Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P51812 (mitogen-activated protein)
 10,636 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We examined downstream signaling events that followed the exposure of PC12 cells to extracellular ATP and UTP, and we compared the effects of these P2 receptor agonists with those of growth factors and other stimuli. Based on early findings, we focused particular attention on the mitogen-activated protein (MAP) kinase pathway. ATP and/or UTP produced increases in tyrosine phosphorylation of multiple proteins, including p42 MAP (ERK2) kinase, related adhesion focal tyrosine kinase (RAFTK) (PYK2, CAKbeta), focal adhesion kinase (FAK), Shc, and protein kinase Cdelta (PKCdelta). MAP (ERK2) kinase activity (quantified by substrate phosphorylation) was increased by UTP, ATP, phorbol 12-myristate 13-acetate, ionomycin, and growth factors. UTP and ATP were equipotent (EC50 approximately 25 microM) in stimulating MAP kinase activity, suggesting that these effects were mediated via the Gi-linked P2Y2 (P2U) receptor. Consistent with this, the UTP- and ATP-promoted activation of MAP kinase was diminished in pertussis toxin-treated cells. Treatment of cells with pertussis toxin also reduced both the UTP-dependent increases in intracellular calcium ion concentration ([Ca2+]i) and the tyrosine phosphorylation of RAFTK. Similarly, when [Ca2+]i elevation was prevented using BAPTA and EGTA, the activation of MAP kinase by UTP and ionomycin was blocked, and the tyrosine phosphorylation of RAFTK was reduced. The UTP-promoted increase in MAP kinase activity was partially reduced in cells in which PKC was down-regulated, suggesting that both PKC-dependent and PKC-independent pathways were involved. PKCdelta, which increases MAP kinase activity in some systems, became tyrosine-phosphorylated within 15 s of exposure of cells to ATP or UTP; but epidermal growth factor, nerve growth factor, and insulin had little effect. UTP also promoted the association of Shc with Grb2. These results suggest that the P2Y2 receptor-initiated activation of MAP kinase was dependent on the elevation of [Ca2+]i, involved the recruitment of Shc and Grb2, and was mediated by RAFTK and PKC.
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PMID:Activation of P2Y2 receptors by UTP and ATP stimulates mitogen-activated kinase activity through a pathway that involves related adhesion focal tyrosine kinase and protein kinase C. 944 69

The effect of anandamide, an endogenous ligand for central (CB1) and peripheral (CB2) cannabinoid receptors, was investigated on the growth of the murine IL-6-dependent lymphoid cell line B9 and the murine IL-3-dependent myeloblastic cell line FDC-P1. In conditions of low serum level, anandamide potentiated the growth of both cytokine-dependent cell lines. Comparison with other fatty acid cannabinoid ligands such as (R)-methanandamide, a ligand with improved selectivity for the CB1 receptor, or palmitylethanolamide, an endogenous ligand for the CB2 receptor, showed a very similar effect, suggesting that cell growth enhancement by anandamide or its analogs could be mediated through either receptor subtype. However, several lines of evidence indicated that this growth-promoting effect was cannabinoid receptor-independent. First, the potent synthetic cannabinoid agonist CP 55940, which displays high affinity for both receptors, was inactive in this model. Second, SR 141716A and SR 144528, which are potent and specific antagonists of CB1 and CB2 receptors respectively, were unable, alone or in combination, to block the anandamide-induced effect. Third, inactivation of both receptors by pretreatment of cells with pertussis toxin did not affect the potentiation of cell growth by anandamide. These data demonstrated that neither CB1 nor CB2 receptors were involved in the anandamide-induced effect. Moreover, using CB2-transfected Chinese hamster ovary cells, we demonstrated that after complete blockade of the receptors by the specific antagonist SR 144528, anandamide was still able to strongly stimulate a mitogen-activated protein (MAP) kinase activity, clearly indicating that the endogenous cannabinoid can transduce a mitogenic signal in the absence of available receptors. Finally, arachidonic acid, a structurally related compound and an important lipid messenger without known affinity for cannabinoid receptors, was shown to trigger MAP kinase activity and cell growth enhancement similar to those observed with anandamide. These findings provide clear evidence for a functional role of anandamide in activating a signal transduction pathway leading to cell activation and proliferation via a non-cannabinoid receptor-mediated process.
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PMID:The endogenous cannabinoid anandamide is a lipid messenger activating cell growth via a cannabinoid receptor-independent pathway in hematopoietic cell lines. 956 6

Several agents that act through G-protein-coupled receptors and also stimulate phosphoinositide-specific phospholipase C (PI-PLC), including angiotensin II, vasopressin, norepinephrine, and prostaglandin (PG) F2alpha, activated the ERK1 (p44mapk) and ERK2 (p42mapk) members of the mitogen-activated protein (MAP) kinase family in primary cultures of rat hepatocytes, measured as phosphorylation of myelin basic protein (MBP) by a partially purified enzyme, immunoblotting, and in-gel assays. All these agonists induced a peak activation (two to threefold increase in MBP-phosphorylation) at 3-5 min, followed by a brief decrease, and then a sustained elevation or a second increase of the MAP kinase activity that lasted for several hours. Although all the above agents also stimulated PI-PLC, implicating a Gq-dependent pathway, the elevations of the concentration of inositol (1,4,5)-trisphosphate did not correlate well with the MAP kinase activity. Furthermore, pretreatment of the cells with pertussis toxin markedly reduced the MAP kinase activation by angiotensin II, vasopressin, norepinephrine, or PGF2alpha. In addition, hepatocytes pretreated with pertussis toxin showed a diminished MAP kinase response to epidermal growth factor (EGF). The results indicate that agonists acting via G-protein-coupled receptors have the ability to induce sustained activation of MAP kinase in hepatocytes, and suggest that Gi-dependent mechanisms are required for full activation of the MAP kinase signal transduction pathway by G-protein-coupled receptors as well as the EGF receptor.
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PMID:Activation of p42/p44 mitogen-activated protein kinase by angiotensin II, vasopressin, norepinephrine, and prostaglandin F2alpha in hepatocytes is sustained, and like the effect of epidermal growth factor, mediated through pertussis toxin-sensitive mechanisms. 957 80

Different forms of phospholipase A2, together with pertussis toxin-sensitive G-proteins, [Ca2+]i (intracellular Ca2+ concentration), protein kinase C, calmodulin, protein tyrosine kinases, mitogen-activated protein kinases and Ca2+/calmodulin-dependent protein kinase appear to play a role in agonist-mediated release of arachidonic acid. Here we report that fibroblasts from 14-day-old mouse embryos with inactivated Gi2alpha (alpha-subunit of the heterotrimeric G-protein Gi2) gene display a marked decrease in the ability of lysophosphatidic acid, thrombin and Ca2+ ionophores to release arachidonic acid compared with their normal counterparts. The requirement for Gi2alpha in the release of arachidonic acid following increased [Ca2+]i may be explained by the incomplete translocation of cytosolic phospholipase A2 observed in Gi2alpha-deficient cells. Paradoxically, inactivation of the Gi2alpha gene resulted in up-regulation of bradykinin receptors and their coupling to increased arachidonic acid release, phospholipase C activity and [Ca2+]i. A concomitant increase in basal phospholipase C activity was also observed in the Gi2alpha-deficient cells. These observations establish a pleiotropic and essential role for Gi2alpha in receptor-phospholipase coupling that contrasts with its less obligatory participation in agonist-mediated inhibition of adenylate cyclase.
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PMID:Agonist-specific alterations in receptor-phospholipase coupling following inactivation of Gi2alpha gene. 957 77

Stimulation of neurotensin (NT) type 1 receptors (NT1-R) in transfected CHO cells is followed by the activation of mitogen-activated protein kinases and the expression of the early response gene krox24. By making point mutations and internal deletions in the krox24 promoter, we show that proximal serum responsive elements (SRE) are involved in transcriptional activation by NT. In addition, we show that the related early response gene c-fos and the Ets protein Elk-1 are also induced by NT. The involvement of NT1-R in NT-mediated activation of krox24, c-fos and Elk-1 was demonstrated by the preventing effect of the specific antagonists SR 48692 and SR 142948. Finally, we show that the activation of krox24 and Elk-1 on the one hand, and that of c-fos on the other hand, result from independent transduction pathways since the former are pertussis toxin-sensitive whereas the latter is insensitive to pertussis toxin.
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PMID:Neurotensin type 1 receptor-mediated activation of krox24, c-fos and Elk-1: preventing effect of the neurotensin antagonists SR 48692 and SR 142948. 971 Feb 57

The recently identified 17-amino acid peptide nociceptin (orphanin FQ) is the endogenous ligand for the opioid receptor-like-1 (ORL-1) receptor. A physiologic role for nociceptin (OFQ) activation of the ORL-1 receptor (OFQR) may be to modulate opioid-induced analgesia. The molecular mechanism by which nociceptin (OFQ) and ORL-1 (OFQR) modify opioid-stimulated effects, however, is unclear. Both ORL-1 (OFQR) and opioid receptors mediate pertussis toxin (PTX)-sensitive signal transduction, indicating these receptors are capable of coupling to Gi/Go proteins. This study determines that nociceptin stimulates an intracellular signaling pathway, leading to activation of mitogen-activated protein (MAP) kinase in CHO cells expressing ORL-1 receptor (OFQR). Nociceptin (OFQ)-stimulated MAP kinase activation was inhibited by PTX or by expression of the carboxyl terminus of beta-adrenergic receptor kinase (betaARKct), which specifically blocks Gbetagamma-mediated signaling. Expression of the proline-rich domain of SOS (SOS-PRO), which inhibits SOS interaction with p21ras, also attenuated nociceptin (OFQ)-stimulated MAP kinase activation. The phosphatidylinositol 3-kinase (PI-3K) inhibitors wortmannin and LY294002 reduced nociceptin (OFQ)-stimulated MAP kinase activation, whereas inhibition of protein kinase C (PKC) activity by bisindolylmaleimide I or cellular depletion of PKC had no effect. In a similar manner, in cells expressing mu-opioid receptor, [D-Ala2,N-Me-Phe4,Gly-ol]-enkephalin (DAMGO; a mu-opioid receptor-selective agonist) stimulated PTX-sensitive MAP kinase activation that was inhibited by wortmannin, LY294002, betaARKct expression, or SOS-PRO expression but not affected by inhibition of PKC activity. These results indicate that both ORL-1 (OFQR) and mu-opioid receptors mediate MAP kinase activation via a signaling pathway using the betagamma-subunit of Gi, a PI-3K, and SOS, independent of PKC activity. In cells expressing both ORL-1 (OFQR) and mu-opioid receptors, pretreatment with nociceptin decreased subsequent nociceptin (OFQ)- or DAMGO-stimulated MAP kinase activation. In contrast, pretreatment of cells with DAMGO decreased subsequent DAMGO-stimulated MAP kinase but had no effect on subsequent nociceptin (OFQ)-stimulated MAP kinase activation. These results demonstrate that nociceptin (OFQ) activation of ORL-1 (OFQR) can modulate mu-opioid receptor signaling in a cellular system.
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PMID:Nociceptin (ORL-1) and mu-opioid receptors mediate mitogen-activated protein kinase activation in CHO cells through a Gi-coupled signaling pathway: evidence for distinct mechanisms of agonist-mediated desensitization. 972 27

1. The mitogen-activated protein (MAP) kinase signalling pathway can be activated by a variety of heterotrimeric Gi/Go protein-coupled and Gq/G11 protein-coupled receptors. The aims of the current study were: (i) to investigate whether the Gi/Go protein-coupled adenosine A1 receptor activates the MAP kinase pathway in transfected Chinese hamster ovary cells (CHO-A1) and (ii) to determine whether adenosine A1 receptor activation would modulate the MAP kinase response elicited by the endogenous P2Y2 purinoceptor. 2. The selective adenosine A1 receptor agonist N6-cyclopentyladenosine (CPA) stimulated time and concentration-dependent increases in MAP kinase activity in CHO-A1 cells (EC50 7.1+/-0.4 nM). CPA-mediated increases in MAP kinase activity were blocked by PD 98059 (50 microM; 89+/-4% inhibition), an inhibitor of MAP kinase kinase 1 (MEKI) activation, and by pre-treating cells with pertussis toxin (to block Gi/Go-dependent pathways). 3. Adenosine A1 receptor-mediated activation of MAP kinase was abolished by pre-treatment with the protein tyrosine inhibitor, genistein (100 microM; 6+/-10% of control). In contrast, daidzein (100 microM), the inactive analogue of genistein had no significant effect (96+/-12 of control). MAP kinase responses to CPA (1 microM) were also sensitive to the phosphatidylinositol 3-kinase inhibitors wortmannin (100 nM; 55+/-8% inhibition) and LY 294002 (30 microM; 40+/-5% inhibition) but not to the protein kinase C (PKC) inhibitor Ro 31-8220 (10 microM). 4. Activation of the endogenous P2Y2 purinoceptor with UTP also stimulated time and concentration-dependent increases in MAP kinase activity in CHO-A1 cells (EC50=1.6+/-0.3 microM). The MAP kinase response to UTP was partially blocked by pertussis toxin (67+/-3% inhibition) and by the PKC inhibitor Ro 31-8220 (10 microm; 45+/-5% inhibition), indicating the possible involvement of both Gi/Go protein and Gq protein-dependent pathways in the overall response to UTP. 5. CPA and UTP stimulated concentration-dependent increases in the phosphorylation state of the 42 kDa and 44 kDa forms of MAP kinase as demonstrated by Western blotting. 6. Co-activation of CHO-A1 cells with CPA (10 nM) and UTP (1 microM) produced synergistic increases in MAP kinase activity which were not blocked by the PKC inhibitor Ro 31-8220 (10 microM). 7. Adenosine A1 and P2Y2 purinoceptor activation increased the expression of luciferase in CHO cells transfected with a luciferase reporter gene containing the c-fos promoter. However, co-activating these two receptors produced only additive increases in luciferase expression. 8. In conclusion, our studies have shown that the transfected adenosine A1 receptor and the endogenous P2Y2 purinoceptor couple to the MAP kinase signalling pathway in CHO-A1 cells. Furthermore, co-stimulation of the adenosine A1 receptor and the P2Y2 purinoceptor produced synergistic increases in MAP kinase activity but not c-fos mediated luciferase expression.
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PMID:Human adenosine A1 receptor and P2Y2-purinoceptor-mediated activation of the mitogen-activated protein kinase cascade in transfected CHO cells. 972 63

Terminal differentiation of skeletal muscle cells in culture is inhibited by a number of different growth factors whose subsequent intracellular signaling events are poorly understood. In this study, we have investigated the role of heterotrimeric G proteins in mediating fibroblast growth factor (FGF)-dependent signals that regulate myogenic differentiation. Pertussis toxin, which ADP-ribosylates and inactivates susceptible G proteins, promotes terminal differentiation in the presence of FGF-2, suggesting that Galpha or Gbeta gamma subunits or both are involved in transducing the FGF-dependent signal(s) that inhibits myogenesis. We found that Gbetagamma subunits are likely to be involved since the expression of the C terminus of beta-adrenergic receptor kinase 1, a Gbetagamma subunit-sequestering agent, promotes differentiation in the presence of FGF-2, and expression of the free Gbeta gamma dimer can replace FGF-2, rescuing cells from pertussis toxin-induced differentiation. Addition of pertussis toxin also blocked FGF-2-mediated activation of mitogen-activated protein kinases (MAPKs). Ectopic expression of dominant active mutants in the Ras/MAPK pathway rescued cells from pertussis toxin-induced terminal differentiation, suggesting that the Gbeta gamma subunits act upstream of the Ras/MAPK pathway. It is unlikely that the pertussis toxin-sensitive pathway is activated by other, as yet unidentified FGF receptors since PDGF (platelet-derived growth factor)-stimulated MM14 cells expressing a chimeric receptor containing the FGF receptor-1 intracellular domain and the PDGF receptor extracellular domain were sensitive to pertussis toxin. Our data suggest that FGF-mediated signals involved in repression of myogenic differentiation are transduced by a pertussis toxin-sensitive G-protein-coupled mechanism. This signaling pathway requires the action of Gbeta gamma subunits and activation of MAPKs to repress skeletal muscle differentiation.
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PMID:Regulation of myogenesis by fibroblast growth factors requires beta-gamma subunits of pertussis toxin-sensitive G proteins. 974 95

To gain insight into the molecular mechanism for nociceptin function, functional coupling of the nociceptin receptor expressed in Chinese hamster ovary (CHO) cells with phospholipase A2 (PLA2) was examined. In the presence of A23187, a calcium ionophore, activation of the nociceptin receptor induced time- and dose-dependent release of arachidonate, which was abolished by pretreatment of the cells with pertussis toxin (PTX). Immunoblot analysis using anti-Ca2+-dependent cytosolic PLA2 (cPLA2) monoclonal antibody demonstrates that activation of the nociceptin receptor induces a time- and dose-dependent electrophoretic mobility shift of cPLA2, suggesting that phosphorylation of cPLA2 is induced by the nociceptin receptor. Pretreatment of the cells with PD98059, a specific mitogen-activated protein kinase/extracellular signal-regulated kinase kinase 1 inhibitor, or staurosporine, a potent inhibitor of serine/threonine protein kinases and tyrosine protein kinases, partially inhibited the nociceptin-induced cPLA2 phosphorylation and arachidonate release. These results indicate that the nociceptin receptor expressed in CHO cells couples with cPLA2 through the action of PTX-sensitive G proteins and suggest that cPLA2 is activated by phosphorylation induced by the nociceptin receptor via mechanisms partially dependent on p44 and p42 mitogen-activated protein kinases.
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PMID:Activation of phospholipase A2 by the nociceptin receptor expressed in Chinese hamster ovary cells. 979 46

Signal transduction pathways involved in the hypertrophic effect of neuropeptide Y (NPY) were investigated in adult cardiomyocytes. Reduction of transforming growth factor-beta activity in serum-supplemented media abolished the induction of hypertrophic responsiveness to NPY. In responsive cells, NPY (100 nM) increased protein synthesis, determined as incorporation of [14C]phenylalanine, by 35 +/- 15% (P < 0.05, n = 16 cultures). In these cells, NPY activated pertussis toxin (PTx)-sensitive G proteins and phosphatidylinositol (PI) 3-kinase. PTx and inhibition of PI 3-kinase abolished the hypertrophic effect of NPY. NPY also activated protein kinase C (PKC) and mitogen-activated protein (MAP) kinase. Inhibition of these two kinases attenuated the induction of creatine kinase (CK)-BB but not the growth response to NPY. In conclusion, NPY stimulates protein synthesis in adult cardiomyocytes via activation of PTx-sensitive G proteins and PI 3-kinase and it induces the fetal-type CK-BB via activation of PKC and MAP kinase.
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PMID:Intracellular signaling leads to the hypertrophic effect of neuropeptide Y. 981 68


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