Caspase-3 controls both cytoplasmic and nuclear events associated with Fas-mediated apoptosis in vivo

Both caspase-1- and caspase-3-like activities are required for Fas-mediated apoptosis. However, the role of caspase-1 and caspase-3 in mediating Fas-induced cell death is not clear. We assessed the contributions of these caspases to Fas signaling in hepatocyte cell death in vitro. Although wild-type, caspase-1(−/−), and caspase-3(−/−) hepatocytes were killed at a similar rate when cocultured with FasL expressing NIH 3T3 cells, caspase-3(−/−) hepatocytes displayed drastically different morphological changes as well as significantly delayed DNA fragmentation. For both wild-type and caspase-1(−/−) apoptotic hepatocytes, typical apoptotic features such as cytoplasmic blebbing and nuclear fragmentation were seen within 6 hr, but neither event was observed for caspase-3(−/−) hepatocytes. We extended these studies to thymocytes and found that apoptotic caspase-3(−/−) thymocytes exhibited similar “abnormal” morphological changes and delayed DNA fragmentation observed in hepatocytes. Furthermore, the cleavage of various caspase substrates implicated in mediating apoptotic events, including gelsolin, fodrin, laminB, and DFF45/ICAD, was delayed or absent. The altered cleavage of these key substrates is likely responsible for the aberrant apoptosis observed in both hepatocytes and thymocytes deficient in caspase-3.