Pretreatment of low dose radiation reduces radiation-induced apoptosis in mouse lymphoma (EL4) cells

Abstract

Induction of an adaptive response to ionizing radiation in mouse lymphoma (EL4) cells was studied by using cell survival fraction
and apoptotic nucleosomal DNA fragmentation as biological end points. Cells in early log phase were pre-exposed to low dose
of γ-rays (0.01 Gy) 4 or 20 hrs prior to high dose γ-ray (4, 8 and 12 Gy for cell survival fraction analysis; 8 Gy for DNA
fragmentation analysis) irradiation. Then cell survival fractions and the extent of DNA fragmentation were measured. Significant
adaptive response, increase in cell survival fraction and decrease in the extent of DNA fragmentation were induced when low
and high dose γ-ray irradiation time interval was 4 hr. Addition of protein or RNA synthesis inhibitor, cycloheximide or 5,6-dichloro-1-β-d-ribofuranosylbenzimidazole
(DRFB), respectively during adaptation period, the period from low dose γ-ray irradiation to high dose γ-ray irradiation,
was able to inhibit the induction of adaptive response, which is the reduction of the extent DNA fragmentation in irradiated
EL4 cells. These data suggest that the induction of adaptive response to ionizing radiation in EL4 cells required both protein
and RNA synthesis.