BAPTA blocks DNA fragmentation and chromatin condensation downstream of caspase-3 and DFF activation in HT-induced apoptosis in HL-60 cells

DFF ((DNA Fragmentation Factor) is a heterodimer composed of 40 kDa (DFF40, CAD) and 45 kDa (DFF45, ICAD) subunits. During apoptosis, activated caspas e-3 cleaves DFF45 and activates DFF40, a DNase that targets nucleosomal lin ker region and cleaves chromatin DNA into nucleosomal fragments. We have pr eviously reported that HT induced apoptosis in HL-60 cells, and intracellul ar Ca2+ chelator BAPTA blocked apoptosis-associated DNA fragmentation induc ed by HT. We report here that HT also induced activation of caspase-3 and c leavage of DFF45. BAPTA prevented neither the caspase-3 activation nor the cleavage of DFF45. Mitochondrial membrane potential was disrupted in BAPTA- AM treated cells. However, BAPTA did prevent DNA fragmentation and chromati n condensation in HT-treated cells. These data suggest a novel role for int racellular calcium in regulating apoptotic nuclease that causes DNA fragmen tation and chromatin condensation.