Endothelin-1, but not ang II, activates MAP kinases through c-Src - Independent ras-raf-dependent pathways in vascular smooth muscle cells

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.