Suppression of the radiation-sensitive phenotype of hamster irs1 and irs2 strains selected for resistance to 3-aminobenzamide

Purpose: The radiosensitive hamster cell lines irs1 and irs2 have phenotypi c similarities to cells defective in the early response to DNA-damaging age nts as a result of mutations of the genes encoding poly(ADP-ribose)polymera se (PARP) or ataxia-telangiectase mutated (ATM). Whether modification of PA RP activity through selection of strains resistant to 3-aminobenzamide (3-A B) would affect the radiosensitive phenotype of irs1 and irs2 was examined. Materials and methods: 3-AB-resistant strains of irs1, irs2 and their paren t line V79 were established and their sensitivity to DNA-damaging agents wa s measured. In some 3-AB-resistant strains, the radiation resistance of DNA synthesis and the induction of apoptosis were also assayed. Additionally, a number of aspects of PARP function were measured. Results: Independently selected 3-AB-resistant strains of irs2 showed nearl y complete suppression of radiation sensitivity, sensitivity to topoisomera se inhibitors, and radioresistant DNA synthesis. 3-AB-resistant strains of irs1 showed partial suppression of phenotype while 3-AB-resistant strains o f V79 had no sensitivity changes. The induction of apoptosis in 3-AB-resist ant strains of irs2 required substantially higher radiation doses than for irs2 itself. 3-AB-resistant strains had no detectable alteration of PARP le vel or cleavage following ionizing irradiation and there were no mutations in the PARP gene. Conclusions: Suppression of radiosensitivity associated with 3-AB resistanc e has important implications for mechanisms of tolerance to damage because it is able to override responses associated with specific genetic defects.