CHEMOTHERAPEUTIC DRUG ACTIVATION OF THE AP24 PROTEASE IN APOPTOSIS - REQUIREMENT FOR CASPASE 3-LIKE-PROTEASES

AP24 is a serine protease that is activated during TNF or UV light-ind uced apoptosis and stimulates DNA fragmentation in isolated nuclei. Th e present study determined whether apoptosis induced by chemotherapeut ic drugs resulted in activation of AP24 and examined the possible rela tionship to caspase activity. We showed that an inhibitor of AP24, DK1 20, could block DNA fragmentation induced in three leukemia cell lines (U937, HL-60, and CEM) by various DNA-damaging drugs including etopos ide, camptothecin, chlorambucil, and the CC1065-related drug, YW201. E toposide-induced activation of intracellular DEVD-pNa cleaving activit y and apoptosis was suppressed by low micromolar concentrations of cel l-permeable inhibitors of caspase-3. Furthermore, these inhibitors als o suppressed activation of AP24. In contrast, DK120 did not prevent et oposide activation of DEVD-pNa cleaving activity, nor did it prevent c leavage of poly(ADP-ribose) polymerase. AP24 isolated from apoptotic c ells following treatment with etoposide activated DNA fragmentation in isolated normal nuclei and was inhibited by DK120, but not by caspase inhibitors. This evidence shows that activation of caspase 3-like pro teases generates signals that contribute to the activation of AP24 whi ch may then induce nuclear DNA fragmentation in chemotherapeutic drug- induced apoptosis. (C) 1998 Academic Press.