Warner B B, Burhans M S, Clark J C, Wispé J R
Department of Pediatrics, University of Cincinnati College of Medicine, Ohio 45267.
Am J Physiol. 1991 Apr;260(4 Pt 1):L296-301. doi: 10.1152/ajplung.1991.260.4.L296.
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.
包括超氧化物歧化酶在内的抗氧化酶对于保护肺部免受氧损伤至关重要。锰超氧化物歧化酶（Mn-SOD）是一种位于线粒体中的超氧阴离子（O2-·）清除剂，线粒体是高氧期间O2-·产生的主要部位。我们研究了巨噬细胞衍生的细胞因子肿瘤坏死因子（TNF-α）对人肺腺癌细胞中Mn-SOD表达的影响。TNF-α以剂量和时间依赖性方式显著增加Mn-SOD活性和mRNA水平。与TNF-α（25 ng/ml）孵育48小时后，Mn-SOD活性增加了3倍，mRNA增加了20倍。为了研究这种增加的机制，将细胞与TNF-α（25 ng/ml）一起孵育48小时，同时加入或不加入放线菌酮（10微克）或放线菌素D（10微克/毫升）。放线菌素D阻断了TNF-α对Mn-SOD mRNA的诱导，但放线菌酮没有。这些发现表明，TNF-α的作用需要基因转录，但不需要新蛋白质中间体的合成。为了验证增加的Mn-SOD可预防氧化损伤这一假设，将肺腺癌细胞在TNF-α（25 ng/ml）中孵育48小时，然后暴露于百草枯（PQ+），一种细胞内O2-·生成剂。与对照组相比，用TNF-α预处理的细胞在PQ+中的存活率显著提高。在对照细胞的半数致死剂量（LD50，6微克）下，95%的TNF-α处理细胞存活，在LD75（10微克）时为85%，在LD90（14微克）时为77%。我们的结果表明，TNF-α在肺腺癌细胞中对Mn-SOD的诱导是在翻译前介导的，并且用TNF-α增加Mn-SOD活性可提供对O2自由基的保护作用。
