Assessment of functional overlaps between human DNA repair pathways for 8-oxoguanine

在生理条件下，活性氧化物种(ROS)的产生和由此导致的DNA损伤是不可避免的，并且可以被外部应激源，如辐射、药物和来自饮食和环境来源的化合物放大。8-氧代-7，8-二氢鸟嘌呤(8-oxoG)是哺乳动物细胞中最常见的氧化DNA损伤，估计每天产生1000。8-OxoG是预致突变的，因为在DNA复制过程中，非规范的(Hoogsteen类型)碱基与腺嘌呤配对。由此产生的8-oxoG：A错配，如果持续到下一轮复制，就会产生特征性的G：C到T：A颠换突变。一种名为“GO系统”的综合防御途径通过从核苷酸池中消除8-oxo-dGTP和从基因组中消除8-oxoG：C和8-oxoG：A损伤来保护免受突变。碱基切除修复(BER)是修复人类细胞中这些DNA损伤的主要机制；然而，几条证据表明，除了典型的BER外，还存在辅助机制。这项拟议的项目专注于确定BER和其他DNA修复途径之间的功能重叠，以保护人类细胞免受8-oxoG的影响。我们将在三个不同的水平上解决与8-oxoG修复潜在相关的替代机制的存在：去除前突变的8-oxoG，在切除后预防毒性，以及纠正最终突变的8-oxoG：A错对。

Generation of reactive oxidative species (ROS) and the resulting damage to DNA are unavoidable under physiological conditions and can be amplified by exogenous stressors, such as radiation, drugs and chemical compounds from diet and environmental sources. With an estimated generation rate of >1000 per day, 8-oxo-7,8-dihydroguanine (8-oxoG) is the most frequent oxidative DNA lesion in mammalian cells. 8-OxoG is pre-mutagenic due to the non-canonical (Hoogsteen type) base pairing with adenine during DNA replication. The resulting 8-oxoG:A mispairs, if persist into the next round of replication, produce characteristic G:C to T:A transversion mutations. A comprehensive defense pathway termed “GO system” protects from mutation by both eliminating 8-oxo-dGTP from the nucleotide pool and removing the 8-oxoG:C and 8-oxoG:A lesions from the genome. Base excision repair (BER) is the primary mechanism for repair of these DNA lesions in human cells; however, several lines of evidence suggested existence of auxiliary mechanisms in addition to the canonical BER. The proposed project is focused at identification of functional overlaps between BER and other DNA repair pathways in safeguarding human cells against the effects of 8-oxoG. We will address the existence of alternative mechanisms potentially relevant to the repair of 8-oxoG at three different levels: removal of pre-mutagenic 8-oxoG, prevention of toxicity at the post-excision step, and correction of the ultimately mutagenic 8-oxoG:A mispairs.