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(Arteriosclerosis, Thrombosis, and Vascular Biology. 2007;27:1960.)
© 2007 American Heart Association, Inc.

Vascular Biology

Endothelin-1, but not Ang II, Activates MAP Kinases Through c-Src–Independent Ras-Raf–Dependent Pathways in Vascular Smooth Muscle Cells

A. Yogi; G.E. Callera; A.C.I. Montezano; A.B. Aranha; R.C. Tostes; E.L. Schiffrin; R.M. Touyz

From the Kidney Research Centre (A.Y., G.E.C., A.C.I.M., A.B.A., R.M.T.), Ottawa Health Research Institute, University of Ottawa, Ontario, Canada; the Department of Pharmacology (A.Y., R.C.T.), Institute of Biomedical Sciences-USP, Sao Paulo, Brazil; and Lady Davis Institute for Medical Research (E.L.S.), Sir Mortimer B. Davis-Jewish General Hospital, McGill University, Montreal, Canada.

Correspondence to Rhian M. Touyz, MD, PhD, Kidney Research Centre, University of Ottawa/Ottawa Health Research Institute, 451 Smyth Rd, Ottawa, ON, KIH 8M5. E-mail rtouyz{at}uottawa.ca

Objective— Endothelin-1 (ET-1) and angiotensin II (Ang II) activate common signaling pathways to promote changes in vascular reactivity, remodeling, inflammation, and oxidative stress. Here we sought to determine whether upstream regulators of mitogen-activated protein kinases (MAPKs) are differentially regulated by ET-1 and Ang II focusing on the role of c-Src and the small GTPase Ras.

Methods and Results— Mesenteric vascular smooth muscle cells (VSMCs) from mice with different disruption levels in the c-Src gene (c-Src^+/– and c-Src^–/–) and wild-type (c-Src^+/+) were used. ET-1 and Ang II induced extracellular signal-regulated kinase (ERK) 1/2, SAPK/JNK, and p38MAPK phosphorylation in c-Src^+/+ VSMCs. In VSMCs from c-Src^+/– and c-Src^–/–, Ang II effects were blunted, whereas c-Src deficiency had no effect in ET-1–induced MAPK activation. Ang II but not ET-1 induced c-Src phosphorylation in c-Src^+/+ VSMCs. Activation of c-Raf, an effector of Ras, was significantly increased by ET-1 and Ang II in c-Src^+/+ VSMCs. Ang II but not ET-1–mediated c-Raf phosphorylation was inhibited by c-Src deficiency. Knockdown of Ras by siRNA inhibited both ET-1 and Ang II–induced MAPK phosphorylation.

Conclusions— Our data indicate differential regulation of MAPKs by distinct G protein–coupled receptors. Whereas Ang II has an obligatory need for c-Src, ET-1 mediates its actions through a c-Src–independent Ras-Raf–dependent pathway for MAPK activation. These findings suggest that Ang II and ET-1 can activate similar signaling pathways through unrelated mechanisms. MAP kinases are an important point of convergence for Ang II and ET-1.

c-Src and Ras involvement in MAPK activation by ET-1 and Ang II was examined. ET-1, but not Ang II, induced MAPK phosphorylation in c-Src–deficient VSMCs. Ras knockdown by siRNA inhibited both Ang II– and ET-1–induced effects. Our findings demonstrate that whereas MAPK regulation by Ang II is c-Src–sensitive, ET-1–mediated actions involve c-Src–independent Ras-Raf–dependent pathways.

Key Words: MAPK • Src tyrosine kinases • Ras • c-Raf • signal transduction • G protein–coupled receptors