Molecular mechanisms of cellular responses to ionizing radiation and reactive oxygen species

(1)It众所周知，诸如X射线、γ射线和α粒子的电离辐射产生称为“簇状损伤”的独特形式的DNA损伤，其包含在DNA的一个或两个螺旋圈内诱导的两个或更多个损伤。电离辐射引起的许多损伤在化学上与氧化代谢副产物产生的活性氧引起的损伤难以区分。然而，电离辐射引起的聚集性损伤比孤立的损伤更不容易修复。因此，聚集性损伤可能具有生物学意义。在这份报告中，我们发现，在细胞核或线粒体中过表达hOGG 1的HeLaS 3细胞比HeLaS 3细胞对γ射线更敏感。我们已经确定了水平的染色体双链断裂的γ-H2 AX焦点的形成，电离辐射产生的集群损伤可能会转换为致命的双链断裂，在尝试碱基切除修复。我们的研究结果表明， ...更多信息 线粒体蛋白中hOGG 1的缺失增强了对γ射线的敏感性，提示线粒体基因组中碱基切除修复的失败也会引起双链断裂。（2）电离辐射和活性氧对DNA产生各种类型的氧化损伤，导致细胞突变。细菌和真核生物都有DNA修复系统来防止突变。氧化性碱基损伤主要通过碱基切除修复（BER）机制修复。然而，没有迹象表明氧化损伤在DNA链上直接逆转。在这项研究中，我们研究了氧化损伤是否直接逆转的DNA链。我们用γ射线照射pUB 3质粒，然后用还原剂二硫苏糖醇（DTT）处理。用pUB 3转化大肠杆菌细胞。结果表明，经DTT处理的pUB 3的转化效率高于未经DTT处理的pUB 3。我们目前正在研究pUB 3的突变谱。少

(1)It is well-known that ionizing radiation such as X-rays, gamma-rays and alpha-particles, produces a unique form of DNA damage called "clustered damage", which contains two or more lesions induced within the one or two helical turns of DNA. Many of the lesions induced by ionizing radiation are chemically indistinguishable from those induced by reactive oxygen species produced as by-products of oxidative metabolism. However, clustered damage induced by ionizing radiation would be less readily repaired than isolated lesions. Therefore clustered damage might be biologically significant. In this report we showed that HeLaS3 cells overexpressing hOGG1 in nucleus or mitochondria were more sensitive to gamma-rays than HeLaS3 cells. We have determined the level of chromosomal double strand breaks by gamma-H2AX foci formation, clustered damages produced by ionizing radiation might be converted to lethal double-strand breaks during attempted base excision repair. Our results that overexpressio … More n of hOGG1 in mitochondria protein enhanced the sensitivity to gamma-rays suggest that double-strand breaks are also induced by abortive base excision repair in mitochondrial genome. (2)Ionizing radiation and reactive oxygen species produce various types of oxidative damage to DNA, which cause mutations in cells. Bacteria and eukaryotes have DNA repair systems to prevent mutations. Oxidative base damages are principally repaired by base excision repair (BER) mechanisms. However, there are no indications that oxidative damages are directly reversed on the DNA strand. In this study, we examined whether oxidative damages are directly reversed on the DNA strand. We used pUB3 plasmid irradiated with gamma-rays and tsubsequently treated with a reducing agent, dithiolthreitol (DTT). E.coli cells were transformed with the pUB3. As a result, the transformation efficiency of pUB3 treated with DTT was higher than that of pUB3 without DTT treatment. We are currently investigating the mutation spectra of the pUB3. Less