title: TopBP1 functions with 53BP1 in the G1 DNA damage checkpoint.
abstract: TopBP1 is a checkpoint protein that colocalizes with ATR at sites of DNA replication stress. In this study, we show that TopBP1 also colocalizes with 53BP1 at sites of DNA double-strand breaks (DSBs), but only in the G1-phase of the cell cycle. Recruitment of TopBP1 to sites of DNA replication stress was dependent on BRCT domains 1-2 and 7-8, whereas recruitment to sites of DNA DSBs was dependent on BRCT domains 1-2 and 4-5. The BRCT domains 4-5 interacted with 53BP1 and recruitment of TopBP1 to sites of DNA DSBs in G1 was dependent on 53BP1. As TopBP1 contains a domain important for ATR activation, we examined whether it contributes to the G1 cell cycle checkpoint. By monitoring the entry of irradiated G1 cells into S-phase, we observed a checkpoint defect after siRNA-mediated depletion of TopBP1, 53BP1 or ATM. Thus, TopBP1 may mediate the checkpoint function of 53BP1 in G1.
authors.affiliation: Department of Molecular Biology, University of Geneva, Geneva, Switzerland.
authors.forename: Rachele
authors.initials: R
authors.lastname: Cescutti
authors.forename: Simona
authors.initials: S
authors.lastname: Negrini
authors.forename: Masaoki
authors.initials: M
authors.lastname: Kohzaki
authors.forename: Thanos D
authors.initials: TD
authors.lastname: Halazonetis
mesh_terms: D015153:Blotting, Western; D001859:Bone Neoplasms / Q000235:genetics* / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000502:physiology*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair; D004261:DNA Replication; D004268:DNA-Binding Proteins / Q000502:physiology*; D016193:G1 Phase / Q000235:genetics*; D018816:Genes, cdc / Q000502:physiology*; D006801:Humans; D047468:Immunoprecipitation; D047908:Intracellular Signaling Peptides and Proteins / Q000502:physiology*; D009687:Nuclear Proteins / Q000502:physiology*; D012516:Osteosarcoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D014407:Tumor Cells, Cultured; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: D002352:Carrier Proteins; D004268:DNA-Binding Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; C110513:TOPBP1 protein, human; C498301:TP53BP1 protein, human; D000071857:Tumor Suppressor p53-Binding Protein 1