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)

Desensitization of p21(ras) after stimulation of cells by growth factors and phorbol 12-myristate 13-acetate (PMA) correlates with hyperphosphorylation of the guanine nucleotide exchange factor Son-of-sevenless (Sos) and its dissociation from the adaptor protein Grb2 (Cherniack, A., Klarlund, J. K., Conway, B. R., and Czech, M. P. (1995) J. Biol. Chem. 270, 1485-1488). To test the role of the Raf/mitogen-activated protein (MAP) kinase pathway, we utilized cells expressing a chimera composed of the catalytic domain of p74Raf-1 and the hormone binding domain of the estradiol receptor (DeltaRaf-1:ER). Estradiol markedly stimulated DeltaRaf-1:ER and the downstream MEK and MAP kinases in these cells as well as Sos phosphorylation. However, the dissociation of Grb2 from Sos observed in response to PMA was not apparent upon DeltaRaf-1:ER activation. Furthermore, stimulation of DeltaRaf-1:ER did not impair GTP loading of p21(ras) in response to platelet-derived growth factor or epidermal growth factor. We conclude that activation of the Raf/MAP kinase pathway alone in these cells is insufficient to cause disassembly of Sos from Grb2 or to interrupt the ability of Sos to catalyze activation of p21(ras).
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PMID:Role of the Raf/mitogen-activated protein kinase pathway in p21ras desensitization. 866 95

Oncogenic Ras transforms cells through the activation of multiple downstream pathways mediated by separate effector molecules, one of which is Raf. Here we report the identification of a second ras-binding protein that can induce cellular transformation in parallel with activation of the Raf/mitogen-activated protein kinase cascade. The Ral guanine nucleotide dissociation stimulator (RalGDS) was isolated from a screen for Ras-binding proteins that specifically interact with a Ras effector-loop mutant, ras(12V,37G), that uncouples Ras from activation of Raf1. RalGDS, like ras(12V, 37G), cooperates synergistically with mutationally activated Raf to induce foci of growth and morphologically transformed NIH 3T3 cells. RalGDS does not significantly enhance MAP kinase activation by activated Raf, suggesting that the cooperativity in focus formation is due to a distinct pathway acting downstream of Ras and parallel to Raf.
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PMID:A role for the Ral guanine nucleotide dissociation stimulator in mediating Ras-induced transformation. 866 85

Insulin-induced differentiation of 3T3 L1 cells can be mimicked by expression of transfected ras oncogenes but is completely blocked by expression of dominant negative Ras mutants, demonstrating that Ras proteins mediate insulin signaling in these mammalian cells. In contrast, transfection of tyrosine kinase oncogenes including trk and src dose not result in adipocytic differentiation. Transfected raf-1 oncogenes induce partial adipocytic differentiation, while dominant negative raf mutants block partially the insulin-induced differentiation process. Exposure of 3T3 L1 cells to insulin results in formation of the active Ras-GTP complex without GAP tyrosine phosphorylation. Insulin treatment of untransfected 3T3 L1 cells also induced quick activation of cytosolic 42 kDa mitogen-activated protein kinase (MAPK) and a 90 kDa S6 kinase (RSK). The activation of these cytosolic serine-threonine kinases was also mimicked by Ras expression (in the absence of insulin) in the same cells transfected with inducible ras oncogenes. Furthermore, insulin-induced activation of MAPK and RSK could be blocked by expression of a transfected, inducible dominant negative Ras mutant (N17). These results indicate that Ras proteins are obligatory intermediates in the activation of cytosolic ERKs by insulin. Insulin treatment of 3T3 L1 cells or expression of transfected ras oncogenes resulted also in hyperphosphorylation of cellular Raf-1. Insulin-induced Raf hyperphosphorylation was inhibited by expression of an inducible, dominant negative Ras mutant (N17). Interestingly, however, expression of transfected raf oncogenes did not induce MAPK or RSK activation, and the insulin-induced activation of these kinases was not blocked by expression of transfected dominant negative raf mutants. These results suggest a functional dissociation between Raf-1 and MAPK/RSK activation in insulin/Ras signaling pathways leading to 3T3 L1 differentiation and are consistent with Raf-1 kinase acting in a parallel pathway to the MAPK/RSK pathway after Ras activation in these cells.
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PMID:The insulin/Ras pathway of adipocytic differentiation of 3T3 L1 cells: dissociation between Raf-1 kinase and the MAPK/RSK cascade. 868 Apr 77

An amino-truncated variant form of the epidermal growth factor receptor (EGFRvIII) has been identified in human brain, breast, lung and ovarian tumors. We have found that overexpression of this mutant EGF receptor in NIH3T3 cells results in transformation as a result of the activation of the receptor kinase via ligand-independent dimerization. Transformation was correlated with tyrosine phosphorylation of only a subset of the proteins observed in cells overexpressing the normal EGF receptor. This suggested that further studies on cells expressing the EGFRvIII might provide insights into the pathways most relevant to transformation. In clones expressing high levels of mutant EGF receptor, the levels of both Grb2 and SHC were decreased. Despite this decrease, much of the endogenous Grb2 immunoprecipitated with EGFRvIII. Interestingly, no increase in ras-GTP loading was found in clones expressing the EGFRvIII and MAP kinase assays indicated only a small increase in activity. These results indicate that high-level expression of the EGFRvIII induces down-regulation of the ras-MAP kinase pathway and that other components involved in EGF receptor signal transduction may play a greater role in neoplastic transformation by the EGFRvIII.
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PMID:Transformational and altered signal transduction by a naturally occurring mutant EGF receptor. 870 May 57

Many studies have identified nitric oxide (NO) and related chemical species (NOx) as having critical roles in neurotransmission, vasoregulation, and cellular signaling. Previous work in this laboratory has focused on elucidating the mechanism of NOx signaling in cells. We have demonstrated that NOx-induced activation of the guanine nucleotide-binding protein p21(ras) leads to nuclear translocation of the transcription factor NFkappaB. Here, we investigated whether intermediary signaling elements, namely the mitogen-activated protein (MAP) kinases, are involved in mediating NOx signaling. We found that NOx activates the extracellular signal-regulated kinase (ERK), p38, and c-Jun NH2-terminal kinase (JNK) subgroups of MAP kinases in human Jurkat T cells. JNK was found to be 100-fold more sensitive to NOx stimulation than p38 and ERK. In addition, the activation of JNK and p38 by NOx was more rapid than ERK activation. Depletion of intracellular glutathione augmented the NOx-induced increase in kinase activity. Furthermore, endogenous NO, generated from NO synthase, activated ERK, and NOx-induced MAP kinase activation was effectively blocked by the farnesyl transferase inhibitor alpha-hydroxyfarnesylphosphonic acid. These data support the hypothesis that critical signaling kinases, such as ERK, p38, and JNK, are activated by NO-related species and thus participate in NO signal transduction. These findings establish a role for multiple MAP kinase signaling pathways in the cellular response to NOx.
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PMID:Differential activation of mitogen-activated protein kinases by nitric oxide-related species. 870 74

Cyclic adenosine monophosphate (cAMP)-dependent protein kinase A (PKA) regulates the activity of growth-factor-induced pathways at the level of cytoplasmic kinases and nuclear transcription factors. We observed that H-89, an inhibitor of PKA, induced mitogen-activated protein (MAP) kinase activity in a 12V-ras-transformed fibroblast cell line. In contrast, H-89 inhibited phorbol-ester-mediated induction of MAP kinase, junB messenger ribonucleic acid (mRNA), and collagenase mRNA in these cells. Phorbol-ester stimulation of a collagenase-promoter reporter construct was also inhibited by H-89. However, stimulation of the collagenase promoter was not inhibited by overexpression of the PKA-inhibitory protein PKI. These data suggest that H-89 inhibits the activity of an enzyme required for phorbol-ester induction of collagenase mRNA, but that this inhibition does not occur at the level of PKA.
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PMID:H-89 inhibits collagenase induction by phorbol ester through a mechanism that does not involve protein kinase A. 873 3

Expression of the neurotrophin-3 (NT-3) receptor (TrkC) and the effects of NT-3 on signal transduction were investigated in highly enriched populations of embryonic rat hippocampal pyramidal neurons grown in bilaminar cultures. PCR analysis revealed that the predominant trkC isoform is K1, which lacks an insert in the kinase domain. Polyclonal TrkC-specific antibodies stained > 90% of the neurons and revealed a single approximately 145-kDa protein in immunoblots of extracts from adult hippocampus and pyramidal neuron cultures. Addition of NT-3 (50 ng/ml) to these cultures induced the tyrosine phosphorylation of TrkC but not TrkB, as determined by anti-phosphotyrosine staining of immunoprecipitates; thus, all the effects of NT-3 are mediated through TrkC. NT-3 also increased the tyrosine phosphorylation of 42-, 44-, 49-, 55-, 95-, and 145-kDa proteins; the pattern induced by brain-derived neurotrophic factor (BDNF) was similar but not identical to that induced by NT-3, suggesting that subtle differences may exist in signaling by TrkB and TrkC receptors. Immunoprecipitation of p21ras from 32P-prelabeled cells showed that NT-3 increased the level of the GTP-bound form of the protein threefold over the control within 5 min. Mitogen-activated protein (MAP) kinase activity was maximally elevated by NT-3 within 2 min and then returned slowly toward baseline over the next 60 min. Tyrosine phosphorylation of phospholipase C-gamma increased rapidly after NT-3, suggesting that this enzyme becomes activated. Consistent with this, the neurotrophin rapidly increased protein kinase C activity as well as intracellular Ca2+ levels. The effects of both NT-3 and BDNF on Ca2+ levels were attenuated in Ca(2+)-free medium, suggesting that both neurotrophins increase Ca2+ flux across the plasma membrane as well as release from internal stores. NT-3 also increased c-Fos expression in > 80% of the cells; the effect peaked at 30 min and declined to baseline by 120 min. Despite the activation of ras-MAP kinase and phosphoinositide signaling pathways, neither NT-3 nor BDNF alone or in combination could sustain hippocampal pyramidal neurons deprived of glial support. We conclude that in this system NT-3 and BDNF do not appear to be acting as classical "neurotrophic" factors and that activation of the MAP kinase pathway is insufficient for the promotion of neuronal survival.
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PMID:Neurotrophin-3 and brain-derived neurotrophic factor activate multiple signal transduction events but are not survival factors for hippocampal pyramidal neurons. 875

Although several oncogenes, including c-myc, ras and c-raf-1, have been implicated in cellular resistance to ionising radiation, there is less information relating oncogene expression to cis-diamminedichloroplatinum (CDDP) resistance. However, transfection of c-myc or v-H-ras and activation of protein kinase C (PKC), which contributes to the RAF-1, MAP kinase signal transduction pathway, can influence therapeutic response to CDDP. Activation of PKC increases CDDP sensitivity, whilst transfected c-myc or v-H-ras induce CDDP resistance. We have previously reported that human in vitro cell lines show different patterns of sensitivity to CDDP and 4 MeV X-irradiation. In these cells radiation sensitivity is related to high levels of expression of the C-raf-1 proto-oncogene. We thus predicted that cells sensitive to CDDP might show a different relationship to c-raf-1 expression. In addition, because cyclin D1 expression can be upregulated by the myc or ras oncogenes, we also chose to study putative relationships between cyclin D1 protein levels and intrinsic cellular sensitivity to CDDP and gamma-irradiation. We report that in the 16 human cell lines which we have studied, high cyclin D1 expression is related to CDDP resistance but has no relationship with radiation responsiveness, whereas high c-raf-1 expression, although related to radiosensitivity has no relationship with CDDP responsiveness.
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PMID:Sensitivity to cis-diamminedichloroplatinum in human cancer cells is related to expression of cyclin D1 but not c-raf-1 protein. 876 May 92

In an effort to determine the role of protein kinase C-delta (PKC-delta) in cellular transformation mediated by the sis proto-oncogene, we cotransfected expression vectors containing cDNAs that encode for c-sis with an ATP binding mutant of PKC-delta (PKC-delta K376R) or wild type PKC-delta (PKC-delta WT) into NIH3T3 cells. Our results showed that expression of PKC-delta K376R severely impaired Sis-induced focus formation, whereas cotransfection of PKC-delta WT cDNA had no effect on Sis-mediated transformation. Consistent with this result, PKC-delta K376R expression also inhibited PDGF-BB-mediated anchorage-independent colony formation. While cotransfection of a vector containing a dominant negative mutant of ras (N17 ras) cDNA potently inhibited Sis-induced transformation, the expression of PKC-delta K376R did not block transformation mediated by v-H-Ras or v-Raf. In addition, PDGF-BB-induced Raf and mitogen-activated protein kinase activation, which are known to be downstream molecules in the Ras cascade, were not affected by the expression of PKC-delta K376R, indicating that PKC-delta and Ras are segregated in mediating Sis-induced transformation. Interestingly, expression of PKC-delta K376R strongly reduced TPA responsive element (TRE) transactivation induced by PDGF stimulation, suggesting that activation of TRE-containing genes, which may be involved in Sis-mediated transformation, are negatively regulated by expression of PKC-delta K376R.
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PMID:Expression of an ATP binding mutant of PKC-delta inhibits Sis-induced transformation of NIH3T3 cells. 876 Dec 94

Extracellular signal-regulated protein kinases (ERKs) are members of the mitogen-activated protein kinase family that are rapidly phosphorylated and activated in response to various extracellular stimuli, including growth factors. Of these, the ERK1 and ERK2 forms are by far the most abundant and the most studied. Much less is known about other ERK forms, including one previously designated ERK4 on the basis of its cross-reactivity with ERK1 and ERK2. We report here that ERK4 in rat PC12 pheochromocytoma cells can be immunoprecipitated by anti-ERK antiserum R2 and have used this re-agent to characterize this species further. We find that ERK4 rapidly becomes tyrosine-phosphorylated in response to nerve growth factor (NGF) and epidermal growth factor (EGF) and, to a lesser degree, in response to insulin and a permeant cyclic AMP analogue. As in the case of ERK1 and ERK2, tyrosine phosphorylation of ERK4 occurs by a ras-dependent pathway in response to NGF and EGF and shows prolonged kinetics for NGF but not EGF treatment. Recognition by multiple antisera directed against various domains of ERK1 supports classification of ERK4 within the ERK family; however, two-dimensional gel analysis clearly distinguishes ERK4 from isoforms of ERK1. These findings thus reveal an additional member of the ERK family that is responsive to growth factors and that could play a distinct role in intracellular signaling.
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PMID:Tyrosine phosphorylation of extracellular signal-regulated protein kinase 4 in response to growth factors. 876 83


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