Angiotensin II type 1 receptor signals through Raf-1 by a protein kinase C-dependent, Ras-independent mechanism

To understand the molecular mechanism by which the angiotensin II (AII) type I receptor (AT(1) receptor) transduces its biological signal, we examined the role of various signaling molecules involved in AT(1) receptor signaling in Chinese hamster ovary cells stably transfected with the AT(1) receptor. AT(1) receptor-transfected cells responded to AII treatment by inhibiting adenylyl cyclase, increasing the intracellular Ca2+ concentration, and activating protein kinase C (PKC)alpha and PKC epsilon. All also activated the c-fos gene and mitogen-activated protein (MAP) kinases. The activation of PKC, the c-fos gene, and MAP kinases was blocked by inhibition of PKC induced by pretreat ment with 12-O-tetradecanoylphorbol-13-acetate but not by pretreatment with pertussis toxin, suggesting that PKC couples to the activation of the the c-fos gene and MAP kinases, In addition, All activated Raf-1 and MAP kinase kinase in a PKC-dependent manner. A dominant negative mutant of Pas had no effect on All-induced MAP kinase or c-fos gene activation. Thus, the AT(1) receptor signals through Raf-l and its downstream signaling molecules by a PKC-dependent mechanism that does not involve Pas activation.