RHO STIMULATES TYROSINE PHOSPHORYLATION OF FOCAL ADHESION KINASE, P130 AND PAXILLIN

The small GTP-binding protein Rho rapidly stimulates the formation of focal adhesions and actin stress fibres when microinjected into serum- starved Swiss 3T3 fibroblasts. This response is inhibited by tyrosine kinase inhibitors, Addition of growth factors such as lysophosphatidic acid and bombesin to Swiss 3T3 cells stimulates a similar response, w hich is dependent on endogenous Rho proteins, To investigate signallin g events regulated by Rho, we have scrape loaded Rho into serum-starve d cells, Activated Rho stimulates the tyrosine phosphorylation of a nu mber of proteins, including three proteins known to localise to focal adhesions, pp125(FAK), p130 and paxillin, Rho-induced phosphorylation of pp125(FAK), p130 and paxillin is observed in the absence of stress fibre formation and is, therefore, independent of Rho-induced actin po lymerisation, We propose that the tyrosine kinase, pp125(FAK), and the putative adapter proteins, paxillin and p130, are components of a Rho -regulated signal transduction pathway, and that these protein tyrosin e phosphorylation events are likely to be important for the regulation of focal adhesion formation.