The multiple untranslated first exons and promoters system of the oestrogen receptor gene in the brain and peripheral tissues of the rat and monkey and the developing rat cerebral cortex

Adaptation of the Porcine Pituitary Transcriptome, Spliceosome and Editome during Early Pregnancy

The physiological mechanisms of the porcine reproduction are relatively well-known. However, transcriptomic changes and the mechanisms accompanying transcription and translation processes in various reproductive organs, as well as their dependence on hormonal status, are still poorly understood. The aim of this study was to gain a principal understanding of alterations within the transcriptome, spliceosome and editome occurring in the pituitary of the domestic pig (Sus scrofa domestica L.), which controls basic physiological processes in the reproductive system. In this investigation, we performed extensive analyses of data obtained by high-throughput sequencing of RNA from the gilts' pituitary anterior lobes during embryo implantation and the mid-luteal phase of the estrous cycle. During analyses, we obtained detailed information on expression changes of 147 genes and 43 long noncoding RNAs, observed 784 alternative splicing events and also found the occurrence of 8729 allele-specific expression sites and 122 RNA editing events. The expression profiles of the selected 16 phenomena were confirmed by PCR or qPCR techniques. As a final result of functional meta-analysis, we acquired knowledge regarding intracellular pathways that induce changes in the processes accompanying transcription and translation regulation, which may induce modifications in the secretory activity of the porcine adenohypophyseal cells.

Postnatal exposure to endosulfan affects uterine development and fertility

Endosulfan is an organochlorine pesticide (OCP) used in large-scale agriculture for controlling a variety of insects and mites that attack food and non-food crops. Although endosulfan has been listed in the Stockholm Convention as a persistent organic pollutant to be worldwide banned, it is still in use in some countries. Like other OCPs, endosulfan is bioaccumulative, toxic and persistent in the environment. Human unintentional exposure may occur through air inhalation, dietary, skin contact, as well as, via transplacental route and breast feeding. Due to its lipophilic nature, endosulfan is rapidly absorbed into the gastrointestinal tract and bioaccumulates in the fatty tissues. Similar to other OCPs, endosulfan has been classified as an endocrine disrupting chemical (EDC). Endocrine action of endosulfan on development and reproductive function of males has been extensively discussed; however, endosulfan effects on the female reproductive tract have received less attention. This review provides an overview of: i) the fate and levels of endosulfan in the environment and human population, ii) the potential estrogenic properties of endosulfan in vitro and in vivo, iii) its effects on uterine development, and iv) the long-term effects on female fertility and uterine functional differentiation during early gestation.

Perinatal exposure to bisphenol A (BPA) impairs neuroendocrine mechanisms regulating food intake and kisspetin system in adult male rats. Evidences of metabolic disruptor hypothesis

Bisphenol A (BPA) is a compound used in the polymerization of plastic polycarbonates. It is an endocrine disruptor and it has been postulated to be an obesogen. Our objective was to determine the influence of perinatal exposure to BPA on body weight, hormone levels, metabolic parameters and hypothalamic signals that regulate food intake and kisspeptin system in adult male rats. Male rats were exposed to 50 μg/kg/day of BPA or vehicle from day 9 of gestation to weaning in the drinking water. Since weaning, they were fed with control or high fat diet for 20 weeks. Perinatal exposure to BPA impaired glucose homeostasis, induced obesity and increased food intake in adult male rats altering hypothalamic signals, partially mimicking and/or producing an exacerbation of the effects of feeding fat diet. We also observed an increase in kisspeptin expression by BPA exposure. Evidences shown in this work support the metabolic disruptor hypothesis for BPA.

Male mammary gland development and methylation status of estrogen receptor alpha in Wistar rats are modified by the developmental exposure to a glyphosate-based herbicide

Postnatal treatment with glyphosate-based herbicides (GBHs) induces endocrine-disrupting effects on the male rat mammary gland. In this study, the effects of developmental exposure to GBH on mammary gland growth and development, and the possible molecular mechanisms involved, were evaluated in pre- and post-pubertal male rats. To this end, pregnant rats were orally exposed through the food to 0, 3.5 or 350 mg GBH/kg bw/day from gestational day 9 until weaning. Mammary gland development and estradiol (E2) and testosterone (T) serum levels of male offspring were evaluated on postnatal day (PND)21 and PND60. Besides, prolactin (PRL) serum levels, proliferation index, androgen (AR) and estrogen receptor alpha (ESR1) expression, ESR1 alternative transcript mRNA levels, and DNA methylation status of ESR1 promoters were assessed on PND60. No differences between groups were observed in mammary gland development at PND21 or in E2 and T levels on both PNDs studied. On PND60, GBH3.5-exposed animals presented similar mammary gland histology but higher AR protein expression than controls, whereas GBH350-exposed males presented a less developed mammary gland, accompanied by a lower proliferation index, similar AR levels, and slightly increased PRL serum levels than controls. In both exposed groups, ESR1 expression was lower than in control rats, being lower in GBH350-exposed rats. GBH also altered the abundance of ESR1 transcript variants by hypermethylation of ESR1 promoters. GHB3.5 decreased only ESR1-OS expression, whereas GBH350 affected ESR1-O, OT and E1 expression. Our results show that developmental exposure to GBH induces epigenetic changes in ESR1, which could be responsible for the altered male mammary gland development observed in GBH350-exposed animals.

Uterine ERα epigenetic modifications are induced by the endocrine disruptor endosulfan in female rats with impaired fertility

High ERα activity may disrupt the window of uterine receptivity, causing defective implantation. We investigated whether implantation failures prompted by endosulfan are associated with aberrant ERα uterine expression and DNA methylation status during the pre-implantation period. ERα-dependent target genes that play a crucial role in the uterine receptivity for embryo attachment and implantation were also investigated. Newborn female rats received corn oil (vehicle, Control), 6 μg/kg/d of endosulfan (Endo6) or 600 μg/kg/d of endosulfan (Endo600) on postnatal days (PND) 1, 3, 5, and 7. On PND90, females were made pregnant and on gestational day 5 (GD5, pre-implantation period) uterine samples were collected. ERα expression was assessed at protein and mRNA levels by immunohistochemistry and real time RT-PCR, respectively. ERα transcript variants mRNA containing alternative 5'-untranslated regions (5'UTRs) were also evaluated. We searched for predicted transcription factors binding sites in ERα regulatory regions and assessed their methylation status by Methylation-Sensitive Restriction Enzymes-PCR technique (MSRE-PCR). The expression of the ERα-dependent uterine target genes, i.e. mucin-1 (MUC-1), insulin-like growth factor-1 (IGF-1), and leukemia inhibitory factor (LIF), was assessed by real time RT-PCR. Both doses of endosulfan increased the expression of ERα and its transcript variants ERα-OS, ERα-O, ERα-OT and ERα-E1. Moreover, a decreased DNA methylation levels were detected in some ERα regulatory regions, suggesting an epigenetic up-regulation of it transcription. ERα overexpression was associated with an induction of its downstream genes, MUC-1 and IGF-1, suggesting that endosulfan might alter the uterine estrogenic pathway compromising uterine receptivity. These alterations could account, at least in part, for the endosulfan-induced implantation failures.

A deregulated expression of estrogen-target genes is associated with an altered response to estradiol in aged rats perinatally exposed to bisphenol A

Here we assessed the effects of perinatal exposure to bisphenol A (BPA) on the uterine response to 17β-estradiol (E2) in aged rats. Pregnant rats were orally exposed to 0.5 or 50 μg BPA/kg/day from gestational day 9 until weaning. On postnatal day (PND) 360, the rats were ovariectomized and treated with E2 for three months. The uterine tissue of BPA50 and BPA0.5 rats showed increased density of glands with squamous metaplasia (GSM) and glands with daughter glands respectively. Wnt7a expression was lower in GSM of BPA50 rats than in controls. The expression of estrogen receptor 1 (ESR1) and its 5'- untranslated exons ESR1-O and ESR1-OT was lower in BPA50 rats. Both doses of BPA modified the expression of coactivator proteins and epigenetic regulatory enzymes. Thus, perinatal BPA-exposed rats showed different glandular abnormalities associated with deregulated expression of E2-target genes. Different mechanisms would be involved depending on the BPA dose administered.

Epigenetic changes in the estrogen receptor α gene promoter: implications in sociosexual behaviors

Estrogen action through estrogen receptor α (ERα) is involved in the control of sexual and social behaviors in adult mammals. Alteration of ERα gene activity mediated by epigenetic mechanisms, such as histone modifications and DNA methylation, in particular brain areas appears to be crucial for determining the extents of these behaviors between the sexes and among individuals within the same sex. This review provides a summary of the epigenetic changes in the ERα gene promoter that correlate with sociosexual behaviors.

Unilateral lesion increases oestrogen receptor α expression in the intact side of the ventromedial hypothalamic nucleus in ovariectomised rats

To determine the relationship between the right and left sides of the ventrolateral ventromedial hypothalamic nucleus (vlVMN) in regulating the expression of oestrogen receptor (ER)α, the unilateral vlVMN was lesioned and the number of ERα-immunoreactive cells and the ERα mRNA level in the intact side of the vlVMN and arcuate nucleus (ARC) were measured in ovariectomised rats. Twenty-four hours after lesioning, brain samples were collected for analysis of ERα expression by immunohistochemistry and the real-time reverse transcriptase-polymerase chain reaction. The number of ERα-immunoreactive cells in the intact side of the vlVMN but not the ARC in the unilateral lesioned group was significantly higher than that in the control or sham-lesioned group. Expression levels of ERα mRNA in the intact side of the vlVMN but not the ARC in unilateral lesioned rats were significantly higher than those in the sham-lesioned group. Of transcript variants with alternative 5'-untranslated regions (0S, 0N, 0, 0T and E1), the ERα 0 transcript level was significantly increased. These results indicate that unilateral damage of vlVMN induces an increase in ERα in the intact side by increasing ERα transcription in a promoter-specific manner. The findings also suggest the existence of new neuroendocrine control system between the right and left sides for the expression of ERα in the vlVMN.

Sex-specific Esr2 mRNA expression in the rat hypothalamus and amygdala is altered by neonatal bisphenol A exposure

Perinatal life is a critical window for sexually dimorphic brain organization, and profoundly influenced by steroid hormones. Exposure to endocrine-disrupting compounds may disrupt this process, resulting in compromised reproductive physiology and behavior. To test the hypothesis that neonatal bisphenol A (BPA) exposure can alter sex-specific postnatal Esr2 (Erβ) expression in brain regions fundamental to sociosexual behavior, we mapped Esr2 mRNA levels in the principal nucleus of the bed nucleus of the stria terminalis (BNSTp), paraventricular nucleus (PVN), anterior portion of the medial amygdaloid nucleus (MeA), super optic nucleus, suprachiasmatic nucleus, and lateral habenula across postnatal days (PNDs) 0-19. Next, rat pups of both sexes were subcutaneously injected with 10 μg estradiol benzoate (EB), 50 μg/kg BPA (LBPA), or 50 mg/kg BPA (HBPA) over the first 3 days of life and Esr2 levels were quantified in each region of interest (ROI) on PNDs 4 and 10. EB exposure decreased Esr2 signal in most female ROIs and in the male PVN. In the BNSTp, Esr2 expression decreased in LBPA males and HBPA females on PND 10, thereby reversing the sex difference in expression. In the PVN, Esr2 mRNA levels were elevated in LBPA females, also resulting in a reversal of sexually dimorphic expression. In the MeA, BPA decreased Esr2 expression on PND 4. Collectively, these data demonstrate that region- and sex-specific Esr2 expression is vulnerable to neonatal BPA exposure in regions of the developing brain critical to sociosexual behavior in rat.

Prenatal bisphenol A exposure alters sex-specific estrogen receptor expression in the neonatal rat hypothalamus and amygdala

Bisphenol A (BPA) exposure is ubiquitous, and in laboratory animals, early-life BPA exposure has been shown to alter sex-specific neural organization, neuroendocrine physiology, and behavior. The specific mechanisms underlying these brain-related outcomes, however, remain largely unknown, constraining the capacity to ascertain the potential human relevance of neural effects observed in animal models. In the perinatal rat brain, estrogen is masculinizing, suggesting that BPA-induced perturbation of estrogen receptor (ESR) expression may underpin later in-life neuroendocrine effects. We hypothesized that prenatal BPA exposure alters sex-specific ESR1 (ERα) and ESR2 (ERβ) expression in postnatal limbic nuclei. Sprague Dawley rats were mated and gavaged on gestational days (GDs) 6-21 with vehicle, 2.5 or 25 μg/kg bw/day BPA, or 5 or 10 μg/kg bw/day ethinyl estradiol. An additional group was restrained but not gavaged (naïve control). Offspring were sacrificed the day after birth to quantify ESR gene expression throughout the hypothalamus and amygdala by in situ hybridization. Relative to the vehicle group, significant effects of BPA were observed on ESR1 and ESR2 expression throughout the mediobasal hypothalamus and amygdala in both sexes. Significant differences in ESR expression were also observed in the mediobasal hypothalamus and amygdala of the naïve control group compared with the vehicle group, highlighting the potential for gavage to influence gene expression in the developing brain. These results indicate that ESR expression in the neonatal brain of both sexes can be altered by low-dose prenatal BPA exposure.

Novel splicing events and post-transcriptional regulation of human estrogen receptor α E isoforms

Expression of the estrogen receptor α (ERα) gene is subject to complex regulation. To elucidate the mechanisms of this regulation, the genomic organization and the physiological role of the multiple 5'-untranslated regions (5'-UTRs) must be determined. Here, we investigated the expression and splicing patterns of the human ERα E isoforms. We identified two novel untranslated exons, N1 and N2, in the 5'-region of the human ERα gene and multiple E isoform mRNA variants generated by alternative usage of non-coding internal exons. Expression of the N1-containing variants was observed only in the human breast adenocarcinoma cell line, MCF7, while the N2-containing variants were expressed in the adult liver and MCF7 cells. We examined post-transcriptional regulation of the variant mRNAs using luciferase reporter assays and quantitative PCR. The insertion of untranslated internal exons into the 5'-UTRs of the E isoforms reduced their translation efficiency, but barely influenced mRNA turnover. Our results indicate that the genomic organization of the human ERα gene and the splicing profiles of the human ERα E isoforms are more complicated than previously reported. Furthermore, the 5'-UTRs of the E isoforms post-transcriptionally control human ERα expression mainly through translational repression.

Complex organization of the 5'-untranslated region of the mouse estrogen receptor α gene: identification of numerous mRNA transcripts with distinct 5'-ends

The 5'-untranslated region (5'-UTR) of the estrogen receptor α (ERα) gene plays an important role in determining its tissue-specific expression. We examined the 5'-UTRs of the mouse ERα mRNA variants in depth using the Basic Local Alignment Search Tool (BLAST), rapid amplification of 5'-cDNA ends (5'-RACE) and RT-PCR. We demonstrated the presence of multiple variants containing unique 5'-UTRs. We mapped the cDNA sequences onto the mouse genome, and found that both alternative splicing from four different leader exons (A, C, F1, and H) to exon 1, and combinations of 12 internal exons (X1, X2, X3, X4, F2/X5, X6, X7, X8, X9, X10, X11, and B) generate multiple ERα transcripts. Mouse exon B, that has homologies with human exon B and rat exon 0T, was used as an internal exon, not as a leader exon. RT-PCR analysis revealed distinct expression patterns of the variants, suggesting that the alternative promoter usage and alternative splicing are regulated in a tissue-specific manner. Our results indicate that the genomic organization of the mouse ERα gene is complicated as previously shown in the rat ERα gene. In addition, both alternative promoter usage and alternative splicing contribute to the remarkable mRNA diversity of the mouse ERα gene.

Alternative promoter usage and alternative splicing of the rat estrogen receptor alpha gene generate numerous mRNA variants with distinct 5'-ends

The 5'-untranslated region (UTR) of the estrogen receptor alpha (ERalpha) gene plays an important role in determining tissue-specific expression. To elucidate the regulatory mechanisms of rat ERalpha gene expression, the genomic organization must be investigated. We therefore analyzed the structure of the rat ERalpha mRNA 5'-UTR using rapid amplification of 5'-cDNA ends (5'-RACE) and RT-PCR. The analysis showed the presence of multiple variants containing unique 5'-UTRs. We mapped the cDNA sequences on the rat genome, and newly identified one leader exon (exon 0U) and ten untranslated internal exons (exons I1-10). Both splicing from four different leader exons (exons 0S, 0N, 0U, and 0/B) onto exon 1 and alternative splicing in combination with eleven internal exons (exons I1-10, and 0T) produce multiple transcripts. RT-PCR analysis revealed that each variant had preferred expression sites, suggesting that promoter usage and splicing are regulated in tissue-specific manners. Moreover, we determined a splicing event to yield Deltaexon 1 variants (0S-2-3-4-5-6-7-8), which are translated into rat 46 kDa ERalpha proteins. Our results indicate that the rat ERalpha gene is more complex than previously thought in terms of genomic organization and that both alternative promoter usage and alternative splicing contribute to the remarkable diversity of ERalpha mRNAs.

Dynamic regulation of estrogen receptor-alpha gene expression in the brain: a role for promoter methylation?

Estrogen has long been known to play an important role in coordinating the neuroendocrine events that control sexual development, sexual behavior and reproduction. Estrogen actions in other, non-reproductive areas of the brain have also been described. It is now known that estrogen can also influence learning, memory, and emotion and has neurotrophic and neuroprotective properties. The actions of estrogen are largely mediated through at least two intracellular estrogen receptors. Both estrogen receptor-alpha and estrogen receptor-beta are expressed in a wide variety of brain regions. Estrogen receptor-alpha (ERalpha), however, undergoes developmental and brain region-specific changes in expression. The precise molecular mechanisms that regulate its expression at the level of gene transcription are not well understood. Adding to the complexity of its regulation, the estrogen receptor gene contains multiple promoters that drive its expression. In the cortex in particular, the ERalpha mRNA expression is dynamically regulated during postnatal development and again following neuronal injury. Epigenetic modification of chromatin is increasingly being understood as a mechanism of neuronal gene regulation. This review examines the potential regulation of the ERalpha gene by such epigenetic mechanisms.

Visualizing forebrain-specific usage of an estrogen receptor α promoter for receptor downregulation in the rat

Transgenic rats expressing enhanced green fluorescent protein (EGFP) under the control of an estrogen receptor (ER) alpha promoter were generated to tag ERalpha-positive neurons in the brain. Two transgenes, one containing sequences for promoter A and DsRed and the other containing sequences for promoter 0/B and EGFP, were injected simultaneously into Wistar rat zygotes. Twenty-two founders with both transgenes were identified. Ten lines of these founders expressed the EGFP tag in the brains of their first filial generation, whereas none similarly expressed the DsRed tag. In two lines selected for the brightness of the EGFP fluorescence in their brains, tagged cells showed essentially the same patterns. Tagged cells were in the preoptic area (POA), bed nucleus of the stria terminalis (BNST), hypothalamic arcuate nucleus and medial amygdala. ERalpha-immunoreactive neurons were identified in all of these structures by immunohistochemistry. In ovariectomized females, approximately 75% of the EGFP-fluorescent cells in the POA-BNST were immunoreactive for ERalpha. In the POA-BNST, ovariectomy increased the number of EGFP-immunopositive cells and estrogen supplementation reversed this effect, indicating that the promoter 0/B is involved in estrogen-induced downregulation of ERalpha. EGFP was also present in cells in the cerebral cortex and hippocampus, which have not previously been associated with endocrine regulation. Conversely, only a few cells were tagged in the hypothalamic ventromedial nucleus, which contained many ERalpha-immunoreactive neurons. This discrepancy could have arisen as a result of differential promoter usage.

Upstream regions of the estrogen receptor alpha proximal promoter transcript regulate ER protein expression through a translational mechanism

Estrogen receptor alpha (ER) mRNA is primarily transcribed from two promoters, the two transcripts share identical sequence encoding the same ER protein but differ in upstream regions. The 5' region of the two transcripts contain upstream open reading frames (uORFs) encoding potential peptides of 20 and 18 amino acids. The peptides have five C-terminal residues in common. These studies were undertaken to determine if the uORFs and encoded peptides differentially affected expression of ER. Expression of green fluorescent protein (GFP) reporter constructs containing upstream proximal promoter transcript sequences with the first 18 codons of ER fused to GFP was tested in HeLa cells. The cells expressed reduced levels of GFP as compared to the pEGFP-N1 parent vector; the effect was dependent on the presence of an intact proximal ER transcript uORF. Similar regulation by the uORF was seen in transfected MCF-7, MDA MB-231 and Ishikawa cells. Only protein expression was affected by eliminating the uORF; RNA levels were unchanged. This indicates the mechanism is translational rather than being an effect of the introduced point mutations on either mRNA stability or transcription. Eliminating the uORF did not significantly increase expression from similar distal promoter transcript ER-GFP constructs. However, study of in-frame fusions of GFP to the entire proximal and distal uORFs and to their translational start motifs showed that the translational start region of the distal uORF was inherently better at initiating translation than the AUG environment of the proximal promoter transcript uORF. The data indicate there are regulatory properties suppressing expression from the ER translation start which are specific to the unique regions of the ER proximal promoter transcript and these are likely associated with the proximal transcript uORF peptide product.

Genomic studies of the spleen protein tyrosine kinase locus reveal a complex promoter structure and several genetic variants

Here we show that the gene of the cytoplasmic tyrosine kinase SYK spans a region of 90kb with 13 coding exons, an alternative exon 14 and at least two 5' untranslated regions exons 1a and 1b. 5' RACE (Rapid amplification of cDNA ends) of human Syk cDNAs demonstrated a complex promoter usage and splicing pattern. We identified three common single nucleotide polymorphisms in the exon la promoter region of the Syk gene as well as a variant Syk cDNA haplotype. This haplotype was characterized by a constellation of 5 silent mutations in the Syk cDNA: 1065(C-T), 1302(G-C), 1338(G-A), 1521(C-T) and 1545(T-C). A hypervariable CATATA(n) repeat polymorphism was also localized to the intron between exons 11 and 12. These novel insights into the genomic organization, promoter structure and genetic variability of Syk will serve as a foundation for detailed molecular epidemiological investigation of its potential role in human cancer biology.

Novel intronic promoter in the rat ER alpha gene responsible for the transient transcription of a variant receptor

To analyze the molecular origin of an ER variant, the truncated ER product-1, transiently expressed at the proestrus in lactotrope cells, we generated a 2.5-kb sequence of a genomic region upstream and downstream the specific sequence truncated ER product-1. Genomic Southern blot analysis showed that truncated ER product-1 is spliced from a noncoding leader exon localized within the intron 4 of the ER alpha gene. Analysis of the promoter sequence revealed the presence of a major transcriptional start site, a canonical TATA box and putative cis regulatory elements for pituitary specific expression as well as an E-responsive element. In transient transfection, the truncated ER product-1 promoter was transcriptionally the most active in the lactotrope cell lines (MMQ). Analysis of truncated ER product-1 functionality showed that: 1) the protein inhibited ER alpha binding to the E-responsive element in electromobility shift assays, 2) inhibited the E2 binding to ER alpha in binding assays, 3) the truncated ER product-1/ER alpha complex antagonized the transcriptional activity elicited by E2, 4) nuclear localization of green fluorescent protein-ER alpha was altered in Chinese hamster ovary cell lines stably expressing truncated ER product-1. Collectively, these data demonstrated that the protein exerts full dominant negative activity against ER alpha. Moreover, truncated ER product-1/ER alpha complex also repressed the activity of all promoters tested to date, suggesting a general inhibitory effect toward transcription. In conclusion, the data suggest that truncated ER product-1 could regulate estrogen signaling via a specific promoter in lactotrope cells.

Differential expression and regulation of estrogen receptors (ERs) in rat pituitary and cell lines: estrogen decreases ERalpha protein and estrogen responsiveness

Estrogen (E) regulates the synthesis and secretion of several pituitary hormones during the reproductive cycle in a cell- and promoter-specific manner. One mechanism underlying cell specificity is the differential expression of estrogen receptor (ER) isoforms. We used in vivo and in vitro rodent pituitary cell models to examine the expression and regulation of ERalpha, ERbeta, and the pituitary-specific ERalpha isoform, truncated estrogen receptor product-1 (TERP-1). In cycling female rat pituitaries, ERbeta messenger RNA (mRNA) levels fell 40% on the morning of proestrus and were suppressed by E or dihydrotestosterone in ovariectomized females. In lactotrope and gonadotrope cell lines (GH3, RC4B, LbetaT2), progesterone (P) or P plus E also suppressed ERbeta. TERP-1 mRNA increased 3-fold at proestrus and in response to E treatment in vivo and in cell lines. ERalpha mRNA levels were not regulated significantly by any treatment in vivo or in cell lines. However, E suppressed ERalpha protein levels in vivo and in cell lines, and reduction of ERalpha protein levels by E or the antiestrogen ICI182,780 reduced E-stimulated transcriptional activation of the PRL promoter in GH3 cells. TERP-1 and ERbeta protein levels were low to undetectable in cell lines, but E stimulated TERP-1. Because E treatment decreases ERbeta mRNA and ERalpha protein and increases levels of TERP-1 (which can suppress ERalpha/beta activity), the dynamic steroid-induced changes in ER expression in the rat pituitary during the midcycle gondaotropin/PRL surge may provide a means for ovarian steroids to limit positive feedback.