PRIMPOL-Mediated Adaptive Response Suppresses Replication Fork Reversal in BRCA-Deficient Cells

Mol Cell. 2020 Feb 6;77(3):461-474.e9. doi: 10.1016/j.molcel.2019.10.008. Epub 2019 Oct 29.


Acute treatment with replication-stalling chemotherapeutics causes reversal of replication forks. BRCA proteins protect reversed forks from nucleolytic degradation, and their loss leads to chemosensitivity. Here, we show that fork degradation is no longer detectable in BRCA1-deficient cancer cells exposed to multiple cisplatin doses, mimicking a clinical treatment regimen. This effect depends on increased expression and chromatin loading of PRIMPOL and is regulated by ATR activity. Electron microscopy and single-molecule DNA fiber analyses reveal that PRIMPOL rescues fork degradation by reinitiating DNA synthesis past DNA lesions. PRIMPOL repriming leads to accumulation of ssDNA gaps while suppressing fork reversal. We propose that cells adapt to repeated cisplatin doses by activating PRIMPOL repriming under conditions that would otherwise promote pathological reversed fork degradation. This effect is generalizable to other conditions of impaired fork reversal (e.g., SMARCAL1 loss or PARP inhibition) and suggests a new strategy to modulate cisplatin chemosensitivity by targeting the PRIMPOL pathway.

Keywords: ATR; BRCA; DNA damage; DNA replication; PRIMPOL; adaptive response; replication fork repriming; replication fork reversal; replication stress response; ssDNA gaps.

Publication types

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

MeSH terms

  • Cell Line, Tumor
  • DNA / genetics
  • DNA Damage / genetics
  • DNA Damage / physiology
  • DNA Helicases / genetics
  • DNA Helicases / metabolism
  • DNA Primase / metabolism*
  • DNA Primase / physiology
  • DNA Replication / drug effects*
  • DNA Replication / genetics
  • DNA Replication / physiology
  • DNA, Single-Stranded / genetics
  • DNA, Single-Stranded / metabolism
  • DNA-Binding Proteins / metabolism
  • DNA-Directed DNA Polymerase / metabolism*
  • DNA-Directed DNA Polymerase / physiology
  • HEK293 Cells
  • Humans
  • Multifunctional Enzymes / metabolism*
  • Multifunctional Enzymes / physiology
  • Ubiquitin-Protein Ligases / genetics
  • Ubiquitin-Protein Ligases / metabolism*


  • DNA, Single-Stranded
  • DNA-Binding Proteins
  • Multifunctional Enzymes
  • DNA
  • BRAP protein, human
  • Ubiquitin-Protein Ligases
  • DNA Primase
  • PrimPol protein, human
  • SMARCAL1 protein, human
  • DNA-Directed DNA Polymerase
  • DNA Helicases