Xu Guotai, Chapman J Ross, Brandsma Inger, Yuan Jingsong, Mistrik Martin, Bouwman Peter, Bartkova Jirina, Gogola Ewa, Warmerdam Daniël, Barazas Marco, Jaspers Janneke E, Watanabe Kenji, Pieterse Mark, Kersbergen Ariena, Sol Wendy, Celie Patrick H N, Schouten Philip C, van den Broek Bram, Salman Ahmed, Nieuwland Marja, de Rink Iris, de Ronde Jorma, Jalink Kees, Boulton Simon J, Chen Junjie, van Gent Dik C, Bartek Jiri, Jonkers Jos, Borst Piet, Rottenberg Sven
Division of Molecular Oncology, The Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands.
The Wellcome Trust Centre for Human Genetics, Roosevelt Drive, Oxford, OX3 7BN, United Kingdom.
Nature. 2015 May 28;521(7553):541-544. doi: 10.1038/nature14328. Epub 2015 Mar 23.
Error-free repair of DNA double-strand breaks (DSBs) is achieved by homologous recombination (HR), and BRCA1 is an important factor for this repair pathway. In the absence of BRCA1-mediated HR, the administration of PARP inhibitors induces synthetic lethality of tumour cells of patients with breast or ovarian cancers. Despite the benefit of this tailored therapy, drug resistance can occur by HR restoration. Genetic reversion of BRCA1-inactivating mutations can be the underlying mechanism of drug resistance, but this does not explain resistance in all cases. In particular, little is known about BRCA1-independent restoration of HR. Here we show that loss of REV7 (also known as MAD2L2) in mouse and human cell lines re-establishes CTIP-dependent end resection of DSBs in BRCA1-deficient cells, leading to HR restoration and PARP inhibitor resistance, which is reversed by ATM kinase inhibition. REV7 is recruited to DSBs in a manner dependent on the H2AX-MDC1-RNF8-RNF168-53BP1 chromatin pathway, and seems to block HR and promote end joining in addition to its regulatory role in DNA damage tolerance. Finally, we establish that REV7 blocks DSB resection to promote non-homologous end-joining during immunoglobulin class switch recombination. Our results reveal an unexpected crucial function of REV7 downstream of 53BP1 in coordinating pathological DSB repair pathway choices in BRCA1-deficient cells.
DNA双链断裂（DSB）的无差错修复是通过同源重组（HR）实现的，而BRCA1是该修复途径的一个重要因素。在缺乏BRCA1介导的HR的情况下，给予PARP抑制剂会诱导乳腺癌或卵巢癌患者肿瘤细胞的合成致死性。尽管这种靶向治疗有好处，但HR的恢复会导致耐药性的产生。BRCA1失活突变的基因回复可能是耐药的潜在机制，但这并不能解释所有情况下的耐药性。特别是，关于不依赖BRCA1的HR恢复知之甚少。在这里，我们表明，在小鼠和人类细胞系中REV7（也称为MAD2L2）的缺失可在BRCA1缺陷细胞中重新建立CTIP依赖性的DSB末端切除，从而导致HR恢复和PARP抑制剂耐药性，而ATM激酶抑制可逆转这种耐药性。REV7以依赖于H2AX-MDC1-RNF8-RNF168-53BP1染色质途径的方式被招募到DSB处，除了在DNA损伤耐受中的调节作用外，它似乎还会阻断HR并促进末端连接。最后，我们确定REV7在免疫球蛋白类别转换重组过程中会阻断DSB切除以促进非同源末端连接。我们的结果揭示了53BP1下游的REV7在协调BRCA1缺陷细胞中病理性DSB修复途径选择方面的意外关键功能。
