title: Activity of OGG1 variants in the repair of pro-oxidant-induced 8-oxo-2'-deoxyguanosine.
abstract: Cells are continuously exposed to damaging reactive oxygen species (ROS), which are produced from both endogenous and exogenous sources. 8-Oxodeoxyguanosine (8-oxodG) is an abundant base lesion formed during oxidative stress which, if not repaired, can give rise to G:C-->T:A transversions in DNA. The 8-oxoguanine DNA glycosylase-1 (OGG1)-initiated base excision repair (BER) pathway operates to remove 8-oxodG lesions. Ogg1 deletion and polymorphism may result in a hypermutator phenotype and susceptibility to oxidative pathologies including cancer. Limited and conflicting evidence exists regarding the repair capacity of a prevalent human OGG1 (hOGG1) polymorphism, the Cys326-hOGG1 variant. The formamidopyrimidine DNA glycosylase (FPG)-modified comet assay was used to investigate the ability of sodium dichromate, potassium bromate and Ro19-8022 (+light) to induce DNA damage in mogg1(-/-) null (KO) and wild-type (WT) mouse embryonic fibroblasts (MEFs) and to assess hOGG1 variant-initiated BER capacities under conditions of oxidative stress. Treatment of WT MEFs with these pro-oxidant agents induced direct DNA strand breaks in a concentration-dependent manner, whereas, identical treatment of KO MEFs produced no effect. In contrast, KO MEFs accumulated significantly more FPG-sensitive sites than WT MEFs. Expression of hOGG1 in KO MEFs restored the WT phenotype in response to all pro-oxidants tested. The results suggest OGG1-initiated BER generates direct DNA strand breaks detected by the conventional comet assay, thus it is important that researchers do not interpret these as direct damage per se but rather a reflection of the repair process. The data also indicate Cys326-hOGG1-initiated BER is transiently impaired with respect to Ser326-hOGG1 (wild-type)- and Gly326-hOGG1 (artificial)-initiated BER following pro-oxidant treatment, possibly via hOGG1 cysteine 326 oxidation. This finding suggests the homozygous cys326/cys326 genotype may be classified as a biomarker of disease susceptibility, which is in support of a growing body of epidemiological evidence.
authors.affiliation: School of Biosciences, The University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: D J
authors.initials: DJ
authors.lastname: Smart
authors.forename: J K
authors.initials: JK
authors.lastname: Chipman
authors.forename: N J
authors.initials: NJ
authors.lastname: Hodges
mesh_terms: D000818:Animals; D001959:Bromates; D002460:Cell Line; D002840:Chromates; D020552:Comet Assay; D053960:DNA Breaks; D045647:DNA Glycosylases / Q000235:genetics* / Q000378:metabolism*; D004260:DNA Repair / Q000502:physiology*; D003839:Deoxyadenosines / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D008027:Light; D051379:Mice; D009153:Mutagens; D016877:Oxidants; D018384:Oxidative Stress; D011110:Polymorphism, Genetic; D011759:Pyrrolidines; D011807:Quinolizines; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D001959:Bromates; D002840:Chromates; D003839:Deoxyadenosines; D009153:Mutagens; D016877:Oxidants; D011759:Pyrrolidines; D011807:Quinolizines; D017382:Reactive Oxygen Species; C019536:potassium bromate; C076809:Ro 19-8022; C078251:2'-deoxy-7,8-dihydro-8-oxoadenosine; C016104:sodium bichromate; D045647:DNA Glycosylases; C479058:oxoguanine glycosylase 1, human; D005978:Glutathione