title: TopBP1 associates with NBS1 and is involved in homologous recombination repair.
abstract: TopBP1 is involved in DNA replication and DNA damage checkpoint. Recent studies have demonstrated that TopBP1 is a direct positive effecter of ATR. However, it is not known how TopBP1 recognizes damaged DNA. Here, we show that TopBP1 formed nuclear foci after exposure to ionizing radiation, but such TopBP1 foci were abolished in Nijmegen breakage syndrome cells. We also show that TopBP1 physically associated with NBS1 in vivo. These results suggested that NBS1 might regulate TopBP1 recruitment to the sites of DNA damage. TopBP1-depleted cells showed hypersensitivity to Mitomycin C and ionizing radiation, an increased frequency of sister-chromatid exchange level, and a reduced frequency of DNA double-strand break induced homologous recombination repair. Together, these results suggested that TopBP1 might be a mediator of DNA damage signaling from NBS1 to ATR and promote homologous recombination repair.
authors.affiliation: Department of Radiation Biology, Research Institute for Radiation Biology and Medicine, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
authors.forename: Ken-ichi
authors.initials: K
authors.lastname: Morishima
authors.forename: Shuichi
authors.initials: S
authors.lastname: Sakamoto
authors.forename: Junya
authors.initials: J
authors.lastname: Kobayashi
authors.forename: Hideki
authors.initials: H
authors.lastname: Izumi
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Suda
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Matsumoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Tauchi
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ide
authors.forename: Kenshi
authors.initials: K
authors.lastname: Komatsu
authors.forename: Shinya
authors.initials: S
authors.lastname: Matsuura
mesh_terms: D002352:Carrier Proteins / Q000378:metabolism*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D004249:DNA Damage / Q000235:genetics*; D004260:DNA Repair / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D009687:Nuclear Proteins / Q000378:metabolism*; D011995:Recombination, Genetic / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C112156:NBN protein, human; D009687:Nuclear Proteins; C110513:TOPBP1 protein, human