title: XLF interacts with the XRCC4-DNA ligase IV complex to promote DNA nonhomologous end-joining.
abstract: DNA nonhomologous end-joining (NHEJ) is a predominant pathway of DNA double-strand break repair in mammalian cells, and defects in it cause radiosensitivity at the cellular and whole-organism levels. Central to NHEJ is the protein complex containing DNA Ligase IV and XRCC4. By searching for additional XRCC4-interacting factors, we identified a previously uncharacterized 33 kDa protein, XRCC4-like factor (XLF, also named Cernunnos), that has weak sequence homology with XRCC4 and is predicted to display structural similarity to XRCC4. We show that XLF directly interacts with the XRCC4-Ligase IV complex in vitro and in vivo and that siRNA-mediated downregulation of XLF in human cell lines leads to radiosensitivity and impaired NHEJ. Furthermore, we establish that NHEJ-deficient 2BN cells derived from a radiosensitive and immune-deficient patient lack XLF due to an inactivating frameshift mutation in its gene, and that reintroduction of wild-type XLF into such cells corrects their radiosensitivity and NHEJ defects. XLF thus constitutes a novel core component of the mammalian NHEJ apparatus.
authors.affiliation: The Gurdon Institute, Cambridge University, UK.
authors.forename: Peter
authors.initials: P
authors.lastname: Ahnesorg
authors.forename: Philippa
authors.initials: P
authors.lastname: Smith
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Jackson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D016384:Consensus Sequence; D000072481:DNA Ligase ATP; D011088:DNA Ligases / Q000378:metabolism*; D004260:DNA Repair; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D015536:Down-Regulation; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D011836:Radiation Tolerance; D016415:Sequence Alignment
chemical_list: D004268:DNA-Binding Proteins; C000607893:LIG4 protein, human; C508551:NHEJ1 protein, human; D009687:Nuclear Proteins; C101467:XRCC4 protein, human; D011088:DNA Ligases; D045643:DNA Repair Enzymes; D000072481:DNA Ligase ATP