Unspecific activation of caspases during the induction of apoptosis by didemnin B in human cell lines

Caspases have been implicated in the induction of apoptosis in most systems studied. The importance of caspases for apoptosis was further investigated using the system of didemnin B-induced apoptosis. We found that benzyloxycarbonyl-VAD-fluoromethylketone, a general caspase inhibitor, inhibits didemnin B-induced apoptosis in HL-60 and Daudi cells. Acetyl-YVAD- chloromethylketone, a caspase-1-like activity inhibitor, inhibits didemnin B- induced apoptosis in Daudi cells, whereas the caspase-3-like activity inhibitor, acetyl-DEVD-aldehyde, has no effect. Using immunoblots to investigate cleavage of caspases-1 and -3, we found that both caspases are activated in both cell lines. We showed that the caspase substrate poly(ADP- ribose)polymerase is cleaved in these cells after didemnin B treatment. In both cell lines, poly(ADP-ribose)polymerase cleavage is inhibited by benzyloxycarbonyl-VAD-fluoromethylketone and also by acetyl-YVAD- chloromethylketone in Daudi cells. These results indicate that a caspase(s) other than caspase-3 is required for didemnin B-induced apoptosis. We show that caspases may be activated during apoptosis that are not required for the progression of apoptosis.