Acta Pharmacologica Sinica 2005 November; 26 (11): 1365-1372; doi: 10.1111/j.1745-7254.2005.00205.x

Aim: To elucidate inhibition of protein kinase C a (PKC a) 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 a 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 G₂/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 a. The content of PKCa 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 PKCa activity might be a potential mechanism for staurosporine to induce apoptosis in this cell line. The clea-vage of survivin and activation of caspase-3 signaling pathway might contribute to PKC a inhibition-induced apoptosis.

Keywords: protein kinase C alpha; caspase-3; survivin protein; apoptosis; staurosporine; carcinoma, squamous cell; mouth