title: Smarcal1 promotes double-strand-break repair by nonhomologous end-joining.
abstract: Smarcal1 is a SWI/SNF-family protein with an ATPase domain involved in DNA-annealing activities and a binding site for the RPA single-strand-DNA-binding protein. Although the role played by Smarcal1 in the maintenance of replication forks has been established, it remains unknown whether Smarcal1 contributes to genomic DNA maintenance outside of the S phase. We disrupted the SMARCAL1 gene in both the chicken DT40 and the human TK6 B cell lines. The resulting SMARCAL1(-/-) clones exhibited sensitivity to chemotherapeutic topoisomerase 2 inhibitors, just as nonhomologous end-joining (NHEJ) null-deficient cells do. SMARCAL1(-/-) cells also exhibited an increase in radiosensitivity in the G1 phase. Moreover, the loss of Smarcal1 in NHEJ null-deficient cells does not further increase their radiosensitivity. These results demonstrate that Smarcal1 is required for efficient NHEJ-mediated DSB repair. Both inactivation of the ATPase domain and deletion of the RPA-binding site cause the same phenotype as does null-mutation of Smarcal1, suggesting that Smarcal1 enhances NHEJ, presumably by interacting with RPA at unwound single-strand sequences and then facilitating annealing at DSB ends. SMARCAL1(-/-)cells showed a poor accumulation of Ku70/DNA-PKcs and XRCC4 at DNA-damage sites. We propose that Smarcal1 maintains the duplex status of DSBs to ensure proper recruitment of NHEJ factors to DSB sites.
authors.affiliation: Department of Radiation Genetics, Kyoto University, Graduate School of Medicine, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Islam Shamima
authors.initials: IS
authors.lastname: Keka
authors.affiliation: Department of Radiation Genetics, Kyoto University, Graduate School of Medicine, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
authors.lastname: Mohiuddin
authors.affiliation: Department of Radiation Genetics, Kyoto University, Graduate School of Medicine, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Maede
authors.affiliation: Department of Radiation Genetics, Kyoto University, Graduate School of Medicine, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Md Maminur
authors.initials: MM
authors.lastname: Rahman
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Tetsushi
authors.initials: T
authors.lastname: Sakuma
authors.affiliation: Division of Genetics and Mutagenesis, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
authors.forename: Masamitsu
authors.initials: M
authors.lastname: Honma
authors.affiliation: Department of Mathematical and Life Sciences, Graduate School of Science, Hiroshima University, Higashi-Hiroshima 739-8526, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Department of Radiation Genetics, Kyoto University, Graduate School of Medicine, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Takeda
authors.affiliation: Department of Radiation Genetics, Kyoto University, Graduate School of Medicine, Yoshida Konoe, Sakyo-ku, Kyoto 606-8501, Japan hiroysasa@rg.med.kyoto-u.ac.jp.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Sasanuma
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000633:toxicity; D002460:Cell Line; D002645:Chickens; D053903:DNA Breaks, Double-Stranded; D004249:DNA Damage; D059766:DNA End-Joining Repair; D004265:DNA Helicases / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D016193:G1 Phase / Q000235:genetics; D017353:Gene Deletion; D006801:Humans; D017434:Protein Structure, Tertiary
chemical_list: D004268:DNA-Binding Proteins; C412482:SMARCAL1 protein, human; D004265:DNA Helicases; D002166:Camptothecin