Identification of 3,<i>N</i><sup>4</sup>-Etheno-5-methyl-2′-deoxycytidine in
Human DNA: A New Modified
Nucleoside Which May Perturb Genome Methylation
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Abstract
Methylation of cytidine at dCpdG sequences regulates
gene expression
and is altered in many chronic inflammatory diseases. Inflammation
generates lipid peroxidation (LPO) products which can react with deoxycytidine,
deoxyadenosine, and deoxyguanosine in DNA to form pro-mutagenic exocyclic
etheno-nucleoside residues. Since 5-methyl-2′-deoxycytidine
(5mdC) residues exhibit increased nucleophilicity at N3, they should
be even better targets for LPO products. We synthesized and characterized
3,<i>N</i><sup>4</sup>-etheno-5-methyl-2′-deoxycytidine-3′-phosphate
and showed that LPO products can indeed form the corresponding etheno-5mdC
(ε5mdC) lesion in DNA <i>in vitro</i>. Our newly developed <sup>32</sup>P-postlabeling method was subsequently used to detect ε5mdC
lesions in DNA from human white blood cells, lung, and liver at concentrations
4–10 times higher than that observed for etheno adducts on
nonmethylated cytidine. Our new detection method can now be used to
explore the hypothesis that this DNA lesion perturbs the DNA methylation
status