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Involvement of protein kinase C-regulated ceramide generation in inostamycin-induced apoptosis
M Kawatani1, S Simizu, H Osada
1Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Yokohama, 223-8522, Japan.
Abstract:
Activation of caspases is commonly involved in the apoptosis induced by various anticancer drugs. However, the upstream events leading to the activation 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 ceramide generation in caspase-3(-like) protease activation induced by inostamycin, a phosphatidylinositol synthesis inhibitor. Treatment of cells with 12-O-tetradecanoyl phorbol-13-acetate (TPA), an activator of PKC, suppressed the release of cytochrome c from mitochondria and the activation of caspase-3(-like) proteases in inostamycin-treated cells, but not in other anticancer drug-treated cells. Inostamycin induced the elevation of intracellular ceramide levels, and fumonisin B1, an inhibitor of ceramide synthase, inhibited inostamycin-induced cytochrome c release, caspase-3(-like) protease activation, and apoptosis. Moreover, TPA also inhibited inostamycin-induced 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.
Insights
Inostamycin triggers apoptosis via protein kinase C (PKC)-regulated ceramide generation, activating caspase proteases. This mechanism is specific to inostamycin, unlike other anticancer drugs, highlighting a novel pathway in cancer drug-induced cell death.
Area of Science:
- Biochemistry
- Cell Biology
- Pharmacology
Background:
- Caspase activation is a common hallmark of anticancer drug-induced apoptosis.
- Upstream signaling pathways leading to caspase activation are diverse and drug-specific.
Purpose of the Study:
- To investigate the roles of protein kinase C (PKC) and ceramide generation in caspase-3(-like) protease activation by inostamycin.
- To elucidate the specific mechanism of inostamycin-induced apoptosis.
Main Methods:
- Cells were treated with inostamycin, a phosphatidylinositol synthesis inhibitor.
- Protein kinase C (PKC) activation was modulated using 12-O-tetradecanoyl phorbol-13-acetate (TPA).
- Ceramide synthesis was inhibited using fumonisin B1.
Main Results:
- TPA suppressed inostamycin-induced cytochrome c release and caspase-3(-like) protease activation.
- Inostamycin treatment led to increased intracellular ceramide levels.
- Fumonisin B1 inhibited inostamycin-induced apoptosis, cytochrome c release, and caspase activation.
- TPA inhibited inostamycin-induced ceramide synthesis.
Conclusions:
- Inostamycin-induced apoptosis is mediated by a pathway involving PKC-regulated ceramide generation.
- This ceramide generation leads to the activation of a caspase cascade, resulting in apoptosis.
- The findings reveal a specific apoptotic mechanism for inostamycin distinct from other anticancer agents.