Stage-specific expression of DNasegamma during B-cell development and its role in B-cell receptor-mediated apoptosis...

Here, we describe the non-redundant roles of caspase-activated DNase (CAD) and DNasegamma during apoptosis in the immature B-cell line WEHI-231. These cells induce DNA-ladder formation and nuclear fragmentation by activating CAD during cytotoxic drug-induced apoptosis. Moreover, these apoptotic manifestations are accompanied by inhibitor of CAD (ICAD) cleavage and are abrogated by the constitutive expression of a caspase-resistant ICAD mutant. No such nuclear changes occur during oxidative stress-induced necrosis, indicating that neither CAD nor DNasegamma functions under necrotic conditions. Interestingly, the DNA-ladder formation and nuclear fragmentation induced by B-cell receptor ligation occur in the absence of ICAD cleavage and are not significantly affected by the ICAD mutant. Both types of nuclear changes are preceded by the upregulation of DNasegamma expression and are strongly suppressed by 4-(4,6-dichloro-[1, 3, 5]-triazin-2-ylamino)-2-(6-hydroxy-3-oxo-3H-xanthen-9-yl)-benzoic acid (DR396), which is a specific inhibitor of DNasegamma. Our results suggest that DNasegamma provides an alternative mechanism for inducing nuclear changes when the working apoptotic cascade is unsuitable for CAD activation.