title: BRCA1-associated exclusion of 53BP1 from DNA damage sites underlies temporal control of DNA repair.
abstract: Following irradiation, numerous DNA-damage-responsive proteins rapidly redistribute into microscopically visible subnuclear aggregates, termed ionising-radiation-induced foci (IRIF). How the enrichment of proteins on damaged chromatin actually relates to DNA repair remains unclear. Here, we use super-resolution microscopy to examine the spatial distribution of BRCA1 and 53BP1 proteins within single IRIF at subdiffraction-limit resolution, yielding an unprecedented increase in detail that was not previously apparent by conventional microscopy. Consistent with a role for 53BP1 in promoting DNA double-strand break repair by non-homologous end joining, 53BP1 enrichment in IRIF is most prominent in the G0/G1 cell cycle phases, where it is enriched in dense globular structures. By contrast, as cells transition through S phase, the recruitment of BRCA1 into the core of IRIF is associated with an exclusion of 53BP1 to the focal periphery, leading to an overall reduction of 53BP1 occupancy at DNA damage sites. Our data suggest that the BRCA1-associated IRIF core corresponds to chromatin regions associated with repair by homologous recombination, and the enrichment of BRCA1 in IRIF represents a temporal switch in the DNA repair program. We propose that BRCA1 antagonises 53BP1-dependent DNA repair in S phase by inhibiting its interaction with chromatin proximal to damage sites. Furthermore, the genomic instability exhibited by BRCA1-deficient cells might result from a failure to efficiently exclude 53BP1 from such regions during S phase.
authors.affiliation: Wellcome Trust and Cancer Research UK Gurdon Institute and Department of Biochemistry, University of Cambridge, Cambridge CB2 1QN, UK. ross.chapman@cancer.org.uk
authors.forename: J Ross
authors.initials: JR
authors.lastname: Chapman
authors.forename: Alex J
authors.initials: AJ
authors.lastname: Sossick
authors.forename: Simon J
authors.initials: SJ
authors.lastname: Boulton
authors.forename: Stephen P
authors.initials: SP
authors.lastname: Jackson
mesh_terms: D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D018929:Cell Culture Techniques; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D053903:DNA Breaks, Double-Stranded; D059766:DNA End-Joining Repair; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: D019313:BRCA1 Protein; D002843:Chromatin; D047908:Intracellular Signaling Peptides and Proteins; C498301:TP53BP1 protein, human; D000071857:Tumor Suppressor p53-Binding Protein 1