Involvement of NF-kappaB in the protection of cell death by tumor necrosis factor in L929 derived TNF resistant C12 cells.

The Tumor necrosis factor (TNF)-resistant C12 cell line was established by continuous exposure of a toxic concentration of TNF to parental murine fibrosarcoma L929 cells. Introduction of the cytosolic phospholipase A2 (cPLA2) gene to C12 cells resulted in restoration of the TNF sensitive phenotype (CPL4 cells). DNA ladder formation and nuclear condensation by TNF exposure suggested that TNF induced apoptotic cell death in L929, C12 and CPL4 cells. TNF-induced activation of transcription factor nuclear factor-kappaB (NF-kappaB) was observed in all 3 cell lines. The activation reached the maximum level at 30 min after the exposure to TNF and thereafter declined slowly. The amount of activated NF-kappaB in C12 cells was about twice as high as that of L929 cells with either dose of TNF tested in this study. It was found that C12 cells expressed latent NF-kappaB twice that of L929 cells. This abundance of latent NF-kappaB would provide a higher response of NF-kappaB in C12 cells. Pretreatment with the known potent NF-kappaB inhibitor pyrolidine dithiocarbamate (PDTC) profoundly suppressed the activation of NF-kappaB induced by TNF and potentiated TNF cytotoxicity in all 3 cell lines. These results are consistent with the recently found anti-apoptotic action of NF-kappaB and suggest that NF-kappaB acts as an acquired TNF resistant factor in C12 cells.