Ho Y S, Dey M S, Crapo J D
Department of Medicine, Duke University Medical Center, Durham, North Carolina 27710, USA.
Am J Physiol. 1996 May;270(5 Pt 1):L810-8. doi: 10.1152/ajplung.1996.270.5.L810.
To understand the molecular mechanisms that upregulate the activities of pulmonary antioxidant enzymes in adult rats during exposure to 85% oxygen, the relative contents of corresponding mRNA in normal and hyperoxic lungs were determined. Hyperoxic exposure drastically induced the expression of lung manganese-containing superoxide dismutase (MnSOD) mRNA. Maximal induction of MnSOD mRNA occurred at days 3 and 5 of exposure to hyperoxia, reaching a 600 and a 340% increase over the levels of air-exposed rats, respectively. In addition, hyperoxia induced lung mRNA for glucose-6-phosphate dehydrogenase, glutathione peroxidase, glyceraldehyde-3-phosphate dehydrogenase, alpha-tubulin, and gamma-actin to different extends at various days of exposure. Hyperoxia had little or no effect on the levels of mRNA for copper/zinc-containing superoxide dismutase (CuZnSOD), catalase, heat shock protein (HSP70), and creatine kinase. Nuclear run-on experiments showed that the transcriptional rate of the MnSOD gene is enhanced in hyperoxic rat lungs by approximately 400% at day 3 of exposure compared with that of controls. The specific activities of CuZnSOD and MnSOD in these lung samples per unit of lung protein or DNA were also determined. The activity of CuZnSOD in hyperoxic lungs was found to be unchanged compared with controls, except a 20% decrease at day 7 of exposure when standardized against protein content of lung homogenate. Changes of CuZnSOD activity were more dramatic in hyperoxic lungs (a 40% increase at days 3, 5, 7, and 14 of exposure) when enzyme activity was normalized using lung DNA content. Surprisingly, no proportional increase of lung MnSOD enzyme activity was observed at days 3 and 5 of oxygen exposure. The increase of MnSOD activity per unit of lung protein also did not parallel the increase in MnSOD protein content at days 5, 7, and 14 of exposure. These data suggest that, in addition to transcriptional activation, translational and/or posttranslational regulation of the MnSOD gene expression may play a critical role in controlling lung MnSOD activity on hyperoxic exposure.
为了解成年大鼠在暴露于85%氧气期间肺抗氧化酶活性上调的分子机制，测定了正常和高氧肺中相应mRNA的相对含量。高氧暴露显著诱导肺含锰超氧化物歧化酶（MnSOD）mRNA的表达。MnSOD mRNA的最大诱导在高氧暴露的第3天和第5天出现，分别比空气暴露大鼠的水平增加了600%和340%。此外，高氧在暴露的不同天数不同程度地诱导肺中葡萄糖-6-磷酸脱氢酶、谷胱甘肽过氧化物酶、甘油醛-3-磷酸脱氢酶、α-微管蛋白和γ-肌动蛋白的mRNA表达。高氧对含铜/锌超氧化物歧化酶（CuZnSOD）、过氧化氢酶、热休克蛋白（HSP70）和肌酸激酶的mRNA水平几乎没有影响。核转录实验表明，与对照组相比，在暴露第3天高氧大鼠肺中MnSOD基因的转录率提高了约400%。还测定了这些肺样本中每单位肺蛋白或DNA的CuZnSOD和MnSOD的比活性。发现高氧肺中CuZnSOD的活性与对照组相比没有变化，但在暴露第7天以肺匀浆蛋白含量标准化时降低了20%。当以肺DNA含量标准化酶活性时，高氧肺中CuZnSOD活性的变化更显著（在暴露第3、5、7和14天增加40%）。令人惊讶的是，在氧气暴露的第3天和第5天未观察到肺MnSOD酶活性成比例增加。在暴露第5、7和14天，每单位肺蛋白的MnSOD活性增加也与MnSOD蛋白含量的增加不平行。这些数据表明，除了转录激活外，MnSOD基因表达的翻译和/或翻译后调控可能在高氧暴露时控制肺MnSOD活性中起关键作用。
