BLAP75在电离辐射损伤修复中的作用以及机制研究

Bloom syndrome is a genetic disease characterized by predisposition to a wide variety of cancers in early life. It is caused by the defective BLM gene, which encodes a RecQ DNA helicase. BLAP75 is a newly identified BLM-associated protein. It has been demonstrated by in vitro biochemical analysis that BLM associates with topoisomerase (Topo) IIIα and BLAP75 to form BTB complex to separate double Holliday junction, an intermediate of homologous recombination, without genetic exchange, which is essential for genome stability. Homologous recombination is a primary error-free way to repair DNA double-strand break, which is a major DNA damage type caused by ionizing radiation. However, little is known about the exact function of BLAP75 in response to ionizing radiation. Our preliminary studies have shown that BLAP75 is recruited to the DNA damage sites to form nuclear foci, BLAP75 proteins accumulate and get post-translational modification upon γ-irradiation. These new observations indicate BLAP75 may play an important role in DNA damage response and repair through its specific interaction with BLM and TopoIIIα to maintain genome stability. The goal of our investigation is to elucidate the function of BLAP75 at cellular and molecular levels and to understand its relevant regulatory mechanisms after ionizing radiation.

BLAP75是新近发现的DNA解螺旋酶BLM的结合蛋白。体外生化实验已经显示BLAP75能与BLM 和TopoIIIα 结合形成BTB复合物，这个复合物在同源重组修复过程中发挥至关重要的作用。由于同源重组是准确无误地修复DNA双链断裂的主要途径，而电离辐射损伤的主要类型就是DNA双链断裂，这就提示BLAP75蛋白在电离辐射损伤修复中很可能是有重要作用的。但是，迄今国内外都还没有这方面的报导。我们的前期预实验结果显示，细胞在辐射照射后BLAP75会被招募到DNA损伤部位形成核foci ，而且BLAP75的蛋白量会增加并受到翻译后修饰作用。这些新发现进一步表明BLAP75在电离辐射损伤修复中会起重要作用。本项目的研究目标就是要从细胞水平和分子水平来阐明BLAP75在电离辐射损伤修复中的作用以及相关的调控机制。

BLAP75（又名RMI1）是DNA解旋酶BLM的结合蛋白。体外生化实验已经显示BLAP75能与BLM 和DNA拓扑异构酶TopoIIIα以及BLAP18/RMI2结合形成BTR复合物，该复合物在同源重组修复DNA过程中发挥至关重要的作用。本项目首先从分子水平上深入研究了BLAP75与BLM 、TopoIIIα的相互作用，发现BLAP75的氨基端部分是与BLM及TopoIIIα蛋白相结合的区域，并在细胞水平上发现了BLAP75蛋白在电离辐射损伤修复中的重要作用。此外，本项目还研究了BLAP75的磷酸化作用，发现BLAP75蛋白不仅在受到电离辐射和紫外线辐射时会被磷酸化，而且在细胞有丝分裂期也会被磷酸化，并且确定了BLAP75的磷酸化位点为第284和292位的丝氨酸，为下一步研究BLAP75的细胞周期调控作用奠定了基础。该研究结果对认识BTR复合物在电离辐射损伤修复中的作用，以及对了解BLAP75的生物学功能都具有重要意义。