STEROID-HORMONES REGULATE THE RELEASE OF IMMUNOREACTIVE BETA-ENDORPHIN FROM THE ISHIKAWA HUMAN ENDOMETRIAL CELL-LINE

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 < 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 < 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 < 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.