Involvement of caspase 3-activated DNase in internucleosomal DNA cleavage induced by diverse apoptotic stimuli

Degradation of chromosomal DNA into nucleosome-sized fragments is one of th e characteristics of apoptotic cell death. Here, we examined whether caspas e-activated DNase (CAD) is responsible for the DNA fragmentation that occur s upon exposure to various apoptotic stimuli. When human Jurkat cells were exposed to etoposide, or UV or gamma radiation, a caspase-3-like protease w as activated, and nuclear DNA was fragmented. Human TF-1 cells, which are d ependent on granulocyte-macrophage colony-stimulating factor (GM-CSF), also underwent apoptosis accompanied by the activation of caspase-3-like protea se and DNA fragmentation, when cultured without the cytokine. Both Jurkat a nd TF-1 cells expressed two forms of ICAD, ICAD-L and ICAD-S, which were cl eaved upon exposure to these apoptotic stimuli. Among eight different caspa ses examined, recombinant caspases 3 and 7 specifically cleaved ICAD synthe sized in a cell-free system. An expression plasmid containing mouse ICAD-L mutated at the caspase-3-recognition sites was then introduced into Jurkat and TF-1 cells. When the transformants were induced to undergo apoptosis (b y treatment with etoposide, UV or gamma radiation for Jurkat cells, or fact or withdrawal for TF-1 cells) they did not show DNA fragmentation, although they still died as a result of these stimuli. These results indicated that CAD, released from ICAD by caspase activation, is involved in the nuclear DNA fragmentation induced by these apoptotic stimuli.