Human Ogg1, a protein involved in the repair of 8-oxoguanine, is inhibited by nitric oxide

NO-mediated inhibition of base excision DNA repair may potentiate oxidative DNA damage in cells and could be relevant to carcinogenesis associated with chronic inflammation. Because 8-oxoguanine, a ubiquitous oxidative DNA lesion, is repaired predominantly by human 8-oxoguanine glycosylase (hOgg1), our aim was to determine whether NO directly inhibits its repair activity. Neither induction of NO-generating enzyme inducible NO synthase nor treatment with S-nitroso-N-acetyl-D-L-pencillamine altered expression of hOgg1 in a human cholangiocarcinoma cell line (KMBC). In contrast, both treatments completely inhibited activity of hOgg1 immunoprecipitated from KMBC cells overexpressing hOgg1 and in a cell-free system. Both NO and peroxynitrite were capable of inhibiting hOgg1 activity. Inhibition of hOgg1 protein was characterized by formation of S-nitrosothiol adducts and loss/ejection of zinc ions. Our data indicate that NO, an inflammatory mediator, directly inhibits a key base excision repair enzyme (hOgg1) responsible for base excision repair of 8-oxoguanine. These data support the concept that NO-mediated inhibition of DNA contributes to the mutagenic environment of chronic inflammation.