Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.12.2 (MEK)
 18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Adult mammalian ventricular cardiomyocytes are terminally differentiated cells that enlarge adaptively by hypertrophy. In this situation, genes normally expressed in the fetal ventricular cardiomyocyte (e.g. atrial natriuretic factor (ANF), beta-myosin heavy chain (beta-MHC), and skeletal muscle (SkM) alpha-actin) are re-expressed, and there is transient expression of immediate early genes (e.g. c-fos). Using appropriate reporter plasmids, we studied the effects of transfection of the constitutively active or dominant negative mitogen-activated protein kinase kinase MEK1 on ANF, beta-MHC, and SkM alpha-actin promoter activities in cultured ventricular cardiomyocytes. ANF expression was stimulated (maximally 75-fold) by the hypertrophic agonist phenylephrine in a dose-dependent manner (EC50, 10 microM), and this stimulation was inhibited by dominant negative MEK1. Cotransfection of dominant negative MEK1 with a dominant negative mitogen-activated protein kinase (extracellular signal-regulated protein kinase (ERK2)) increased this inhibition. Transfection with constitutively active MEK1 constructs doubled ANF promoter activity. The additional cotransfection of wild-type ERK2 stimulated ANF promoter activity by about 5-fold. Expression of beta-MHC and SkM alpha-actin was also stimulated. Promoter activity regulated by activator protein-1 or c-fos serum response element consensus sequences was also increased. We conclude that the MEK1/ERK2 cascade may play a role in regulating gene expression during hypertrophy.
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PMID:The mitogen-activated protein kinase kinase MEK1 stimulates a pattern of gene expression typical of the hypertrophic phenotype in rat ventricular cardiomyocytes. 749 96

Mechanical stress induces cardiac hypertrophy and expression of specific genes in the cardiac myocytes. External stimuli are generally transduced into the nucleus through the activation of a protein kinase cascade. We have previously shown that stretching cardiomyocytes stimulates the activity of protein kinase C (PKC), mitogen-activated protein (MAP) kinase and S6 protein kinase. In the present study, we examined two other kinases, Raf-1 kinase and MAP kinase kinase, which are supposed to lie between PKC and MAP kinase in the protein kinase cascade. Stretching cardiocytes by using the in vitro system induced hyperphosphorylation of Raf-1 kinase and activation of MAP kinase kinase. The protein kinases activated by mechanical stress are similar to those activated by growth factors. We examined the possible involvement of angiotensin II (Ang II) in the protein synthesis and gene expression induced by mechanical stress. CV11974, an Ang II-receptor antagonist, partially suppressed the increases in amino acid incorporation, c-fos gene expression and MAP kinase activity induced by stretching. These results suggest that a variety of protein kinases are activated by mechanical stress and that locally produced Ang II may in part play important roles in converting mechanical stimuli into biochemical signals.
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PMID:Protein kinase cascade activated by mechanical stress in cardiocytes: possible involvement of angiotensin II. 755 78

Insulin stimulates the activity of mitogen-activated protein kinase (MAPK) via its upstream activator, MAPK kinase (MEK), a dual specificity kinase that phosphorylates MAPK on threonine and tyrosine. The potential role of MAPK activation in insulin action was investigated with the specific MEK inhibitor PD98059. Insulin stimulation of MAPK activity in 3T3-L1 adipocytes (2.7-fold) and L6 myotubes (1.4-fold) was completely abolished by pretreatment of cells with the MEK inhibitor, as was the phosphorylation of MAPK and pp90Rsk, and the transcriptional activation of c-fos. Insulin receptor autophosphorylation on tyrosine residues and activation of phosphatidylinositol 3'-kinase were unaffected. Pretreatment of cells with PD98059 had no effect on basal and insulin-stimulated glucose uptake, lipogenesis, and glycogen synthesis. Glycogen synthase activity in extracts from 3T3-L1 adipocytes and L6 myotubes was increased 3-fold and 1.7-fold, respectively, by insulin. Pretreatment with 10 microM PD98059 was without effect. Similarly, the 2-fold activation of protein phosphatase 1 by insulin was insensitive to PD98059. These results indicate that stimulation of the MAPK pathway by insulin is not required for many of the metabolic activities of the hormone in cultured fat and muscle cells.
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PMID:Mitogen-activated protein kinase kinase inhibition does not block the stimulation of glucose utilization by insulin. 765 64

A PC-12 pheochromocytoma cell line is described with roughly equivalent levels of functional receptors for nerve growth factor (NGF), epidermal growth factor (EGF), and insulin. Each of these receptors undergoes autophosphorylation upon binding of their respective ligands, and causes the activation of phosphatidylinositol-3 kinase via a mechanism involving tyrosine phosphorylation. In the case of insulin, this activation is due to the tyrosine phosphorylation of its major cellular substrate, IRS-1. Despite the presence of functional receptors in these cells, insulin does not stimulate the activity of the mitogen-activated protein (MAP) kinase, despite a 5- to 8-fold activation observed with both NGF and EGF under the same conditions. This failure to activate MAP kinase was not due to the insulin-dependent dephosphorylation of the enzyme, but correlated with the lack of activation of the MAP kinase kinase, although this enzyme was also activated by NGF and EGF. Similarly, the activation of the raf and ras protooncogenes in these cells was not observed with insulin, whereas NGF and EGF produced marked activation. In addition, insulin-dependent induction of the c-fos protein was impaired, in comparison to NGF. In contrast to a lack of effect on the MAP kinase pathway, these PC-12 cells were metabolically responsive to insulin, exhibiting increases in glucose, lipid, and protein synthesis in response to the hormone. The differential responses of phosphorylation events to insulin, NGF, and EGF in these cells indicates that divergence of signaling pathways may occur at or near the insulin receptor.
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PMID:Divergence of signaling pathways for insulin in PC-12 pheochromocytoma cells. 768 84

Mitogen activated protein kinases (MAP) or extracellular signal regulated protein kinases (ERK) are a family of protein serine/threonine kinases that are activated very rapidly in response to many extracellular stimuli. elk-1, an ets related gene codes for two transcriptional factors elk-1, which regulates c-fos transcription and delta elk-1, both of which are substrates for MAP kinases. A part of the C-terminal transcriptional activation domain (ETA-2) which is common to both the proteins was previously shown to function as an activator of MAP kinases. In this report, in an attempt to investigate the mechanism of activation of MAP kinases, purified preparations of recombinant elk-1 and P44mpk/ERK-1/ERK-2 proteins were used to show the association of elk-1 proteins with MAP kinases. The specific interactions of elk-1 proteins with MAP kinases were confirmed by co-immunoprecipitation studies. Thus elk-1 proteins appear to regulate the activity of MAP kinases by interacting with them ensuring a conformational change and stimulating their autophosphorylation and activation property. The activation was dependent on the presence of ATP and Mg2+. In vitro phosphorylation of elk-1 protein was not regulatory for autonomous DNA binding activity of elk-1 protein. Cells which were exposed to EGF showed a rapid stimulation of an elk-1 specific kinase activity, probably MAP kinase which phosphorylated MBP and was found to be associated with immobilized GST-elk-1. Furthermore, dephosphorylation studies indicate that elk-1 proteins can activate only tyrosine phosphorylated MAP kinase. These results demonstrate the presence of an alternative pathway/mechanism (other than MAP kinase kinase, MAPKK/Mek) for the activation of MAP kinases with tyrosine phosphorylation occurring before serine/threonine autophosphorylation and activation by elk-1 proteins.
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PMID:elk-1 proteins interact with MAP kinases. 820 31

Expression of phosphoenolpyruvate carboxykinase (PEPCK), the rate-limiting step in hepatic gluconeogenesis, is primarily regulated at the level of gene transcription. Insulin and phorbol esters inhibit basal PEPCK transcription and antagonize the induction of PEPCK gene expression by glucocorticoids and glucagon (or its second messenger cAMP). Insulin activates a signaling cascade involving Ras --> Raf --> p42/p44 mitogen-activated protein (MAP) kinase kinase (MEK) --> p42/p44 MAP kinase (ERK 1 and 2). Recent reports suggest that activation of this Ras/MAP kinase pathway is critical for the effects of insulin on mitogenesis and c-fos transcription but is not required for insulin action on metabolic processes such as glycogen synthesis, lipogenesis, and Glut-4-mediated glucose transport. We have used three distinct approaches to examine the role of the Ras/MAP kinase pathway in the regulation of PEPCK transcription by insulin in H4IIE-derived liver cells: (i) chemical inhibition of Ras farnesylation, (ii) infection of cells with an adenovirus vector encoding a dominant-negative mutant of Ras, and (iii) use of a chemical inhibitor of MEK. Although each of these methods blocks insulin activation of MAP kinase, none alters insulin antagonism of cAMP- and glucocorticoid-stimulated PEPCK transcription. Although phorbol esters activate MAP kinase and mimic the effects of insulin on PEPCK gene transcription, inhibition of MEK has no effect on phorbol ester inhibition of PEPCK gene transcription. Using the structurally and mechanistically distinct phosphatidylinositol 3-kinase (PI 3-kinase) inhibitors, wortmannin and LY 294002, we provide further evidence supporting a role for PI 3-kinase activation in the regulation of PEPCK gene transcription by insulin. We conclude that neither insulin nor phorbol ester regulation of PEPCK gene transcription requires activation of the Ras/MAP kinase pathway and that insulin signaling to the PEPCK promoter is dependent on PI 3-kinase activation.
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PMID:Insulin regulation of phosphoenolpyruvate carboxykinase gene expression does not require activation of the Ras/mitogen-activated protein kinase signaling pathway. 856 35

The mitogen-activated protein kinase (MAPK) family is comprised of key regulatory proteins that control the cellular response to both proliferation and stress signals. In this study we investigated the factors controlling MAPK activation by H2O2 and explored the impact of altering the pathways to kinase activation on cell survival following H2O2 exposure. Potent activation (10-20-fold) of extracellular signal-regulated protein kinase (ERK2) occurred within 10 min of H2O2 treatment, whereupon rapid inactivation ensued. H2O2 activated ERK2 in several cell types and also moderately activated (3-5-fold) both c-Jun N-terminal kinase and p38/RK/CSBP. Additionally, H2O2 increased the mRNA expression of MAPK-dependent genes c-jun, c-fos, and MAPK phosphatase-1. Suramin pretreatment completely inhibited H2O2 stimulation of ERK2, highlighting a role for growth factor receptors in this activation. Further, ERK2 activation by H2O2 was blocked by pretreatment with either N-acetyl-cysteine, o-phenanthroline, or mannitol, indicating that metal-catalyzed free radical formation mediates the initiation of signal transduction by H2O2. H2O2-stimulated activation of ERK2 was abolished in PC12 cells by inducible or constitutive expression of the dominant negative Ras-N-17 allele. Interestingly, PC12/Ras-N-17 cells were more sensitive than wild-type PC12 cells to H2O2 toxicity. Moreover, NIH 3T3 cells expressing constitutively active MAPK kinase (MEK, the immediate upstream regulator of ERK) were more resistant to H2O2 toxicity, while those expressing kinase-defective MEK were more sensitive, than cells expressing wild-type MEK. Taken together, these studies provide insight into mechanisms of MAPK regulation by H2O2 and suggest that ERK plays a critical role in cell survival following oxidant injury.
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PMID:Activation of mitogen-activated protein kinase by H2O2. Role in cell survival following oxidant injury. 862 53

The serine/threonine protein kinase Raf-1 is a component of a conserved intracellular signaling cascade that controls responses to various extracellular stimuli. Transcription from several promoters, including the oncogene-responsive element in the polyomavirus enhancer, the c-fos promoter, as well as other AP-1- and Ets-dependent promoters, can be induced by Raf-1 kinase. Previously, we have shown that activated Raf-1 kinase transactivates the human immunodeficiency virus type 1 (HIV-1) long terminal repeat and have identified the NF-kappaB binding motif as a Raf-1-responsive element (RafRE). We now report that Raf-1 kinase-induced transactivation from the HIV RafRE involves the purine-rich-repeat-binding protein (GABP), which is composed of two distinct subunits (alpha and beta). GABP alpha is an Ets oncogene-related DNA-binding protein, and GABP beta contains four ankyrin-like repeats that have been shown to be essential in protein-protein interactions. In electrophoretic mobility shift assays using nuclear extracts from human Jurkat T cells, a protein-DNA complex which was supershifted with antiserum against GABP alpha and GABP beta was observed. Purified recombinant GABP alpha and beta interact with the HIV RafRE as judged from DNA binding assays. Cotransfection experiments with GABP alpha and beta and Raf-1 kinase demonstrate synergistic transactivation of the HIV-1 promoter. Point mutations in the HIV RafRE abolished the Raf-1 kinase as well as GABP alpha- and beta-induced transactivation. The observed Raf-1-GABP synergism presumably involves phosphorylation of GABP subunits, as treatment of cells with Raf-1 kinase activators serum and 12-O-tetradecanoylphorbol-13-acetate increases phosphorylation of GABP in vivo. However, GABP is not a target of Raf-1 kinase; instead, it is a substrate of mitogen-activated protein kinase (MAPK/ERK), since in vitro phosphorylation of GABP alpha and beta was achieved by the reconstituted protein kinase cascade but not with purified Raf-1 or MEK. These results suggest that Raf-1 kinase- induced activation of the HIV-1 promoter is mediated by the classical cytoplasmic cascade resulting in MAPK/ERK-mediated phosphorylation of GABP alpha and beta. Because the HIV RafRE corresponds to a region within the promoter which is essential for regulation of HIV-1 expression, the data indicate that in addition to NK-kappaB, GABP transcription factors are important for induced expression of HIV.
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PMID:Raf-1 kinase targets GA-binding protein in transcriptional regulation of the human immunodeficiency virus type 1 promoter. 864 52

The mitogen-activated protein kinase (MAPK) cascade plays an important role in carcinogenic development. Herein, we show that the skin tumor promoter butylated hydroxytoluene hydroperoxide (BHTOOH) stimulates a rapid and potent (14- to 20-fold) activation of extracellular signal-regulated kinase (ERK) in vivo and in cultured mouse keratinocytes. BHTOOH also moderately (5-fold) activated c-jun-N-terminal kinase, and 38-kDa MAPK-related protein in these same cells. N-acetylcysteine and o-phenanthroline abolished ERK activation by BHTOOH, consistent with a requirement for metal-dependent formation of reactive intermediates. Indeed, 4-CD3-BHTOOH, an analogue that generates less of the metabolite BHT-quinone methide (2,6-di-tert-butyl-4-methylene-2,5-cyclohexadienone) and fewer tumors in vivo, accordingly exhibited diminished potency for activating ERK. ERK activation by BHTOOH was inhibited by suramin, and by expression of dominant-negative Ras-N-17 in PC12 cells, suggesting overlap between the pathways for BHTOOH and growth factor signaling. Induction of MAPK-dependent genes c-fos and MAPK phosphatase-1 by BHTOOH was also blocked by Ras-N-17 expression. Moreover, expression of Ras-N-17 or kinase-defective MAPK kinase (MEK) diminished cell survival following BHTOOH exposure. Similarly, pretreatment with suramin or the MEK inhibitor PD098059 also potentiated the toxicity of BHTOOH. On the other hand, expression of constitutively active MEK enhanced cell survival. Thus, we demonstrate that the MAPK cascade is critical to the cellular response to BHTOOH. This study suggests a functional role for MAPK activation in tumor promotion stimulated by oxidants and other agents.
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PMID:Mitogen-activated protein kinase (MAPK) activation by butylated hydroxytoluene hydroperoxide: implications for cellular survival and tumor promotion. 875 15

The HBx protein of hepatitis B virus is a dual-specificity activator of transcription, stimulating signal transduction pathways in the cytoplasm and transcription factors in the nucleus, when expressed in cell lines in culture. In the cytoplasm, HBx was shown to stimulate the Ras-Raf-mitogen-activated protein kinase (MAP kinase) cascade, which is essential for activation of transcription factor AP-1. Here we show that HBx protein stimulates two independently regulated members of the MAP kinase family when expressed transiently in cells. HBx protein stimulates the extracellular signal-regulated kinases (ERKs) and the c-Jun N-terminal kinases (JNKs). HBx activation of ERKs and JNKs leads to induction and activation of AP-1 DNA binding activity involving transient de novo synthesis of c-Fos protein and prolonged synthesis of c-Jun, mediated by N-terminal phosphorylation of c-Jun carried out by HBx-activated JNK. New c-Jun synthesis was blocked by coexpression with a dominant-negative MAP kinase kinase (MEK kinase, MEKK-1), confirming that HBx stimulates the prolonged synthesis of c-Jun by activating JNK signalling pathways. Activation of the c-fos gene was blocked by coexpression with a Raf-C4 catalytic mutant, confirming that HBx induces c-Fos by acting on Ras-Raf linked pathways. HBx activation of ERK and JNK pathways resulted in prolonged accumulation of AP-1-c-Jun dimer complexes. HBx activation of JNK and sustained activation of c-jun, should they occur in the context of hepatitis B virus infection, might play a role in viral transformation and pathogenesis.
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PMID:Hepatitis B virus HBx protein induces transcription factor AP-1 by activation of extracellular signal-regulated and c-Jun N-terminal mitogen-activated protein kinases. 876 4


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