title: Structure-specific endonucleases xpf and mus81 play overlapping but essential roles in DNA repair by homologous recombination.
abstract: DNA double-strand breaks (DSB) occur frequently during replication in sister chromatids and are dramatically increased when cells are exposed to chemotherapeutic agents including camptothecin. Such DSBs are efficiently repaired specifically by homologous recombination (HR) with the intact sister chromatid. HR, therefore, plays pivotal roles in cellular proliferation and cellular tolerance to camptothecin. Mammalian cells carry several structure-specific endonucleases, such as Xpf-Ercc1 and Mus81-Eme1, in which Xpf and Mus81 are the essential subunits for enzymatic activity. Here, we show the functional overlap between Xpf and Mus81 by conditionally inactivating Xpf in the chicken DT40 cell line, which has no Mus81 ortholog. Although mammalian cells deficient in either Xpf or Mus81 are viable, Xpf inactivation in DT40 cells was lethal, resulting in a marked increase in the number of spontaneous chromosome breaks. Similarly, inactivation of both Xpf and Mus81 in human HeLa cells and murine embryonic stem cells caused numerous spontaneous chromosome breaks. Furthermore, the phenotype of Xpf-deficient DT40 cells was reversed by ectopic expression of human Mus81-Eme1 or human Xpf-Ercc1 heterodimers. These observations indicate the functional overlap of Xpf-Ercc1 and Mus81-Eme1 in the maintenance of genomic DNA. Both Mus81-Eme1 and Xpf-Ercc1 contribute to the completion of HR, as evidenced by the data that the expression of Mus81-Eme1 or Xpf-Ercc1 diminished the number of camptothecin-induced chromosome breaks in Xpf-deficient DT40 cells, and to preventing early steps in HR by deleting XRCC3 suppressed the nonviability of Xpf-deficient DT40 cells. In summary, Xpf and Mus81 have a substantially overlapping function in completion of HR.
authors.affiliation: Department of Radiation Genetics, and Frontier Technology Center, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Kikuchi
authors.forename: Takeo
authors.initials: T
authors.lastname: Narita
authors.forename: Van T
authors.initials: VT
authors.lastname: Pham
authors.forename: Junko
authors.initials: J
authors.lastname: Iijima
authors.forename: Kouji
authors.initials: K
authors.lastname: Hirota
authors.forename: Islam Shamima
authors.initials: IS
authors.lastname: Keka
authors.lastname: Mohiuddin
authors.forename: Katsuya
authors.initials: K
authors.lastname: Okawa
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hori
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Fukagawa
authors.forename: Jeroen
authors.initials: J
authors.lastname: Essers
authors.forename: Roland
authors.initials: R
authors.lastname: Kanaar
authors.forename: Matthew C
authors.initials: MC
authors.lastname: Whitby
authors.forename: Kaoru
authors.initials: K
authors.lastname: Sugasawa
authors.forename: Yoshihito
authors.initials: Y
authors.lastname: Taniguchi
authors.forename: Katsumi
authors.initials: K
authors.lastname: Kitagawa
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takeda
mesh_terms: D000818:Animals; D016923:Cell Death / Q000235:genetics; D045744:Cell Line, Tumor; D002645:Chickens; D002869:Chromosome Aberrations; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D004720:Endonucleases / Q000235:genetics* / Q000378:metabolism*; D006367:HeLa Cells; D059765:Homologous Recombination; D006801:Humans; D051379:Mice
chemical_list: D004268:DNA-Binding Proteins; C095888:xeroderma pigmentosum group F protein; D004720:Endonucleases