Deoxyribonuclease induction in apoptotic cytotoxic T lymphocytes

IL-2-dependent CTLL2 cells, upon IL-2 deprivation, die by apoptosis, which is accompanied by the fragmentation of genomic DNA. Two major deoxyribonuclease activities were detected in the extract of IL-2-deprived CTLL2 cells in a zymographic assay. They were designated nuc-58 and nuc-40, based on their apparent molecular mass of 58 and 40 kDa. The activity of both DNases was greatly induced in CTLL2 cells deprived of IL-2 or treated with the kinase inhibitor staurosporine. Deregulated expression of bcl-2 cDNA suppressed the induction of both nuclease activities. Nuc-58 was dependent on both Ca2+ and Mg2+ ions alone. Nuc-40 showed a preferential nuclear localization over that of nuc-58, which was found primarily in the cytoplasm. Optimal activity of both DNases required neutral pH and was inhibited by zinc ions. The physicochemical characteristics of the nucleases indicate that they are novel DNases associated with apoptosis in CTLL2 cells.