Boyer J C, Kaufmann W K, Brylawski B P, Cordeiro-Stone M
Department of Pathology, University of North Carolina, Chapel Hill 27599-7525.
Cancer Res. 1990 May 1;50(9):2593-8.
Postreplication repair (PRR) was quantified in normal human fibroblasts and in xeroderma pigmentosum (XP) variant fibroblasts after treatment with UV or benzo[a]pyrene diol epoxide-I (BPDE-I). PRR may be defined as the elimination of discontinuities in the daughter-strand DNA and the replicative bypass of lesions in the DNA template. Pathways of PRR reduce the number of DNA growing points that are blocked at template lesions and increase the rate of growth of nascent DNA on damaged templates. Rates of DNA synthesis and strand growth were measured in solvent- and carcinogen-treated cells by velocity sedimentation analyses of radiolabeled nascent DNA in alkaline sucrose gradients. Logarithmically growing normal fibroblasts displayed D0 values of 6.3 J/m2 and 0.37 microM for the inhibition of DNA synthesis in active replicons by UV and BPDE-I, respectively. Under identical conditions, the XP variant cells exhibited D0 values of 1.5-2.0 J/m2 and 0.27-0.31 microM. Pulse-chase experiments were performed in cells synchronized at the beginning of the S phase. Normal and XP variant cells displayed inhibition of DNA strand growth by UV, with D0 values of 21.6 and 7.0 J/m2, respectively. The D0 values for the inhibition of DNA strand growth by BPDE-I were 0.85 microM for the normal cells and 0.62-0.79 microM for the XP variant cells. The inhibitions of DNA replication by UV and BPDE-I were also analyzed in terms of DNA lesion frequencies. Based on the D0 values for inhibition of DNA replication, we concluded that the XP variant cells express maximally 25-33% of the total PRR activity observed in normal fibroblasts after UV treatment. Conceivably, this deficiency in PRR activity results in the XP variant's increased risk of cancers induced by sunlight, because XP variant cells and normal fibroblasts are equally proficient in excision repair. Both normal and XP variant fibroblasts, however, displayed similar PRR activities in response to BPDE-I treatment.
在用紫外线或苯并[a]芘二醇环氧化物-I（BPDE-I）处理后，对正常人成纤维细胞和着色性干皮病（XP）变异型成纤维细胞中的复制后修复（PRR）进行了定量分析。PRR可定义为消除子链DNA中的间断以及DNA模板中损伤的复制性绕过。PRR途径减少了在模板损伤处受阻的DNA生长点数量，并提高了受损模板上新生DNA的生长速率。通过在碱性蔗糖梯度中对放射性标记的新生DNA进行速度沉降分析，测量了溶剂处理和致癌物处理细胞中的DNA合成速率和链生长速率。对数生长的正常人成纤维细胞对紫外线和BPDE-I抑制活性复制子中DNA合成的D0值分别为6.3 J/m2和0.37 μM。在相同条件下，XP变异型细胞的D0值为1.5 - 2.0 J/m2和0.27 - 0.31 μM。在S期开始时同步化的细胞中进行了脉冲追踪实验。正常细胞和XP变异型细胞对紫外线抑制DNA链生长的D0值分别为21.6和7.0 J/m2。正常细胞对BPDE-I抑制DNA链生长的D0值为0.85 μM，XP变异型细胞为0.62 - 0.79 μM。还根据DNA损伤频率分析了紫外线和BPDE-I对DNA复制的抑制作用。基于抑制DNA复制的D0值，我们得出结论，紫外线处理后，XP变异型细胞的PRR总活性最高仅为正常人成纤维细胞中观察到的25% - 33%。可以想象，PRR活性的这种缺陷导致XP变异型细胞因阳光诱导癌症的风险增加，因为XP变异型细胞和正常人成纤维细胞在切除修复方面同样熟练。然而，正常成纤维细胞和XP变异型成纤维细胞在对BPDE-I处理的反应中表现出相似的PRR活性。
