Gadd45α在基因组稳定性和基因表达调控中的作用

【作者】 贾立立；

【导师】 樊飞跃； 詹启敏； 张春明；

【作者基本信息】 中国协和医科大学 ， 放射医学， 2009， 博士

【摘要】 基因组不稳定是人类肿瘤的特征。它的主要类型之一是染色体不稳定(CIN),是由维持细胞基因组完整性的基因发生突变所引起的。多种体内外因素均能使细胞DNA受到损伤,如外界的物理化学因素(放射线、紫外线和多种致癌物)、体内代谢产生的自由基以及自发性DNA复制异常等。DNA在损伤后能否及时得到修复是保障基因组稳定、减少基因突变和肿瘤发生的重要环节。DNA双链断裂修复可通过非同源重组和同源重组方式进行。损伤修复完成的细胞再次进入细胞周期,而无法获得完全修复的细胞则启动细胞凋亡机制,从而维持了细胞群体的基因组稳定性。这一系列自我调节的异常将导致基因组不稳定性的发生,促进细胞的恶性转化。Gadd45α和]BRCA1是两个重要的抑癌蛋白,它们在细胞周期检测点和DNA修复过程中发挥重要作用。我们的研究发现,Gadd45α敲除后Y染色体长臂出现大片段的缺失,提示Gadd45α可能与DNA重组修复有关。由于肿瘤抑癌基因BRCA1在DNA损伤后的重组修复中发挥重要作用,我们进一步研究了Gadd45α对BRCA1的调控作用。结果表明,Gadd45α可以在转录水平上调控BRCA1的表达,但是Gadd45α蛋白不影响BRCA1的启动子的活性,而且Gadd45α蛋白并不能与BRCA1的启动子区直接结合。细胞免疫荧光发现,Gadd45α蛋白也不影响BRCA1的亚细胞定位。以上结果表明Gadd45α可以调控BRCA1的表达,维持基因组稳定性,但是其调控的分子机制仍有待于进一步的研究。更多还原

【Abstract】 The common character of human tumor is genomic instability. One of the major types for genomic instability is chromosomal instability(CIN), which is mainly caused by mutations of genes that maintain cell genomic stability. Of the many intrinsic and extrinsic types of DNA damage that can be created inside mammalian cells, such as exogenous physic and chemical agents (irradiation, UV and certain carcinogens), or cellular sources such as oxidative damage or replication blocks in the DNA. DNA damage is a relatively common event in the life of a cell, and may lead to mutation, carcinogenesis, or cell death. In response to DNA damage, cell will undergo growth arrest, presumably to allow time for DNA repair. There are at least two mechanisms for the repair of DSB, homologous recombination (HR) and non-homologous end-joining (NHEJ). Normally,cells that finish DNA repair return to cell cycle, but other cells without complete DNA repair will be removed by apoptosis before DNA replication or chromosal segregion. However, if apoptosis is inhibited due to inactivation of regulatory machinery. This stuation increases the risk of CIN at several levels, and cells that are sufficiently fit to survive can be at a growth advantage, which lead to cancer. Gadd45a and BRCA1 are two important proteins involved in the control of cell cycle progression and apoptosis, both of them play key roles in homologous recombination.In this paper, we have found that when knockdown Gadd45a, a large deletion is shown on Y chromosome long arm(Yq). The Y chromosome is particularly vulnerable to DNA damage, partly because of its genetic structure and partly because it cannot correct double-stranded DNA deletions by homologous recombination. We then further confirmed that Gadd45a can be involved in the regulation of BRCA1 expression at the transcriptional level, but Gadd45a does not increase its promoter activity, Gadd45a protein also can not binding BRCA1 promoter directly. Cell immunofluorescence experiments show that Gadd45a does not affect BRCA1 subcellular localization.These studies have demostrated that Gadd45a can regulate BRCA1 expression in mRNA and protein expression level, providing a novel find that BRCA1 may be regulated by its previously-defined downstream gene Gadd45α. However the mechanisms regarding Gadd45a regulation of BRCA1 remain to be defined.更多还原