Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.24 (mitogen-activated protein kinase)
95,810 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

cRaf-1 is a mitogen-activated protein kinase that is the main effector recruited by GTP-bound Ras in order to activate the MAP kinase pathway. Inactive Raf is found in the cytosol in a complex with Hsp90, Hsp50 (Cdc37) and the 14-3-3 proteins. GTP-bound Ras binds Raf and is necessary but not sufficient for the stable activation of Raf that occurs in response to serum, epidermal growth factor, platelet-derived growth factor or insulin. These agents cause a two- to threefold increase in overall phosphorylation of Raf on serine/threonine residues, and treatment of cRaf-1 with protein (serine/threonine) phosphatases can deactivate it, at least partially. The role of 14-3-3 proteins in the regulation of Raf's kinase activity is uncertain and is investigated here. Active Raf can be almost completely deactivated in vitro by displacement of 14-3-3 using synthetic phosphopeptides. Deactivation can be substantially reversed by addition of purified recombinant bacterial 14-3-3; however, Raf must have been previously activated in vivo to be reactivated by 14-3-3 in vitro. The ability of 14-3-3 to support Raf activity is dependent on phosphorylation of serine residues on Raf and on the integrity of the 14-3-3 dimer; mutant monomeric forms of 14-3-3, although able to bind Raf in vivo, do not enable Raf to be activated in vivo or restore Raf activity after displacement of 14-3-3 in vitro. The 14-3-3 protein is not required to induce dimerization of Raf. We propose that dimeric 14-3-3 is needed both to maintain Raf in an inactive state in the absence of GTP-bound Ras and to stabilize an active conformation of Raf produced during activation in vivo.
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PMID:A dimeric 14-3-3 protein is an essential cofactor for Raf kinase activity. 966 34

Genetic screens in Drosophila have identified p50(cdc37) to be an essential component of the sevenless receptor/mitogen-activated kinase protein (MAPK) signaling pathway, but neither the function nor the target of p50(cdc37) in this pathway has been defined. In this study, we examined the role of p50(cdc37) and its Hsp90 chaperone partner in Raf/Mek/MAPK signaling biochemically. We found that coexpression of wild-type p50(cdc37) with Raf-1 resulted in robust and dose-dependent activation of Raf-1 in Sf9 cells. In addition, p50(cdc37) greatly potentiated v-Src-mediated Raf-1 activation. Moreover, we found that p50(cdc37) is the primary determinant of Hsp90 recruitment to Raf-1. Overexpression of a p50(cdc37) mutant which is unable to recruit Hsp90 into the Raf-1 complex inhibited Raf-1 and MAPK activation by growth factors. Similarly, pretreatment with geldanamycin (GA), an Hsp90-specific inhibitor, prevented both the association of Raf-1 with the p50(cdc37)-Hsp90 heterodimer and Raf-1 kinase activation by serum. Activation of Raf-1 via baculovirus coexpression with oncogenic Src or Ras in Sf9 cells was also strongly inhibited by dominant negative p50(cdc37) or by GA. Thus, formation of a ternary Raf-1-p50(cdc37)-Hsp90 complex is crucial for Raf-1 activity and MAPK pathway signaling. These results provide the first biochemical evidence for the requirement of the p50(cdc37)-Hsp90 complex in protein kinase regulation and for Raf-1 function in particular.
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PMID:p50(cdc37) acting in concert with Hsp90 is required for Raf-1 function. 1002 54

Basal and stress-induced synthesis of the components of the highly conserved heat shock protein Hsp90 chaperone complex require the heat shock transcription factor (HSF); Saccharomyces cerevisiae cells expressing the HSF allele HSF(1-583) reversibly arrest growth at 37 degrees C in the G(2)/M phase of the cell cycle due to diminished expression of these components. A suppressor mutant capable of restoring high-temperature growth to HSF(1-583) cells was identified, harboring a disruption of the SCH9 protein kinase gene, homologous to the protein kinase A and protein kinase B/Akt families of mammalian growth control kinases. Loss of Sch9 in HSF(1-583) cells derepresses Hsp90 signal transduction functions as demonstrated by restoration of transcriptional activity by the mammalian glucocorticoid receptor and the heme-dependent transcription factor Hap1, and by enhanced pheromone-dependent signaling through the Ste11 mitogen-activated protein kinase (MAPK). Moreover, Sch9-deficient cells with normal levels of Hsp90 chaperone complex components display hyperactivation of the pheromone response MAPK pathway in the absence of pheromone. These results demonstrate that the evolutionarily conserved function of the Hsp90 chaperone complex as a signal transduction facilitator is modulated by a growth regulatory kinase.
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PMID:The Sch9 protein kinase regulates Hsp90 chaperone complex signal transduction activity in vivo. 1054 7

During Xenopus oocyte maturation, the Mos protein kinase is synthesized and activates the MAP kinase cascade. In this report, we demonstrate that the synthesis and activation of Mos are two separable processes. We find that Hsp90 function is required for activation and phosphorylation of Mos and full activation of the MAP kinase cascade. Once Mos is activated, Hsp90 function is no longer required. We show that Mos interacts with both Hsp90 and Hsp70, and that there is an inverse relationship between association of Mos with these two chaperones. We propose that Mos protein kinase is activated by a novel mechanism involving sequential association with Hsp70 and Hsp90 as well as phosphorylation. We also present evidence for a two-phase activation of MAP kinase in Xenopus oocytes.
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PMID:Hsp90 is required for c-Mos activation and biphasic MAP kinase activation in Xenopus oocytes. 1074 20

The inhibitor of the Hsp90 chaperone Geldanamycin has been reported to have several cellular effects, such as inhibition of v-src activity or destabilization of Raf-1 among others. We show now that Geldanamycin treatment induces different phenotypes in different cell lines. In PC12 cells, it triggers apoptosis, whereas in the murine neuroblastoma N2A, it induces differentiation with neurite outgrowth. Geldanamycin effects cannot be mimicked by inhibition of the c-src protein tyrosine kinases, and nerve growth factor does not protect PC12 cells from apoptosis. Mitogen-activated protein kinase activities ERK and JNK are activated differently according to cell type: in PC12 cells JNK is activated, and its inhibition abolishes apoptosis, but not ERK; in N2A cells, both ERK and JNK are activated, but with peak activities at different times.
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PMID:Opposite effects of the Hsp90 inhibitor Geldanamycin: induction of apoptosis in PC12, and differentiation in N2A cells. 1117 4

The growth-stimulating effects of thrombin are mediated primarily via activation of a G protein-coupled receptor, PAR-1. Because PAR-1 has no intrinsic tyrosine kinase activity, yet requires tyrosine phosphorylation events to induce mitogenesis, we investigated the role of the Janus tyrosine kinases (JAKs) in thrombin-mediated signaling. JAK2 was activated rapidly in rat vascular smooth muscle cells (VSMC) treated with thrombin, and signal transducers and activators of transcription (STAT1 and STAT3) were phosphorylated and translocated to the nucleus in a JAK2-dependent manner. AG-490, a JAK2-specific inhibitor, and a dominant negative JAK2 mutant inhibited thrombin-induced ERK2 activity and VSMC proliferation suggesting that JAK2 is upstream of the Ras/Raf/MEK/ERK pathway. To elucidate the functional significance of JAK-STAT activation, we studied the effect of thrombin on heat shock protein (Hsp) expression, based upon the following: 1) reports that thrombin stimulates reactive oxygen species production in VSMC; 2) the putative role of Hsps in modulating cellular responses to reactive oxygen species; and 3) the presence of functional STAT1/3-binding sites in Hsp70 and Hsp90beta promoters. Indeed, thrombin up-regulated Hsp70 and Hsp90 protein expression via enhanced binding of STATs to cognate binding sites in the Hsp70 and Hsp90 promoters. Together, these results suggest that JAK-STAT pathway activation is necessary for thrombin-induced VSMC growth and Hsp gene expression.
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PMID:Thrombin regulates vascular smooth muscle cell growth and heat shock proteins via the JAK-STAT pathway. 1127 37

17-(Allylamino)-17-demethoxygeldanamycin (17-AAG) is an ansamycin antibiotic that binds to a conserved pocket in Hsp90 and induces the degradation of proteins that require this chaperone for conformational maturation. 17-AAG causes a retinoblastoma (RB)-dependent G1 block in cancer cells and is now in clinical trial. In breast cancer cells, G1 block is accompanied by differentiation and followed by apoptosis. The differentiation is characterized by specific changes in morphology and induction of milk fat proteins and lipid droplets. In cells lacking RB, neither G1 arrest nor differentiation occurs; instead, they undergo apoptosis in mitosis. Introduction of RB into these cells restores the differentiation response to 17-AAG. Inhibitors of the ras, mitogen-activated protein kinase, and phosphatidylinositol 3-kinase pathways cause accumulation of milk fat proteins and induction of lipid droplets when associated with G1 arrest but do not cause morphological changes. Thus, regulation of Hsp90 function by 17-AAG in breast cancer cells induces RB-dependent morphological and functional mammary differentiation. G1 arrest is sufficient for some but not all aspects of the phenotype. Induction of differentiation may be responsible for some of the antitumor effects of this drug.
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PMID:Inhibition of heat shock protein 90 function by ansamycins causes the morphological and functional differentiation of breast cancer cells. 1130 72

Our previous works demonstrated that ligands of macrophage scavenger receptor (MSR) induce protein kinases (PKs) including protein-tyrosine kinase (PTK) and up-regulate urokinase-type plasminogen activator expression (Hsu, H. Y., Hajjar, D. P., Khan, K. M., and Falcone, D. J. (1998) J. Biol. Chem. 273, 1240--1246). To continue to investigate MSR ligand-mediated signal transductions, we focus on ligands, oxidized low density lipoprotein (OxLDL), and fucoidan induction of the cytokines tumor necrosis factor-alpha (TNF) and interleukin 1 beta (IL-1). In brief, in murine macrophages J774A.1, OxLDL and fucoidan up-regulate TNF production; additionally, fucoidan but not OxLDL induces IL-1 secretion, prointerleukin 1 (proIL-1, precursor of IL-1) protein, and proIL-1 message. Simultaneously, fucoidan stimulates activity of interleukin 1-converting enzyme. We further investigate the molecular mechanism by which ligand binding-induced PK-mediated mitogen-activated protein kinase (MAPK) in regulation of expression of proIL-1 and IL-1. Specifically, fucoidan stimulates activity of p21-activated kinase (PAK) and of the MAPKs extracellular signal-regulated kinase (ERK), c-Jun NH(2)-terminal kinase (JNK), and p38. Combined with PK inhibitors and genetic mutants of Rac1 and JNK in PK activity assays, Western blotting analyses, and IL-1 enzyme-linked immunosorbent assay, the role of individual PKs in the regulation of proIL-1/IL-1 was extensively dissected. Moreover, tyrosine phosphorylation of pp60Src as well as association between pp60Src and Hsp90 play important roles in fucoidan-induced proIL-1 expression. We are the first to establish two fucoidan-mediated signaling pathways: PTK(Src)/Rac1/PAK/JNK and PTK(Src)/Rac1/PAK/p38, but not PTK/phospholipase C-gamma 1/PKC/MEK1/ERK, playing critical roles in proIL-1/IL-1 regulation. Our current results indicate and suggest a model for MSR ligands differentially modulating specific PK signal transduction pathways, which regulate atherogenesis-related inflammatory cytokines TNF and IL-1.
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PMID:Ligands of macrophage scavenger receptor induce cytokine expression via differential modulation of protein kinase signaling pathways. 1139 Mar 74

The GR is a hormone-activated transcription factor that acts to regulate specific gene expression. In the absence of hormone, the GR and other steroid receptors have been shown to form complexes with several mammalian heat shock proteins. As heat shock proteins are produced by cells as an adaptive response to stress, speculation has existed that communication between the heat shock and glucocorticoid hormone signal pathways must exist. Only recently has evidence to support this hypothesis been reported. In almost all cases, the evidence has been of an ability of heat shock to cause a potentiation of the glucocorticoid hormone response. In this proposal, evidence is now presented that heat shock signaling can, in turn, be regulated by glucocorticoids. In mouse L929 cells stably expressing a chloramphenicol acetyltransferase reporter controlled by the human heat shock protein70 promoter and containing known binding sites for heat shock transcription factor 1 treatment with glucocorticoid agonist (dexamethasone) results in a dose-dependent decrease of stress-induced chloramphenicol acetyltransferase gene expression. In these cells, inhibition of heat shock protein70 promoter activity by dexamethasone was completely blocked by GR antagonist (RU486). Similar treatment of L929 cells stably expressing a chloramphenicol acetyltransferase reporter under the control of the constitutively active SV40 promoter showed no such inhibition by dexamethasone. More importantly, dexamethasone was also found to inhibit heat shock-induced expression of the major heat shock proteins-heat shock proteins70, 90, and 110. Thus, the inhibitory effect of dexamethasone appears to apply to most, if not all, heat shock transcription factor 1-regulated genes. Although dexamethasone did not prevent the DNA-binding function of heat shock-activated heat shock transcription factor 1, it did inhibit a constitutively active mutant of human heat shock transcription factor 1 under nonstress conditions, suggesting that dexamethasone repression of heat shock transcription factor 1 was primarily through an inhibition of heat shock transcription factor 1 transcription enhancement activity. To more accurately characterize the stage of GR signaling responsible for inhibition of heat shock transcription factor 1, a series of Chinese hamster ovary cells containing either no GR, wild-type mouse GR, or single-point mutations of GR were employed. Dexamethasone inhibition of heat shock-induced heat shock transcription factor 1 activity was observed in the presence of wild-type GR, but not in Chinese hamster ovary cells lacking GR, suggesting that signaling cascades other than GR were not involved in this effect of dexamethasone. Consistent with this conclusion was the observation that dexamethasone had no effect on activity of the MAPKs (ERK1, ERK2, or c-jun N-terminal kinase), which are known to negatively regulate heat shock transcription factor 1. Dexamethasone inhibition of heat shock transcription factor 1 was not seen in Chinese hamster ovary cells expressing GR defective for DNA-binding function. Moreover, dissociation of GR/Hsp90/Hsp70 complexes was observed in response to hormone for both the wild-type and DNA binding-defective forms of GR, demonstrating that release of Hsp90 or Hsp70 (both of which are known to keep heat shock transcription factor 1 in its inactive state) could be ruled out as a potential mechanism. Thus, it appears that GR-mediated transactivation or transrepression is required for the inhibitory effect of dexamethasone on heat shock transcription factor 1 activity. Taken as a whole, these results provide evidence for a novel mechanism of cross-talk in which signaling by the GR can attenuate the heat shock response in cells through an inhibition of the transcription enhancement activity of HSF1.
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PMID:Inhibition of heat shock transcription factor by GR. 1146 62

An internal tandem duplication of the juxtamembrane (JM) domain of FLT3, a family of ligand-activated receptor tyrosine kinases, has been found in 20% of cases of acute myeloid leukemia (AML), and this mutation is correlated with leukocytosis and a poor prognosis. As a therapeutic approach, we previously reported that herbimycin A (HA) inhibited the growth of tandemly duplicated FLT3 (TDFLT3)-transformed cells (Leukemia 2000; 14: 374). Here, we have investigated the mechanism behind the cytotoxicity of HA, an ansamycin derivative which is now known to target Hsp90. The treatment with HA or another Hsp90 inhibitor, radicicol, induced selective apoptosis in TDFLT3-transformed 32D cells (TDFLT3/32D). The tyrosine-phosphorylation of TDFLT3 was inhibited by HA, whereas FLT3 ligand-induced phosphorylation of wild-type FLT3 (WtFLT3) was not. The downstream signal molecules MAPK, Akt and STAT5a were also dephosphorylated by HA in TDFLT3/32D. Immunoprecipitation analysis showed that TDFLT3 but not WtFLT3 formed a complex with Hsp90, and that the HA treatment dissociated TDFLT3 from the Hsp90 chaperone complex. These findings imply that targeting of Hsp90 will facilitate the development of anti-TDFLT3 therapy, and that Hsp90 is closely involved in the oncogenic activation of FLT3.
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PMID:Selective apoptosis of tandemly duplicated FLT3-transformed leukemia cells by Hsp90 inhibitors. 1214 95


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