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Abstract
Tumour necrosis factor a (TNFα) cytotoxicity is mediated, at least in part, by oxidative stress and phospho-lipase A2 activation. The first post-receptor events to be observed in TNFα-sensitive lines are the generation of superoxide anion (O2−) within the mitochondria and the activation of phospholipase A2. Using the lipophilic dye JC-1 to determine mitochondrial membrane potential, we showed that TNFα induces time-dependent alterations in mitochondrial membrane potential in L929 cells but not in the TNFα-resistant L929.12 subclone. Heat shock (HS) proteins (HSP) and superoxide dismutase (SOD) have been shown to protect cells from TNFα cytotoxicity, while glucose regulated proteins (GRP) and annexins might also be involved in cellular protection. We thus compared the expression of HSP, grp78 and annexin 1 as well as SOD activity in TNFα sensitive and resistant lines. We found no difference in the expression of HSP, grp78 or annexin 1, but an increase in the constitutive activity of SOD in the L929.12 cells as compared to L929. Furthermore, SOD was inducible by TNFα in L929 cells, but not in L929.12 cells. These data suggest that in TNFα-resistant lines, mitochondrial damage by TNFα is prevented by an increase in SOD rather than in overexpression of stress proteins or annexins.