An upstream region of the rat luteinizing hormone β gene binds estrogen receptor and confers estrogen responsiveness

Chronic estradiol exposure suppresses luteinizing hormone surge without affecting kisspeptin neurons and estrogen receptor alpha in anteroventral periventricular nucleus†

Mammalian ovulation is induced by a luteinizing hormone surge, which is triggered by elevated plasma estrogen levels; however, chronic exposure to high levels of estradiol is known to inhibit luteinizing hormone secretion. In the present study, we hypothesized that the inhibition of the luteinizing hormone surge by chronic estradiol exposure is due to the downregulation of the estrogen receptor alpha in kisspeptin neurons at hypothalamic anteroventral periventricular nucleus, which is known as the gonadotropin-releasing hormone/luteinizing hormone surge generator. Animals exposed to estradiol for 2 days showed an luteinizing hormone surge, whereas those exposed for 14 days showed a significant suppression of luteinizing hormone. Chronic estradiol exposure did not affect the number of kisspeptin neurons and the percentage of kisspeptin neurons with estrogen receptor alpha or c-Fos in anteroventral periventricular nucleus, but it did affect the number of kisspeptin neurons in arcuate nucleus. Furthermore, chronic estradiol exposure did not affect gonadotropin-releasing hormone neurons. In the pituitary, 14-day estradiol exposure significantly reduced the expression of Lhb mRNA and LHβ-immunoreactive areas. Gonadotropin-releasing hormone-induced luteinizing hormone release was also reduced significantly by 14-day estradiol exposure. We revealed that the suppression of an luteinizing hormone surge by chronic estradiol exposure was induced in association with the significant reduction in kisspeptin neurons in arcuate nucleus, luteinizing hormone expression in the pituitary, and pituitary responsiveness to gonadotropin-releasing hormone, and this was not caused by changes in the estrogen receptor alpha-expressing kisspeptin neurons in anteroventral periventricular nucleus and gonadotropin-releasing hormone neurons, which are responsible for estradiol positive feedback.

Regulation of reproduction via tight control of gonadotropin hormone levels

Mammalian reproduction is controlled by the hypothalamic-pituitary-gonadal axis. GnRH from the hypothalamus regulates synthesis and secretion of gonadotropins, LH and FSH, which then control steroidogenesis and gametogenesis. In females, serum LH and FSH levels exhibit rhythmic changes throughout the menstrual or estrous cycle that are correlated with pulse frequency of GnRH. Lack of gonadotropins leads to infertility or amenorrhea. Dysfunctions in the tightly controlled ratio due to levels slightly outside the normal range occur in a larger number of women and are correlated with polycystic ovaries and premature ovarian failure. Since the etiology of these disorders is largely unknown, studies in cell and mouse models may provide novel candidates for investigations in human population. Hence, understanding the mechanisms whereby GnRH regulates gonadotropin hormone levels will provide insight into the physiology and pathophysiology of the reproductive system. This review discusses recent advances in our understanding of GnRH regulation of gonadotropin synthesis.

Identification of estrogen-responsive genes based on the DNA binding properties of estrogen receptors using high-throughput sequencing technology

Estrogens are important endocrine hormones that control physiological functions in reproductive organs, and play a pivotal role in the generation and progression of breast cancer. Therapeutic drugs including anti-estrogen and aromatase inhibitors are used to treat patients with breast cancer. The estrogen receptors, ERα and ERβ, function as hormone-dependent transcription factors that directly regulate the expression of their target genes. Therefore, a better understanding of the function and regulation of estrogen-responsive genes provides insight into the gene regulation network associated with breast cancer. Recent technological developments in high-throughput sequencing have enabled the genome-wide identification of estrogen-responsive genes. Further elucidating the estrogen gene cascade is critical for advancements in the diagnosis and treatment of breast cancer.

Androgen receptor drives transcription of rat PACAP in gonadotrope cells

Gonadotropin expression is precisely regulated within the hypothalamic-pituitary-gonadal axis through the complex interaction of neuropeptides, gonadal steroids. and both gonadal- and pituitary-derived peptides. In the anterior pituitary gland, the neuropeptide pituitary adenylate cyclase-activating polypeptide (PACAP) modulates gonadotropin biosynthesis and secretion, acting both alone and in conjunction with GnRH. Steroid hormone feedback also influences gonadotropin expression via both direct and indirect mechanisms. Evidence from nonpituitary tissues suggests that PACAP may be a target for gonadal steroid regulation. In the present study, we show that androgen markedly stimulates rat (r) PACAP promoter-reporter activity in the LβT2 mature mouse gonadotrope cell line. 5'-Serial deletion analysis of reporter constructs identifies 2 regions of androgen responsiveness located at (-915 to -818) and (-308 to -242) of the rPACAP promoter. Androgen receptor (AR) binds directly to DNA cis-elements in each of these regions in vitro. Site-directed mutagenesis of 3 conserved hormone response element half-sites straddling the (-308 to -242) region dramatically blunts androgen-dependent PACAP promoter activity and prevents AR binding at the mutated promoter element. Chromatin immunoprecipitation demonstrates that endogenous AR binds the homologous region on mouse chromatin in LβT2 cells in both the presence and absence of androgen. These data demonstrate that androgen stimulates PACAP gene expression in the pituitary gonadotrope via direct binding of AR to a specific cluster of evolutionarily conserved hormone response elements in the proximal rPACAP gene promoter. Thus, androgen regulation of pituitary PACAP expression may provide an additional layer of control over gonadotropin expression within the hypothalamic-pituitary-gonadal axis.

Estrogen receptor alpha signaling pathways differentially regulate gonadotropin subunit gene expression and serum follicle-stimulating hormone in the female mouse

Estrogen, acting via estrogen receptor (ER)alpha, regulates serum gonadotropin levels and pituitary gonadotropin subunit expression. However, the cellular pathways mediating this regulation are unknown. ERalpha signals through classical estrogen response element (ERE)-dependent genomic as well as nonclassical ERE-independent genomic and nongenomic pathways. Using targeted mutagenesis in mice to disrupt ERalpha DNA binding activity, we previously demonstrated that ERE-independent signaling is sufficient to suppress serum LH levels. In this study, we examined the relative roles of ERE-dependent and -independent estrogen signaling in estrogen regulation of LH, FSH, prolactin, and activin/inhibin subunit gene expression, pituitary LH and FSH protein content, and serum FSH levels. ERE-independent signaling was not sufficient for estrogen to induce pituitary prolactin mRNA or suppress pituitary LHbeta mRNA, LH content, or serum FSH in estrogen-treated ovariectomized mice. However, ERE-independent signaling was sufficient to reduce pituitary glycoprotein hormone alpha-subunit, FSHbeta, and activin-betaB mRNA expression. Together with previous serum LH results, these findings suggest ERE-independent ERalpha signaling suppresses serum LH via reduced secretion, not synthesis. Additionally, ERE-dependent and ERE-independent ERalpha pathways may distinctly regulate steps involved in the synthesis and secretion of FSH.

Effects of changing gonadotropin-releasing hormone pulse frequency and estrogen treatment on levels of estradiol receptor-alpha and induction of Fos and phosphorylated cyclic adenosine monophosphate response element binding protein in pituitary gonadotropes: studies in hypothalamo-pituitary disconnected ewes

Estrogen receptor-alpha (ER alpha) levels in gonadotropes are increased during the follicular phase of the ovine estrous cycle, a time of increased frequency of pulsatile secretion of GnRH and elevated plasma estrogen levels. In the present study, our first aim was to determine which of these factors causes the rise in the number of gonadotropes with ER alpha. Ovariectomized hypothalamo-pituitary disconnected ewes (n = 4-6) received the following treatments: 1) no treatment, 2) injection (im) of 50 microg estradiol benzoate (EB), 3) pulses (300 ng iv) of GnRH every 3 h, 4) GnRH treatment as in group 3 and EB treatment as in group 2, 5) increased frequency of GnRH pulses commencing 20 h before termination, and 6) GnRH treatment as in group 5 with EB treatment. These treatments had predictable effects on plasma LH levels. The number of gonadotropes in which ER alpha was present (by immunohistochemistry) was increased by either GnRH treatment or EB injection, but combined treatment had the greatest effect. Immunohistochemistry was also performed to detect phosphorylated cAMP response element binding protein (pCREB) and Fos protein in gonadotropes. The number of gonadotropes with Fos and with pCREB was increased only in group 6. We conclude that either estrogen or GnRH can up-regulate ER alpha in pituitary gonadotropes. On the other hand, during the period of positive feedback action of estrogen, the appearance of pCREB and Fos in gonadotropes requires the combined action of estrogen and increased frequency of GnRH input. This suggests convergence of signaling for GnRH and estrogen.

Differential regulation of gonadotropin-releasing hormone (GnRH)I and GnRHII messenger ribonucleic acid by gonadal steroids in human granulosa luteal cells

In humans, reproduction was generally believed to be controlled by only one form of GnRH (called mammalian GnRH or GnRHI). However, recently, a second form of GnRH, analogous to chicken GnRHII, was discovered in several tissues, including the human ovary. The regulation and function of GnRHI in the hypothalamus has been well studied. However, the function and regulation of GnRHI, and particularly GnRHII in the ovary, is less well understood. Because gonadal sex steroids are one of the main regulators of reproduction, we investigated, in the present study, the regulation of GnRHI and GnRHII mRNA expression by 17beta-estradiol (E2) and RU486 (a progesterone antagonist) in human granulosa luteal cells (hGLCs). The levels of the mRNA transcripts encoding the two GnRH forms were examined using semiquantitative RT-PCR followed by Southern blot analysis. With time in culture, GnRHI and GnRHII mRNA levels significantly increased, by 120% and 210%, at d 8 and d 1, respectively. The levels remained elevated until the termination of these experiments at d 10. A 24-h treatment of hGLCs with E2 (10(-9) to 10(-7) M) resulted in a dose-dependent decrease and increase in mRNA expression of GnRHI and GnRHII, respectively. E2 (10(-9) M) significantly decreased GnRHI mRNA levels (by 55%) and increased GnRHII mRNA levels (by 294%). Time-course studies demonstrated that E2 (10(-9) M) significantly decreased GnRHI mRNA levels in a time-dependent manner, with maximal inhibition of 77% at 48 h. In contrast, GnRHII mRNA levels significantly increased in a time-dependent fashion, reaching a maximum level of 280% at 24 h. Cotreatment of hGLCs with E2 and tamoxifen (an E2 antagonist) reversed the inhibitory and stimulatory effects of E2 on the mRNA expression of GnRHI and GnRHII, respectively. Time- and dose-dependent treatment with RU486 did not affect GnRHI mRNA levels in hGLCs. In contrast, RU486 treatment significantly increased GnRHII mRNA levels in hGLCs in a time- and dose-dependent fashion, with a maximum increase being observed at 24 h (with 10(-5)M RU486). In summary, the present study demonstrated that the expression of GnRHI and GnRHII at the transcriptional level is differently regulated by E2 and P4 in hGLCs.

Molecular characterization of LH-beta and FSH-beta subunits and their regulation by estrogen in the goldfish pituitary

The gonadal steroids, along with gonadotropin-releasing hormone (GnRH) are involved in the regulation of gonadotropin (GtH) production in vertebrates. Goldfish have an annual reproductive cycle, characterized by seasonal fluctuations in the circulating levels of the reproductive hormones, including 17beta-estradiol (E2). The purpose of the present study was to investigate the effect of E2 on basal and GnRH-induced GtH subunit (alpha, FSH-beta and LH-beta) gene expression in the goldfish pituitary. Northern analyses were performed to determine changes in steady state mRNA levels. Both in vivo and in vitro treatment with E2 resulted in a stimulation of all three GtH subunit mRNA levels, although a higher concentration was required for the stimulation of the FSH-beta subunit mRNA levels. The effect of E2 on GnRH-induced GtH mRNA level was also investigated and demonstrated that E2 influences the GnRH-induced GtH subunit mRNA levels in a seasonally dependent manner. Overall, the present results indicate that E2 stimulates GtH subunit mRNA levels directly at the level of the pituitary in a seasonally dependent manner in goldfish.

Estrogen receptor null mice: what have we learned and where will they lead us?

All scientific investigations begin with distinct objectives: first is the hypothesis upon which studies are undertaken to disprove, and second is the overall aim of obtaining further information, from which future and more precise hypotheses may be drawn. Studies focusing on the generation and use of gene-targeted animal models also apply these goals and may be loosely categorized into sequential phases that become apparent as the use of the model progresses. Initial studies of knockout models often focus on the plausibility of the model based on prior knowledge and whether the generation of an animal lacking the particular gene will prove lethal or not. Upon the successful generation of a knockout, confirmatory studies are undertaken to corroborate previously established hypotheses of the function of the disrupted gene product. As these studies continue, observations of unpredicted phenotypes or, more likely, the lack of a phenotype that was expected based on models put forth from past investigations are noted. Often the surprising phenotype is due to the loss of a gene product that is downstream from the functions of the disrupted gene, whereas the lack of an expected phenotype may be due to compensatory roles filled by alternate mechanisms. As the descriptive studies of the knockout continue, use of the model is often shifted to the role as a unique research reagent, to be used in studies that 1) were not previously possible in a wild-type model; 2) aimed at finding related proteins or pathways whose existence or functions were previously masked; or 3) the subsequent effects of the gene disruption on related physiological and biochemical systems. The alpha ERKO mice continue to satisfy the confirmatory role of a knockout quite well. As summarized in Table 4, the phenotypes observed in the alpha ERKO due to estrogen insensitivity have definitively illustrated several roles that were previously believed to be dependent on functional ER alpha, including 1) the proliferative and differentiative actions critical to the function of the adult female reproductive tract and mammary gland; 2) as an obligatory component in growth factor signaling in the uterus and mammary gland; 3) as the principal steroid involved in negative regulation of gonadotropin gene transcription and LH levels in the hypothalamic-pituitary axis; 4) as a positive regulator of PR expression in several tissues; 5) in the positive regulation of PRL synthesis and secretion from the pituitary; 6) as a promotional factor in oncogene-induced mammary neoplasia; and 7) as a crucial component in the differentiation and activation of several behaviors in both the female and male. The list of unpredictable phenotypes in the alpha ERKO must begin with the observation that generation of an animal lacking a functional ER alpha gene was successful and produced animals of both sexes that exhibit a life span comparable to wild-type. The successful generation of beta ERKO mice suggests that this receptor is also not essential to survival and was most likely not a compensatory factor in the survival of the alpha ERKO. In support of this is our recent successful generation of double knockout, or alpha beta ERKO mice of both sexes. The precise defects in certain components of male reproduction, including the production of abnormal sperm and the loss of intromission and ejaculatory responses that were observed in the alpha ERKO, were quite surprising. In turn, certain estrogen pathways in the alpha ERKO female appear intact or unaffected, such as the ability of the uterus to successfully exhibit a progesterone-induced decidualization response, and the possible maintenance of an LH surge system in the hypothalamus. [ABSTRACT TRUNCATED]

NMDA receptor type 2D gene as target for estrogen receptor in the brain

Although it is well known that estrogen exerts its effect in the brain, the direct target genes transcriptionally regulated by estrogen or rather estrogen receptor (ER) are almost unknown. During the search for estrogen receptor-binding sites from human CpG island library, we found one genomic DNA fragment corresponding to the putative 3'-untranslated region of human NMDA receptor subunit 2D (NR2D) gene. It contained at least four half palindromic estrogen responsive elements (hEREs) within two hundred nucleotides, which was conserved also in the rat. Interestingly, the NR2D mRNA is co-localized with ERalpha and/or ERbeta mRNA in a number of regions of rat brain. We have also demonstrated that NR2D mRNA is up-regulated in rat hypothalamus by estrogen possibly via hEREs identified here. Thus, we suggest that NR2D is one of the direct targets of estrogen receptors which are involved in reproductive as well as non-reproductive actions in the brain.

Steroidogenic factor-1 and early growth response protein 1 act through two composite DNA binding sites to regulate luteinizing hormone beta-subunit gene expression

Recent in vivo and in vitro studies have implicated the orphan nuclear receptor, steroidogenic factor-1 (SF-1), and the early growth response protein 1 (Egr-1) in the transcriptional regulation of the luteinizing hormone beta-subunit (LHbeta) gene. We have previously demonstrated the ability of SF-1 to bind to and transactivate the rat LHbeta gene promoter acting at a consensus gonadotrope-specific element (GSE) located at position -127. We have now identified a second functional GSE site at position -59. In addition, based on electrophoretic mobility shift assay, in vitro translated Egr-1 is shown to bind to two putative Egr-1 binding sites (positions -112 and -50), which appear to be paired with the identified GSE sites. By transient transfection assay in pituitary-derived GH3 cells, it was seen that Egr-1 increases promoter activity of region -207/+5 of the rat LHbeta gene promoter through action at both Egr-1 sites. Furthermore, LHbeta gene promoter activity is markedly augmented in the presence of both factors together relative to activity in the presence of SF-1 or Egr-1 alone (150-fold versus 14-fold and 12-fold, respectively). These data define two composite SF-1-Egr-1 response-elements in the proximal LHbeta gene promoter and suggest that SF-1 and Egr-1 act synergistically to increase expression of the LHbeta gene in the gonadotrope.

Identification of cis-acting deoxyribonucleic acid elements that mediate gonadotropin-releasing hormone stimulation of the rat luteinizing hormone beta-subunit gene

GnRH plays a critical role in reproductive development and function by regulating the biosynthesis and secretion of the pituitary gonadotropins, LH and FSH. Although it is known that GnRH induces gonadotropin subunit gene transcription, the mechanism by which this occurs has not been elucidated. Studies have been hindered by the lack of available cell lines that express the LH and FSH subunit genes and respond to GnRH. We have transfected the rat pituitary GH3 cell line with the rat GnRH receptor complementary DNA. These cells, when cotransfected with regulatory regions of the LH or FSH subunit genes fused to a luciferase reporter gene, respond to GnRH with an increase in promoter activity comparable to that seen in primary rat pituitary cells. In this study, we have used this cell model to identify cis-acting elements of the LHbeta gene that mediate stimulation by GnRH. Analysis of a series of 5'-deletion and internal deletion constructs has revealed two regions of the rat LHbeta gene promoter involved in mediating the response to GnRH, region A (-490/-352) and region B (-207/-82). Fusion of region A upstream of a heterologous minimal promoter linked to the luciferase gene conferred GnRH responsiveness to the promoter, whereas region B did not. However, the presence of both regions A and B conferred a greater GnRH response than region A alone. Electrophoretic mobility shift assay revealed the presence of a protein(s) binding to region A using GH3 as well as alphaT3-1 nuclear extracts. Thus, region A (-490/-352) confers GnRH responsiveness to the LHbeta subunit gene and binds to a protein(s) present in pituitary cell lines. DNA sequences in region B (-207/-82) also contribute to GnRH responsiveness. The identification of putative GnRH response elements in the rat LHbeta gene promoter will aid in elucidation of the mechanisms of regulation of gene expression by GnRH.

Steroidogenic factor-1 (SF-1) and the regulation of expression of luteinising hormone and follicle stimulating hormone b-subunits in the sheep anterior pituitary in vivo

Luteinising hormone (LH) and follicle stimulating hormone (FSH) comprise a common alpha-subunit and hormone-specific beta-subunit, are expressed in gonadotroph cells of the anterior pituitary and during the sheep oestrous cycle, are regulated by gonadotrophin releasing hormone (GnRH), ovarian peptides and steroids. Transcription factor steroidogenic factor-1 (SF-1) transactivates the common alpha-subunit and LH beta subunit in other species. We investigated whether SF-1 regulates beta-subunit expression and the regulation of SF-1 expression in vivo in sheep. Immunocytochemistry co-localised SF-1, LH and FSH to sheep pituitary gonadotrophs and electrophoretic mobility shift assays (EMSA) demonstrated that SF-1 bound to the LH beta promoter in vitro. No SF-1 DNA binding site was found in the FSH beta promoter. No difference in mean levels of SF-1, FSH beta, LH beta and GnRHr mRNA was measured between the luteal and follicular phases of the oestrous cycle. However SF-1 mRNA levels were correlated to those of LH beta in individual luteal phase animals (r = 0.88, p < 0.05), when the transcription rate of LH beta was significantly higher (p < 0.01). GnRH antagonist treatment of luteal animals did not produce a significant reduction in mRNA levels of LH beta, SF-1 and FSH beta. Administering oestradiol benzoate with GnRH antagonist reduced levels of SF-1 and FSH beta mRNA from luteal values (p < 0.005). We conclude that: (1) expression of SF-1 is not solely dependent on GnRH and is downregulated by oestradiol; (2) the LH beta transcription rate is increased during the luteal phase but is not related to levels of LH beta or SF-1 mRNA; and (3) SF-1 does not appear to directly regulate expression of FSH beta, but may regulate expression indirectly.

Presence of distinct cis-acting elements on gonadotropin gene promoters in diverse species dictates the selective recruitment of different transcription factors by steroidogenic factor-1

The nuclear receptor steroidogenic factor-1 (SF-1) regulates the cell-specific expression of the pituitary gonadotropin subunit genes. Several potential DNA-binding sites for SF-1, estrogen receptor (ER) and the immediate-early transcription factor NGFI-A are found in LHbeta genes from many species. In this study, we have examined the action and interaction of these transcription factors on LHbeta gene promoters from two representative vertebrate species, i.e. rat and salmon. Cotransfection studies in COS-1 cells have shown that the action of SF-1 on salmon gonadotropin IIbeta (sGTHIIbeta) gene promoter was dramatically enhanced when combined with ER. The rat LHbeta promoter was activated by SF-I or ER individually, but these two factors, however, were unable to act in synergism on this promoter. In contrast, NGFI-A, specifically in cooperation with SF-1, transactivated the rat LHbeta gene expression but was ineffective on the sGTHIIbeta gene. Gel shift experiments showed that this lack of activation was due to the low affinity of the salmon NGFI-A-responsive element for its binding protein. In conclusion, our studies demonstrate that differential recruitment of distinct transcription factors by SF-1 might be a common mechanism to activate the cell-specific gonadotropin gene expression in different species.

Pituitary Sex Steroid Receptors: Localization and Function

The pituitary contains estrogen receptor (ER), progesterone receptor (PR), and androgen receptor (AR). In accordance with immunocytochemistry, it is agreed that sex hormone receptors reside into the nucleus. All three receptors are found predominantly in gonadotrophs and lactotrophs, and less frequently in other cell types. ER plays a major role in prolactin (PRL) production and lactotroph proliferation, and protracted estrogen administration induces lactotroph hyperplasia and adenoma in rodents. Most research on PR and AR is focused on their role in the fine-tuning of gonadotropin secretion during estrous cycle. Contrary to the effect in nontumorous pituitary, estrogens can inhibit the proliferation of transplantable rat pituitary tumors and of cell lines derived from them. In humans, despite the presence of ER in all types of adenohypophysial tumors, the role of estrogen in tumor cell proliferation is still unclear. Few results indicate that tumor growth is stimulated by estrogen, and inhibited by progesterone and androgen. Novel data reveal that steroid hormones can act directly on plasma membrane or via other receptors, and interact with growth factors, oncogenes, and other transcription factors. The mechanisms by which steroid hormones control cell proliferation remain a major challenge for future research.

Luteinizing hormone deficiency and female infertility in mice lacking the transcription factor NGFI-A (Egr-1)

The immediate-early transcription factor NGFI-A (also called Egr-1, zif/268, or Krox-24) is thought to couple extracellular signals to changes in gene expression. Although activins and inhibins regulate follicle-stimulating hormone (FSH) synthesis, no factor has been identified that exclusively regulates luteinizing hormone (LH) synthesis. An analysis of NGFI-A-deficient mice derived from embryonic stem cells demonstrated female infertility that was secondary to LH-beta deficiency. Ovariectomy led to increased amounts of FSH-beta but not LH-beta messenger RNA, which suggested a pituitary defect. A conserved, canonical NGFI-A site in the LH-beta promoter was required for synergistic activation by NGFI-A and steroidogenic factor-1 (SF-1). NGFI-A apparently influences female reproductive capacity through its regulation of LH-beta transcription.

The 1994 Stevenson Award Lecture. Follicle-stimulating hormone and luteinizing hormone: a tale of two gonadotropins

Although most gonadotropes synthesize both luteinizing hormone and follicle-stimulating hormone, the transcription, content, and secretion rates of the two gonadotropins can be separated. The signals external to the gonadotropic cells that appear to be important in the differential regulation are gonadotropin-releasing hormone pulse frequency (high pulse frequency favors luteinizing hormone), steroid feedback (works on both but induces a more powerful negative feedback on luteinizing hormone), and gonadal peptide feedback (activin increases follicle-stimulating hormone; inhibin and follistatin decrease it). We know very little about the pathways within the gonadotropes that favor one gonadotropin rather than another. It is expected that the cloning of the genes for both gonadotropins and the use of specific cell lines and transfections will lead to elucidation of these pathways.

Regulation of Xenopus laevis estrogen receptor gene expression is mediated by an estrogen response element in the protein coding region

To investigate the 17 beta-estradiol induction of the mRNA coding for the Xenopus laevis estrogen receptor (XER), we cloned the promoter and the 5'-flanking region of the ER gene. Transcription initiation sites were identified by primer extension, and confirmed by the polymerase chain reaction. The promoter and 5'-flanking region contain an imperfect TATA box and a potential CAAT box at -51. Sequence analysis and transfections indicated that no functional estrogen response element (ERE) was present in approximately 3 kb of 5'-flanking region. An imperfect ERE, GGTCAGTTTGACG, which differs from the consensus ERE sequence by 1 nucleotide, was detected in the protein coding region of the gene, approximately 480 nucleotides downstream of the transcription initiation site. In transient transfections using a simple promoter containing two copies of this Xenopus estrogen receptor ERE (XERE), we observed an estrogen-dependent increase in CAT activity of four- to five-fold, to a level approximately 20-fold greater than the activity of the control plasmid lacking the XEREs. In competition gel mobility-shift assays, the XERE exhibited a weak, but clearly detectable, ability to compete for binding of human ER to a labeled consensus ERE. Because it exhibits sequence-specific binding to the ER in competition gel mobility-shift assays, and is able to confer estrogen-dependent transcription on a simple synthetic promoter, the novel XERE, located in the protein coding region of the XER gene appears to represent a weak, but functional, ERE.

Modulation of hepatocyte growth factor gene expression by estrogen in mouse ovary

Hepatocyte growth factor (HGF) is expressed in a variety of tissues and cell types under normal conditions and in response to various stimuli such as tissue injury. In the present study, we demonstrate that the transcription of the HGF gene is stimulated by estrogen in mouse ovary. A single injection of 17 beta-estradiol results in a dramatic and transient elevation of the levels of mouse HGF mRNA. Sequence analysis has found that two putative estrogen responsive elements (ERE) reside at -872 in the 5'-flanking region and at +511 in the first intron, respectively, of the mouse HGF gene. To test whether these ERE elements are responsible for estrogen induction of HGF gene expression, chimeric plasmids containing variable regions of the 5'-flanking sequence of HGF gene and the coding region for chloramphenicol acetyltransferase (CAT) gene were transiently transfected into both human endometrial carcinoma RL 95-2 cells and mouse fibroblast NIH 3T3 cells to assess hormone responsiveness. Transfection results indicate that the ERE elements of the mouse HGF gene can confer estrogen action to either homologous or heterologous promoters. Nuclear protein extracts either from RL95-2 cells transfected with the estrogen receptor expression vector or from mouse liver bound in vitro to ERE elements specifically, as shown by band shift assay. Therefore, our results demonstrate that the HGF gene is transcriptionally regulated by estrogen in mouse ovary; and such regulation is mediated via a direct interaction of the estrogen receptor complex with cis-acting ERE elements identified in the mouse HGF gene.

Differential impact of flanking sequences on estradiol- vs 4-hydroxytamoxifen-liganded estrogen receptor binding to estrogen responsive element DNA

The mechanism by which antiestrogens antagonize the ability of estrogen receptor (ER) to induce the transcription of estrogen-regulated genes is only partially understood. To examine the effect of estrogen responsive element (ERE) stereoalignment and flanking sequences on estradiol-liganded ER (E2-ER)-ERE and antiestrogen-liganded ER (4-hydroxytamoxifen-liganded ER or 4-OHT-ER)-ERE binding, several dimeric EREs, containing a perfect inverted repeat (5'-GGTCAgagTGACC-3') but lacking the AT-rich flanking sequences typical of highly estrogen-responsive promoters, were cloned into a plasmid vector. The ERE centers of symmetry were spaced 1.5, 2.0, 3.0, 6.4 and 6.7 helical turns apart. E2-ER and 4-OHT-ER binding to these constructs was specific and saturable, but orientation-independent and, in contrast to our earlier work with E2-ER binding to AT-rich EREs, not cooperative. The affinity of E2-ER binding decreased as the distance between adjacent EREs was increased, suggesting that E2-ER binding to closely spaced EREs is more stable (Kd = 0.38, 0.58, 0.83, 1.23, and 0.96 nM, respectively, for the above spacings). In contrast, the affinity of 4-OHT-ER binding increased with increased ERE spacing (Kd = 2.90, 4.79, 1.39, 1.77, and 0.92 nM, respectively). The presence of AT-rich sequences flanking the ERE increased the binding affinity of E2-ER and 4-OHT-ER, an increase reflected in slower dissociation rates of ER from these EREs. The AT-rich sequence also enhanced the binding capacity of E2-ER but not 4-OHT-ER. Since the binding capacity of 4-OHT-ER is identical with or without an AT-rich region, we suggest that flanking sequences are more important in stabilizing E2-ER binding and may be critical for cooperative binding to stereoaligned EREs.

Estrogen receptor binds to the salmon GnRH gene in a region with long palindromic sequences

Footprinting and gel shift assays demonstrated that the human estrogen receptor (hER) specifically binds to two estrogen response element (ERE)-like motifs in the gonadotropin releasing hormone (GnRH) gene promoter region of Atlantic salmon (Salmo salar). The two ER binding sites are situated approximately 1.5 kb upstream of the transcriptional start site of the GnRH gene and are localized 49 bp from each other. Each ERE-like motif is composed of two palindromic ERE half-sites interspaced by 8 and 9 nucleotides, respectively. The salmon GnRH gene promoter region contains an almost perfect 426-bp-long palindromic sequence that might form a cruciform structure.

Analysis of estrogen receptor interaction with tertiary-structured estrogen responsive elements

An initial crucial step in estrogen activation of gene expression is the interaction of the estrogen receptor with a specific nucleotide sequence [estrogen responsive element (ERE)]. Previously, we found that the estrogen receptor binds preferentially and with high affinity to the lower strand of the rat prolactin imperfect ERE which contains tertiary structure (Lannigan DA and Notides AC, Proc Natl Acad Sci USA 86: 863-867, 1989). Using perfect and imperfect EREs from the upstream region of the chicken vitellogenin II gene, we have now extended our findings and have determined that the estrogen receptor preferentially interacts with either perfect or imperfect EREs which contain tertiary structure. A similar structure is present in a synthetic 42 bp oligonucleotide corresponding to the lower strand of a perfect ERE with flanking sequences from the rat prolactin ERE. Moreover, deviations from the ERE consensus sequence decrease the binding of the estrogen receptor to the tertiary-structured ERE. We also have determined that ERE flanking sequences contribute to the affinity of the receptor for the tertiary-structured ERE. Furthermore, ERE flanking sequences can influence the types of interactions that the estrogen receptor makes with the tertiary-structured ERE.

Non-random distribution and co-localization of purine/pyrimidine-encoded information and transcriptional regulatory domains

In order to detect sequence-based information predictive for the location of eukaryotic transcriptional regulatory domains, the frequencies and distributions of the 36 possible purine/pyrimidine reverse complement hexamer pairs was determined for test sets of real and random sequences. The distribution of one of the hexamer pairs (RRYYRR/YYRRYY, referred to as M1) was further examined in a larger set of sequences (> 32 genes, 230 kb). Predominant clusters of M1 and the locations of eukaryotic transcriptional regulatory domains were found to be associated and non-randomly distributed along the DNA consistent with a periodicity of approximately 1.2 kb. In the context of higher ordered chromatin this would align promoters, enhancers and the predominant clusters of M1 longitudinally along one face of a 30 nm fiber. Using only information about the distribution of the M1 motif, 50-70% of a sequence could be eliminated as being unlikely to contain transcriptional regulatory domains with an 87% recovery of the regulatory domains present.

Expression of luteinising hormone-beta subunit chloramphenicol acetyltransferase (LH-beta-CAT) fusion gene in rat pituitary cells: induction by cyclic 3'-adenosine monophosphate (cAMP)

In this study we determined the activity of the rat luteinising hormone-beta gene promoter in a heterologous rat pituitary cell line (GH3 cells). 1.7 kb of LH-beta 5' flanking sequence and the first 5 bp of the 5' untranslated region were ligated to the chloramphenicol acetyltransferase (CAT) receptor gene (LH-beta-CAT) and transiently transfected by calcium phosphate precipitation into subconfluent cultures of GH3 cells. Basal low-level CAT activity was only detected in GH3 cells, being absent in two non-pituitary cell lines (BeWo and HeLa) RNase analysis revealed that mRNA from transfected GH3 cells protected a fragment of labelled antisense probe of correct size for transcription initiation from the LH-beta CAP site, confirming that promoter activity reflected correctly initiated LH-beta-CAT fusion gene transcripts. CAT activity was consistently induced by an average of 3-5-fold from the full-length 1.7 kb promoter, in a dose- and time-dependent manner, by forskolin, dibutyryl cAMP, and 8-bromo cAMP implying presence of a cAMP-responsive cis-acting domain in the LH-beta promoter region. Transfection of deletion mutants delta-615-CAT, delta-385-CAT and delta-250-CAT each reduced forskolin inducibility to 1.7-fold but did not abolish induction completely suggesting a domain between -1.7 and -0.6 kb contained a cAMP-responsive element(s) (CRE). Further deletion of LH-beta 5' flanking sequences to delta-85-CAT restored forskolin induction to wild-type levels (3-5-fold), suggesting the presence of a weak inhibitory element between -600 and -85 kb, and a cAMP-responsive domain in the proximal promoter region. The LH-beta promoter does not contain perfect tandem repeat palindromic CRE DNA sequences, though there are several octanucleotide sequences differing by only 1 bp from AP-2 binding sites, the consensus CRE, and the vasointestinal peptide gene CRE. Although these data suggest that the LH-beta gene is cAMP responsive this is likely mediated by several and complex protein interactions with multiple DNA sequences in the proximal and distal LH-beta promoter enhancer.

Structural characterization and tissue-specific expression of the mRNAs encoding isoenzymes from two rat mitochondrial creatine kinase genes

Creatine kinase (CK; EC 2.7.3.2) isoenzymes play prominent roles in energy transduction. Mitochondrial CK (MtCK) reversibly catalyzes the transfer of high energy phosphate to creatine and exists, in the human, as two isoenzymes encoded by separate genes. We report here the cDNA sequences of the two isoenzymes of MtCK in the rat. Rat sarcomeric MtCK has 87% nucleotide identity in the 1257 bp coding region and 82% in the 154 bp 3' untranslated region as compared with human sarcomeric MtCK. Rat ubiquitous MtCK has 92% nucleotide identity over the 1254 bp coding region with human ubiquitous MtCK and 81% identity of the 148 by 3' untranslated region. Nucleotide identity between the rat sarcomeric and ubiquitous MtCK coding regions is 70%, with no conservation of their 3' untranslated regions. Thus, MtCK sequence is conserved in a tissue-specific, rather than species-specific, manner. Conservation of the 3' untranslated regions is highly unusual and suggests a regulatory function for this region. The NH2-terminal transit peptide sequences share 82% amino acid homology between rat and human sarcomeric MtCKs and 92% homology between rat and human ubiquitous MtCKs, but have only 41% homology to each other. This tissue-specific conservation of the transit peptides suggests receptor specificity in mitochondrial uptake. Rat sarcomeric MtCK mRNA is expressed only in skeletal muscle and heart, but rat ubiquitous MtCK mRNA is expressed in many tissues, with highest levels in brain, gut and kidney. Ubiquitous MtCK mRNA levels are dramatically regulated in uterus and placenta during pregnancy. Coexpression of sarcomeric and ubiquitous MtCK with their cytosolic counterparts, MCK and BCK, respectively, supports the creatine phosphate shuttle hypothesis and suggests that expression of these genes is coordinately regulated.

Effect of Ovariectomy or Oestrogen Implants upon Pituitary Function in Female Hypogonadal Mice Bearing Normal Fontal Preoptic Area Grafts

Abstract The effects of ovariectomy and oestrogen feedback for 10 days upon pituitary and serum luteinizing hormone (LH) content, pituitary glycoprotein subunit messenger ribonucleic acid (mRNA) and prolactin mRNA content in normal females, female hypogonadal mice and hypothalamic grafted female hypogonadal mice, bearing a graft of normal mouse preoptic area tissue into the third ventricle, have been investigated. In normal females ovariectomy resulted in a rise in serum LH, LHbeta-subunit and common alpha-subunit mRNAs with no significant change in pituitary LH content or follicle-stimulating hormone (FSH) beta-subunit mRNA. In the hypogonadal females, preoptic area grafting resulted in an elevation in all of the above parameters into the normal range. Ovariectomy in this group resulted in a further elevation of serum LH, LHbeta-subunit and alpha-subunit mRNAs with no change in pituitary LH content or FSHbeta-subunit mRNA, which in all cases were comparable to ovariectomized normal animals. Oestrogen treatment caused a fall in pituitary LH content and the serum LH fell below the detection of the assay. LHbeta-subunit and a-subunit mRNA mirrored this fall but there was no change in FSHbeta-subunit hybridization. These experiments suggest that even though normal neuronal input to the gonadotrophin-releasing hormone neurons is disrupted, oestrogen-induced negative feedback can still occur in grafted female hypogonadal animals. Gonadotrophin-releasing hormone neurons are reported to lack oestrogen receptors but feedback within this graft by co-transplanting oestrogen-sensitive neurons remains a possibility, as does feedback at the level of the host median eminence where graft axons extend to the pituitary portal vessels. The similarity of the response in normal and grafted animals indicates that these actions of oestrogen may be effected predominantly at the pituitary level.

Gonadotropin-releasing hormone pulses: regulators of gonadotropin synthesis and ovulatory cycles

The data reviewed present evidence that the pattern of GnRH secretion is an important factor in the regulation of gonadotropin subunit gene expression, gonadotropin synthesis, and secretion. The information on regulation of mRNA expression by GnRH pulses should be considered with some caution, as the experiments were performed in male rats and may not accurately reflect events in female primates or humans. However, an overall pattern emerges which suggests that common factors may be involved in all mammalian species. If current evidence is correct, and only a single gonadotropin-releasing hormone exists, then mechanisms to differentially regulate the three gonadotropin genes may involve changes in GnRH secretion. Alterations in GnRH pulse frequency and amplitude are recognized by the pituitary gonadotrope cell and could be the mechanism used to effect differential expression of the gonadotropin subunit genes. Differential regulation of subunit gene expression would be expected to be critically important in the establishment of pubertal maturation, and subsequently in the maintenance of ovulatory cycles in women. Our hypotheses, proposing a major role of pulsatile GnRH secretion in the regulation of human reproduction, are summarized in schematic form in Fig. 14 for men and Fig. 15 for women. In utero and during the first few months of life, GnRH is secreted at a relatively fast frequency (approximately 1 pulse/hour). During the first year, GnRH secretion is inhibited and both the amplitude and apparent frequency of pulsatile release is markedly reduced. The mechanisms involved in inhibiting GnRH release remain unclear in humans. Similarly, the mechanisms involved in the disinhibition of GnRH secretion, which first occurs during sleep at the initiation of puberty, are unclear, but in humans do not appear to involve opiates. In males, the increased frequency and amplitude of GnRH secretion favor LH synthesis and release, which in turn stimulates testosterone secretion (Fig. 14). Testosterone acts at the hypothalamus, perhaps through opioid mechanisms, to inhibit GnRH pulse frequency and to maintain a regular pattern of pulses occurring approximately every 90-110 min in adult males. In females, the mechanisms involving alterations in the patterns of GnRH secretion to regulate reproduction appear more complex. This may reflect the need to differentially synthesize and secrete FSH and LH at different times during reproductive cycles to allow orderly follicular maturation and ovulation. As shown in Fig. 15, we hypothesize that the events during the first decade of life and through the initiation of nocturnal GnRH secretion at puberty are similar in both sexes.(ABSTRACT TRUNCATED AT 400 WORDS)