Christina T. Teng

Estrogen-related Receptor, hERR1, Modulates Estrogen Receptor-mediated Response of Human Lactoferrin Gene Promoter

We have shown previously that estrogen-stimulated transcription from the human lactoferrin gene in RL95-2 endometrium carcinoma cells is mediated through an imperfect estrogen response element (ERE) at the 5′-flanking region of the gene. Upstream from the ERE, a DNA sequence (−418 to −378, FP1) was selectively protected from DNase I digestion by nuclear extracts from endometrial and mammary gland cell lines. In this report, using the electrophoresis mobility shift assay, site-directed mutagenesis, and DNA methylation interference analyses, we show that three different nuclear proteins bind to the FP1 region (C1, C2, and C3 sites). The nuclear receptor, COUP-TF, binds to the C2 site. Mutations in the C1 binding region abolish C1 complex formation and reduce estrogen-dependent transcription from the lactoferrin ERE. When the imperfect ERE of the lactoferrin gene is converted to a perfect palindromic structure, the enhancing effect of the C1 binding element for estrogen responsiveness was abolished. We isolated a complementary DNA (cDNA) clone from an RL95-2 expression library that encodes the C1 site-binding protein. The encoded polypeptide maintains 99% amino acid identity with the previously described orphan nuclear receptor hERR1. A 2.2-kilobase mRNA was detected in RL95-2 cells by the newly isolated cDNA but not by the first 180 base pair of the published hERR1 sequence. By Western analysis, a major 42-kDa protein is detected in the RL95-2 nuclear extract with antibody generated against GST-hERR1 fusion protein. Finally, we show that the hERR1 interacts with the human estrogen receptor through protein-protein contacts.

COUP-TF acts as a competitive repressor for estrogen receptor-mediated activation of the mouse lactoferrin gene.

We previously demonstrated that the estrogen response module (mERM) of the mouse lactoferrin gene, which contains an overlapping chicken ovalbumin upstream promoter transcription factor (COUP-TF)- and estrogen receptor-binding element, is responsible for estrogen induction. In this report we show that COUP-TF represses the mERM response to estrogen stimulation. Mutation and deletion of the COUP-TF-binding element or reduction of the endogenous COUP-TF increases mERM estrogen responsiveness. Likewise, overexpression of the COUP-TF expression vector blocked the estrogen-stimulated response of mERM in transfected cells. The molecular mechanism of this repression is due to the competition between COUP-TF and the estrogen receptor for binding at identical contact sites in the overlapping region of the mERM. Our results indicate that two members of the steroid-thyroid receptor superfamily work in concert to modulate lactoferrin gene expression.

Bisphenol A affects androgen receptor function via multiple mechanisms

Bisphenol A (BPA), is a well-known endocrine disruptor compound (EDC) that affects the normal development and function of the female and male reproductive system, however the mechanisms of action remain unclear. To investigate the molecular mechanisms of how BPA may affect ten different nuclear receptors, stable cell lines containing individual nuclear receptor ligand binding domain (LBD)-linked to the β-Gal reporter were examined by a quantitative high throughput screening (qHTS) format in the Tox21 Screening Program of the NIH. The results showed that two receptors, estrogen receptor alpha (ERα) and androgen receptor (AR), are affected by BPA in opposite direction. To confirm the observed effects of BPA on ERα and AR, we performed transient transfection experiments with full-length receptors and their corresponding response elements linked to luciferase reporters. We also included in this study two BPA analogs, bisphenol AF (BPAF) and bisphenol S (BPS). As seen in African green monkey kidney CV1 cells, the present study confirmed that BPA and BPAF act as ERα agonists (half maximal effective concentration EC50 of 10-100 nM) and as AR antagonists (half maximal inhibitory concentration IC50 of 1-2 μM). Both BPA and BPAF antagonized AR function via competitive inhibition of the action of synthetic androgen R1881. BPS with lower estrogenic activity (EC50 of 2.2 μM), did not compete with R1881 for AR binding, when tested at 30 μM. Finally, the effects of BPA were also evaluated in a nuclear translocation assays using EGPF-tagged receptors. Similar to 17β-estradiol (E2) which was used as control, BPA was able to enhance ERα nuclear foci formation but at a 100-fold higher concentration. Although BPA was able to bind AR, the nuclear translocation was reduced. Furthermore, BPA was unable to induce functional foci in the nuclei and is consistent with the transient transfection study that BPA is unable to activate AR.

Estrogen receptor α and estrogen receptor-related receptor α1 compete for binding and coactivator

Abstract The human estrogen receptor (ERα) and the human estrogen receptor-related receptor (ERRα1, NR3B1a) are members of the steroid/thyroid hormone receptor superfamily. We previously cloned an isoform of ERRα1 cDNA and demonstrated that ERRα1 binds to the human lactoferrin gene promoter and enhances estrogen responsiveness during transient transfection experiments. In this study, we show that ERRα1 and ERα may interfere in each others transcriptional activity by competition for binding and coactivator. A VP16-ERRα1 chimera was constructed and transiently transfected into human endometrial carcinoma HEC-1B cells. This chimera activated reporter constructs containing the human lactoferrin gene estrogen response element (ERE) and the synthetic palindromic 3X-ERE, suggesting that ERRα1 binds to these EREs. Therefore, ERRα1 can compete with ERα for binding to the same EREs. ERRα1 is organized into modules which include a N-terminal region that shows repression function, a Zn-finger region that binds DNA and an activation region at the C terminus. The activation function of ERRα1 was mapped to the conserved AF2 region in the C-terminus by deletion analysis. The transactivation activity of ERRα1 can be enhanced by coactivator (SRC-1a) and suppressed by ERα in the presence of estrogen, suggesting that SRC-1a is required by both receptors for their activity. The repression of ERRα1 activation function by estrogen bound ERα, however, could not be reversed by increasing concentration of SRC-1a in the cells. This finding is consistent with the squelching phenomenon that exists between ERα and other steroid receptor family members. The studies demonstrated that ERRα1 and ERα may potentially regulate the same target gene independently as well as interfere with each others functional activity by competition for binding and coactivator.

Assignment of the lactotransferrin gene to human chromosome 3 and to mouse chromosome 9

Lactotransferrin (LTF), a member of the transferrin family of genes, is the major iron-binding protein in milk and body secretions. The amino acid sequence of LTF consists of two homologous domains homologous to proteins in the transferrin family. Recent isolation of cDNA encoding mouse LTF has expedited the mapping of both mouse and human LTF genes. Southern blot analysis of DNA from mouse-Chinese hamster and human-mouse somatic cell hybrids maps the LTF gene to mouse chromosome 9 and to human chromosome 3, respectively. Furthermore, analysis of cell hybrids containing defined segments of human chromosome 3 demonstrates that the gene is located in the 3q21-qter region. These results suggest that LTF and associated genes of the transferrin family have existed together on the same chromosomal region for 300–500 million years.

Differential Expression and Estrogen Response of Lactoferrin Gene in the Female Reproductive Tract of Mouse, Rat, and Hamster

Abstract Lactoferrin, an iron-binding glycoprotein, kills bacteria and modulates inflammatory and immune responses. Presence of lactoferrin in the female reproductive tract suggests that the protein may be part of the mucosal immune system and act as the first line of defense against pathogenic organisms. We have discovered that lactoferrin is a major estrogen-inducible protein in the uterus of immature mice and is up-regulated by physiological levels of estrogen during proestrous in mature mice. In the present study, we examined lactoferrin gene expression and its response to estrogen stimulation in the female reproductive tract of several strains of immature mouse, rat, and hamster. The lactoferrin expression in the cycling adult female rat was also evaluated. Lactoferrin gene polymorphism exists among the different mouse strains. In the three inbred mouse strains studied, lactoferrin gene expression is stimulated by estrogen in the immature uterus, although it is less robust than in the outbred CD-1 mouse. We found that the lactoferrin gene is constitutively expressed in the epithelium of the vagina and the isthmus oviduct; however, it is estrogen inducible in the uterus of immature mice and rats. Furthermore, lactoferrin is elevated in the uterine epithelium of the mature rat during the proestrous and estrous stages of the estrous cycle. Estrogen stimulation of lactoferrin gene expression in the reproductive tract of an immature hamster is limited to the vaginal epithelium. The present study demonstrates differential expression and estrogen responsiveness of the lactoferrin gene in different regions of the female rodent reproductive tract and variation among the rodent species studied.

Endocrine-Disrupting Chemicals (EDCs): In Vitro Mechanism of Estrogenic Activation and Differential Effects on ER Target Genes

Background: Endocrine-disrupting chemicals (EDCs) influence the activity of estrogen receptors (ERs) and alter the function of the endocrine system. However, the diversity of EDC effects and mechanisms of action are poorly understood. Objectives: We examined the agonistic activity of EDCs through ERα and ERβ. We also investigated the effects of EDCs on ER-mediated target genes. Methods: HepG2 and HeLa cells were used to determine the agonistic activity of EDCs on ERα and ERβ via the luciferase reporter assay. Ishikawa cells stably expressing ERα were used to determine changes in endogenous ER target gene expression by EDCs. Results: Twelve EDCs were categorized into three groups on the basis of product class and similarity of chemical structure. As shown by luciferase reporter analysis, the EDCs act as ER agonists in a cell type– and promoter-specific manner. Bisphenol A, bisphenol AF, and 2-2-bis(p-hydroxyphenyl)-1,1,1-trichloroethane (group 1) strongly activated ERα estrogen responsive element (ERE)-mediated responses. Daidzein, genistein, kaempferol, and coumestrol (group 2) activated both ERα and ERβ ERE-mediated activities. Endosulfan and kepone (group 3) weakly activated ERα. Only a few EDCs significantly activated the “tethered” mechanism via ERα or ERβ. Results of real-time polymerase chain reaction indicated that bisphenol A and bisphenol AF consistently activated endogenous ER target genes, but the activities of other EDCs on changes of ER target gene expression were compound specific. Conclusion: Although EDCs with similar chemical structures (in the same group) tended to have comparable ERα and ERβ ERE-mediated activities, similar chemical structure did not correlate with previously reported ligand binding affinities of the EDCs. Using ERα-stable cells, we observed that EDCs differentially induced activity of endogenous ER target genes.

EADB: An Estrogenic Activity Database for Assessing Potential Endocrine Activity

Endocrine-active chemicals can potentially have adverse effects on both humans and wildlife. They can interfere with the bodys endocrine system through direct or indirect interactions with many protein targets. Estrogen receptors (ERs) are one of the major targets, and many endocrine disruptors are estrogenic and affect the normal estrogen signaling pathways. However, ERs can also serve as therapeutic targets for various medical conditions, such as menopausal symptoms, osteoporosis, and ER-positive breast cancer. Because of the decades-long interest in the safety and therapeutic utility of estrogenic chemicals, a large number of chemicals have been assayed for estrogenic activity, but these data exist in various sources and different formats that restrict the ability of regulatory and industry scientists to utilize them fully for assessing risk-benefit. To address this issue, we have developed an Estrogenic Activity Database (EADB; http://www.fda.gov/ScienceResearch/BioinformaticsTools/EstrogenicActivityDatabaseEADB/default.htm) and made it freely available to the public. EADB contains 18,114 estrogenic activity data points collected for 8212 chemicals tested in 1284 binding, reporter gene, cell proliferation, and in vivo assays in 11 different species. The chemicals cover a broad chemical structure space and the data span a wide range of activities. A set of tools allow users to access EADB and evaluate potential endocrine activity of chemicals. As a case study, a classification model was developed using EADB for predicting ER binding of chemicals.

Methylation and expression of the lactoferrin gene in human tissues and cancer cells.

The lactoferrin gene promoter contains GC-rich regions that harbor consensus sequences for a variety of transcription factors. Previous work in our laboratory has demonstrated a link between methylation at the CpG sites of the mouse lactoferrin gene promoter and the level of its expression. The current work investigates the methylation profile in three regions of the human lactoferrin gene by bisulfite genomic sequencing. In addition, the methylation profiles of normal leukocyte DNA, and leukemia cell line and patient DNA were compared. The three regions are located at the −504/−190, which includes the estrogen response element, the −282/+271 which contains the lactoferrin promoter and the +1087/+1476, a region within the first intron that has the alternative delta lactoferrin promoter. Differential methylations were found within all the regions. Increased methylation at the CpG sites and the presence of non-CpG methylation of the lactoferrin promoters were found in the cancer samples.

Interplay between estrogen-related receptor alpha (ERRα) and gamma (ERRγ) on the regulation of ERRα gene expression

Abstract Estrogen-related receptor alpha (ERRα) modulates estrogen receptor (ER)-mediated activity and is participating in the energy homeostasis by regulation of downstream target genes. The ERRα gene itself is proposed to be regulated by peroxisome proliferator-activated receptor γ coactivator (PGC-1α) through an autoregulatory loop under physiological stimulation. We have previously shown that the close family member ERRγ is a positive regulator of ERRα gene expression. ERRα and ERRγ are coexpressed in metabolically active tissues such as heart, kidney and muscle, yet the physiological role of ERRγ and its relationship with ERRα in gene regulation are currently unknown. The present study examined the interplay of ERRγ and ERRα in regulation of ERRα gene expression. Using real-time PCR analyses we found that ERRγ, like the ERRα and PGC-1α is induced in mouse liver during fasting. Overexpression of ERRγ in the HEC-1B cells robustly stimulated the multi-hormone response element (MHRE) of the ERRα gene promoter and this activity was repressed by increasing expression of ERRα. The two ERRs bind MHRE simultaneously in electrophoretic mobility shift assay (EMSA) and they were detected as multimeric complexes in cells by coimmunoprecipitation. Although ERRα and ERRγ share high sequence identity, they differ in biochemical and molecular characteristics as examined by trypsin digestion, reporter activation and coactivator interaction and utilization. Using chromatin immunoprecipitation (ChIP) assay, we showed that ectopic expression of both ERRα and ERRγ modifies chromatin structure at the MHRE region while ectopic expression of PGC-1α in HEC-1B cells promotes ERRγ but not ERRα occupancy at the MHRE region of the ERRα gene promoter and enhances the recruitment of coactivator SRC1. These data suggested that ERRα and ERRγ regulate ERRα gene expression with different molecular mechanisms.