Influence of temperature on radiation-induced inhibition of DNA supercoiling

The influence of subnormal temperatures (2, 15 and 28 degrees C) on the eff ects of radiation in MCF-7 cell cultures was studied using the fluorescent (halo) nucleoid assay. Increasing the propidium iodide (PI) concentration ( 0.5-7.5 mu g/ml PI) resulted in relaxation, i,e, in increasing nucleoid are a; higher concentrations up to 50 mu g/ml caused rewinding that resulted in nucleoid contraction. Rewinding was inhibited by X irradiation (2, 4 and 8 Gy) in a dose-dependent way. Incubation at subnormal temperature did not i nfluence the nucleoid area but did reduce radiation-induced inhibition of r ewinding after 4 Gy, The low temperature (2 degrees C) during rather than p rior to irradiation appeared to protect from radiation-induced inhibition o f nucleoid rewinding, Decreased temperature during irradiation may change t he conditions so as to reduce DNA-matrix damage induced by radiation. (C) 1 999 by Radiation Research Society.