C-JUN AP-1 AS POSSIBLE MEDIATORS OF TUMOR NECROSIS FACTOR-ALPHA-INDUCED APOPTOTIC RESPONSE IN MOUSE JB6 TUMOR-CELLS/

Sensitivity to cell killing by tumor necrosis factor (TNF)-alpha was s een in the JB6-derived transformed mouse RT101 cell variants previousl y described as resistant to 12-O-tetradecanoylphorbol-13-acetate (TPA) -induced killing, while the TPA-sensitive variants were resistant to k illing by TNF-alpha. Morphological and biochemical changes characteris tic of apoptosis were found to precede TNF-alpha-induced cell death in TNF-alpha-sensitive (TNFs) but not TNF-alpha-resistant (TNFr) cells. In TNFr cells, TNF-alpha increased the cell cycle rate. The onset of c ellular damage in TNFs cells, as indicated by propidium iodide uptake, was seen as early as 6 h after TNF-alpha treatment. 4,6-diamidino-2-p henylindole staining revealed chromosomal condensation approximately 4 6 h after TNF-alpha treatment. The DNA oligonucleosomal ladder of 180 bp and its multiples, a characteristic feature of apoptosis, was seen at 48 h. Little or no significant differences were found in the basal or induced levels of mRNA expression of several potential apoptosis me diator genes or apoptosis inhibitor genes. A dephosphorylated species of anti-c-Jun immunoprecipitated protein appeared in TNFs cells at 3 h posttreatment, accompanied by a parallel increase in AP-1 activity. H igher constitutive levels of the antioxidant enzymes superoxide dismut ase and catalase were found in TNFr cells, but TNF-alpha did not signi ficantly affect the activities of these enzymes or differentially indu ce their expression. The findings suggest that the preferential and tr ansient increase in c-Jun dephosphorylation and AP-1 transcriptional a ctivity may contribute to the preferential apoptotic response in TNFs cells; and that the greater constitutive oxidant defense in TNFr cells may contribute to their resistance.