PIF1 helicase promotes break-induced replication in mammalian cells

Shibo Li, Hailong Wang, Sanaa Jehi, Jun Li, Shuo Liu, Zi Wang, Lan Truong, Takuya Chiba, Zefeng Wang, Xiaohua Wu*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)


Break-induced replication (BIR) is a specialized homologous-recombination pathway for DNA double-strand break (DSB) repair, which often induces genome instability. In this study, we establish EGFP-based recombination reporters to systematically study BIR in mammalian cells and demonstrate an important role of human PIF1 helicase in promoting BIR. We show that at endonuclease cleavage sites, PIF1-dependent BIR is used for homology-initiated recombination requiring long track DNA synthesis, but not short track gene conversion (STGC). We also show that structure formation-prone AT-rich DNA sequences derived from common fragile sites (CFS-ATs) induce BIR upon replication stress and oncogenic stress, and PCNA-dependent loading of PIF1 onto collapsed/broken forks is critical for BIR activation. At broken replication forks, even STGC-mediated repair of double-ended DSBs depends on POLD3 and PIF1, revealing an unexpected mechanism of BIR activation upon replication stress that differs from the conventional BIR activation model requiring DSB end sensing at endonuclease-generated breaks. Furthermore, loss of PIF1 is synthetically lethal with loss of FANCM, which is involved in protecting CFS-ATs. The breast cancer-associated PIF1 mutant L319P is defective in BIR, suggesting a direct link of BIR to oncogenic processes.

Original languageEnglish
Article numbere104509
JournalEMBO Journal
Issue number8
Publication statusPublished - 2021 Apr 15


  • PIF1
  • break-induced replication
  • long track gene conversion
  • replication stress
  • short track gene conversion

ASJC Scopus subject areas

  • Neuroscience(all)
  • Molecular Biology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Immunology and Microbiology(all)


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