ABSTRACT
PURPOSE: The widely used chemotherapeutic agents exert their anti-cancer effects by the inducing of apoptosis in sensitive tumor cells. Recently, the protective effect of zinc ion on apoptosis has been reproted. However, it is not well understood about the effects of zinc ion on the anticancer drug-induced apoptosis. In general, zinc inhibits a nuclear endonuclease, thereby causing inhibition of apoptosis. In addition, there is other possibility that zinc can prevent apoptosis at earlier stage such as the activation of caspase-3 than that of the activation of endonuclease. Therefore, we investigated the effects of zinc ion on the apoptosis of HL-60 cells caused by adriamycin (ADR). METHODS: HL-60 cells were cultured in RPMI 1640 and treated with various concentrations and time periods of ADR with or without pretreatment of zinc ion. Cellular DNA was extracted and analyzed by electrophoresis on a 1.5% agarose gel to detect DNA fragmentation. The activity of caspase-3 was measured by the proteolytic cleavage of the fluorogenic substrate DEVD-AMC. Poly-ADP-ribose polymerase (PARP) cleavage was analyzed by western blotting using anti-PARP antibody. RESULTS: ADR induced the apoptotic death of HL-60 cells in a dose and time dependent manner, which was characterized by increasing ladder-pattern DNA fragmentation. Pretreatment of HL-60 cells with zinc ion caused potent inhibition of ADR-induced apoptosis. Consistent with apoptotic death of HL-60 cells, ADR induced the catalytic activation of caspase-3. After pretreatment of zinc ion, the activation of caspase-3 and the proteolysis of PARP induced by ADR were markedly inhibited. CONCLUSION: These results indicate that zinc ion prevents the ADR-induced apoptosis of HL-60 cells through an inhibition of caspase-3 activity, which occurs upstream from the activation of endonuclease.