Redistribution of cytochrome C is not an essential requirement in C-2-ceramide induced apoptosis in HL-60 cells

bcl-2 has been shown to enhance cell survival by inhibiting apoptosis. The present study investigates the potential role of bcl-2 on apoptosis in HL-6 0 cells induced by different agents. HL-60/bcl-2 and control HL-60/neo cell s were obtained by transfection of bcl-2 cDNA or the neomycin-resistant gen e, respectively. Staurosporine (STS) promoted DNA fragmentation dose-depend ently in the 6 h exposure assay while C-2-ceramide was relatively slow in t he induction of apoptosis (similar to 40% after 24 h) and required higher c oncentrations (> 20 mu M). Caspases inhibitors, Ac- YVAD-cmk (100 mu M) and zVAD-fmk (20 mu M) had no effect on DNA fragmentation themselves. However, they blocked C-2-ceramide-induced caspase-3 cleavage and apoptosis, but no t the release of cytochrome c from the mitochondria. In addition, we found that both Ac-YVAD-cmk and zVAD-fmk failed to protect STS-induced apoptosis in HL-60 cells. Overexpression of bcl-2 inhibited STS and C-2-ceramide indu ced cytochrome c redistribution, caspase-3 activation and apoptosis. These results suggest a protective role of bcl-2 in the regulation of apoptosis a nd cytochrome c release is unlikely to be involved in the final common path way in apoptosis.