title: Bcl-2 inhibits nuclear homologous recombination by localizing BRCA1 to the endomembranes.
abstract: 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.
authors: CNRS, UMR217, Fontenay aux Roses, France.
authors: Corentin
authors: C
authors: Laulier
authors: Aurélia
authors: A
authors: Barascu
authors: Josée
authors: J
authors: Guirouilh-Barbat
authors: Gaëlle
authors: G
authors: Pennarun
authors: Catherine
authors: C
authors: Le Chalony
authors: François
authors: F
authors: Chevalier
authors: Gaëlle
authors: G
authors: Palierne
authors: Pascale
authors: P
authors: Bertrand
authors: Jean Marc
authors: JM
authors: Verbavatz
authors: Bernard S
authors: BS
authors: Lopez
mesh_terms: D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D019398:Genes, BRCA1; D006367:HeLa Cells; D006801:Humans; D018613:Microscopy, Confocal / Q000379:methods; D008856:Microscopy, Fluorescence / Q000379:methods; D008928:Mitochondria / Q000378:metabolism; D008957:Models, Genetic; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011995:Recombination, Genetic; D013347:Subcellular Fractions / Q000378:metabolism
chemical_list: D019253:Proto-Oncogene Proteins c-bcl-2