Chemotherapeutic Agent CPT-11 Induces the New Expression of the Apoptosis Initiator to the Cytoplasm

CPT-11, a derivative of camptothecin, induced apoptotic cell death characterized by chromosomal DNA fragmentation in human hepatoma PLC cellsin vitro.Cell viability of PLC cells was significantly decreased by CPT-11 in a dose-dependent manner, and CPT-11-induced cytotoxic activity was completely prevented by an interleukin-1β converting enzyme-like protease inhibitor YVAD and a protein synthesis inhibitor cycloheximide. To examine the roles of the cytoplasm and the nucleus in CPT-11-induced apoptosis, we prepared cytoplasts from PLC cells and nuclei from rat hepatocytes (RHN). Apoptotic cell death as characterized by cell fragmentation was observed in whole PLC cells but not in PLC cytoplasts after incubation with CPT-11. In addition, CPT-11 could not induce chromosomal DNA fragmentation in RHN. In contrast, the extracts of CPT-11-treated PLC cells, which mainly contained cytosol proteins, induced chromosomal DNA fragmentation of RHN in a dose-dependent manner. These results indicate that CPT-11-induced apoptosis required the presence of both the cytoplasm and the nucleus and suggest that the apoptosis required thede novosynthesis of an apoptosis initiator.