title: Homologous recombination contributes to the repair of DNA double-strand breaks induced by high-energy iron ions.
abstract: To test the contribution of homologous recombinational repair (HRR) in repairing DNA damage sites induced by high-energy iron ions, we used (1) HRR-deficient rodent cells carrying a deletion in the RAD51D gene and (2) syngeneic human cells impaired for HRR by RAD51D or RAD51 knockdown using RNA interference. We found that in response to exposure to iron ions, HRR contributed to cell survival in rodent cells and that HRR deficiency abrogated RAD51 focus formation. Complementation of the HRR defect by human RAD51D rescues both enhanced cytotoxicity and RAD51 focus formation. For human cells irradiated with iron ions, cell survival was decreased, and in p53 mutant cells, the levels of mutagenesis were increased when HRR was impaired. Human cells synchronized in S phase exhibited a more pronounced resistance to iron ions compared with cells in G(1) phase, and this increase in radioresistance was diminished by RAD51 knockdown. These results indicate a role for RAD51-mediated DNA repair (i.e. HRR) in removing a fraction of clustered lesions induced by charged-particle radiation. Our results are the first to directly show the requirement for an intact HRR pathway in human cells in ensuring DNA repair and cell survival after exposure to high-energy high-LET radiation.
authors.affiliation: Lawrence Berkeley National Laboratory, Life Sciences Division, Berkeley, California 94720, USA.
authors.forename: Faria
authors.initials: F
authors.lastname: Zafar
authors.forename: Sara B
authors.initials: SB
authors.lastname: Seidler
authors.forename: Amy
authors.initials: A
authors.lastname: Kronenberg
authors.forename: David
authors.initials: D
authors.lastname: Schild
authors.forename: Claudia
authors.initials: C
authors.lastname: Wiese
mesh_terms: D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D002470:Cell Survival / Q000235:genetics / Q000528:radiation effects; D006224:Cricetinae; D003412:Cricetulus; D053903:DNA Breaks, Double-Stranded / Q000528:radiation effects*; D004260:DNA Repair / Q000235:genetics*; D016195:G2 Phase / Q000235:genetics / Q000528:radiation effects; D055785:Gene Knockdown Techniques; D006801:Humans; D007501:Iron / Q000633:toxicity*; D016296:Mutagenesis / Q000528:radiation effects; D009154:Mutation / Q000528:radiation effects; D051135:Rad51 Recombinase / Q000172:deficiency / Q000235:genetics; D011836:Radiation Tolerance / Q000235:genetics; D011995:Recombination, Genetic; D016196:S Phase / Q000235:genetics / Q000528:radiation effects; D013937:Thymidine Kinase / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: D016159:Tumor Suppressor Protein p53; D007501:Iron; D013937:Thymidine Kinase; D051135:Rad51 Recombinase