Gonadotropins decrease estrogen receptor-beta messenger ribonucleic acid stability in rat granulosa cells

Spatiotemporal expression analysis of nuclear estrogen receptors in the zebrafish ovary and their regulation in vitro by endocrine hormones and paracrine factors

Estradiol (E2) stimulates luteinizing hormone receptor (lhcgr) expression via nuclear estrogen receptors (nERs) in the zebrafish ovary. We have demonstrated that endocrine hormones such as gonadotropin (hCG) and paracrine factors such as epidermal growth factor (EGF) and pituitary adenylate cyclase-activating peptide (PACAP) can modulate E2-induced lhcgr expression in vitro. These observations raised a question on whether these hormones and factors exert their effects via regulating the expression of nERs. In this study, we first characterized the spatiotemporal expression profiles of three nER subtypes in the zebrafish ovary, including esr1 (ERα), esr2a (ERβ2) and esr2b (ERβ1). All three nERs increased their expression at the pre-vitellogenic stage and peaked at mid- (esr1 and esr2a) or late vitellogenic (esr2b) stage, followed by a significant decline at the full-grown stage. RT-PCR analysis showed that esr1 and esr2b were exclusively expressed in the follicle layer while esr2a was expressed in both compartments. We then examined how E2, hCG, PACAP and EGF regulated the expression of nERs in cultured zebrafish follicle cells. E2 quickly increased esr1 but reduced esr2a and esr2b expression from 1.5 to 12h of treatment. Similarly, EGF down-regulated esr2a significantly at 1.5h and this effect was further intensified at 24h. hCG decreased the expression of all three nER subtypes with similar potency throughout the 24-h time-course. Interestingly, PACAP exerted a biphasic regulation on esr2a. Our present study suggests that nERs, especially esr2a, provide potential target points for other hormones and factors to modulate E2 activity during folliculogenesis in the zebrafish.

Protective Effect of Progesterone during Pregnancy against Ovarian Cancer

There have been several epidemiologic studies supporting the protective role of pregnancy, although the mechanism is not clear. High level of progesterone, which is crucial in maintaining pregnancy, has been supposed to be one of the causative factors. Progesterone is produced at the corpus luteum in the early pregnancy and the placenta in the late pregnancy period. In several experimental studies, progesterone was reported to induce apoptosis of ovarian cancer cells through intrinsic and extrinsic pathways. In addition, progesterone has been shown to exert its anticancer effect through genomic and non-genomic action. The objective of this review is to discuss the protective mechanism of pregnancy against ovarian cancer focusing on the steroid hormone, progesterone.

Estrogen receptor alpha 46 is reduced in tamoxifen resistant breast cancer cells and re-expression inhibits cell proliferation and estrogen receptor alpha 66-regulated target gene transcription

Resistance to endocrine therapy is a major clinical problem in breast cancer. The role of ERalpha splice variants in endocrine resistance is largely unknown. We observed reduced protein expression of an N-terminally truncated ERalpha46 in endocrine-resistant LCC2, LCC9, and LY2 compared to MCF-7 breast cancer cells. Transfection of LCC9 and LY2 cells with hERalpha46 partially restored growth inhibition by TAM. Overexpression of hERalpha46 in MCF-7 cells reduced estradiol (E(2))-stimulated endogenous pS2, cyclin D1, nuclear respiratory factor-1 (NRF-1), and progesterone receptor transcription. Expression of oncomiR miR-21 was lower in TAM-resistant LCC9 and LY2 cells compared to MCF-7 cells. Transfection with ERalpha46 altered the pharmacology of E(2) regulation of miR-21 expression from inhibition to stimulation, consistent with the hypothesis that hERalpha46 inhibits ERalpha activity. Established miR-21 targets PTEN and PDCD4 were reduced in ERalpha46-transfected, E(2)-treated MCF-7 cells. In conclusion, ERalpha46 appears to enhance endocrine responses by inhibiting selected ERalpha66 responses.

Expression of estrogen receptors in the hypothalamo-pituitary-ovarian axis in middle-aged rats after re-instatement of estrus cyclicity

During reproductive aging female rats enter an anovulatory state of persistent estrus (PE). In an animal model of re-instatement of estrus cyclicity in middle-aged PE rats we injected the animals with progesterone (0.5 mg progesterone/kg body weight) at 12:00 for 4 days whereas control animals received corn oil injections. After the last injection animals were analyzed at 13:00 and 17:00. Young regular cycling rats served as positive controls and were assessed at 13:00 and 17:00 on proestrus. Progesterone treatment of middle-aged PE rats led to occurrence of luteinizing hormone (LH), follicle stimulating hormone (FSH), and prolactin surges in a subset of animals that were denoted as responders. Responding middle-aged rats displayed a reduction of ER-β mRNA in the preoptic area which was similar to the effect in young rats. Within the mediobasal hypothalamus, only young rats showed a decline of ER-α mRNA expression. A decrease of ER-α mRNA levels in the pituitary was observed in progesterone-responsive rats and in young animals. ER-β mRNA expression was reduced in young regular cycling rats. ER-β mRNA levels in the ovary were reduced following progesterone treatment in PE rats and in young rats. Taken together our data show that cyclic administration of progesterone reinstates ovulatory cycles in intact aging females which have already lost their ability to display spontaneous cyclicity. This treatment leads to the occurrence of preovulatory LH, FSH and prolactin surges which are accompanied by differential modulation of ERs in the hypothalamus, the pituitary and the ovary.

The molecular control of corpus luteum formation, function, and regression

The corpus luteum (CL) is one of the few endocrine glands that forms from the remains of another organ and whose function and survival are limited in scope and time. The CL is the site of rapid remodeling, growth, differentiation, and death of cells originating from granulosa, theca, capillaries, and fibroblasts. The apparent raison d'etre of the CL is the production of progesterone, and all the structural and functional features of this gland are geared toward this end. Because of its unique importance for successful pregnancies, the mammals have evolved a complex series of checks and balances that maintains progesterone at appropriate levels throughout gestation. The formation, maintenance, regression, and steroidogenesis of the CL are among the most significant and closely regulated events in mammalian reproduction. During pregnancy, the fate of the CL depends on the interplay of ovarian, pituitary, and placental regulators. At the end of its life span, the CL undergoes a process of regression leading to its disappearance from the ovary and allowing the initiation of a new cycle. The generation of transgenic, knockout and knockin mice and the development of innovative technologies have revealed a novel role of several molecules in the reprogramming of granulosa cells into luteal cells and in the hormonal and molecular control of the function and demise of the CL. The current review highlights our knowledge on these key molecular events in rodents.

Immunohistochemical localization of estrogen receptors ERalpha and ERbeta in the spiny mouse (Acomys cahirinus) ovary during postnatal development

This study was designed to determine the expression pattern of estrogen receptor (ER) subtypes in the Acomys cahirinus ovarian cells during its postnatal development. Immunohistochemical studies revealed the presence of ERalpha and ERbeta in germinal epithelium cells and interstitial tissue. Both these ER subtypes were also seen in granulosa cells and oocytes of growing follicles, however, the level of ERbeta expression was higher in comparison with ERalpha. In contrast to ERbeta, ERalpha protein was also present in theca cells. The expression of ERs increased with animals' age, but it decreased during follicular maturation. Moreover, the immunolocalization of ER subtypes in luteal cells showed that not ERbeta, but ERalpha expression is up-regulated throughout corpus luteum development. These immunohistochemical studies demonstrate, for the first time, that ERalpha is also expressed in the mouse granulosa cells and it may be a mediator of estrogen action in granulosa cells proliferation and differentiation.

The Ah receptor inhibits estrogen-induced estrogen receptor β in breast cancer cells

We have studied the effect of the aryl hydrocarbon receptor ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on estrogen receptor (ER) beta gene expression in the human breast cancer cell line, T47D. TCDD inhibited 17beta-estradiol (E2)-induced up-regulation of both ER beta wild type and ER beta cx mRNA. Cycloheximide pre-treatment had no inhibitory effect, and the estimated half-life of ER beta mRNA of about 33 min was not changed by any hormone administration. Chromatin immunoprecipitation experiments showed recruitment of ER alpha to the ER beta promoter. Gel mobility shift experiments revealed an E2-induced protein binding to a half site estrogen response element in the ER beta promoter, and TCDD reduced that binding. These results show that ER alpha regulates the expression of its own heterodimerization partner, ER beta, in T47D cells. TCDD, an anti-estrogenic compound, inhibits ER alpha-mediated induction of ER beta mRNA. These findings add to our understanding of cross talk between dioxin and estrogen signaling in human cells.

Update on estrogen signaling

Our understanding of estrogen signaling has undergone a true paradigm shift over recent years, following the discovery in 1995 of a second estrogen receptor, estrogen receptor beta (ERbeta). In many contexts ERbeta appears to antagonize the actions of ERalpha (yin/yang relationship) although there also exist genes that are specifically regulated by one of the two receptors. Studies of ERbeta knockout mice have shown that ERbeta exerts important functions in the ovary, central nervous system, mammary gland, prostate gland, hematopoiesis, immune system, vessels and bone. The use of ERbeta-specific ligands against certain forms of cancer represents one of the many pharmaceutical possibilities that have been created thanks to the discovery of ERbeta.

Uterine response to estradiol under action of chorionic gonadotropin in mice

This work examined the effect of chorionic gonadotropin on proliferative and morphogenetic reactions in the uterus under short- and long-term estrogen treatments. Ovariectomized mice received a single injection with estradiol dipropionate (2 micro g per 100 g; subcutaneously, sc) or vehicle and injections with human chorionic gonadotropin (10 IU per 100 g; sc) or vehicle twice a day for 2 days. Other groups of animals received injections with estradiol once a week or vehicle and injections with chorionic gonadotropin or vehicle once a day for 30 days. The uteri were removed 48 h after the last estradiol or vehicle injection. In animals treated with estradiol and chorionic gonadotropin for a month, the incidence of atypical endometrial hyperplasia was significantly higher. In animals treated with estradiol and chorionic gonadotropin for 2 days or for a month, uterine mass was slightly increased, the number of mitotic cells and BrdU-labeled cells was greater in luminal epithelium, glandular epithelium, stromal and myometrial cells, whereas the expression of estrogen receptors-alpha was lower in all uterine compartments, than in control. In mice who received estradiol and chorionic gonadotropin for 2 days, levels of beta-catenin and glycogen synthase kinase-3beta in luminal and glandular epithelia were lower. In animals treated with estradiol and chorionic gonadotropin for a month, the level of beta-catenin was slightly higher, and the expression of glycogen synthase kinase-3beta was lower in luminal and glandular epithelia. Thus, chorionic gonadotropin exerts estradiol-induced proliferative and morphogenetic changes in the uterus. This action of chorionic gonadotropin is associated with decreased expression of estrogen receptors-alpha and with changes in expression of beta-catenin and glycogen synthase kinase-3beta in the uterus.