THE ANGIOTENSIN-II AT(1) RECEPTOR IS TYROSINE AND SERINE PHOSPHORYLATED AND CAN SERVE AS A SUBSTRATE FOR THE SRC FAMILY OF TYROSINE KINASES

Angiotensin II AT(1) receptor signal transduction has recently been sh own to function through the phospholipase C isozyme, PLC-gamma. Since PLC-gamma is known to interact with phosphotyrosine containing protein s through SH2 domains, we examined the phosphorylation state of the AT (1) receptor. Immunoprecipitation of the P-32 labeled AT(1) receptor from rat aortic smooth muscle cells followed by alkali hydrolysis dem onstrated the presence of tyrosine phosphorylation. Phosphoamino acid analysis of the excised bands demonstrated the presence of phosphoseri ne and phosphotyrosine residues. A fusion protein comprising the intra cellular tail of the AT(1) receptor was used to screen for candidate k inases, and the src kinase family displayed high activity. In summary, this study shows that the AT(1) receptor is serine and tyrosine phosp horylated in vivo and suggests that a soluble kinase related to the sr c family may be responsible for the tyrosine phosphorylation. (C) 1994 Academic Press, Inc.