title: BRCA1 and BARD1 colocalize mainly in the cytoplasm of breast cancer tumors, and their isoforms show differential expression.
abstract: BRCA1 has been found to be absent or miss localized in the cytoplasm in a relevant proportion of breast cancer tumors with no germline mutations. BRCA1 main function is in the nucleus, and its interaction with BARD1 is relevant for its nuclear translocation and retention. Our aim was to analyze the sub-cellular localization of BRCA1 and BARD1 in breast cancer tumors, and determine the level of expression of their splice variants BRCA1-Δ11q and BARD1-α and BARD1-β. BRCA1 and BARD1 expressions were performed by immunohistochemistry and immunofluorescence in 103 breast cancer tumors. Colocalization was determined by confocal microscopy. Transcript variants were determined by qRT-PCR. We found BRCA1 localized in the cytoplasm with BARD1 in 51.4 % of tumors. An exclusive nuclear localization of both proteins was observed in 7/103 tumors (6.8 %). Indeed, these tumors displayed an apparent nucleolar colocalization of BARD1 and BRCA1. In relation to splice variants, there is a tendency to an overexpression of BARD1-α mRNA (30 % of tumors) and a decreased expression of BARD1-β (41 %). BRCA1 full-length was downregulated in 63 % of tumors, and 37 % showed BRCA1-Δ11q variant overexpressed. Our findings contribute to a better understanding of the expression and sub-cellular localization of BRCA1 in breast cancer tumors. Interaction of BRCA1 and BARD1 seems to be not affected in 58.2 % of tumors, which showed colocalization of both proteins. The absence of BRCA1 in 41 % of tumors reveals a BRCAness phenotype, constituting an excellent marker for therapy sensitivity, to platinum drugs or PARP inhibitors.
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: David
authors.initials: D
authors.lastname: Wiener
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: Patricia
authors.initials: P
authors.lastname: Gajardo-Meneses
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: Victoria
authors.initials: V
authors.lastname: Ortega-Hernández
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: Cristóbal
authors.initials: C
authors.lastname: Herrera-Cares
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: Sebastián
authors.initials: S
authors.lastname: Díaz
authors.affiliation: Unidad de Anatomía Patológica, Hospital Clínico San Borja Arriarán, Santiago, Chile.
authors.forename: Wanda
authors.initials: W
authors.lastname: Fernández
authors.affiliation: Unidad de Anatomía Patológica, Hospital Clínico San Borja Arriarán, Santiago, Chile.
authors.forename: Valeria
authors.initials: V
authors.lastname: Cornejo
authors.affiliation: Unidad de Patología Mamaria, Hospital Clínico San Borja Arriarán, Santiago, Chile.
authors.forename: Jorge
authors.initials: J
authors.lastname: Gamboa
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: Teresa
authors.initials: T
authors.lastname: Tapia
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile.
authors.forename: Carolina
authors.initials: C
authors.lastname: Alvarez
authors.affiliation: Laboratory of Human Molecular Genetics, Department of Cellular and Molecular Biology, Faculty of Biological Sciences, Pontificia Universidad Católica de Chile, Portugal 49 3rd floor, Postal code 8330025, Santiago, Chile. pcarvallo@bio.puc.cl.
authors.forename: Pilar
authors.initials: P
authors.lastname: Carvallo
mesh_terms: D017398:Alternative Splicing; D019313:BRCA1 Protein / Q000235:genetics* / Q000378:metabolism*; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism* / Q000473:pathology; D002467:Cell Nucleus / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D011485:Protein Binding; D020033:Protein Isoforms; D021381:Protein Transport; D025521:Tumor Suppressor Proteins / Q000235:genetics* / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D019313:BRCA1 Protein; D020033:Protein Isoforms; D025521:Tumor Suppressor Proteins; C102449:BARD1 protein, human; D044767:Ubiquitin-Protein Ligases
keywords: BARD1-α mRNA; BARD1-β mRNA; BRCA1 expression in cancer; BRCA1-Δ11q; BRCA1/BARD1 tumor localization; Breast cancer tumor