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

(1)众所周知，X射线、伽马射线和阿尔法粒子等电离辐射会产生一种独特的DNA损伤形式，称为“簇状损伤”，它包含在DNA的一个或两个螺旋转弯内引起的两个或两个以上损伤。许多由电离辐射引起的损伤在化学上与由氧化代谢副产物产生的活性氧引起的损伤无法区分。然而，电离辐射引起的聚集性损伤比孤立损伤更不容易修复。因此，聚集性损害可能在生物学上具有重大意义。在这份报告中，我们发现在细胞核或线粒体中过表达hOGG1的HeLaS3细胞比HeLaS3细胞对伽马射线更敏感。我们已经通过伽马-H_2AX焦点形成确定了染色体双链断裂的水平，在试图的碱基切除修复过程中，电离辐射产生的簇状损伤可能会转化为致命的双链断裂。我们过度表达…的结果线粒体蛋白中较多的hOGG1增加了对伽马射线的敏感性，提示线粒体基因组中的双链断裂也是由流产的碱基切除修复引起的。(2)电离辐射和活性氧物种对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DNA链上的氧化损伤可以直接逆转。在这项研究中，我们检查了氧化损伤是否直接在DNA链上逆转。我们使用经伽马射线照射的pUB3质粒，然后用二硫代苏糖醇(DTT)处理。用pUB3转化大肠杆菌细胞。结果表明，经DTT处理的pUB3的转化效率高于未经DTT处理的pUB3。我们目前正在研究pUB3的突变谱。较少

(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