KRAS is one of the most mutated genes in human cancer. It is controlled by a G4 motif located upstream of the transcription start site. In this paper, we demonstrate that 8-oxoguanine (8-oxoG), being more abundant in G4 than in non-G4 regions, is a new player in the regulation of this oncogene. We designed oligonucleotides mimicking the KRAS G4-motif and found that 8-oxoG impacts folding and stability of the G-quadruplex. Dimethylsulphate-footprinting showed that the G-run carrying 8-oxoG is excluded from the G-tetrads and replaced by a redundant G-run in the KRAS G4-motif. Chromatin immunoprecipitation revealed that the base-excision repair protein OGG1 is recruited to the KRAS promoter when the level of 8-oxoG in the G4 region is raised by H₂O₂. Polyacrylamide gel electrophoresis evidenced that OGG1 removes 8-oxoG from the G4-motif in duplex, but when folded it binds to the G-quadruplex in a non-productive way. We also found that 8-oxoG enhances the recruitment to the KRAS promoter of MAZ and hnRNP A1, two nuclear factors essential for transcription. All this suggests that 8-oxoG in the promoter G4 region could have an epigenetic potential for the control of gene expression.

中文翻译：

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Kirsten ras（KRAS）基因的调节性G4基序对鸟嘌呤氧化敏感：对转录的影响

KRAS是人类癌症中突变最严重的基因之一。它由位于转录起始位点上游的G4基序控制。在本文中，我们证明了8-氧鸟嘌呤（8-oxoG）在G4中比在非G4地区更丰富，是调节这种癌基因的新参与者。我们设计了模仿KRAS G4-基序的寡核苷酸，发现8-oxoG影响G-四链体的折叠和稳定性。硫酸二甲酯的足迹表明，携带8-oxoG的G-run被排除在G-tetrads之外，而被KRAS G4-motif中的多余G-run取代。染色质免疫沉淀显示，当H升高G4区的8-oxoG水平时，碱基切除修复蛋白OGG1被募集到KRAS启动子。₂ O ₂。聚丙烯酰胺凝胶电泳表明，OGG1从G4-基序中以双链体形式去除了8-oxoG，但折叠后它以非生产性方式与G-四链体结合。我们还发现8-oxoG增强了MAZ和hnRNP A1（转录必需的两个核因子）对KRAS启动子的募集。所有这些表明，启动子G4区域中的8-oxoG可能具有控制基因表达的表观遗传潜能。