Regulation of estrogen activity by sulfation in human Ishikawa endometrialadenocarcinoma cells

Sulfation is an important conjugation reaction in the metabolism of steroid s. Steroids sulfates do not interact with the appropriate hormone receptors ; additionally, the presence of the charged sulfate moiety increases the aq ueous solubility and excretion of most steroids. Estrogen sulfotransferase (EST) is the major form of human cytosolic ST involved in the conjugation o f estrogens. EST is important in the inactivation of beta-estradiol (E2) du ring the luteal phase of the menstrual cycle. EST has a significantly highe r affinity for the sulfation of E2 and 17 alpha-ethinylestradiol (EE2) than for other potent estrogens such as diethylstilbestrol (DES) and equine est rogens. The ability of EST to sulfate these estrogenic compounds at physiol ogic concentrations is important in regulating their activation of the ER i n estrogen responsive cells. Human Ishikawa endometrial adenocarcinoma (ISH ) cells possess an estrogen receptor (ER)-regulated alkaline phosphatase (A lkPhos) which is used to assay ER activation. To study the effects of EST a ctivity on the ER activation of different estrogenic compounds, ISH cells w ere stably transformed with an EST expression vector. Dose-response curves for the induction of AlkPhos activity by the different estrogenic compounds were generated with EST/ISH and control pcDNA/ISH cells. EST/ISH cells wer e 200-fold less sensitive to E2 and EE2 than were control cells. No differe nces were observed in the dose-response curves for DES between EST/ISH and pcDNA/ISH cells. EST/ISH cells were approximately 3-10-fold less sensitive to the equine estrogens equilin and 17-equilin as compared to control cells . The ability of EST to decrease the ER activation of an estrogen correlate s with the sulfation of these compounds at nanomolar concentrations by EST/ ISH and pcDNA/ISH ISH cells. These results indicate that EST is capable of efficiently inactivating E2 and EE2 but is significantly less effective in inhibiting the ER binding of other potent estrogenic compounds. (C) 1999 El sevier Science Ltd. All rights reserved.