Oxygen-induced DNA damage and its repair mechamism

氧自由基可以通过正常的细胞代谢产生，被认为在诱变和肿瘤发生中发挥着重要作用。在DNA氧化损伤的各种类型中，8-氧代-7，8-二氢鸟嘌呤(8-oxoG)是最重要的，因为它的丰度和突变性。MTH1基因编码一种酶，将8-oxo-dGTP分解为核苷酸池中的单磷酸，从而防止颠倒突变的发生。通过基因打靶，我们建立了MTH1基因敲除细胞系和小鼠。当在出生18个月后进行检查时，与野生型小鼠相比，MTH1缺陷小鼠的肺、肝脏和胃中形成了更多的肿瘤。MTH1缺陷小鼠将为研究MTH1蛋白在正常条件和氧化应激下的作用提供一个有用的模型。最近的研究表明，人MTH1蛋白比8-oxo-dGTP更有效地降解2-羟基-dATP，并且具有更高的亲和力。目前对MTH1缺失突变小鼠的突变研究将为进一步了解MTH1的作用提供更多的信息。我们在人类MTH1基因中发现了单核苷酸多态性，它改变了其转录产物的剪接模式，我们进一步研究了8-oxoG DNA糖基酶(OGG1)和2-OH-A/腺嘌呤DNA糖基酶(MYH)在人细胞中的表达和定位。真实的OGG1和MYH蛋白存在于线粒体和细胞核中，它们在细胞内的定位被发现通过每个转录物的选择性剪接来调节。

Oxygen radicals, which can be produced through normal cellular metabolism, are thought to play an important role in mutagenesis and tumorigenesis. Among various classes of oxidative DNA damage, 8-oxo-7,8-dihydroguanine (8-oxoG) is most important because of its abundance and mutagenicity.The MTH1 gene encodes an enzyme that hydrolyzes 8-oxo-dGTP to monophosphate in the nucleotide pool, thereby preventing occurrence of transversion mutations. By means of gene targeting, we have established MTH1 gene-knockout cell lines and mice. When examined 18 months after birth, a greater number of tumors were formed in the lungs, livers and stomachs of MTH1-deficient mice, as compared with wild-type mice. The MTH1-deficient mouse will provide a useful model for investigating the role of the MTH1 protein in normal conditions and under oxidative stress.Recent studies showed that the human MTH1 protein hydrolyzed 2-hydroxy-dATP more efficiently and with higher affinity than 8-oxo-dGTP.Current studies on mutagenesis with MTH1-null mutant mice will provide more insight into the role of the sanitizing enzyme, MTH1.We found a single nucleotide polymorphism in human MTH1 gene which alters splicing patterns of its transcripts, and that a novel MTH1 polypeptide with an additional mitochondrial targeting signal is produced from the altered MTH1 mRNA.We further characterized expression and intracellular localization of 8-oxoG DNA glycosylase (OGG1) and 2-OH-A/adenine DNA DNA glycosylase (MYH) in human cells. The authentic OGG1 and MYH proteins present in mitochondria as well as in nuclei, and their intracellular localization were found to be regulated by alternative splicing of each transcript.