Involvement of cytochrome c and caspases in apoptotic cell death of human submandibular gland ductal cells induced by concanamycin A

In the present study, we found that a specific inhibitor of vacuolar type H+-ATPase (V-ATPase), concanamycin A, induced apoptosis in a human submandibular gland ductal cancer cell line, HSG. Immunoblot analysis revealed that cytochrome c was released from mitochondria into the cytoplasm when HSG cells were cultured with concanamycin A for 6 h. The maximum activities of caspase-3 and -9 were reached in HSG cells after 18 and 12 h culture of concanamycin A, respectively. Both caspase-3 and -9 were cleaved to an active form in HSG cells cultured with concanamycin A. Interestingly, concanamycin A decreased the level of heat shock protein 27 (HSP27) in HSG cells. Taken together, these findings suggest that apoptosis in HSG cells induced by concanamycin A is regulated by cytochrome c released from mitochondria into cytoplasm and the subsequent activation of caspases, and that HSP27 may interfere with caspase-dependent apoptotic cell death induced by concanamycin A.