The role of the Cockayne syndrome proetin

在CS细胞中，细胞核和线粒体DNA中氧化DNA损伤的修复存在缺陷，这可能是该疾病的主要潜在原因。先前我们发现，CSB缺陷细胞在氧化应激后会积累氧化碱基8-羟基鸟嘌呤和8-羟基腺嘌呤，这与CSB和氧鸟嘌呤DNA糖基酶（OGG1）在体内处于一个复合物中的观察结果一致，氧鸟嘌呤DNA糖基酶是8-氧og修复的主要DNA糖基酶。我们还发现CSB蛋白与nei样DNA糖基酶NEIL1物理相互作用，NEIL1也参与氧化碱基的修复。这种相互作用显著刺激NEIL1的催化活性，包括糖基化酶和ap裂解酶。观察到CSB缺陷小鼠在脑组织中积累了明显更高水平的氧化DNA碱基，包括fapyadenine和fapyguanine，支持CSB蛋白在体内氧化损伤清除中的作用。

In CS cells, there are deficiencies in the repair of oxidative DNA damage in the nuclear and mitochondrial DNA, and this may be a major underlying cause of the disease. Previously we found that CSB-deficient cells accumulate oxidized bases, 8-hydroxyguanine and 8-hydroxyadenine, after oxidative stress, consistent with the observation that CSB and oxoguanine DNA glycosylase (OGG1), the major DNA glycosylase for 8-oxoG repair, are in a complex in vivo. We also found that the CSB protein physically interacts with the Nei-like DNA glycosylase, NEIL1, which is also involved in the repair of oxidized bases. This interaction significantly stimulates NEIL1 catalytic activities, both the glycosylase as well as the AP-lyase. The observation that CSB-deficient mice accumulate significantly higher levels of several oxidized DNA bases in brain tissue, including fapyadenine and fapyguanine, supports a role for the CSB protein in the removal of oxidized lesions in vivo. Previously we demonstrated that the CSB protein also interacts with PARP1, a protein involved in the early steps of single-strand break repair, and that these two proteins cooperate in the cellular responses to oxidative stress. CSB is a substrate for PARP-1 ribosylation and it is likely that these two proteins function together in the process of base excision. Our results indicate that the CSB protein plays an important role in the repair of oxidative DNA damage and that accumulation of unrepaired lesions, particular in target tissues, like the brain, may be relevant to the CS pathology, which is characterized by severe early onset neurodegeneration. To further explore the role of CSB in mitochondria, we evaluated the mitochondrial localization of CSB following oxidative stress. We found increased CSB localization to mitochondria following menadione treatment, which causes a form of oxidative stress. Additionally, we found reduced 8-oxo-guanine, uracil, and 5-hydroxy-uracil incision activities in CSB-deficient cells compared to wild-type cells. This deficiency correlated with a loss of mitochondrial inner membrane associated BER activities. These CSB-dependent changes had a functional consequence because we observed elevated mtDNA mutations in CSB deficient cells. Together the results suggest that CSB plays a direct role in mitochondrial BER by helping to recruit, stabilize, and/or retain BER proteins in repair complexes that in mitochondria are associated with the inner membrane.