Combined effects of ionizing radiation and cycloheximide on gene expression

We performed experiments to determine the effects of ionizing radiation exposure on expression of genes such as β‐actin, c‐ fos , histone H4, c‐ myc , c‐j un , Rb, and p53 after exposure of Syrian hamster embryo (SHE) cells to the protein synthesis inhibitor cycloheximide. The purpose of these experiments was to determine the role of a labile protein in the radiation‐induced response. The results revealed that when ionizing radiation (either fission‐spectrum neutrons or γ rays) was administered 15 min after cycloheximide treatment of SHE cells, the radiation 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 labile protein is required for the maintenance of specific gene transcription and mRNA accumulation after radiation exposure, especially at high dose‐rates. © 1995 Wiley‐Liss, Inc.