title: A comparison of BRCA1 nuclear localization with 14 DNA damage response proteins and domains: identification of specific differences between BRCA1 and 53BP1 at DNA damage-induced foci.
abstract: BRCA1 is an important mediator of the DNA damage response pathway. Previous studies have identified a number of proteins that associate with BRCA1 at nuclear foci after ionizing radiation (IR)-induced DNA damage. However, the co-localization patterns of BRCA1 and various DNA damage response proteins have not yet been systematically quantified and compared within the same experimental system. In this study, a new inducible human cell line was established to allow unambiguous detection of YFP-BRCA1 at nuclear foci. Quantitative 2-D microscopic analysis was performed to compare the intranuclear co-localization of YFP-BRCA1 with 10 cellular proteins and 4 cellular domains before and after IR. Intriguingly, YFP-BRCA1 displayed significantly better focal co-localization with BARD1, RAP80 and Abraxas than with the upstream foci-initiating proteins gamma H2AX and MDC1. In contrast to previous reports, we found that the co-localization between YFP-BRCA1 and 53BP1 foci was surprisingly weak. Quantitative analyses of 3-D confocal images showed that approximately 60% of 53BP1 foci were unrelated to YFP-BRCA1 foci, approximately 35% of foci were abutting and only approximately 5% of foci co-localized. The YFP-BRCA1 and 53BP1 nuclear foci were distinctively separated within the first 3h after IR. In addition, in situ nuclear retention analysis revealed YFP-BRCA1 and BARD1 are less mobile than 53BP1 at IR-induced nuclear foci. Our findings indicate that BRCA1-BARD1 and 53BP1 are proximal but not overlapping at DNA break sites and are consistent with recent evidence for distinct roles of these proteins in the DNA damage response pathway.
authors.affiliation: Westmead Institute for Cancer Research, The University of Sydney, Westmead Millennium Institute at Westmead Hospital, Westmead, NSW 2145, Australia. mythmok@mythmok.com
authors.forename: Myth T S
authors.initials: MT
authors.lastname: Mok
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000528:radiation effects; D019313:BRCA1 Protein / Q000235:genetics / Q000378:metabolism*; D002453:Cell Cycle; D002460:Cell Line; D004249:DNA Damage; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism*; D012326:RNA Splicing; D000071857:Tumor Suppressor p53-Binding Protein 1
chemical_list: D019313:BRCA1 Protein; C492913:BRCA1 protein, human; D047908:Intracellular Signaling Peptides and Proteins; C498301:TP53BP1 protein, human; D000071857:Tumor Suppressor p53-Binding Protein 1