COMBINED EFFECTS OF IONIZING-RADIATION AND CYCLOHEXIMIDE ON GENE-EXPRESSION

We performed experiments to determine the effects of ionizing radiatio n exposure on expression of genes such as beta-actin, c-fos, histone H 4, c-myc, c-jun, Rb, and p53 after exposure of Syrian hamster embryo ( SHE) cells to the protein synthesis inhibitor cycloheximide. The purpo se of these experiments was to determine the role of a labile protein in the radiation-induced response. The results revealed that when ioni zing radiation (either fission-spectrum neutrons or gamma rays) was ad ministered 15 min after cycloheximide treatment of SHE cells, the radi ation exposure reduced cycloheximide-mediated gene induction of c-fos, histone H4, and c-jun. In addition, dose-rate differences were found when radiation exposure most significantly inhibited the cycloheximide response. Our results suggest that ionizing radiation does not act as a general protein-synthesis inhibitor and that the presence of a labi le protein is required for the maintenance of specific gene transcript ion and mRNA accumulation after radiation exposure, especially at high dose-rates. (C) 1995 Wiley-Liss, Inc.