Low-Dose-Rate Irradiation Suppresses the Expression of Cell Cycle-Related Genes, Resulting in Modification of Sensitivity to Anti-Cancer Drugs

The biological effects of low-dose-rate (LDR) radiation exposure in nuclear power plant accidents and medical uses of ionizing radiation (IR), although being a social concern, remain unclear. In this study, we evaluated the effects of LDR-IR on global gene expression in human cells and aimed to clarify the mechanisms. RNA-seq analyses demonstrated that relatively low dose rates of IR modify gene expression levels in TIG-3 cells under normoxic conditions, but those effects were attenuated under hypoxia-mimicking conditions. Gene set enrichment analysis demonstrated that LDR-IR significantly decreased gene expression related to cell division, cell cycle, mitosis, and the Aurora kinase B and FOXM1 pathways. Quantitative RT-PCR confirmed the down-regulation of AURKB and FOXM1 genes in TIG-3 cells with LDR-IR or hypoxia-mimicking treatments without any dose-rate effect. Knock-down experiments suggested that HIF-1 alpha and HIF-2 alpha, as well as DEC1, participated in down-regulation of AURKB and FOXM1 under DFOM treatments, but to a lesser extent under LDR-IR treatment. FACS and microscopic analyses demonstrated that LDR-IR induced G0/G1 arrest and increased micronucleus or chromosome condensation. Finally, MTT assays demonstrated that LDR-IR decreased sensitivity to paclitaxel or barasertib in TIG-3 cells but not in A549 cells. In conclusion, LDR-IR modifies global gene expression and cell cycle control, resulting in a reduction of sensitivity to anti-cancer chemotherapy in non-cancer cells and thus a reduction in untoward effects (GA).