Ovarian Steroid Estrogen Research Articles

Aberrant activation of estrogen receptor-α signaling in Mettl14-deficient uteri impairs embryo implantation.

The precise control of endometrial receptivity is crucial for successful embryo implantation, which is strictly regulated by the ovarian steroid hormones estrogen and progesterone. Despite our improved understanding of the genetic regulation of implantation downstream of the action of hormones, we do not know much about the epigenetic regulation that occurs during early pregnancy. To investigate the role of the N6-methyladenosine (m6A) RNA modification in embryo implantation, we generated mice with conditional deletion of Mettl14, a core component of the m6A writer complex, in the uterus. These mice were infertile due to implantation failure. We showed that Mettl14-deficient uteri had aberrant upregulation of estrogen receptor α (ERα) signaling and ERα phosphorylation, but progesterone receptor (PGR) signaling was largely unaffected. Additionally, Mettl14 deletion led to abnormal activation of the innate immune pathway in Mettl14-deficient uteri. This effect was accompanied by the infiltration of immune cells, such as macrophages and dendritic cells, into the basal region of the endometrial epithelium. Methylated RNA immunoprecipitation sequencing (MeRIP-seq) showed that genes involved in the innate immune response had decreased m6A peaks in Mettl14-deficient mice. These results suggest that Mettl14 plays a crucial role in successful implantation by precisely regulating both ERα signaling and innate immunity in the uterus.

Resveratrol alleviates zea-induced decidualization disturbance in human endometrial stromal cells

Decidualization, which endows the endometrium competency to adopt developing embryo and maintain appropriate milieu for following growth, is a pivotal process for human pregnancy. The delicate collaboration between ovarian steroid hormones estrogen and progesterone governs the process of decidualization and subsequent establishment of embryo implantation. Mycotoxin zearalenone (ZEA) is well known as endocrine disruptor due to its potent estrogenic activity. In this study, we investigated effects of ZEA on decidualization of human endometrial stromal cells. Results indicated that ZEA exhibited its inhibitory action through nuclear translocation of ERα. ZEA exposure led to dampened progress of decidualization, which could be attenuated by estrogen receptor antagonist. Notably, resveratrol (RSV) administration restored impaired decidualization process by induction of anti-oxidative gene glutathione peroxidase 3 (GPX3). This study provides novel insights into the mechanism underlying adverse effects of ZEA in human decidual stromal cells and suggests RSV a potential therapeutic candidate to alleviate ZEA-induced cytotoxicity during decidualization.

Interleukin-13 receptor subunit alpha-2 is a target of progesterone receptor and steroid receptor coactivator-1 in the mouse uterus†.

The endometrium, composed of epithelial and stromal cell compartments, is tightly regulated by the ovarian steroid hormones estrogen (E2) and progesterone (P4) during early pregnancy. Through the progesterone receptor (PGR), steroid receptor coactivators, and other transcriptional coregulators, progesterone inhibits E2-induced cell proliferation and induces the differentiation of stromal cells in a process called decidualization to promote endometrial receptivity. Although interleukin-13 receptor subunit alpha-2 (Il13ra2) is expressed in the human and mouse endometrium, its potential role in the steroid hormone regulation of the endometrium has not been thoroughly examined. In this study, we employed PGR knockout mice and steroid receptor coactivator-1 knockout mice (SRC-1-/-) to profile the expression of Il13ra2 in the murine endometrium and determine the role of these transcriptional regulators in the hormone-responsiveness of Il13ra2 expression. Furthermore, we utilized a well-established decidualization-inducing steroidogenic cocktail and a siRNA-based knockdown of IL13RA2 to determine the importance of IL13RA2 in the decidualization of primary human endometrial stromal cells. Our findings demonstrate that Il13ra2 is expressed in the subepithelial stroma of the murine endometrium in response to ovarian steroid hormones and during early pregnancy in a PGR- and SRC-1-dependent manner. Furthermore, we show that knockdown of IL13RA2 before in vitro decidualization of primary human endometrial stromal cells partially compromises the full decidualization response. We conclude that Il13ra2 is a downstream target of progesterone through PGR and SRC-1 and plays a role in mediating the stromal action of ovarian steroid hormones.

Analysis of heart and neural crest derivatives-expressed protein 2 (HAND2)-progesterone interactions in peri-implantation endometrium†.

Implantation is restricted to a narrow window when the local endometrial microenvironment is supportive of the invading embryo. The ovarian steroid hormones estrogen (E) and progesterone (P) are principal regulators of uterine receptivity. Suppression of E-dependent proliferation of luminal epithelium (LE) by P is mandatory for embryo implantation. Here, we report that the balance of E receptor α (ERα) and P receptors (PR) activity controls HAND2 expression, a key transcription factor that determines the fate of the implanting embryo and thereby pregnancy outcome. As a model, we used wild-type mice as well as mice in which either both PR isoforms or the A-isoform was genetically ablated (PRKO and PRAKO, respectively). Detailed spatiotemporal analyses of PR, HAND2, and ERα expression at implantation site demonstrated co-expression of HAND2 and PR but not ERα. Furthermore, in hormonally treated ovariectomized WT, PRAKO and PRKO mice, E suppresses endometrial HAND2 expression. Adding P together with E partially rescues HAND2 expression in WT, but not PRAKO and PRKO animals. Therefore, infertility in PRAKO mice is at least in part associated with the loss of PR-A-regulated HAND2 expression.

Hormone dependent uterine epithelial-stromal communication for pregnancy support

Human fertility is a relatively inefficient process. Despite the presence of visibly healthy embryos, 30% of pregnancies generated by assisted reproductive technology (ART) fail before the second trimester. The uterine microenvironment plays a critical role in establishing and maintaining a successful pregnancy that requires coordinated communication between the epithelial and stromal cells of the endometrium. The epithelial cells must cease proliferation and become permissive for the conceptus (embryo and associated extraembryonic membranes), while the stromal cells undergoes mesenchymal-to-epithelioid transformation to form the decidua in support of subsequent embryo development. The ovarian steroids Estrogen (E2) and Progesterone (P4) are the major hormones governing these processes. These hormones act via their nuclear receptors, the estrogen receptor, ESR1, and progesterone receptor, PGR, to direct the transcription of genes that orchestrate epithelial and stromal cell communication. This review will discuss the molecular mechanisms utilized by steroid hormones that regulate uterine receptivity, as well, establish and maintain pregnancy.

The role of steroid hormones in breast cancer stem cells.

Breast cancer stem cells (BCSCs) are potent tumor-initiating cells in breast cancer, the most common cancer among women. BCSCs have been suggested to play a key role in tumor initiation which can lead to disease progression and formation of metastases. Moreover, BCSCs are thought to be the unit of selection for therapy-resistant clones since they survive conventional treatments, such as chemotherapy, irradiation, and hormonal therapy. The importance of the role of hormones for both normal mammary gland and breast cancer development is well established, but it was not until recently that the effects of hormones on BCSCs have been investigated. This review will discuss recent studies highlighting how ovarian steroid hormones estrogen and progesterone, as well as therapies against them, can regulate BCSC activity.

Paracrine activation of WNT/β-catenin pathway in uterine leiomyoma stem cells promotes tumor growth

Uterine leiomyomas are extremely common estrogen and progesterone-dependent tumors of the myometrium and cause irregular uterine bleeding, severe anemia, and recurrent pregnancy loss in 15-30% of reproductive-age women. Each leiomyoma is thought to arise from a single mutated myometrial smooth muscle stem cell. Leiomyoma side-population (LMSP) cells comprising 1% of all tumor cells and displaying tumor-initiating stem cell characteristics are essential for estrogen- and progesterone-dependent in vivo growth of tumors, although they have remarkably lower estrogen/progesterone receptor levels than mature myometrial or leiomyoma cells. However, how estrogen/progesterone regulates the growth of LMSP cells via mature neighboring cells is unknown. Here, we demonstrate a critical paracrine role of the wingless-type (WNT)/β-catenin pathway in estrogen/progesterone-dependent tumorigenesis, involving LMSP and differentiated myometrial or leiomyoma cells. Estrogen/progesterone treatment of mature myometrial cells induced expression of WNT11 and WNT16, which remained constitutively elevated in leiomyoma tissues. In LMSP cells cocultured with mature myometrial cells, estrogen-progesterone selectively induced nuclear translocation of β-catenin and induced transcriptional activity of its heterodimeric partner T-cell factor and their target gene AXIN2, leading to the proliferation of LMSP cells. This effect could be blocked by a WNT antagonist. Ectopic expression of inhibitor of β-catenin and T-cell factor 4 in LMSP cells, but not in mature leiomyoma cells, blocked the estrogen/progesterone-dependent growth of human tumors in vivo. We uncovered a paracrine role of the WNT/β-catenin pathway that enables mature myometrial or leiomyoma cells to send mitogenic signals to neighboring tissue stem cells in response to estrogen and progesterone, leading to the growth of uterine leiomyomas.

Expression Profiling of Nuclear Receptors Identifies Key Roles of NR4A Subfamily in Uterine Fibroids

Uterine fibroids (UFs), also known as uterine leiomyomas, are benign, fibrotic smooth muscle tumors. Although the GnRH analog leuprolide acetate that suppresses gonadal steroid hormones is used as a treatment, it has significant side effects, thereby limiting its use. Availability of more effective therapy is limited because of a lack of understanding of molecular underpinnings of the disease. Although ovarian steroid hormones estrogen and progesterone and their receptors are clearly involved, the role of other nuclear receptors (NRs) in UFs is not well defined. We used quantitative real-time PCR to systematically profile the expression of 48 NRs and identified several NRs that were aberrantly expressed in UFs. Among others, expression of NR4A subfamily members including NGFIB (NR4A1), NURR1 (NR4A2), and NOR1 (NR4A3) were dramatically suppressed in leiomyoma compared with the matched myometrium. Restoration of expression of each of these NR4A members in the primary leiomyoma smooth muscle cells decreased cell proliferation. Importantly, NR4As regulate expressions of the profibrotic factors including TGFβ3 and SMAD3, and several collagens that are key components of the extracellular matrix. Finally, we identify NR4A members as targets of leuprolide acetate treatment. Together, our results implicate several NRs including the NR4A subfamily in leiomyoma etiology and identify NR4As as potential therapeutic targets for treating fibrotic diseases.

Epithelial-Stromal Interaction and Progesterone Receptors in the Mouse Uterus

Healthy uterine function depends on the balanced interaction of the ovarian steroids estrogen and progesterone (P4) signaling through their respective receptors. The expression of each receptor is regulated by the other through crucial cross talk between the epithelial and stromal compartments. Ablation of the progesterone receptor (PR) results in complete infertility in mice, and evidence increasingly demonstrates that the PR is a major mediator of epithelial-stromal cross talk and events leading to the disruption of this communication can lead to P4 resistance in the uterus. This resistance, through impaired P4 signaling, can be at the level of the PR itself, coregulators, and downstream effectors. The mechanisms underlying P4 resistance is of critical importance in women's health because this defect is seen in a wide variety of diseases including infertility, endometriosis, endometrial carcinoma, polycystic ovarian syndrome, and leiomyomas. By using mouse models of PR signaling, many of these mechanisms are beginning to be elucidated and aid in the development of effective therapies for treatment of uterine diseases.

HoxA-11 and FOXO1A Cooperate to Regulate Decidual Prolactin Expression: Towards Inferring the Core Transcriptional Regulators of Decidual Genes

BackgroundDuring the menstrual cycle, the ovarian steroid hormones estrogen and progesterone control a dramatic transcriptional reprogramming of endometrial stromal cells (ESCs) leading to a receptive state for blastocyst implantation and the establishment of pregnancy. A key marker gene of this decidualization process is the prolactin gene. Several transcriptional regulators have been identified that are essential for decidualization of ESCs, including the Hox genes HoxA-10 and HoxA-11, and the forkhead box gene FOXO1A. While previous studies have identified downstream target genes for HoxA-10 and FOXO1A, the role of HoxA-11 in decidualization has not been investigated. Here, we show that HoxA-11 is required for prolactin expression in decidualized ESC. While HoxA-11 alone is a repressor on the decidual prolactin promoter, it turns into an activator when combined with FOXO1A. Conversely, HoxA-10, which has been previously shown to associate with FOXO1A to upregulate decidual IGFBP-1 expression, is unable to upregulate PRL expression when co-expressed with FOXO1A. By co-immunoprecipitation and chromatin immunoprecipitation, we demonstrate physical association of HoxA-11 and FOXO1A, and binding of both factors to an enhancer region (−395 to −148 relative to the PRL transcriptional start site) of the decidual prolactin promoter. Because FOXO1A is induced upon decidualization, it serves to assemble a decidual-specific transcriptional complex including HoxA-11. These data highlight cooperativity between numerous transcription factors to upregulate PRL in differentiating ESC, and suggest that this core set of transcription factors physically and functionally interact to drive the expression of a gene battery upregulated in differentiated ESC. In addition, the functional non-equivalence of HoxA-11 and HoxA-10 with respect to PRL regulation suggests that these transcription factors regulate distinct sets of target genes during decidualization.

Regulation of Expression of Cytokine Signal Transducer STAT3 by C/EBPbeta Contributes to Human Endometrial Stromal Decidualization.

The human endometrium is a dynamic tissue that undergoes proliferation, differentiation and shedding during each menstrual cycle. The sequential actions of ovarian steroids estrogen (E) and progesterone (P) induce a unique endometrial stromal differentiation and remodeling process, known as predecidualization, which is a prerequisite for successful implantation. The molecular pathways underlying this hormonally induced cellular transformation event remain poorly understood. We have recently identified C/EBPβ, a CCAAT box-binding transcription factor, as a unique regulator of decidualization in mice. In this study, using an in vitro decidualization system in which primary human endometrial stromal cells (HESC) undergo decidualization upon addition of E, P, and a cyclic AMP analog, we established that C/EBPβ plays an essential role in human stromal differentiation. Attenuation of endogenous C/EBPβ function by a dominant negative mutant of this transcription factor blocked the decidualization process. Similar results were obtained by siRNA-mediated down regulation of C/EBPβin HESCs. In order to identify the molecular pathways regulated by C/EBPβ during decidualization, we performed gene expression profiling experiments using normal and C/EBP β-deficient HESCs. Our studies revealed that several key regulators of decidualization, such as BMP2 and Wnt4, operate downstream of C/EBP beta. We also identified the interleukin 11 receptor alpha (IL-11Ralpha) and the signal transducer and activator of transcription 3 (STAT3) as prominent downstream targets of C/EBPβ. STAT3 mediates the signaling by several cytokines including IL11. Chromatin immunoprecipitation experiments indicated that C/EBPβ controls the expression of STAT3 by directly interacting with its promoter. siRNA-mediated down regulation of STAT3 expression in HESCs resulted in significantly reduced differentiation of these cells, indicating an important role for this cytokine signal transducer in the decidualization process. Collectively, our observations established that C/EBPβis a central regulator of human endometrial stromal differentiation. This study further revealed that STAT3 is a critical downstream mediator of the function of C/EBPβ, providing a novel link between C/EBPβ and cytokine signaling pathways that regulate endometrial functions during decidualization. (Supported by NIH grant U54 HD55787). (poster)

Associations of genetic variants in the estrogen receptor coactivators PPARGC1A, PPARGC1B and EP300 with familial breast cancer

The mitogen effect of the ovarian steroid estrogen is a strong risk factor for breast cancer development. This effect is mainly mediated by the estrogen receptor alpha, a hormone inducible transcription factor, which activates gene expression through recruiting multiple coactivators, such as PPARGC1A, PPARGC1B and EP300. We tested the hypothesis that non-conservative, putative functional amino acid exchanges in PPARGC1A, PPARGC1B and EP300 act as low-penetrance familial breast cancer risk factors. The analysis of 816 BRCA1/2 mutation-negative familial breast cancer patients and 1012 controls revealed an association of the PPARGC1A Thr612Met polymorphism with familial breast cancer (OR = 1.35, 95% CI 1.00-1.81, P = 0.049), high-risk familial breast cancer (OR = 1.51, 95% CI 1.08-2.12, P = 0.017) and bilateral familial breast cancer (OR = 2.30, 95% CI 1.24-4.28, P = 0.009). Logistic regression analyses of the PPARGC1B Ala203Pro variant showed an increased familial breast cancer risk of heterozygous and homozygous variant allele carriers (OR = 1.48, 95% CI 1.15-1.91, P = 0.002). The genotype-combination analysis of the associated PPARGC1A Thr612Met variant and the associated PPARGC1B Ala203Pro variant suggests an allele dose-dependent breast cancer risk (P(trend) = 0.0004). Our results indicate for the first time the importance of inherited variants in the estrogen receptor coactivator genes PPARGC1A and PPARGC1B for familial breast cancer susceptibility. Owing to their impact on estrogen signaling, these polymorphisms might also influence adjuvant anti-estrogen therapy, using agents such as tamoxifen and raloxifen, and outcome of breast cancer patients.

Cochaperone immunophilin FKBP52 is critical to uterine receptivity for embryo implantation

Embryo implantation in the uterus is a critical step in mammalian reproduction, requiring preparation of the uterus receptive to blastocyst implantation. Uterine receptivity, also known as the window of implantation, lasts for a limited period, and it is during this period blastocysts normally implant. Ovarian steroid hormones estrogen and progesterone (P(4)) are the primary regulators of this process. The immunophilin FKBP52 serves as a cochaperone for steroid hormone nuclear receptors to govern appropriate hormone action in target tissues. Here we show a critical role for FKBP52 in mouse implantation. This immunophilin has unique spatiotemporal expression in the uterus during implantation, and females missing the Fkbp52 gene have complete implantation failure due to lack of attainment of uterine receptivity. The overlapping uterine expression of FKBP52 with nuclear progesterone receptor (PR) in wild-type mice together with reduced P(4) binding to PR, attenuated PR transcriptional activity and down-regulation of several P(4)-regulated genes in uteri of Fkbp52(-/-) mice, establishes this cochaperone as a critical regulator of uterine P(4) function. Interestingly, ovulation, another P(4)-mediated event, remains normal. Collectively, the present investigation provides evidence for an in vivo role for this cochaperone in regulating tissue-specific hormone action and its critical role in uterine receptivity for implantation.

Effect of Estrogen-Serotonin Interactions on Mood and Cognition

Both the neurotransmitter serotonin and the ovarian steroid estrogen have been implicated in the modulation of mood and cognition. Although significant functional interactions between estrogen and serotonin are acknowledged, the nature of their relationship has not been fully elucidated. Research using ovariectomized animals has identified estrogen-induced changes in serotonin transmission, binding, and metabolism in brain regions implicated in the regulation of affect and cognition. Studies in humans, particularly of menopausal women undergoing estrogen treatment, have provided some support for these findings and identified instances in which change in mood or cognition is accompanied by alterations in serotonin function and hormonal status. However, it is apparent that further research is required to understand the neural processes involved in the interplay between estrogen and serotonin. By reviewing animal and human data regarding estrogen and serotonin's effects on mood and cognition, the authors aim to better define their relationship and highlight areas for further research.

Steroid receptors and cell cycle in normal mammary epithelium.

The ovarian steroids estrogen and progesterone (E(2) and P) are essential for normal mammary gland growth and development; however, the mechanisms by which they influence the proliferative activity of the mammary epithelium remain unclear. Mammary epithelial cells cells expressing the receptors for E(2) and P (ER and PR respectively) are separate from, although often adjacent to, those capable of proliferating, implying that the ovarian steroids act indirectly via paracrine or juxtacrine growth factors to stimulate entry into the cell cycle. A large number of candidate factors have been identified in a variety of different experimental systems, and it appears that transforming growth factor beta may play a role in preventing proliferation of steroid receptor-containing cells. Dysregulation of the strict inverse relationship between ERalpha expression and proliferation is detectable in premalignant human breast lesions, indicating that it might be essential to the tumorigenic process. Challenges for the future include determining which of the candidates identified as being mediators of the effects of E(2) are physiologically and clinically relevant as well as finding out how ERalpha-containing cells become proliferative during tumorigenesis. Answering these questions could greatly increase our understanding of the factors controlling mammary gland development and the processes leading to cancer formation.

Role of differentiation in carcinogenesis and cancer prevention

Ductal carcinoma is the malignant disease most frequently diagnosed in American women. This cancer type originates in Stem Cells 1, epithelial cells that are the main components of the undifferentiated mammary gland. The susceptibility of Stem Cells 1 to become transformed has been attributed to their high rate of cell proliferation, their ability to bind and activate the carcinogen and their low DNA reparative activity. Epidemiological evidence indicates that a woman's lifetime risk for developing breast cancer is decreased by a full-term pregnancy at a young age. The protection conferred by pregnancy is the result of the differentiation of the organ. The reproduction of the hormonal milieu of an early full-term pregnancy by administration of human chorionic gonadotropin (hCG) to virgin rats induces lobular development, completing the cycle of differentiation of the breast that converts the highly susceptible Stem Cell 1 into a resistant Stem Cell 2 through a process of induction of a specific genomic signature in the mammary epithelium. Both pregnancy and hCG exert a protective effect on the mammary gland by reducing the incidence of 7,12-dimethyl-benz(a)anthracene (DMBA)-induced carcinomas. Although differentiation significantly reduces cell proliferation in the mammary epithelium, the differentiated Stem Cell 2 remains capable of responding with proliferation to given stimuli, such as a new pregnancy; it is also capable of metabolizing the carcinogen and of repairing DNA damage more efficiently than the Stem Cell 1. The basic biological concept is that the conversion of the susceptible Stem Cell 1 to a refractory Stem Cell 2 after pregnancy or hCG treatment of virgin rats results from the differentiation of the mammary gland, a phenomenon manifested at morphological, cell kinetic and functional levels. Morphological changes consist of a progressive branching of the mammary parenchyma and lobule formation, which in turn result in a reduction in cell growth fraction and lengthening of the cell cycle. The functional changes comprise increased synthesis of inhibin, β-casein and other milk-related bioactive peptides. In addition, pregnancy or hCG also increases the expression of programmed cell death genes, including TRPM2, ICE, p53, c-myc, and bcl-XS, inducing as well apoptosis, and downregulation of cyclins. Programmed cell death genes were activated through a p53-dependent process, modulated by c-myc, and with partial dependence on the bcl-2 family-related genes. Data generated using the cDNA microarray techniques have allowed us to demonstrated that while lobular development regressed after the cessation of pregnancy or hormone administration, programmed cell death genes remained activated, and new sets of genes reached a peak of maximal expression while others became downregulated, creating a genomic signature that is specific for both pregnancy and hCG treatment, but significantly different from those induced by the ovarian steroid hormones estrogen and progesterone. These mechanisms play a role in the protection exerted by hCG from chemically induced carcinogenesis, and might be even involved in the lifetime reduction in breast cancer risk induced in women by full-term and multiple pregnancies. In addition, hCG inhibits the progression of DMBA-induced mammary tumors on the early phases of tumor progression (i.e. intraductal proliferation, in situ carcinomas and invasive carcinomas). These observations led us to infer that hCG, like pregnancy, induces early genomic changes that lead the mammary gland to full differentiation, and that these changes result in a permanently imprinted genomic signature that regulates the long-lasting refractoriness of the mammary gland to carcinogenesis. The permanence of these changes makes them ideal surrogate markers of hCG effect in the evaluation of this hormone as a breast cancer preventive agent.

Oxytocin secretion induced by osmotic stimulation in rats during the estrous cycle and after ovariectomy and hormone replacement therapy

Hyperosmolality is a potent stimulus for the secretion of oxytocin. Oxytocinergic neurons are modulated by estrogen and oxytocin secretion in rats varies according to the phase of the estrous cycle, with higher activity during proestrus. We investigated the oxytocin secretion induced by an osmotic stimulus (0.5 M NaCl) in female rats. Plasma oxytocin and the oxytocin contents in the neurohypophysis and the paraventricular and supraoptic nuclei were determined during the morning (8–9 h) and afternoon (17–18 h) of the estrous cycle and after ovariectomy followed or not by hormone replacement. Plasma oxytocin peaked in control animals during proestrus. Oxytocin content decreased in the paraventricular and supraoptic nuclei during proestrus and estrus compared to diestrus and increased in the neurohypophysis during proestrus morning. No significant difference was observed in the oxytocin content of the neurohypophysis, nuclei or plasma between ovariectomized animals and ovariectomized animals treated with estrogen or estrogen plus progesterone. Therefore, any ovarian factor other than estrogen or progesterone seems to play a direct or indirect role in the increase in oxytocin secretion. The osmotic stimulus caused an increase in plasma oxytocin throughout the estrous cycle. A reduction in oxytocin content during diestrus and an increase during proestrus were observed in the paraventricular nuclei. In ovariectomized animals, the treatment with estrogen potentiated the response of oxytocin to the osmotic stimulus, with the response being even stronger in the case of estrogen plus progesterone. In conclusion, the ovarian steroids estrogen plus progesterone could modulate the osmoreceptor mechanisms related to oxytocin secretion.

Induction of glucose-regulated protein 78 in rat uterine glandular epithelium during uterine sensitization for the decidual cell reaction.

Endometrial receptivity for implantation and sensitization for decidualization in rodents is a transient state under the control of the ovarian steroids estrogen and progesterone. It is unclear, however, what molecular events mediate the onset of uterine receptivity. Messenger RNA differential display was performed on endometrial RNA from ovariectomized rats differentially sensitized for decidualization. Maximally sensitized uteri were at the equivalent of Day 5 of pseudopregnancy, and temporally nonsensitized uteri at Day 4 or 6; hormonally nonsensitized uteri were from animals on Day 5 treated with low or high doses of estradiol on Day 4. A cDNA with endometrial expression restricted to maximally sensitized uteri was isolated, cloned, and sequenced. The cDNA matched the sequence for glucose-regulated protein 78 (GRP78), a heat shock 70-related protein that resides in the lumen of the endoplasmic reticulum (ER) and has roles in several cellular processes including multimeric protein assembly, the degradation of proteins, and the storage and regulation of ER luminal calcium. Northern blot analysis indicated a dramatic increase in GRP78 mRNA levels restricted to the sensitized, Day 5 endometrium, suggesting a role in the onset of the sensitized phase. In situ hybridization and immunohistochemistry experiments localized the up-regulation of GRP78 within the receptive endometrium to the glandular epithelium.

Murine progesterone receptor expression in proliferating mammary epithelial cells during normal pubertal development and adult estrous cycle. Association with eralpha and erbeta status.

The ovarian steroids estrogen and progesterone are important in directing the normal growth and development of the mouse mammary gland. Previously, we have demonstrated that the majority of proliferating mammary epithelial cells do not express estrogen receptor-alpha (ERalpha). In this study we examined the relationship between progesterone receptor (PR) expression and proliferation in mammary epithelial cells using simultaneous immunohistochemistry for progesterone receptor (PR) and tritiated thymidine [(3)H]-Tdr) autoradiography. Results showed that the majority (>80%) of mammary epithelial cells labeled with [(3)H]-Tdr were PR-positive in the terminal end buds (TEBs) of pubertal mice and the ducts of pubertal and adult mice. Whereas the majority of mammary epithelial cells were also PR-positive, the basal cell population, which comprises the minority of mammary epithelial cells in the mammary ducts, was predominantly PR-negative. Nevertheless, the PR-positive phenotype remained the major proliferating cell type in the basal population. These findings suggest that the progesterone signaling pathway is involved in the proliferation of basal cell populations, potentially directing formation of tertiary side branching during pubertal development and alveolar bud formation in adult glands. A proportion of the basal cells exhibited weak expression of ERbeta, suggesting that the role of ERbeta in mediating normal estrogen-induced responses should be further studied. (J Histochem Cytochem: 47:1323-1330, 1999)

Steroid-regulated molecular markers of implantation.

The endometrium acquires the ability to implant the developing embryo within a specific time window, termed the "receptive phase." During this period the endometrium undergoes pronounced structural and functional changes induced by the ovarian steroids estrogen and progesterone, which prepare it to be receptive to invasion by the embryo. These steroid-induced molecules, when identified, may serve as useful markers of uterine receptivity. In the present article, we provide a brief description of the molecules that have emerged as candidate markers of steroid hormone action in rodents and humans during implantation.