BUFALIN INDUCES APOPTOSIS AND INFLUENCES THE EXPRESSION OF APOPTOSIS-RELATED GENES IN HUMAN LEUKEMIA-CELLS

A low concentration of bufalin, a component of bufadienoides in the tr aditional Chinese medicine chan'su, was shown previously to induce dif ferentiation of a broad range of human leukemia cell lines. In the pre sent study, we found that bufalin at concentrations of 10(-7) M and hi gher induced apoptosis in human leukemia cells, such as HL60, ML1, but not in mouse leukemia M1 cells. A mere 15 min pretreatment of HL60 ce lls with 10(-6) M bufalin, followed by incubation for 15 h without buf alin, caused fragmentation of DNA and a decrease in cell viability, in dicating that the signal for induction of apoptosis is triggered rapid ly upon treatment with bufalin. Bufalin-induced apoptosis in HL60 cell s was inhibited by ZnCl2, an inhibitor of endonuclease, but not by cyc loheximide, an inhibitor of protein synthesis. Northern blot analysis revealed that the levels of expression of the c-myc and bcl-2 genes in HL60 cells decreased with time after treatment with bufalin, These re sults suggest that bufalin induces apoptosis specifically in human leu kemia cells by altering the expression of these genes involved in apop tosis.