Ras activation is necessary for integrin-mediated activation of extracellular signal-regulated kinase 2 and cytosolic phospholipase A2 but not for cytoskeletal organization.
Cell adhesion to the extracellular matrix triggers a cascade of intracellular biochemical signals regulated by the integrin family of receptors. Recent evidence suggests that integrin engagement may activate a mitogen-activated protein (MAP) kinase cascade that may cooperate with more clearly defined mitogenic signaling pathways to regulate cell proliferation, adhesion, and migration. Here we report that the adhesion-dependent activation of the MAP kinase Erk2 (extracellular signal-regulated kinase 2) occurs in serum-starved NIH3T3 cells, and that this activation of Erk2 is preceded by the activation of the small GTP-binding protein Ras in fibronectin-adherent cells. Inhibition of Ras signaling by expression of a dominant-inhibitory mutant of Ras (N17Ras) in NIH3T3 cells blocked adhesion-dependent activation of Erk2, although the focal adhesion kinase (FAK) was still activated in these cells. Furthermore, activation of this Ras-MAP kinase pathway activated cytosolic phospholipase A2, leading to the release of arachidonic acid metabolites, and N17Ras also inhibited these events. However, N17Ras expression does not inhibit cell adhesion, spreading, or focal contact and stress fiber formation. These results suggest that, while integrin-dependent activation of this MAP kinase pathway is Ras-dependent, the integrin-dependent activation of FAK and several morphological events are Ras-independent. Thus, integrin-mediated signals involved in regulating cell morphology appear to diverge from those regulating MAP kinase activation at a level upstream of Ras activation.
Clark
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Howard Hughes Medical Institute, Center for Cancer Research, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Hynes
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D016475:3T3 Cells; D000818:Animals; D001095:Arachidonic Acids / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002448:Cell Adhesion; D015815:Cell Adhesion Molecules / Q000378:metabolism; D003599:Cytoskeleton / Q000502:physiology* / Q000648:ultrastructure; D003600:Cytosol / Q000201:enzymology; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; D005799:Genes, Dominant; D016023:Integrins / Q000502:physiology*; D007700:Kinetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D016296:Mutagenesis; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection; D018631:ras Proteins / Q000096:biosynthesis / Q000378:metabolism*
D001095:Arachidonic Acids; D015815:Cell Adhesion Molecules; D016023:Integrins; D011994:Recombinant Proteins; D003907:Dexamethasone; D011505:Protein-Tyrosine Kinases; D051417:Focal Adhesion Kinase 1; D051416:Focal Adhesion Protein-Tyrosine Kinases; C496051:Ptk2 protein, mouse; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D010741:Phospholipases A; D054467:Phospholipases A2; D018631:ras Proteins