Cas phosphorylation regulates focal adhesion assembly

Abstract

AbstractIntegrins link the cytoskeleton to the extracellular matrix for cell attachment and migration. Integrin ligation activates tyrosine kinases and stimulates phosphorylation of several integrin-associated proteins. However, the role of such phosphorylation in the assembly of integrin adhesions is unclear. Using spreading or migrating epithelial cells, we provide evidence that phosphorylated Cas (p130Cas, BCAR1), its binding partner, Crk, and inactive focal adhesion kinase (FAK) cluster together with inactive integrins at the cell periphery at sites that subsequently develop into focal adhesions containing F-actin, active integrins, active FAK and core adhesome proteins such as vinculin and talin. Cas, Crk, Src family kinases (SFK) and Rac1 are required for focal adhesion formation and cell spreading. Rac1 provides positive feedback onto Cas through reactive oxygen, opposed by negative feedback from the ubiquitin proteasome system. The results suggest that SFK-Cas-Crk-Rac1 signaling precedes and regulates focal adhesion assembly in epithelial cells.