Hormesis effect of low dose radiation on cellular DNA repair

Objective: To study radio-adaptive response of mutagenesis and repair of DNA double-strand breaks (DSB) in mammalian cells induced by low dose γ-rays, and to detect low dose radiation-induced proteins. Methods: Mouse SR-1 cells were irradiated with 60Co γ-rays. Mutations at hprt locus were assayed by 6-thioguanine selective culture method. DNA DSBs were measured by pulsed field gel electrophoresis. Southwestern blot hybridization was employed to detect radiation-induced proteins. Results: Preexposure of SR-1 cells to 1 cGy at 18 h and 24 h before challenging dose significantly decreased the frequency of hprt gene mutations induced by following 3 Gy challenge. Preexposure of SR-1 cells to single 1 cGy as well as to 1 cGy per day for 10 successive days significantly increased the cellular capacity of rejoining 3 Gy-induced DNA DSBs. A newly synthesized protein bound to damaged DNA was detected at 16 h after 1 cGy exposure. Conclusion: Proteins possibly involved in the process of DNA repair were induced by low dose radiation-up regulating the expression of some specific genes. Such induced proteins lead to increase of cellular DNA repair capacity as well as radio-adaptive response of cells to gene mutations