Bcl-2 Inhibits Nuclear Homologous Recombination by Localizing BRCA1 to the Endomembranes

• Published in: Cancer research (Chicago, Ill.) Ill.), 2011-05, Vol.71 (10), p.3590-3602
• Main Authors: LAULIER, Corentin, BARASCU, Aurélia, GUIROUILH-BARBAT, Josee, PENNARUN, Gaëlle, LE CHALONY, Catherine, CHEVALIER, François, PALIERNE, Gaëlle, BERTRAND, Pascale, MARC VERBAVATZ, Jean, LOPEZ, Bernard S
• Format: Article
• Language: English
• Subjects: Antineoplastic agents; Biochemistry; Biochemistry, Molecular Biology; Biological and medical sciences; Cancer; Cell Line, Tumor; Cell Membrane - metabolism; Cytoplasm - metabolism; Endoplasmic Reticulum - metabolism; Gene Expression Regulation, Neoplastic; Genes, BRCA1; HeLa Cells; Humans; Life Sciences; Medical sciences; Microscopy, Confocal - methods; Microscopy, Fluorescence - methods; Mitochondria - metabolism; Models, Genetic; Molecular biology; Pharmacology. Drug treatments; Proto-Oncogene Proteins c-bcl-2 - metabolism; Recombination, Genetic; Simian virus 40; Subcellular Fractions - metabolism; Tumors
• ISSN: 0008-5472; 1538-7445
• DOI: 10.1158/0008-5472.can-10-3119

Genetic stability requires coordination of a network of pathways including DNA repair/recombination and apoptosis. In addition to its canonical anti-apoptotic role, Bcl-2 negatively impacts genome stability. In this study, we identified the breast cancer tumor suppressor BRCA1, which plays an essential role in homologous recombination (HR), as a target for Bcl-2 in the repression of HR. Indeed, ionizing radiation-induced BRCA1 foci assembly was repressed when Bcl-2 was expressed ectopically, in human SV40 fibroblasts, or spontaneously, in lymphoma t(14:18) cells and in HeLa and H460 cancer cell lines. Moreover, we showed that the transmembrane (TM) domain of Bcl-2 was required for both inhibition of BRCA1 foci assembly and the inhibition of HR induced by a double-strand break targeted into an intrachromosomal HR substrate by the meganuclease I-SceI. Fluorescence confocal microscopy, proximity ligation assay, and electron microscopy analyses as well as Western blot analysis of subcellular fractions showed that Bcl-2 and BRCA1 colocalized to mitochondria and endoplasmic reticulum in a process requiring the TM domain of Bcl-2. Targeting BRCA1 to the endomembranes depletes BRCA1 from the nucleus and, thus, accounts for the inhibition of HR. Furthermore, our findings support an apoptosis-stimulatory role for the cytosolic form of BRCA1, suggesting a new tumor suppressor function of BRCA1. Together, our results reveal a new mode of BRCA1 regulation and for HR in the maintenance of genome stability.