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)

Using transient overexpression and microinjection approaches, we examined SHPTP2's function in growth factor signaling. Overexpression of catalytically inactive SHPTP2 (PTP2CS) but not catalytically inactive SHPTP1, inhibited mitogen-activated protein (MAP) kinase activation and Elk-1 transactivation following epidermal growth factor (EGF) stimulation of 293 cells. An SHPTP2 mutant with both C-terminal tyrosyl phosphorylation sites converted to phenylalanine (PTP2YF) was also without effect; moreover, PTP2YF rescued PTP2CS-induced inhibition of EGF-induced Elk-1 transactivation. PTP2CS did not inhibit transactivation by activated Ras, suggesting that SHPTP2 acts upstream of or parallel to Ras. Neither PTP2CS nor PTP2YF inhibited platelet-derived growth factor (PDGF)-induced Elk-1 transactivation. Thus, protein-tyrosine phosphatase activity, but not tyrosyl phosphorylation of SHPTP2, is required for the immediate-early responses to EGF but not to PDGF. To determine whether SHPTP2 is required later in the cell cycle, we assessed S-phase entry in NIH 3T3 cells microinjected with anti-SHPTP2 antibodies or with a glutathione S-transferase (GST) fusion protein encoding both SH2 domains (GST-SH2). Microinjection of anti-SHPTP2 antibodies prior to stimulation inhibited EGF- but no PDGF- or serum-induced S-phase entry. Anti-SHPTP2 antibodies or GST-SH2 fusion protein could inhibit EGF-induced S-phase entry for up to 8 h after EGF addition. Although MAP kinase activation was detected shortly after EGF stimulation, no MAP kinase activation was detected around the restriction point. Therefore, SHPTP2 is absolutely required for immediate-early and late events induced by some, but not all, growth factors, and the immediate-early and late signal transduction pathways regulated by SHPTP2 are distinguishable.
Mol Cell Biol 1996 Mar
PMID:Multiple requirements for SHPTP2 in epidermal growth factor-mediated cell cycle progression. 862 63

The p38 mitogen-activated protein (MAP) kinase signal transduction pathway is activated by proinflammatory cytokines and environmental stress. The detection of p38 MAP kinase in the nucleus of activated cells suggests that p38 MAP kinase can mediate signaling to the nucleus. To test this hypothesis, we constructed expression vectors for activated MKK3 and MKK6, two MAP kinase kinases that phosphorylate and activate p38 MAP kinase. Expression of activated MKK3 and MKK6 in cultured cells caused a selective increase in p38 MAP kinase activity. Cotransfection experiments demonstrated that p38 MAP kinase activation causes increased reporter gene expression mediated by the transcription factors ATF2 and Elk-1. These data demonstrate that the nucleus is one target of the p38 MAP kinase signal transduction pathway.
Mol Cell Biol 1996 Mar
PMID:MKK3- and MKK6-regulated gene expression is mediated by the p38 mitogen-activated protein kinase signal transduction pathway. 862 69

The Ras-GTPase-activating protein (RasGAP) is an important modulator of p21ras - dependent signal transduction in Xenopus oocytes and in mammalian cells. We investigated the role of the RasGAP SH3 domain in signal transduction with a monoclonal antibody against the SH3 domain of RasGaP. This antibody prevented the activation of the maturation-promoting factor complex (cyclin B-p34cdc2) by oncogenic Ras. The antibody appears to be specific because as little as 5 ng injected per oocyte reduced the level of Cdc2 activation by 50% whereas 100 ng of nonspecific immunoglobulin G did not affect Cdc2 activation. The antibody blocked the Cdc2 activation induced by oncogenic Ras but not that induced by progesterone, which acts independently of Ras. A peptide corresponding to positions 317 to 326 of a sequence in the SH3 domain of human RasGAP blocked Cdc2 activation, whereas a peptide corresponding to positions 273 to 305 of a sequence in the N-terminal moiety of the SH3 domain of RasGAP had no effect. The antibody did not block the mitogen-activated protein (MAP) kinase cascade (activation of MAPK/ERK kinase [MEK], MAP kinase, and S6 kinase p90rsk). Surprisingly, injection of the negative MAP kinase mutant protein ERK2 K52R (containing a K-to-R mutation at position 52) blocked the Cdc2 activation induced by oncogenic Ras as well as blocking the activation of MAP kinase. Thus, MAP kinase is also implicated in the regulation of Cdc2 activity. In this study, we further investigated the regulation of the synthesis of the c-mos oncogene product, which is necessary for the activation of Cdc2. We report that the synthesis of the c-mos oncogene product, which is necessary for the activation antibody to the SH3 domain of RasGAP and by injecting the negative MAP kinase mutant protein ERK2 K52R. These results suggest that oncogenic Ras activates two signaling mechanisms: the MAP kinase cascade and a signaling pathway implicating the SH3 domain of RasGAP. These mechanisms might control Mos protein expression implicated in Cdc2 activation.
Mol Cell Biol 1996 Jun
PMID:The Ras-GTPase-activating protein SH3 domain is required for Cdc2 activation and mos induction by oncogenic Ras in Xenopus oocytes independently of mitogen-activated protein kinase activation. 864 28

To elucidate signal transduction pathways leading to neuronal differentiation, we have investigated a conditionally immortalized cell line from rat hippocampal neurons (H19-7) that express a temperature sensitive simian virus 40 large T antigen. Treatment of H19-7 cells with the differentiating agent basic fibroblast growth factor at 39 degrees C, the nonpermissive temperature for T function, resulted in the activation of c-Raf-1, MEK, and mitogen-activated protein (MAP) kinases (ERK1 and -2). To evaluate the role of Raf-1 in neuronal cell differentiation, we stably transfected H19-7 cells with v-raf or an oncogenic human Raf-1-estrogen receptor fusion gene (deltaRaf-1:ER). deltaRaf-1:ER transfectants in the presence of estradiol for 1 to 2 days expressed a differentiation phenotype only at the nonpermissive temperature. However, extended exposure of the deltaRaf-1:ER transfectants to estradiol or stable expression of the v-raf construct yielded cells that extended processes at the permissive as well as the nonpermissive temperature, suggesting that cells expressing the large T antigen are capable of responding to the Raf differentiation signal. deltaRaf-1:ER, MEK, and MAP kinase activities in the deltaRaf-1:ER cells were elevated constitutively for up to 36 h of estradiol treatment at the permissive temperature. At the nonpermissive temperature, MEK and ERKs were activated to a significantly lesser extent, suggesting that prolonged MAP kinase activation may not be sufficient for differentiation. To test this possibility, H19-7 cells were transfected or microinjected with constitutively activated MEK. The results indicate that prolonged activation of MEK or MAP kinases (ERK1 and -2) is not sufficient for differentiation of H19-7 neuronal cells and raise the possibility that an alternative signaling pathway is required for differentiation of H19-7 cells by Raf.
Mol Cell Biol 1996 Apr
PMID:Raf, but not MEK or ERK, is sufficient for differentiation of hippocampal neuronal cells. 865 19

The transcription and expression of platelet-derived growth factor (PDGF) receptors (PDGFRs) is down-regulated as a consequence of entry into the replicative cell cycle (Vaziri, C., and Faller, D. V. (1995) Mol. Cell. Biol. 15, 1244-1253). In this study, we have investigated the expression of PDGFRs during terminal differentiation, a process in which cells exit from the cell cycle. When treated with appropriate hormonal stimuli, 3T3-L1 fibroblasts initiate a differentiation program resulting in conversion to lipid-accumulating, adipocyte-like cells. Pre-adipocytes express amounts of PDGFalphaR and PDGFbetaR mRNA and protein that are similar to levels expressed in other murine 3T3 fibroblasts. In contrast, the expression of both alpha and beta receptor transcripts is greatly reduced in differentiated 3T3-L1 cells. The loss of PDGFR mRNA following induction of differentiation precedes morphological conversion as well as the induction of many adipocyte-specific genes. The amounts of cell surface PDGFR protein diminish in parallel with the mRNA levels during differentiation, as shown by Western blotting and PDGF-binding assays. The reduced expression of PDGFRs does not reflect a general down-regulation of growth factor receptors, as expression of the type 1 FGFR is unaffected by terminal differentiation. The PDGFbetaR promoter drives strong expression of a luciferase reporter gene in pre-adipocytes, but not in differentiated cells, indicating that the decrease in PDGFR expression following induction of differentiation is a transcriptionally regulated event. Decreased PDGFR expression in differentiated cells is associated with impaired biological responsiveness to PDGF, as shown by reduced activation of mitogen-activated protein-kinase following PDGF stimulation, and decreased chemotactic responsiveness to PDGF. Our data suggest that PDGFR down-regulation is an important mechanism for reducing PDGF-responsiveness in terminally differentiated 3T3-L1 cells.
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PMID:Down-regulation of platelet-derived growth factor receptor expression during terminal differentiation of 3T3-L1 pre-adipocyte fibroblasts. 866 75

Kss1 and Fus3 are mitogen-activated protein kinases (MAPKs or ERKs), and Ste7 is their activating MAPK/ERK kinase (MEK), in the pheromone response pathway of Saccharomyces cerevisiae. To investigate the potential role of specific interactions between these enzymes during signaling, their ability to associate with each other was examined both in solution and in vivo. When synthesized by in vitro translation, Kss1 and Fus3 could each form a tight complex (Kd of approximately 5 nM) with Ste7 in the absence of any additional yeast proteins. These complexes were specific because neither Hog1 nor Mpk1 (two other yeast MAPKs), nor mammalian Erk2, was able to associate detectably with Ste7. Neither the kinase catalytic core of Ste7 nor the phosphoacceptor regions of Ste7 and Kss1 were necessary for complex formation. Ste7-Kss1 (and Ste7-Fus3) complexes were present in yeast cell extracts and were undiminished in extracts prepared from a ste5delta-ste11delta double mutant strain. In Ste7-Kss1 (or Ste7-Fus3) complexes isolated from naive or pheromone-treated cells, Ste7 phosphorylated Kss1 (or Fus3), and Kss1 (or Fus3) phosphorylated Ste7, in a pheromone-stimulated manner; dissociation of the high-affinity complex was shown to be required for either phosphorylation event. Deletions of Ste7 in the region required for its stable association with Kss1 and Fus3 in vitro significantly decreased (but did not eliminate) signaling in vivo. These findings suggest that the high-affinity and active site-independent binding observed in vitro facilitates signal transduction in vivo and suggest further that MEK-MAPK interactions may utilize a double-selection mechanism to ensure fidelity in signal transmission and to insulate one signaling pathway from another.
Mol Cell Biol 1996 Jul
PMID:Signaling in the yeast pheromone response pathway: specific and high-affinity interaction of the mitogen-activated protein (MAP) kinases Kss1 and Fus3 with the upstream MAP kinase kinase Ste7. 866 80

The mitogen-activated protein (MAP) kinases are a family of serine/threonine kinases that are regulated by distinct extracellular stimuli. The currently known members include extracellular signal-regulated protein kinase 1 (ERK1), ERK2, the c-Jun N-terminal kinase/stress-activated protein kinases (JNK/SAPKs), and p38 MAP kinases. We find that overexpression of the Ste20-related enzymes p21-activated kinase 1 (PAK1) and PAK2 in 293 cells is sufficient to activate JNK/SAPK and to a lesser extent p38 MAP kinase but not ERK2. Rat MAP/ERK kinase kinase 1 can stimulate the activity of each of these MAP kinases. Although neither activated Rac nor the PAKs stimulate ERK2 activity, overexpression of either dominant negative Rac2 or the N-terminal regulatory domain of PAK1 inhibits Ras-mediated activation of ERK2, suggesting a permissive role for Rac in the control of the ERK pathway. Furthermore, constitutively active Rac2, Cdc42hs, and RhoA synergize with an activated form of Raf to increase ERK2 activity. These findings reveal a previously unrecognized connection between Rho family small G proteins and the ERK pathway.
Mol Cell Biol 1996 Jul
PMID:Actions of Rho family small G proteins and p21-activated protein kinases on mitogen-activated protein kinase family members. 866 87

Infection with Listeria monocytogenes induces the activation of mitogen-activated protein (MAP) kinase in several tissue culture cell lines (P.Tang, I. Rosenshine, and B. B. Finlay, Mol. Biol. Cell 5:455-464, 1994). After various mutants were examined, the bacterial factor responsible for MAP kinase activation was identified as listeriolysin O (LLO). Growth supernatant containing LLO or purified LLO alone can induce MAP kinase tyrosine phosphorylation in HeLa cells. Single-amino-acid mutations in LLO that do not affect its membrane binding capacity but reduce its cytolytic activity also reduced its ability to induce MAP kinase activity in HeLa cells. Streptolysin O, another sulfhydryl-activated hemolysin, and the detergent saponin are also able to activate MAP kinase in target cells. Thus, the increased MAP kinase activity observed in L. monocytogenes-infected cells is most likely a result of the permeabilization of the host cell membrane by LLO and may not be linked with invasion.
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PMID:Listeriolysin O activates mitogen-activated protein kinase in eucaryotic cells. 867 52

Tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) by the activated receptors for insulin, IGF-1, and various cytokines creates binding sites for signaling proteins with Src homology 2 domains (SH2 proteins). Determining the role of specific SH2 proteins during insulin signaling has been difficult because IRS-1 possesses as many as 18 potential tyrosine phosphorylation sites, several of which contain redundant motifs. Using 32D cells, which contain no endogenous IRS proteins, we compared the signaling ability of an IRS-1 molecule in which 18 potential tyrosine phosphorylation sites were replaced by phenylalanine (IRS-1(F18)) with two derivative molecules which retained three YMXM motifs (IRS-1(3YMXM)) or the two COOH-terminal SHP2-Fyn binding sites (IRS-1(YCT)). During insulin stimulation, IRS-1(F18) failed to undergo tyrosine phosphorylation or mediate activation of the phosphotidylinositol (PI) 3'-kinase or p70(s6k); IRS-1(YCT) was tyrosine phosphorylated but also failed to mediate these signaling events. Neither IRS-1(3YMXM) nor IRS-1(YCT) mediated activation of mitogen-activated protein kinases. IRS-1(F18) and IRS-1(YCT) partially mediated similar levels of insulin-stimulated mitogenesis at high insulin concentrations, however, suggesting that IRS-1 contains phosphotyrosine-independent elements which effect mitogenic signals, and that the sites in IRS-l(YCT) do not augment this signal. IRS-1(3YMXM) mediated the maximal mitogenic response to insulin, although the response to insulin was more sensitive with wild-type IRS-1. By contrast, the association of IRS-1(3YMXM) with PI 3'-kinase was more sensitive to insulin than the association with IRS-1. Thus, the binding of SH2 proteins (such as PI 3'-kinase) by YMXM motifs in IRS-1 is an important element in the mitogenic response, but other elements are essential for full mitogenic sensitivity.
Mol Cell Biol 1996 Aug
PMID:YMXM motifs and signaling by an insulin receptor substrate 1 molecule without tyrosine phosphorylation sites. 875 13

The yeast pheromone response pathway is mediated by two G protein-linked receptors, each of which is expressed only in its specific cell type. The STE3DAF mutation results in inappropriate expression of the a-factor receptor in MATa cells. Expression of this receptor in the inappropriate cell type confers resistance to pheromone-induced G1 arrest, a phenomenon that we have termed receptor inhibition. The ability of STE3DAF cells to cycle in the presence of pheromone was found to correlate with reduced phosphorylation of the cyclin-dependent kinase inhibitor Far1p. Measurement of Fus3p mitogen-activated protein (MAP) kinase activity in wild-type and STE3DAF cells showed that induction of Fus3p activity was the same in both strains at times of up to 1 h after pheromone treatment. However, after 2 or more hours, Fus3p activity declined in STE3DAF cells but remained high in wild-type cells. The level of inducible FUS1 RNA paralleled the changes seen in Fus3p activity. Short-term activation of the Fus3p MAP kinase is therefore sufficient for the early transcriptional induction response to pheromone, but sustained activation is required for cell cycle arrest. Escape from the cell cycle arrest response was not seen in wild-type cells treated with low doses of pheromone, indicating that receptor inhibition is not simply a result of weak signaling but rather acts selectively at late times during the response. STE3DAF was found to inhibit the pheromone response pathway at a step between the G beta subunit and Ste5p, the scaffolding protein that binds the components of the MAP kinase phosphorylation cascade. Overexpression of Ste20p, a kinase thought to act between the G protein and the MAP kinase cascade, suppressed the STE3DAF phenotype. These findings are consistent with a model in which receptor inhibition acts by blocking the signaling pathway downstream of G protein dissociation and upstream of MAP kinase cascade activation, at a step that could directly involve Ste20p.
Mol Cell Biol 1996 Aug
PMID:Loss of sustained Fus3p kinase activity and the G1 arrest response in cells expressing an inappropriate pheromone receptor. 875 48


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