Comparison of the reactions to stress produced by X-rays or electromagnetic fields (50Hz) and heat: induction of heat shock genes and cell cycle effects in human cells

Abstract

Summary The effects of irradiation (200kV X-ray, 5 Gy), extremely low frequency electromagnetic fields (ELF-EMF, 50 Hz, 60±0.2 µT) and/or heat shock (HS, 41°C for 30 min) on the expression of several heat shock genes (HSP27, HSP60, HSP70, HSP75, HSP78, HSP90) in human HL-60 leukaemia cells was studied by RT-PCR. In addition, the effects of these stressors on cell cycle progression in exponentially and asynchronously growing cell cultures were studied by flow cytometry. The dynamics of cell division during successive cell cycles was monitored by fluorescence-labelling of the cells with carboxyfluorescein succinimidyl ester (CFSE). Finally, the cell cycle distribution was studied by staining with propidium iodide (PI). With respect to HSP gene expression the three stressors produced similar effects. The combination of stressors (ELF-EMF and HS or Radiation and HS) strongly induced transcription of the HSP70 gene above the level induced by each stressor alone. The cell cycle analysis, however, revealed striking differences in the cellular response to each stressor. Of particular interest was the observed thermoprotective effect of ELFEMF in heat shocked cells, an effect that was not seen in cells which were exposed to X-rays in the presence of thermal stress.