Angiotensin II stimulates tyrosine phosphorylation of the focal adhesion-associated protein paxillin in aortic smooth muscle cells.

Treatment of vascular smooth muscle cells (SMC) with angiotensin II (AII) leads to an increase in the tyrosine phosphorylation of multiple cellular substrates. Here, we have demonstrated that AII stimulates tyrosine phosphorylation of the focal adhesion-associated protein paxillin in rat aortic SMC. AII-induced phosphorylation of paxillin was detectable within 1 min and was sustained up to 60 min. Preincubation with the AT1-selective antagonist losartan abolished this response. The stimulatory effect of AII on paxillin tyrosine phosphorylation was observed only in aortic SMC and not in other target cells such as adrenal zona glomerulosa cells, chromaffin cells, or hepatocytes. The effect of AII was dependent on the activation of phospholipase C. Chelation of intracellular calcium completely inhibited the ability of AII to stimulate paxillin tyrosine phosphorylation, while selective inhibition of protein kinase C partially attenuated the response. In contrast, treatment of the cells with pertussis toxin had no effect on AII-induced paxillin tyrosine phosphorylation. These findings identify paxillin as a new substrate for AII-stimulated tyrosine phosphorylation and suggest a role for cytoskeleton-associated proteins in the growth response of aortic SMC.