MicroRNAs down-regulate homologous recombination in the G1 phase of cycling cells to maintain genomic stability.
MicroRNAs down-regulate homologous recombination in the G1 phase of cycling cells to maintain genomic stability.
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DOI：
10.7554/elife.02445
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发表时间：
2014-04-30
期刊：
影响因子：
7.7
通讯作者：
Chowdhury D
中科院分区：
文献类型：
--
作者：
Choi YE;Pan Y;Park E;Konstantinopoulos P;De S;D'Andrea A;Chowdhury D
同源重组（HR）介导的DNA双链断裂（DSB）修复仅限于细胞周期的复制后阶段。G1期HR的启动阻断了非同源末端连接（NHEJ），从而损害DSB修复。HR在G1期细胞中的完成可导致杂合性缺失（洛），这是潜在的致癌性。我们进行了功能获得性筛选以鉴定调节HR介导的DSB修复的miRNA，并且在这些miRNA中，miR-1255 b、miR-148 b * 和miR-193 b * 特异性抑制G1期的HR途径。这些miRNA靶向HR因子BRCA 1、BRCA 2和RAD 51的转录物，并且抑制miR-1255 b、miR-148 b * 和miR-193 b * 会增加BRCA 1/BRCA 2/RAD 51的表达，特别是在G1期，导致DSB修复受损。CtIP（一种BRCA 1相关DNA末端切除蛋白）的缺失挽救了这种表型。此外，在卵巢肿瘤的独立队列中，miR-1255 b、miR-148 b * 和miR-193 b * 的缺失与洛性缺失事件/染色体畸变和BRCA 1表达的显著增加相关。DOI：www.example.com细胞中的DNA每天被破坏数千次。最严重的损伤之一是双螺旋中的两条链都被破坏了。这种双链断裂可以删除基因，甚至杀死细胞。事实上，传统的癌症治疗通过造成不可修复的双链断裂来杀死癌细胞。相反，如果双链断裂被错误修复，经常暴露于DNA损伤剂的正常细胞可能成为肿瘤。一个有效和准确的双链断裂修复系统需要到位，以防止这种转变。因此，深入了解双链断裂修复及其相关因素对于深入了解癌症的病因和改善癌症治疗都很重要。细胞已经进化出几种不同的方法来检测和修复双链断裂。例如，一种叫做同源重组的方法，使用未受损的DNA分子作为模板，可以复制以产生新的DNA。由于它需要一个现成的DNA模板，这种方法只适用于细胞生长周期中有许多DNA拷贝的阶段，即DNA复制后阶段。特别是，同源重组在复制前G1期不起作用。如果在G1期尝试同源重组，它将阻止细胞修复断裂DNA链的其他方法。一个重要的挑战是了解同源重组是如何被限制在细胞周期的特定部分。虽然与双链修复早期阶段相关的某些蛋白质被认为决定了DNA修复的类型，但这一过程的细节尚未完全了解。一组被认为与此有关的分子是microRNA，它通常限制某些基因产生的蛋白质的数量。然而，由于单个microRNA分子可以与几种蛋白质相关联，并且由于单个蛋白质可以与几种microRNA分子相关联，因此已经证明难以确定特定microRNA分子的确切作用。Choi等人现在表明，七种microRNA分子可以控制同源重组，特别是三种microRNA在细胞周期的G1期限制同源重组。如果这些microRNA在G1期被抑制，这允许同源重组开始，并且反直觉地看到更多的双链断裂。然而，如果一个参与启动同源修复的基因（称为CtIP）被沉默，而microRNA被抑制，那么DNA断裂就被修复了。确切地说，microRNA分子如何在细胞周期的不同阶段产生不同的作用，将需要通过未来的研究来研究。DOI：www.example.com网站
Homologous recombination (HR)-mediated repair of DNA double-strand break (DSB)s is restricted to the post-replicative phases of the cell cycle. Initiation of HR in the G1 phase blocks non-homologous end joining (NHEJ) impairing DSB repair. Completion of HR in G1 cells can lead to the loss-of-heterozygosity (LOH), which is potentially carcinogenic. We conducted a gain-of-function screen to identify miRNAs that regulate HR-mediated DSB repair, and of these miRNAs, miR-1255b, miR-148b*, and miR-193b* specifically suppress the HR-pathway in the G1 phase. These miRNAs target the transcripts of HR factors, BRCA1, BRCA2, and RAD51, and inhibiting miR-1255b, miR-148b*, and miR-193b* increases expression of BRCA1/BRCA2/RAD51 specifically in the G1-phase leading to impaired DSB repair. Depletion of CtIP, a BRCA1-associated DNA end resection protein, rescues this phenotype. Furthermore, deletion of miR-1255b, miR-148b*, and miR-193b* in independent cohorts of ovarian tumors correlates with significant increase in LOH events/chromosomal aberrations and BRCA1 expression. DOI: http://dx.doi.org/10.7554/eLife.02445.001 The DNA in a cell is damaged thousands of times every day. One of the most serious types of damage involves something breaking both of the strands in the double helix. Such a double-strand break can delete genes or even kill the cell. In fact, conventional cancer therapy kills cancer cells by causing irreparable double-strand breaks. Conversely, a normal cell that is constantly exposed to DNA damaging agents can become a tumor if double-strand breaks are incorrectly repaired. An efficient and accurate double-strand break repair system needs to be in place to prevent this transformation. Therefore, an in-depth understanding of double-strand break repair and the factors involved are important for both gaining insight into the cause of cancer and to improve cancer therapy. Cells have evolved several different ways to detect and repair double-strand breaks. A method called homologous recombination, for example, uses an undamaged DNA molecule as a template that can be copied to make new DNA. Since it needs a readily available DNA template, this method only works in phases of the cell growth cycle where there are many copies of DNA—that is, in the post-DNA replication phases. In particular, homologous recombination does not work during the pre-replication, G1 phase. If homologous recombination is attempted during G1, it will block the other methods employed by cells to repair broken strands of DNA. An important challenge is to understand how homologous recombination is restricted to particular parts of the cell cycle. Although certain proteins associated with the early stages of double-strand repair are thought to determine the type of DNA repair that occurs, the details of this process are not fully understood. One group of molecules that are thought to be involved are microRNAs, which normally limit the number of proteins produced from certain genes. However, since a single microRNA molecule can be associated with several proteins, and since a single protein can be associated with several microRNA molecules, it has proved difficult to establish the exact effects of a specific microRNA molecule. Choi et al. now show that seven microRNA molecules can control homologous recombination, and three microRNAs in particular restrict homologous recombination during the G1 phase of the cell cycle. If these microRNAs are inhibited during the G1 phase, which allows homologous recombination to start, and counter-intuitively more double-stranded breaks are seen. However, if a gene involved in starting homologous repair–called CtIP—is silenced while the microRNAs are inhibited, then the DNA breaks are repaired. Exactly, how the microRNA molecules produce different effects during different phases of the cell cycle will be need to be investigated by future studies. DOI: http://dx.doi.org/10.7554/eLife.02445.002