Role of Ras/PKCζ/MEK/ERK1/2 signaling pathway in angiotensin II-induced vascular smooth muscle cell proliferation

The role of protein kinase C (PKC) and its cross talk with extracellular signal-regulated kinase (ERK) cascade in angiotensin II (AngII)-elicited vascular smooth muscle cell (VSMC) proliferation are still unclear. In this study, the PKC pathway of AngII to activate ERK1/2 and induce cell proliferation was investigated in rat aortic smooth muscle cells. The proliferation of VSMCs was tested by [3H]-thymidine incorporation assay. Phosphorylated and non-phosphorylated PKCζ, ERK1/2, Elk-1, and mitogen-activated ERK-activating kinase (MEK) were estimated by Western blot analysis. The interactions of signal molecules were examined by immunoprecipitation. AngII-induced VSMC proliferation and activation of ERK1/2 and nuclear transcription factor Elk-1 were all down-regulated by PKC non-specific inhibitor (staurosporine) and PKCζ pseudosubstrate inhibitor (PS-PKCζ). Dominant negative Ras transfection into VSMCs decreased AngII-induced PKCζ and ERK1/2 phosphorylation. AngII stimulated the association of PKCζ with Ras. AngII-induced MEK phosphorylation was inhibited by PKCζ pseudosubstrate inhibitor and the PKCζ-MEK complex was detected by immunoprecipitation. These results suggest that PKCζ isoform is involved in VSMC proliferation and Elk-1 activation. AngII can activate ERK1/2 by Ras/PKCζ/MEK pathway, which may be one of the important signal transduction pathways in AngII-induced VSMC proliferation.