Molecular mechanism for suppressing oxidative DNA damage

氧化性DNA损伤被认为有助于致癌、衰老和神经退行性变。研究表明，氧化性DNA损伤在癌组织中积累。例如，与周围正常组织相比，在肺癌组织中观察到更高水平的氧化性碱损伤。另一项研究报道，与正常组织相比，乳腺癌组织DNA中的8-oxoG、8-羟基腺嘌呤和2，6-二氨基-4-羟基-5-甲酰胺基嘧啶增加了9倍。此外，癌症的累积风险随着人类年龄的增长而急剧增加。一般而言，癌症可被视为一种老化的退化性疾病。基于主要测量8-氧代-7，8-二氢-2 '-脱氧鸟苷5'-三磷酸（8-氧代-dGTP）增加的研究，存在氧化性DNA损伤随年龄积累的证据。在正常细胞代谢期间，在细胞的核苷酸库中形成8-氧代-7，8-二氢-2 '-脱氧鸟苷5'-三磷酸（8-氧代-dGTP）。当掺入DNA时，8-oxo-dGTP引起突变。微生物含有8-氧代 ...更多信息 - dGTP酶，一种将8-氧代-dGTP特异性降解为8-氧代-dGMP的酶。通过基因靶向，我们建立了MTH 1基因和8-氧代-dGT酶活性缺陷的小鼠品系。与MTH 1 +/+细胞的值相比，在两个独立分离的MTH 1-/- ES细胞系中观察到HPRT基因中自发突变的频率高约2倍。然后，我们检查了衍生的突变小鼠对自发性肿瘤发生的易感性。将由约50只雄性和50只雌性组成的野生型或突变型小鼠维持在SPF条件下，并在1.5年后进行尸检。MTH 1 +/+和MTH 1-/-小鼠的存活率无显著差异。然而，病理学检查显示肿瘤发生率有统计学显著差异。观察到野生型和突变小鼠之间肺中肿瘤形成频率的明显差异，而MTH 1-/-小鼠的胃和肝脏中也可能形成更多的肿瘤。8-Oxo-dGT 3在保护动物免受氧诱导的DNA损伤引起的自发性肿瘤发生中起重要作用，MTH 1缺陷小鼠为研究MTH 1蛋白在正常和氧化应激下的体内作用提供了一个新的和有用的模型系统。少

Oxidative DNA damage is thought to contribute to carcinogenesis, aging, and neurological degeneration. Studies have shown that oxidative DNA damage accumulates in cancerous tissue. For example, higher levels of oxidative base damage were observed in lung cancer tissue compared with surrounding normal tissue. Another study reported a 9-fold increase in 8-oxoG, 8-hydroxyadenine, and 2,6-diamino-4-hydroxy-5-formamidopyrimidine in DNA from breast cancer tissue compared with normal tissue. Further, the cumulative risk of cancer increases dramatically with age in humans. In genreal terms cancer can be regarded as a degenerative disease of ageing. There is evidence for the accumulation of oxidative DNA damage with age based on studies mainly measuring an increase in 8-oxoG.8-Oxo-7,8-dihydro-2'-deoxyguanosine 5'-triphosphate (8-oxo-dGTP) is formed in the nucleotide pool of a cell during normal cellular metabolism. When incorporated into DNA, 8-oxo-dGTP causes mutation. Organisms posseces 8-oxo … More -dGTPase, an enzyme that specifically degrades 8-oxo-dGTP to 8-oxo-dGMP. By means of gene targeting, we established mouse lines deficient in the MTH1 gene, and 8-oxo-dGTPase activity. An approximately 2-fold higher frequency of spontaneous mutations in the HPRT gene was observed in two independently isolated MTH1-/- ES cell lines, compared with the value of MTH1+/+ cells. We then examined susceptibility of the derived mutant mice to spontaneous tumorigenesis. Wild type or mutant mice consisting of approximately 50 male and 50 female were maintained under SPF conditions and necropsied after 1.5 years. No significant difference in survival rates of MTH1+/+ and MTH1-/- mice. However, pathological examination revealed a statistically significant difference in the incidence of tumors. A distinct difference in the frequency of tumor formation in lungs between wild-type and mutant mice was observed while more tumors were likely to be formed in the stomach and in liver of MTH1-/- mice as well. 8-Oxo-dGTPase appears to play an important role to protect animals from the spontaneous tumorigenesis caused by the oxygen-induced DNA damage.The MTH1-deficient mouse provides a new and useful model system in which to explore the in vivo role of the MTH1 protein in normal and under oxidative stress. Less