Involvement of protein kinase C-regulated ceramide generation in inostamycin-induced apoptosis

Activation of caspases is commonly involved in the apoptosis induced by var ious anticancer drugs. However, the upstream events leading to the activati on of caspases seem to be specific to each anticancer drug. In the present study, we examined the possible involvement of protein kinase C (PKC) and c eramide generation in caspase-3(-like) protease activation induced by inost amycin, a phosphatidylinositol synthesis inhibitor. Treatment of cells with 12-O-tetrade-canoyl phorbol-13-acetate (TPA), an activator of PKC, suppres sed the release of cytochrome c from mitochondria and the activation of cas pase-3(-like) proteases in inostamycin-treated cells, but not in other anti cancer drug-treated cells. Inostamycin induced the elevation of intracellul ar ceramide levels, and fumonisin B1, an inhibitor of ceramide synthase, in hibited inostamycin-induced cytochrome c release, caspase-3(-like) protease activation, and apoptosis. Moreover, TPA also inhibited inostamycin-induce d ceramide synthesis. Taken together, our results suggest that inostamycin- induced apoptosis is mediated by PKC-regulated ceramide generation, leading to the activation of a caspase cascade. (C) 2000 Academic Press.