PIF1 helicase promotes break‐induced replication in mammalian cells |
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Authors: | Shibo Li Hailong Wang Sanaa Jehi Jun Li Shuo Liu Zi Wang Lan Truong Takuya Chiba Zefeng Wang Xiaohua Wu |
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Institution: | 1. Department of Molecular Medicine, The Scripps Research Institute, La Jolla CA, USA ; 2. Biomedical Gerontology Laboratory, Department of Health Science and Social Welfare, School of Human Sciences, Waseda University, Tokorozawa Japan ; 3. CAS Key Laboratory of Computational Biology, University of Chinese Academy of Sciences, Shanghai Institute of Biological Sciences, Chinese Academy of Sciences, Shanghai China |
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Abstract: | 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. |
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Keywords: | break‐ induced replication long track gene conversion PIF1 replication stress short track gene conversion |
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