ET-1-induced growth promoting responses involving ERK1/2 and PKB signaling and Egr-1 expression are mediated by Ca2+/CaM-dependent protein kinase-II in vascular smooth muscle cells

Endothelin-1 (ET-1), a potent vasoactive peptide with a pathogenic role in vascular diseases, has been shown to induce the activation of ERK1/2, PKB and the expression of a transcriptional regulator, the early growth response 1 (Egr-1), key mediators of hypertrophic and proliferative responses in vascular smooth muscle cells (VSMC). We have demonstrated earlier that ET-1 requires H2O2 generation to activate these signaling pathways and Ca2+, calmodulin (CaM) and Ca2+/CaM-dependent protein kinase II (CaMKII), play a critical role to trigger H2O2-induced effects in VSMC. However, an involvement of CaMKII in mediating ET-1-induced responses in VSMC remains unknown. Therefore, by utilizing pharmacological inhibitors of CaM, CaMKII, a CaMKII inhibitor peptide and CaMKII knockdown techniques, we have investigated the contribution of CaM and CaMKII in ET-1-induced ERK1/2 and PKB signaling, Egr-1 expression and hypertrophic and proliferative responses in VSMC. W-7 and calmidazolium, antagonists of CaM, as well as KN-93, an inhibitor of CaMKII activity, attenuated ET-1-induced ERK1/2 and PKB phosphorylation. In addition, transfection of VSMC with a CaMKII inhibitory peptide suppressed ET-1-evoked ERK1/2 and PKB phosphorylation. Similarly, siRNA-mediated CaMKII silencing reduced ET-1-produced ERK1/2 and PKB phosphorylation. CaM and CaMKII blockade also significantly lowered the ET-1-induced protein and DNA synthesis as well as Egr-1 expression. These findings demonstrate that CaMKII plays a critical role in ET-1-induced growth promoting signaling pathways as well as hypertrophic and proliferative responses in VSMC.