Role of calcium in apoptosis of HL-60 cells induced by harringtonine.

The effect of Ca(2+) on HT-induced apoptosis in HL-60 cells was examined. Characteristics of apoptosis induced by harringtonine (HT) or campothecin (CAM) could not be abolished by extracellular calcium chelator EGTA; however, an intracellular Ca(2+) chelator BAPTA-AM could block HT or CAM-induced HL-60 cell apoptosis. Requirement of intracellular calcium for HT-induced apoptosis is further supported by the fact that intracellular Ca(2+) -depleted HL-60 cells could not undergo HT-induced apoptosis. No significant increase of intracellular Ca(2+) was found after HT treatment. By using video enhancement contrast microscopy (VEC), the dynamic changes of intracellular calcium distribution over the whole period of apoptosis in the same individual cell were detected. The results demonstrated the movement of Ca(2+) from cytosol to nucleus after initiation of apoptosis by treatment with HT.