Oxygens in DNA are main targets for ethylnitrosourea in normal and xeroderma pigmentosum fibroblasts and fetal rat brain cells
Oxygens in DNA are main targets for ethylnitrosourea in normal and xeroderma pigmentosum fibroblasts and fetal rat brain cells
复制标题
DNA 中的氧是正常和着色性干皮病成纤维细胞以及胎鼠脑细胞中乙基亚硝基脲的主要靶标
作者：
B. Singer;W. Bodell;J. E. Cleaver;G. Thomas;M. Rajewsky;W. Thon
化学致癌研究中的主要问题之一是在细胞或动物中鉴定已知的体外实验中的核酸加合物。用致癌物乙基亚硝脲(EtNU)处理培养中的正常人或干皮病(XP)人成纤维细胞或胎鼠脑细胞(FBC)，使细胞存活(每100,000个碱基中有2-5个乙基)，我们发现其DNA中烷基产物的性质和比例与DNA与EtNU在体外高度烷基化时(每100个碱基中有1个乙基)非常相似。定量的产物有乙基磷酸三酯、7-乙基鸟嘌呤(7-EtG)、3-乙基腺嘌呤(3-ETA)、O6-乙基脱氧鸟苷(O6-EtdGuo)、O2-乙基胸苷(O2-EtThd)、O4-乙基胸苷和O2-乙基胞嘧啶(O2-等)。在这里，我们提出了第一个实验证据，证明在EtNU处理的细胞中，嘧啶氧原子是主要的反应部位。目前用纯化的DNA和Poly(DG)·Poly(DC)进行的模型实验与早期对单链多核苷酸的研究(参考文献6，10，表1)的比较表明，Watson-Crick碱基配对并不显著阻碍氧的烷基化。这与之前关于碱基对氮的反应性很低的研究结果形成了鲜明对比。我们解释这一现象的基础是，只有氧原子有一对电子没有直接参与氢键。
ONE of the major problems in the study of chemical carcinogenesis is to identify in cells or animals the nucleic acid adducts known from in vitro experiments. When normal or xeroderma pigmentosum (XP) human fibroblasts or fetal rat brain cells (FBC) in culture are treated with the carcinogen, ethylnitrosourea (EtNU), to an extent permitting good cell survival (2–5 ethyl groups per 100,000 bases), we find that the nature and proportion of the alkyl products in their DNA are remarkably similar to those found when DNA is alkylated with EtNU to a high extent in vitro (1 ethyl group per 100 bases). The products quantified in this study are ethylphosphotriesters, 7-ethylguanine (7-EtG), 3-ethyladenine (3-EtA), O6-ethyl-deoxyguanosine (O6-EtdGuo), O2-ethylthymidine (O2-EtThd), O4-ethylthymidine and O2-ethylcytosine (O2-EtC). We present here the first experimental evidence that pyrimidine oxygen atoms are major sites of reaction in cells treated with EtNU. A comparison of the present model experiments with purified DNA and poly(dG) · poly(dC) with earlier studies on single-stranded polynucleotides (refs 6, 10, Table 1) indicates that Watson–Crick base-pairing does not significantly hinder alkylation of the oxygens. This is in contrast to previous findings concerning the very low reactivity of base-paired nitrogens. We explain this on the basis that only the oxygens have a pair of electrons not directly involved in hydrogen bonding.