title: Regulation of E2F1 by BRCT domain-containing protein TopBP1.
abstract: The E2F transcription factor integrates cellular signals and coordinates cell cycle progression. Our prior studies demonstrated selective induction and stabilization of E2F1 through ATM-dependent phosphorylation in response to DNA damage. Here we report that DNA topoisomerase IIbeta binding protein 1 (TopBP1) regulates E2F1 during DNA damage. TopBP1 contains eight BRCT (BRCA1 carboxyl-terminal) motifs and upon DNA damage is recruited to stalled replication forks, where it participates in a DNA damage checkpoint. Here we demonstrated an interaction between TopBP1 and E2F1. The interaction depended on the amino terminus of E2F1 and the sixth BRCT domain of TopBP1. It was specific to E2F1 and was not observed in E2F2, E2F3, or E2F4. This interaction was induced by DNA damage and phosphorylation of E2F1 by ATM. Through this interaction, TopBP1 repressed multiple activities of E2F1, including transcriptional activity, induction of S-phase entry, and apoptosis. Furthermore, TopBP1 relocalized E2F1 from diffuse nuclear distribution to discrete punctate nuclear foci, where E2F1 colocalized with TopBP1 and BRCA1. Thus, the specific interaction between TopBP1 and E2F1 during DNA damage inhibits the known E2F1 activities but recruits E2F1 to a BRCA1-containing repair complex, suggesting a direct role of E2F1 in DNA damage checkpoint/repair at stalled replication forks.
authors.affiliation: Division of Hematology and Oncology, Department of Medicine, University of Alabama at Birmingham, Birmingham, Alabama 35294-3300, USA.
authors.forename: Kang
authors.initials: K
authors.lastname: Liu
authors.forename: Fang-Tsyr
authors.initials: FT
authors.lastname: Lin
authors.forename: J Michael
authors.initials: JM
authors.lastname: Ruppert
authors.forename: Weei-Chin
authors.initials: WC
authors.lastname: Lin
mesh_terms: D017209:Apoptosis / Q000502:physiology; D064007:Ataxia Telangiectasia Mutated Proteins; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D002478:Cells, Cultured; D004249:DNA Damage / Q000187:drug effects / Q000502:physiology; D004261:DNA Replication; D004268:DNA-Binding Proteins; D004317:Doxorubicin / Q000494:pharmacology; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; D050703:E2F2 Transcription Factor; D050699:E2F3 Transcription Factor; D050704:E2F4 Transcription Factor; D005786:Gene Expression Regulation; D006801:Humans; D009687:Nuclear Proteins; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D016196:S Phase / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D025521:Tumor Suppressor Proteins
chemical_list: D019313:BRCA1 Protein; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050684:E2F Transcription Factors; D050687:E2F1 Transcription Factor; C493753:E2F1 protein, human; D050703:E2F2 Transcription Factor; C493761:E2F2 protein, human; D050699:E2F3 Transcription Factor; D050704:E2F4 Transcription Factor; C493762:E2F4 protein, human; D009687:Nuclear Proteins; D011994:Recombinant Proteins; C110513:TOPBP1 protein, human; D014157:Transcription Factors; D025521:Tumor Suppressor Proteins; D004317:Doxorubicin; C576324:ATM protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases