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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)

Integrin receptors play important roles in organizing the actin-containing cytoskeleton and in signal transduction from the extracellular matrix. The initial steps in integrin function can be analyzed experimentally using beads coated with ligands or anti-integrin antibodies to trigger rapid focal transmembrane responses. A hierarchy of transmembrane actions was identified in this study. Simple integrin aggregation triggered localized transmembrane accumulation of 20 signal transduction molecules, including RhoA, Rac1, Ras, Raf, MEK, ERK, and JNK. In contrast, out of eight cytoskeletal molecules tested, only tensin coaccumulated. Integrin aggregation alone was also sufficient to induce rapid activation of the JNK pathway, with kinetics of activation different from those of ERK. The tyrosine kinase inhibitors herbimycin A or genistein blocked both the accumulation of 19 out of 20 signal transduction molecules and JNK- and ERK-mediated signaling. Cytochalasin D had identical effects, whereas three other tyrosine kinase inhibitors did not. The sole exception among signaling molecules was the kinase pp125FAK which continued to coaggregate with alpha 5 beta 1 integrins even in the presence of these inhibitors. Tyrosine kinase inhibition also failed to block the ability of ligand occupancy plus integrin aggregation to trigger transmembrane accumulation of the three cytoskeletal molecules talin, alpha-actinin, and vinculin; these molecules accumulated even in the presence of cytochalasin D. However, it was necessary to fulfill all four conditions, i.e., integrin aggregation, integrin occupancy, tyrosine kinase activity, and actin cytoskeletal integrity, to achieve integrin-mediated focal accumulation of other cytoskeletal molecules including F-actin and paxillin. Integrins therefore mediate a transmembrane hierarchy of molecular responses.
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PMID:Integrin function: molecular hierarchies of cytoskeletal and signaling molecules. 759 97

In the endothelial cell line EAhy 926, 1-oleoyl-lysophosphatidic acid (LPA) stimulated the tyrosine phosphorylation of the pp42 isoform of mitogen-activated protein (MAP) kinase. Maximum phosphorylation was observed within 5 min of LPA addition, but the response was sustained for up to 120 min. Re-addition of LPA after 60 min stimulated a further sustained increase in the tyrosine phosphorylation of MAP kinase. In cells pretreated with phorbol 12-myristate 13-acetate (PMA; 24 h) or preincubated with the protein kinase C inhibitor Ro-318220, LPA-induced tyrosine phosphorylation of pp42 MAP kinase was substantially reduced at 2 min but potentiated at 60 min. Ro-318220 in combination with either PMA or pertussis toxin pretreatment abolished the LPA response at all time points, suggesting an involvement of protein kinase C in the pertussis toxin-sensitive part of the pathway. Agents which raised intracellular cyclic AMP levels did not affect the initial phase of LPA-stimulated MAP kinase activation, but abolished the late phase. However, this effect was prevented by Ro-318220, implicating a greater role for protein kinase C than protein kinase A in the regulation of sustained MAP kinase responses. LPA stimulated an increase in the tyrosine phosphorylation of focal adhesion kinase pp125 (pp125FAK) in EAhy 926 cells which was both protein kinase C- and pertussis toxin-independent. These results are discussed in terms of the pathways regulating both MAP kinase and pp125FAK in response to LPA in the EAhy 926 endothelial cells line.
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PMID:Regulation of lysophosphatidic acid-stimulated tyrosine phosphorylation of mitogen-activated protein kinase by protein kinase C- and pertussis toxin-dependent pathways in the endothelial cell line EAhy 926. 774 5

Integrins can function as signal-transducing receptors capable of modulating cell growth and gene expression (Juliano, R. L., and Haskill, S. (1993) J. Cell Biol. 120, 577-585; Hynes, R. O. (1992) Cell 69, 11-25). An early event in integrin signaling in fibroblasts and other cells involves activation of pp125FAK, a cytoplasmic tyrosine kinase (Hanks, S. K., Calalb, M. B., Harper, M. C., and Patel, S. K. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 8487-8491; Schaller, M. D., Borgman, C. A., Cobb, B. S., Vines, R. R., Reynolds, A. B., and Parsons, J. T. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 5192-5196). Here we report a novel aspect of integrin-mediated signal transduction. We demonstrate that adhesion of cells to substrata coated with extracellular matrix proteins, or with a synthetic peptide containing the RGD sequence, can cause activation of mitogen-activated protein (MAP) kinases in 3T3 or REF52 fibroblasts. Activation of MAP kinases seems to depend on integrin engagement rather than simply on cell attachment. Thus, MAP kinases are activated when cells adhere to substrata coated with the integrin ligands fibronectin or laminin, but not when cells adhere to poly-D-lysine, a nonspecific adhesion-promoting polypeptide. Treatment of cells with cytochalasin D, an inhibitor of actin microfilament assembly, almost completely blocks adhesion-induced MAP kinase activation, indicating a critical role for the cytoskeleton. In REF52 cells, we have observed that activation of MAP kinases is accompanied by redistribution of the protein to the nucleus, suggesting that the activated kinases may impinge on factors regulating gene expression. Thus, integrin-mediated cell adhesion seems a sufficient stimulus to cause activation and nuclear translocation of MAP kinases. This may have important implications for the regulation of cell growth and differentiation by the extracellular matrix.
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PMID:Integrin-mediated cell adhesion activates mitogen-activated protein kinases. 792 88

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

Accumulating evidence suggests that the VLA/CD29 molecule plays an important role in T-cell costimulation, and CD4+CD29/VLA+ memory T cells play a key role in induction of CD8 killer effector T cells which are considered to be a major population involved in graft rejection. To target limited elements of the T-lymphocyte population, we have described the preparation of a bispecific antibody-toxin conjugate designed to target CD4+CD29+ memory T cells. We also showed that the solid-phase crosslinking of VLA-4 by the antibody against this molecule or by its ligand, the CS-1 region of fibronectin, stimulates tyrosine phosphorylation of 140, 120-105, 80-70, 60-55, 50 and 45 kilodalton proteins. In addition, we identified the pp140 protein as PLC gamma, pp120 protein as pp125FAK, pp70 and pp50 proteins as paxillin, and pp60-55 proteins as pp59fyn and pp56lck, and pp45 as MAP kinase, respectively. Moreover, we demonstrated that pp125FAK is directly associated with paxillin. The paxillin binding domain of pp125FAK is homologous to the paxillin binding domain of vinculin. Mutations in the conserved amino acid residues between pp125FAK and vinculin result in the loss of paxillin-binding activity. Because VLA/CD29 is preferentially expressed on CD4 memory T cells, the above described system will be used to develop a novel drug design for providing selective immunosuppression useful for organ transplantation.
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PMID:Selective immunomodulation: utilization of CD29/VLA molecules. 885 91

Many G protein-coupled receptors (e.g. that of angiotensin II) activate phospholipase Cbeta, initially increasing intracellular calcium and activating protein kinase C. In the WB and GN4 rat liver epithelial cell lines, agonist-induced calcium signals also stimulate tyrosine phosphorylation and subsequently increase the activity of c-Jun N-terminal kinase (JNK). We have now purified the major calcium-dependent tyrosine kinase (CADTK), and by peptide and nucleic acid sequencing identified it as a rat homologue of human PYK2. CADTK/PYK2 is most closely related to p125(FAK) and both enzymes are expressed in WB and GN4 cells. Angiotensin II, which only slightly increases p125(FAK) tyrosine phosphorylation in GN4 cells, substantially increased CADTK tyrosine autophosphorylation and kinase activity. Agonists for other G protein-coupled receptors (e.g. LPA), or those increasing intracellular calcium (thapsigargin), also stimulated CADTK. In comparing the two rat liver cell lines, GN4 cells exhibited approximately 5-fold greater angiotensin II- and thapsigargin-dependent CADTK activation than WB cells. Although maximal JNK activation by stress-dependent pathways (e.g. UV and anisomycin) was equivalent in the two cell lines, calcium-dependent JNK activation was 5-fold greater in GN4, correlating with CADTK activation. In contrast to JNK, the thapsigargin-dependent calcium signal did not activate mitogen-activated protein kinase and Ang II-dependent mitogen-activated protein kinase activation was not correlated with CADTK activation. Finally, while some stress-dependent activators of the JNK pathway (NaCl and sorbitol) stimulated CADTK, others (anisomycin, UV, and TNFalpha) did not. In summary, cells expressing CADTK/PYK2 appear to have two alternative JNK activation pathways: one stress-activated and the other calcium-dependent.
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PMID:Activation of a novel calcium-dependent protein-tyrosine kinase. Correlation with c-Jun N-terminal kinase but not mitogen-activated protein kinase activation. 893 45

We previously demonstrated that in white fat cell precursors alpha2-adrenoceptor stimulation lead to the phosphorylation of p44 and p42 mitogen-activated protein kinases and an increase in cell number. Regulation of cell adhesion and cell cytoskeleton plays a crucial role in the control of cell growth by various growth factors. Here, we report that in mouse 3T3F442A preadipocytes expressing 2500 fmol/mg protein of the human alpha2C10-adrenoceptor (alpha2AF2 cells), alpha2-adrenergic stimulation rapidly restored the spreading of cells previously retracted by serum withdrawal. This effect was pertussis toxin sensitive and was blocked by pretreatment of the cells with dihydrocytochalasin B (a blocker of actin polymerization), genistein (a tyrosine kinase inhibitor), or agents that increase cell cAMP content. Spreading was accompanied by cell membrane ruffling, formation of lamelipodia and filipodia, appearance of focal adhesion plaques, and induction of actin stress fibers. alpha2-Adrenergic stimulation also lead to a rapid Gi- and actin-dependent tyrosine phosphorylation of the pp125 focal adhesion kinase (FAK) as well as of the p42 and p44 mitogen-activated protein kinases. alpha2-Adrenergic-dependent spreading and FAK and mitogen-activated protein kinase phosphorylation were also observed in 3T3F442A preadipocytes permanently expressing 20 fmol/mg protein of the human alpha2C10-adrenoceptor (alpha2AF3 cells) as well as in BFC-1beta preadipocytes, which constitutively express 25 fmol/mg protein of mouse alpha2A-adrenoceptors. In BFC-1beta preadipocytes, alpha2-adrenergic-dependent spreading and pp125FAK phosphorylation were counteracted by beta-adrenergic stimulation. Our results suggest that alpha2-adrenergic control of actin polymerization and focal adhesion assembly could play a crucial role in the regulation of preadipocyte growth by the sympathetic nervous system.
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PMID:alpha2-Adrenoceptor stimulation promotes actin polymerization and focal adhesion in 3T3F442A and BFC-1beta preadipocytes. 894 Mar 38

We and others have recently cloned a non-receptor, calcium-dependent tyrosine kinase (CADTK; also known as PYK2, CAKbeta, and RAFTK) that shares both overall domain structure and 45% amino acid identity with p125(FAK). We have studied the signaling, activation, and potential function of these related enzymes in GN4 rat liver epithelial cells that express CADTK and p125(FAK) at roughly similar levels. p125(FAK) is nearly fully tyrosine-phosphorylated in resting GN4 cells. In contrast, while CADTK is not tyrosine-autophosphorylated in untreated cells, angiotensin II increases CADTK Tyr(P) by 5-10-fold. With regard to signaling, CADTK activation is correlated with stimulation of c-Jun N-terminal kinase and p70(S6K) pathways but not with the stimulation of mitogen-activated protein kinase or p90(RSK). In this report we assessed the contribution of CADTK and p125(FAK) to tyrosine phosphorylation of focal contact proteins. In adherent GN4 cells, the constitutive activity of p125(FAK) was correlated with basal paxillin, tensin, and p130(CAS) tyrosine phosphorylation. A rapid increase in the tyrosine phosphorylation of each protein was detected after treatment with angiotensin II or other agonists that stimulate CADTK; the prolonged 3-4-fold increase in paxillin tyrosine phosphorylation was the most substantial change. In the WB cell line that expresses 3-fold less CADTK than GN4 cell line agonist-dependent paxillin tyrosine phosphorylation is similarly reduced. Immunoprecipitation of CADTK from GN4 cells revealed CADTK. paxillin complexes that persisted in 500 mM NaCl but not in 0.1% SDS cell lysis buffer. The complexes were largely independent of the tyrosine phosphorylation state of either protein. Surprisingly, we did not detect p125(FAK).paxillin complexes in immunoprecipitates using either of two p125(FAK) antibodies. When CADTK and p125(FAK) were transiently overexpressed in 293(T) cells, both enzymes associated with paxillin, but the avidity of CADTK appeared to be greater. In addition, in transfected 293(T) cells, complexes between CADTK and another potential substrate, p130(CAS), were detected. In summary, in GN4 rat liver epithelial cells stimulation of CADTK was highly correlated with paxillin tyrosine phosphorylation; in addition, CADTK but not p125(FAK) was complexed to paxillin at detectable levels. This suggests that agonist-dependent cytoskeletal changes in epithelial cells might proceed, in part, by CADTK-dependent mechanisms.
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PMID:Paxillin is tyrosine-phosphorylated by and preferentially associates with the calcium-dependent tyrosine kinase in rat liver epithelial cells. 916 70

Vascular endothelial growth factor (VEGF) stimulated the tyrosine phosphorylation of multiple components in confluent human umbilical vein endothelial cells (HUVECs) including bands of Mr 205,000, corresponding to the VEGF receptors Flt-1 and KDR, and Mr 145,000, 120,000, 97,000, and 65,000-70,000. VEGF caused a striking and transient increase in mitogen-activated protein (MAP) kinase activity and stimulated phospholipase C-gamma tyrosine phosphorylation, but it had no effect on phosphatidylinositol 3'-kinase activity. VEGF caused a marked increase in tyrosine phosphorylation of p125 focal adhesion kinase (p125(FAK)), which was both rapid and concentration-dependent. VEGF produced similar effects on p125(FAK) in the endothelial cell line ECV.304. VEGF stimulated tyrosine phosphorylation of the 68-kDa focal adhesion-associated component, paxillin, with similar kinetics and concentration dependence to that for p125(FAK). Thrombin and the phorbol ester, phorbol 12-myristate 13-acetate, also increased p125(FAK) tyrosine phosphorylation in HUVECs. The effect of VEGF on p125(FAK) tyrosine phosphorylation was completely inhibited by the actin filament-disrupting agent cytochalasin D and was partially inhibited by the protein kinase C inhibitor GF109203X. Inhibition of the MAP kinase pathway using a specific inhibitor of MAP kinase kinase had no effect on p125(FAK) tyrosine phosphorylation. VEGF stimulated migration and actin stress fiber formation in confluent HUVEC, and VEGF-induced p125(FAK)/paxillin tyrosine phosphorylation was accompanied by increased immunofluorescent staining of p125(FAK), paxillin, and phosphotyrosine in focal adhesions in confluent cultures of HUVECs. These findings identify p125(FAK) and paxillin as components in a VEGF-stimulated signaling pathway and suggest a novel mechanism for VEGF regulation of endothelial cell functions.
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PMID:Vascular endothelial growth factor stimulates tyrosine phosphorylation and recruitment to new focal adhesions of focal adhesion kinase and paxillin in endothelial cells. 918 76

We propose a model for signaling events induced by fluid shear stress that incorporates many of the features discussed in this paper (FIG. 4). First, heterotrimeric G-proteins, as well as a small G-proteins, are activated by flow. Indeed, a G protein appears to be required for ERK1/2 activation by flow because ERK1/2 activation is completely inhibited by GDP-beta S. Then, flow activates phospholipase C and generates IP3 and diacylglycerol (DG). IP3 releases Ca2+ from internal Ca2+ stores via IP3 receptor and DG activates PKC. Nollert and colleagues have shown that flow activates PLC and increases IP3. It is possible that several different PKC isozymes are activated by flow including both Ca(2+)-dependent and Ca(2+)-independent isozymes. These different isozymes may have specific downstream substrates. For example, PKC-epsilon may be involved in activation of ERK1/2, while the PKC isozyme responsible for activation of JNK remains unknown. It is also possible that these PKC isozymes may be important in gene transcription events. For example, PKC-zeta has been suggested to be involved in NF-kappa B-mediated gene transcription. Longer term changes in endothelial cell morphology and structure are likely to involve separate kinases. Important candidates for these changes include members of the c-Src and FAK families. c-Src is now considered to be a component of the focal adhesion complex and regulate focal adhesion formation and/or cytoskeletal rearrangement. Recently, stretch, another mechanostress, has been shown to activate c-Src in fetal rat lung cells. It has been clarified that ERK1/2 and JNK are regulated by the small G-proteins, Ras and Rac/Cdc42H, respectively, and their effectors in parallel with each other. Rac and Rho are also thought to be involved in membrane ruffling and/or cytoskeletal rearrangement. Fluid shear stress causes stress fiber formation and focal adhesion rearrangement. Recent study by Malek and Izumo suggested the importance of microtubules in shear stress-induced morphological change and actin stress fiber formation. It is clear that the focal adhesion complex plays an important role in shear stress-induced signal and it is interesting to speculate that shear stress-induced signaling has cross-talk with signaling induced by integrins. As a general model we propose that the integration between the rapid events stimulated by shear stress and the longer term events is mediated by tyrosine kinases that serve to regulate these multiple signal transduction pathways.
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PMID:Fluid shear stress-mediated signal transduction: how do endothelial cells transduce mechanical force into biological responses? 918 80


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