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:2.7.12.2 (MEK)
18,161 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Previous studies of Saccharomyces cerevisiae have identified several meiosis-specific genes whose products are required for wild-type levels of meiotic recombination and for normal synaptonemal complex (SC) formation. Several of these mutants were examined in a physical assay designed to detect heteroduplex DNA (hDNA) intermediates in meiotic recombination. hDNA was not detected in the rec102, mei4 and hop1 mutants; it was observed at reduced levels in red1, mek1 and mer1 strains and at greater than the wild-type level in zip1. These results indicate that the REC102, MEI4, HOP1, RED1, MEK1 and MER1 gene products act before hDNA formation in the meiotic recombination pathway, whereas ZIP1 acts later. The same mutants assayed for hDNA formation were monitored for meiotic chromosome pairing by in situ hybridization of chromosome-specific DNA probes to spread meiotic nuclei. Homolog pairing occurs at wild-type levels in the zip1 and mek1 mutants, but is substantially reduced in mei4, rec102, hop1, red1 and mer1 strains. Even mutants that fail to recombine or to make any SC or SC precursors undergo a significant amount of meiotic chromosome pairing. The in situ hybridization procedure revealed defects in meiotic chromatin condensation in mer1, red1 and hop1 strains.
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PMID:Heteroduplex DNA formation and homolog pairing in yeast meiotic mutants. 853 92

TCR engagement stimulates the activation of the protein kinase Raf-1. Active Raf-1 phosphorylates and activates the mitogen-activated protein (MAP) kinase/extracellular signal-regulated kinase kinase 1 (MEK1), which in turn phosphorylates and activates the MAP kinases/extracellular signal regulated kinases, ERK1 and ERK2. Raf-1 activity promotes IL-2 production in activated T lymphocytes. Therefore, we sought to determine whether MEK1 and ERK activities also stimulate IL-2 gene transcription. Expression of constitutively active Raf-1 or MEK1 in Jurkat T cells enhanced the stimulation of IL-2 promoter-driven transcription stimulated by a calcium ionophore and PMA, and together with a calcium ionophore the expression of each protein was sufficient to stimulate NF-AT activity. Expression of MEK1-interfering mutants inhibited the stimulation of IL-2 promoter-driven transcription and blocked the ability of constitutively active Ras and Raf-1 to costimulate NF-AT activity with a calcium ionophore. Expression of the MAP kinase-specific phosphatase, MKP-1, which blocks ERK activation, inhibited IL-2 promoter and NF-AT-driven transcription stimulated by a calcium ionophore and PMA, and in addition, MKP-1 neutralized the transcriptional enhancement caused by active Raf-1 and MEK1 expression. We conclude that the MAP kinase signal transduction pathway consisting of Raf-1, MEK1, and ERK1 and ERK2 functions in the stimulation IL-2 gene transcription in activated T lymphocytes.
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PMID:MEK1 and the extracellular signal-regulated kinases are required for the stimulation of IL-2 gene transcription in T cells. 855 75

Treatment of U937 human leukemic cells with the phorbol ester PMA, activates both mitogen-activated protein kinase (MAPK) and stress-activated protein kinase (SAPK), stimulates c-Jun phosphorylation and transcriptional activity, and induces a macrophage-like differentiation of U937 cells. The involvement of the MAPK pathway in mediating both the early phosphorylation and transcriptional activation events and the chronic differentiation of U937 cells was examined utilizing constitutively active MAPK kinase (MEK1) mutants. Transient expression of an activated MEK1 construct in U937 cells was found to stimulate MAPK and SAPK activity, as well as enhancing AP1-, SRE- and c-Jun-mediated transcriptional activity. Transient transfection of MAPK phosphatase-1 (MKP-1), a protein phosphatase which preferentially dephosphorylates and inactivates MAPK, inhibited the functional effects of both PMA and the constitutively active MEK1 mutants. To determine whether specific activation of the MEK/MAPK pathway was sufficient to induce hematopoietic differentiation, U937 cell lines were established that conditionally expressed the activated MEK1 mutant under the control of the human IIa metallothionein promoter. The induction of constitutively active MEK1 protein expression resulted in an increase in MEK1 activity, c-Jun and AP-1 transcriptional activity and an inhibition of U937 cell growth. However, this growth inhibition was not accompanied by U937 cell differentiation. These results suggest that a cross-talk mechanism exists between the MAPK and SAPK signal transduction pathways in U937 cells and that PMA-mediated SAPK activation may involve the MAPK pathway. Furthermore, selective activation of the MEK/MAPK pathway utilizing a constitutively active MEK1 mutant, while growth inhibitory, was not sufficient to induce the macrophage-like differentiation of U937 cells.
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PMID:Constitutively active MAP kinase kinase (MEK1) stimulates SAP kinase and c-Jun transcriptional activity in U937 human leukemic cells. 857 Jan 88

Mitogen-activated protein (MAP) kinases require dual phosphorylation on threonine and tyrosine residues in order to gain enzymatic activity. This activation is carried out by a family of enzymes known as MAP kinase kinases (MKKs or MEKs). It appears that there are at least four subgroups in this family; MEK1/MEK2 subgroup that activates ERK1/ERK2, MEK5 that activates ERK5/BMK1, MKK3 that activates p38, and MKK4 that activates p38 and Jun kinase. Here we describe the characteristics of a new MKK termed MKK6. The clones we isolated encode two splice isoforms of human MKK6 comprised of 278 and 334 amino acids, respectively, and one murine MKK6 with 237 amino acids. Sequence information derived from cDNA cloning indicated that MKK6 is most closely related to MKK3. The functional data revealed from co-transfection assays suggests that MKK6, like MKK3, selectively phosphorylates p38. Unlike the previously described MKKs (or MEKs), MKK6 exists in a variety of alternatively spliced isoforms with distinct patterns of tissue expression. This suggests novel mechanisms regulating activation and/or function of various forms of MKK6.
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PMID:Characterization of the structure and function of a novel MAP kinase kinase (MKK6). 862 75

Activation of the mitogen-activated protein kinase cascade is a critical event in mitogenic growth factor signal transduction. Mitogen-activated protein kinase is directly activated by a dual specific kinase, MEK, which itself is activated by serine phosphorylation. The c-Raf kinase has been implicated in mediating the signal transduction from mitogenic growth factor receptors to MEK activation. Recently, the B-Raf kinase was shown to be capable of phosphorylating and activating MEK as a result of growth factor stimulation. In this report, we used the yeast two-hybrid screening to isolate MEK interacting proteins. All three members of the Raf family kinases were identified as positive clones when the mutant MEK1S218/222A, in which the two phosphorylation serine residues were substituted by alanines, was used as a bait, whereas no positive clones were isolated when the wild type MEK1 was used as a bait in a similar screening. These results suggest that elimination of the phosphorylation sites of a target protein (MEK1 in our study) may stabilize the interaction between the kinase (Raf) and its substrate (MEK1), possibly due the formation of a nonproductive complex. These observations seem to suggest a general strategy using mutants to identify the upstream kinase of a phosphoprotein or the downstream targets of a kinase. Although c-Raf and B-Raf have been implicated in growth factor-induced MEK activation, little is known about A-Raf. We observed that stimulation of Hela cells with epidermal growth factor resulted in a rapid and transient activation of A-Raf, which is then capable of phosphorylating and activating MEK1. Interestingly, A-Raf does not activate MEK2, although c-Raf can activate both MEK1 and MEK2. Our data demonstrated that A-Raf is, indeed, a MEK1 activator and may play a role in growth factor signaling.
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PMID:Selective activation of MEK1 but not MEK2 by A-Raf from epidermal growth factor-stimulated Hela cells. 862 29

We investigated the effect of cyclic AMP-dependent protein kinase (PKA ) on v-Mos kinase activity. Increase in PKA activity in vivo brought about either by forskolin treatment or by overexpression of PKA catalytic subunit resulted in a significant inhibition of v-Mos kinase activity. The purified PKA catalytic subunit was able to phosphorylate recombinant p37v-mos in vitro, suggesting that the mechanism of in vivo inhibition of v-Mos kinase involves direct phosphorylation by PKA. Combined tryptic phosphopeptide two-dimensional mapping analysis and in vitro mutagenesis studies indicated that Ser-56 is the major in vivo phosphorylation site on v-Mos. In vivo phosphorylation at Ser-56 correlated with slower migration of the v-Mos protein during sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, even though Ser-56 was phosphorylated by PKA, this phosphorylation was not involved in the inhibition of v-Mos kinase. The alanine-for-serine substitution at residue 56 did not affect the ability of v-Mos to autophosphorylate in vitro or, more importantly, to activate MEK1 in transformed NIH 3T3 cells. We identified Ser-263 phosphorylation, the Ala-263 mutant of v-Mos was not inhibited by forskolin treatment. From our results, we propose that the known inhibitory role of PKA in the initiation of oocyte maturation in mice could be explained at least in part by its inhibition of Mos kinase.
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PMID:Inhibition of v-Mos kinase activity by protein kinase A. 862 81

To discern MEK1 and MEK2 specificity for their substrate, extracellular signal-regulated kinase (ERK), site-directed mutagenesis was performed on the amino acid residues flanking the regulatory phosphorylation sites of ERK1. These ERK1 mutants were analyzed for the ability to act as a substrate for MEK1 and MEK2. Based on both phosphorylation and activation analyses, the mutants could be divided into four classes: 1) dramatically decreased phosphorylation and activation, 2) enhanced basal kinase activity, 3) preferentially enhanced phosphorylation of tyrosine and decreased phosphorylation of threonine, and 4) increased threonine phosphorylation with an increase in activation. In general, the residues proximal to the regulatory phosphorylation sites of ERK1 had greater influence on both phosphorylation and activation. This is consistent with the highly specific recognition of the ERK1 regulatory sites by MEK. Mutation of Arg-208 or Thr-207 to an alanine residue significantly altered the relative phosphorylation on Thr-202 and Tyr-204. The Arg-208 to alanine mutant increased the phosphorylation of Tyr-204 approximately 4-fold yet almost completely eliminated the phosphorylation on Thr-202. In contrast, mutation of Gly-199 to alanine resulted in an increased phosphorylation of Thr-202 relative to Tyr-204. This suggests that both Gly-199 and Arg-208 play important roles in determining the relative phosphorylation of Thr-202 and Tyr-204. Our results demonstrate that residues in the phosphorylation lip of ERK play an important role in the recognition and phosphorylation by MEK.
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PMID:Characterization of ERK1 activation site mutants and the effect on recognition by MEK1 and MEK2. 862 67

A common response of cells to mitogenic and hypertrophic factors is the activation of high rates of protein synthesis. To investigate the molecular basis of this action, we have used the recently developed MAP kinase/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor PD 98059 to examine the involvement of the ERK pathway in the regulation of global protein synthesis by growth factors in rat aortic smooth muscle cells (SMC). Incubation with PD 98059 blocked angiotensin II (AII)-dependent phosphorylation and enzymatic activity of both MEK1 and MEK2 isoforms, leading to inhibition of the phosphorylation and activation of p44(mapk) and p42(mapk). The compound was found to selectively inhibit activation of the ERK pathway by AII, but not the stimulation of p70 S6 kinase, phospholipase C, or tyrosine phosphorylation. Most importantly, treatment of aortic SMC with PD 98059 potently inhibited AII-stimulated protein synthesis with a half-maximal inhibitory concentration of 4.3 microM. The effect of PD 98059 was not restricted to AII, since the compound also blocked to various extent the induction of protein synthesis by growth factors acting through tyrosine kinase receptors, G protein-coupled receptors, or protein kinase C. These results provide strong evidence that activation of ERK isoforms is an obligatory step for growth factor-induced protein synthesis in aortic SMC.
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PMID:Inhibition of growth factor-induced protein synthesis by a selective MEK inhibitor in aortic smooth muscle cells. 866 42

We reported recently that angiotensin II (AII) and phorbol 12-myristate 13-acetate (PMA) transiently inhibit interleukin 6 (IL-6)-stimulated tyrosine phosphorylation of signal transducers and activators of transcription 3 (Stat3) and subsequent formation of sis-inducing factor-A (SIF-A). However, the AII-mediated inhibition was independent of PMA-sensitive isoforms of protein kinase C (Bhat, G. J., Thekkumkara, T. J., Thomas, W. G., Conrad, K. M., and Baker, K. M. (1995) J. Biol. Chem. 270, 19059-19065). In this study, we demonstrate that the inhibition of IL-6-induced Stat3/SIF-A by AII is concentration-dependent and does not involve degradation of Stat3 protein. We hypothesized that the activation profile of the AII- and PMA-induced mitogen-activated protein (MAP) kinase cascade may be different from that of IL-6 and could contribute to the inhibitory effect; therefore, blocking the MAP kinase pathway at the level of MAPK kinase (MAPKK) would attenuate this inhibitory effect. AII and PMA rapidly induced high levels of MAP kinase activity (8-fold), which contrasted with the delayed and weak activation by IL-6 (1. 7-fold). Treatment of cells with PD98059, a specific inhibitor of MAPKK1, attenuated the inhibitory effects of AII and PMA on IL-6-induced Stat3 tyrosine phosphorylation and SIF-A formation. These data suggest that differences in magnitude and/or duration of activation of the MAP kinase cascade differentially affects the status of Stat3 tyrosine phosphorylation, and that MAPKK1 or a downstream intermediate is involved in the inhibition of IL-6-induced Stat3 by AII and PMA. Modulatory cross-talk between AII and IL-6 may have relevance in pathophysiological conditions such as cardiac hypertrophy and in acute phase and inflammatory responses.
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PMID:Angiotensin II interferes with interleukin 6-induced Stat3 signaling by a pathway involving mitogen-activated protein kinase kinase 1. 879 9

Antigen stimulation of mast cells via the IgE receptor, Fc epsilon RI, results in recruitment of the cytosolic tyrosine kinases, Lyn and Syk, and the phosphorylation of proteins. We examined the effects of the glucocorticoid dexamethasone on these events in a cultured (RBL-2H3) mast cell line. Nanomolar concentrations of dexamethasone suppressed phosphorylation of proteins that were associated with the activation of the mitogen-activated protein (MAP) kinase/phospholipase A2 pathway without inhibiting initial events. For example, tyrosine phosphorylation of the subunits of Fc epsilon RI, Lyn, or Syk or of the Ras-guanine nucleotide exchange factor, Vav, was not suppressed in cells treated with up to 1 microM dexamethasone. In contrast, phosphorylation of Raf1, MEK1, p42mapk, and cytosolic phospholipase A2, as well as the associated increase in MAP kinase activity and release of arachidonic acid, were markedly inhibited in cells treated with as little as 10 nM dexamethasone--a concentration that only partially inhibited hydrolysis of inositol phospholipids or release of secretory granules. Prolonged exposure to dexamethasone also resulted in a partial decrease in expression of MEK1, p42mapk, and cytosolic phospholipase A2, which may contribute further to the effects of dexamethasone on this pathway. Activation of the MAP kinase/phospholipase A2 pathway by the calcium-mobilizing agent thapsigargin was similarly suppressed in dexamethasone-treated cells. These findings suggested that an early step in the pathway, possibly a step immediately before the activation of Raf1, was suppressed by low concentrations of dexamethasone.
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PMID:Activation of the mitogen-activated protein kinase cascade is suppressed by low concentrations of dexamethasone in mast cells. 880 35


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