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

---

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

1. Extracellular ATP and UTP have been reported to activate a nucleotide receptor that mediates phosphoinositide and phosphatidylcholine hydrolysis by phospholipases C and D, respectively. Here we report that ATP and UTP potently stimulate mesangial cell proliferation. 2. Both nucleotides stimulate phosphorylation and activation of mitogen-activated protein kinase and a biphasic phosphorylation of the up-stream mitogen-activated protein kinase kinase. 3. When added at 100 microM, ATP gamma S, UTP and ATP were the most potent activators of mitogen-activated protein kinase. beta gamma-imido-ATP was somewhat less active and ADP and 2-methylthio-ATP caused a weak induction of enzyme activity. Activation of mitogen-activated protein kinase by both ATP and UTP is dose-dependently attenuated by the P2-receptor antagonist, suramin. 4. The protein kinase C activator 12-0-tetradecanoylphorbol 13-acetate, but not the biologically inactive 4 alpha-phorbol 12,13-didecanoate, increased mitogen-activated protein kinase activity in mesangial cells, suggesting that protein kinase C may mediate nucleotide-induced stimulation of mitogen-activated protein kinase. 5. Down-regulation of protein kinase C -alpha and -delta isoenzymes by 4 h or 8 h treatment with phorbol ester partially inhibited ATP- and UTP-triggered mitogen-activated protein kinase activation. Moreover, a 24 h treatment of mesangial cells with phorbol ester, a regimen that also causes depletion of protein kinase C-epsilon did not further reduce the level of mitogen-activated protein kinase stimulation. 6. The specific protein kinase C inhibitor, CGP 41251, which displayed a selectivity for the Ca2+-dependent isoenzymes, as compared to the Ca2+-independent isoenzymes did not inhibit nucleotide stimulated mitogen-activated protein kinase phosphorylation, thus implicating the involvement of a Ca2+-independent protein kinase C isoform.7. In summary, these results suggest that ATP and UTP trigger the activation of the mitogen-activated protein kinase signalling cascade in mesangial cells and this may be responsible for the potent mitogenic activity of both nucleotides.
...
PMID:Stimulation by extracellular ATP and UTP of the mitogen-activated protein kinase cascade and proliferation of rat renal mesangial cells. 788 2

The regulation of mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) was studied in freshly isolated adult rat heart preparations. In contrast to the situation in ventricular myocytes cultured from neonatal rat hearts, stimulation of MAPK activity by 1 mumol/L phorbol 12-myristate 13-acetate (PMA) was not consistently detectable in crude extracts. After fast protein liquid chromatography, MAPK isoforms p42MAPK and p44MAPK and two peaks of MEK were shown to be activated > 10-fold in perfused hearts or ventricular myocytes exposed to 1 mumol/L PMA for 5 minutes. The identities of MAPK or MEK were confirmed by immunoblotting and, for MAPK, by the "in-gel" myelin basic protein phosphorylation assay. In retrogradely perfused hearts, high coronary perfusion pressure (120 mm Hg for 5 minutes), norepinephrine (50 mumol/L for 5 minutes), or isoproterenol (50 mumol/L for 5 minutes) stimulated MAPK and MEK approximately 2- to 5-fold. In isolated myocytes, endothelin 1 (100 nmol/L for 5 minutes) also stimulated MAPK, but stimulation by norepinephrine or isoproterenol was difficult to detect. Immunoblotting showed that the relative abundances of MAPK and MEK protein in ventricles declined to < 20% of their postpartal abundances after 50 days. This may explain the difficulties encountered in assaying the activity of MAPK in crude extracts from adult hearts. We conclude that potentially hypertrophic agonists and interventions stimulate the MAPK cascade in adult rats and suggest that the MAPK cascade may be an important intracellular signaling pathway in this response.
...
PMID:Regulation of mitogen-activated protein kinase cascade in adult rat heart preparations in vitro. 792 40

The phorbol ester PMA/TPA (phorbol 12-myristate 13-acetate) is a potent tumor promoter which mimics distinct intracellular signalling events triggered by activated growth factor receptors, e.g. the activation of MAP kinases. The largest known family of TPA-binding proteins comprise members of the protein kinase C (PKC) family although other TPA-binding proteins outside the PKC family have recently been identified. In this report we addressed the mechanism and the pathway by which TPA induces the activation of MAPkinases. Using recombinant proteins and in vitro phosphorylation reactions we identified the components in the signal transduction pathway from TPA to MAPkinase and we show that the activation of MAPkinase by TPA requires the presence of protein kinase C, c-raf and the MAPkinase activator MEK. We also find that the activation of raf autophosphorylation in vitro correlates with the ability of Raf to signal to MAPkinase. Thus the activation of Raf by PKC apparently can trigger the same signalling pathway as oncogenic Raf or Raf activation by ras in combination with tyrosine phosphorylation.
...
PMID:Signalling from TPA to MAP kinase requires protein kinase C, raf and MEK: reconstitution of the signalling pathway in vitro. 793 44

We have recently described the properties of delta Raf-1:ER, a fusion protein consisting of an oncogenic form of human Raf-1 and the hormone binding domain of the human estrogen receptor. In this study, we demonstrate that activation of delta Raf-1:ER in quiescent 3T3 cells (C2 cells), while sufficient to promote morphological oncogenic transformation, was insufficient to promote the entry of cells into DNA synthesis. Indeed, activation of delta Raf-1:ER potently inhibited the mitogenic response of cells to platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) treatment. Addition of beta-estradiol to quiescent C2 cells led to rapid, sustained activation of delta Raf-1:ER and MEK but only two- to threefold activation of p42 mitogen-activating protein (MAP) kinase activity. Addition of PDGF or EGF to quiescent C2 cells in which delta Raf-1:ER was inactive led to rapid activation of Raf-1, MEK, and p42 MAP kinase activities, and entry of the cells into DNA synthesis. In contrast, when delta Raf-1:ER was activated in quiescent C2 cells prior to factor addition, there was a significant inhibition of certain aspects of the signaling response to subsequent treatment with PDGF or EGF. The expression and activation of PDGF receptors and the phosphorylation of p70S6K in response to PDGF treatment were unaffected by prior activation of delta Raf-1:ER. In contrast, PDGF-mediated activation of Raf-1 and p42 MAP kinases was significantly inhibited compared with that of controls. Interestingly, the mitogenic and signaling responses of quiescent C2 cells to stimulation with fetal bovine serum or phorbol myristate acetate were unaffected by prior activation of delta Raf-1:ER. It seems likely that at least two mechanisms contribute to the effects of delta Raf-1:ER in these cells. First, activation of delta Raf-1:ER appeared to uncouple the activation of Raf-1 from the activation of the PDGF receptor at the cell surface. This may be due to the fact that mSOS1 is constitutively phosphorylated as a consequence of the activation of delta Raf-1:ER. Second, quiescent C2 cells expressing activated delta Raf-1:ER appear to contain an inhibitor of the MAP kinase pathway that, because of its apparent sensitivity to sodium orthovanadate, may be a phosphotyrosine phosphatase. It is likely that the inhibitory effects of delta Raf-1:ER observed in these cells are a manifestation of the activation of some of the feedback inhibition pathways that normally modulate a cell's response to growth factors. 3T3 cells expressing delta Raf-1:ER will be a useful tool in unraveling the role of Raf-1 kinase activity in the regulation of such pathways.
...
PMID:Inhibition of platelet-derived growth factor- and epidermal growth factor-mediated mitogenesis and signaling in 3T3 cells expressing delta Raf-1:ER, an estradiol-regulated form of Raf-1. 796 25

Intracellular signalling following mitogenic stimulation of quiescent cells involves the initiation of a phosphorylation cascade that leads to the rapid and reversible activation of the mitogen-activated protein (MAP) kinases ERK1 and ERK2. MAP kinase activation is mediated by dual phosphorylation within the motif Thr-Glu-Tyr by MAP kinase kinase (MEK). Following activation, the MAP kinases translocate into the nucleus where they phosphorylate several transduction targets, including transcription factors. We have previously identified PAC1 as an immediate-early mitogen-inducible tyrosine phosphatase in nuclei of T cells. Here we present several lines of evidence indicating that PAC1 is a physiologically relevant MAP kinase phosphatase. Recombinant PAC1 in vitro is a dual-specific Thr/Tyr phosphatase with stringent substrate specificity for MAP kinase. Constitutive expression of PAC1 in vivo leads to inhibition of MAP kinase activity normally stimulated by epidermal growth factor, phorbol myristyl acetate, or T-cell receptor crosslinking. The inactivation of MAP kinase by PAC1 results in inhibition of MAP kinase-regulated reporter gene expression.
...
PMID:Control of MAP kinase activation by the mitogen-induced threonine/tyrosine phosphatase PAC1. 810 50

The protein kinase cascade Raf-MAPKK/MEK-MAPK/ERK connects protein tyrosine kinase receptors in the membrane with control of transcription factor activity in the nucleus. We have examined whether Raf is obligatory for activation of this cascade and whether this signaling pathway is relevant to transformation. By use of transient assays with epitope-tagged ERK-1 cDNA and a dominant inhibitory mutant of Raf-1 we found that serum and 12-O-tetradecanoylphorbol-13-acetate as well as representatives of three classes of oncogenes (protein tyrosine kinases abl/src, Ras, and protein serine/threonine kinases mos/cot) were all Raf-dependent for stimulation of MAPK. All of the MAPK stimulating oncogenes were also activators of Raf kinase as judged by shift induction. It thus appears that there is little or no redundancy in pathways used by growth regulators for activation of MAPK/ERK. Furthermore, the ability to stimulate MAPK/ERK appears to be critical for transformation by oncogenic Raf-1 and ERK-1 and -2 synergized with v-raf in a focus induction assay on NIH3T3 cells and kinase dead mutants of ERK-2 were inhibitory. Raf/ERK synergism was also observed in transcriptional transactivation of the oncogene-response element in the polyoma enhancer. We conclude that this Raf signaling pathway, which connects to many upstream activators and downstream effectors, is essential for transformation by most oncogenes.
...
PMID:Mitogen-activated protein kinase/extracellular signal-regulated protein kinase activation by oncogenes, serum, and 12-O-tetradecanoylphorbol-13-acetate requires Raf and is necessary for transformation. 812 67

Incubation of polymorphonuclear leukocytes with chemoattractants, granulocyte-macrophage colony-stimulating factor (GM-CSF), or phorbol 12-myristate 13-acetate (PMA) activated both mitogen-activated protein kinase kinase (MAPKK) and mitogen-activated protein kinase (MAPK). Activation by chemoattractants was rapid and transient, being maximal by 1 min and decreasing by 10 min. The order of efficacy was formyl-met-leu-phe > C5a > > LTB4 > interleukin 8 > platelet-activating factor. In contrast, activation by GM-CSF or PMA was slow and sustained being maximal at 5 min and with little decrease by 30 min. Sustained MAPK activation required continuous activation of the MAPKK. The MAPKK induced by N-formylmethionyl-leucyl-phenylalanine, GM-CSF, or PMA was resolved into two forms by anion exchange chromatography (Mono Q). Both corresponded to a 45-kDa MAPKK antigen by Western blotting and were inactivated by serine/threonine protein phosphatase 2A. Rechromatography of both forms after dephosphorylation resulted in the antigen's eluting slightly earlier on the Mono Q gradient than when in the active state. However, the two peaks remained separate, suggesting that they are not merely different phosphoforms of the same enzyme. The MAPK cascade is a signaling pathway common to many polymorphonuclear leukocyte stimulants, which may be activated transiently or in a sustained manner.
...
PMID:Characterization of two different forms of mitogen-activated protein kinase kinase induced in polymorphonuclear leukocytes following stimulation by N-formylmethionyl-leucyl-phenylalanine or granulocyte-macrophage colony-stimulating factor. 814 33

Treatment of adipocytes with insulin or phorbol 12-myristate 13-acetate (PMA) results in transient activation of mitogen-activated protein kinase kinase (MEK) (Tmax = 90 s) and mitogen-activated protein kinase (MAPK) (Tmax = 300 s). We have identified a novel insulin-stimulated MEK kinase (I-MEKK) in the 100,000 x g infranatant that shows rapid phasic kinetics that temporally precede that of MEK. Maximal activation of I-MEKK occurs within 20 +/- 5 s (S.D., n = 3) followed by complete inactivation by 30 +/- 10 s (S.D., n = 3). I-MEKK was characterized by anion-exchange and gel filtration chromatography and separated into two distinct activities of approximately 56 kDa that phosphorylated and activated MEK. I-MEKKs did not co-elute on anion exchange with c-Raf or 73-kDa MEK kinase (MEKK), suggesting they are distinct enzymes. Protein phosphatase 2A inactivated both I-MEKKs in vitro and in the intact cell okadaic acid blocked inactivation in the presence of insulin. These results suggest activation of I-MEKK involves phosphorylation on serine or threonine residues. I-MEKK was not activated by PMA, suggesting that in adipocytes the enzyme represents a divergence point between signal transduction pathways mediated by insulin and those activating protein kinase C.
...
PMID:Insulin activates a novel adipocyte mitogen-activated protein kinase kinase kinase that shows rapid phasic kinetics and is distinct from c-Raf. 817 93

Stimulation of T cells with antibodies directed towards the T cell receptor complex results in the activation of mitogen-associated protein kinase (MAPK). Two pathways have been described in other cell types that can lead to MAPK activation. One of these pathways involves the activation of Ras, leading to the activation of Raf-1, and the subsequent activation of MEK (MAPK or ERK kinase). The contribution of this pathway in T cells for anti-CD3 or phorbol myristate acetate (PMA)-mediated MAPK activation was examined. We detected the kinase activities of Raf-1 and MEK towards their substrates (MEK for Raf-1 and MAPK for MEK) in this pathway leading to the activation of MAPK. Stimulation of the T cells with either anti-CD3 antibody or PMA resulted in a rapid activation of both Ras and Raf-1. MEK activity towards kinase-active or -inactive recombinant MAPK also increased upon stimulation. In addition, both MAPK and p90rsk were activated in these cells. We suggest that activation of MAPK and the subsequent activation of ribosomal S6 kinase (p90rsk) occurs by the Ras/Raf-1/MEK cascade in T lymphocytes stimulated by ligation of the T cell receptor complex.
...
PMID:Ligation of the T cell receptor complex results in activation of the Ras/Raf-1/MEK/MAPK cascade in human T lymphocytes. 818 45

Recently, it has been reported that Raf-1 kinase (Raf-1) has mitogen-activated protein kinase kinase kinase (MAPKKK) activity in various cells, although Raf-1 and MAP kinase kinase (MAPKK) can be phosphorylated by MAP kinase (MAPK) in vitro. Here we show that the maximal hyperphosphorylation of Raf-1 and MAPKK (10 min) was substantially achieved after the maximal activation of MAPKKK of Raf-1, MAPKK (2-5 min), and MAPK in Chinese hamster ovary cells overexpressing human insulin receptor (CHO-HIR cells) treated with insulin or 12-O-tetradecanoylphorbol-13-acetate (TPA). Moreover, we show that overexpression of MAPK in CHO-HIR cells resulted in enhanced hyperphosphorylation of Raf-1, MAPKK, and mammalian homolog of son of sevenless (mSos) after insulin or TPA stimulation as compared with parental cells. Furthermore, the maximal hyperphosphorylation of Raf-1 appears to be accompanied by a significant decrease in MAPKKK activity. These results suggest that 1) signals initiated by insulin and TPA converge on Raf-1 and activate its MAPKKK activity and 2) Raf-1, MAPKK, and mSos not only lie upstream of MAPK but also are phosphorylated by MAPK, directly or indirectly, and at least Raf-1 kinase activity might be down-regulated by this feedback mechanism.
...
PMID:Feedback regulation of mitogen-activated protein kinase kinase kinase activity of c-Raf-1 by insulin and phorbol ester stimulation. 819 29


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>

---