title: XRCC3 deficiency results in a defect in recombination and increased endoreduplication in human cells.
abstract: XRCC3 was inactivated in human cells by gene targeting. Consistent with its role in homologous recombination, XRCC3(-/-) cells showed a two-fold sensitivity to DNA cross-linking agents, a mild reduction in sister chromatid exchange, impaired Rad51 focus formation and elevated chromosome aberrations. Furthermore, endoreduplication was increased five- seven-fold in the mutants. The T241M variant of XRCC3 has been associated with an increased cancer risk. Expression of the wild-type cDNA restored this phenotype, while expression of the variant restored the defective recombinational repair, but not the increased endoreduplication. RPA, a protein essential for homologous recombination and DNA replication, is associated with XRCC3 and Rad52. Overexpression of RPA promoted endoreduplication, which was partially complemented by overexpression of the wild-type XRCC3 protein, but not by overexpression of the variant protein. Overexpression of Rad52 prevented endoreduplication in RPA-overexpressing cells, in XRCC3(-/-) cells and in the variant-expressing cells, suggesting that deregulated RPA was responsible for the increased endoreduplication. These observations offer the first genetic evidence for the association between homologous recombination and replication initiation having a role in cancer susceptibility.
authors.affiliation: Department of Human Genetics, Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Yoshihara
authors.forename: Mari
authors.initials: M
authors.lastname: Ishida
authors.forename: Aiko
authors.initials: A
authors.lastname: Kinomura
authors.forename: Mari
authors.initials: M
authors.lastname: Katsura
authors.forename: Takanori
authors.initials: T
authors.lastname: Tsuruga
authors.forename: Satoshi
authors.initials: S
authors.lastname: Tashiro
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Asahara
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Miyagawa
mesh_terms: D000376:Agmatine / Q000031:analogs & derivatives* / Q000494:pharmacology; D002460:Cell Line; D002877:Chromosomes, Human / Q000235:genetics / Q000378:metabolism; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004249:DNA Damage / Q000187:drug effects; D004260:DNA Repair / Q000235:genetics / Q000502:physiology*; D018076:DNA, Complementary / Q000235:genetics; D004268:DNA-Binding Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D015870:Gene Expression; D018390:Gene Targeting; D006801:Humans; D016685:Mitomycin / Q000494:pharmacology; D011003:Ploidies; D051721:Rad52 DNA Repair and Recombination Protein; D011995:Recombination, Genetic; D051716:Replication Protein A; D013386:Succinates / Q000494:pharmacology
chemical_list: D003432:Cross-Linking Reagents; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; C068976:MMC complex; C497194:RAD52 protein, human; C497167:RPA1 protein, human; D051721:Rad52 DNA Repair and Recombination Protein; D051716:Replication Protein A; D013386:Succinates; C110901:X-ray repair cross complementing protein 3; D016685:Mitomycin; D000376:Agmatine