Primary explants of human uroepithelium show an unusual response to low- dose irradiation with cobalt-60 gamma rays

Recent results using very low doses of radiation have suggested that there is a hypersensitive region where cultures show an enhanced level of cell killing leading to a non-monotonic survival curve. This effect has been observed at doses below 2 Gy in mammalian systems and at much higher doses in insect cells. In this paper we report observation of the effect in primary human uroepithelial cell cultures. The effect was measured using a postirradiation proliferation assay where irradiated explants of standard size were allowed to proliferate for 14 days after exposure to ⁶⁰Co γ irradiation. By 14 days the majority of cultures derived from explants irradiated with 2-5 Gy showed little evidence of growth inhibition and cell numbers approached or even exceeded those obtained in the controls. There was, however, a significant reduction in cell number and growth rate in all cultures exposed to doses lower than 1 Gy. Oncoprotein (p53, c-myc, bcl-2, p21 ras) and EGFR expression were also measured in these cultures and were significantly increased. Morphological evidence of apoptosis was present in all irradiated cultures at 4 h after exposure, but this persisted for longer periods in cultures exposed to low doses.