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‐jun, 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.