Identification of ATIC as a novel target for chemoradiosensitization
Menée sur des lignées cellulaires de différents types de cancer, cette étude analyse l'effet de l'inhibition ou de la réduction de l'expression du gène ATIC sur la sensibilité des cellules tumorales aux rayonnements ionisants et sur la réparation des dommages causés à l'ADN par l'irradiation
Purpose : Mutations in the gene encoding 5-aminoimidazole-4-carboxamide ribonucleotide formyltransferase/IMP cyclohydrolase (ATIC), a bifunctional enzyme that catalyzes the final two steps of the purine de novo biosynthetic pathway, were identified in a subject referred for radiation sensitivity testing. Functional studies were carried out to determine if ATIC inhibition was radiosensitizing, and if so, to elucidate the mechanism of this effect and to determine if small molecule inhibitors of ATIC could act as effective radiosensitizing agents. Methods and Materials : Both siRNA knockdown and small molecule inhibitors were used to inactivate ATIC in cell culture. Clonogenic survival assays, the neutral comet assay, and
γH2AX staining were used to assess the effects of ATIC inhibition or depletion on cellular DNA damage responses. Results
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Depletion of ATIC or inhibition of its transformylase activity significantly reduced the surviving fraction of cells in clonogenic survival assays in multiple cancer cell lines. In the absence of ionizing radiation exposure, ATIC knockdown or chemical inhibition activated cell cycle checkpoints, shifting cells to the more radiosensitive G2/M phase of the cell cycle, and depleted cellular ATP, but did not result in detectable DNA damage. Cells in which ATIC was knocked down or inhibited and then treated with ionizing radiation displayed increased numbers of DNA double-strand breaks (DSBs), and a delay in the repair of those breaks relative to irradiated, but otherwise untreated, controls. Supplementation of culture media with exogenous ATP ameliorated the DNA repair phenotypes. Conclusions
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These findings implicate ATIC as an effective, and previously unrecognized, target for chemoradiosensitization and more broadly suggest that purine levels in cells may have an underappreciated role in modulating the efficiency of DNA damage responses that could be exploited in radiosensitizing strategies.