Madugundu Guru S, Cadet Jean, Wagner J Richard
Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, 3001 12e Avenue Nord, Québec J1H 5N4, Canada.
Département de Médecine Nucléaire et Radiobiologie, Faculté de Médecine et des Sciences de la Santé, Université de Sherbrooke, 3001 12e Avenue Nord, Québec J1H 5N4, Canada Institut Nanosciences & Cryogénie/DSM, CEA/Grenoble, 38054 Grenoble, France.
Nucleic Acids Res. 2014 Jun;42(11):7450-60. doi: 10.1093/nar/gku334. Epub 2014 May 22.
The methylation and oxidative demethylation of cytosine in CpG dinucleotides plays a critical role in the regulation of genes during cell differentiation, embryogenesis and carcinogenesis. Despite its low abundance, 5-methylcytosine (5mC) is a hotspot for mutations in mammalian cells. Here, we measured five oxidation products of 5mC together with the analogous products of cytosine and thymine in DNA exposed to ionizing radiation in oxygenated aqueous solution. The products can be divided into those that arise from hydroxyl radical (•OH) addition at the 5,6-double bond of 5mC (glycol, hydantoin and imidazolidine products) and those that arise from H-atom abstraction from the methyl group of 5mC including 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC). Based on the analysis of these products, we show that the total damage at 5mC is about 2-fold greater than that at C in identical sequences. The formation of hydantoin products of 5mC is favored, compared to analogous reactions of thymine and cytosine, which favor the formation of glycol products. The distribution of oxidation products is sequence dependent in specific ODN duplexes. In the case of 5mC, the formation of 5hmC and 5fC represents about half of the total of •OH-induced oxidation products of 5mC. Several products of thymine, cytosine, 5mC, as well as 8-oxo-7,8-dihydroguanine (8oxoG), were also estimated in irradiated cells.
CpG二核苷酸中胞嘧啶的甲基化和氧化去甲基化在细胞分化、胚胎发育和癌变过程中的基因调控中起着关键作用。尽管5-甲基胞嘧啶（5mC）含量较低，但它是哺乳动物细胞中突变的热点。在这里，我们在含氧水溶液中测量了暴露于电离辐射的DNA中5mC的五种氧化产物以及胞嘧啶和胸腺嘧啶的类似产物。这些产物可分为两类：一类是由5mC的5,6-双键处添加羟基自由基（•OH）产生的（二醇、乙内酰脲和咪唑烷产物），另一类是由5mC甲基上的氢原子提取产生的，包括5-羟甲基胞嘧啶（5hmC）和5-甲酰基胞嘧啶（5fC）。基于对这些产物的分析，我们表明在相同序列中，5mC处的总损伤比C处大约大2倍。与胸腺嘧啶和胞嘧啶的类似反应相比，5mC乙内酰脲产物的形成更受青睐，后者更有利于二醇产物的形成。在特定的寡核苷酸双链体中，氧化产物的分布取决于序列。就5mC而言，5hmC和5fC的形成约占5mC的•OH诱导氧化产物总量的一半。在受辐照细胞中还估计了胸腺嘧啶、胞嘧啶、5mC以及8-氧代-7,8-二氢鸟嘌呤（8oxoG）的几种产物。
