Department of Molecular Biology, University of Geneva, 1205, Geneva, Switzerland.
Center for Chromosome Stability and Center for Healthy Aging, Department of Cellular and Molecular Medicine, University of Copenhagen, Blegdamsvej 3B, 2200, Copenhagen N, Denmark.
Cell Res. 2020 Nov;30(11):997-1008. doi: 10.1038/s41422-020-0358-x. Epub 2020 Jun 19.
DNA replication stress, a feature of human cancers, often leads to instability at specific genomic loci, such as the common fragile sites (CFSs). Cells experiencing DNA replication stress may also exhibit mitotic DNA synthesis (MiDAS). To understand the physiological function of MiDAS and its relationship to CFSs, we mapped, at high resolution, the genomic sites of MiDAS in cells treated with the DNA polymerase inhibitor aphidicolin. Sites of MiDAS were evident as well-defined peaks that were largely conserved between cell lines and encompassed all known CFSs. The MiDAS peaks mapped within large, transcribed, origin-poor genomic regions. In cells that had been treated with aphidicolin, these regions remained unreplicated even in late S phase; MiDAS then served to complete their replication after the cells entered mitosis. Interestingly, leading and lagging strand synthesis were uncoupled in MiDAS, consistent with MiDAS being a form of break-induced replication, a repair mechanism for collapsed DNA replication forks. Our results provide a better understanding of the mechanisms leading to genomic instability at CFSs and in cancer cells.
DNA 复制压力是人类癌症的一个特征，通常会导致特定基因组位置的不稳定性，如常见的脆弱位点（CFSs）。经历 DNA 复制压力的细胞也可能表现出有丝分裂 DNA 合成（MiDAS）。为了理解 MiDAS 的生理功能及其与 CFSs 的关系，我们在使用 DNA 聚合酶抑制剂 aphidicolin 处理的细胞中，以高分辨率绘制了 MiDAS 的基因组位点。MiDAS 位点表现为明确的峰，在细胞系之间基本保持一致，并包含所有已知的 CFSs。MiDAS 峰映射在大的、转录的、起始源贫的基因组区域内。在用 aphidicolin 处理的细胞中，这些区域即使在晚期 S 期也仍未复制；然后，MiDAS 在细胞进入有丝分裂后完成其复制。有趣的是，MiDAS 中前导链和滞后链的合成是解耦的，这与 MiDAS 是一种断裂诱导复制的形式一致，这是一种用于修复 DNA 复制叉崩溃的修复机制。我们的研究结果提供了对导致 CFSs 和癌细胞中基因组不稳定性的机制的更好理解。
