title: TopBP1 interacts with BLM to maintain genome stability but is dispensable for preventing BLM degradation.
abstract: The Bloom syndrome helicase BLM and topoisomerase-IIβ-binding protein 1 (TopBP1) are key regulators of genome stability. It was recently proposed that BLM phosphorylation on Ser338 mediates its interaction with TopBP1, to protect BLM from ubiquitylation and degradation (Wang et al., 2013). Here, we show that the BLM-TopBP1 interaction does not involve Ser338 but instead requires BLM phosphorylation on Ser304. Furthermore, we establish that disrupting this interaction does not markedly affect BLM stability. However, BLM-TopBP1 binding is important for maintaining genome integrity, because in its absence cells display increased sister chromatid exchanges, replication origin firing and chromosomal aberrations. Therefore, the BLM-TopBP1 interaction maintains genome stability not by controlling BLM protein levels, but via another as-yet undetermined mechanism. Finally, we identify critical residues that mediate interactions between TopBP1 and MDC1, and between BLM and TOP3A/RMI1/RMI2. Taken together, our findings provide molecular insights into a key tumor suppressor and genome stability network.
authors: The Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK; The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK.
authors: Andrew N
authors: AN
authors: Blackford
authors: The Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK; Institute of Biochemistry and Biophysics, PAS, 02-106 Warsaw, Poland.
authors: Jadwiga
authors: J
authors: Nieminuszczy
authors: The Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK.
authors: Rebekka A
authors: RA
authors: Schwab
authors: The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK.
authors: Yaron
authors: Y
authors: Galanty
authors: The Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK; The Wellcome Trust Sanger Institute, Hinxton, Cambridge CB10 1SA, UK. Electronic address: s.jackson@gurdon.cam.ac.uk.
authors: Stephen P
authors: SP
authors: Jackson
authors: The Weatherall Institute of Molecular Medicine, University of Oxford, Oxford OX3 9DS, UK. Electronic address: wojciech.niedzwiedz@imm.ox.ac.uk.
authors: Wojciech
authors: W
authors: Niedzwiedz
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000595:Amino Acid Sequence; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D018797:Cell Cycle Proteins; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D042822:Genomic Instability; D006367:HeLa Cells; D006801:Humans; D008969:Molecular Sequence Data; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D053484:RecQ Helicases / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; C413163:MDC1 protein, human; D009687:Nuclear Proteins; C501527:RMI1 protein, human; C533196:RMI2 protein, human; C110513:TOPBP1 protein, human; D015534:Trans-Activators; D012694:Serine; C097151:Bloom syndrome protein; D053484:RecQ Helicases; D004264:DNA Topoisomerases, Type I