PRETREATMENT OF LOW-DOSE RADIATION REDUCES RADIATION-INDUCED APOPTOSIS IN MOUSE LYMPHOMA (EL4) CELLS

Induction of an adaptive response to ionizing radiation in mouse lymph oma (EL4) cells was studied by using cell survival fraction and apopto tic nucleosomal DNA fragmentation as biological end points. Cells in e arly log phase were pre-exposed to low dose of gamma-rays (0.01 Gy) 4 or 20 hrs prior to high dose gamma-ray (4, 8 and 12 Gy for cell surviv al fraction analysis; 8 Gy for DNA fragmentation analysis) irradiation . Then cell survival fractions and the extent of DNA fragmentation wer e measured. Significant adaptive response, increase in cell survival f raction and decrease in the extent of DNA fragmentation were induced w hen low and high dose gamma-ray irradiation time interval was 4 hr. Ad dition of protein or RNA synthesis inhibitor, cycloheximide or 5,6-dic hloro-1-beta-d-ribofuranosylbenzimidazole (DRFB), respectively during adaptation period, the period from low dose gamma-ray irradiation to h igh dose gamma-ray irradiation, was able to inhibit the induction of a daptive response, which is the reduction of the extent DNA fragmentati on in irradiated EL4 cells. These data suggest that the induction of a daptive response to ionizing radiation in EL4 cells required both prot ein and RNA synthesis.