TNF-ALPHA ALTERS MITOCHONDRIAL-MEMBRANE POTENTIAL IN L929 BUT NOT IN TNF-ALPHA-RESISTANT L929.12 CELLS - RELATIONSHIP WITH THE EXPRESSION OF STRESS PROTEINS, ANNEXIN-1 AND SUPEROXIDE-DISMUTASE ACTIVITY

Tumour necrosis factor alpha (TNF alpha) cytotoxicity is mediated, at least in part, by oxidative stress and phospholipase A2 activation. Th e first post-receptor events to be observed in TNF alpha-sensitive lin es are the generation of superoxide anion (O-2(-)) within the mitochon dria and the activation of phospholipase A2. Using the lipophilic dye JC-1 to determine mitochondrial membrane potential, we showed that TNF alpha induces time-dependent alterations in mitochondrial membrane po tential in L929 cells but not in the TNF alpha-resistant L929.12 subcl one. Heat shock (HS) proteins (HSP) and superoxide dismutase (SOD) hav e been shown to protect cells from TNF alpha cytotoxicity, while gluco se regulated proteins (GRP) and annexins might also be involved in cel lular protection. We thus compared the expression of HSP, grp78 and an nexin 1 as well as SOD activity in TNF alpha sensitive and resistant l ines. We found no difference in the expression of HSP, grp78 or annexi n 1, but an increase in the constitutive activity of SOD in the L929.1 2 cells as compared to L929. Furthermore, SOD was inducible by TNF alp ha in L929 cells, but not in L929.12 cells. These data suggest that in TNF alpha-resistant Lines, mitochondrial damage by TNF alpha is preve nted by an increase in SOD rather than in overexpression of stress pro teins or annexins.