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)

It has recently been reported that protein-tyrosine kinase activity is required for thrombin-induced growth in vascular smooth muscle cells (VSMC). In the present study, we have identified several phosphoproteins that are tyrosine-phosphorylated in response to thrombin in quiescent VSMC. These proteins are insulin-like growth factor-1 receptor beta-subunit (IGF-IR beta), insulin receptor substrate-1 (IRS-1), and phospholipase C-gamma 1 (PLC-gamma 1). Thrombin-stimulated phosphorylation of these proteins was rapid; it was maximal at 1 min and reduced thereafter. Thrombin also activated mitogen-activated protein kinases (MAPK) in quiescent VSMC in a biphasic manner with a rapid and larger peak at 10 min (6-fold) followed by a sustained smaller second peak at 2 h (2-fold). Inhibition of protein-tyrosine kinase activity by the use of two structurally different protein-tyrosine kinase inhibitors, genistein and herbimycin A, significantly blocked the thrombin-induced tyrosine phosphorylation of IGF-1R beta, IRS-1, and PLC-gamma 1 and decreased thrombin-stimulated DNA synthesis. In contrast, however, inhibition of protein-tyrosine kinase activity had no effect on thrombin activation of MAPK. Collectively, these findings suggest a role for tyrosine phosphorylation of IGF-IR beta, IRS-1, and PLC-gamma 1 in thrombin-induced mitogenic signaling events in VSMC. Furthermore, while protein tyrosine phosphorylation is essential for thrombin-induced DNA synthesis, it is not required for thrombin-stimulated MAPK activation. Since thrombin rapidly activated Src in VSMC, Src may be involved in the cross-talk between the G-protein-coupled receptor agonist and a tyrosine kinase receptor such as IGF-1R.
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PMID:Thrombin stimulates phosphorylation of insulin-like growth factor-1 receptor, insulin receptor substrate-1, and phospholipase C-gamma 1 in rat aortic smooth muscle cells. 749 60

Mitogenic stimulation of Swiss 3T3 fibroblasts with bombesin results in receptor-mediated activation of a complex array of effectors, including phospholipase C beta and mitogen-activated protein (MAP) kinase. Incubation of Swiss 3T3 fibroblasts with the 11-amino acid [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P peptide inhibited bombesin-stimulated cell proliferation and phospholipase C beta activation even at high bombesin concentrations. The peptide did not inhibit the activation of phospholipase C beta by a GTPase-deficient form of the Gq-like protein, G16, indicating that the peptide does not inhibit phospholipase C beta and is acting at a point upstream of the activated form of the G protein alpha subunit. The peptide inhibited MAP kinase activation at low bombesin concentrations, but unlike phospholipase C beta, this inhibition could be overcome with 30 nM bombesin. In control Swiss 3T3 cells, bombesin did not measurably activate Ras or Raf-1 above basal levels. Following incubation of the cells with the [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P peptide, 50 nM bombesin activated Raf-1 4-6-fold over basal levels. Platelet-derived growth factor-stimulated activities of PLC, Ras, Raf-1, and MAP kinase were unaltered after incubation of Swiss 3T3 cells with the [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P peptide, as was platelet-derived growth factor-stimulated growth of the Swiss 3T3 cells. Thus, the peptide behaves as an antagonist that differentially inhibited phospholipase C beta and MAP kinase signal transduction pathways. The growth arrest observed with the peptide indicates that the bombesin-stimulated activation of MAP kinase is not sufficient to support mitogenesis in Swiss 3T3 cells.
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PMID:Differential modulation of bombesin-stimulated phospholipase C beta and mitogen-activated protein kinase activity by [D-Arg1,D-Phe5,D-Trp7,9,Leu11]substance P. 753 38

Pleckstrin homology (PH) domains are 90-110 amino acid regions of protein sequence homology that are found in a variety of proteins involved in signal transduction and growth control. We have previously reported that the PH domains of several proteins, including beta ARK1, PLC gamma, IRS-1, Ras-GRF, and Ras-GAP, expressed as glutathione S-transferase fusion proteins, can reversibly bind purified bovine brain G beta gamma subunits in vitro with varying affinity. To determine whether PH domain peptides would behave as antagonists of G beta gamma subunit-mediated signal transduction in intact cells, plasmid minigene constructs encoding these PH domains were prepared, which permit transient cellular expression of the peptides. Pertussis toxin-sensitive, G beta gamma subunit-mediated inositol phosphate (IP) production was significantly inhibited in COS-7 cells transiently coexpressing the alpha 2-C10 adrenergic receptor (AR) and each of the PH domain peptides. Pertussis toxin-insensitive, Gq alpha subunit-mediated IP production via coexpressed M1 muscarinic acetylcholine receptor (M1 AChR) was attenuated only by the PLC gamma PH domain peptide, suggesting that the inhibitory effect of most of the PH domain peptides was G beta gamma subunit-specific. Stimulation of the mitogen-activated protein (MAP) kinase pathway by Gi-coupled receptors in COS-7 cells has been reported to require activation of p21ras and to be independent of protein kinase C. Since several proteins involved in activation contain PH domains, the effect of PH domain peptide expression on alpha 2-C10 AR-mediated p21ras-GTP exchange and MAP kinase activation as well as direct G beta gamma subunit-mediated activation of MAP kinase was determined. In each assay, coexpression of the PH domain peptides resulted in significant inhibition. Increasing G beta gamma subunit expression surmounted PH domain peptide-mediated inhibition of MAP kinase activation. These data suggest that the PH domain peptides behave as specific antagonists of G beta gamma-mediated signaling in intact cells and that interactions between PH domains and G beta gamma subunits or structurally related proteins may play a role in the activation of mitogenic signaling pathways by G protein-coupled receptors.
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PMID:Effect of cellular expression of pleckstrin homology domains on Gi-coupled receptor signaling. 776 89

We recently have demonstrated that EGF receptor (EGFR)-induced cell motility requires receptor kinase activity and autophosphorylation (P. Chen, K. Gupta, and A. Wells. 1994. J. Cell Biol. 124:547-555). This suggests that the immediate downstream effector molecule contains a src homology-2 domain. Phospholipase C gamma (PLC gamma) is among the candidate transducers of this signal because of its potential roles in modulating cytoskeletal dynamics. We utilized signaling-restricted EGFR mutants expressed in receptor devoid NR6 cells to determine if PLC activation is necessary for EGFR-mediated cell movement. Exposure to EGF (25 nM) augmented PLC activity in all five EGFR mutant cell lines which also responded by increased cell movement. Basal phosphoinositide turnover was not affected by EGF in the lines which do not present the enhanced motility response. The correlation between EGFR-mediated cell motility and PLC activity suggested, but did not prove, a causal link. A specific inhibitor of PLC, U73122 (1 microM) diminished both the EGF-induced motility and PLC responses, while its inactive analogue U73343 had no effect on these responses. Both the PLC and motility responses were decreased by expression of a dominant-negative PLC gamma-1 fragment in EGF-responsive infectant lines. Lastly, anti-sense oligonucleotides (20 microM) to PLC gamma-1 reduced both responses in NR6 cells expressing wild-type EGFR. These findings strongly support PLC gamma as the immediate post receptor effector in this motogenic pathway. We have demonstrated previously that EGFR-mediated cell motility and mitogenic signaling pathways are separable. The point of divergence is undefined. All kinase-active EGFR mutants induced the mitogenic response while only those which are autophosphorylated induced PLC activity. U73122 did not affect EGF-induced thymidine incorporation in these motility-responsive infectant cell lines. In addition, the dominant-negative PLC gamma-1 fragment did not diminish EGF-induced thymidine incorporation. All kinase active EGFR stimulated mitogen-activated protein (MAP) kinase activity, regardless of whether the receptors induced cell movement; this EGF-induced MAP kinase activity was not affected by U73122 at concentrations that depressed the motility response. Thus, the signaling pathways which lead to motility and cell proliferation diverge at the immediate post-receptor stage, and we suggest that this is accomplished by differential activation of effector molecules.
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PMID:Epidermal growth factor receptor-mediated cell motility: phospholipase C activity is required, but mitogen-activated protein kinase activity is not sufficient for induced cell movement. 796 64

The exchange of nerve growth factor receptor/Trk and epidermal growth factor receptor (EGFR) phospholipase C gamma (PLC gamma) binding sites resulted in the transfer of their distinct affinities for this Src homology 2 domain-containing protein. Relative to wild-type EGFR, the PLC gamma affinity increase of the EGFR switch mutant EGFR.X enhanced its inositol trisphosphate (IP3) and calcium signals and resulted in a more sustained mitogen-activated protein (MAP) kinase activation and accelerated receptor dephosphorylation. In parallel, EGFR.X exhibited a significantly decreased mitogenic and transforming potential in NIH 3T3 cells. Conversely, the transfer of the EGFR PLC gamma binding site into the Trk cytoplasmic domain context impaired the IP3/calcium signal and attenuated the MAP kinase activation and receptor dephosphorylation, but resulted in an enhancement of the ETR.X exchange mutant mitogenic and oncogenic capacity. Our findings establish the significance of PLC gamma affinity for signal definition, the role of this receptor tyrosine kinase substrate as a negative feedback regulator and the importance of this regulatory function for mitogenesis and its disturbance in oncogenic aberrations.
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PMID:Transforming potentials of epidermal growth factor and nerve growth factor receptors inversely correlate with their phospholipase C gamma affinity and signal activation. 859 8

It is generally accepted that in endothelial cells the occupation of bradykinin B2 receptors, which are linked to the guanine nucleotide-dependent regulatory proteins, Gi and Gq, results in the activation of phospholipase C-beta1 (PLC-beta1), followed by a transient increase in the formation of inositol 1,4,5-trisphosphate (IP3) and diacylglycerol. The PLC-beta1 isoform, in contrast to the gamma1 isoform, is present only at a low level in cultured endothelial cells, implying that PLC-gamma1 activation may play an important role in endothelial signaling pathways. In cultured human endothelial cells, bradykinin induced a rapid increase in the tyrosine phosphorylation of several Triton-soluble proteins. Immunoprecipitation of tyrosine-phosphorylated proteins from bradykinin-stimulated cells followed by Western blotting using the respective antibodies facilitated the identification of a 77 kiloDalton (kDa) protein as paxillin, a 130 kDa protein as PLC-gamma1, and a 42/44 kDa doublet as mitogen-activated protein (MAP) kinase. The bradykinin-induced tyrosine phosphorylation of PLC-gamma1 was relatively transient and was associated with an increase in intracellular levels of IP3. Bradykinin also induced the rapid and transient activation of phosphotyrosine phosphatases localized mainly in the Triton X-100-soluble cell fraction; this tyrosine phosphatase activity was apparently initiated after the release of Ca2+ from intracellular stores.
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PMID:Tyrosine phosphorylation and bradykinin-induced signaling in endothelial cells. 929 62

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

Hepatocyte growth factor (HGF) is a potent mitogen for hepatocytes and various epithelial cells. Unexpectedly, it has been reported to inhibit the growth of hepatoma cells in vitro. To clarify this phenomenon, we examined the effects of recombinant baculovirus-expressed HGF on the growth of 6 human hepatoma cell lines. The growth of Hep3B and HepG2 cells was markedly stimulated to 1.8- and 1.7-fold, respectively, PLC/PRF/5 to 1.4-fold, and SK-Hep-1 to 1.2-fold in a dose-dependent manner under HGF concentrations below 20 ng/ml. Neither HuH-7 nor HCC36 were affected. None of these cells were inhibited. All these cells expressed c-Met, the membrane receptor for HGF, and their c-Met would be activated to be phosphorylated upon addition of HGF. They also contained the ERK2 subgroup of mitogen-activated protein kinases (MAPKs). When HGF was added, their ERK2 would also be phosphorylated. The extent of ERK2 phosphorylation was partially correlated to their growth response to HGF. In conclusion, HGF could stimulate the growth of certain human hepatoma cells, probably through activation of c-Met and MAPKs.
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PMID:Hepatocyte growth factor stimulates the growth and activates mitogen-activated protein kinase in human hepatoma cells. 967 88

The role of diacylglycerol (DAG) in hormonal induction of S phase was investigated in primary cultures of rat hepatocytes. In this model, several agonists that bind to G protein-coupled receptors act as comitogens when added to the cells soon after plating (i.e., in Go/early Gl phase), while the cells are most responsive to the mitogenic effect of epidermal growth factor (EGF) at 24-48 h of culturing (i.e., mid/late Gl). It was found that the cellular concentration of DAG rose markedly and progressively during the first 24 h of culturing. Exposure of the hepatocytes at 3 h to alpha1-adrenergic stimulation (norepinephrine with timolol), vasopressin, or angiotensin II further increased this rise, producing a sustained increase in the DAG level. Norepinephrine, which was the most efficient comitogen, produced the most prolonged DAG elevation. In contrast, no significant increase of DAG was found in response to EGF, neither at 3 nor at 24 h, using concentrations that markedly stimulated the ERK subgroup of the mitogen-activated protein kinases (MAPK) and DNA synthesis. Addition of Bacillus cereus phosphatidylcholine-specific phospholipase C (PC-PLC) strongly elevated DAG, while Streptomyces phospholipase D (PLD) increased phosphatidic acid (PA) but not DAG. B. cereus PC-PLC and the protein kinase C (PKC) activator tetradecanoyl phorbol-acetate (TPA), like norepinephrine, vasopressin, and angiotensin II, stimulated MAPK and enhanced the stimulatory effect of EGF on DNA synthesis. The PKC inhibitor GF109203X did not diminish the effect of EGF on MAPK or DNA synthesis, but strongly inhibited the effects of norepinephrine, vasopressin, angiotensin II, TPA and B. cereus PC-PLC on MAPK and almost abolished the enhancement by these agents of EGF-stimulated DNA synthesis. These results suggest that although generation of DAG is not a direct downstream response mediating the effects of the EGF receptor in hepatocytes, a sustained elevation of DAG with activation of PKC markedly increases the responsiveness to EGF. Mechanisms involving DAG and PKC seem to play a role in the comitogenic effects of various agents that bind to G protein-coupled receptors and activate the cells early in Gl, such as norepinephrine, angiotensin II, and vasopressin.
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PMID:Role of diacylglycerol (DAG) in hormonal induction of S phase in hepatocytes: the DAG-dependent protein kinase C pathway is not activated by epidermal growth factor (EGF), but is involved in mediating the enhancement of responsiveness to EGF by vasopressin, angiotensin II, and norepinephrine. 1039 90

Stimulation of the T cell antigen receptor (TCR) induces tyrosine phosphorylation of numerous intracellular proteins. We have recently investigated the role of the adaptor protein Shb in the early events of T cell signaling and observed that Shb associates with Grb2, linker for activation of T cells (LAT) and the TCR zeta-chain in Jurkat cells. We now report that Shb also associates with phospholipase C-gamma1 (PLC-gamma1) in these cells. Overexpression of Src homology 2 domain defective Shb caused diminished phosphorylation of LAT and consequently the activation of mitogen-activated protein kinases was decreased upon TCR stimulation. In addition, the Shb mutant also blocked phosphorylation of PLC-gamma1 and the increase in cytoplasmic Ca(2+) following TCR stimulation. Nuclear factor for activation of T cells is a major target for Ras and calcium signaling pathways in T cells following TCR stimulation, and the overexpression of the mutant Shb prevented TCR-dependent activation of the nuclear factor for activation of T cells. Consequently, endogenous interleukin-2 production was decreased under these conditions. The results indicate a role for Shb as a link between the TCR and downstream signaling events involving LAT and PLC-gamma1 and resulting in the activation of transcription of the interleukin-2 gene.
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PMID:Requirement of the Src homology 2 domain protein Shb for T cell receptor-dependent activation of the interleukin-2 gene nuclear factor for activation of T cells element in Jurkat T cells. 1048 57


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