title: Activation of Rac and Cdc42 by integrins mediates cell spreading.
abstract: Adhesion to ECM is required for many cell functions including cytoskeletal organization, migration, and proliferation. We observed that when cells first adhere to extracellular matrix, they spread rapidly by extending filopodia-like projections and lamellipodia. These structures are similar to the Rac- and Cdc42-dependent structures observed in growth factor-stimulated cells. We therefore investigated the involvement of Rac and Cdc42 in adhesion and spreading on the ECM protein fibronectin. We found that integrin-dependent adhesion led to the rapid activation of p21-activated kinase, a downstream effector of Cdc42 and Rac, suggesting that integrins activate at least one of these GTPases. Dominant negative mutants of Rac and Cdc42 inhibit cell spreading in such a way as to suggest that integrins activate Cdc42, which leads to the subsequent activation of Rac; both GTPases then contribute to cell spreading. These results demonstrate that initial integrin-dependent activation of Rac and Cdc42 mediates cell spreading.
authors.affiliation: Department of Vascular Biology, The Scripps Research Institute, La Jolla, California 92037, USA.
authors.forename: L S
authors.initials: LS
authors.lastname: Price
authors.forename: J
authors.initials: J
authors.lastname: Leng
authors.forename: M A
authors.initials: MA
authors.lastname: Schwartz
authors.forename: G M
authors.initials: GM
authors.lastname: Bokoch
mesh_terms: D016475:3T3 Cells; D000818:Animals; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D002462:Cell Membrane / Q000201:enzymology / Q000502:physiology; D002465:Cell Movement / Q000502:physiology*; D004789:Enzyme Activation; D005353:Fibronectins / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*; D016023:Integrins / Q000502:physiology*; D051379:Mice; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein; D054462:p21-Activated Kinases; D020744:rac GTP-Binding Proteins
chemical_list: D018797:Cell Cycle Proteins; D005353:Fibronectins; D016023:Integrins; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins