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Query: UNIPROT:P51812 (mitogen-activated protein)
 10,636 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Rat 1a fibroblasts transformed by the Gi2 oncogene, gip2, exhibit a constitutively elevated mitogen-activated protein (MAP) kinase activity that correlates with enhanced tyrosine phosphorylation of the p42 MAP kinase polypeptide. The MAP kinase activity in gip2 transformed cells is 50-60% of the pertussis toxin-sensitive, thrombin-stimulated activity observed in wild-type Rat 1a cells. A similar activation of MAP kinase is observed in src but not ras or raf transformed Rat 1a cells, indicating that the persistent MAP kinase activity results from the action of the specific oncoprotein and is not the consequence of cellular transformation. The enhanced transactivation function of c-Jun characteristic of the transformed phenotype, measured using a collagenase promoter-CAT reporter gene, is observed in gip2, src, ras, and raf transformed Rat 1a cells. The regulatory networks controlled by the four transforming oncogenes therefore alter the activity of specific transcription factors, but only gip2 and src constitutively activate MAP kinase. The findings demonstrate that the catalytic activity of growth factor-regulated cytoplasmic kinases are selectively and stably activated as a consequence of specific oncogene expression.
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PMID:MAP kinase is constitutively activated in gip2 and src transformed rat 1a fibroblasts. 131 14

The normal cellular homologue of the acutely transforming oncogene v-raf is c-raf-1, which encodes a serine/threonine protein kinase that is activated by many extracellular stimuli. The physiological substrates of the protein c-Raf-1 are unknown. The mitogen-activated protein (MAP) kinases Erk1 and 2 are also activated by mitogens through phosphorylation of Erk tyrosine and threonine residues catalysed by a protein kinase of relative molecular mass 50,000, MAP kinase-kinase (MAPK-K). Here we report that MAPK-K as well as Erk1 and 2 are constitutively active in v-raf-transformed cells. MAPK-K partially purified from v-raf-transformed cells or from mitogen-treated cells can be deactivated by phosphatase 2A. c-Raf-1 purified after mitogen stimulation can reactivate the phosphatase 2A-inactivated MAPK-K over 30-fold in vitro. c-Raf-1 reactivation of MAPK-K coincides with the selective phosphorylation at serine/threonine residues of a polypeptide with M(r) 50,000 which coelutes precisely on cation-exchange chromatography with the MAPK-K activatable by c-Raf-1. These results indicate that c-Raf-1 is an immediate upstream activator of MAPK-K in vivo. To our knowledge, MAPK-K is the first physiological substrate of the c-raf-1 protooncogene product to be identified.
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PMID:Raf-1 activates MAP kinase-kinase. 132

Activation of human neutrophils by the chemotactic peptide formyl-methionyl-leucyl-phenylalanine (fMLP) induces tyrosine phosphorylation of several polypeptides, including a prominent band of approximately 41 kDa. A polypeptide of identical electrophoretic mobility was recognized by a monoclonal antibody raised against a sequence corresponding to amino acids 325-345 of ERK-1, one of a family of mitogen-activated protein (MAP) kinases. To establish the possible identity of these polypeptides, extracts from control and fMLP-treated cells were immunoprecipitated with immobilized antiphosphotyrosine antibodies. Reactivity with anti-ERK-1 antibodies was observed only in the precipitate of chemoattractant-stimulated cells. These data imply that a MAP kinase constitutes at least part of the tyrosine-phosphorylated 41-kDa polypeptide. By using an in vitro renaturation assay, treatment of intact cells with fMLP was found to stimulate several protein kinases, including one of approximately 41 kDa. Renaturation of samples immunoprecipitated with antiphosphotyrosine antibodies revealed the presence of an active protein kinase in chemoattractant-stimulated, but not in control cells. The immunoprecipitated kinase comigrated with the 41-kDa tyrosine phosphorylated polypeptide and the anti-ERK-1 reactive band. We conclude that a MAP kinase closely related or identical to ERK-1 is tyrosine phosphorylated and activated when human neutrophils are stimulated by chemotactic peptides. The rapid phosphorylation of this kinase, which is apparent within seconds, is compatible with a role in the activation of the respiratory burst and/or other neutrophil responses.
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PMID:Chemoattractant-induced tyrosine phosphorylation and activation of microtubule-associated protein kinase in human neutrophils. 138 63

Previous studies have shown that the noncatalytic carboxy-terminal tail of the p70 S6 kinase (amino acids 422 to 525) contains an autoinhibitory pseudosubstrate domain that is phosphorylated in situ during activation and in vitro by mitogen-activated protein kinases. The present study shows that a recombinant p70 deleted of the carboxy-terminal tail (p70 delta CT104) nevertheless exhibits a basal and serum-stimulated 40S kinase activity and susceptibility to inhibition by wortmannin very similar to those of the parent, full-length p70 kinase. Carboxy-terminal deletion reduces the extent of maximal inhibition produced by rapamycin, from > 95% in the full-length p70 to 60 to 80% in p70 delta CT104, without altering the sensitivity to rapamycin inhibition (50% inhibitory concentration of 2 nM). Serum activation of p70 delta CT104, as with the parent, full-length p70, is accompanied by an increase in 32P content (about twofold) in situ and a slowing in electrophoretic mobility; both modifications are inhibited by pretreatment with wortmannin or rapamycin. 32P-peptide maps of p70 delta CT104 show multisite phosphorylation, and wortmannin and rapamycin appear to cause preferential dephosphorylation of the same subset of sites. Thus, it is likely that activation of the kinase requires phosphorylation of p70 at sites in addition to those previously identified in the carboxy-terminal tail. Evidence that the carboxy-terminal tail actually functions as a potent intramolecular inhibitor of kinase activity in situ is uncovered by deletion of a short acidic segment (amino acids 29 to 46) from the p70 amino-terminal noncatalytic region. Deletion of amino acids 29 to 46 causes a >95% inhibition of p70 activity despite continue phosphorylation of the carboxy-terminal tail in situ; additional deletion of the carboxy-terminal tail (yielding p70 delta 29-46/ delta CT104) increases activity 10-fold, to a level approaching that of p70 delta CT104. Deletion of residues 29 to 46 also abolishes completely the sensitivity of p70 to inhibition by rapamycin but does not alter the susceptibility to activation by serum of inhibition by wortmannin. Although the mechanisms underlying the effects of the delta 29-46 deletion are not known, they are not attributable to loss of the major in situ p70 phosphorylation site at Ser-40. Thus, activation of the p70 S6 kinase involves multiple, independent inputs directed at different domains of the p70 polypeptide. Disinhibition from the carboxy-terminal tail requires, in addition to its multisite phosphorylation, an activating input dependent on the presence of amino acids 29 to 46; this p70-activating input may be the same as that inhibited by rapamycin but is distinct from that arising from the wortmannin-inhibitable phosphatidylinositol 3-kinase. In addition, as exemplified by the rapamycin-resistant but mitogen- and wortmannin-sensitive p70 delta 29-46/ delta CT104 mutant, a further activating input, which probably involves site-specific phosphorylation in the segment between amino acids 46 to 421, is necessary.
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PMID:Multiple independent inputs are required for activation of the p70 S6 kinase. 773 16

Treatment of primary cultures of rat cerebral cortical astrocytes with extracellular ATP caused a 3- to 4-fold stimulation of mitogen-activated protein (MAP) kinase activity. Studies with agonists and antagonists of P1 and P2 purinergic receptors indicated that this activation is mediated by ATP/P2 purinergic receptors rather than adenosine/P1 purinergic receptors. Increased cAMP levels did not significantly inhibit the activation of MAP kinase by ATP but did inhibit the stimulation of MAP kinase by basic fibroblast growth factor, a polypeptide growth factor that activates the Ras/Raf kinase signaling pathway. These data indicate that ATP/P2 purinergic receptors are coupled to MAP kinase by a signal transduction pathway that is independent of the Raf kinase pathway.
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PMID:Signaling by ATP receptors in astrocytes. 781 32

Integrins can function as signal-transducing receptors capable of modulating cell growth and gene expression (Juliano, R. L., and Haskill, S. (1993) J. Cell Biol. 120, 577-585; Hynes, R. O. (1992) Cell 69, 11-25). An early event in integrin signaling in fibroblasts and other cells involves activation of pp125FAK, a cytoplasmic tyrosine kinase (Hanks, S. K., Calalb, M. B., Harper, M. C., and Patel, S. K. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 8487-8491; Schaller, M. D., Borgman, C. A., Cobb, B. S., Vines, R. R., Reynolds, A. B., and Parsons, J. T. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 5192-5196). Here we report a novel aspect of integrin-mediated signal transduction. We demonstrate that adhesion of cells to substrata coated with extracellular matrix proteins, or with a synthetic peptide containing the RGD sequence, can cause activation of mitogen-activated protein (MAP) kinases in 3T3 or REF52 fibroblasts. Activation of MAP kinases seems to depend on integrin engagement rather than simply on cell attachment. Thus, MAP kinases are activated when cells adhere to substrata coated with the integrin ligands fibronectin or laminin, but not when cells adhere to poly-D-lysine, a nonspecific adhesion-promoting polypeptide. Treatment of cells with cytochalasin D, an inhibitor of actin microfilament assembly, almost completely blocks adhesion-induced MAP kinase activation, indicating a critical role for the cytoskeleton. In REF52 cells, we have observed that activation of MAP kinases is accompanied by redistribution of the protein to the nucleus, suggesting that the activated kinases may impinge on factors regulating gene expression. Thus, integrin-mediated cell adhesion seems a sufficient stimulus to cause activation and nuclear translocation of MAP kinases. This may have important implications for the regulation of cell growth and differentiation by the extracellular matrix.
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PMID:Integrin-mediated cell adhesion activates mitogen-activated protein kinases. 792 88

In addition to their role in bacterial killing, reactive oxygen intermediates (ROI) produced by the NADPH oxidase may participate in the regulation of intracellular pathways. We have recently demonstrated that ROI produced by the oxidase regulate tyrosine phosphorylation in neutrophils, possibly by alterations in the cellular redox state. The purpose of the present study was to characterize the identities of certain of the redox-sensitive tyrosine-phosphorylated substrates and the significance of the increased phosphorylation. As a prominent 42-44-kDa phosphorylated band was noted in oxidant-treated cells, we investigated the possible phosphorylation and activation of mitogen-activated protein (MAP) kinase under these conditions. Immunoprecipitation of MAP kinase followed by immunoblotting with anti-phosphotyrosine antibodies indicated that a 42-44-kDa polypeptide was tyrosine-phosphorylated in response to treatment of cells, either with the oxidizing agent diamide or with H2O2 in cells where catalase was inhibited. Using an in vitro renaturation assay with myelin basic protein as the substrate, oxidant-induced stimulation of kinase activity of a 42-44-kDa band was observed in both whole cell extracts and in MAP kinase immunoprecipitates. The mechanism of redox-sensitive activation of MAP kinase was examined. First, exposure of cells to oxidants caused a significant increase in the activity of MEK (the putative activator of MAP kinase), as determined by an in vitro kinase assay using recombinant catalytically inactive glutathione S-transferase-MAP kinase as the substrate. Additionally, oxidant treatment of cells resulted in inhibition of the activity of CD45, a protein tyrosine phosphatase known to dephosphorylate and inactivate MAP kinase. We conclude that oxidant treatment of neutrophils can activate MAP kinase by stimulating its tyrosine and (presumably) threonine phosphorylation via MEK activation, a response that may be potentiated by inhibition of MAP kinase dephosphorylation by phosphatases such as CD45.
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PMID:Activation of the mitogen-activated protein kinase signaling pathway in neutrophils. Role of oxidants. 798 67

The 85-kDa cytoplasmic phospholipase A2 (cPLA2) is the major hormone and growth factor-regulated enzyme that catalyzes release of arachidonic acid in mammalian cells. Activation of cPLA2 requires elevation of intracellular Ca2+ and the phosphorylation of the cPLA2 enzyme by mitogen-activated protein (MAP) kinase. Down-regulation of protein kinase C by phorbol esters or pertussis toxin catalyzed ADP-ribosylation of Gi proteins inhibits thrombin and ATP receptor-stimulated MAP kinase and arachidonic acid release, indicating that functional protein kinase C and Gi proteins are required for G protein regulation of arachidonic acid release. A mutant G alpha i2 subunit having Gly203 mutated to Thr (alpha i2G203T) inhibited thrombin and ATP receptor stimulation of arachidonic acid release independent of adenylyl cyclase inhibition, Ca2+ mobilization, and MAP kinase activation. Overexpression of the wild-type alpha i2 polypeptide or the inactive mutant alpha i2G204A (Gly204 mutated to Ala) polypeptide had no effect on thrombin or ATP receptor stimulation of arachidonic acid release. The phenotype observed with expression of the mutant alpha i2G203T polypeptide defines a role for Gi2 in the control of cPLA2 activity and subsequent arachidonic acid release in addition to the regulation of intracellular Ca2+ levels and MAP kinase activity.
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PMID:Expression of a mutant Gi2 alpha subunit inhibits ATP and thrombin stimulation of cytoplasmic phospholipase A2-mediated arachidonic acid release independent of Ca2+ and mitogen-activated protein kinase regulation. 829 38

In somatic cells, the Raf-1 serine/threonine protein kinase is activated by several polypeptide growth factors. We investigated the role of Raf-1 in progesterone-induced meiotic maturation of Xenopus laevis oocytes. Raf-1 enzymatic activity and phosphorylation (reflected by a mobility shift on sodium dodecyl sulfate gels) were increased in oocytes following progesterone stimulation. The increase in Raf-1 activity was concurrent with an elevation in the activity of mitogen-activated protein (MAP) kinase. When RNA encoding an oncogenic form of Raf-1 (v-Raf) was injected into immature oocytes, MAP kinase mobility shift, germinal vesicle breakdown, and histone H1 phosphorylation increased markedly. When RNA encoding a dominant-negative version of Raf-1 was injected, progesterone-induced oocyte maturation was blocked. When RNA encoding Xenopus mos (mosxe) was injected into oocytes, Raf-1 and MAP kinase mobility shifts were observed after several hours. Also, when antisense mosxe oligonucleotides were injected into oocytes, progesterone-induced Raf-1 and MAP kinase mobility shifts were blocked. Finally, when antisense mosxe oligonucleotides were coinjected with v-Raf RNA into oocytes, histone H1 kinase activation, germinal vesicle breakdown, and MAP kinase mobility shift occurred. These findings suggest that Raf-1 activity is required for progesterone-induced oocyte maturation and that Raf-1 is downstream of mosxe activity.
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PMID:Raf-1 protein kinase is important for progesterone-induced Xenopus oocyte maturation and acts downstream of mos. 832 Dec 23

Bacterial LPS stimulation of murine macrophages leads to increased tyrosine phosphorylation and activation of the 42- and 44-kDa mitogen-activated protein kinases (MAPK) and the activation of stress-activated protein kinases (SAPK)/c-Jun N-terminal kinase (JNK) and p38, related to the high osmolarity glycerol protein kinase in Saccharomyces cerevisiae (HOG1). LPS caused a rapid increase (10 min) in phosphotransferase activity toward myelin basic protein (MBP), a polypeptide that encompassed the first 169 residues of c-Jun fused to gluthathione S-transferase (GST-c-Jun (1-169)) and 27-kDa heat shock protein (hsp27). MonoQ fractionation of cell extracts resolved phosphotransferase activity peaks toward MBP, GST-c-Jun (1-169), and hsp27, which contained MAPK, SAPK/JNK, and MAPKAPK2, respectively, as indicated by immunoblotting data. In RAW 264.7 macrophages, LPS stimulation of MAPKAPK2, a substrate of p38 HOG1 and MAPK, appeared to occur predominantly via p38 HOG1 and not the MAPK. PMA, which activated the MAPK as potently as LPS, did not strongly activate MAPKAPK2, as assessed by hsp27 phosphorylation. Consistent with p38 HOG1-mediating LPS activation of MAPKAPK2, treatment with LPS, but not PMA, increased the tyrosine phosphorylation of p38 HOG1, a modification known to elevate the enzymatic capacity of this kinase. In LPS-treated cells, the activity of SAPK/JNK was increased 5- to 10-fold, as measured by precipitating SAPK/JNK with Abs or immobilized GST-c-Jun and performing an in vitro kinase assay. In addition, the kinases thought to be upstream of SAPK/JNK, SAPK/ERK kinase 1 (SEK1), and MAPK/ERK kinase kinase 1 (MEKK1), were activated following LPS, but not PMA, exposure (5-fold and 2.5-fold, respectively.
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PMID:Activation of multiple proline-directed kinases by bacterial lipopolysaccharide in murine macrophages. 866 21


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