title: Nuclear-cytoplasmic shuttling of BARD1 contributes to its proapoptotic activity and is regulated by dimerization with BRCA1.
abstract: The breast cancer-associated protein, BARD1, colocalizes with BRCA1 in nuclear foci in the S phase and after DNA damage, and the two proteins form a stable heterodimer implicated in DNA repair, protein ubiquitination, and control of mRNA processing. BARD1 has a BRCA1-independent proapoptotic activity; however, little is known about its regulation. Here, we show that BARD1 localization and apoptotic activity are regulated by nuclear-cytoplasmic shuttling. We identified a functional CRM1-dependent nuclear export sequence (NES) near the N-terminal RING domain of BARD1. The NES forms part of the BRCA1 dimerization domain, and coexpression of BRCA1 resulted in masking of the NES and nuclear retention of BARD1. In transient expression assays, BARD1 apoptotic activity was stimulated by nuclear export, and both apoptotic function and nuclear export were markedly reduced by BRCA1. Similar findings were obtained for endogenous BARD1. Silencing BRCA1 expression by siRNA, or disrupting the endogenous BARD1/BRCA1 interaction by peptide competition caused a reduction in BARD1 nuclear localization and foci formation, and increased the level of cytoplasmic BARD1 correlating with increased apoptosis. Our findings suggest that BRCA1/BARD1 heterodimer formation is important for optimal nuclear targeting of BARD1 and its role in DNA repair and cell survival.
authors.affiliation: Westmead Institute for Cancer Research, University of Sydney, Westmead Millennium Institute at Westmead Hospital, Westmead NSW 2145, Australia.
authors.forename: José Antonio
authors.initials: JA
authors.lastname: Rodriguez
authors.forename: Stefan
authors.initials: S
authors.lastname: Schüchner
authors.forename: Wendy W Y
authors.initials: WW
authors.lastname: Au
authors.forename: Megan
authors.initials: M
authors.lastname: Fabbro
authors.forename: Beric R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D019313:BRCA1 Protein / Q000378:metabolism*; D001483:Base Sequence; D001940:Breast / Q000166:cytology; D001943:Breast Neoplasms / Q000378:metabolism / Q000473:pathology; D002352:Carrier Proteins / Q000737:chemistry / Q000378:metabolism*; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D017931:DNA Primers; D019281:Dimerization; D004847:Epithelial Cells; D005260:Female; D005434:Flow Cytometry; D005822:Genetic Vectors; D006801:Humans; D008969:Molecular Sequence Data; D021381:Protein Transport; D016196:S Phase; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D025521:Tumor Suppressor Proteins; D044767:Ubiquitin-Protein Ligases; D016335:Zinc Fingers
chemical_list: D019313:BRCA1 Protein; D002352:Carrier Proteins; D017931:DNA Primers; D025521:Tumor Suppressor Proteins; C102449:BARD1 protein, human; D044767:Ubiquitin-Protein Ligases