Placental expression of estrogen receptor beta and its hormone binding variant – comparison with estrogen receptor alpha and a role for estrogen receptors in asymmetric division and differentiation of estrogen-dependent cells

Abstract

During human pregnancy, the production of 17-beta-estradiol (E2) rises steadily to eighty fold at term, and placenta has been found to specifically bind estrogens. We have recently demonstrated the expression of estrogen receptor alpha (ER-alpha) protein in human placenta and its localization in villous cytotrophoblast (CT), vascular pericytes, and amniotic fibroblasts. In vitro, E2 stimulated development of large syncytiotrophoblast (ST) aggregates. In the present study we utilized ER-beta affinity purified polyclonal (N19:sc6820) and ER-alpha monoclonal (clone h-151) antibodies. Western blot analysis revealed a single ~52 kDa ER-beta band in chorionic villi (CV) protein extracts. In CV, strong cytoplasmic ER-beta immunoreactivity was confined to ST. Dual color immunohistochemistry revealed asymmetric segregation of ER-alpha in dividing villous CT cells. Prior to separation, the cell nuclei more distant from ST exhibited high ER-alpha, while cell nuclei associated with ST showed diminution of ER-alpha and appearance of ER-beta. In trophoblast cultures, development of ST aggregates was associated with diminution of ER-alpha and appearance of ER-beta immunoreactivity. ER-beta was also detected in endothelial cells, amniotic epithelial cells and fibroblasts, extravillous trophoblast (nuclear and cytoplasmic) and decidual cells (cytoplasmic only). In addition, CFK-E12 (E12) and CWK-F12 (F12) monoclonal antibodies, which recognize ~64 kDa ER-beta with hormone binding domain, showed nuclear-specific reactivity with villous ST, extravillous trophoblast, and amniotic epithelium and fibroblasts. Western blot analysis indicated abundant expression of a ~64 kDa ER-beta variant in trophoblast cultures, significantly higher when compared to the chorionic villi and freshly isolated trophoblast cell protein extracts. This is the first report on ER-beta expression in human placenta and cultured trophoblast. Our data indicate that during trophoblast differentiation, the ER-alpha is associated with a less, and ER-beta with the more differentiated state. Enhanced expression of ~64 kDa ER-beta variant in trophoblast cultures suggests a unique role of ER-beta hormone binding domain in the regulation of trophoblast differentiation. Our data also indicate that asymmetric segregation of ER-alpha may play a role in asymmetric division of estrogen-dependent cells.

Estrogen receptor (ER)-β isoforms: A key to understanding ER-β signaling

“…Interestingly, ER-␤5 was the only isoform that could be detected in placenta. Our data are in agreement with a recent finding that ER-␤ with a molecular weight (52 kDa) comparable with ER-␤5 was dominantly expressed in the placenta (19). A wide distribution of ER-␤5 in various tissues and cell lines raises an intriguing question of whether the current understanding of ER-␤'s action based largely on ER-␤1 is complete, because heteodimerization of ER-␤5 with ER-␤1 significantly enhances the overall activity in a liganddependent manner.…”

Placental villous vascular endothelial growth factor expression and vascularization after estrogen suppression during the last two-thirds of baboon pregnancy

“…For example, estrogen increased VEGF gene transcription in estrogen receptor a-and b-positive MCF-7 breast cells, but decreased VEGF expression in estrogen receptor a-negative, b-positive MDA breast cells [25,26]. Interestingly, villous cytotrophoblasts are estrogen receptor a-and b-positive while extravillous cytotrophoblasts are estrogen receptor a-negative and b-positive [27,28]. The cell-specific regulation of VEGF in the primate placenta, therefore, may reflect presence/absence of estrogen receptor subtypes, as well as functional co-activators/ repressors, that modulate estrogen-regulated target gene transcription [29].…”

Estrogen receptors (review). Part 2.

“…РЭβ обнаружен в синцитиотрофобласте хорионического ворсинок, в эндотелиальных клетках, амниотических эпителиальных клетках и фибробластах, вневорсинчатом трофобласте и децидуальных клетках [5,26]. Поскольку трофобласт является основным источником плацентарных гормонов, экспрессия РЭβ клетками трофобласта может быть вовлечена в стимуляцию гормональной продукции плаценты эстрогенами.…”

“…Данные, полученные при исследовании плаценты, показывают, что при дифференциации трофобластов РЭα ассоциируется с менее, а РЭβ − с более дифференцированным состоянием клеточного слоя [5]. Полученные результаты свидетельствуют о том, что эстрогены, действующие через РЭα, принимают активное участие в процессе дифференцировки цитотрофобласта в синцитиальные структуры.…”

“…Последовательность наблюдений позволила этим же авторам прийти к выводу о возможности взаимодополняющих и последовательных эффектов РЭα и РЭβ, поскольку РЭα, по-видимому, необходим для базового развития чувствительных к эстрогену тканей, а РЭβдля их функционального созревания, что указывает на уникальную роль гормон-связывающего домена РЭβ в регуляции функции плаценты. Данный вывод подтверждался еще и тем, что терминальное старение и дегенерация чувствительных к эстрогену клеток сопровождалась прогрессирующей потерей экспрессии РЭβ [5].…”