CYTOKINE-INDUCED APOPTOSIS IN TRANSFORMED MURINE FIBROBLASTS INVOLVESSYNTHESIS OF ENDOGENOUS NITRIC-OXIDE

The purpose of this study was to determine whether the synthesis of en dogenous nitric oxide (NO) is involved in the apoptosis of murine L929 transformed fibroblasts. L929 parental cells and L929 cells selected for resistance to tumor necrosis factor (TNF-alpha) were incubated in vitro with various concentrations of TNF-alpha, interleukin-1, and lip opolysaccharide (LPS) in the presence or absence of mouse interferon-g amma (IFN-gamma). The combination of subthreshold concentrations of IF N-gamma with the cytokines or LPS produced significant cell death with in 48 h incubation. This cell death was associated with the induction of high levels of NO. Both cell death and NO production were significa ntly inhibited by the addition of N(G)-methyl-L-arginine (NMA), a spec ific inhibitor of nitric oxide synthase. The synergistic cytotoxicity was associated with extensive internucleosomal DNA fragmentation. NMA also inhibited this process. These data demonstrate the involvement of endogenous NO in cytokine-induced apoptosis of transformed cells.