title: Focal adhesion kinase overexpression enhances ras-dependent integrin signaling to ERK2/mitogen-activated protein kinase through interactions with and activation of c-Src.
abstract: Cell adhesion to extracellular matrix proteins such as fibronectin (FN) triggers a number of intracellular signaling events including the increased tyrosine phosphorylation of the cytoplasmic focal adhesion protein-tyrosine kinase (PTK) and also the stimulation of the mitogen-activated protein kinase ERK2. Focal adhesion kinase (FAK) associates with integrin receptors, and FN-stimulated phosphorylation of FAK at Tyr-397 and Tyr-925 promotes the binding of Src family PTKs and Grb2, respectively. To investigate the mechanisms by which FAK, c-Src, and Grb2 function in FN-stimulated signaling events to ERK2, we expressed wild type and mutant forms of FAK in human 293 epithelial cells by transient transfection. FAK overexpression enhanced FN-stimulated activation of ERK2 approximately 4-fold. This was blocked by co-expression of the dominant negative Asn-17 mutant Ras, indicating that FN stimulation of ERK2 was Ras-dependent. FN-stimulated c-Src PTK activity was enhanced by wild type FAK expression, whereas FN-stimulated activation of ERK2 was blocked by expression of the c-Src binding site Phe-397 mutant of FAK. Expression of the Grb2 binding site Phe-925 mutant of FAK enhanced activation of ERK2, whereas a kinase-inactive Arg-454 mutant FAK did not. Expression of wild type and Phe-925 FAK, but not Phe-397 FAK, enhanced p130(Cas) association with FAK, Shc tyrosine phosphorylation, and Grb2 binding to Shc after FN stimulation. FN-induced Grb2-Shc association is another pathway leading to activation of ERK2 via Ras. The inhibitory effects of Tyr-397 FAK expression show that FAK-mediated association and activation of c-Src is essential for maximal signaling to ERK2. Moreover, multiple signaling pathways are activated upon the formation of an FAK.c-Src complex, and several of these can lead to Ras-dependent ERK2 mitogen-activated protein kinase activation.
authors.affiliation: Salk Institute for Biological Studies, Molecular Biology and Virology Laboratory, La Jolla, California 92037, USA. dschlaep@scripps.edu
authors.forename: D D
authors.initials: DD
authors.lastname: Schlaepfer
authors.forename: T
authors.initials: T
authors.lastname: Hunter
mesh_terms: D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000096:biosynthesis*; D002460:Cell Line; D004789:Enzyme Activation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D006801:Humans; D016023:Integrins / Q000378:metabolism*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D011505:Protein-Tyrosine Kinases / Q000096:biosynthesis*; D016392:Proto-Oncogene Proteins pp60(c-src) / Q000378:metabolism*; D015398:Signal Transduction; D014162:Transfection; D018631:ras Proteins / Q000378:metabolism*
chemical_list: D015815:Cell Adhesion Molecules; D016023:Integrins; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496050:PTK2 protein, human; D016392:Proto-Oncogene Proteins pp60(c-src); C496051:Ptk2 protein, mouse; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D018631:ras Proteins