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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)

Engagement of membrane IgM on a number of human and murine B-cell lines induced activation of a Mn(2+)-preferring serine/threonine kinase that phosphorylated microtubule-associated protein-2 (MAP-2) in vitro. B-cell MAP-2 kinase (MAP-2K) activity could be fractionated into two peaks by sequential DEAE and hydrophobic chromatography. Although peak I included two tyrosine phosphoproteins of molecular mass 36 and 38 kDa, peak II showed a single 42-kDa tyrosine phosphoprotein (pp42). Since all kinase activity could be removed from peak II material over an antiphosphotyrosine immune affinity column, it suggests that pp42 is identical with lymphoid MAP-2K. Although peak I activity showed a similarity to peak II with regard to its preference for Mn2+, sensitivity to phosphatase exposure, and resistance to a range of common serine kinase inhibitors, it is not clear whether these activities are related. MAP-2 kinase activity could also be induced by treatment with the phorbol ester, phorbol myristate 13-acetate, suggesting that protein kinase C may also be involved with MAP-2K regulation. Although MAP-2K activity reached a peak response within minutes of receptor ligation, there were differences in the rates of dephosphorylation of pp42 and decline of MAP-2K activity in different B-cell lines. The tyrosine phosphatase inhibitor, vanadate, transformed a rapidly reversible MAP-2K response in BAL 17.2 cells into a sustained state of activation that resembled the kinetics of activation in WEHI-231 cells. The latter finding implies involvement of a tyrosine phosphatase, which opposes the effect of an inducing tyrosine kinase.
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PMID:Stimulation of B-cells via the membrane immunoglobulin receptor or with phorbol myristate 13-acetate induces tyrosine phosphorylation and activation of a 42-kDa microtubule-associated protein-2 kinase. 165 69

Ligation of CD3/TCR on T-cells induces transient activation of lymphoid MAP-2 kinase (MAP-2K), a 43 kDa serine kinase which itself is a substrate of an unidentified tyrosine kinase (pp43). The reversibility of the MAP-2K response agrees with removal of tyrosine phosphates from pp43. Since both activity as well as tyrosine phosphorylation of MAP-2K could be prolonged by Na3VO4, a phosphotyrosine phosphatase inhibitor, we studied the effect of the common CD45 isoform, which is a member of the CD45 phosphatase family, on MAP-2K activity in vivo and in vitro. We demonstrate the ability of purified CD45 phosphatase to remove tyrosine phosphates from partially purified lymphoid MAP-2K. Utilizing the approach of heterologous receptor aggregation, we also showed that CD45 could inhibit the induction of MAP-2K activity in intact Jurkat cells during CD3 or CD3 + CD4 stimulation. We therefore suggest that this phosphatase may control the activity of lymphoid MAP-2K in vivo.
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PMID:Evidence for involvement of glycoprotein-CD45 phosphatase in reversing glycoprotein-CD3-induced microtubule-associated protein-2 kinase activity in Jurkat T-cells. 171 Aug 91

Signaling via the alpha-beta T cell Ag receptor (Ti)-CD3 complex is a complicated event that implicates several protein kinases, most notably protein kinase C (PKC). We have recently identified a serine kinase in T lymphocytes with the following characteristics: molecular mass 43 kDa, in vitro substrate affinity for microtubule associated protein 2 (MAP-2) with a preference for Mn2+ during the catalytic reaction, and elution from DEAE resin over a salt range 100 to 200 mM NaCl. This kinase is activated in a rapidly reversible fashion during ligation of CD3/Ti by a process which involves prior phosphorylation; in vitro exposure of activated 43-kDa MAP-2 kinase (MAP-K) to an immobilized phosphatase abrogated its kinase activity. We now show that a MAP-2K response could also be obtained during treatment with mAb to Ti and the specific PKC agonist, PMA. Although the kinetics of the former response was rapidly reversible, PMA elicited a more prolonged response. The dose responsiveness for PMA was similar to the requirements for PKC activation in intact lymphocytes. Moreover, as with PKC, we found that the CD3-induced MAP-2K response could be further enhanced by using a second layer cross-linking antibody. The specificity of CD3/Ti in the Jurkat cell response is demonstrated by the fact that OKT-11(CD2) and anti-CD4 mAb did not stimulate a MAP-2K response. It was also not possible to elicit a response in a Jurkat cell mutant that lacks surface expression of CD3 and Ti. The specificity of PKC in these events was further explored with the cell permeant diacylglycerol, 1-oleoyl-2-acetylglycerol, and the nonagonist phorbol ester, 4 alpha-phorbol 12,13-didecanoate: whereas the former was an effective inducer of the MAP-2K response, the latter failed to yield any stimulation. Prior exposure of Jurkat cells to 100 mM PMA for 24 h eliminated greater than 60% of the MAP-2K response during anti-CD3 treatment. This response could also be inhibited in dose-dependent fashion by prior treatment of Jurkat cells with the potent PKC inhibitor 1-(5-isoquinolinesulfonyl) 2-methylpiperazine dihydrochloride. Although a Ca2(+)-ionophore failed to synergize with PMA at inducing a MAP-2K response, depletion of extracellular Ca2+ by EGTA abrogated anti-CD3 responsiveness. The events culminating in MAP-2K activation were slightly inhibited in the presence of cholera toxin but not pertussis toxin.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Stimulation of MAP-2 kinase activity in T lymphocytes by anti-CD3 or anti-Ti monoclonal antibody is partially dependent on protein kinase C. 215 31

Treatment of Jurkat T-cells with anti-CD-3 monoclonal antibodies resulted in the rapid and transient activation of a serine kinase which utilized the microtubule-associated protein, MAP-2, as a substrate in vitro. The kinase was also activated on treatment of Jurkat cells with phytohaemagglutinin, but with a different time course. The activation of the MAP-2 kinase by anti-CD-3 antibodies was dose-dependent, with maximal activity observed at concentrations of greater than 500 ng/ml. Normal human E-rosette-positive T-cells also exhibited induction of MAP-2 kinase activity during anti-CD-3 treatment. The enzyme was optimally active in the presence of 2 mM-Mn2+; lower levels of activity were observed with Mg2+, even at concentrations up to 20 mM. The kinase was partially purified by passage over DE-52 Sephacel with the activity eluting as a single peak at 0.25 M-NaCl. The molecular mass was estimated to be 45 kDa by gel filtration. The activation of the MAP-2 kinase was probably due to phosphorylation of this enzyme as treatment with alkaline phosphatase diminished its activity. These data demonstrate that the stimulation of T-cells through the CD-3 complex results in the activation of a novel serine kinase which may be critically involved in signal transduction in these cells.
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PMID:Complexing of the CD-3 subunit by a monoclonal antibody activates a microtubule-associated protein 2 (MAP-2) serine kinase in Jurkat cells. 255 97

Activation of the mitogen-activated protein (MAP) kinase pathway is believed to play a critical role in normal and pathophysiological proliferation of mesangial cells. Recent studies have shown that MAP kinase activation by growth factors in other cell types involves activation of the low-molecular-weight G protein Ras and the protooncogene serine kinase c-Raf-1. In this study, the role of this pathway in rat renal mesangial cells was assessed. Platelet-derived growth factor (PDGF), epidermal growth factor (EGF), as well as phorbol esters (PMA) rapidly activated MAP kinase three- to fourfold in these cells. PDGF and EGF, but not PMA, were able to activate c-Raf-1 and Ras activity. Stimulation of mesangial cells with the inflammatory mediator prostaglandin E2 (PGE2) or elevation of intracellular adenosine 3',5'-cyclic monophosphate (cAMP) by treatment with forskolin markedly blunted activation of MAP kinase induced by PDGF and EGF, but not by PMA. Consistent with this observation, PGE2 abolished growth factor-induced activation of c-Raf-1. However, Ras activation induced by growth factors was not affected by PGE2 and forskolin. These results suggest that MAP kinase activation can occur by at least two separate pathways in mesangial cells. Tyrosine kinase receptors activate MAP kinase through activation of Ras and Raf. This pathway can be blocked by PGE2 and elevation of cAMP, presumably by interfering with the ability of Ras to activate Raf. In addition, activation of protein kinase C by phorbol esters can activate MAP kinase in a Ras/Raf-independent manner.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Inhibition of MAP kinase by prostaglandin E2 and forskolin in rat renal mesangial cells. 748 69

Mesoderm induction is a critical early step in vertebrate development, involving changes in gene expression and morphogenesis. In Xenopus, normal mesoderm formation depends on signalling through the fibroblast growth factor (FGF) tyrosine kinase receptor. One important signalling pathway from receptor tyrosine kinases involves p21ras (ref. 5). Ras associates with the serine kinase c-Raf-1 in a GTP-dependent manner, and this complex phosphorylates and activates MAPK/ERK kinase (MEK), a protein kinase with dual specificity. MEK then activates p42mapk and (at least in mammals) p44mapk, members of the mitogen-activated protein (MAP) kinase family. FGF activates MAP kinase during mesoderm induction, and the use of dominant-negative constructs suggests that mesoderm induction by FGF requires both Ras and Raf. However, these experiments do not reveal whether Ras and Raf do act through MAP kinase to induce mesoderm or whether another pathway, such as the phosphatidylinositol 3-kinase cascade, is involved. Here we show that expression of active forms of MEK or of MAP kinase induces ventral mesoderm of the kind elicited by FGF. Overexpression of a Xenopus MAP kinase phosphatase blocks mesoderm induction by FGF, and causes characteristic defects in mesoderm formation in intact embryos, whereas inhibition of the P13 kinase and p70 S6 kinase pathways has no effect on mesoderm induction by FGF. FGF induces different types of mesoderm in a dose-dependent manner; strikingly, this is mimicked by expressing different levels of activated MEK. Together, these experiments demonstrate that activation of MAP kinases is necessary and sufficient for mesoderm formation.
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PMID:Mesoderm induction in Xenopus caused by activation of MAP kinase. 754 Nov 16

Activation of the mitogen-activated protein kinase (MAPK) pathway is believed to play a critical role in normal and pathophysiologic proliferation of mesangial cells. Recent studies have shown that MAP kinase activation by growth factors in other cell types involves activation of the low molecular weight G-protein ras and the protooncogene serine kinase c-raf-1. In this study the role of this pathway in rat renal mesangial cells was assessed. 20ng/ml of platelet-derived growth factor (PDGF), 10(-8) mol/L epidermal growth factor (EGF) as well as phorbol ester (10(-6) mol/L PMA) rapidly activated MAP kinase by 3-4 fold in these cells. PDGF and EGF, but not PMA were able to activate c-raf-1 and ras activity. Stimulation with inflammatory mediator PGE2 (50 mumol/L) or elevation of Intracellular cAMP by treatment of cells with forskolin (25 mumol/L) markedly blunted activation of MAP kinase induced by PDGF and EGF, but not PMA. Consistent with this observation, PGE2 abolished growth factor induced activation of c-raf-1. However, ras activation induced by growth factor was not affected by PGE2 and forskolin. These results suggest that MAP kinase activation can occur by at least two separate pathways in mesangial cells. Tyrosine kinase receptors activate MAP kinase through activation of ras and raf. This pathway can be blocked by PGE2 and elevation of cAMP, presumably by interfering with the ability of ras to activate raf. In addition, activation of protein kinase C by phorbol esters can activate MAP kinase in a ras/raf-independent manner. This pathway is not sensitive to inhibition by PGE2 or cAMP. It is likely that activation of each of these pathways, both resulting in a stimulated MAP kinase, will have different physiologic consequences in mediating mesangial cells growth.
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PMID:[Inhibition of growth factor stimulation of mitogen-activated protein kinase by prostaglandin E2 in rat renal mesangial cells]. 778 49

We previously showed that purified, bacterially expressed oncogenic human rasH protein blocks or delays the progression of the embryonic cell cycle into M-phase in activated Xenopus egg extracts. This block correlates with the suppression of the activation of p34cdc2 kinase (Pan, B.-T., Chen, C.-T., and Lin, S.-M. (1994) J. Biol. Chem. 269, 5968-5975). In an attempt to identify kinases that are involved in mediating the effect of oncogenic Ras on the cell cycle, we assayed aliquots of activated Xenopus egg extracts, which were incubated at 25 degrees C for various times in the absence and presence of oncogenic Ras, for their kinase activities toward a calf thymus histone fraction (Hf1). We find that the suppression of the histone H1 kinase activity of p34cdc2 by oncogenic Ras correlates with a simultaneous stimulation of a histone H2b serine kinase activity. Using a histone H2b in-the-gel kinase assay, we further show that the stimulated histone H2b kinase activity is attributed mainly to a 96-kDa kinase and slightly to p42mapk. Although Xenopus p90rsk is also activated by oncogenic Ras, we demonstrate that activated p90rsk is not responsible for the 96-kDa histone H2b kinase activity. The identity of the 96-kDa kinase remains unclear. Our data suggests that the 96-kDa kinase may be involved in mediating the effect of oncogenic Ras on the embryonic cell cycle of Xenopus.
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PMID:Oncogenic ras stimulates a 96-kDa histone H2b kinase activity in activated Xenopus egg extracts. Correlation with the suppression of p34cdc2 kinase. 796 38

We previously reported that epidermal growth factor (EGF) induced the disruption of gap junctional communication (gjc) and serine phosphorylation of connexin43 (Cx43) in T51B rat liver epithelial cells. However, the cascade of events linking EGF receptor activation to these particular responses have not been fully characterized. Furthermore, the serine kinase(s) acting directly on Cx43 remain unidentified. In the current study, we demonstrate that downmodulation of 12-0-tetradecanoylphorbol 13-acetate (TPA)-sensitive protein kinase C (PKC) activity does not affect EGF's ability to reduce junctional permeability or phosphorylate Cx43 in T51B cells. EGF in the presence or absence of chronic TPA treatment stimulated marked increases in Cx43 phosphorylation on numerous sites as determined by two-dimensional tryptic phosphopeptide mapping. Computer-assisted sequence analysis of Cx43 identified several protein kinase phosphorylation consensus sites including two sites for mitogen-activated protein (MAP) kinase. EGF stimulated activation of MAP kinase in a time- and dose-dependent manner where the kinetics of kinase activity corroborated its possible involvement in mediating EGF's effects. Moreover, purified MAP kinase directly phosphorylated Cx43 on serine residues in vitro. Two-dimensional tryptic and chymotryptic phosphopeptide mapping demonstrated that the in vitro phosphopeptides represented a specific subset of the in vivo phosphopeptides produced in response to EGF after chronic TPA treatment. Therefore, EGF-induced disruption of gjc and phosphorylation of Cx43 may be mediated in part by MAP kinase in vivo.
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PMID:Epidermal growth factor stimulates the disruption of gap junctional communication and connexin43 phosphorylation independent of 12-0-tetradecanoylphorbol 13-acetate-sensitive protein kinase C: the possible involvement of mitogen-activated protein kinase. 824 69

The substrate specificity of mitogen-activated protein (MAP) kinase-activated protein kinase-2 (MAPKAP kinase-2) was investigated by using synthetic peptides related to the N-terminus of glycogen synthase. The minimum sequence required for efficient phosphorylation was found to be Xaa-Xaa-Hyd-Xaa-Arg-Xaa-Xaa-Ser-Xaa-Xaa, where Hyd is a bulky hydrophobic residue (Phe > Leu > Val >> Ala), and the peptide Lys-Lys-Phe-Asn-Arg-Thr-Leu-Ser-Val-Ala was phosphorylated with a Km of 9.3 microM and Vmax. of 10 mumol/min per mg. MAPKAP kinase-1 (a homologue of ribosomal protein S6 kinase) also requires an arginine three residues N-terminal to the serine (position n-3), but not a hydrophobic residue at position n-5. Neither MAPKAP kinase-1 nor MAPKAP kinase-2 could tolerate a proline residue at position n + 1, indicating that their specificities do not overlap with that of MAP kinase. The specificity of calmodulin-dependent protein kinase-II resembled that of MAPKAP kinase-2, except that it could tolerate replacement of the arginine by a lysine and the phosphorylation-site serine by a threonine residue. Partial cDNAs encoding MAPKAP kinase-2 were isolated from rabbit and human skeletal muscle and human teratocarcinoma libraries, and Northern-blotting experiments revealed a single 3.3 kb mRNA transcript present at similar levels in six human tissues examined. The catalytic domain was most similar (35-40% identity) to calmodulin-dependent protein kinases II and IV, phosphorylase kinase, putative serine kinase H1 and the C-terminal domain of MAPKAP kinase-1, which form one branch of the protein kinase phylogenetic tree. The sequence N-terminal to the catalytic domain is proline-rich and contains two putative SH3-binding sites. The threonine residue phosphorylated by MAP kinase lies immediately C-terminal to the catalytic domain and is followed by a nuclear localization signal, Lys-Lys-(Xaa)10-Lys-Arg-Arg-Lys-Lys, near the C-terminus.
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PMID:The substrate specificity and structure of mitogen-activated protein (MAP) kinase-activated protein kinase-2. 828 84


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