Isolation and characterization of apoptosis-resistant mutants from a radiosensitive mouse lymphoma cell line

To analyze specific genes related to radiation-induced apoptosis, 12 apoptosis-resistant clones were isolated from cells of the radiosensitive mouse thymic lymphoma 3SB line after treatment with ethyl methanesulfonate. Five of 12 clonal cell lines were recloned and were examined for their susceptibility to X-ray-induced apoptosis. A cell survival assay showed that all five secondary cell lines were two to three times more resistant to X rays than 3SB cells. When 3SB cells were exposed to 5 Gy of X rays, the fraction of cells stained with erythrosin B increased quickly within 8 h of incubation after irradiation. However, no apoptosis occurred in these secondary mutant cells. In particular, the percentage of cells undergoing apoptosis in one clone, 1B1C4, was low even after incubation for 48 h. In contrast to X rays, after exposure to 20 J/ m2 UV radiation, the proportion of apoptotic cells in these mutant cells increased and reached about 60 to 100% at 24 h, indicating a difference in the ability of X rays...