Graduate Center for Toxicology, University of Kentucky, Lexington, KY 40536-0298, USA.
Oncogene. 2012 Apr 26;31(17):2129-39. doi: 10.1038/onc.2011.407. Epub 2011 Sep 12.
Manganese superoxide dismutase is a nuclear encoded primary antioxidant enzyme localized exclusively in the mitochondrial matrix. Genotoxic agents, such as ultraviolet (UV) radiation, generates oxidative stress and cause mitochondrial DNA (mtDNA) damage. The mtDNA polymerase (Polγ), a major constituent of nucleoids, is responsible for the replication and repair of the mitochondrial genome. Recent studies suggest that the mitochondria contain fidelity proteins and MnSOD constitutes an integral part of the nucleoid complex. However, it is not known whether or how MnSOD participates in the mitochondrial repair processes. Using skin tissue from C57BL/6 mice exposed to UVB radiation, we demonstrate that MnSOD has a critical role in preventing mtDNA damage by protecting the function of Polγ. Quantitative-PCR analysis shows an increase in mtDNA damage after UVB exposure. Immunofluorescence and immunoblotting studies demonstrate p53 translocation to the mitochondria and interaction with Polγ after UVB exposure. The mtDNA immunoprecipitation assay with Polγ and p53 antibodies in p53(+/+) and p53(-/-) mice demonstrates an interaction between MnSOD, p53 and Polγ. The results suggest that these proteins form a complex for the repair of UVB-associated mtDNA damage. The data also demonstrate that UVB exposure injures the mtDNA D-loop in a p53-dependent manner. Using MnSOD-deficient mice we demonstrate that UVB-induced mtDNA damage is MnSOD dependent. Exposure to UVB results in nitration and inactivation of Polγ, which is prevented by addition of the MnSOD mimetic Mn(III)TE-2-PyP(5+). These results demonstrate for the first time that MnSOD is a fidelity protein that maintains the activity of Polγ by preventing UVB-induced nitration and inactivation of Polγ. The data also demonstrate that MnSOD has a role along with p53 to prevent mtDNA damage.
锰超氧化物歧化酶是一种核编码的主要抗氧化酶，仅定位于线粒体基质中。遗传毒性剂，如紫外线 (UV) 辐射，会产生氧化应激并导致线粒体 DNA (mtDNA) 损伤。线粒体 DNA 聚合酶 (Polγ) 是核小体的主要组成部分，负责线粒体基因组的复制和修复。最近的研究表明，线粒体含有保真蛋白，MnSOD 是核小体复合物的组成部分。然而，目前尚不清楚 MnSOD 是否以及如何参与线粒体修复过程。使用暴露于 UVB 辐射的 C57BL/6 小鼠的皮肤组织，我们证明 MnSOD 通过保护 Polγ 的功能在防止 mtDNA 损伤方面起着关键作用。定量 PCR 分析显示，UVB 暴露后 mtDNA 损伤增加。免疫荧光和免疫印迹研究表明，UVB 暴露后 p53 易位到线粒体并与 Polγ 相互作用。用 Polγ 和 p53 抗体进行 mtDNA 免疫沉淀测定，在 p53(+/+) 和 p53(-/-) 小鼠中证明了 MnSOD、p53 和 Polγ 之间的相互作用。结果表明，这些蛋白质形成一个复合物，用于修复与 UVB 相关的 mtDNA 损伤。该数据还表明，UVB 暴露以依赖 p53 的方式损伤 mtDNA D-环。使用 MnSOD 缺陷型小鼠，我们证明了 UVB 诱导的 mtDNA 损伤依赖于 MnSOD。UVB 暴露会导致 Polγ 的硝化和失活，MnSOD 模拟物 Mn(III)TE-2-PyP(5+) 的加入可防止这种情况发生。这些结果首次表明，MnSOD 是一种保真蛋白，通过防止 UVB 诱导的 Polγ 硝化和失活来维持其活性。该数据还表明，MnSOD 与 p53 一起在防止 mtDNA 损伤方面发挥作用。
