Expression of cyclin A in human leukemia cell line HL-60 following treatment with doxorubicin and etoposide: the potential involvement of cyclin A in apoptosis.

We investigated expression of cyclin A in HL-60 cells after induction of apoptosis with doxorubicin and etoposide. Following apoptotic trigger, both cells arrested in G2/M phase of the cell cycle and changes in morphology were noticed. Moreover, compared to control, the number of cells with cyclin A expression was changed and translocation of this protein from the nucleus to the cytoplasm was observed. The decrease in the number of cells with cyclin A expression, followed by the increase, and cyclin A distribution throughout the cell, appeared to be dose-dependent. Cells treated with lower doses of doxorubicin and etoposide as well as the untreated cells were found to have cyclin A scattered mainly throughout the nucleus. However, immunogold labeling of cyclin A in both cell lines treated with 5- and 10-microM doses of doxorubicin, and 20 and 200 microM of etoposide was observed more often in the cytoplasm than in the nucleus. Cells with features of apoptosis with bodies resembling micro-nuclei labeled with gold particles for cyclin A were recognized. However, the small amount of giant cells was also seen. These results suggest that cyclin A expression is linked to cell death pathways.