Hydroxyl-radical-induced oxidation of 5-methylcytosine in isolated and cellular DNA.
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.
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.
Guru S
GS
Madugundu
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.
Jean
J
Cadet
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 richard.wagner@usherbrooke.ca.
J Richard
JR
Wagner
D044503:5-Methylcytosine / Q000737:chemistry*; D003596:Cytosine / Q000737:chemistry / Q000378:metabolism; D004247:DNA / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D004249:DNA Damage; D019175:DNA Methylation; D017665:Hydroxyl Radical / Q000737:chemistry*; D010084:Oxidation-Reduction; D013941:Thymine / Q000737:chemistry / Q000378:metabolism
D017665:Hydroxyl Radical; D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA; D013941:Thymine