Tumor necrosis factor-alpha increases Mn-SOD expression: protection against oxidant injury.
Antioxidant enzymes, including superoxide dismutase, are important for protecting the lung against O2 injury. Manganese superoxide dismutase (Mn-SOD) is a superoxide anion (O2-.) scavenger located in the mitochondria, a primary site of O2-. production during hyperoxia. We studied the effects of tumor necrosis factor (TNF-alpha), a macrophage-derived cytokine, on Mn-SOD expression in human pulmonary adenocarcinoma cells. TNF-alpha significantly increased Mn-SOD activity and mRNA in a dose-and time-dependent manner. Mn-SOD activity was increased 3-fold and mRNA 20-fold after a 48-h incubation with TNF-alpha (25 ng/ml). To examine the mechanism of this increase, cells were incubated for 48 h with TNF-alpha (25 ng/ml) with or without cycloheximide (10 microns) or actinomycin D (10 micrograms/ml). Actinomycin D blocked the induction of Mn-SOD mRNA by TNF-alpha, but cycloheximide did not. These findings suggest that the effect of TNF-alpha requires gene transcription but not synthesis of new protein intermediates. To test the hypothesis that increased Mn-SOD protects against oxidative injury, pulmonary adenocarcinoma cells were incubated in TNF-alpha (25 ng/ml) for 48 h and then exposed to paraquat (PQ+), an intracellular O2-. generator. Cells pretreated with TNF-alpha had significantly improved survival in PQ+ compared with controls. At the LD50 (6 microns) for control cells, 95% of TNF-alpha-treated cells survived, 85% at the LD75 (10 microns), and 77% at the LD90 (14 microns). Our results suggest that the induction of Mn-SOD by TNF-alpha in pulmonary adenocarcinoma cells is pretranslationally mediated and that increasing Mn-SOD activity with TNF-alpha confers protection against O2 radicals.
Warner
B B
BB
Department of Pediatrics, University of Cincinnati College of Medicine, Ohio 45267.
Burhans
M S
MS
Clark
J C
JC
Wispé
J R
JR
D000199:Actins / Q000235:genetics; D000230:Adenocarcinoma; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007527:Isoenzymes / Q000235:genetics* / Q000378:metabolism; D007700:Kinetics; D008175:Lung Neoplasms; D010269:Paraquat / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000187:drug effects / Q000235:genetics*; D011994:Recombinant Proteins / Q000494:pharmacology; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism; D013481:Superoxides / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D000199:Actins; D007527:Isoenzymes; D012333:RNA, Messenger; D011994:Recombinant Proteins; D014409:Tumor Necrosis Factor-alpha; D013481:Superoxides; D003609:Dactinomycin; D003513:Cycloheximide; D013482:Superoxide Dismutase; D010269:Paraquat