title: Deficiency in Bre1 impairs homologous recombination repair and cell cycle checkpoint response to radiation damage in mammalian cells.
abstract: The pathway involving Bre1-dependent monoubiquitination of histone H2B lysine 123, which leads to Dot1-dependent methylation of histone H3 lysine 79 (H3K79me2), has been implicated in survival after exposure to ionizing radiation in Saccharomyces cerevisiae. We found that depletion of mammalian homologs of Bre1 compromises the response to ionizing radiation, leading to increased radiosensitivity and a G(2)/M checkpoint defect. The deficiency in Bre1a/b function was also associated with increased sensitivity to crosslinking drugs and defective formation of Rad51 foci in mouse cells, suggesting a defect in homologous recombinational repair analogous to that seen in Saccharomyces. In budding yeast, H3K79me2 is important for the recruitment of the checkpoint signaling protein Rad9 to sites of double-strand breaks (DSBs). However, in mammalian cells, 53BP1 (the Rad9 ortholog) in addition to H3K79me2 recognizes a different residue, H4K20me2, and some studies argue that it is H4K20me2 and not H3K79me2 that is the preferred target for 53BP1. We show here that depletion of Bre1b specifically reduced dimethylation of H3K79 without affecting dimethylation of H4K20. Thus our data suggest that the observed defects in the radiation response of Bre1a/b-deficient cells are associated with reduced H3K79me2 and not with H4K20me2.
authors.affiliation: Department of Radiation Oncology, Stanford University School of Medicine, Stanford, California 94305-5152, USA.
authors.forename: Sophia B
authors.initials: SB
authors.lastname: Chernikova
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Dorth
authors.forename: Olga V
authors.initials: OV
authors.lastname: Razorenova
authors.forename: John C
authors.initials: JC
authors.lastname: Game
authors.forename: J Martin
authors.initials: JM
authors.lastname: Brown
mesh_terms: D000818:Animals; D001483:Base Sequence; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects*; D002455:Cell Division / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D045744:Cell Line, Tumor; D002699:Chlorambucil / Q000494:pharmacology; D016195:G2 Phase / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects; D055785:Gene Knockdown Techniques; D006657:Histones / Q000378:metabolism; D006801:Humans; D008745:Methylation / Q000187:drug effects / Q000528:radiation effects; D051379:Mice; D034741:RNA, Small Interfering / Q000235:genetics; D051135:Rad51 Recombinase / Q000378:metabolism; D011836:Radiation Tolerance / Q000235:genetics; D011995:Recombination, Genetic / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects*; D044767:Ubiquitin-Protein Ligases / Q000172:deficiency* / Q000235:genetics* / Q000378:metabolism; D054875:Ubiquitination / Q000187:drug effects / Q000235:genetics / Q000528:radiation effects
chemical_list: D006657:Histones; D034741:RNA, Small Interfering; D002699:Chlorambucil; C506646:RNF20 protein, human; C413363:RNF40 protein, human; D044767:Ubiquitin-Protein Ligases; D051135:Rad51 Recombinase