Institute of Bioinformatics and Applied Biotechnology, Electronics City, Bangalore, India.
Manipal Academy of Higher Education, Manipal, Karnataka, India.
Mol Carcinog. 2019 Feb;58(2):219-233. doi: 10.1002/mc.22921. Epub 2018 Oct 25.
Efficient DNA repair is indispensable for maintaining genomic integrity in humans. Cancer associated deletions and mutations are mainly due to misrepaired DNA double-strand breaks (DSBs). Classical nonhomologous end joining (c-NHEJ) and homologous recombination (HR) are two major DSB repair pathways in humans. An error prone, alternative NHEJ pathway that utilizes microhomology was also reported in cancer cells and to a lesser extent in normal cells. In the present study, we evaluated the efficiency of various DSB repair pathways in the most common lymphoma, the diffuse large B cell lymphoma (DLBCL). Here we show that DNA repair through c-NHEJ pathway is limited in SUDHL8, a cell line derived from a DLBCL patient. Unlike c-NHEJ, microhomology mediated end joining (MMEJ) was predominant at physiological temperature. Consistent with the observation, expression level of repair proteins such as LIGASE I, LIGASE III, PARP1, CtIP, and MRE11 was higher in DLBCL cells when compared to c-NHEJ proteins. Further, inhibition of LIGASE I or MRE11, led to reduction in the efficiency of MMEJ in DLBCL cells. Besides, HR-mediated DSB repair occurring through gene conversion was observed. Thus, our results reveal the predominance of MMEJ over c-NHEJ in repairing DSBs in DLBCL cells, while error-free repair through HR was also evident.
高效的 DNA 修复对于维持人类基因组完整性是不可或缺的。与癌症相关的缺失和突变主要是由于 DNA 双链断裂（DSB）的修复错误。经典的非同源末端连接（c-NHEJ）和同源重组（HR）是人类中两种主要的 DSB 修复途径。在癌细胞中也报道了一种易错的、利用微同源性的替代 NHEJ 途径，在正常细胞中则较少。在本研究中，我们评估了最常见的淋巴瘤——弥漫性大 B 细胞淋巴瘤（DLBCL）中各种 DSB 修复途径的效率。在这里，我们显示了源自 DLBCL 患者的细胞系 SUDHL8 中 c-NHEJ 途径的 DNA 修复是有限的。与 c-NHEJ 不同，微同源介导的末端连接（MMEJ）在生理温度下占主导地位。与观察结果一致，与 c-NHEJ 蛋白相比，DLBCL 细胞中修复蛋白（如 LIGASE I、LIGASE III、PARP1、CtIP 和 MRE11）的表达水平更高。此外，抑制 LIGASE I 或 MRE11 会降低 DLBCL 细胞中 MMEJ 的效率。此外，还观察到通过基因转换发生的 HR 介导的 DSB 修复。因此，我们的结果揭示了 MMEJ 在修复 DLBCL 细胞中的 DSB 方面优于 c-NHEJ，而 HR 介导的无错误修复也是显而易见的。
