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)

Figure 2 summarizes our current interpretation of data concerning signals from the activated PDGF receptor involved in directed migration and proliferation of human arterial SMC. Binding of PDGF (PDGF-BB or PDGF-AA) causes PDGF-receptor dimerization, tyrosine autophosphorylation, and subsequent binding of several molecules containing SH2 domains to the activated receptor. Binding and activation of PLC gamma by the PDGF receptor leads to PIP2 hydrolysis, resulting in generation of diacylglycerol (DAG) and IP3. Subsequently, intracellular levels of calcium are elevated as a result of IP3-mediated calcium release from intracellular compartments. The decreased levels of PIP2 and increased levels of calcium both favor actin-filament disassembly by inducing capping of actin-filament barbed ends and actin-monomer sequestration. A localized, and transient, actin-filament disassembly enables the cell to extend filopodia towards PDGF, thereby enabling chemotaxis to take place. At a later time and/or in a different compartment, actin-filament assembly is promoted by PDGF by a mechanism that is not completely understood, but that may involve small GTP-binding proteins, such as Rho, and formation of DAG. Migration on collagen requires functional alpha 2 beta 1 integrins, which may either constitute a permissive state required for a cell to migrate, or which may be actively involved in intracellular signals leading to migration. PDGF-induced DNA synthesis and proliferation involves activation of Ras, MAP kinase kinase, and MAP kinase. Cross-talk between PKA signaling and tyrosine-kinase receptor signaling results in PKA inhibition of the MAP kinase cascade, probably at the level of Raf. Activation of PI 3-kinase, or a PI 3-kinase-like enzyme, is also likely to contribute to the mitogenic effects of PDGF in these cells (Bornfeldt, unpublished observation). What determines if a SMC will migrate and/or proliferate in response to PDGF? Results are starting to emerge that show regulation of expression of molecules involved in intracellular signaling with different phenotypic states of SMC. For example, expression of PLC gamma is very low in intact vascular wall (where SMC show a "contractile phenotype"), and induced when SMC are converted to a "synthetic phenotype" in culture. Proliferation and expression of MAP kinase, but not calcium signaling, appear to be regulated by the extracellular matrix, and the profile of integrin expression is different in SMC in culture compared to SMC in the vascular wall. Thus, the relation between expression of signaling molecules involved in migration and signaling molecules involved in proliferation, as well as cross-talk between different signal-transduction pathways, may determine the net effect of PDGF.
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PMID:Platelet-derived growth factor. Distinct signal transduction pathways associated with migration versus proliferation. 748 87

Immunoprecipitates of metabolically labeled PC12 cells consistently contained a 43-kDa protein that was associated with Shc, a signal-transducing protein with a single SH2 domain. Following affinity chromatography with immobilized recombinant glutathione S-transferase (GST)-Shc fusion protein, the 43-kDa protein was identified as actin by mass spectrometry and immunoblotting. Cosedimentation experiments using purified actin and GST-Shc showed that Shc binds directly to F-actin, confirming Shc-actin interaction in vivo. Various GST-truncated Shc fusion proteins were prepared and used in actin cosedimentation assays. Constructs containing the SH2 and collagen homology domains were not precipitated, and those containing the amino-terminal domain were. Thus, Shc-actin interactions do not occur in the region of tyrosine phosphorylation and leave the SH2 domain free to bind to other tyrosine-phosphorylated molecules. Although the major pool of Shc in unstimulated PC12 cells is soluble, two other pools are associated with the cytoskeleton and the submembranous cytoskeleton. Upon nerve growth factor stimulation, approximately 50% of the soluble Shc translocates to both cytoskeleton environments within 2 min, decreasing thereafter. When cells were pretreated with cytochalasin D, a drug that disrupts actin filaments, Shc translocation to the cytoskeleton was abolished. However, in the submembranous fraction, the Shc level was elevated in resting cells following cytochalasin D treatment. The kinetics of translocation, compared to mitogen-activated protein kinase activation, and the nature of the Shc-actin interaction suggest that the cytoskeletal association of Shc, induced by growth factors, may be related to membrane ruffling and actin fiber reorganization.
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PMID:Src homologous and collagen (Shc) protein binds to F-actin and translocates to the cytoskeleton upon nerve growth factor stimulation in PC12 cells. 749 22

Human platelets pretreated with indomethacin release arachidonic acid predominantly through the activity of cytosolic phospholipase A2 (cPLA2), an 85-kDa protein. This enzyme is regulated by an increase in intracellular Ca2+, a necessary condition of for arachidonic acid liberation, and by phosphorylation. Phosphorylation of cPLA2 enhanced the Ca(2+)-induced arachidonic acid release in platelets stimulated by the ionophore A23187 and phorbol ester (phorbol 12,13-dibutyrate (PDBu)). In thrombin-stimulated platelets, however, phosphorylation appeared not to be necessary for arachidonic acid release since the latter response was not impaired in the presence of staurosporine, which inhibited phosphorylation. Collagen, thrombin, and PDBu induced phosphorylation of platelet cPLA2 as well as activation of mitogen-activated protein kinase (MAPK; p42mapk and p44mapk). cPLA2 activation was not dependent on protein kinase C (PKC) in thrombin- and collagen-stimulated platelets, as preincubation with the PKC inhibitor Ro 31-8220 neither interfered with cPLA2 phosphorylation nor reduced arachidonic acid release. However, collagen- and thrombin-induced activation of MAPK was inhibited by Ro 31-8220, indicating that PKC is necessary for MAPK stimulation in platelets. Although MAPK may underlie phosphorylation of cPLA2 in PDBu-activated human platelets, our results provide evidence for PKC- and MAPK-independent phosphorylation of cPLA2 in platelets stimulated by the physiological activators collagen and thrombin.
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PMID:Cytosolic phospholipase A2 is phosphorylated in collagen- and thrombin-stimulated human platelets independent of protein kinase C and mitogen-activated protein kinase. 759 75

Adhesion to extracellular matrix mediates cell cycle progression in mid-late G1; this effect involves an integrin-dependent organization of the cytoskeleton and a consequent change in cell shape. In an effort to identify potential signal-transducing agents that are associated with integrin-dependent shape changes, we looked for kinase activities that were stimulated by long-term adhesion of G0-synchronized NIH-3T3 cells to fibronectin-coated dishes. Several kinase activities were stimulated by this procedure, two of which migrated at 42 and 44 kDa and phosphorylated myelin basic protein in vitro. Blotting with anti-phosphotyrosine and anti-mitogen-activated protein (MAP) kinase antibodies identified these enzymes as ERK 1 and ERK 2. In contrast to the rapid and transient activation of these MAP kinases by platelet-derived growth factor, stimulation of MAP kinase activity by fibronectin was gradual, persistent, and associated with cell spreading rather than cell attachment itself. Cytochalasin D blocked the activation of MAP kinase activity that was induced by the binding of cells to fibronectin. Moreover, MAP kinase was also activated by adhesion of cells to vitronectin and type IV collagen; these effects were also associated with cell spreading. These results distinguish the regulation of G1 phase MAP kinase activity by soluble mitogens and extracellular matrix. They also implicate MAP kinase in shape-dependent cell cycle progression.
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PMID:Integrin-dependent activation of MAP kinase: a link to shape-dependent cell proliferation. 761 63

Adherence of human neutrophils to plastic, fibronectin, or collagen-coated surfaces modifies their response to several agonists including granulocyte-macrophage colony-stimulating factor (GM-CSF), tumor necrosis factor alpha (TNF-alpha), and fMet-Leu-Phe, permitting them to trigger superoxide anion (O2-) release, which they are unable to do as cells in suspension. Adherence of neutrophils causes a slight decrease in the basal level of tyrosine phosphorylation compared with that of suspended cells. The addition of GM-CSF, however, brings all proteins to a level of phosphorylation at least equal to that seen in suspended cells. In the case of a 130-kDa (p130) and a 42-kDa (p42) protein, the increase in tyrosyl phosphorylation in response to GM-CSF challenge is clearly larger in adherent than in suspended cells (6- and 4-fold increases for p130 and p42, respectively, in adherent cells vs. 1.7- and 2.1-fold in suspended cells). This is even more patient in the case of collagen-coated plates (9.4-fold increase for p42). Therefore, once neutrophils attach to surfaces, they become primed and respond to GM-CSF with greater potency than when they are in suspension. By Western blot analysis with anti-MAP kinase antibodies, we demonstrate that p42 is one member of the mitogen-activating protein kinase, namely the p42MAPK. The tyrosyl phosphorylation of p42MAPK is elevated in GM-CSF-treated adherent neutrophils in a time-dependent fashion as measured by the formation of a doublet composed of the phospho (or activated) form and the dephospho (or inactive) form of MAP kinase. MAP kinase activation and tyrosine phosphorylation are inhibited by tyrosine kinase inhibitors genistein and tyrphostin-23. Our results indicate that adherence acts to prime neutrophils for enhanced functionality and that tyrosine phosphorylation is involved in this process.
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PMID:Priming of tyrosine phosphorylation in GM-CSF-stimulated adherent neutrophils. 772 26

It is known that mechanical stress directly changes the conformation of the functional proteins, or directly activates enzymes such as phospholipase in the plasma membrane. The integrin-cytoskeleton complex may be an alternative candidate structure for a mechanoreceptor and a transducer. The cytoskeleton has been also shown to play an important role in secretion. Mechanical stress may stimulate the secretion of some cytokines or angiotensin II, which may generate multiple intracellular signals as a secondary event. External stimuli are generally transduced into the nucleus through the activation of protein kinase cascade. Stretching of cardiac myocytes stimulates the activity of PKC, Raf-1 kinase, MAP kinase kinase. MAP kinase and S6 kinase. In cardiac myocytes, mechanical stress directly induces gene expression as well as protein synthesis. Immediate early genes are first induced, and then fetal-type genes are reinduced. Both in hypertrophied hearts and in the experimental model of cardiac hypertrophy induced by pressure overload. Ca(2+)-ATPase content of cardiac myocytes is depressed. Reduced function of sarcoplasmic reticulum causes insufficient decrease of intracellular calcium in diastole and induces slowing of ventricular relaxation. In the interstitium of pressure overloaded hearts, the accumulation of collagen fiber is increased. The abnormal deposit leads to increased chamber stiffness and diastolic dysfunction. Furthermore, TGF-beta and tissue renin-angiotensin system are up-regulated in pressure overloaded hearts, both of which accelerate the interstitial fibrosis.
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PMID:Interaction of cardiac myocytes and non-myocytes in mechanical stress-induced hypertrophy. 777 62

Src homology/collagen (SHC) proteins are thought to participate in signaling through both receptor tyrosine kinases, such as the insulin receptor and the EGF (epidermal growth factor) receptor, and cytoplasmic tyrosine kinases, such as v-src and v-fps. Here we approached the insulin-induced and the insulin-like-growth-factor-I-induced (IGF-I-induced) phosphorylation of SHC proteins, and the possible role of these proteins in insulin and IGF-I signaling. First, we showed that SHC proteins are phosphorylated on tyrosine residues upon insulin and IGF-I treatment of fibroblasts transfected with a SHC cDNA construct. More important, ligand-activated insulin and IGF-I receptors phosphorylate SHC proteins in vitro, indicating that SHC proteins could be direct substrates for insulin and IGF-I receptors. Further, insulin or IGF-I treatment of SHC-transfected fibroblasts leads to immunoprecipitation of SHC proteins with insulin-receptor substrate 1 (IRS-1). We next looked at the possible effect of SHC proteins on biological responses in SHC-transfected fibroblasts. We found that the expression of exogenous SHC proteins results in an increased basal MEK (MAPK/ERK-activating kinase) activity. Further, neither the basal nor the insulin-induced or IGF-I-induced PtdIns-3-kinase activity were modified by expression of exogenous SHC proteins. These results illustrate that SHC proteins are implicated in the MAP (mitogen-activated protein)-kinase pathway, but not in that of PtdIns-3-kinase. Finally, we show that SHC-transfected cells, unlike control cells, are able to advance into the early phases of the cell cycle, and are more sensitive to the growth-promoting effect of insulin. In conclusion, SHC proteins are substrates for insulin and IGF-I receptors, and would appear to function as early post-receptor signaling components.
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PMID:Involvement of Src-homology/collagen (SHC) proteins in signaling through the insulin receptor and the insulin-like-growth-factor-I-receptor. 803 92

The importance of epidermal growth factor (EGF) receptor expression level and autophosphorylation sites in src homology and collagen protein (SHC) tyrosine phosphorylation has been studied. In contrast to EGF-induced tyrosine phosphorylation of the GTPase-activating protein for ras (rasGAP) and phospholipase C-gamma 1 (PLC-gamma 1), SHC tyrosine phosphorylation occurs at a very low receptor density in parental NIH3T3 mouse fibroblasts expressing less than 1 x 10(4) EGF receptors per cell. In transfected NIH3T3 cells expressing human EGF receptors (approximately 4 x 10(5) receptors per cell), maximal levels of SHC and PLC-gamma 1 tyrosine phosphorylation occur when approximately 4 x 10(4) receptors or more are occupied by ligand. At lower levels of receptor occupancy only SHC phosphorylation was significant. Also, EGF treatment of mouse keratinocytes, which represent a physiological target of EGF, express a low number of EGF receptors (approximately 2 x 10(4) receptors per cell), and stringently require EGF to grow, results in intense SHC tyrosine phosphorylation, compared to rasGAP or PLC-gamma 1. SHC is also efficiently tyrosine phosphorylated by an EGF receptor deletion mutant (Dc214) that is devoid of autophosphorylation sites, but which remains mitogenically responsive to EGF. The EGF receptor mutant Dc214 is able to activate the ras guanine nucleotide exchanger and phosphorylate mitogen-activated protein kinase (MAPK), presumable as a result of complex formation between tyrosine phosphorylated SHC and GRB2. These results indicate that potent EGF-induced SHC tyrosine phosphorylation can be triggered in cells having relatively few receptors. Also, our data show that EGF receptors are able to phosphorylate SHC, activate the exchange of guanine nucleotide on ras and phosphorylate MAPK by a mechanism that does not require receptor autophosphorylation sites and, therefore, the src homology 2 (SH2):phosphotyrosine-dependent interaction of SHC or GRB2 with the EGF receptor.
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PMID:Potent SHC tyrosine phosphorylation by epidermal growth factor at low receptor density or in the absence of receptor autophosphorylation sites. 803 6

By applying Western blot analysis using anti-phosphotyrosine antibodies, primary human dermal fibroblasts were examined after having been cultured on type I collagen-coated surfaces or in free-floating type I collagen gels. In both systems cells showed enhanced tyrosine phosphorylation of a M(r) 120,000 protein (pp120) and of a M(r) 42,000 protein (pp42). Phosphorylation was apparent 6 h at the latest after initiation of the culture and was only slightly induced on polylysine or on plastic. In contrast to pp42, pp120 was rapidly dephosphorylated in cells suspended by trypsinization or released from collagen gels by collagenase treatment, but regained phosphorylation in cells cultured in/on type I collagen. Two human sarcoma cell lines (HT-1080 and RD) exhibited identical tyrosine phosphorylation of pp120 but not of pp42. pp120 is identical with pp125FAK, a novel tyrosine kinase localized in focal adhesions, as proved by immunological cross-reactivity with anti-pp125FAK antibodies. Our results suggest that tyrosine phosphorylation is involved in signal transduction triggered by two- and three-dimensional type I collagen-fibroblast contact.
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PMID:Three-dimensional contact with type I collagen mediates tyrosine phosphorylation in primary human fibroblasts. 812 56

Hepatic stellate cells become activated into myofibroblast-like cells during the early stages of hepatic injury associated with fibrogenesis. The subsequent dysregulation of hepatic stellate cell collagen gene expression is a central pathogenetic step during the development of cirrhosis. The cytoplasmic Raf and mitogen-activated protein (MAPK) kinases were found to differentially regulate alpha I(I) collagen gene expression in activated stellate cells. This suggests an unappreciated branch point exists between Raf and MAPK. A MAPK-stimulatory signal was mapped to the most proximal NF-1 and Sp-1 binding domains of the 5'-untranslated region of the collagen gene. A Raf-inhibitory signal was mapped to a further upstream binding domain involving a novel 60-kDa DNA-binding protein (p60). The cell-specific expression and induction of p60 in stellate cells during the early stages of hepatic fibrogenesis in vivo suggest a central role for this pathway during liver injury and stellate cell activation.
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PMID:Raf and mitogen-activated protein kinase regulate stellate cell collagen gene expression. 862 42


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