BRCA1 Haploinsufficiency Is Masked by RNF168-Mediated Chromatin Ubiquitylation

• Published in: Molecular cell Vol. 73; no. 6; pp. 1267 - 1281.e7
• Main Authors: Zong, Dali, Adam, Salomé, Wang, Yifan, Sasanuma, Hiroyuki, Callén, Elsa, Murga, Matilde, Day, Amanda, Kruhlak, Michael J., Wong, Nancy, Munro, Meagan, Ray Chaudhuri, Arnab, Karim, Baktiar, Xia, Bing, Takeda, Shunichi, Johnson, Neil, Durocher, Daniel, Nussenzweig, André
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 21.03.2019
• Subjects: Animals; BRCA1; BRCA1 Protein - genetics; BRCA2 Protein - genetics; cancer; Cell Line, Tumor; Chromatin - enzymology; Chromatin - genetics; chromatin ubiquitylation; DNA Damage; Fanconi Anemia Complementation Group N Protein - genetics; Fanconi Anemia Complementation Group N Protein - metabolism; Female; Fibroblasts - enzymology; genome stability; Haploinsufficiency; homologous recombination; Mice; Mice, Inbred C57BL; Mice, Knockout; Mutation; Neoplasms - drug therapy; Neoplasms - enzymology; Neoplasms - genetics; Neoplasms - pathology; PALB2; Poly(ADP-ribose) Polymerase Inhibitors - pharmacology; RAD51; Rad51 Recombinase - genetics; Rad51 Recombinase - metabolism; Recombinational DNA Repair; replication fork protection; resection; RNF168; Tumor Suppressor p53-Binding Protein 1 - genetics; Tumor Suppressor p53-Binding Protein 1 - metabolism; Ubiquitin-Protein Ligases - deficiency; Ubiquitin-Protein Ligases - genetics; Ubiquitin-Protein Ligases - metabolism; Ubiquitination; RNF168; genome stability; RAD51; haploinsufficiency; homologous recombination; chromatin ubiquitylation; cancer; BRCA1; replication fork protection; PALB2; resection
• ISSN: 1097-2765; 1097-4164
• DOI: 10.1016/j.molcel.2018.12.010

BRCA1 functions at two distinct steps during homologous recombination (HR). Initially, it promotes DNA end resection, and subsequently it recruits the PALB2 and BRCA2 mediator complex, which stabilizes RAD51-DNA nucleoprotein filaments. Loss of 53BP1 rescues the HR defect in BRCA1-deficient cells by increasing resection, suggesting that BRCA1’s downstream role in RAD51 loading is dispensable when 53BP1 is absent. Here we show that the E3 ubiquitin ligase RNF168, in addition to its canonical role in inhibiting end resection, acts in a redundant manner with BRCA1 to load PALB2 onto damaged DNA. Loss of RNF168 negates the synthetic rescue of BRCA1 deficiency by 53BP1 deletion, and it predisposes BRCA1 heterozygous mice to cancer. BRCA1+/−RNF168−/− cells lack RAD51 foci and are hypersensitive to PARP inhibitor, whereas forced targeting of PALB2 to DNA breaks in mutant cells circumvents BRCA1 haploinsufficiency. Inhibiting the chromatin ubiquitin pathway may, therefore, be a synthetic lethality strategy for BRCA1-deficient cancers. [Display omitted] •The E3 ubiquitin ligase RNF168 supports BRCA1-independent homologous recombination•RNF168 acts redundantly with BRCA1 to load PALB2 onto damaged DNA•Targeting RNF168 could induce synthetic lethality in BRCA1-deficient cancers•The function of BRCA1 in replication fork protection is separable from its HR role BRCA1 facilitates DNA end resection and RAD51 filament formation during homologous recombination. Zong et al. demonstrate that the RNF168-mediated chromatin ubiquitylation pathway acts redundantly with BRCA1 to promote RAD51-dependent homologous recombination. RNF168 activity is essential to prevent overt genome instability and tumorigenesis in BRCA1 heterozygous mice, independent of p53 mutation.