Chinese hamster V79 cells' dependence on background ionizing radiation for optimal growth.

The study of depriving cells from background ionizing radiation for the past decades has provided valuable insights into its role in cellular homeostasis control. To explore the existence of such response in eukaryotic cells, we grew Chinese hamster (Cricetulus griseus) V79 cells for 23 days using three different dose rates: 0.91 (below background), 35 (surface control) and 72 nGy h-1 (underground KCl-amended control). We did not observe a significant difference in cell number during the course of the experiment. However, cells grown at below background showed significantly lower viability compared to those grown at both control levels after 5 days of incubation and lasted, intermittently, for up to 21 days. We also observed a clear differentiation between the underground and the surface controls that could be explained by the variety of radiation sources present during cell growth under unshielded conditions. To explore the molecular mechanisms for these responses we performed transcriptome analysis on samples collected on days 2 and 5, but only samples from day 5 resulted in significant regulation. Gene enrichment analysis revealed two control-dependent general transcriptional responses. When compared the underground-KCl control, below-background cells showed the upregulation of processes intended for the response to drugs, metals and mechanical stimuli. In comparison, the response relative to the surface control was characterized by the upregulation of responses to organic substances and abiotic stimuli involved in the regulation of signaling, as well as to cell proliferation and homeostatic control of the number of cell processes.