Identification of an Essential Signaling Cascade for Mitogen-activated Protein Kinase Activation by Angiotensin II in Cultured Rat Vascular Smooth Muscle Cells

In cultured rat vascular smooth muscle cells, angiotensin II (Ang II) induced a rapid increase in mitogen-activated protein kinase (MAPK) activity through the Ang II type 1 receptor, which was insensitive to pertussis toxin but was abolished by the phospholipase C inhibitor, U73122. The Ang II-induced MAPK activation was not affected by the protein kinase C inhibitor, GF109203X, and was only partially impaired by pretreatment with a phorbol ester, whereas both treatments completely prevented MAPK activation by the phorbol ester. Intracellular Ca 2+ chelation by TMB-8, but not extracellular Ca 2+ chelation or inhibition of Ca 2+ influx, abolished Ang II-induced MAPK activation. The calmodulin inhibitor, calmidazolium, and the tyrosine kinase inhibitor, genistein, completely blocked MAPK activation by Ang II as well as by the Ca 2+ ionophore A23187. Ang II caused a rapid increase in the binding of GTP to p21 ras , and this was inhibited by genistein, TMB-8, and calmidazolium but not by pertussis toxin or GF109203X. These data suggest that Ang II-induced MAPK activation through the Ang II type 1 receptor could be mediated by p21 ras activation through a currently unidentified tyrosine kinase that lies downstream of G q -coupled Ca 2+ /calmodulin signals.