BRCA2 prevents R - loop accumulation and associates with TREX-2 mRNA export factor PCID2

摘要

Genome instability is central to ageing, cancer and other diseases. It is not only proteins involved in DNA replication or the DNA damage response (DDR) that are important for maintaining genome integrity: from yeast to higher eukaryotes, mutations in genes involved in pre-mRNA splicing and in the biogenesis and export of messenger ribonucleoprotein (mRNP) also induce DNA damage and genome instability. This instability is frequently mediated by R-loops formed by DNA-RNA hybrids and a displaced single-stranded DNA. Here we show that the human TREX-2 complex, which is involved in mRNP biogenesis and export, prevents genome instability as determined by the accumulation of γ-H2AX (Ser-139 phosphorylated histone H2AX) and 53BP1 foci and single-cell electrophoresis in cells depleted of the TREX-2 subunits PCID2, GANP and DSS1. We show that the BRCA2 repair factor, which binds to DSS1 , also associates with PCID2 in the cell. The use of an enhanced green fluorescent protein-tagged hybrid-binding domain of RNase H1 and the S9.6 antibody did not detect R-loops in TREX-2-depleted cells, but did detect the accumulation of R-loops in BRCA2-depleted cells. The results indicate that R-loops are frequently formed in cells and that BRCA2 is required for their processing. This link between BRCA2 and RNA-mediated genome instability indicates that R-loops may be a chief source of replication stress and cancer-associated instability.%R-环(自然出现的三链核酸结构,由一个RNA-DNA杂合体和被取代的单链DNA组成)是基因组不稳定性的潜在诱导因素之一。这项研究显示,TREX-2(在"信使核糖核蛋白"(mRNP)的生物生成和输出中所涉及的一种复合物)通过与乳腺癌易感基因因子BRCA2相互作用来处理R-环。不含BRCA2的人细胞会积累高水平的R-环。在肿瘤抑制因子与R-环之间的这一出乎意料的相互作用表明,R-环也许是造成复制应激和肿瘤发生的一个主要原因。