[The mechanism of apoptosis induced by anticancer agents in human leukemia HL-60 cells].

The present study was designed to investigate the contribution of proteases in anticancer agents-induced apoptosis of human leukemia HL-60 cells. A serine protease inhibitor TPCK and an ICE-like protease inhibitor VAD-FMK prevented etoposide, camptothecin and ara-C-induced internucleosomal DNA cleavage. Using a cell-free system, we have examined the inhibitory mechanism of these inhibitors on etoposide-induced internucleosomal DNA cleavage. We found that cell lysates prepared from etoposide-treated HL-60 cells undergoing apoptosis contain the significant activity to induce internucleosomal DNA fragmentation in isolated nuclei. On the other hand, we could not detect such activity in the cell lysates from untreated HL-60 cells. Treatment of the cell lysates with a serine protease inhibitor TPCK abrogated the DNA fragmenting activity. An ICE-like protease inhibitor VAD-FMK had no effect on this DNA fragmenting activity in vitro. However, the formation of TPCK-sensitive DNA fragmenting activity in etoposide-treated cells was blocked by the VAD-FMK. These data indicate that serine and ICE-like proteases may be involved in etoposide-induced apoptosis at the different stages, and especially a serine protease may be closely associated with the final step for induction of DNA fragmentation during apoptosis in HL-60 cells.