Data_Sheet_1_Xeroderma Pigmentosum C (XPC) Mutations in Primary Fibroblasts Impair Base Excision Repair Pathway and Increase Oxidative DNA Damage.docx

Xeroderma Pigmentosum C (XPC) is a multi-functional protein that is involved not only in the repair of bulky lesions, post-irradiation, via nucleotide excision repair (NER) per se but also in oxidative DNA damage mending. Since base excision repair (BER) is the primary regulator of oxidative DNA damage, we characterized, post-Ultraviolet B-rays (UVB)-irradiation, the detailed effect of three different XPC mutations in primary fibroblasts derived from XP-C patients on mRNA, protein expression and activity of different BER factors. We found that XP-C fibroblasts are characterized by downregulated expression of different BER factors including OGG1, MYH, APE1, LIG3, XRCC1, and Polβ. Such a downregulation was also observed at OGG1, MYH, and APE1 protein levels. This was accompanied with an increase in DNA oxidative lesions, as evidenced by 8-oxoguanine levels, immediately post-UVB-irradiation. Unlike in normal control cells, these oxidative lesions persisted over time in XP-C cells having lower excision repair capacities. Taken together, our results indicated that an impaired BER pathway in XP-C fibroblasts leads to longer persistence and delayed repair of oxidative DNA damage. This might explain the diverse clinical phenotypes in XP-C patients suffering from cancer in both photo-protected and photo-exposed areas. Therapeutic strategies based on reinforcement of BER pathway might therefore represent an innovative path for limiting the drawbacks of NER-based diseases, as in XP-C case.

着色性干皮病C型（XPC）是一种多功能蛋白，不仅通过核苷酸切除修复（NER）本身参与照射后粗大损伤的修复，还涉及氧化性DNA损伤的修复。鉴于碱基切除修复（BER）是氧化性DNA损伤的主要调节因子，我们研究了紫外线B射线（UVB）照射后，来自XP-C患者的原代成纤维细胞中三种不同XPC突变对mRNA、蛋白表达及多种BER因子活性的详细影响。我们发现，XP-C成纤维细胞表现出多种BER因子包括OGG1、MYH、APE1、LIG3、XRCC1和Polβ的下调表达，这种下调亦体现在OGG1、MYH和APE1蛋白水平上。此现象伴随DNA氧化损伤的增加，如8-氧鸟嘌呤水平在UVB照射后立即升高。与正常对照细胞不同，这些氧化损伤在XP-C细胞中持续存在，且其切除修复能力较低。综合来看，我们的结果表明，XP-C成纤维细胞中BER途径的受损导致氧化DNA损伤的持久性和修复延迟。这或许可以解释XP-C患者中，无论是在光保护区还是光暴露区，发生癌症的多种临床表型。因此，基于增强BER途径的治疗策略可能代表了一种创新途径，以限制NER相关疾病，如XP-C病例中的不利影响。