Dynamics of progesterone binding in nuclei and cytosol of estrogen-induced adenocarcinoma cells in primary culture

Abstract

Short-term primary cell culture has been used to characterize the regulation of progesterone binding sites in cells from a renal adenocarcinoma induced by estrogen in Syrian hamsters. At low cell density, the cells divide in culture with a population doubling time of 24 h. The cells are predominantly epithelial, bear motile cilia, and contain specific estrogen binding sites. The addition of estrogen (10 −8 M) to the growth medium results in a significant increase in progesterone binding sites in the cytosol of cultured cells. The affinity constant for the cytosol binding reaction at 0°C is 10 9 M −1, similar to that of the progesterone receptor in other estrogen target tissues. Binding of labeled progesterone to nuclei is maximal one-half hour after the hormone is added to cells in culture. The affinity constant for the nuclear binding reaction at 37°C is also 10 9 M −1. The amount of labeled progesterone bound to cytosol binding sites at 37°C is about one-fifth of that bound to nuclear sites. No change in progesterone binding sites was found upon reincubation of the cytosol at 0°C. These data are not consistent with appreciable translocation of cytoplasmic binding sites to nuclei.