title: Caffeine could not efficiently sensitize homologous recombination repair-deficient cells to ionizing radiation-induced killing.
abstract: Caffeine inhibits ATM and ATR, two important checkpoint regulators, abolishes ionizing radiation-induced checkpoint response, and radiosensitizes cells. Radiation-induced DNA double-strand breaks (DSBs) are repaired by two major processes, homologous recombination repair (HRR) and nonhomologous end joining (NHEJ). It remains unclear which repair process, HRR or NHEJ, is affected when the checkpoint responses are abolished by caffeine. In this study we observed the effect of caffeine on gene-targeted DT40 chicken lymphoblast cells. We show that caffeine efficiently abolishes S- and G(2)-phase checkpoint responses after irradiation in all cell lines tested and greatly radiosensitizes wild-type and ATM(-/-) cells, the partially checkpoint-deficient cells. However, caffeine has a much smaller radiosensitizing effect on RAD54(-/-) cells and has no effect on RAD51-deficient cells. RAD51 and RAD54 are the important factors for HRR. Our results indicate that the checkpoint responses abolished by caffeine (S and G(2)) mainly affect HRR, which results in cell radiosensitization.
authors.affiliation: Department of Radiation Oncology, Kimmel Cancer Center of Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
authors.forename: Huichen
authors.initials: H
authors.lastname: Wang
authors.forename: Xiang
authors.initials: X
authors.lastname: Wang
authors.forename: George
authors.initials: G
authors.lastname: Iliakis
authors.forename: Ya
authors.initials: Y
authors.lastname: Wang
mesh_terms: D000818:Animals; D030161:Avian Proteins; D002110:Caffeine / Q000494:pharmacology*; D002453:Cell Cycle; D002460:Cell Line; D002645:Chickens; D004247:DNA / Q000378:metabolism; D004265:DNA Helicases; D004260:DNA Repair / Q000187:drug effects / Q000528:radiation effects; D045643:DNA Repair Enzymes; D004268:DNA-Binding Proteins / Q000378:metabolism; D004307:Dose-Response Relationship, Radiation; D005434:Flow Cytometry; D005656:Fungal Proteins / Q000378:metabolism; D016195:G2 Phase; D008954:Models, Biological; D009154:Mutation; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051135:Rad51 Recombinase; D011836:Radiation Tolerance / Q000187:drug effects*; D011995:Recombination, Genetic; D016196:S Phase / Q000187:drug effects / Q000528:radiation effects; D029701:Saccharomyces cerevisiae Proteins; D013997:Time Factors
chemical_list: D030161:Avian Proteins; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D010726:Phosphodiesterase Inhibitors; D029701:Saccharomyces cerevisiae Proteins; D002110:Caffeine; D004247:DNA; C495150:RAD51 protein, Gallus gallus; D051135:Rad51 Recombinase; C075468:RAD54 protein, S cerevisiae; D004265:DNA Helicases; D045643:DNA Repair Enzymes