Down-Regulation of Protein Kinase C-ϵ by Prolonged Incubation with PMA Inhibits the Proliferation of Vascular Smooth Muscle Cells

Abstract

Background/Aims: Phorbol myristate acetate (PMA) exerts a pleiotropic effect on the growth and differentiation of various cells. Protein kinase Cs (PKCs) plays a central role in mediating the effects of PMA on cells. The present study investigated whether the down-regulation of protein kinase C-ϵ (PKC-ϵ) is involved in the inhibition of vascular smooth muscle cell (VSMC) proliferation caused by prolonged PMA incubation. Methods: Using cell counting, Cell Counting Kit-8 (CCK-8) and EdU incorporation assay on VSMCs, we evaluated the inhibitory effects of prolonged incubation of PMA, of lentiviruses carrying the short-hairpin RNAs (shRNA) of PKC-ϵ and of the PKC-ϵ inhibitor peptide on the proliferation and viability of cells. The effect of PKC-ϵ down-regulation on growth of rat breast cancer SHZ-88 cells was also measured. Results: The prolonged incubation of VSMCs with PMA for up to 72 hours resulted in attenuated cell growth rates in a time-dependent manner. The expression of PKC-ϵ, as assessed by Western blotting, was also decreased accordingly. Notably, the number of EdU-positive cells and the cell viability of VSMCs were decreased by shRNA of PKC-ϵ and the PKC-ϵ inhibitor peptide, respectively. The proliferation of rat breast cancer SHZ-88 cells was also attenuated by lentivirus-induced shRNA silencing of PKC-ϵ. Conclusions: Prolonged incubation of PMA can inhibit the expression of PKC-ϵ. The effect results in the inhibition of VSMC proliferation. PKC-ϵ silencing can also attenuate breast cancer cell growth, suggesting that PKC-ϵ may be a potential target for anti-cancer drugs.