title: BRCA1 protein and nucleolin colocalize in breast carcinoma tissue and cancer cell lines.
abstract: The breast and ovarian cancer susceptibility gene BRCA1 encodes a tumor suppressor. BRCA1 protein, which is involved in DNA damage response, has been thought to be found primarily in cell nuclei. In the present investigation, immunohistological studies of BRCA1 protein in frozen breast cancer tissue and MCF7 and HeLa cell lines revealed BRCA1 expression in both nucleoli and nucleoplasmic foci. Immunoelectron microscopic studies of estrogen-stimulated MCF7 cells demonstrated BRCA1 protein localization in the granular components of the nucleolus. Moreover, immunofluorescence of BRCA1 and nucleolin double-labeling showed colocalization in both nucleoli and nucleoplasmic foci in breast tumor cells and asynchronously growing MCF7 and HeLa cells. Multiparameter analysis of BRCA1 and nucleolin in relation to cell cycle position (DNA content) showed expression during G1-S and persistence of BRCA1 during G2/M. After gamma-irradiation of MCF7 cells, BRCA1 protein dispersed from nucleoli and nucleoplasmic foci to other nucleoplasmic sites, which did not colocalize with nucleolin. Small interfering RNA-mediated knockdown of BRCA1 protein resulted in decreased immunofluorescence staining, which was confirmed by Western blotting. The observed colocalization of BRCA1 and nucleolin raises new possibilities for the nucleoplasm-nucleolus pathways of these proteins and their functional significance.
authors.affiliation: Department of Pathology, Box 1194, Mt. Sinai School of Medicine, 1 Gustave L. Levy Place, New York, NY 10029, USA. Natalie.Tulchin@mssm.edu
authors.forename: Natalie
authors.initials: N
authors.lastname: Tulchin
authors.forename: Monique
authors.initials: M
authors.lastname: Chambon
authors.forename: Gloria
authors.initials: G
authors.lastname: Juan
authors.forename: Steven
authors.initials: S
authors.lastname: Dikman
authors.forename: James
authors.initials: J
authors.lastname: Strauchen
authors.forename: Leonard
authors.initials: L
authors.lastname: Ornstein
authors.forename: Blase
authors.initials: B
authors.lastname: Billack
authors.forename: Nicholas T
authors.initials: NT
authors.lastname: Woods
authors.forename: Alvaro N A
authors.initials: AN
authors.lastname: Monteiro
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D019313:BRCA1 Protein / Q000378:metabolism* / Q000648:ultrastructure; D001943:Breast Neoplasms / Q000276:immunology / Q000378:metabolism* / Q000473:pathology* / Q000648:ultrastructure; D002453:Cell Cycle; D045744:Cell Line, Tumor; D002466:Cell Nucleolus / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D005629:Frozen Sections; D055785:Gene Knockdown Techniques; D006801:Humans; D047569:Laser Scanning Cytometry; D010750:Phosphoproteins / Q000378:metabolism*; D021381:Protein Transport; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D000097796:Nucleolin
chemical_list: D000911:Antibodies, Monoclonal; D019313:BRCA1 Protein; D010750:Phosphoproteins; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D000097796:Nucleolin