Effect of low dose irradiation on estrogen receptor level in MCF-7 breast cancer cells

Exposure of MCF-7 cells to single and/or repeated low gamma -ray doses (0.5 to 8 Gy) resulted in a decrease in the capacity of these cells to concentr ate tritiated estradiol ([H-3]E-2) (reduction of the number of binding site s). The decrease in the [H-3]E-2-binding capacity was higher than the survi val rate, indicating that it could not be ascribed to cell death. Moreover, such low irradiation doses failed to similarly affect the specific incorpo ration of [H-3]ORG 2058, even when the progesterone receptor was induced by E-2, a finding that rejects the hypothesis of a nonspecific effect on all steroid hormone receptors. This loss of [H-3]E-2 binding was reflected by t he elimination of the estrogen receptor alpha (ER) when the latter was asse ssed by immunocytochemistry. However, additional immunochemical studies (We stern blot data) performed on cell extracts under denaturing conditions fai led to show any similar elimination of the ER peptide, suggesting that the loss of E-2-binding capacity would be relevant to subtle changes in the ER structure and/or ER-associated proteins. The loss of binding capacity, prod uced by a 3-Gy irradiation, failed to decrease the sensitivity of the cells to E-2, since progesterone receptor induction and growth stimulation were maintained. Insufficient ER diminution may explain this observation. (C) 20 01 Wiley-Liss, Inc.