Effect of DNA Glycosylases OGG1 and Neil1 on Oxidized G-Rich Motif in the KRAS Promoter

The promoter of the Kirsten ras (KRAS) proto-oncogene contains, upstream of the transcription start site, a quadruplex-forming motif called 32R with regulatory functions. As guanine under oxidative stress can be oxidized to 8-oxoguanine (8OG), we investigated the capacity of glycosylases 8-oxoguanine glycosylase (OGG1) and endonuclease VIII-like 1 (Neil1) to excise 8OG from 32R, either in duplex or G-quadruplex (G4) conformation. We found that OGG1 efficiently excised 8OG from oxidized 32R in duplex but not in G4 conformation. By contrast, glycosylase Neil1 showed more activity on the G4 than the duplex conformation. We also found that the excising activity of Neil1 on folded 32R depended on G4 topology. Our data suggest that Neil1, besides being involved in base excision repair pathway (BER), could play a role on KRAS transcription.