Analysis of a novel back-up repair system for UV-induced DNA damage in human cells.

我们建立了一种超灵敏检测生物剂量紫外光诱导的环丁烷嘧啶二聚体（CPD）和（6-4）光产物（6-4PPs）的方法，并提出人类细胞可能存在一种新的主要针对6-4PPs的修复系统，而不是核苷酸切除修复系统。在本研究中，我们获得了以下发现：1.即使在来自xpa（-/-）或xpg（-/-）基因敲除小鼠的胚胎成纤维细胞中也观察到6-4PPs的去除（24小时后30-50%）。此外，在那些效率较低的细胞中也检测到对CPD的去除（48小时后20-30%）。2.稳定表达AlwNI型突变XPA的HeLa细胞没有显示出任何核苷酸切除修复活性的损害，表明该突变XPA蛋白不具有显性负效应。3.我们进一步敏化了CPD的检测方法，使我们能够确定暴露于低至0.1 J/m^2的非杀伤剂量的Was的细胞中CPD的修复动力学。在此条件下，我们发现，干皮病pimentosum细胞显着去除CPD（48小时后约40%）。4.我们可以观察到，当人细胞被预暴露于0.2 J/m^2时，在1 J/m^2的紫外线照射后，细胞的修复效率有微弱的增强。然而，我们需要更广泛的实验来确定后备修复系统是否在适应性反应的控制下，综合这些结果，我们得出结论，哺乳动物细胞具有一定的后备修复系统，独立于XPA和XPG，其主要去除6-4PP，但也去除CPD，效率较低。

We have established a super-sensitive detection method for measuring cyclobutane pyrimidine dimers (CPDs) and (6-4)photoproducts (6-4PPs) induced by biological doses of ultraviolet (UV) light and suggested that human cells might have a novel repair system mainly for 6-4PPs other than nucleotide excision repair which has been thought to be only repair system for those lesions in humans so far. In this study, we have obtained the following findings.1.The removal of 6-4PPs was observed even in the embryonic fibroblasts derived from xpa(-/-) or xpg(-/-) knock-out mice (30-50% after 24 hr). In addition, the removal of CPDs was also detected in those cells with a less efficiency (20-30% after 48 hr).2.HeLa cells stably expressing AlwNI-type mutant XPA did not show any impairment of nucleotide excision repair activity, suggesting that this mutant XPA protein does not have a dominant-negative effect.3.We have further sensitized the detection method for CPDs, enabling us to determine the repair kinetics of CPDs in cells exposed to non-killing doses of Was low as 0.1 J/m^2. Under this condition, we have found that xeroderma pimentosum cells significantly remove CPDs (〜40% after 48hr).4.We could observe some weak enhancement of repair efficiency after UV irradiation of 1 J/m^2 when the human cells had been pie-exposed to 0.2 J/m^2. However, we need more extensive experiments to conclude whether the back-up repair system is under the control of adaptive responses.Taken together with those results, we concluded that mammalian cells have a certain back-up repair system, independent of XPA and XPG, which removes mainly 6-4PP but also CPDs with a less efficiency.