Steroid hormones regulate the release of immunoreactive beta-endorphin from the Ishikawa human endometrial cell line.

Abstract

Immunoreactive beta-endorphin (IR-beta END) is present in human endometrium. Several indirect lines of evidence suggest that endometrial beta END is under steroid hormone control, i.e. IR-beta END is detectable in the secretory, but not the proliferative, endometrium, and progesterone administration increases the concentration of IR-beta END in uterine secretions of ovariectomized gilts. To study the effect of steroid hormones on endometrial beta END, we first questioned whether Ishikawa human endometrial adenocarcinoma cells (which respond to steroid hormones) express the proopiomelanocortin (POMC) gene. Indeed, on Northern blot analysis, a RNA similar or identical in size to pituitary POMC mRNA was present in Ishikawa cell RNA extracts. IR-beta END was also present in Ishikawa cell extracts and culture medium, which coeluted with synthetic human beta END in a Sephadex G-50 column. Ishikawa cells released most of their IR-beta END into the culture medium. Estradiol decreased the release of IR-beta END from Ishikawa cells, an effect that was dependent upon dose and time. The maximal effect was observed after a 4-day exposure to 10 nM estradiol (44 +/- 6% of the control value; n = 6; P less than 0.001). This effect was almost completely counteracted by a 100-fold excess of the antiestrogen 4-hydroxytamoxifen. Progesterone and dihydrotestosterone did not have a statistically significant effect on IR-beta END release. Dexamethasone had effects similar to those of estradiol, i.e. decreased the release of IR-beta END in a time- and dose-dependent manner. The maximal effect was detected after a 4-day exposure to 10 nM dexamethasone (53 +/- 6% of the control value; n = 6; P less than 0.001). Interestingly, the antiprogestin-antiglucocorticoid RU486 exhibited agonistic properties, i.e. diminished the release of IR-beta END in a time- and dose-dependent fashion, possibly via the glucocorticoid receptor. Its maximal effect was reached after a 4-day exposure to 10 nM RU486 (55 +/- 6% of the control value; n = 6; P less than 0.001). In conclusion, our data demonstrate that the release of IR-beta END from Ishikawa cells in culture is inhibited by estradiol and dexamethasone, suggesting that endometrial beta END is under estrogen and glucocorticoid regulation, as is the case with hypothalamic and pituitary POMC-derived peptides. This is the first time that the in vitro release of a peripheral-extracranial POMC-derived peptide has been found to be under the direct control of estrogens and glucocorticoids.