Gene/Protein Disease Symptom Drug Enzyme Compound
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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)

The involvement of tyrosine phosphorylation during macrophage infection with Leishmania amazonensis amastigotes was investigated. PTK antagonists such as genistein, herbimycin A, geldanamycin and tyrphostin 25 had no significant effect on adhesion to, or entry into, murine peritoneal macrophages, but increased parasite intracellular survival. LPS-induced tyrosine phosphorylation of target host proteins assessed by immunoprecipitation and Western blot was impaired or reversed by living amastigotes soon after 60 min-infection. Such reversion was not due to parasite-secreted molecules but was contact-dependent, as assessed by cytochalasin D treatment of macrophage monolayers prior to infection. Paraformaldehyde-fixed or sodium vanadate-treated amastigotes exerted no significant effect on overall macrophage tyrosine phosphorylation. Immunoprecipitation of proteins employing 4G10 anti-phosphotyrosine antibody followed by Western blotting revealed that tyrosine phosphorylation of 120, 85, 60, 44 and 35 kDa proteins was selectively reversed by amastigote infection. Inhibition, measured by densitometry was from about 66-100% of uninfected cells. None of these proteins was immunoprecipitated from amastigote-infected macrophage lysates but all of them except for p85 were recovered after treatment of parasites with 100 microM sodium orthovanadate prior to infection, a treatment that inhibits Leishmania amastigote protein ecto-phosphatase. The 44 kDa protein was identified as ERK1 MAP kinase (MAPK) by Western blot. Amastigote infection also decreased tyrosine phosphorylation induced by zymosan particles. Vanadate treatment of amastigotes prior to infection significantly decreased parasite intracellular survival. The action of a putative leishmanial ecto-protein phosphatase (PPase) is suggested.
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PMID:Altered tyrosine phosphorylation of ERK1 MAP kinase and other macrophage molecules caused by Leishmania amastigotes. 1047 71

In this study we have investigated the down-regulation of epidermal growth factor (EGF) receptor signaling by protein-tyrosine phosphatases (PTPs) in COS1 cells. The 45-kDa variant of the PTP TCPTP (TC45) exits the nucleus upon EGF receptor activation and recognizes the EGF receptor as a cellular substrate. We report that TC45 inhibits the EGF-dependent activation of the c-Jun N-terminal kinase, but does not alter the activation of extracellular signal-regulated kinase 2. These data demonstrate that TC45 can regulate selectively mitogen-activated protein kinase signaling pathways emanating from the EGF receptor. In EGF receptor-mediated signaling, the protein kinase PKB/Akt and the mitogen-activated protein kinase c-Jun N-terminal kinase, but not extracellular signal-regulated kinase 2, function downstream of phosphatidylinositol 3-kinase (PI 3-kinase). We have found that TC45 and the TC45-D182A mutant, which is capable of forming stable complexes with TC45 substrates, inhibit almost completely the EGF-dependent activation of PI 3-kinase and PKB/Akt. TC45 and TC45-D182A act upstream of PI 3-kinase, most likely by inhibiting the recruitment of the p85 regulatory subunit of PI 3-kinase by the EGF receptor. Recent studies have indicated that the EGF receptor can be activated in the absence of EGF following integrin ligation. We find that the integrin-mediated activation of PKB/Akt in COS1 cells is abrogated by the specific EGF receptor protein-tyrosine kinase inhibitor tyrphostin AG1478, and that TC45 and TC45-D182A can inhibit activation of PKB/Akt following the attachment of COS1 cells to fibronectin. Thus, TC45 may serve as a negative regulator of growth factor or integrin-induced, EGF receptor-mediated PI 3-kinase signaling.
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PMID:The protein-tyrosine phosphatase TCPTP regulates epidermal growth factor receptor-mediated and phosphatidylinositol 3-kinase-dependent signaling. 1048 21

Cripto-1 (CR-1), a member of the epidermal growth factor-CFC peptide family, activates the ras/raf/mitogen-activated protein/extracellular signal-regulated kinase/mitogen-activated protein kinase pathway. In the present study, the role of CR-1 in the phosphatidylinositol 3'-kinase (PI3K)/AKT (protein kinase B)/glycogen synthase kinase 3beta (GSK-3beta)-dependent signaling pathway was evaluated in human SiHa cervical carcinoma cells. Our data demonstrate that CR-1 can enhance the tyrosine phosphorylation of the p85 regulatory subunit of PI3K and transiently induce the phosphorylation of AKT in a time- and dose-dependent manner. In addition, CR-1 was found to induce the phosphorylation of GSK-3beta. Phosphorylation of AKT and GSK-3beta by CR-1 can be blocked by LY294002, a specific inhibitor of PI3K, thus leading to apoptosis. Finally, the apoptotic effect of LY294002 can be partially rescued by exogenous CR-1. In summary, our data suggest that human CR-1 may function as a survival factor through a PI3K-dependent signaling pathway involving AKT and GSK-3beta.
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PMID:Cripto-1 induces phosphatidylinositol 3'-kinase-dependent phosphorylation of AKT and glycogen synthase kinase 3beta in human cervical carcinoma cells. 1049 95

Platelet activation results in shape change, release of granule contents, aggregation and clot retraction. An intense intracellular 'machinery' is engaged to achieve these functions. Thrombin is one of the most important agonists for platelet recruitment and aggregation which is mediated by the binding of fibrinogen to its adhesive receptor: the glycoprotein (GP) IIb/IIIa complex or integrin alphaIIbbeta(3). The numerous biological processes consecutive to thrombin binding to platelet membrane are mainly controlled by phosphorylation mechanisms organized into signalling pathways. Schematically, the phospholipase Cbeta pathway activated by G protein coupled to the seven transmembrane thrombin receptors, provides the first intracellular relay and would generate regulators such as protein kinase C, phosphorylated pleckstrin but also modifications of the intracellular domain of beta(3). This inside-out signalling would lead to some changes in the extracellular domain of GPIIb/IIIa increasing access of fibrinogen to the receptor. Ligand interaction with GPIIb/IIIa induced reorganization of the cytoskeleton and would mediate the outside-in signals which involve a series of intracellular events including tyrosine kinases, phosphatidylinositol 3 kinases, MAP kinases and phosphatases. Some of these pathways and/or signalling metabolites could be associated to some well-characterized platelet functions: cortactin phosphorylation is involved in platelet shape change, phosphatidylinositol 3 kinase (p85) in the stabilisation of platelet aggregates and MAP kinase (p44) in postaggregation events. But in fact the sequence of events which has been described has to be viewed as integrated networks. At least three biochemical processes govern the highly integrated organization to send just the appropriate quanta of signal for a specific need: the reorganisation of the cytoskeleton following the binding of fibrinogen to alphaIIbbeta(3), the structure of the signal transducers that contain SH2, SH3, and PH domains leading to the formation of macromolecules of signalling and the crosstalk phenomena between the different pathways. Elucidating the mechanisms of such networks becomes an increasingly exciting project.
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PMID:Platelet signal transduction pathways: could we organize them into a 'hierarchy'? 1049 30

Alternate splicing of mRNA encoding c-KIT results in isoforms which differ in the presence or absence of four amino acids (GNNK) in the juxtamembrane region of the extracellular domain of the receptor. In this study we show that these isoforms of human c-KIT, expressed at similar levels in NIH3T3 cells, display differential effects on various attributes of transformation. The GNNK- isoform strongly promoted anchorage independent growth (colony formation in semi-solid medium), loss of contact inhibition (focus formation), and led to tumorigenicity in nude mice. In contrast, the GNNK+ isoform elicited colony formation but relatively poor focus formation and no tumorigenicity. Saturation binding analysis indicated that the isoforms do not differ significantly in their affinity for the KIT ligand, Steel Factor (SLF). Negligible ligand-independent receptor phosphorylation was observed in either case but, after ligand stimulation, the GNNK- isoform displayed more rapid and extensive tyrosine autophosphorylation and faster internalization. Both isoforms recruited the p85 subunit of phosphatidylinositol 3-kinase and led to similar phosphorylation of its downstream effector c-Akt, but the GNNK- isoform gave rise to more MAP kinase phosphorylation. Thus the c-KIT isoforms display different signalling characteristics and have different transforming activity in NIH3T3 cells.
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PMID:Isoforms of c-KIT differ in activation of signalling pathways and transformation of NIH3T3 fibroblasts. 1052 34

In Con8 rat mammary epithelial tumor cells, the synthetic glucocorticoid dexamethasone stimulates the remodeling of the apical junction (tight and adherens junctions) and the transepithelial electrical resistance (TER), which reflects tight junction sealing. Indirect immunofluorescence revealed that dexamethasone induced the recruitment of endogenous Ras and the p85 regulatory subunit of phosphatidylinositol (PI) 3-kinase to regions of cell-cell contact, concurrently with the stimulation of TER. Expression of dominant-negative RasN17 abolished the dexamethasone stimulation in TER, whereas, dexamethasone induced the reorganization of tight junction and adherens junction proteins, ZO-1 and beta-catenin, as well as F-actin, to precise regions of cell-cell contact in a Ras-independent manner. Confocal microscopy revealed that RasN17 and the p85 regulatory subunit of PI 3-kinase co-localized with ZO-1 and F-actin at the tight junction and adherens junction, respectively. Treatment with either of the PI 3-kinase inhibitors, wortmannin or LY294002, or the MEK inhibitor PD 098059, which prevents MAPK signaling, attenuated the dexamethasone stimulation of TER without affecting apical junction remodeling. Similar to dominant-negative RasN17, disruption of both Ras effector pathways using a combination of inhibitors abolished the glucocorticoid stimulation of TER. Thus, the glucocorticoiddependent remodeling of the apical junction and tight junction sealing can be uncoupled by their dependence on Ras and/or PI 3-kinase-dependent pathways, implicating a new role for Ras and PI 3-kinase cell signaling events in the steroid control of cell-cell interactions.
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PMID:Requirement for Ras and phosphatidylinositol 3-kinase signaling uncouples the glucocorticoid-induced junctional organization and transepithelial electrical resistance in mammary tumor cells. 1055 43

Angiopoietin-1 is a unique growth factor which induces Tie2 receptor autophosphorylation and interaction with signal transduction molecules, GRB2 and p85 subunit of PI 3-kinase, but no detectable mitogenic response. Here we show that PI 3-kinase-dependent activation of Akt and attachment to extracellular matrix are required for angiopoietin-1-mediated endothelial cell survival. Apoptosis of growth factor-deprived cells grown in monolayer was decreased by angiopoietin-1 and correlated with Akt activation. In contrast, angiopoietin-1, bFGF or VEGF failed to protect cells in suspension culture. Ceramide, an intermediate of several apoptotic pathways, interferes with growth factor-mediated Akt activation. Ceramide induced endothelial cell death and abolished angiopoietin-1-mediated activation of Akt and the effect on cell survival. In addition, we found that PI 3-kinase activity is necessary for migration of endothelial cells in response to Angiopoietin-1. A transient activation of MAPK/ERKs was also detected within 10 min after stimulation with angiopoietin-1. In contrast to VEGF-mediated biological effects, inhibition of MAPK/ERKs by PD98059 in endothelial cells did not affect angiopoietin-1 mediated survival or migration. These findings indicate significant differences in intracellular signaling between VEGF and angiopoietin-1 and that PI 3-kinase lipid products are key mediators of the biological effects of angiopoietin-1.
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PMID:Role of PI 3-kinase in angiopoietin-1-mediated migration and attachment-dependent survival of endothelial cells. 1058 89

Insulin receptor substrate (IRS) proteins are tyrosine phosphorylated and mediate multiple signals during activation of the receptors for insulin, insulin-like growth factor 1 (IGF-1), and various cytokines. In order to distinguish common and unique functions of IRS-1, IRS-2, and IRS-4, we expressed them individually in 32D myeloid progenitor cells containing the human insulin receptor (32D(IR)). Insulin promoted the association of Grb-2 with IRS-1 and IRS-4, whereas IRS-2 weakly bound Grb-2; consequently, IRS-1 and IRS-4 enhanced insulin-stimulated mitogen-activated protein kinase activity. During insulin stimulation, IRS-1 and IRS-2 strongly bound p85alpha/beta, which activated phosphatidylinositol (PI) 3-kinase, protein kinase B (PKB)/Akt, and p70(s6k), and promoted the phosphorylation of BAD. IRS-4 also promoted the activation of PKB/Akt and BAD phosphorylation during insulin stimulation; however, it weakly bound or activated p85-associated PI 3-kinase and failed to mediate the activation of p70(s6k). Insulin strongly inhibited apoptosis of interleukin-3 (IL-3)-deprived 32D(IR) cells expressing IRS-1 or IRS-2 but failed to inhibit apoptosis of cells expressing IRS-4. Consequently, 32D(IR) cells expressing IRS-4 proliferated slowly during insulin stimulation. Thus, the activation of PKB/Akt and BAD phosphorylation might not be sufficient to inhibit the apoptosis of IL-3-deprived 32D(IR) cells unless p85-associated PI 3-kinase or p70(s6k) are strongly activated.
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PMID:IRS-4 mediates protein kinase B signaling during insulin stimulation without promoting antiapoptosis. 1059 15

Cell adhesion mediated by beta1 integrin receptors leads to the initiation of intracellular signals that affect cell differentiation and survival. Here we have analysed the mechanism by which the alpha4beta1 integrin activates the mitogen-activated protein kinase pathway in HL60 cells, a myelomonocytic cell line that lacks the expression of focal adhesion kinase. A role for phosphoinositide 3-kinase (PI-3K) in alpha4 integrin-mediated activation of extracellular signal-regulated protein kinase 2 (ERK2) is suggested by the ability of PI-3K inhibitors and a dominant-negative form of the p85 subunit of PI-3K to block the activation of ERK2 by integrin. Stimulation of alpha4beta1 integrins on HL60 cells also leads to increased tyrosine phosphorylation of the 120 kDa adaptor protein Cbl. PI-3K activity associated with Cbl also increases on the stimulation of alpha4beta1 integrins, although immunodepletion experiments suggest that Cbl-associated PI-3K does not account for all of the PI-3K activity induced on the stimulation of integrins in these cells. The expression of wild-type Cbl or the 70Z/3 Cbl mutant enhances basal ERK2 activity in transfectants with a minimal effect on alpha4 integrin-mediated ERK2 activity. In contrast, overexpression of the Hut Cbl truncation mutant, which does not associate with p85, has no effect on the ERK2 pathway. These results suggest that PI-3K has a major role in coupling alpha4beta1 integrins to ERK2 activation in myeloid cells and that the Cbl adaptor protein has a role in basal, but not alpha4beta1 integrin-mediated, activation of ERK2.
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PMID:Role of phosphoinositide 3-kinase and the Cbl adaptor protein in coupling the alpha4beta1 integrin to mitogen-activated protein kinase signalling. 1062 May 16

The Gab1 protein is tyrosine phosphorylated in response to various growth factors and serves as a docking protein that recruits a number of downstream signaling proteins, including phosphatidylinositol 3-kinase (PI-3 kinase). To determine the role of Gab1 in signaling via the epidermal growth factor (EGF) receptor (EGFR) we tested the ability of Gab1 to associate with and modulate signaling by this receptor. We show that Gab1 associates with the EGFR in vivo and in vitro via pTyr sites 1068 and 1086 in the carboxy-terminal tail of the receptor and that overexpression of Gab1 potentiates EGF-induced activation of the mitogen-activated protein kinase and Jun kinase signaling pathways. A mutant of Gab1 unable to bind the p85 subunit of PI-3 kinase is defective in potentiating EGFR signaling, confirming a role for PI-3 kinase as a downstream effector of Gab1. Inhibition of PI-3 kinase by a dominant-interfering mutant of p85 or by Wortmannin treatment similarly impairs Gab1-induced enhancement of signaling via the EGFR. The PH domain of Gab1 was shown to bind specifically to phosphatidylinositol 3,4,5-triphosphate [PtdIns(3,4,5)P3], a product of PI-3 kinase, and is required for activation of Gab1-mediated enhancement of EGFR signaling. Moreover, the PH domain mediates Gab1 translocation to the plasma membrane in response to EGF and is required for efficient tyrosine phosphorylation of Gab1 upon EGF stimulation. In addition, overexpression of Gab1 PH domain blocks Gab1 potentiation of EGFR signaling. Finally, expression of the gene for the lipid phosphatase PTEN, which dephosphorylates PtdIns(3,4, 5)P3, inhibits EGF signaling and translocation of Gab1 to the plasma membrane. These results reveal a novel positive feedback loop, modulated by PTEN, in which PI-3 kinase functions as both an upstream regulator and a downstream effector of Gab1 in signaling via the EGFR.
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PMID:A novel positive feedback loop mediated by the docking protein Gab1 and phosphatidylinositol 3-kinase in epidermal growth factor receptor signaling. 1064 29


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