells to 40 J/m 2 UV-C was examined. After irradiation, the cells were incubated for 0 or 30 minutes (control) or 0, 15, 30, and 45 minutes (ATF2) at 37oC and then collected. The electrophoretic mobility of ATF2 during SDS-PAGE was examined by protein immuno-blot analysis as described above. The two electrophoretic mobility forms of ATF2 were observed in ATF2 -transfected cells, but not in control cells. The phosphorylation state of wild-type (Thr 69,71 ) ATF2 and mutated (Ala 69 ' 71 ) ATF2 was examined in cells labeled with [ 32 ]P, treated without and with 40 J/m 2 UV-C, and then incubated at 37oC for 30 minutes (Hai et al . (1989) supra) . The ATF2 proteins were isolated by immunoprecipitation and analyzed by SDS-PAGE and autoradiography. The phosphorylated ATF2 proteins were examined by phosphoamino acid analysis as described above. Both forms of ATF2 contained phosphoserine, but only wild-type ATF2 contained phosphothreonine . Tryptic phosphopeptide mapping was used to compare ATF2 phosphorylated in vi tro by JNKl with ATF2 phosphorylated in COS-1 cells. A map was also prepared with a sample composed of equal amounts of in vivo and in vi tro phosphorylated ATF2 (Mix) . Mutation of ATF2 at Thr 69 and Thr 71 resulted in the loss of two tryptic phosphopeptides in maps of ATF2 isolated from UV- irradiated cells. These phosphopeptides correspond to mono- and bis -phosphorylated peptides containing Thr 6 and Thr 71 . Both of these phosphopeptides were found in maps of ATF2 phosphorylated by JNKl in vi tro . Example 12. Inhibition of ATF2 -Stimulated Gene Expression by Mutation of the Phosphorylation Sites Thr 69 and Thr 71 A fusion protein consisting of ATF2 and the GAL4 DNA binding domain was expressed in CHO cells as described above. The activity of the GAL4-ATF2 fusion protein was measured in co-transfection assays w th the reporter plasmid pG5ElbLuc (Seth et al . (1992) J. Biol. Chem. 267:24796, hereby specifically incorporated by reference) . The reporter plasmid contains five GAL4 sites cloned upstream of a minimal promoter element and the firefly luciferase gene. Transfection efficiency was monitored with a control plasmid that expresses 2- galactosidase (pCHHO; Pharmacia-LKB Biotechnology). The luciferase and β-galactosidase activity detected in cell extracts was measured as the mean activity ratio of three experiments (Gupta et al . (1993) Proc. Natl. Acad. Sci. USA 90:3216, hereby specifically incorporated by reference). The results , shown in Table 1, demonstrate the importance of phosphorylation at Thr 69 and Thr 71 for transcriptional activity. TABLE 1. INHIBITION OF ATF-2 STIMULATED GENE EXPRESSION BY MUTATION OF THE PHOSPHORYLATION SITES THR 69 ' 71 Example 13. Effect of Dominant -Negative JNKl Mutant on ATF2 Function The luciferase reporter plasmid system was used to determine the effect of point mutations at the ATF2 phosphorylation sites Thr 69 and Thr 71 in serum-treated CHO cells transfected with wild-type (Thr 183 , Tyr 185 ) or mutant (Ala 183 , Phe 185 ) JNKl. Control experiments were done with mock-transfected cells. The CHO cells were serum-starved for 18 hours and then incubated without or with serum for 4 hours. Expression of wild-type ATF2 caused a small increase in serum- stimulated ATF2 transcriptional activity. In contrast, mutant JNKl inhibited both control and serum-stimulated ATF2 activity. Example 14. Effect of Tumor Suppressor Gene Product Rb and Adenovirus Oncoorotem ElA on ATF2- St muiated Gene Expression The effect of expression of the Rb tumor suppressor gene product and adenovirus oncoprotem ElA on ATF2 transcriptional activity were investigated with a luciferase reporter plasmid and GAL4-ATF2 (residues 1- 505), as described above. Cells were transfected with wild-type (Thr 69 ' 71 ) or mutated (Ala 69 ' 71 ) ATF2. No effect of Rb or ElA on luciferase activity was detected in the absence of GAL4-ATF2. Rb and ElA were found to increase ATF2 -stimulated gene expression of both wild-type and mutated ATF2. However, mutated ATF2 caused a lower level of reporter gene expression than did wild-type ATF2. These results indicate a requirement for ATF2 phosphorylation (cn Thr 65 and Thr 71 ) plus either Rb or ElA for maximal transcriptional activity. Example 15. Substrate Specificity of p38 MAP Kinase Substrate phosphorylation by p38 MAP kinase was examined by incubation of bacterially-expressed p38 MAP kinase with IcB, cMyc, EGF-R, cytoplasmic phospholipase A 2 (cPLA 2 ) , c-Jun, and mutated ATF2 (Thr 69 ' 71 ) and ATP [γ- 32 P] (Raingeaud et al . (1995) J. Biol. Chem 270:7420, herein specifically incorporated by reference) . GST-I/.B was provided by Dr D. Baltimore (Massachusetts Institute of Technology). GST-cMyc (Alvarez et al . (1991) J. Biol. Chem. 266:15277), GST-EGF-R (residues 647-688) (Koland et al . (1990) Biochem. Biophys. Res. Commun. 166:90), and GST-c-Jun (Derijard et al . (1994) supra) have been described. The phospnorylation reaction was terminated after 30 minutes by addition of Laemmli sample buffer. The pnosphorylated proteins were resolved by SDS-PAGE and detected by autoradiography. The rate phosphorylation of the substrate proteins was quantitated by Phosphorimager (Molecular Dynamics Inc.) analysis. The relative phosphorylation of ATF2 , MBP, EGF-R, and IκB was 1.0, 0.23, 0.04, and 0.001, respectively. Example 16. Binding of P38 MAP Kinase to ATF2 Cell extracts expressing epitope-tagged JNKl and p38 MAP kinase were cupated with a GST fusion protem containing the activation domain of ATF2 (residues 1-109) immobilized on GSH agarose. The supernatant was removed and the agarose was washed extensively. Western blot analysis of the supernatant and agarose-bound fractions was conducted as follows: proteins were fractionated by SDS-PAGE, electrophoretically transferred to an Immobilon-P membrane, and probed with monoclonal antibodies to phosphotyrosme (PY20) and the Flag epitope (M2). Immunocomplexes were detected using enhanced chemiluminescence (Amersham International PLC) . Control experiments were performed using immobilized GST. Example 17. p38 MAP Kinase and JNKl Activation by Pro- Inflammatory Cytokines and Environmental Stress The effect of phorbol ester, EGF, UV radiation, osmotic stress, IL-1, tumor necrosis factor (TNF), and LPS on p38 MAP kinase and JNKl activity were measured m immunecomplex protem kinase assays using ATP[γ- 32 P] and ATF2 as substrates. TNFα; and IL-lα were from Genzyme Corp. Lipolysacchaπde (LPS) was isolated from lyophilized Salmonella minesota Re595 bacteria as described (Mathison et a. (1988) J. Clin. Invest. 81:1925). Phorbol myristate acetate was from Sigma. EGF was purified from mouse salivary glands (Davis (1988) J. Biol. Chem. 263:9462). Kinase assays were performed using immunoprecipitates of p38 and JNK. The immunocomplexes were washed twice with kinase buffer (described above) , and the assays initiated by the addition of 1 μg of ATF2 and 50 μM [γ- 32 P]ATP (10 Ci/mmol) in a final volume of 25 μl . The reactions were terminated after 30 minutes at 30oc by addition of Laemmli sample buffer. The phosphorylation of ATF2 was examined after SDS-PAGE by autoradiography, and the rate of ATF2 phosphorylation quantitated by Phosphorimager analysis . The results are shown in Table 2. Exposure of HeLa cells to 10 nM phorbol myristate acetate very weakly activated p38 and JNKl. Similarly, treatment with 10 nM EGF only weakly activated p38 and JNKl. By contrast, treatment with 40 J/m 2 UV-C, 300 mM sorbitol, 10 ng/ml interleukin-1, and 10 ng/ml TNFα strongly activated p38 and JNKl activity. The effect of LPS on the activity of p38 was examined using CHO cells that express human CD14. Exposure of CHO cells to 10 ng/ml LPS only slightly activated p38 and JNKl activity. TABLE 2. p38 AND JNKl ACTIVATION BY PRO- INFLAMMATORY CYTOKINES AND ENVIRONMENTAL STRESS. Example 18. p38 MAP Kinase Activation by Dual Phosphorylation on Tyr and Thr COS-1 cells expressing wild-type (Thr 180 , Tyr 182 ) or mutated (Ala 180 , Phe 182 ) p38 MAP kinase were treated without and with UV-C (40 J/m 2 ) . The cells were harvested 30 minutes following exposure with or without UV radiation. Control experiments were performed using mock-transfected cells. The level of expression of epitope-tagged p38 MAP kinase and the state of Tyr phosphorylation of p38 MAP kinase was examined by Western blot analysis using the M2 monoclonal antibody and the phosphotyrosine monoclonal antibody PY20. Immune complexes were detected by enhanced chemiluminescence. Wild-type and mutant p38 were expressed at similar levels. Western blot analysis showed that UV radiation caused an increase in the Tyr phosphorylation of p38. The increased Tyr phosphorylation was confirmed by phosphoamino acid analysis of p38 isolated from [ 32 P] phosphate-labeled cells. The results also showed that UV radiation increased Thr phosphorylation of p38. The increased phosphorylation or. Tyr and Thr was blocked by mutated p38. Wild-type and mutated p38 were isolated from the COS-1 cells by immunoprecipitation. Protein kinase activity was measured in the immune complex using [γ- 32 P]ATP and GST-ATF2 as substrates. The phosphorylated GST-ATF2 was detected after SDS-PAGE by autoradiography. UV radiation resulted in a marked increase in the activity of wild-type p38, while the mutant p38 was found to be catalytically inactive. These results show that p38 is activated by dual phosphorylation within the Thr- Gly-Tyr motif. Example 19. MAP Kinase Phosphatase Inhibits p38 MAP kinase Activation The cells were treated without and with 40 J/m 2 UV-C. Control experiments were performed using mock- transfected ceils (control) and cells transfected with the catalytically inactive mutated phosphatase mPACl (Cys 257 /Ser) and human MKPl. The activity of p38 MAP kinase was measured with an immunecomplex protein kinase assay employing [γ- 32 P]ATP and GST-ATF2 as substrates. The expression of PACl or MKPl was found to inhibit p38 phosphorylation, demonstrating that p38 can be regulated by the dual specificity pnosphatases PACl and MKPl. Example 20. Subcellular Distribution of p38 MAP Kinase Epitope-tagged p38 MAP kinase was expressed in COS cells. The cells were treated without or with 40 J/m 2 UV radiation and then incubated for 60 minutes at 37oc. The p38 MAP kinase was detected by indirect immunofluorescence using the M2 monoclonal antibody. The images were acquired by digital imaging microscopy and processed for image restoration. Immunocvtochemi s ry Coverslips (22mm x 22mm No. 1; Gold Seal Cover Glass; Becton-Dickmson) were pre- reated by boiling m 0.1 N HCl for 10 minutes, rinsed in distilled water, autoclaved and coated with 0.01% poly-L-lysme (Sigma; St. Louis MO). The coverslips were placed at the bottom of 35 mm multiwell tissue culture plates (Becton Dickinson, UK) . Transfected COS-1 cells were plated directly on the coverslips and allowed to adhere overnight in Dulbecco's modified Eagle's medium supplemented with 5% fetal calf serum (Gibco-BRL) . Twenty-four hours post-transfection, the cells were rinsed once and incubated at 37oc for 30 minutes in 25 mM Hepes, pH 7.4, 137 mM NaCl, 6 mM KCl , 1 mM MgCl 2 , 1 mM CaCl 2 , 10 mM glucose. The cells were rinsed once with phosphate-buffered saline and the coverslips removed from the tissue culture wells. Cells were fixed in fresh 4% paraformaldehyde in phosphate-buffered saline for 15 minutes at 22°C. The cells were permeabilized with 0.25% Triton ® X-100 in phosphate-buffered saline for 5 minutes and washed three times in DWB solution (150 mM NaCl, 15 mM Na citrate, pH 7.0 , 2% horse serum, 1% (w/v) bovine serum albumin, 0.05% Triton ® X-100) for 5 minutes. The primary antibody (M2 anti-FLAG monoclonal antibody, Eastman-Kodak Co., New Haven, CT) was diluted 1:250 DWB and applied to the cells m a humidified environment at 22oC for 1 hour. The cells were again washed three times as above and fluorescein isothiocyanate-ccnjugated goat anti-mouse Ig secondary antibody (Kirkegaard & Perry Laboratories Inc. Gaithersburg, MD) was applied at a 1:250 dilution for 1 hour at 22°c in a humidified environment. The cells were then washed three times in DWB and then mounted onto slides with Gel -Mount [Biomeda Corp. Foster City, CA) for immunofluorescence analysis. Control experiments were performed to assess the specificity of the observed immunofluorescence . No fluorescence was detected when the transfected cells were stained in the absence of the primary M2 monoclonal antibody, or mock-transfected cells. Digi tal Imaging Mi croscopy and Ima e Restora tion Digital images of the fluorescence distribution in single cells were obtained using a Nikon 60x Planapo objective (numerical aperture = 1.4) on a Zeiss IM-35 microscope equipped for epifluorescence as previously described (Carrington et al . (1990) in: Non-invasive Techniques in Cell Biology, Fosbett & Grinstein, eds., Wiley-Liss, NY; pp. 53-72; Fay et al . (1989) J. Microsci. 153:133-149). Images of various focal planes were obtained with a computer controlled focus mechanism and a thermoelectrically cooled charged-coupled device camera (model 220; Photometries Ltd., Tucson, AZ) . The exposure of the sample to the excitation source was determined by a computer-controlled shutter and wavelength selector system (MVI, Avon, MA). The charge-coupled device camera and microscope functions were controlled by a microcomputer, and the data acquired from the camera were transferred to a Silicon Graphics model 4D/GTX workstation (Mountainview, CA) for image processing. Images were corrected for non-uniformities in sensitivity and for the dark current of the charge coupled device detector. The calibration of the microscopy blurring was determined by measuring the instrument's point spread function as a series of optical sections at 0.125μm intervals of a 0.3 μm diameter fluorescently labeled latex bead (Molecular Probes Inc.) . The image restoration algorithm used is based upon the theory of ill -posed problems and obtains quantitative dye density values within the cell that are substantially more accurate than those in an unprocessed image (Carrington et al. (1990) supra ; Fay et al . (1989) supra) . After image processing, individual optical sections of cells were inspected and analyzed using computer graphics software on a Silicon Graphics workstation. p38 MAP kinase was observed at the cell surface, in the cytoplasm, and in the nucleus. After irradiation, an increased localization of cytoplasmic p38 to the perinuclear region was detected. Example 21. Activation of the MKK Signal Transduction Pathway by Osmotic Shock CHO cells were co-transfected with the plasmid pCMV-Flag-Jnkl and pRSV-Neo (Derijard et al . (1994) supra) . A stable cell line expressing epitope-tagged Jnkl (Flag; Immunex Corp.) was isolated by selection with Genetic (Gibco-BRL) . The cells were incubated with 0, 100, 150, 300, 600, or 1000 mM sorbitol for 1 hour at 37oc The cells were collected m lysis buffer 20 mM Tris, pH 7.4, 1% TRITON ® X-100, 2 mM EDTA, 137 M NaCl, 25 mM jβ-glyceropnosphate, 1 mM orthovanadate, 2 mM pyrophosphate, 10% glycerol, 1 mM phenylmethylsuifonyi fluoride, 10 μg/ml leupeptm) and a soluble extract was obtained by centrifugation at 100,000 g for 30 minutes at 4°C. The epitope-tagged JNKl was isolated by immunoprecipitation with the monoclonal antibody M2 (Immunex Corp.). The lmmunoprecipitates were washed extensively with lysis puffer. Immunecomplex kinase assays were done in 25 μl of 25 mM Hepes, pH 7.4 , 25 mM MgCl 2 , 25 mM β-glycerophospnate , 2 mM dithiothreitol , 100 μM orthovanadate, and 50 μM ATP [γ- 32 P] (10 Ci/mmole) with 2.5 μg of bacteπally expressed c-Jun (residues 1-79) fused to glutatnione-S-transferase (GST) as a sucstrate. The phosphorylation of c-Jun was examined after SDS-PAGE by autoradiography and Phosphorimager (Molecular Dynamics Inc.) analysis. JNKl activation was observed at all concentrations of sorbitol exposure. The time course of JNKl protem kinase activation was measured m cells πcupated in medium supple m ented with 300 mM sornitol as described above. Increased JNKl activity was observed within 5 minutes of exposure to sorbitol, with maximum activity occurring after 15-30 minutes . Mutation of JNKl at the phosphorylation sites Thr 133 and Tyr 135 blocked the activation of JNKl protem kinase activity by osmotic shock. CHO cells were transfected with vector, wild-type JNKl (Thr 183 , Tyr 185 ) , and mutated JNKl (Ala 183 , Phe 185 ) . The cells were incubated in medium supplemented without or with 300 mM sorbitol for 15 minutes before measurement of JNKl prote kinase activity as described above. JNKl activation was seen in the wild-type but not mutated JNKl. Example 22. Molecular Cloning of MKK7 RT-PCR was employed to identify a fragment of a novel mammalian MAP kinase kinase. The primers designed for the protocol, ATNGCNGTNAARCARATG (SEQ ID NO: 23) and ATNCKYTCNGGNGCCATRTA (SEQ ID NO: 24) , were based on the sequence of the Drosophila MAP kinase kinase hep (Glise et al. (1995) Cell 83:451-461). Murine testis mRNA was used as the template. A single product (461 bp) was detected following RT-PCR amplification of mur e testis mRNA. Sequence analysis identified this PCR product as a fragment of a novel mammalian MAP kinase kinase. Full- length murine cDNA clones were isolated by screening a murine testis library (Stratagene Inc.). The cDNA clones were examined by sequencing with an Applied Biosystems model 373A machine. A group of seven clones was identified by sequence analysis to contain a single long open reading frame that encoded a putative protem kinase (Fig. 9 and Fig. 10; SEQ ID NO: 17 and SEQ ID NO: 18) . In-frame termination codons were detected in the 5' and 3' regions cf tnese clones. This sequence includes protein kinase sub-domains I - XI and s related to the MAP kinase Kinase group. The novel protem kinase was designated MKK7. The sites of activating phosphorylation of MAP kinase kinases located in sub- domain VIII are conserved m MKK7. Comparison of MKK7 with other members of the mammalian MAP kinase kinase group demonstrates that MKK7 is related to the JNK activator MKK4. One additional cDNA clone isolated from the λ phage library differed from the other seven clones. This clone contained the same 3 ' untranslated region and coding region of MKK7, but had a different 5' region that lacked an in-frame termination codon. This clone represents an alternatively spliced form of MKK7 (MKK7b; Fig. 11; SEQ ID NO: 19) . The MKK7b cDNA clone does not have an initiation codon in the alternative 5' region; this cDNA therefore encodes the same MKK7 protem kinase as the other clones that were isolated. However, if the MKK7b cDNA clone is not full-length it is possible that additional 5' sequence may include an in-frame initiation codon. If true, MKK7b is predicted to fuse the sequence M- [?] -SPAPAPSQRAALQLPLANDGGSRSPSSESSPQHPTPPTRPRH- (SEQ ID NO: 33) to the initiating methionme of MKK7 (Fig. 9) . Although the Drosophila MAP kinase kinase hep shares substantial sequence similarity with MKK7 , the sequence of the NH2- terminal extension of MKK7b is not conserved in the hep prote kinase. Three additional clones encoded MKK7 splice variants that differ m the 5' and 3' regions. These clones (MKK7c (Fig. 13), MKK7d (Fig. 14), and MKK7e (Fig. 15)) are full-length because of the presence of in- frame termination codons in the 5' and 3' regions . A human cDNA library was screened with a full- length mouse MKK7 cDNA probe. A single clone was identified and squenced. A partial MKK7 sequence was identified (Fig. 12; SEQ ID NO: 25 and SEQ ID NO: 26) tr.at is missing the 3' end. The sequence is most homologous to mouse MKK7c . The sequences of MKK7 , MKK7b, hep, and human MKK7 cDNAs have been deposited in Genbank with accession numbers U93030, U93031, U93032, and AF00319 respectively. Example 23. Expression of MKK7 MKK7 expression was examined by Northern blot analysis of mRNA isolated from different tissues. The analysis was done with poly A+ mRNA (2 μg) isolated from different tissues and fractionated by denaturing agarose gel electrophoresis and transferred to a nylon membrane (Clontech) . The blot was probed with MKK4 and MKK7 cDNAs labeled by random priming with [α.- 32 P]dATP (Amersnam International PLC) . MKK7 was found to be widely expressed in murine tissues. A single MKK7 transcript (approximately 4.0-kb) was detected in all of the tissues examined, except for testis where two MKK7 transcripts (4.0 kb and 1.5 kb) were detected. The highest levels of MKK7 expression were in testis. Significant expression of MKK7 was also observed in heart, brain, lung, liver, and kidney. This contrasts with MKK4 expression which was highest in brain although significant amounts of expression were ooserved brain, liver, muscle, heart, and kidney. Althougn MKK4 and MKK7 are co-expressed, the relative abundance of each MAP kinase kinase is different in each of tne tissues examined. Example 24. Specific Activation of JNK by MKK7 m vi tro To examine the specificity of MKK7, in vi tro protem kinase assays were performed. A bacterial MKK7 expression vector was prepared by sub-cloning an MKK7 cDNA (Eco RI and Pvu II fragment) into the Eco RI and Sma I sites of pGEX-5Xl ( Pharmacia-LKB) The glutatnione-S- transferase (GST) fusion protem was purified by affinity chromatograpny (Smith and Johnson (1988) Gene 67:31-40). The recombinant proteins GST-ATF2 (Gupta et al . 1995) Science 267:389-393), GST-cJun (Derijard (1994) supra) , GST-cMyc (Alvarez et al . (1991) J. Biol. Chem. 256:15277- 15285), GST-ERK2 (Seth et al . (1992) J. Biol. Chem. 267:24796-24804), GST-p38, (Raingeaud et al . (1995) J. Biol. Chem. 270:7420-7426), and GST-JNKl (Derijard (1994) supra) have been described. Protem kinase assays were performed m kinase buffer (25 mM 4- (2 -hydroxyethyl) -1-- piperazmeethansulfomc acid (pH 7.4), 25 mM β- glycerophosphate, 25 mM MgCl 2 , 2 mM dithiothreitol, 0.1 mM orthovanadate) . The assays were initiated by the addition of 1 μg of substrate proteins and 50 μM [γ- 32PJATP (10 Ci/mmoi) in a final volume of 25 μl . The reactions were terminated after 30 minutes at 25 3 C by addition of Laemmli sample buffer. The phosphorylation of the substrate proteins was examined after SDS- polyacrylamide gel electrophoresis (PAGE) by autoradiography . Recombinant MAP kinases were incubated with GST (control) or GST-MKK7 using the substrate ATP[γ- 32 P] . Recombinant MKK7 purified from bacteria was not observed to autophosphoryiate . Incu aticn of the recombinant MKK7 with MAP kinases demonstrated that MKK7 phosphorylated JNKl, but not p38 or ERK2. MKK7 was phosphorylated by p38 and JNKl. The significance of the retrophosphorylation of the MAP kinase kinase by the MAP kinase is unclear, but similar retrophosphorylation has been detected kinase assays using MKK4 (Derijard (1995) supra) and the Drosophila JNK activator hep (Sluss (1996) supra) . To test './nether the phospnorylation of JNKl by MKK7 caused increased protem kinase activity, experiments using ATF2 as the JNK substrate were performed. GST-MKK7 was incubated in a protein Kinase assay with reco omant JNKl. JNK activity was measured by including the JNK substrate ATF2 in each assay. ATF2 was not phosphorylated by MKK7 , out was weakly phospnorylated by JNKl. Incubation of MKK7 with JNKl caused phosphorylation of JNKl and a large increase m ATF2 phosphorylation. These data indicate that MKK7 phosphorylates and activates JNKl. To confirm this conclusion, the effect of replacement of the JNK dual phosphorylation motif Thr-Pro-Tyr with Ala-Pro-Phe was examined. MKK7 did not phosphorylate the mutated JNKl (APF) protem. Furthermore, MKK7 did not increase ATF2 phosphorylation by the mutated JNKl protem kinase. Thus, MKK7 is a JNK activator in vi tro . Example 25. Specific Activation of JNK by MKK7 m vivo To examine the specificity of MKK7 in vivo, cotransfection assays were performed. CHO cells were maintained m Dulbecco's modified Eagle's medium supplemented with fetal calf serum (5%; Gibco-BRL) . The cells were transfected with the lipofectamme reagent according to the manufacturer's recommendations (Gibco- BRL) (Derijard (1994) supra) . Cells were co-transfected with vectors encoding epitope-tagged JNKl together with an empty expression vector (control) or an expression vector encoding MKK4 or MKK7. The epitope tag was derived from the hemagglutmm protem (HA) of the influenza virus. JNKl was isolated by immunoprecipitation of cell lysates. The cells were solubilized with lysis buffer (20 mM Tris (pH 7.4), 1% TRITON X-100 ® , 10% glycerol, 137 mM NaCl, 2 mM EDTA, 25 mM -glycerophosphate, 1 mM Na orthovanadate, 2 mM pyrophosphate, 1 mM PMSF, 10 μg/ml leupeptm) and centrifuged at 100,000 X g for 15 minutes at 4°C. The epitope-tagged prote kinases were lmmunoprecipitated by incubation for 3 hours at 4°C with an anti -HA monoclonal antibody bound to protem-G Sepharose (Pharmacia-LKB Biotechnology Inc . ) . The lmmunoprecipitates were washed three times with lysis buffer (Gupta et al . (1995) Science 267:389-393). Protem kinase activity was measured in the immunecomplex with [γ- 32 P]ATP and c-Jun as substrates. The product of the phosphorylation reaction was visualized after SDS-PAGE by autoradiography. The ERK2 and p38 MAP kinases were not activated by co- expressed MKK7. Control experiments demonstrated that the ERK2 and p38 MAP kinases were activated by their respective cognate MAP kinase kinases, MKKl and MKK6. In contrast, MKK7 did activate JNKl. Interestingly, the activation of JNKl by co-expressed MKK7 was greater than that caused by the previously described JNK activator MKK4. Together, these data establish that MKK7 can 5 function as a specific activator of JNK in cultured cells. Example 26. Activation of the JNK Signal Transduction Pathway bv MKK7 The JNK signaling pathway is known to regulate AP- 0 1 transcriptional activity (Whitmarsh (1996) supra) . To test the hypothesis that the expression of MKK7 would cause increased AP-1 transcriptional activity, a co- transfection assay was employed using a luciferase reporter gene that contains three AP-1 sites cloned 5 upstream of a minimal promoter element (Rincon and Flavell (1994) ΞMBO J. 13:4370-4381). Luciferase reporter gene expression was measured in co-transfection assays using the 0.5 μg of the reporter plasmid pTRE- luciferase (Rincon (1994) supra) and 0.25 μg of the β- C galactosidase expression vector pCHllO (Pharmacia-LKB) . Experiments using GAL4 fusion proteins were performed using 0.25 μg of CGAL4-ATF2 (residues 1-109), 0.5 μg of the reporter plasmid pG5ElbLuc, and 0.25 μg of pCHllO (Gupta et al . (1995) supra) . The effect of protein 5 kinases was examined by co-transfection with 0.3 μg of an empty expression vector or a protein kinase expression vector. The ERK2 , p38, JNKl, MKKl, MKK3 , MKK4 , and MKK6 expression vectors have been described. The cells were harvested 36 hours post -transfection. The β- 0 galactosidase and luciferase activity in the cell lysates was measured as described (Gupta (1995) supra) . Expression of MKK4 , MKK7 , or JNKl did not cause marked changes in AP-1 reporter gene expression (Fig. I6A) . In contrast, co-expression of MKK7 with JNKl caused increased AP-1 -dependent reporter gene expression. Consistent with the observation that MKK4 causes weaker activation of JNK than MKK7, co-expression of MKK4 with JNK caused a smaller increase AP-1 reporter gene expression (Fig. 16A) . Together, these data demonstrate that MKK7 can function as an activator of the JNK signal transduction pathway. To further examine the effect of MKK7 on transcriptional activity, the effect of MKK7 on the transcription factor ATF2 was investigated. Previous studies have demonstrated that ATF2 is a target of the JNK signal transduction pathway (van Dam et al . 1995) supra ; Gupta et al . (1995) supra ; Livingstone et al (1995) supra) . JNK phosphorylates two sites (Thr-69 and Thr- 71) in the NH 2 - terminal activation domain of ATF2 and increases transcriptional activity. A GAL4 fusion protein strategy was employed to monitor the transcriptional activity of the activation domain of ATF2 (Gupta (1995) supra) . Measurement of reporter gene expression demonstrated that the coexpression of MKK4 with JNKl caused increased transcriptional activity (Fig. 16B) . A similar level of reporter gene expression was caused by expression of MKK7 and a larger increase was detected when MKK7 was co-expressed with JNKl. The more potent effect of MKK7, compared with MKK4 , on transcriptional activity is consistent with the relative effects of MKK7 and MKK4 on JNK activation. To confirm that the increased reporter gene expression was mediated by ATF2 phosphorylation, the effect of replacement of the sites of ATF2 phosphorylation (Thr-69 and Thr- 71) with Ala was examined. The mutated ATF2 protem was not regulated by MKK4 , MKK7, or JNKl (Fig. 16B) . Together, these data demonstrate that MKK7 can regulate a physiological target of the JNK signaling pathway. Use The MKK polypeptides and polynucleotides of the invention are useful for identifying reagents that modulate the MKK signal transduction pathways. Reagents that modulate an MKK signal transduction pathway can oe identified by their effect on MKK synthesis, MKK phosphorylation, or MKK activity. For example, the effect of a reagent on MKK activity can be measured by the m vi tro kinase assays described above. MKK is incubated without (control) and with a test reagent under conditions sufficient to allow the components to react, then the effect of the test reagent on kinase activity is subsequently measured Reagents that inhibit an MKK signal transduction pathway can be used in the treatment of MKK-mediated disorders. Reagents that stimulate an MKK signal transduction pathway can be used in a number of ways, including induction of programmed cell death (apoptosis) m tissues. For example, the elimination of UV damaged cells can be used to prevent cancer. Generally, for identification of a reagent that inhibits the MKK signal transduction pathway, a kinase assay (see, for example, Example 3) is used. A range of reagent concentrations (e.g , 1.0 nM to 100 mM) are aoded to a test system that includes an MKK substrate and a radioactive marjcer such as [γ-- 2 P]ATP. Appropriate substrate molecules include p38, JNKl, JNK2 , or ATF2. The incorporation of labelled phosphorus (e.g., [ 32 ] P or [ 33 ]P) into the substrate is determined, and the results obtained with the test reagent compared to control values. Of particular interest are reagents that result m inhibition of [ 32 ] P incorporation of about 80% or more. Phosphorylation may also be examined using a reagent that is phosphorylation-dependent , for example, an antibody. Phosphorylation-dependent antibodies may be made using MKK7 phosphorylated on the activating sites, Ser 198 and Thr 202 . This may be accomplished by immunizing animals with a synthetic peptide (for example, approximately 15 ammo acids in length) corresponding to the MKK7 sequence with phosphorylated Ser 198 and Thr 202 . Methods of producing such antibodies are known m the art. Such antibodies are useful for the detection of activated MKK7 m tissues and cell extracts (e.g. on Western blots) and may be used Assays that test the effect of a reagent on MKK synthesis can also be used to identify compounds that inhibit MKK signal transduction pathways. The effect of the test reagent on MKK expression is measured by, for example, Western blot analysis with an antibody specific for an MKK. Antibody binding is visualized by autoradiography or chemiluminescence, and is quantitated. The effect of the test reagent on MKK mRNA expression can be examined, for example, by Northern blot analysis using a polynucleotide probe or by polymerase chain reaction. Reagents found to inhibit MKK signal transduction pathways can be used as therapeutic agents for the treatment of MKK-mediated disorders. Such reagents are also useful in drug design for elucidation of the specific molecular features neeαed to inhibit MKK signal transduction pathways. In addition, the invention provides a method for the treatment of MKK-mediated stress-related and inflammatory disorders . The method includes administration of an effective amount of a therapeutic reagent that inhibits MKK function. Suitable reagents inhibit either MKK activity or expression. The concentration of the reagent to be administered is determined based on a number of factors, including the appropriate dosage, the route of administration, and the specific condition being treated. The appropriate dose of a reagent is determined by methods known to those skilled in the art including routine experimentation to optimize the dosage as necessary for the individual patient and specific MKK-mediated disorder being treated. Specific therapeutically effective amounts appropriate for administration are readily determined by one of ordinary skill in the art (see, for example, Remington' s Pharmaceutical Sciences. 18th ed. , Gennaro, ed., Mack Publishing Company, Easton, PA, 1990) . Dosages may range from about 0.1-10 mg/kilo/day. The invention provides methods for both acute and prophylactic treatment of stress-related and inflammatory disorders. For example, it is envisioned that ischemic heart disease will be treated during episodes of ischemia and oxidative stress following reperfusion. In addition, a patient at risk for ischemia can be treated prior to ischemic episodes. In another example, a therapeutic agent that inhibits MKK function or activity is administered to control inflammatory responses by inhibiting the secretion of inflammatory cytokines, including TNF and IL-1. Stress-related proliferative disorders can also be treated by the method of the invention by administering a therapeutic reagent that inhibits MKK function or activity. Such therapeutic reagents can be used alone or in combination with other therapeutic reagents, for example, with chemotherapeutic agents in the treatment of malignancies. Indeed, the control of stress-activated MKK by the therapeutic reagents provided by this invention can modulate symptoms caused by other therapeutic strategies that induce stress. The therapeutic reagents employed are compounds which inhibit MKK function or activity, including polynucleotides, polypeptides, and other molecules such as antisense oligonucleotides and ribozymes, which can be made according to the invention and techniques known to the art. Polyclonal or monoclonal antibodies (including fragments or derivatives thereof) that bind epitopes of MKK also can be employed as therapeutic reagents. Ξ Dominant -negative forms of MKK which effectively displace or compete with MKK for substrate binding and/or phosphorylation can be used to decrease protem kinase activity. Dominant-negative forms can be created by mutations within the catalytic domain of the protem 0 kinases, using methods known in the art, and as described above (Example 13) . The catalytic residues are conserved m ail the MKK isoforms. For example, mutation of Lys 76 inhibits MKK7 activity. Similarly, mutation of the conserved sites of activating phosphorylation (Ser 198 , Thr 2:2 ) inhibits MKK7 activity. These k ase-mactive forms of MKK7 act as dominant-negative inhibitors. In some cases, augmentation of MKK activity is desirable, e.g., induction of apoptosis. The methods of the invention can be used to identify reagents capable of 0 increasing MKK function or activity. Alternatively, increased activity is achieved by over-expression of MKK. When an MKK-mediated disorder is associated with under- expression of MKK, or expression of a mutant MKK polypeptide, a sense polynucleotide sequence (the DNA coding strand) or MKK polypeptide can be introduced into the cell to enhance normal MKK activity. If necessary, these treatments are targeted to specific cells by their mode of administration (e.g., by use of cell-type specific viral vectors) , or by placing MKK7 nucleic acids m recombinant constructs with cell-type specific or inducible promotors by methods known in the art. For example, MKK7 nucleic acid-conta ing vectors can be constructed by recombinant DNA technology methods standard in the art. Vectors can be plasmid, viral, or others known in the art, used for replication and expression in mammalian cells. Expression of the sequence encoding the MKK7 nucleic acid can be by any promoter known in the art to act in mammalian, preferably human cells. Such promoters can be inducible or constitutive. Such promoters include, but are not limited to: the SV40 early promoter region (Bernoist et al., Nature 290:304, 1981); the promoter contained in the 3' long terminal repeat of Rous sarcoma virus (Yamamoto et al . , Cell 22:787-797, 1988); the herpes thymidine kinase promoter (Wagner et al . , Proc . Natl . Acad . Sci . USA 78:1441, 1981); or the regulatory sequences of the metallothionein gene (Brinster et al . , Nature 296:39, 1988) . The antibodies of the invention can be administered parenterally by injection or by gradual infusion over time. The monoclonal antibodies of the invention can be administered intravenously, intraperitoneally, intramuscularly, subcutaneously, intracavity, or transdermally. Preparations for parenteral administration of a polypeptide or an antibody of the invention include sterile aqueous or non-aqueous solutions, suspensions, and emulsions. Examples of non-aqueous solvents are propylene glycol, polyethylene glycol, vegetable oils such as olive oil, and injectable organic esters such as ethyl oleate. Aqueous carriers include water, alcoholic/aqueous solutions, emulsions or suspensions, including saline and buffered media. Parenteral vehicles include sodium chloride solution, Ringer's dextrose, dextrose and sodium chloride, lactated Ringer's, or fixed oils. Intravenous vehicles include fluid and nutrient replenishers, electrolyte replenishers (such as those based on Ringer's dextrose) and the like. Preservatives and other additives can also be present, such as, for example, antimicrobials, antioxidants, chelating agents, and inert gases, and the like. Polynucleotide sequences, including antisense sequences, can be therapeutically administered by various techniques known to those skilled in the art. Such therapy would achieve its therapeutic effect by introduction of the MKK polynucleotide into cells of mammals having a MKK-mediated disorder. Delivery of MKK polynucleotides can be achieved using free polynucleotide or a recombinant expression vector such as a chimeric virus or a colloidal dispersion system. Especially preferred for therapeutic delivery of nucleotide sequences is the use of targeted liposomes. Targeting of the therapeutic reagent to specific tissues is desirable to increase the efficiency of delivery. The targeting can be achieved by passive mechanisms via the route of administration. Active targeting to specific tissues can also be employed. The use of liposomes, colloidal suspensions, and viral vectors allows targeting to specific tissues by changing the composition of the formulation containing the therapeutic reagent, for example, by including molecules that act as receptors for components of the target tissues. Examples include sugars, glycoplipids , polynucleotides, or proteins. These molecules can be included with the therapeutic reagent. Alternatively, these molecules can be included by indirect methods, for example, by inclusion of a polynucleotide that encodes the molecule, or by use of packaging systems that provide targeting molecules. Those skilled in the art will know, or will ascertain with the use of the teaching provided herein, which molecules and procedures will be useful for delivery of the therapeutic reagent to specific tissues. Transgenic animals MKK polypeptides can also be expressed in transgenic animals . These animals represent a model system for the study of disorders that -are caused by or exacerbated by overexpression or underexpression of MKK, and for the development of therapeutic agents that modulate the expression or activity of MKK. For example, dominant -negative and constitutively activated aileles could be expressed in mice to establish physiological function. Transgenic animals can be farm animals (pigs, goats, sheep, cows, horses, rabbits, and the like) rodents (such as rats, guinea pigs, and mice) , non-human primates (for example, baboons, monkeys, and chimpanzees) , and domestic animals (for example, dogs and cats) . Transgenic mice are especially preferred. Any technique known in the art can be used to introduce a MKK transgene into animals to produce the founder lines of transgenic animals. Such techniques include, but are not limited to, pronuclear microinj ection (U.S. Pat. No. 4,873,191); retrovirus mediated gene transfer into germ lines (Van der Putten et al., Proc . Natl . Acad . Sci . , USA 82:6148, 1985); gene targeting into embryonic stem cells (Thompson et al . , Cell 56:313, 1989); and electroporation of embryos (Lo, Mol . Cell . Biol . 3:1803, 1983). Especially useful are the methods described in Yang et al . (Proc. Natl Acac . Sci . USA 94:3004-3009, 1997) The present invention provides for transgenic animals that carry the MKK transgene in all their cells, as well as animals that carry the transgene in some, but not all of their cells. That is, the invention provides for mosaic animals. The transgene can be integrated as a single transgene or in concatamers, e.g., head-to-head tandems or head-to-tail tandems. The transgene can also be selectively introduced into and activated in a particular cell type (Lasko et al . , Proc . Natl . Acad. Sci . USA 89:6232, 1992). The regulatory sequences required for such a cell-type specific activation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art. When it is desired that the MKK transgene be integrated into the chromosomal site of the endogenous MKK gene, gene targeting is preferred. Briefly, when such a technique is to be used, vectors containing some nucleotide sequences homologous to an endogenous MKK gene are designed for the purpose of integrating, via homologous recombination with chromosomal sequences, into and disrupting the function of the nucleotide sequence of the endogenous gene. The transgene also can be selectively introduced into a particular cell type, thus inactivating the endogenous MKK gene in only that cell type (Gu et al., Science 265:103, 1984). The regulatory sequences required for such a cell -type specific inactivation will depend upon the particular cell type of interest, and will be apparent to those of skill in the art. These techniques are useful for preparing "knock outs" having no functional MKK gene. Once transgenic animals have been generated, the expression of the recombinant MKK gene can be assayed utilizing standard techniques. Initial screening may be accomplished by Southern blot analysis or PCR techniques to determine whether integration of the transgene has taken place. The level of mRNA expression of the transgene in the tissues of the transgenic animals may also be assessed using techniques which include, but are not limited to, Northern blot analysis of tissue samples obtained from the animal, in si tu hybridization analysis, and RT-PCR. Samples of MKK gene-expressing tissue can also be evaluated immunocytochemically using antibodies specific for the MKK transgene product . For a review of techniques that can be used to generate and assess transgenic animals, skilled artisans can consult Gordon (Intl. Rev. Cytol . 115:171-229, 1989), and may obtain additional guidance from, for example: Hogan et al. Manipulating the Mouse Embryo, Cold Spring Harbor Press, Cold Spring Harbor, NY, 1986);, Krimpenfort et al. (Bio /Technology 9:86, 1991), Palmiter et al . ( Cell 41:343, 1985), Kraemer et al . (Genetic Manipulation of the Early Mammalian Embryo, Cold Spring Harbor Press, Cold Spring Harbor, NY, 1985), Hammer et al. (Nature 315:680, 1985), Purcel et al . ( Sci ence, 244:1281, 1986), Wagner et al . (U.S. Patent No. 5,175,385), and Krimpenfort et al . (U.S. Patent No. 5,175,384) (the latter two publications are hereby incorporated by reference) . Other Embodiments It is to be understood that while the invention has been described in conjunction with the detailed description thereof, that the foregoing description is intended to illustrate and not limit the scope of the invention, which is defined by the scope of the appended claims. Other aspects, advantages, and modifications are within the scope of the following claims.

Claims: CLAIMS 1. A substantially pure mammalian mitogen- activated protein kinase kinase (MKK7) polypeptide having serine, threonine, and tyrosine kinase activity, and phosphorylating mitogen-activated protein (MAP) kinase JNK, but not p38. 2. A polypeptide of claim 1 comprising the amino acid sequence of SEQ ID NO: 18, SEQ ID NO: 20, SEQ ID NO:26, SEQ ID NO:28, SEQ ID NO:30, or SEQ ID NO:32. 3. An isolated polynucleotide sequence encoding a polypeptide of claim 1. 4. An isolated polynucleotide sequence of claim 3 comprising the sequence of SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, or SEQ ID NO: 31, or degenerate variants thereof, or a polynucleotide sequence fully complementary to the sequence of SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, or SEQ ID NO: 31, or degenerate variants thereof. 5. An isolated polynucleotide sequence of claim 3 comprising a polynucleotide sequence that hybridizes under stringent hybridization conditions to the sequence of SEQ ID NO: 17, SEQ ID NO: 19, SEQ ID NO: 25, SEQ ID NO: 27, SEQ ID NO: 29, SEQ ID NO: 31, or a complement thereof . 6. A recombinant expression vector containing a polynucleotide sequence of claim 3. 7. A recombinant host cell comprising a polynucleotide sequence of claim 3. 8. A purified antibody that binds specifically to a polypeptide of claim 1. 9. A purified antibody that binds specifically to a polypeptide of claim 2. 10. A method of measuring the activity of a mitogen-activated protein kinase kinase (MKK7) in a biological test sample, said method comprising: a) incubating said test sample with an MKK substrate for the MKK polypeptide of claim 1 and labeled phosphate under conditions sufficient to allow phosphorylation of said substrate; and b) determining the rate of incorporation of labeled phosphate into said substrate, wherein said rate of incorporation is a measure of MKK7 activity. 11. A method of claim 10, wherein said MKK substrate is selected from the group consisting of JNK MAP kinases, activating transcription factor-2 (ATF2) , ATFa, cAMP response element binding protein (CRE-BPa) , and c-Jun. 12. A method of claim 10, wherein said biological test sample is fluid, cells, or tissue obtained from a mammal . 13. A method for measuring the synthesis of MKK7 in a biological test sample, the method comprising the steps of: a) obtaining a biological sample; b) contacting said biological sample with an antibody that specifically binds an MKK7 polypeptide of claim 1; and c) detecting said antibody bound to MKK7 polypeptide, wherein the level of MKK7 synthesis is determined by the amount of bound antibody. 14. A method for measuring the level of expression of MKK7 in a test sample, the method comprising the steps of : a) isolating total or polyadenylated RNA from the test sample; b) incubating the RNA with a polynucleotide probe specific for an MKK7 polynucleotide of claim 3 ; and c) determining the amount of said probe hybridized to the RNA, wherein the level of expression of MKK7 is directly related to the amount of MKK7 probe hybridized to the RNA. 15. A method for identifying a reagent that modulates MKK7 activity, said method comprising: a) obtaining a test sample containing MKK7; b) incubating said test sample with an MKK substrate for the MKK polypeptide of claim 1, a range of reagent concentrations, and labeled phosphate under conditions sufficient to allow phosphorylation of said subtrate when said reagent is not present; c) detecting phosphorylation of said substrate; and d) comparing the effect of said reagent on MKK7 activity relative to a control, wherein any variation compared to control indicates a reagent able to modulate MKK7 substrate phosphorylation. 16. A method of claim 15, wherein said MKK7 substrate is one or more of JNK, ATF2 , ATFa, CRE-BPa, and c-Jun. 17. A method of claim 15 wherein said modulation is inhibition of MKK7 activity. 18. A method for identifying a reagent that modulates MKK7 synthesis, said method comprising: a) providing a sample capable of MKK7 synthesis; b) incubating said sample with a range of reagent concentrations under conditions that allow synthesis of MKK7 when said reagent is not present; c) detecting an MKK7 polypeptide of claim 1; and d) comparing the effect of said reagent on MKK7 synthesis relative to a control, wherein any variation compared to control indicates a reagent able to modulate MKK7. 19. A method of claim 18 wherein said modulation is inhibition of MKK7 synthesis. 20. A method for identifying a reagent that modulates MKK7 expression, said method comprising: a) providing a sample capable of expressing MKK7; b) incubating said sample with a range of concentrations of said reagent under conditions where MKK7 is expressed in the absence of said reagent; c) isolating total or polyadenylated RNA from the sample; d) incubating the RNA with a polynucleotide probe specific for a MKK7 nucleic acid of claim 3; and e) comparing the effect of said reagent on MKK7 RNA expression relative to a control, wherein any variation compared to control indicates a reagent able to modulate MKK7 expression. 21. A method of treating an MKK7 -mediated disorder in a patient, the method comprising administering to the patient a therapeutically effective amount of a reagent that modulates MKK7 activity. 22. The method of claim 21, wherein said MKK7- mediated disorder is selected from the group consisting of ischemic heart disease, kidney failure, oxidative liver damage, respiratory distress syndrome, heat and radiation burns, septic shock, rheumatoid arthritis, autoimmune disorders, and inflammatory diseases. 23. A method of treating an MKK7-associated disorder in a patient, comprising administering to the patient a therapeutically effective amount of an MKK7 polypeptide. 24. The method of claim 23, wherein said MKK7- associated disorder is ischemic heart disease, kidney failure, oxidative liver damage, respiratory distress syndrome, heat and radiation burns, septic shock, rheumatoid arthritis, autoimmune disorders, or inflammatory diseases.

Inventors: DAVIS ROGER J, TOURNIER CATHY, WHITMARSH ALAN, DAVIS, ROGER, J., TOURNIER, CATHY, WHITMARSH, ALAN
Applicants: UNIV MASSACHUSETTS, UNIVERSITY OF MASSACHUSETTS
Application year: 1998
Main classification: C07H21
IPC codes: A61K31, A61K38, A61K45, A61K48, A61P1, A61P9, A61P11, A61P13, A61P17, A61P29, A61P37, A61P43, C07K16, C12N1, C12N5, C12N9, C12N15, C12Q1, G01N33