Down-regulation of protein kinase C attenuates the oxidant hydrogen peroxide-mediated activation of phospholipase A2 in pulmonary vascular smooth muscle cells

Abstract

Exposure of rabbit pulmonary vascular smooth muscle cells to H2O2 dose-dependently stimulates the cell membrane associated protein kinase C (PKC) activity, phospholipase A2 (PLA2) activity, phospholipase A2 (PLA2) activity, and arachidonic acid (AA0) release. Pretreatment of the cells with staurosporine (an inhibitor of PKC) prevents AA release and PLA2 activity caused by H2O2. Treatment of the cells with 4 beta-PMA (an active phorbol ester), or 4 alpha-PMA (an inactive phorbol ester) does not affect basal AA release. In contrast, 4 beta-PMA significantly stimulates the cell membrane associated PKC activity. Treatment of the cells with 4 beta-PMA for a short time (up-regulation of PKC) augments PLA2 activity and AA release caused by a sub-optimal dose of H2O2 (0.4 mM). Under this condition, staurosporine prevents the stimulatory effects of 4 beta-PMA on membrane PLA2 activity, and AA release. In contrast to the up-regulation, pretreatment with 4 beta-PMA for a longer time (down-regulation of PKC) does not appreciably augment PLA2 activity and AA release caused by 0.4 mM H2O2. Treatment of the cells with an intracellular Ca2+ antagonist TBM-8 prevents H2O2 induced membrane PLA2 activity and AA release without affecting membrane PKC activity. Treatment of the cells with TMB-8 before addition of 4 beta-PMA (up-regulation of PKC) followed by incubation with 0.4 mM H2O2 does not augment PLA2 activity and AA release, although membrane PKC activity increases under this condition.