重离子辐射诱发细胞早熟性衰老的机理研究

发布时间：2018-05-24 17:53

本文选题：电离辐射 + 细胞周期阻滞　；参考：《中国科学院大学(中国科学院近代物理研究所)》2016年博士论文

【摘要】：细胞衰老是细胞不可逆的失去增殖能力的过程,最早由Hayflick等人发现,被认为是机体抑制肿瘤发生的重要屏障。但是也有研究表明衰老细胞可以通过分泌表型促进肿瘤发生。因此,细胞衰老与肿瘤之间的关系还需要进一步的研究。而对细胞衰老发生的分子机理的理解,有助于我们开发新的肿瘤治疗策略。目前已经发现多种基因毒性刺激都能诱发细胞发生早熟性细胞衰老,如端粒缩短、原癌基因激活、辐射损伤、活性氧损伤等,这些刺激都能引发DNA损伤。因此,DNA损伤信号活化可能是引发细胞衰老的主要原因。但是,DNA损伤引发细胞衰老的分子机制目前还不完全清楚。另外,细胞发生DNA损伤会导致细胞周期阻滞。之前的衰老模型认为,DNA损伤通过激活p53/p21通路,诱发G1期阻滞后发生细胞衰老。但是最近的研究发现衰老细胞中也存在G2期细胞。目前还不清楚这些G2期细胞是如何发生衰老的。为了研究DNA损伤诱发细胞衰老的分子机制,并探究G2期细胞发生衰老的机理,本论文以人黑色素瘤细胞系92-1和A375为研究材料,采用碳离子、铁离子以及X-射线等多种电离辐射处理细胞产生DNA损伤,通过比较不同电离辐射处理诱发细胞中DNA损伤的性质以及在染色体上分布的差异,来探究DNA损伤和细胞衰老之间的关系;同时,通过检测衰老相关的半乳糖苷酶的活性,相关蛋白的表达、细胞周期进程,来探究G2期细胞发生衰老的机理。实验结果表明,碳离子、铁离子以及X-射线等电离辐射引发细胞衰老都存在剂量依赖性和剂量饱和效应;而在相同剂量下,高LET的重离子诱发更高比例的细胞发生衰老。高LET的重离子辐照诱发的DNA损伤多为复杂损伤,不容易被修复;而低LET的X-射线诱发的端粒区域的DNA损伤同样不易被修复。这些持续存在的DNA损伤能够维持DDR信号通路的持续激活。并最终诱发p21的持续表达,导致细胞发生衰老。在发生G2期阻滞的细胞中,p21是决定细胞命运的关键因素:在p21上调表达的细胞中,p21通过诱发Aurora A激酶的降解,迫使细胞跳过M期,进入四倍体G1期后发生细胞衰老;而在不能有效上调表达p21的细胞中,Aurora A激酶持续表达,受辐照细胞发生短暂的G2期阻滞后进入M期,随后发生凋亡。因此,p21的上调与Aurora A激酶的下调是G2期阻滞细胞发生细胞衰老的关键事件。
[Abstract]:Cell senescence is the irreversible process of cell loss of proliferation. It was first discovered by Hayflick et al. It is considered to be an important barrier to inhibit tumor occurrence. But studies have also shown that aging cells can promote tumorigenesis by secreting phenotypes. Therefore, the relationship between cell senescence and tumor needs further study. Understanding the molecular mechanism of cell senescence is helpful for us to develop new tumor therapy strategies. Many genotoxic stimuli have been found to induce early maturing cell senescence, such as telomere shortening, proto-oncogene activation, radiation damage, reactive oxygen damage and so on. These stimuli can induce DNA damage. Therefore, activation of DNA damage signal may be the main cause of cell senescence. However, the molecular mechanism of cellular senescence caused by DNA damage is not fully understood. In addition, cell DNA damage can lead to cell cycle arrest. The previous aging model suggested that p53/p21 damage induced cell senescence after G 1 arrest by activating the p53/p21 pathway. But recent studies have found that G 2 phase cells also exist in aging cells. It is not clear how these G 2 cells age. In order to study the molecular mechanism of senescence induced by DNA damage and the mechanism of senescence in G2 phase cells, human melanoma cell lines 92-1 and A375 were used in this study. DNA damage was induced by various ionizing radiation treatments such as iron ions and X-rays. By comparing the properties of DNA damage induced by different ionizing radiation treatments and the differences in the distribution of DNA on chromosomes, To explore the relationship between DNA damage and cell senescence, and to explore the mechanism of senescence by detecting the activity of senescence related galactosidase, the expression of related proteins and cell cycle process. The results showed that there were dose-dependent and dose-saturated effects on cell senescence induced by ionizing radiation such as carbon ion, iron ion and X- ray, while high LET heavy ions induced a higher proportion of cell senescence at the same dose. The DNA damage induced by heavy ion irradiation with high LET is complex and not easily repaired, while the DNA damage in telomere region induced by low LET is also difficult to repair. These persistent DNA damage can maintain the sustained activation of DDR signaling pathway. And eventually induce the sustained expression of p21, leading to cell senescence. P21 is the key factor to determine the fate of cells in G2 phase arrest. In p21 up-regulated cells, p21 induces the degradation of Aurora A kinase, forcing cells to skip M phase and enter tetraploid G1 phase to develop cell senescence. However, the expression of Aurora A kinase could not be effectively upregulated in the cells with p21 expression. The irradiated cells entered M phase after a brief G2 arrest and then apoptosis. Therefore, the up-regulation of p21 and the down-regulation of Aurora A kinase are the key events to block cell senescence in G2 phase.
【学位授予单位】：中国科学院大学(中国科学院近代物理研究所)
【学位级别】：博士
【学位授予年份】：2016
【分类号】：Q274

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