title: High levels of wild-type BRCA2 suppress homologous recombination.
abstract: Endogenous levels of the BRCA2 (breast cancer susceptibility 2) protein promote homologous recombination by regulating the essential strand exchange protein RAD51. To examine BRCA2 function in homologous recombination, we expressed human BRCA2 in control mouse hybridoma cells, as well as those that were depleted of endogenous Brca2 by small interfering RNA. With moderate human BRCA2 expression, homologous recombination was stimulated. Conversely, a higher level of BRCA2 reduced homologous recombination and DNA-damage-induced Rad51 foci formation. Cells expressing high levels of BRCA2 feature normal growth, increased sensitivity to mitomycin C, and increased illegitimate recombination. BRCA2-overexpressing cells are also characterized by suppression of p53 transcriptional regulation and a corresponding reduction in the expression of the p53-responsive genes Noxa and p21. Notably, in cells expressing high levels of BRCA2, small interfering RNA depletion of human BRCA2 or ectopic expression of Rad51 increases homologous recombination and decreases illegitimate recombination. Thus, high levels of wild-type BRCA2 perturb Rad51-mediated homologous recombination, and relatively normal recombination responses can be restored by rebalancing recombination factors.
authors.affiliation: Department of Molecular and Cellular Biology, College of Biological Science, University of Guelph, Guelph, Ontario, Canada N1G 2W1.
authors.forename: Alissa C
authors.initials: AC
authors.lastname: Magwood
authors.forename: Maureen M
authors.initials: MM
authors.lastname: Mundia
authors.forename: Mark D
authors.initials: MD
authors.lastname: Baker
mesh_terms: D000818:Animals; D024682:BRCA2 Protein / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D004249:DNA Damage; D005786:Gene Expression Regulation; D016158:Genes, p53; D059765:Homologous Recombination / Q000187:drug effects; D006801:Humans; D006825:Hybridomas; D051379:Mice; D016685:Mitomycin / Q000494:pharmacology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics; D034741:RNA, Small Interfering; D051135:Rad51 Recombinase / Q000235:genetics / Q000378:metabolism*
chemical_list: D024682:BRCA2 Protein; C551750:BRCA2 protein, human; C106711:BRCA2 protein, mouse; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D034741:RNA, Small Interfering; D016685:Mitomycin; D051135:Rad51 Recombinase; C495154:Rad51 protein, mouse