title: Embryonic stem cells deficient for Brca2 or Blm exhibit divergent genotoxic profiles that support opposing activities during homologous recombination.
abstract: The breast cancer susceptibility protein, Brca2 and the RecQ helicase, Blm (Bloom syndrome mutated) are tumor suppressors that maintain genome integrity, at least in part, through homologous recombination (HR). Brca2 facilitates HR by interacting with Rad51 in multiple regions, the BRC motifs encoded by exon 11 and a single domain encoded by exon 27; however, the exact importance of these regions is not fully understood. Blm also interacts with Rad51 and appears to suppress HR in most circumstances; however, its yeast homologue Sgs1 facilitates HR in response to some genotoxins. To better understand the biological importance of these two proteins, we performed a genotoxic screen on mouse embryonic stem (ES) cells impaired for either Brca2 or Blm to establish their genotoxic profiles (a cellular dose-response to a wide range of agents). This is the first side-by-side comparison of these two proteins in an identical genetic background. We compared cells deleted for Brca2 exon 27 to cells reduced for Blm expression and find that the Brca2- and Blm-impaired cells exhibit genotoxic profiles that reflect opposing activities during HR. Cells deleted for Brca2 exon 27 are hypersensitive to gamma-radiation, streptonigrin, mitomycin C and camptothecin and mildly resistant to ICRF-193 which is similar to HR defective cells null for Rad54. By contrast, Blm-impaired cells are hypersensitive to ICRF-193, mildly resistant to camptothecin and mitomycin C and more strongly resistant to hydroxyurea. These divergent profiles support the notion that Brca2 and Blm perform opposing functions during HR in mouse ES cells.
authors.affiliation: The Department of Molecular Medicine and Institute of Biotechnology, The University of Texas Health Science Center at San Antonio, 15355 Lambda Drive San Antonio, TX 78245-3207, USA.
authors.forename: Teresa
authors.initials: T
authors.lastname: Marple
authors.forename: Tae Moon
authors.initials: TM
authors.lastname: Kim
authors.forename: Paul
authors.initials: P
authors.lastname: Hasty
mesh_terms: D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D000477:Alkylating Agents / Q000633:toxicity; D000818:Animals; D000970:Antineoplastic Agents / Q000633:toxicity; D024682:BRCA2 Protein / Q000235:genetics* / Q000378:metabolism; D002166:Camptothecin / Q000633:toxicity; D003432:Cross-Linking Reagents / Q000633:toxicity; D004249:DNA Damage; D004265:DNA Helicases / Q000235:genetics* / Q000378:metabolism; D053595:Embryonic Stem Cells / Q000378:metabolism; D005047:Etoposide / Q000633:toxicity; D020869:Gene Expression Profiling; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D053484:RecQ Helicases; D011995:Recombination, Genetic; D059003:Topoisomerase Inhibitors
chemical_list: D000477:Alkylating Agents; D000970:Antineoplastic Agents; D024682:BRCA2 Protein; D003432:Cross-Linking Reagents; D009687:Nuclear Proteins; D017382:Reactive Oxygen Species; D059003:Topoisomerase Inhibitors; D005047:Etoposide; D000251:Adenosine Triphosphatases; C097151:Bloom syndrome protein; D004265:DNA Helicases; C103534:Rad54l protein, mouse; D053484:RecQ Helicases; D002166:Camptothecin