Räz Michael H, Dexter Hannah R, Millington Christopher L, van Loon Barbara, Williams David M, Sturla Shana J
Department of Health Sciences and Technology, ETH Zürich , Schmelzbergstrasse 9, 8092 Zürich, Switzerland.
Center for Chemical Biology, Department of Chemistry, Krebs Institute, University of Sheffield , Sheffield S3 7HF, United Kingdom.
Chem Res Toxicol. 2016 Sep 19;29(9):1493-503. doi: 10.1021/acs.chemrestox.6b00168. Epub 2016 Aug 24.
The generation of chemical alkylating agents from nitrosation of glycine and bile acid conjugates in the gastrointestinal tract is hypothesized to initiate carcinogenesis. O(6)-carboxymethylguanine (O(6)-CMG) is a product of DNA alkylation derived from nitrosated glycine. Although the tendency of the structurally related adduct O(6)-methylguanine to code for the misincoporation of TTP during DNA replication is well-established, the impact of the presence of the O(6)-CMG adduct in a DNA template on the efficiency and fidelity of translesion DNA synthesis (TLS) by human DNA polymerases (Pols) has hitherto not been described. Herein, we characterize the ability of the four human TLS Pols η, ι, κ, and ζ and the replicative Pol δ to bypass O(6)-CMG in a prevalent mutational hot-spot for colon cancer. The results indicate that Pol η replicates past O(6)-CMG, incorporating dCMP or dAMP, whereas Pol κ incorporates dCMP only, and Pol ι incorporates primarily dTMP. Additionally, the subsequent extension step was carried out with high efficiency by TLS Pols η, κ, and ζ, while Pol ι was unable to extend from a terminal mismatch. These results provide a first basis of O(6)-CMG-promoted base misincorporation by Y- and B-family polymerases potentially leading to mutational signatures associated with colon cancer.
胃肠道中甘氨酸和胆汁酸共轭物亚硝化产生化学烷基化剂被认为是致癌作用的起始因素。O(6)-羧甲基鸟嘌呤（O(6)-CMG）是亚硝化甘氨酸导致的DNA烷基化产物。虽然结构相关的加合物O(6)-甲基鸟嘌呤在DNA复制过程中导致TTP错误掺入的倾向已得到充分证实，但DNA模板中O(6)-CMG加合物的存在对人类DNA聚合酶（Pols）跨损伤DNA合成（TLS）的效率和保真度的影响迄今尚未见报道。在此，我们表征了四种人类TLS Pols η、ι、κ和ζ以及复制性Pol δ在结肠癌常见突变热点处绕过O(6)-CMG的能力。结果表明，Pol η能越过O(6)-CMG进行复制，掺入dCMP或dAMP，而Pol κ仅掺入dCMP，Pol ι主要掺入dTMP。此外，TLS Pols η, κ和ζ能高效进行后续延伸步骤，而Pol ι无法从末端错配处延伸。这些结果为Y家族和B家族聚合酶导致的O(6)-CMG促进的碱基错掺入提供了首个依据，这种错掺入可能导致与结肠癌相关的突变特征。
