Rapid Fluctuations in the Levels of Specific Estradiol-Binding Sites in Endometrial Cells in Culture*

Publisher Website
Google Scholar
Abstract
Levels of specific estradiol (E2) binding sites were measured during 5–6 consecutive days in primary cultures of stromal and epithelial cells from 7 specimens of human proliferative and secretory endometrium. Large day to day variations were noted, as we previously reported. Levels of binding sites were also measured hourly (1–30 h after plating) in 11 cultures of an endometrial adenocarcinoma cell line (HEC). In these experiments, striking increases and decreases were found to occur within periods as short as 2 h. The rapidity of these changes suggests reversible unmasking or activation of binding sites for E2, rather than new synthesis of binders. Elevated levels were found immediately before periods of accelerated increase in the amounts of DNA per dish, both in cultures of endometrial fibroblasts and in partially synchronized cultures of HEC cells, indicating a possible relation between levels of specific binding sites and the cell cycle. However, since elevated levels have also been found in nongrowing and apparently nonsynchronous cells, it is possible that such fluctuations are more generally related to the metabolic state of the cell. Measurements of levels of specific E2-binding sites in nuclei and cytoplasm in both endometrial fibroblast and HEC cell cultures showed limited translocation to the nucleus in spite of the high concentration of [3H]E2 (100 nM) used for labeling. At this concentration, [3H]E2 appears to label nontranslocatable cytoplasmic binders whose affinity for E2 may be lower than that of translocatable receptors usually detected during incubations with less than 20 nM [3H]E2. The results demonstrate that studies on levels of estrogen-binding proteins in cell cultures should include frequent serial measurements and point to the need for further investigation of the possibility that these levels are regulated by mechanisms heretofore unexplored. (Endocrinology108: 1744, 1981)