A RAD18-UBC13-PALB2-RNF168 axis mediates replication fork recovery in BRCA1-deficient cancer cells

Nucleic Acids Res. 2024 Aug 27;52(15):8861-8879. doi: 10.1093/nar/gkae563.

Abstract

BRCA1/2 proteins function in genome stability by promoting repair of double-stranded DNA breaks through homologous recombination and by protecting stalled replication forks from nucleolytic degradation. In BRCA1/2-deficient cancer cells, extensively degraded replication forks can be rescued through distinct fork recovery mechanisms that also promote cell survival. Here, we identified a novel pathway mediated by the E3 ubiquitin ligase RAD18, the E2-conjugating enzyme UBC13, the recombination factor PALB2, the E3 ubiquitin ligase RNF168 and PCNA ubiquitination that promotes fork recovery in BRCA1- but not BRCA2-deficient cells. We show that this pathway does not promote fork recovery by preventing replication fork reversal and degradation in BRCA1-deficient cells. We propose a mechanism whereby the RAD18-UBC13-PALB2-RNF168 axis facilitates resumption of DNA synthesis by promoting re-annealing of the complementary single-stranded template strands of the extensively degraded forks, thereby allowing re-establishment of a functional replication fork. We also provide preliminary evidence for the potential clinical relevance of this novel fork recovery pathway in BRCA1-mutated cancers, as RAD18 is over-expressed in BRCA1-deficient cancers, and RAD18 loss compromises cell viability in BRCA1-deficient cancer cells.

MeSH terms

  • BRCA1 Protein* / deficiency
  • BRCA1 Protein* / genetics
  • BRCA1 Protein* / metabolism
  • Cell Line, Tumor
  • DNA Repair
  • DNA Replication*
  • DNA-Binding Proteins* / genetics
  • DNA-Binding Proteins* / metabolism
  • Fanconi Anemia Complementation Group N Protein* / genetics
  • Fanconi Anemia Complementation Group N Protein* / metabolism
  • Humans
  • Proliferating Cell Nuclear Antigen / genetics
  • Proliferating Cell Nuclear Antigen / metabolism
  • Ubiquitin-Conjugating Enzymes* / genetics
  • Ubiquitin-Conjugating Enzymes* / metabolism
  • Ubiquitin-Protein Ligases* / genetics
  • Ubiquitin-Protein Ligases* / metabolism
  • Ubiquitination

Substances

  • Ubiquitin-Protein Ligases
  • RAD18 protein, human
  • BRCA1 Protein
  • DNA-Binding Proteins
  • Ubiquitin-Conjugating Enzymes
  • BRCA1 protein, human
  • Fanconi Anemia Complementation Group N Protein
  • PALB2 protein, human
  • UBE2N protein, human
  • Proliferating Cell Nuclear Antigen
  • UBE2A protein, human
  • PCNA protein, human