Effects of ionizing radiation on expression of genes encoding cytoskeletal elements: Kinetics and dose effects

We examined the modulation in expression of genes encoding three cytoskeletal elements (β‐actin, γ‐actin, and α‐tubulin) in Syrian hamster embryo (SHE) cells following exposure to ionizing radiations. Early‐passage SHE cells were irradiated in plateau phase with various low doses (12‐200 cGy) of neutrons, γ‐rays, or x‐rays. RNA samples were prepared from cells at different times postexposure and were analyzed for levels of specific transcripts by northern blots. The results revealed that α‐tubulin was induced by both high‐linear energy of transfer (LET) (neutrons) and low‐LET (γ‐rays and x‐rays) radiations with similar kinetics. The peak in α‐tubulin mRNA accumulation occurred between 1 and 3 h postexposure; for γ‐actin mRNA, accumulation was similarly induced. For both γ‐actin and α‐tubulin, the higher the dose during the first hour postexposure (up to 200 cGy γ‐rays), the greater the level of mRNA induction. In contrast, mRNA specific for β‐actin showed decreased accumulation during the first hour following radiation exposure, and remained low up to 3 h postexposure. These results document the differential modulation of genes specific for cytoskeletal elements following radiation exposure. In addition, they demonstrate a decrease in the ratio of β‐actin:γ‐actin mRNA within the first 3 h following γ‐ray exposure. These changes in mRNA accumulation are similar to those reported in some transformed cell lines and in cells treated with tumor promoters, which suggests a role for changes in actin‐ and tubulin‐mRNA expression in radiation‐mediated transformation.