title: Identification of a functional nuclear export sequence in BRCA1.
abstract: Germ-line mutations in the tumor suppressor gene Brca1 confer increased susceptibility to breast and ovarian cancers. BRCA1 is a 1863-amino acid protein with roles in transcriptional regulation and the cellular responses to DNA damage. Given its function in these nuclear processes, the subcellular localization of BRCA1 is an important issue and has been the object of recent controversy. BRCA1 contains two nuclear localization signals and is most frequently detected in the cell nucleus by immunofluorescence microscopy. In this study, we show that BRCA1 is a nuclear-cytoplasmic shuttling protein, capable of both entering and exiting the nucleus. We identified a functional Rev-type nuclear export sequence ((81)QLVEELLKIICAFQLDTGL) near the amino terminus of BRCA1 that facilitates export via the CRM1/exportin pathway. Mutational inactivation of this nuclear export sequence, or treatment of cells with the CRM1-specific export inhibitor leptomycin B, induced nuclear accumulation of ectopic full-length BRCA1. Moreover, overexpression of the CRM1 export receptor resulted in decreased nuclear localization of endogenous BRCA1. The unexpected ability of BRCA1 to shuttle between nucleus and cytoplasm may have implications for the regulation and function of this tumor suppressor.
authors.affiliation: Westmead Institute for Cancer Research, University of Sydney, Westmead Millennium Institute, Westmead, 2145 New South Wales, Australia.
authors.forename: J A
authors.initials: JA
authors.lastname: Rodríguez
authors.forename: B R
authors.initials: BR
authors.lastname: Henderson
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D019313:BRCA1 Protein / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001940:Breast; D001943:Breast Neoplasms; D002352:Carrier Proteins / Q000378:metabolism; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004285:Dogs; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism; D005231:Fatty Acids, Unsaturated / Q000494:pharmacology; D005260:Female; D006801:Humans; D028884:Karyopherins; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D021381:Protein Transport / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014407:Tumor Cells, Cultured; D000097606:Exportin 1 Protein
chemical_list: D000903:Antibiotics, Antineoplastic; D019313:BRCA1 Protein; D002352:Carrier Proteins; D005231:Fatty Acids, Unsaturated; D028884:Karyopherins; D018160:Receptors, Cytoplasmic and Nuclear; D011994:Recombinant Proteins; D000097606:Exportin 1 Protein; C038753:leptomycin B