BRCA1 Haploinsufficiency Is Masked by RNF168-Mediated Chromatin Ubiquitylation

Mol Cell. 2019 Mar 21;73(6):1267-1281.e7. doi: 10.1016/j.molcel.2018.12.010. Epub 2019 Jan 28.

Abstract

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.

Keywords: BRCA1; PALB2; RAD51; RNF168; cancer; chromatin ubiquitylation; genome stability; haploinsufficiency; homologous recombination; replication fork protection; resection.

Publication types

  • Research Support, N.I.H., Intramural
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Animals
  • BRCA1 Protein / genetics*
  • BRCA2 Protein / genetics
  • Cell Line, Tumor
  • Chromatin / enzymology*
  • Chromatin / genetics
  • DNA Damage
  • Fanconi Anemia Complementation Group N Protein / genetics
  • Fanconi Anemia Complementation Group N Protein / metabolism
  • Female
  • Fibroblasts / enzymology*
  • Haploinsufficiency*
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Mutation
  • Neoplasms / drug therapy
  • Neoplasms / enzymology*
  • Neoplasms / genetics
  • Neoplasms / pathology
  • Poly(ADP-ribose) Polymerase Inhibitors / pharmacology
  • Rad51 Recombinase / genetics
  • Rad51 Recombinase / metabolism
  • Recombinational DNA Repair
  • 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*

Substances

  • BRCA1 Protein
  • BRCA1 protein, human
  • BRCA2 Protein
  • BRCA2 protein, mouse
  • Brca1 protein, mouse
  • Chromatin
  • Fanconi Anemia Complementation Group N Protein
  • PALB2 protein, human
  • Palb2 protein, mouse
  • Poly(ADP-ribose) Polymerase Inhibitors
  • TP53BP1 protein, human
  • Trp53bp1 protein, mouse
  • Tumor Suppressor p53-Binding Protein 1
  • RNF168 protein, human
  • RNF168 protein, mouse
  • Ubiquitin-Protein Ligases
  • RAD51 protein, human
  • Rad51 Recombinase
  • Rad51 protein, mouse