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

活性氧（reactive oxidation species， ROS）的产生及其对DNA的损伤在生理条件下是不可避免的，并可被外源应激源放大，如辐射、药物、饮食和环境中的化合物。8-氧-7,8-二氢鸟嘌呤（8-oxoG）是哺乳动物细胞中最常见的DNA氧化损伤，估计每天的生成速率为1000个。8-OxoG由于在DNA复制过程中与腺嘌呤的非规范（Hoogsteen型）碱基配对而具有前诱变性。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的翻转突变。一种被称为“氧化石墨烯系统”的综合防御途径通过从核苷酸库中消除8-oxo-dGTP和从基因组中去除8-oxoG:C和8-oxoG:A损伤来防止突变。碱基切除修复（BER）是人类细胞修复这些DNA损伤的主要机制；然而，一些证据表明，除了规范误码率之外，还存在辅助机制。该计划的重点是鉴定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修复相关的潜在替代机制的存在：去除致突变前的8-oxoG，在切除后步骤预防毒性，以及纠正最终致突变的8-oxoG:A错配。

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.