Transient administration of estradiol-17 beta establishes an autoregulatory loop permanently inducing estrogen receptor mRNA

Dexamethasone activates c-Jun NH2-terminal kinase (JNK) which interacts with GR and protects it from ubiquitin-mediated degradation in NSCLC cells

Dexamethasone-mediated pharmacological activation of the glucocorticoid receptor (GR) is widely used in the treatment regimen of hematological malignancies and solid cancers. However, DEX sensitivity towards patients primarily depends on the endogenous protein levels of GR. We observed that DEX treatment leads to an increase in GR protein levels despite inhibition of neo-protein synthesis in non-small cell lung cancer (NSCLC) cells. Mechanistically, DEX-stimulation concomitantly increased the JNK phosphorylation and GR protein levels, however the JNK stimulation preceds GR upregulation. Moreover, we also observed that DEX-mediated phosphorylation is partially mediated by upregulation in MEKK1 phosphorylation. Further, GR protein levels were significantly decreased in JNK inhibitor (JNKi, SP600125) treated cells whereas MG132 treatment restored GR levels indicating that DEX induced JNK activity regulated the GR protein levels through proteasomal-degradation pathway. Next, we showed that DEX led to JNK activation which physically interacts with GR and protects it from ubiquitination-mediated degradation. Furthermore, at basal level GR interacts with JNK in cytoplasm whereas upon DEX stimulation GR and pJNK both localized to nucleus and interact with each other. Next, we show that JNK-mediated GR stabilization affects its nuclear transcriptional functional activity in NSCLC cells. In line with these in vitro data, patient dataset analysis also shows that increased levels of both JNK and GR contributes towards better prognosis of NSCLC patients. Taken together, our data shows that DEX treatment may lead to positive feedback regulation of GR by activating JNK and thus highlights importance of GR-JNK crosstalk in NSCLC.

YAP inhibits ERα and ER+ breast cancer growth by disrupting a TEAD-ERα signaling axis

Hippo signaling restricts tissue growth by inhibiting the transcriptional effector YAP. Here we uncover a role of Hippo signaling and a tumor suppressor function of YAP in estrogen receptor positive (ER⁺) breast cancer. We find that inhibition of Hippo/MST1/2 or activation of YAP blocks the ERα transcriptional program and ER⁺ breast cancer growth. Mechanistically, the Hippo pathway transcription factor TEAD physically interacts with ERα to increase its promoter/enhancer occupancy whereas YAP inhibits ERα/TEAD interaction, decreases ERα occupancy on its target promoters/enhancers, and promotes ERα degradation by the proteasome. Furthermore, YAP inhibits hormone-independent transcription of ERα gene (ESR1). Consistently, high levels of YAP correlate with good prognosis of ER⁺ breast cancer patients. Finally, we find that pharmacological inhibition of Hippo/MST1/2 impeded tumor growth driven by hormone therapy resistant ERα mutants, suggesting that targeting the Hippo-YAP-TEAD signaling axis could be a potential therapeutical strategy to overcome endocrine therapy resistance conferred by ERα mutants.

The direct and indirect effects of kisspeptin-54 on granulosa lutein cell function

STUDY QUESTION

What are the in vivo and in vitro actions of kisspeptin-54 on the expression of genes involved in ovarian reproductive function, steroidogenesis and ovarian hyperstimulation syndrome (OHSS) in granulosa lutein (GL) cells when compared with traditional triggers of oocyte maturation?

SUMMARY ANSWER

The use of kisspeptin-54 as an oocyte maturation trigger augmented expression of genes involved in ovarian steroidogenesis in human GL cells including, FSH receptor (FSHR), LH/hCG receptor (LHCGR), steroid acute regulatory protein (STAR), aromatase, estrogen receptors alpha and beta (ESR1, ESR2), 3-beta-hydroxysteroid dehydrogenase type 2 (3BHSD2) and inhibin A (INHBA), when compared to traditional maturation triggers, but did not alter markers of OHSS.

WHAT IS KNOWN ALREADY

hCG is the most widely used trigger of oocyte maturation, but is associated with an increased risk of OHSS. The use of GnRH agonists to trigger oocyte maturation is a safer alternative to hCG. More recently, kisspeptin-54 has emerged as a novel therapeutic option that safely triggers oocyte maturation even in women at high risk of OHSS. Kisspeptin indirectly stimulates gonadotropin secretion by acting on hypothalamic GnRH neurons. Kisspeptin and its receptor are also expressed in the human ovary, but there is limited data on the direct action of kisspeptin on the ovary.

STUDY DESIGN SIZE, DURATION

Forty-eight women undergoing IVF treatment for infertility consented to kisspeptin-54 triggering and/or granulosa cell collection and were included in the study. Twelve women received hCG, 12 received GnRH agonist and 24 received kisspeptin-54 to trigger oocyte maturation. In the kisspeptin-54 group, 12 received one injection of kisseptin-54 (9.6 nmol/kg) and 12 received two injections of kisspeptin-54 at a 10 h interval (9.6 nmol/kg × 2).

PARTICIPANTS/MATERIALS, SETTING, METHODS

Follicular fluid was aspirated and pooled from follicles during the retrieval of oocytes for IVF/ICSI. GL cells were isolated and either RNA extracted immediately or cultured in vitro ± kisspeptin or hCG.

MAIN RESULTS AND THE ROLE OF CHANCE

GL cells from women who had received kisspeptin-54 had a 14-fold and 8-fold higher gene expression of FSHR and a 2-fold (ns) and 2.5-fold (P < 0.05) higher expression of LHCGR than GL cells from women who had received hCG or GnRH agonist, respectively. CYP19A1 expression was 3.6-fold (P < 0.05) and 4.5-fold (P < 0.05) higher, STAR expression was 3.4-fold (P < 0.01) and 1.8-fold (P < 0.05) higher, HSD3B2 expression was 7.5- (P < 0.01) and 2.5-fold higher (P < 0.05), INHBA was 2.5-fold (P < 0.01) and 2.5-fold (P < 0.01) higher in GL cells from women who had received kisspeptin-54 than hCG or GnRHa, respectively. ESR1 (P < 0.05) and ESR2 (P < 0.05) both showed 3-fold higher expression in cells from kisspeptin treated than GnRHa treated women. Markers of vascular permeability and oocyte growth factors were unchanged (VEGFA, SERPINF1, CDH5, amphiregulin, epiregulin). Gene expression of kisspeptin receptor was unchanged. Whereas treating GL cells in vitro with hCG induced steroidogenic gene expression, kisspeptin-54 had no significant direct effects on either OHSS genes or steroidogenic genes.

LIMITATIONS REASONS FOR CAUTION

Most women in the study had PCOS, which may limit applicability to other patient groups. For the analysis of the in vitro effects of kisspeptin-54, it is important to note that GL cells had already been exposed in vivo to an alternate maturation trigger.

WIDER IMPLICATIONS OF THE FINDINGS

The profile of serum gonadotropins seen with kisspeptin administration compared to other triggers more closely resemble that of the natural cycle as compared with hCG. Thus, kisspeptin could potentially permit an ovarian environment augmented for steroidogenesis, in particular progesterone synthesis, which is required for embryo implantation.

STUDY FUNDING/COMPETING INTEREST(S)

Dr Owens is supported by an Imperial College London PhD Scholarship. Dr Abbara is supported by an National Institute of Health Research Academic Clinical Lectureship. The authors do not have any conflict of interest to declare.

TRIAL REGISTRATION NUMBER

ClinicalTrials.gov NCT01667406.

Sensitization of vitellogenin gene expression by low doses of octylphenol is mediated by estrogen receptor autoregulation in the Bombina orientalis (Boulenger) male liver

This study aimed to elucidate the mechanisms by which alkylphenols disrupt endocrine function in wild amphibians in Korea. To this end, the effects of 4-tert-octylphenol (OP), 17β-estradiol (E2), and estrogen receptor (ER) agonists on the expression profiles of vitellogenin (VTG) and ERs were examined in livers obtained from male Bombina orientalis toads. A single injection of E2 (10μg/kg; 0.03μmol/kg) induced transcription of VTG mRNA at 2 days post injection; however, injection of either the ERα-selective agonist propyl-(1H)-pyrazole-1,3,5-triyl-trisphenol (PPT, 50μg/kg; 0.12μmol/kg) or the ERβ-selective agonist 2,3-bis-(4-hydroxyphenyl)-propionitrile (DPN, 50μg/kg; 0.20μmol/kg) did not affect the expression of VTG. This finding suggests that both ERα and ERβ are required to induce transcription of VTG in the male B. orientalis liver. Interestingly, E2, PPT, and DPN induced transcription of ERα, which was also reflected on the protein level; however, these alkylphenols did not affect ERβ transcription. Similarly, VTG transcription was induced by a single injection of 1-100mg/kg (0.04-484.66μmol/kg) OP, while 0.1mg/kg (0.48μmol/kg) OP had no effect on VTG transcription. This result suggests that the lowest observable effect concentration (LOEC) of OP for induction of VTG transcription in the male liver is 1mg/kg (4.84μmol/kg). Furthermore, treatment with E2 (10μg/kg; 0.03μmol/kg) or OP (1mg/kg; 4.84μmol/kg) significantly upregulated ERα transcription, and a 10mg/kg (48.46μmol/kg) dose of OP significantly upregulated ERβ transcription. The ER antagonist ICI 182,780 decreased the basal levels of ERα and ERβ mRNA, and also prevented E2-mediated and OP-mediated induction of VTG, ERα, and ERβ transcription. A second injection of 0.1mg/kg (0.48μmol/kg) OP after a two-day interval significantly upregulated the transcription of VTG and ERα, but not of ERβ. These results suggest that sensitization of VTG transcription by repeated exposure to OP is mediated by the induction of ERα. Different combinations of alkylphenols that are ubiquitous in the freshwater system in Korea could potentially exert a synergistic effect on endocrine disruption. Thus, chronic exposure to alkylphenols, even at their NOECs, could still disrupt endocrine function in B. orientalis.

A single low dose of cadmium exposure induces benign prostate hyperplasia like condition in rat: A novel benign prostate hyperplasia rodent model

Abnormal prostate growth is the most prevalent pathological sign in aged human males, as reflected by high incidence of benign prostate hyperplasia (BPH) and prostate cancer. In spite of the high prevalence, the etiology and pathophysiology of BPH is unclear due to the lack of any established rodent model for study. It has been demonstrated that the cadmium (Cd) mimics the activity of androgen or estrogen by interacting with the steroid hormone receptors in the prostate and elicits BPH, but the specific receptor which binds to Cd is still unknown. Our lab studies with BPH patients highlighted a strong co-relation between smokings with increased Cd content. Changes in the maximum urinary flow rate (Qmax) and prostatic acid phosphatase (PAP) level further supports that Cd can induce BPH like condition. Therefore, the present study was aimed to induce BPH like condition in rats by Cd administration. The dose of cadmium was standardized in an age- and time-dependent manner, which was further examined by prostate weight, histology, and PAP levels that elucidated the pathogenesis of BPH. Further to understand the molecular basis, steroid hormone receptor antagonist experiment was performed. Gene expression and immunohistochemistry data suggest that Cd induces hyperplasia like condition by activating the androgen receptor and estrogen receptor-α and suppresses the action of estrogen receptor-β. The experimental model used here is a cost effective, less time consuming and potentially valuable tool for investigating the respective functions of epithelial and stromal hormone receptors. The applicability of this model would be helpful in understanding the pathogenesis of BPH and its progression.

Increased OPG/RANKL ratio in the conditioned medium of soybean-treated osteoblasts suppresses RANKL-induced osteoclast differentiation

Soybean is a major dietary source of isoflavones, particularly daidzein and genistein, which stimulate osteoblastic functions that are initiated by binding to estrogen receptor (ER)-α and ER-β found on osteoblasts. However, coupled with a low expression of ER-α and ER-β in osteoclasts, the inhibitory effects of soy isoflavones on osteoclast differentiation is likely mediated through paracrine factors produced by osteoblasts. Therefore, in this study, we investigated whether soybean can indirectly inhibit osteoclast differentiation through the modulation of osteoclastic factors produced by osteoblasts. Treatment with soybean extracts increased the levels of osteoprotegerin (OPG) and decreased those of receptor activator of nuclear factor-κB ligand (RANKL) in the conditioned medium (CM) of MC3T3-E1 osteoblasts. Subsequently, the RANKL-induced RAW264.7 osteoclast formation was markedly inhibited by treatment with CM collected from MC3T3-E1 osteoblasts incubated with soybean extracts (S-CM). Similarly, S-CM significantly attenuated the RANKL-induced increase in the mRNA and protein levels of matrix metalloproteinase-9 (MMP-9), a potential biomarker gene of osteoclast differentiation, through the suppression of nuclear factor of activated T cells c1 (NFATc1) activation. Of note, a soybean concentration of 0.001 mg/ml further increased the OPG/RANKL ratio compared to treatment with a 0.1 mg/ml soybean concentration and was overall, more effective at inhibiting RANKL-induced osteoclast formation and MMP-9 expression. Taken together, our data demonstrate that treatment with soybean extracts stimulates the secretion of OPG and inhibits that of RANKL, thus inhibiting RANKL-induced osteoclast differentiation through the suppression of NFATc1 activation.

Separate regions of glucocorticoid receptor, coactivator TIF2, and comodulator STAMP modify different parameters of glucocorticoid-mediated gene induction

Increased specificity in steroid-regulated gene expression is a long-sought goal of endocrinologists. Considerable progress has resulted from the discovery of coactivators, corepressors, and comodulators that adjust the total activity (A(max)) of gene induction. Two less frequently quantitated, but equally potent, means of improving specificity are the concentration of agonist steroid required for half-maximal activity (EC(50)) and the residual or partial agonist activity displayed by most antisteroids (PAA). It is usually assumed that the modulatory activity of transcriptional cofactors coordinately regulates A(max), EC(50), and PAA. Here we examine the hypothesis that these three parameters can be independently modified by separate protein domains. The test system involves three differently sized fragments of each of three factors (glucocorticoid receptor [GR], coactivator TIF2, and comodulator STAMP), which are shown to form a ternary complex and similarly affect the induction properties of transfected and endogenous genes. Twenty-five different fragment combinations of the ternary complex are examined for their ability to modulate the A(max), EC(50), and PAA of a transiently transfected synthetic reporter gene. Different combinations selectively alter one, two, or all three parameters. These results clearly demonstrate that A(max), EC(50), and PAA can be independently regulated under some conditions by different pathways or molecular interactions. This new mechanistic insight suggests that selected activities of individual transcription factors are attractive targets for small molecules, which would have obvious clinical applications for increasing the specificity of steroids during endocrine therapies.

A dynamic model of transcriptional imprinting derived from the vitellogenesis memory effect

Transcriptional memory of transient signals can be imprinted on living systems and influence their reactivity to repeated stimulations. Although they are classically ascribed to structural chromatin rearrangements in eukaryotes, such behaviors can also rely on dynamic memory circuits with sustained self-amplification loops. However, these phenomena are either of finite duration, or conversely associated to sustained phenotypic changes. A mechanism is proposed, in which only the responsiveness of the target gene is durably reset at a higher level after primary stimulation, using the celebrated but still puzzling vitellogenesis memory effect. The basic ingredients of this system are: 1), a positive autoregulation of the estrogen receptor α gene; 2), a strongly cooperative action of the estradiol receptor on vitellogenin expression; and 3), a variant isoform of the estradiol receptor with two autonomous transcription-activating modules, one of which is signal-independent and the other, signal-dependent. Realistic quantification supports the possibility of a multistationary situation in which ligand-independent activity is unable by itself to prime the amplification loop, but can click the system over a memory threshold after a primary stimulation. This ratchet transcriptional mechanism can have developmental and ecotoxicological importance and explain lifelong imprinting of past exposures without apparent phenotypic changes before restimulation and without need for persistent chromatin modifications.

Mechanisms and significance of nuclear receptor auto- and cross-regulation

The number of functional hormone receptors expressed by a cell in large part determines its responsiveness to the hormonal signal. The regulation of hormone receptor gene expression is therefore a central component of hormone action. Vertebrate steroid and thyroid hormones act by binding to nuclear receptors (NR) that function as ligand-activated transcription factors. Nuclear receptor genes are regulated by diverse and interacting intracellular signaling pathways. Nuclear receptor ligands can regulate the expression of the gene for the NR that mediates the hormone's action (autoregulation), thus influencing how a cell responds to the hormone. Autoregulation can be either positive or negative, the hormone increasing or decreasing, respectively, the expression of its own NR. Positive autoregulation (autoinduction) is often observed during postembryonic development, and during the ovarian cycle, where it enhances cellular sensitivity to the hormonal signal to drive the developmental process. By contrast, negative autoregulation (autorepression) may become important in the juvenile and adult for homeostatic negative feedback responses. In addition to autoregulation, a NR can influence the expression other types of NRs (cross-regulation), thus modifying how a cell responds to a different hormone. Cross-regulation by NRs is an important means to temporally coordinate cell responses to a subsequent (different) hormonal signal, or to allow for crosstalk between hormone signaling pathways.

Molecular identification of estrogen receptors (ERalpha and ERbeta) and their differential expression during VTG synthesis in the liver of lizard Podarcis sicula

In non-mammalian vertebrates yolk deposition in the oocytes is a hormone-dependent, gender-specific process. Produced by the ovary under gonadotropin stimulation, Estradiol 17-beta (E(2)) plays a key role in the liver synthesis of vitellogenin (VTG) which in turn is taken up by vitellogenic oocytes in the ovary. In many species a negative role in liver synthesis of VTG in females is also played by progesterone. Experimental administration of E(2) induces the expression of the VTG silent gene also in the liver of males of all the species studied. However, the role of the two isoforms of estrogen receptors, ERalpha and beta, in this process is still unclear. In order to elucidate what kind of ER is involved in the liver synthesis of VTG in the lizard Podarcis sicula, we obtained by means of RT-PCR two fragments of 430bp and 130bp from total ovarian mRNA, encoding respectively for ERalpha and ERbeta. Expression analysis of these two specific isoforms of ERs in the liver showed that in non-breeding females, and in wildlife untreated males only ERbeta is expressed. In breeding vitellogenic females and in E(2)-treated males both alpha and beta receptors are expressed. Furthermore, in females experimentally treated with progesterone during the breeding period, expression of ERalpha disappears. Conversely, treatment of females with E(2) in the non-breeding period induces expression of ERalpha. Immunohistochemical analysis and Western blotting showed that the presence of irVTG in liver and plasma is always parallel to hepatic expression of ERalpha in all the different experimental conditions. Our data strongly suggest that expression of ERalpha may be necessary for VTG synthesis in Podarcis. The possible modulatory role of ERbeta is also discussed.

Site-specific effects of 17beta-estradiol in hornyhead turbot (Pleuronichthys verticalis) collected from a wastewater outfall and reference location

Studies throughout the southern California bight have indicated persistent estrogenic activity in male hornyhead turbot (Pleuronichthys verticalis). Plasma 17beta-estradiol (E2) concentrations correlated with gonadal DNA damage in fish collected near a wastewater treatment plant outfall, but not from fish collected at the reference location. When the same species was collected from the same reference location and treated with E2, no relationship between uptake and gonadal DNA damage was observed. To evaluate the site-specific effects of E2 in fish from a wastewater outfall and fish from a reference location, male hornyhead turbot from each location were exposed to 15 microg/L aqueous E2 in a time-course experiment, with fish sampled every 12 h for 48 h. Concentrations of E2 were measured in the aqueous exposure and in plasma from the fish. Vitellogenin (vtg) was also measured in the plasma, and 8-oxo-7,8-dihydro-2'-deoxyguanosine levels in male gonads were measured as an indicator of DNA damage. Untreated fish from the outfall had significantly lower E2 in the plasma relative to the untreated reference fish, and this trend was consistent at each time point in the E2-treated fish. Vtg was significantly induced after 36 h of exposure in fish from both sites and no significant differences were observed between the sites. A significant increase of oxidative DNA damage was observed in E2-treated fish from the outfall population and the damage was significantly correlated with plasma E2 concentrations only in fish from the outfall after 48 h. These results indicated that there were significant differences in E2 disposition and gonadal genotoxicity between the hornyhead turbot populations following exposure to E2, suggesting that fish at wastewater outfalls may be more sensitive to DNA damage, which may be temporally related to concentrations of E2 in plasma.

Modulation of basal and squamous cell carcinoma by endogenous estrogen in mouse models of skin cancer

Patched1 heterozygous mice (Ptch1(+/-)) are useful for basal cell carcinoma (BCC) studies, being remarkably susceptible to BCC induction by ultraviolet or ionizing radiation. Analogously, skin carcinogenesis-susceptible (Car-S) mice are elective for studies of papilloma and squamous cell carcinoma (SCC) induction. We previously reported a striking effect of gender on BCC induction in Ptch1(+/-) mice, with total resistance of females; likewise, Car-S females show increased skin tumor resistance relative to males. Here, we investigated the protective role of endogenous estrogen in skin keratinocyte tumorigenesis. Control (CN) and ovariectomized Ptch1(+/-) or Car-S females were irradiated for BCC induction or topically treated with chemical carcinogens for SCC induction. Susceptibility to BCC or SCC was dramatically increased in ovariectomized Ptch1(+/-) and Car-S females and restored to levels observed in males. Remarkably, progression of initially benign papillomas to malignant SCC occurred only in ovariectomized Car-S females. We explored the mechanisms underlying tumor progression and report overexpression of estrogen receptor (ER)-alpha, downregulation of ERbeta and upregulation of cyclin D1 in papillomas from ovariectomized Car-S relative to papillomas from CN females. Thus, an imbalanced ERalpha/ERbeta expression may be associated with estrogen-mediated modulation of non-melanoma skin carcinogenesis, with a key role played by cyclin D1. Our findings underscore a highly protective role of endogenous estrogen against skin tumorigenesis by diverse agents in two independent mouse models of skin cancer.

Upregulation of estrogen receptor alpha and vitellogenin in eelpout (Zoarces viviparus) by waterborne exposure to 4-tert-octylphenol and 17beta-estradiol

The mechanisms of action of an estrogenic chemical have been examined in a viviparous fish the eelpout (Zoarces viviparus), by identification of an upregulated estrogenic pathway--the induction of hepatic estrogen receptor mRNA, hepatic estrogen binding activity and plasma vitellogenin. A relative quantitative RT-PCR assay has been established to measure hepatic estrogen receptor alpha (ER) mRNA levels in eelpout. Assay conditions were optimised using control and induced samples to ascertain its applicability in the actual working range of ER mRNA concentrations. beta-Actin was co-amplified and used as an internal standard. Time-course effects of water exposure to 0.5 microg/L 17beta-estradiol (E(2)) and 25 microg/L of the xeno-estrogen 4-tert-octylphenol (4-tert-OP) on ER mRNA levels in the male eelpout was examined. After 48 h of exposure, ER transcripts were induced 15-fold and 6-fold in the E(2)- and OP-treated fish, respectively. This difference, however, was not apparent after 1 week of exposure, when similar high levels of ER mRNA were present in both groups (20-fold induction). This indicates that the estrogenic capacity of 4-tert-OP increases with exposure time. The effect of treatment was also evaluated by examining the induction of specific E(2) binding capacity in hepatic cytosolic extracts and by measuring vitellogenin in plasma. Both parameters were also induced by the treatments, but later in the time course. The measurement of ER mRNA by the RT-PCR assay showed to be the most sensitive method for the detection of estrogenic responses in eelpout.

Expression ofGCR1, the transcriptional activator of glycolytic enzyme genes in the yeastSaccharomyces cerevisiae, is positively autoregulated by Gcr1p

When regulation of GCR1 expression was analysed using a GCR1-lacZ fusion, lacZ expression levels were decreased in the Deltagcr1 or Deltagcr2 mutant. RT-PCR analysis of genomic GCR1 transcript confirmed the dependency of GCR1 expression on the Gcr1p-Gcr2p complex. Examination of the 5' non-coding region of GCR1 identified three putative Gcr1p binding sites (CT-boxes) in the -100 to -200 region of GCR1, and the putative binding sites for Rap1p (RPG-box) and Abf1p were also identified nearby. The region containing putative cis-elements was analysed by cloning it upstream of the CYC1TATA-lacZ fusion. The GCR1(UAS)-CYC1TATA-lacZ fusion showed a moderate activity and, as expected, the activity was drastically reduced in the Deltagcr1 or Deltagcr2 mutant. Systematic deletion and mutation analyses of cis-elements in this region demonstrated that the putative binding sites for Rap1p and Abf1p were not involved in the promoter activity of GCR1(UAS) and only one of the three CT-boxes showed GCR1- and GCR2-dependent promoter activity. In contrast to the expression of glycolytic genes, where a RPG-box adjacent to the CT-box is required for strong promoter activities, CT-box-dependent expression of GCR1 did not require the RPG-box. Also, a contribution of Sgc1p, an E-box binding transcription factor, to the expression of GCR1 was suggested, based on its disruption analysis.

Differential hormonal regulation of estrogen receptors ERalpha and ERbeta and androgen receptor expression in rat efferent ductules

Estrogen receptors, in addition to the androgen receptor (AR), are expressed at high levels in efferent ductules of the male reproductive tract and it is now well recognized that estrogen receptor (ER) alpha is required for the maintenance of normal structure and function of the ductules. However, little is known regarding the hormonal regulation of the receptors themselves in the male. In the present study, efferent ductule ligation and castration, followed by replacement with testosterone, dihydro-testosterone (DHT) or estradiol was used to investigate the relative importance of circulating and luminal sources of steroid for the modulation of ERalpha, ERbeta and AR in rat efferent ductules. Uni- or bilateral castration and ligation did not affect the expression of ERalpha and ERbeta, but bilateral castration caused down-regulation of AR. Replacement with DHT and testosterone alone or in combination with estradiol caused the recovery of AR expression to control levels. A slight recovery of AR was also observed after estrogen replacement. ERalpha expression was decreased to nearly undetectable levels after estrogen replacement. On the other hand, ERbeta did not show evident effects following any of the treatments, suggesting a constitutive expression of this receptor. This differential modulation of the steroid hormone receptors highlights the importance of maintaining a physiological androgen-estrogen balance to regulate the structure and function of efferent ductules in the male.

The aryl hydrocarbon receptor-mediated disruption of vitellogenin synthesis in the fish liver: Cross-talk between AHR- and ERalpha-signalling pathways

BACKGROUND: In the fish liver, the synthesis of egg yolk protein precursor vitellogenin (VTG) is under control of the estrogen receptor alpha (ERalpha). Environmental contaminants such as 2,3,7,8-tetrachloro-dibenzo-p-dioxin (TCDD) are suspected to have antiestrogenic effects. The aryl hydrocarbon receptor (AHR) is the initial cellular target for TCDD and related compounds. The AHR is a ligand-activated transcription factor that stimulates the expression of the genes encoding xenobiotic metabolizing enzymes, such as cytochrome P450 1A (CYP1A). In this study, the effects of activation of AHR on the hepatic expression of VTG and ERalpha genes, in primary cultured salmon hepatocytes, have been investigated. RESULTS: The expression of the genes encoding VTG and ERalpha were strongly induced by 17beta-estradiol (E2). However, the expression of VTG was disrupted by exposure of the cells to TCDD while CYP1A expression was enhanced. The effect of TCDD on VTG and CYP1A expression was annulled by the AHR-inhibitor alpha-naphthoflavone. Furthermore, exposure of the cells to TCDD abolished E2-induced accumulation of ERalpha mRNA. The AHR-mediated inhibitory effects on the expression of the VTG and ERalpha genes may occur at transcriptional and/or post-transcriptional levels. Nuclear run-off experiments revealed that simultaneous exposure of the cells to E2 and TCDD strongly inhibited the initiation of transcription of the VTG and ERalpha genes. In addition, inhibition of RNA synthesis by actinomycin D treatment showed that post-transcriptional levels of VTG and ERalpha mRNAs were not significantly altered upon treatment of the cells with TCDD. These results suggested that activation of AHR may inhibit the transactivation capacity of the ERalpha. Further, electrophoretic mobility shift assays using nuclear extracts prepared from cells treated for one or two hours with E2, alone or in mixture with TCDD, showed a strong reduction in the DNA binding activities upon TCDD treatment. These results also suggested that activation of the AHR signalling pathway caused a marked decrease in the number of the nuclear ERalpha or that activated AHR blocked the ability of ERalpha to bind to its target DNA sequence. Finally, our results from Northern hybridizations indicated that E2 treatment of the cells did not cause any significant effect on the TCDD-induced levels of CYP1A mRNA. CONCLUSION: In fish hepatocytes E2 induces ERalpha and VTG gene expression. The presence of dioxin (TCDD) abolishes this induction, probably through the action of AHR in complex with AHR nuclear translocator, and possibly by direct interference with the auto-regulatory transcriptional loop of ERalpha. Furthermore, E2 does not interfere with TCDD induced CYP1A gene expression, suggesting that cross-talk between the ERalpha- and AHR-signalling pathways is unidirectional.

Multifarious effects of estrogen on the pituitary gonadotrope with special emphasis on studies in the ovine species

The gonadotrope is a complex cell that expresses receptors for gonadotropin releasing hormone (GnRH) and estrogen. It has synthetic machinery for the production of 3 gonadotropin subunits which are assembled into two gonadotropins, luteinising hormone (LH) and follicle stimulating hormone (FSH). The production and secretion of LH and FSH are differentially regulated by GnRH and estrogen. Patterns of secretion of LH are dictated by the pulsatile release of GnRH from the median eminence as well as the feedback effects of estrogen. The means by which estrogen plays such an important role in the regulation of LH and FSH is reviewed in this chapter, with emphasis on work that has been done in the sheep. Estrogen regulates the second messenger systems in the gonadotrope as well as the number of GnRH receptors and the function of ion channels in the plasma membrane. Estrogen also regulates gene expression in these cells. Additionally, GnRH appears to regulate the level of estrogen receptor in the ovine gonadotrope, so there is substantial cross-talk between the signalling pathways for GnRH and estrogen. No clear picture has emerged as to how estrogen exerts a positive feedback effect on the gonadotrope and it is suggested that this might be forthcoming from more definitive studies on the way that estrogen regulates the second messenger systems and the trafficking of secretory vesicles.

Vitellogenin from female and estradiol-stimulated male river lampreys (Lampetra fluviatilis L.)

The influence of estradiol-17beta (E(2)) on vitellogenesis is well documented for a number of oviparous craniates. We have examined the role that estradiol-17beta plays in the induction and regulation of vitellogenin synthesis in the maturing European river lamprey, Lampetra fluviatilis. In both females and males the estradiol-17beta concentrations in the plasma reached comparable maximum values in March, only a few weeks before spawning. Throughout the spawning run, the vitellogenin titer in the blood of females remains rather constant while the ovary volume increases. In contrast, we never found circulating VTG in untreated male lampreys. The synthesis and secretion of the yolk precursor molecule can be induced in males, however, by high doses of estradiol injected into the coelom. Lamprey vitellogenin was isolated from the blood of maturing females as well as from hormone-stimulated males and identified by its immunological and electrophoretic properties. In the blood plasma of both maturing female and estradiol-treated male lampreys it always appears simultaneously in two different molecular forms: a vitellogenin monomer with an apparent molecular weight of 310-330kDa and a dimer. After SDS treatment, vitellogenin is represented as a 212-kDa polypeptide.

The percentage of pituitary gonadotropes with immunoreactive oestradiol receptors increases in the follicular phase of the ovine oestrous cycle

During the oestrous cycle, there is an alteration in gonadotrope responsiveness to gonadotropin releasing hormone (GnRH). One cellular mechanism that may be involved in these changes at the pituitary level is the hormonal regulation of oestrogen receptor (ER) expression. Using double-label immunohistochemistry, we examined the proportion of gonadotropes, lactotropes and somatotropes with immunoreactive (ir) oestrogen receptor alpha (ERalpha) in pituitary sections from ewes at three stages of the ovine oestrous cycle (n = 8 per group). The percentage of ERalpha positive cells that also stained positive for luteinizing hormone (LH) increased in the transition from the luteal phase to the follicular phase (n = 8), with no further increase at the time of oestrus (n = 8). In the pituitaries from the luteal phase sheep, only a small number (15%) of lactotropes and 4% of somatotropes were found to contain ir-ERalpha and there were no alterations across the oestrous cycle. When we examined pituitaries from ovariectomized (OVX) ewes treated (i.m.) with either oestradiol benzoate (50 microg) or oil vehicle for 2, 4, 6 or 16 h (n = 4 per group), there was no effect of treatment. In fact, the percentage of gonadotropes that were ERalpha-positive in OVX ewes was similar to that observed in the pituitaries from the follicular phase ewes, both of which display a high frequency of pulsatile GnRH secretion. We conclude that the number of gonadotropes that contain ir-ERalpha increases in the follicular phase of the oestrous cycle and this may enhance the responsiveness of these cells to oestrogen and GnRH. We suggest that this may be due to increased pulsatile GnRH input rather than rising oestrogen levels.

An array of positioned nucleosomes potentiates thyroid hormone receptor action in vivo

The assembly of the genome into chromatin imposes a poorly understood set of rules and constraints on action by regulatory factors. We investigated the role played by chromatin infrastructure in enabling an acute response of the Xenopus TRbetaA gene to thyroid hormone receptor (TR), an extensively studied member of the nuclear hormone receptor superfamily. We found that in addition to the known TR response element (TRE) in the promoter, full range regulation required an upstream enhancer that contained multiple nonconsensus TREs and augmented ligand action at high receptor levels. An array of translationally positioned nucleosomes formed over the TRbetaA locus in vivo; unliganded TR engaged this array in linker DNA between two nucleosomes and via TREs on the surface of histone octamers. Remarkably, assembly of enhancer DNA into mature chromatin potentiated binding by TR to its target response elements and enabled a greater range of regulation by TR than was observed on immature chromatin templates. Because assembly of enhancer DNA into chromatin increased TR binding to the nonconsensus TREs, we hypothesize that chromatin disruption targeted by liganded TR to the enhancer may lead to receptor release from the template and to an attenuation of response to hormone.

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

We have previously shown that the preovulatory LH surge down-regulates estrogen receptor-beta (ERbeta) messenger RNA (mRNA) levels selectively in the granulosa cells of preovulatory follicles. To gain insight into the underlying mechanisms, we examined whether the LH-induced loss of ERbeta mRNA expression in rat granulosa cells is attributable to the hormone-induced changes at the level of transcription and/or mRNA degradation. When the rate of ERbeta gene transcription was assessed in cultured granulosa cells, by nuclear run-off assays, we observed only a marginal effect of hCG on ERbeta gene transcription. In contrast, when ERbeta mRNA levels were estimated in granulosa cells that were cultured in the presence of 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB), an RNA synthesis inhibitor, we observed a significant inhibitory effect of human CG (hCG) on ERbeta mRNA expression at a magnitude similar to that observed in the absence of DRB. Forskolin (FSK) and 2-O-tetradecanol-phorbol-13-acetate (TPA), pharmacological agents that mimic LH actions in granulosa cells, also showed similar effects. Thus, these results suggest that LH decreases ERbeta mRNA expression in the granulosa cells of preovulatory follicles, primarily by destabilizing the preexisting ERbeta mRNA. We next determined the decay rate of the ERbeta mRNA in granulosa cells that were cultured in the presence of DRB and additional hCG, FSK, or TPA for various time periods, by estimating ERbeta mRNA levels, using semiquantitative RT-PCR assays and subsequent linear regression analyses. The half-life of the ERbeta mRNA in the presence of vehicle was 17.87 +/- 1.2 h (n = 4). hCG dramatically decreased the half-life of the ERbeta mRNA (4.85 +/- 0.49 h, n = 4). Similarly, both FSK and TPA decreased the half-life of the ERbeta mRNA to 3.57 +/- 0.31 h and 4.02 +/- 0.13 h, respectively. We extended these findings by examining whether the LH-induced down-regulation of the ERbeta mRNA is cycloheximide-sensitive. When granulosa cells were cultured in the presence of cycloheximide, a protein synthesis inhibitor, the inhibitory effects of hCG, FSK, and TPA on ERbeta mRNA levels were abolished. Similar results were obtained in the presence or absence of DRB, indicating that the hormone-induced destabilization of the ERbeta mRNA is coupled with translation processes. Taken together, our results demonstrate that LH decreases ERbeta mRNA expression, predominantly at the posttranscriptional level, in a cycloheximide-sensitive manner.

Induction of proliferative lesions of the uterus, testes, and liver in swiss mice given repeated injections of sodium arsenate: possible estrogenic mode of action

Inorganic arsenic (As) is a human carcinogen but has not been unequivocally proven carcinogenic in rodents. For instance, one older study indicates that repeated iv injections of sodium arsenate might induce lymphomas in Swiss mice (58% incidence) (Osswald and Goerttler, Verh. Dtsch. Ges. Pathol. 55, 289-293, 1971), but it was considered inadequate for critical evaluation of carcinogenic potential largely because of issues in experimental design. Therefore, we studied repeated iv sodium arsenate injection and neoplastic response in male and female Swiss mice. Groups (n = 25) of mice received sodium arsenate (0.5 mg/kg, iv) or saline (control) once/week for 20 weeks and were observed for a total of 96 weeks when the study ended. Differences in survival and body weights were unremarkable. In females, arsenate induced marked increases in the incidence and severity of cystic hyperplasia of the uterus compared against controls. Arsenate also was associated with a rare adenocarcinoma of the uterus. Hyperplastic uterine epithelium from arsenate-exposed animals showed strong positive immunostaining for the proliferating cell nuclear antigen (PCNA). There was also an upregulation of estrogen receptor (ER) immunoreactive protein in the early lesions of uterine luminal and glandular hyperplasia, although a progressive decrease in its expression was seen in the severe hyperplastic or neoplastic epithelium. In common with the preneoplastic and neoplastic gynecological lesions in humans, the levels of immunoreactive inducible nitric oxide synthase (iNOS) and 3-nitrotyrosine-containing proteins were greater in the uterine hyperplastic epidermis and their intensity was positively correlated with the severity of the lesions. Arsenate-induced uterine hyperplastic lesions also showed a strong upregulation of cyclin D1, an estrogen-associated gene product essential for progression through the G1 phase of the cell cycle. In other tissues, arsenate increased testicular interstitial cell hyperplasia incidence and severity over control but without affecting the incidence of tubular degeneration. Arsenate also induced increases in hepatic proliferative lesions (HPL; foci of alteration + neoplasia), but only in females. Significant skin changes (incidence of hyperkeratotic lesions) and renal lesions (severity of nephropathy) also occurred in arsenate-treated females. Thus, repeated arsenate exposure, though not outright tumorigenic in the present study, was associated with proliferative, preneoplastic lesions of the uterus, testes, and liver. Estrogen treatment has been associated with proliferative lesions and tumors of the uterus, female liver, and testes in other studies, supporting a hypothesis that arsenate might somehow act through an estrogenic mode of action.

Characterization of a cytosolic estrogen receptor and its up-regulation by 17 beta-estradiol and the xenoestrogen 4-tert-octylphenol in the liver of eelpout (Zoarces viviparus)

Estrogen binding activity was revealed in the cytosolic fraction of hepatic extracts from adult male and female eelpout (Zoarces viviparus). The binding moiety was characterized by a single class of high affinity binding sites (K(d)=0.59+/-0.05 nM in males and 1.06+/-0.10 nM in females). The affinity was significantly higher in males. Binding sites were satiable and binding capacity was significantly elevated in vitellogenic females (2.92+/-0.28 pmol/g) compared to males (1.67+/-0.11 pmol/g). The binding was specific to known estrogens but not to other tested steroids. The binding moiety was able to bind to DNA-cellulose and was extractable by high salt concentrations. A time-course study of estrogen binding activity in liver cytosol and of vitellogenin (Vtg) in plasma, after intraperitoneal (i.p.) injections of 17 beta-estradiol (E(2)) in male eelpout, was carried out. It was shown that both are inducible by E(2). Estrogen binding activity was significantly elevated 48 h and Vtg 72 h after E(2) treatment. The binding moiety was hereafter designated as a cytosolic estrogen receptor (ER). The estrogenicity of 4-tert-octylphenol (OP) was evaluated by measuring ER and Vtg after i.p. treatment. OP-treatment increased both receptor levels and Vtg concentrations in male fish, indicating that OP acts as an estrogen in male eelpout.

Effect of estradiol on estrogen receptor expression in rat uterine cell types

In rodent uterus, both up- and down-regulation of estrogen receptor alpha (ERalpha) messenger ribonucleic acid (mRNA) and protein levels by estradiol has been demonstrated; however, it is not known which of the uterine compartments (endometrial epithelium, stroma, myometrium) respond to estradiol with autoregulation of ERalpha. The purpose of the present study was to investigate and compare the kinetics and cell type-specific effects of estradiol on uterine ERalpha expression in immature and adult rats. Ovariectomized female rats were injected s.c. with sesame oil or estradiol-17beta. Uteri were collected and analyzed for changes in ERalpha mRNA using RNase protection assays (RPA) and in situ hybridization using radiolabeled probes specific for ERalpha. Immunohistochemical analysis was performed with a polyclonal antibody specific to ERalpha. Expression of ERalpha in the uterine epithelial cells decreased at 3 and 6 h after estradiol administration to immature and adult rats, respectively. At 24 h, ERalpha mRNA levels in the immature and mature rat uterus were higher than pretreatment levels but returned to baseline by 72 h. Pretreatment with cycloheximide did not block the 3-h repressive effect of estradiol, suggesting that the estradiol-induced decrease in ERalpha mRNA occurs independent of new protein synthesis. A decrease in ERalpha mRNA and protein was also observed in uterine epithelia at 3 and 6 h after an estradiol injection to immature and adult rats, and intensity of both the in situ hybridization signal and the immunostaining in the epithelium increased at 24 and 72 h. However, the periluminal stromal cells in the adult uterus and the majority of stromal cells of the immature uterus appeared to have increased ERalpha expression. The results indicate that down-regulation of ERalpha in the epithelia and up-regulation of stromal ERalpha play a role in early events associated with estradiol-induced cell proliferation of the uterine epithelia.

Oestradiol up-regulates oestrogen receptor, cyclophilin, and glyceraldehyde phosphate dehydrogenase mRNA concentrations in endometrium, but down-regulates them in liver

Oestradiol regulates reproductive physiology and cardiovascular health in women. In the endometrium of ovariectomized ewes, previous work demonstrated that a single dose of oestradiol (50 microg) up-regulates oestrogen receptor-alpha (ER) and progesterone receptor (PR) gene expression within 24 h. Here we compared responses to different doses of oestradiol and different dosing regimens in two diverse tissues: endometrium and liver. ER, c-fos, cyclophilin and glyceraldehyde phosphate dehydrogenase (GAPDH) mRNA concentrations were analyzed on replicate RNA slot blots in both tissues, while PR and apolipoprotein AI (apo AI) mRNA concentrations were only analyzed in endometrium or liver, respectively. Along with ER mRNA, oestradiol strongly up-regulated GAPDH and cyclophilin mRNA concentrations in endometrium. In liver, however, oestradiol down-regulated them, along with apo AI mRNA. Responses to different doses and dose regimens, including repeated 50 microg doses, were similar to those evoked by a single 50 microg dose of oestradiol. Thus, oestradiol appears to have all-or-none effects which include up-regulation of ER, cyclophilin and GAPDH gene expression in endometrium and down-regulation of ER, apo AI, cyclophilin and GAPDH gene expression in liver. These results illustrate the sharp contrast between two mammalian tissues in their responses to physiological levels of oestradiol.

Chromatin remodeling regulated by steroid and nuclear receptors

Coactivators and corepressors regulate transcription by controlling interactions between sequence-specific transcription factors, the basal transcriptional machinery and the chromatin environment. This review consider the access of nuclear and steroid receptors to chromatin, their use of corepressors and coactivators to modify chromatin structure and the implications for transcriptional control. The assembly of specific nucleoprotein architectures and targeted histone modification emerge as central controlling elements for gene expression.

Differential regulation of two genes implicated in fish reproduction: vitellogenin and estrogen receptor genes

In rainbow trout as well as in other species, variability of estrogen receptor (ER) gene expression according to the cell type and the physiological state reflects a differential cell and gene sensitivity to estrogen. We previously demonstrated that expression of the rainbow trout estrogen receptor (rtER) and vitellogenin (Vg) genes were induced differently by estrogens in rainbow trout liver. Therefore, these two genes offered a suitable model to study the influence of ER concentration on gene transcriptional activities. In the present study we show that the transcription rate of rtER and Vg genes during an estrogenic treatment are affected differently by variation of cellular ER concentration. We demonstrate that rtER gene exhibits a low threshold response to loaded estrogen receptor, and increasing ER amounts do not affect the transcriptional response of this gene during an estrogenic stimulation. On the contrary, Vg gene expression requires the presence of a higher loaded estrogen receptor level to be induced, and its transcriptional response is directly proportional to the amount of synthesised ER.

Human estrogen receptor (ER) gene promoter-P1: estradiol-independent activity and estradiol inducibility in ER+ and ER- cells

Estrogen receptor (ER) is expressed at a low level in normal tissues such as breast and uterus but at a high level in breast and endometrial carcinomas. A proximal element (ERF-1) located between positions +133 and +204 relative to the promoter P1 major initiation site has been recently identified in ER+ cells and contributes to the differential promoter activity between ER+ and ER- cells. In this study, MCF7 and HeLa cells were transfected with chloramphenicol acetyltransferase constructs containing ER gene promoter P1 sequences. We show here that the sequences lying between nucleotides +13 to +212 are also essential for transcription at the ER gene promoter P1 in ER- cells, which do not express ERF-1. Interestingly, on gel shift experiments, a complex specific to ER- cells forms in the region spanning nucleotides +123 to +210. We also show that promoter P1 is responsive to estradiol in cells expressing endogenous (MCF7) or exogenous ER. We further demonstrate, using mutational analysis and gel retardation assays, that the three half-estrogen response elements located between nucleotides -420 and -892 are responsible for the estradiol inducibility of promoter P1. Because estradiol has a mitogenic effect on both breast and endometrial epithelial cells, our data would give an insight into the role of estrogens in the occurrence of breast and endometrial carcinomas.

Vigilin, a ubiquitous protein with 14 K homology domains, is the estrogen-inducible vitellogenin mRNA 3'-untranslated region-binding protein

RNA-binding proteins containing KH domains are widely distributed. One KH domain protein of unknown function, vigilin (also known as the high density lipoprotein-binding protein), contains 14 KH domains and is ubiquitous in vertebrate cells. We previously used RNA gel mobility shift assays to describe an estrogen-inducible protein which binds specifically to a segment of the 3'-untranslated region (3'-UTR) of vitellogenin mRNA, an area which has been implicated in the estrogen-mediated stabilization of vitellogenin mRNA. Here we show that the vitellogenin mRNA-binding protein (VitRNABP) is vigilin. The VitRNABP was isolated as a 150-155-kDa protein on a vitellogenin mRNA 3'-UTR affinity column. Peptide microsequencing revealed that the purified protein was vigilin, a conclusion confirmed in Western blot analysis with antibodies to vigilin. Direct confirmation that vigilin is the VitRNABP was obtained from RNA gel mobility shift assays which demonstrated that antibodies to chicken vigilin supershifted the Xenopus VitRNABP band. Xenopus liver vigilin mRNA and the VitRNABP exhibited similar induction by estrogen, providing additional confirmation that vigilin is the estrogen-inducible protein which binds to the 3'-UTR of estrogen-stabilized vitellogenin mRNA. These data support a role for vigilin in the hormonal control of mRNA metabolism.

Estrogen receptor (ER) and its messenger ribonucleic acid expression in the genital tract of female mice exposed neonatally to tamoxifen and diethylstilbestrol

BACKGROUND

Tamoxifen (Tx) is known as an antiestrogen because of its competitive inhibition of estrogen binding to estrogen receptor (ER), and it is used as an estrogen antagonist in the human breast. However, Tx is known to have estrogen agonist activity in the human fetal reproductive tracts and vaginal epithelium and endometrium of postmenopausal women as has been known in the mouse uterus. Therefore, we examined estrogenic potency of Tx on the uterus and vagina in newborn mice and adult ovariectomized mice.

METHODS

Using immunohistochemistry and in situ hybridization, we studied changes in expression of ER protein and ER mRNA in the uterus and vagina of C57BL/Tw mice exposed neonatally to 100 micrograms Tx and 0.03-3 micrograms diethylstilbestrol (DES), and changes in expression of ER mRNA in the ovariectomized adult mice given injections of 100 micrograms Tx and 3 micrograms DES.

RESULTS

Nuclei of the epithelial and stromal cells in the vagina and of the stromal cells in the uterus showed strong ER immunostaining on the day of birth (= day 0), whereas nuclei of the epithelial cells in the uterus exhibited the ER immunostaining by day 5. In uterine epithelial cells, however, ER was induced by DES, 17 beta-estradiol, testosterone or Tx 24 h after a single injection on day 0, but not by the injection of 5 alpha-dihydrotestosterone, progesterone, or epidermal growth factor. ER in uterine epithelial cells was detected even 12 h after a single injection of 3 micrograms DES on day 0. ER mRNA expression of uterine and vaginal epithelial cells of newborn mice increased 4 h after a single injection of 3 micrograms DES. ER mRNA expression of uterine and vaginal stromal cells in neonatal mice increased 4 h after a single injection of 100 micrograms Tx. In uterine epithelial and stromal cells and vaginal epithelial cells of ovariectomized adult mice, ER mRNA expression increased 12 h after a single injection of 3 micrograms DES and 100 micrograms Tx.

CONCLUSIONS

The present study indicates that Tx acts as ER inducer in the uterus and vagina of neonatal and ovariectomized adult mice. However, responsiveness of reproductive tracts to Tx is different between newborn and adult mice.

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.

Regulatory gene INO4 of yeast phospholipid biosynthesis is positively autoregulated and functions as a transactivator of fatty acid synthase genes FAS1 and FAS2 from Saccharomyces cerevisiae

The sequence motif 5' TYTTCACATGY 3' functions as an upstream activation site common to both yeast fatty acid synthase genes, FAS1 and FAS2. In addition, this UASFAS element is shared by all so far characterized genes of yeast phospholipid biosynthesis. We have investigated the influence of a functional INO4 gene previously described as a regulator of inositol biosynthesis on the expression of FAS1 and FAS2. In a delta ino4 null allele strain, both genes are expressed at only 50% of wild type level. Using individual UASFAS sequence motifs inserted into a heterologous test system, a drastic decrease of reporter gene expression to 2-10% of the wild type reference was observed in the delta ino4 mutant. In gel retardation assays, the protein-DNA complex involving the previously described FAS binding factor 1, Fbf1, was absent when using a protein extract from the delta ino4 mutant. On the other hand, this signal was enhanced with an extract from cells grown under conditions of inositol/choline derepression. Subsequent experiments demonstrated that INO4 expression is itself affected by phospholipid precursors, mediated by an UASFAS element in the INO4 upstream region. Thus, in addition of being an activator of phospholipid biosynthetic genes, INO4 is also subject to a positive autoregulatory loop in its own biosynthesis.

Xenopus transcription factors: key molecules in the developmental regulation of differential gene expression

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A correlation of thyroid hormone receptor gene expression with amphibian metamorphosis

The expression of the thyroid hormone (TH) receptor genes alpha (TR alpha) and beta (TR beta) in Xenopus laevis begins after the embryo hatches. The TR alpha mRNA increases throughout the premetamorphosis stage of tadpole development, is maximal by prometamorphosis, and falls after climax of metamorphosis to a lower level in frogs. The TR beta mRNA is barely detectable during premetamorphosis. In synchrony with the onset of endogenous TH synthesis by the thyroid gland (prometamorphosis), the level of TR beta mRNA rises in parallel with endogenous TH, reaching a peak at the climax of metamorphosis (stage 61) and drops to approximately 10% of its peak level after metamorphosis. As suggested by this correlation, exogenous TH up-regulates TR beta mRNA as much as 20-fold during premetamorphosis, whereas TH up-regulates TR alpha mRNA by approximately 2-fold during the same period. Up-regulation of TR beta mRNA is the earliest response to exogenous TH by competent tadpoles yet detected.

Estrogen receptor level determines sex-specific in vitro transcription from the Xenopus vitellogenin promoter

Female-specific expression of the Xenopus laevis vitellogenin gene was reconstituted in vitro by addition of recombinant vaccinia-virus-produced estrogen receptor to nuclear extracts from male livers, in which this gene is silent. Transcription enhancement was at least 30 times and was selectively restricted to vitellogenin templates containing the estrogen-responsive unit. Thus, in male hepatocytes, estrogen receptor is the limiting regulatory factor that in the female liver controls efficient and accurate sex-specific expression of the vitellogenin gene. Furthermore, the Xenopus liver factor B, which is essential in addition to the estrogen receptor for the activation of this gene, was successfully replaced in the Xenopus extract by purified human nuclear factor I, identifying factor B of Xenopus as a functional homolog of this well-characterized human transcription factor.

Retinoic acid, dibutyryl-cAMP, and differentiation affect the expression of retinoic acid receptors in F9 cells

Expression of the retinoic acid receptors alpha and beta (RAR-alpha and RAR-beta) was examined in F9 cells, an embryonal carcinoma cell model established for the study of retinoid metabolism and function. Addition of retinoic acid to F9 cell medium caused a dose-dependent increase in RAR-beta mRNA within 3 hr that reached 5- to 30-fold greater than the constitutively expressed mRNA by 24 hr. The elevation in mRNA resulted from increased transcription, as demonstrated by nuclear run-on transcription, did not require protein synthesis, and required the constant presence of retinoic acid. N6,O2'-Dibutyryl-cAMP attenuated the retinoic acid-induced increase in RAR-beta mRNA by a post-transcriptional mechanism. In contrast, RAR-alpha mRNA in F9 stem cells was affected less (1.2- to 1.4-fold increase) by retinoic acid and decreased 3-fold transiently when fresh serum was added to the medium. Differentiation of F9 cells resulted in increased steady-state levels of RAR-beta mRNA in primitive (4-fold), parietal (3-fold), and visceral (8-fold) endoderm but decreased steady-state levels of RAR-alpha mRNA in primitive (2-fold), parietal (3-fold), and visceral (1.4-fold) endoderm. These data demonstrate that RAR-beta is a primary target gene for retinoic acid in a characterized model of retinoid function, indicate that constitutive expression of both RAR-beta and RAR-alpha is dependent upon the differentiation state, and suggest hormonal modulation of RAR-beta by cAMP and modulation of RAR-alpha by serum factors. These results distinguish the effects of serum, cAMP, and retinoic acid on the expression of RAR from the effects mediated by differentiation.

Ribosome loading, but not protein synthesis, is required for estrogen stabilization of Xenopus laevis vitellogenin mRNA

We have examined the effect of protein synthesis and of ribosome loading on the estrogen-mediated stabilization of hepatic Xenopus laevis vitellogenin mRNA. Removal of estradiol-17 beta from the culture medium, which destabilizes vitellogenin mRNA, does not alter the density of ribosomes on polysomal vitellogenin mRNA, or change the proportion of vitellogenin mRNA associated with the endoplasmic reticulum. Cycloheximide, which inhibits elongation, without changing the density of ribosomes on vitellogenin mRNA, does not block estrogen-mediated stabilization. In contrast, 2-(4-methyl-2,6-dinitroanilino)-N-methylpropionamide, (MDMP), which inhibits initiation, greatly reduces the density of ribosomes on vitellogenin mRNA, and completely blocks estrogen-mediated stabilization. Vitellogenin mRNA in MDMP treated cells is degraded at a rate similar to that seen when untreated cells are transferred from medium containing estrogen to estrogen-free medium. This suggests that a ribosome-associated degradative system may not be responsible for vitellogenin mRNA degradation. The failure of estrogen to stabilize vitellogenin mRNA in MDMP-treated cells is not due to the release of vitellogenin mRNA from the endoplasmic reticulum. Vitellogenin mRNA in MDMP-treated cells remains associated with the endoplasmic reticulum in small polysomes containing 3-5 ribosomes. These data demonstrate that maintaining a high density of ribosomes on vitellogenin mRNA, but not continuing protein synthesis, is necessary for estrogen-mediated stabilization of vitellogenin mRNA.

Role of glucocorticoids in the chromaffin-neuron developmental decision

Chromaffin cells and sympathetic neurons develop from a common neural crest-derived progenitor cell. The developmental fate of this cell differs depending upon whether it migrates to the sympathetic ganglion or to the adrenal gland primordium, suggesting that local environmental signals control its differentiation. Glucocorticoid (GC) is a good candidate for an important adrenal environmental signal. These steroids are known to regulate PNMT, an adrenal-specific enzyme. However, in vivo observations suggest that the adrenal microenvironment influences the phenotype of sympatho-adrenal progenitor cells as early as E14.5, 2 days before PNMT is first expressed by developing chromaffin cells. Using cDNA probes, we find that GC receptor mRNA can be detected in the embryonic adrenal at least one full day before the initial appearance of PNMT mRNA. This observation is compatible with the idea that the apparent early influence of the adrenal microenvironment reflects the action of GC on progenitors which have migrated into this environment. In support of this, we show that similar influences can be exerted by GC on PC12 cells, which contain GC receptor mRNA but do not express or induce PNMT mRNA. Taken together, these data suggest that other factors in addition to the presence of the GC receptor may be necessary for the developmental appearance of PNMT expression.