RNF8 ubiquitylation of XRN2 facilitates R-loop resolution and restrains genomic instability in BRCA1 mutant cells
Rehna Krishnan, Mariah Lapierre, Brandon Gautreau, Kevin C. Nixon, Samah El Ghamrasni, Parasvi S. Patel, Jun Hao, V. Talya Yerlici, Kiran Kumar Naidu Guturi, Jonathan St‐Germain, Francesca Mateo, Amine Saad, Arash Algouneh, Rebecca Earnshaw, Duan Shili, Alma Seitova, Joshua W. Miller, Negin Khosraviani, Adam Penn, Brandon Ho, Otto Sánchez, M. Prakash Hande, Jean‐Yves Masson, Grant W. Brown, Moulay A. Alaoui‐Jamali, John J. Reynolds, C.H. Arrowsmith, Brian Raught, Miguel Ángel Pujana, Karim Mekhail, Grant S. Stewart, Anne Hakem, Razqallah Hakem
Abstract
Breast cancer linked with BRCA1/2 mutations commonly recur and resist current therapies, including PARP inhibitors. Given the lack of effective targeted therapies for BRCA1-mutant cancers, we sought to identify novel targets to selectively kill these cancers. Here, we report that loss of RNF8 significantly protects Brca1-mutant mice against mammary tumorigenesis. RNF8 deficiency in human BRCA1-mutant breast cancer cells was found to promote R-loop accumulation and replication fork instability, leading to increased DNA damage, senescence, and synthetic lethality. Mechanistically, RNF8 interacts with XRN2, which is crucial for transcription termination and R-loop resolution. We report that RNF8 ubiquitylates XRN2 to facilitate its recruitment to R-loop-prone genomic loci and that RNF8 deficiency in BRCA1-mutant breast cancer cells decreases XRN2 occupancy at R-loop-prone sites, thereby promoting R-loop accumulation, transcription-replication collisions, excessive genomic instability, and cancer cell death. Collectively, our work identifies a synthetic lethal interaction between RNF8 and BRCA1, which is mediated by a pathological accumulation of R-loops.