title: Influence of double-strand-break repair pathways on radiosensitivity throughout the cell cycle in CHO cells.
abstract: Unrepaired DNA double-strand breaks (DSBs) produced by ionizing radiation (IR) are a major determinant of cell killing. To determine the contribution of DNA repair pathways to the well-established cell cycle variation in IR sensitivity, we compared the radiosensitivity of wild-type CHO cells to mutant lines defective in nonhomologous end joining (NHEJ), homologous recombination repair (HRR), and the Fanconi anemia pathway. Cells were irradiated with IR doses that killed approximately 90% of each asynchronous population, separated into synchronous fractions by centrifugal elutriation, and assayed for survival (colony formation). Wild-type cells had lowest resistance in early G1 and highest resistance in S phase, followed by declining resistance as cells move into G2/M. In contrast, HR-defective cells (xrcc3 mutation) were most resistant in early G1 and became progressively less resistant in S and G2/M, indicating that the S-phase resistance in wild-type cells requires HRR. Cells defective in NHEJ (dna-pk(cs) mutation) were exquisitely sensitive in early G1, most resistant in S phase, and then somewhat less resistant in G2/M. Fancg mutant cells had almost normal IR sensitivity and normal cell cycle dependence, suggesting that Fancg contributes modestly to survival and in a manner that is independent of cell cycle position.
authors.affiliation: Biosciences Directorate, L441 Lawrence Livermore National Laboratory, P.O. Box 808, Livermore, CA 94551-0808, USA.
authors.forename: John M
authors.initials: JM
authors.lastname: Hinz
authors.forename: N Alice
authors.initials: NA
authors.lastname: Yamada
authors.forename: Edmund P
authors.initials: EP
authors.lastname: Salazar
authors.forename: Robert S
authors.initials: RS
authors.lastname: Tebbs
authors.forename: Larry H
authors.initials: LH
authors.lastname: Thompson
mesh_terms: D000818:Animals; D016466:CHO Cells; D002453:Cell Cycle / Q000502:physiology*; D006224:Cricetinae; D003412:Cricetulus; D004249:DNA Damage; D004260:DNA Repair / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics; D052241:Fanconi Anemia Complementation Group G Protein; D006657:Histones / Q000378:metabolism; D009154:Mutation; D011836:Radiation Tolerance / Q000235:genetics*; D011839:Radiation, Ionizing; D011995:Recombination, Genetic / Q000235:genetics*
chemical_list: D004268:DNA-Binding Proteins; D052241:Fanconi Anemia Complementation Group G Protein; D006657:Histones; C110901:X-ray repair cross complementing protein 3