Effect of protein kinase C alpha, caspase‐3, and survivin on apoptosis of oral cancer cells induced by staurosporine 1

Aim: To elucidate inhibition of protein kinase C α (PKC α) activity by staurosporine on apoptosis of oral cancer cell line tongue squamous cell carcinoma (TSCCa) cells and to clarify the role of survivin and caspase‐3 in mediating apoptosis. Methods: TSCCa cell viability was measured by MTT assay after 100 nmol/L staurosporine treatment. Apoptotic cells were identified by using phase contrast microscopy, acridine orange/ethidium bromide staining, and flow cytometry. Level of PKC α and its subcellular location were investigated using Western blot analysis. Expression of survivin and caspase‐3 were evaluated using immunocytochemistry. Results: Staurosporine significantly inhibited the cell viability of TSCCa cells in a dose‐ and time‐dependent manner. Marked cell accumulation in G 2 /M phase was observed after 100 nmol/L staurosporine exposure for 6 h and 12 h. In addition, the percentage of apoptosis increased in a time‐dependent manner, from 2.9% in control cultures to approximately 27.4% at 100 nmol/L staurosporine treatment for 24 h. Staurosporine displayed difference in inhibitory efficacy between cytosolic and membrance‐derived PKC α. The content of PKCα in membrane versus cytosol decreased quickly, from 0.45 in ethanol‐treated control cultures to 0.18 after staurosporine exposure for 24 h ( P <0.01). After treatment with staurosporine, a time‐dependent reduction of survivin and an activation of caspase‐3 were observed in TSCCa cells. Conclusion: Staurosporine inhibited cell viability and promoted apoptosis in TSCCa cells. Inhibition of PKCα activity might be a potential mechanism for staurosporine to induce apoptosis in this cell line. The cleavage of survivin and activation of caspase‐3 signaling pathway might contribute to PKC α inhibition‐induced apoptosis.