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Molecular mechanism to cause high incidence of cancer in Bloom syndrcme

布卢姆综合征致癌高发的分子机制

基本信息

批准号：
13214007
负责人：
ENOMOTO Takemi
金额：
$ 37.12万
依托单位：
Tohoku Universty
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research on Priority Areas
财政年份：
2001
资助国家：
日本
起止时间：
2001 至 2004
项目状态：
已结题

项目摘要

Bloom's syndrome is autosomal disorder characterized by predisposition to wide variety of cancers. In this study, I intended to clarify the function of the Bloom syndrome gene product (BLM) at the molecular level, using budding yeasts that have a BLM homologue, SGS1 as well as higher eukaryotic cells. Genetical analyses using yeasts indicated that Sgs1 functions to suppress homologous recombination under normal condition. However, Sgs1 was required to induce homologous recombination when cells were injured with DNA damaging agents. It has been revealed that the interaction of Sgs1 with DNA topoisomerase III (Top3) is essential for Sgs1 to fulfill its function and that Sgs1 functions in the Rad52 recombination pathway involving Rad51 but not Mre11.To elucidate the function of Top3 and functional relationship between BLM and Top3 in higher eukaryotic cells, we constructed cells with various genetic backgrounds whose Top3a expression is controllable. Depletion of Top3a from the cells caused accumulation of cells in G2 phase, enlargement of nuclei, chromosome gaps and breaks that occurred at the same position of sister chromatids, and inhibition of transition from metaphase to anaphase and that these events were suppressed by disruption of BLM gene, indicating a functional interaction between BLM and Top3a. Based on the results obtained in this study, we reached the conclusion that Top3a and BLM are implicated in the decatenation of DNA in newly synthesized sister chromatids. In addition, it has been indicated that BLM and Top3a function cooperatively to suppress the formation of sister chromatid exchange. Finally, epistatic analyses using various gene knockout cells, suggested that BLM functions in the recombination pathway involving XRCC3 under damage induced condition.

布卢姆综合征是一种常染色体疾病，其特征是易患多种癌症。在这项研究中，我打算使用具有 BLM 同源物 SGS1 的芽殖酵母以及高等真核细胞，在分子水平上阐明布卢姆综合征基因产物 (BLM) 的功能。使用酵母进行的遗传分析表明，Sgs1 在正常条件下具有抑制同源重组的功能。然而，当细胞受到 DNA 损伤剂损伤时，Sgs1 需要诱导同源重组。研究表明，Sgs1与DNA拓扑异构酶III（Top3）的相互作用对于Sgs1实现其功能至关重要，并且Sgs1在涉及Rad51但不涉及Mre11的Rad52重组途径中发挥作用。为了阐明Top3的功能以及BLM和Top3在高等真核细胞中的功能关系，我们构建了具有多种遗传背景且Top3a表达可控的细胞。细胞中 Top3a 的耗尽导致细胞在 G2 期积累、细胞核增大、姐妹染色单体同一位置发生染色体间隙和断裂，以及中期到后期转变的抑制，并且这些事件通过 BLM 基因的破坏而受到抑制，表明 BLM 和 Top3a 之间存在功能相互作用。根据本研究获得的结果，我们得出结论：Top3a 和 BLM 与新合成的姐妹染色单体中 DNA 的串联有关。此外，已经表明BLM和Top3a协同发挥作用来抑制姐妹染色单体交换的形成。最后，使用各种基因敲除细胞的上位分析表明，在损伤诱导条件下，BLM 在涉及 XRCC3 的重组途径中发挥作用。