Disruption of cell-substrate adhesion activates the protein tyrosine kinase pp60(c-src)

Treatment of confluent chicken embryo fibroblasts (CEFs) with trypsin resul ts in a dose- and time-dependent increase in c-Src protein tyrosine kinase (PTK) activity. A similar, but less marked, increase in c-Src PTK activity occurs upon incubation of CEFs in calcium-free phosphate-buffered saline, w hich also causes a decrease in cell-substrate adhesion. The increase in c-S rc PTK activity following disruption of cell-substrate adhesion correlates with a decrease in the phosphorylation of c-Src at the regulatory site, Tyr 527. The phosphotyrosine phosphatase inhibitor phenylarsine oxide blocks th e increase in c-Src PTK activity seen following treatment with trypsin and the morphological changes associated with the disruption of cell-substrate adhesion. In contrast, disruption of cell-substrate adhesion causes a decre ase in FAK PTK activity that rapidly returns to control levels when the cel ls are plated on fibronection-coated dishes. Treatment of cells with cytoch alasin D, which disrupts actin filaments but not cell-substrate adhesion, c auses only a slight increase in c-Src PTK activity. Thus, these studies dem onstrate a ligand-independent mechanism for the activation of c-Src that is consistent with its role in both cell adhesion and cell motility, Furtherm ore, these data suggest that similar to adhesion, loss of adhesion is not a passive process but can activate specific signaling pathways that may have significant effects on cellular function. (C) 2000 Academic Press.