Department of Chemistry, New Mexico Institute of Mining and Technology, 801 Leroy Pl., Socorro, NM, 87801, USA.
Department of Neurosurgery, University of Oklahoma Health Science Center, Oklahoma City, OK, 73104, USA.
Sci Rep. 2020 Aug 28;10(1):14253. doi: 10.1038/s41598-020-71203-7.
Persistent R-loops (RNA-DNA hybrids with a displaced single-stranded DNA) create DNA damage and lead to genomic instability. The 5'-3'-exoribonuclease 2 (XRN2) degrades RNA to resolve R-loops and promotes transcription termination. Previously, XRN2 was implicated in DNA double strand break (DSB) repair and in resolving replication stress. Here, using tandem affinity purification-mass spectrometry, bioinformatics, and biochemical approaches, we found that XRN2 associates with proteins involved in DNA repair/replication (Ku70-Ku80, DNA-PKcs, PARP1, MCM2-7, PCNA, RPA1) and RNA metabolism (RNA helicases, PRP19, p54(nrb), splicing factors). Novel major pathways linked to XRN2 include cell cycle control of chromosomal replication and DSB repair by non-homologous end joining. Investigating the biological implications of these interactions led us to discover that XRN2 depletion compromised cell survival after additional knockdown of specific DNA repair proteins, including PARP1. XRN2-deficient cells also showed enhanced PARP1 activity. Consistent with concurrent depletion of XRN2 and PARP1 promoting cell death, XRN2-deficient fibroblast and lung cancer cells also demonstrated sensitivity to PARP1 inhibition. XRN2 alterations (mutations, copy number/expression changes) are frequent in cancers. Thus, PARP1 inhibition could target cancers exhibiting XRN2 functional loss. Collectively, our data suggest XRN2's association with novel protein partners and unravel synthetic lethality between XRN2 depletion and PARP1 inhibition.
持久的 R 环（带有移位单链 DNA 的 RNA-DNA 杂交体）会造成 DNA 损伤并导致基因组不稳定。5'-3'-外切核酸酶 2（XRN2）通过降解 RNA 来解决 R 环并促进转录终止。先前，XRN2 被牵连到 DNA 双链断裂（DSB）修复和解决复制应激中。在这里，我们使用串联亲和纯化-质谱、生物信息学和生化方法，发现 XRN2 与涉及 DNA 修复/复制（Ku70-Ku80、DNA-PKcs、PARP1、MCM2-7、PCNA、RPA1）和 RNA 代谢（RNA 解旋酶、PRP19、p54(nrb)、剪接因子）的蛋白质相关联。与 XRN2 相关的新主要途径包括细胞周期控制染色体复制和非同源末端连接修复 DSB。研究这些相互作用的生物学意义使我们发现，XRN2 耗尽后，在进一步敲低特定 DNA 修复蛋白（包括 PARP1）后，会损害细胞存活。XRN2 缺陷细胞也显示出增强的 PARP1 活性。与同时耗尽 XRN2 和 PARP1 促进细胞死亡一致，XRN2 缺陷成纤维细胞和肺癌细胞也对 PARP1 抑制敏感。XRN2 改变（突变、拷贝数/表达变化）在癌症中很常见。因此，PARP1 抑制可能靶向表现出 XRN2 功能丧失的癌症。总的来说，我们的数据表明 XRN2 与新的蛋白质伴侣的关联，并揭示了 XRN2 耗尽和 PARP1 抑制之间的合成致死性。
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