Ligand-dependent repression of the erythroid transcription factor GATA-1 by the estrogen receptor

Whole blood transcriptome analysis for age- and gender-specific gene expression profiling in Japanese individuals

Whole blood transcriptome analysis is a valuable approachin medical research, primarily due to the ease of sample collection and the richness of the information obtained. Since the expression profile of individual genes in the analysis is influenced by medical traits and demographic attributes such as age and gender, there has been a growing demand for a comprehensive database for blood transcriptome analysis. Here, we performed whole blood RNA sequencing (RNA-seq) analysis on 576 participants stratified by age (20-30s and 60-70s) and gender from cohorts of the Tohoku Medical Megabank (TMM). A part of female segment included pregnant women. We did not exclude the globin gene family in our RNA-seq study, which enabled us to identify instances of hereditary persistence of fetal hemoglobin based on the HBG1 and HBG2 expression information. Comparing stratified populations allowed us to identify groups of genes associated with age-related changes and gender differences. We also found that the immune response status, particularly measured by neutrophil-to-lymphocyte ratio (NLR), strongly influences the diversity of individual gene expression profiles in whole blood transcriptome analysis. This stratification has resulted in a data set that will be highly beneficial for future whole blood transcriptome analysis in the Japanese population.

How nutrition regulates hematopoietic stem cell features

Our dietary choices significantly impact all the cells in our body. Increasing evidence suggests that diet-derived metabolites influence hematopoietic stem cell (HSC) metabolism and function, thereby actively modulating blood homeostasis. This is of particular relevance because regulating the metabolic activity of HSCs is crucial for maintaining stem cell fitness and mitigating the risk of hematologic disorders. In this review, we examine the current scientific knowledge of the impact of diet on stemness features, and we specifically highlight the established mechanisms by which dietary components modulate metabolic and transcriptional programs in adult HSCs. Gaining a deeper understanding of how nutrition influences our HSC compartment may pave the way for targeted dietary interventions with the potential to decelerate aging and improve the effectiveness of transplantation and cancer therapies.

Role of Nuclear Receptors in Controlling Erythropoiesis

Nuclear receptors (NRs), are a wide family of ligand-regulated transcription factors sharing a common modular structure composed by an N-terminal domain and a ligand-binding domain connected by a short hinge linker to a DNA-binding domain. NRs are involved in many physiological processes, including metabolism, reproduction and development. Most of them respond to small lipophilic ligands, such as steroids, retinoids, and phospholipids, which act as conformational switches. Some NRs are still "orphan" and the search for their ligands is still ongoing. Upon DNA binding, NRs can act both as transcriptional activators or repressors of their target genes. Theoretically, the possibility to modulate NRs activity with small molecules makes them ideal therapeutic targets, although the complexity of their signaling makes drug design challenging. In this review, we discuss the role of NRs in erythropoiesis, in both homeostatic and stress conditions. This knowledge is important in view of modulating red blood cells production in disease conditions, such as anemias, and for the expansion of erythroid cells in culture for research purposes and for reaching the long-term goal of cultured blood for transfusion.

Protective role of estrogen against excessive erythrocytosis in Monge's disease

Monge's disease (chronic mountain sickness (CMS)) is a maladaptive condition caused by chronic (years) exposure to high-altitude hypoxia. One of the defining features of CMS is excessive erythrocytosis with extremely high hematocrit levels. In the Andean population, CMS prevalence is vastly different between males and females, being rare in females. Furthermore, there is a sharp increase in CMS incidence in females after menopause. In this study, we assessed the role of sex hormones (testosterone, progesterone, and estrogen) in CMS and non-CMS cells using a well-characterized in vitro erythroid platform. While we found that there was a mild (nonsignificant) increase in RBC production with testosterone, we observed that estrogen, in physiologic concentrations, reduced sharply CD235a+ cells (glycophorin A; a marker of RBC), from 56% in the untreated CMS cells to 10% in the treated CMS cells, in a stage-specific and dose-responsive manner. At the molecular level, we determined that estrogen has a direct effect on GATA1, remarkably decreasing the messenger RNA (mRNA) and protein levels of GATA1 (p < 0.01) and its target genes (Alas2, BclxL, and Epor, p < 0.001). These changes result in a significant increase in apoptosis of erythroid cells. We also demonstrate that estrogen regulates erythropoiesis in CMS patients through estrogen beta signaling and that its inhibition can diminish the effects of estrogen by significantly increasing HIF1, VEGF, and GATA1 mRNA levels. Taken altogether, our results indicate that estrogen has a major impact on the regulation of erythropoiesis, particularly under chronic hypoxic conditions, and has the potential to treat blood diseases, such as high altitude severe erythrocytosis.

Genome-Wide Transcriptional Regulation of the Long Non-coding RNA Steroid Receptor RNA Activator in Human Erythroblasts

Erythropoiesis of human hematopoietic stem cells (HSCs) maintains generation of red blood cells throughout life. However, little is known how human erythropoiesis is regulated by long non-coding RNAs (lncRNAs). By using ChIRP-seq, we report here that the lncRNA steroid receptor RNA activator (SRA) occupies chromatin, and co-localizes with CTCF, H3K4me3, and H3K27me3 genome-wide in human erythroblast cell line K562. CTCF binding sites that are also occupied by SRA are enriched for either H3K4me3 or H3K27me3. Transcriptome-wide analyses reveal that SRA facilitates expression of erythroid-associated genes, while repressing leukocyte-associated genes in both K562 and CD36-positive primary human proerythroblasts derived from HSCs. We find that SRA-regulated genes are enriched by both CTCF and SRA bindings. Further, silencing of SRA decreases expression of the erythroid-specific markers TFRC and GYPA, and down-regulates expression of globin genes in both K562 and human proerythroblast cells. Taken together, our findings establish that the lncRNA SRA occupies chromatin, and promotes transcription of erythroid genes, therefore facilitating human erythroid transcriptional program.

GATA1 and cooperating mutations in myeloid leukaemia of Down syndrome

Myeloid leukaemia of Down syndrome (ML-DS) is an acute megakaryoblastic/erythroid leukaemia uniquely found in children with Down syndrome (constitutive trisomy 21). It has a unique clinical course, being preceded by a pre-leukaemic condition known as transient abnormal myelopoiesis (TAM), and provides an excellent model to study multistep leukaemogenesis. Both TAM and ML-DS blasts carry acquired N-terminal truncating mutations in the erythro-megakaryocytic transcription factor GATA1. These result in exclusive production of a shorter isoform (GATA1s). The majority of TAM cases resolve spontaneously without the need for treatment; however, around 10% acquire additional cooperating mutations and transform to leukaemia, with differentiation block and clinically significant cytopenias. Transformation is driven by the acquisition of additional mutation(s), which cooperate with GATA1s to perturb normal haematopoiesis.

The Roles of Cholesterol and Its Metabolites in Normal and Malignant Hematopoiesis

Hematopoiesis is sustained throughout life by hematopoietic stem cells (HSCs) that are capable of self-renewal and differentiation into hematopoietic progenitor cells (HPCs). There is accumulating evidence that cholesterol homeostasis is an important factor in the regulation of hematopoiesis. Increased cholesterol levels are known to promote proliferation and mobilization of HSCs, while hypercholesterolemia is associated with expansion of myeloid cells in the peripheral blood and links hematopoiesis with cardiovascular disease. Cholesterol is a precursor to steroid hormones, oxysterols, and bile acids. Among steroid hormones, 17β-estradiol (E2) induces HSC division and E2-estrogen receptor α (ERα) signaling causes sexual dimorphism of HSC division rate. Oxysterols are oxygenated derivatives of cholesterol and key substrates for bile acid synthesis and are considered to be bioactive lipids, and recent studies have begun to reveal their important roles in the hematopoietic and immune systems. 27-Hydroxycholesterol (27HC) acts as an endogenous selective estrogen receptor modulator and induces ERα-dependent HSC mobilization and extramedullary hematopoiesis. 7α,25-dihydroxycholesterol (7α,25HC) acts as a ligand for Epstein-Barr virus-induced gene 2 (EBI2) and directs migration of B cells in the spleen during the adaptive immune response. Bile acids serve as chemical chaperones and alleviate endoplasmic reticulum stress in HSCs. Cholesterol metabolism is dysregulated in hematologic malignancies, and statins, which inhibit de novo cholesterol synthesis, have cytotoxic effects in malignant hematopoietic cells. In this review, recent advances in our understanding of the roles of cholesterol and its metabolites as signaling molecules in the regulation of hematopoiesis and hematologic malignancies are summarized.

Influence of diet and metabolism on hematopoietic stem cells and leukemia development following ionizing radiation exposure

PURPOSE

The review aims to discuss the prominence of dietary and metabolic regulators in maintaining hematopoietic stem cell (HSC) function, long-term self-renewal, and differentiation.

RESULTS

Most adult stem cells are preserved in a quiescent, nonmotile state in vivo which acts as a "protective state" for stem cells to reduce endogenous stress provoked by DNA replication and cellular respiration as well as exogenous environmental stress. The dynamic balance between quiescence, self-renewal and differentiation is critical for supporting a functional blood system throughout life of an organism. Stress-conditions, for example ionizing radiation exposure can trigger the blood forming HSCs to proliferate and migrate through extramedullary tissues to expand the number of HSCs and increase hematopoiesis. In addition, a wealth of investigation validated that deregulation of this balance plays a critical pathogenic role in various different hematopoietic diseases including the leukemia development.

CONCLUSION

The review summarizes the current knowledge on how alterations in dietary and metabolic factors could alter the risk of leukemia development following ionizing radiation exposure by inhibiting or even reversing the leukemic progression. Understanding the influence of diet, metabolism, and epigenetics on radiation-induced leukemogenesis may lead to the development of practical interventions to reduce the risk in exposed populations.

Associations between Serum Sex Hormone Concentrations and Whole Blood Gene Expression Profiles in the General Population

Background

Despite observational evidence from epidemiological and clinical studies associating sex hormones with various cardiometabolic risk factors or diseases, pathophysiological explanations are sparse to date. To reveal putative functional insights, we analyzed associations between sex hormone levels and whole blood gene expression profiles.

Methods

We used data of 991 individuals from the population-based Study of Health in Pomerania (SHIP-TREND) with whole blood gene expression levels determined by array-based transcriptional profiling and serum concentrations of total testosterone (TT), sex hormone-binding globulin (SHBG), free testosterone (free T), dehydroepiandrosterone sulfate (DHEAS), androstenedione (AD), estradiol (E2), and estrone (E1) measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and immunoassay. Associations between sex hormone concentrations and gene expression profiles were analyzed using sex-specific regression models adjusted for age, body mass index, and technical covariables.

Results

In men, positive correlations were detected between AD and DDIT4 mRNA levels, as well as between SHBG and the mRNA levels of RPIA, RIOK3, GYPB, BPGM, and RAB2B. No additional significant associations were observed.

Conclusions

Besides the associations between AD and DDIT4 expression and SHBG and the transcript levels of RPIA, RIOK3, GYPB, BPGM, and RAB2B, the present study did not indicate any association between sex hormone concentrations and whole blood gene expression profiles in men and women from the general population.

Identification of NuRSERY, a new functional HDAC complex composed by HDAC5, GATA1, EKLF and pERK present in human erythroid cells

To clarify the role of HDACs in erythropoiesis, expression, activity and function of class I (HDAC1, HDAC2, HDAC3) and class IIa (HDAC4, HDAC5) HDACs during in vitro maturation of human erythroblasts were compared. During erythroid maturation, expression of HDAC1, HDAC2 and HDAC3 remained constant and activity and GATA1 association (its partner of the NuRD complex), of HDAC1 increased. By contrast, HDAC4 content drastically decreased and HDAC5 remained constant in content but decreased in activity. In erythroid cells, pull down experiments identified the presence of a novel complex formed by HDAC5, GATA1, EKLF and pERK which was instead undetectable in cells of the megakaryocytic lineage. With erythroid maturation, association among HDAC5, GATA1 and EKLF persisted but levels of pERK sharply decreased. Treatment of erythroleukemic cells with inhibitors of ERK phosphorylation reduced by >90% the total and nuclear content of HDAC5, GATA1 and EKLF, suggesting that ERK phosphorylation is required for the formation of this complex. Based on the function of class IIa HDACs as chaperones of other proteins to the nucleus and the erythroid-specificity of HDAC5 localization, this novel HDAC complex was named nuclear remodeling shuttle erythroid (NuRSERY). Exposure of erythroid cells to the class II-selective HDAC inhibitor (HDACi) APHA9 increased γ/(γ+β) globin expression ratios (Mai et al., 2007), suggesting that NuRSERY may regulate globin gene expression. In agreement with this hypothesis, exposure of erythroid cells to APHA9 greatly reduced the association among HDAC5, GATA1 and EKLF. Since exposure to APHA9 did not affect survival rates or p21 activation, NuRSERY may represent a novel, possibly less toxic, target for epigenetic therapies of hemoglobinopaties and other disorders.

Oestrogen increases haematopoietic stem-cell self-renewal in females and during pregnancy

Sexually dimorphic mammalian tissues, including sexual organs and the brain, contain stem cells that are directly or indirectly regulated by sex hormones^1-6. An important question is whether stem cells also exhibit sex differences in physiological function and hormonal regulation in tissues that do not exhibit sex-specific morphological differences. The terminal differentiation and function of some haematopoietic cells are regulated by sex hormones^7-10 but haematopoietic stem cell (HSC) function is thought to be similar in both sexes. Here we show that mouse HSCs exhibit sex differences in cell cycle regulation by estrogen. HSCs in females divide significantly more frequently than in males. This difference depended on the ovaries but not the testes. Administration of estradiol, a hormone produced mainly in the ovaries, increased HSC cell division in males and females. Estrogen levels increased during pregnancy, increasing HSC division, HSC frequency, cellularity, and erythropoiesis in the spleen. HSCs expressed high levels of estrogen receptor α (ERα). Conditional deletion of ERα from HSCs reduced HSC division in female, but not male, mice and attenuated the increases in HSC division, HSC frequency, and erythropoiesis during pregnancy. Estrogen/ERα signaling promotes HSC self-renewal, expanding splenic HSCs and erythropoiesis during pregnancy.

Activation of mitogen- and stress-activated kinase 1 is required for proliferation of breast cancer cells in response to estrogens or progestins

Growth of breast cancers is often dependent on ovarian steroid hormones making the tumors responsive to antagonists of hormone receptors. However, eventually the tumors become hormone independent, raising the need to identify downstream targets for the inhibition of tumor growth. One possibility is to focus on the signaling mechanisms used by ovarian steroid hormones to induce breast cancer cell proliferation. Here we report that the mitogen- and stress-activated kinase 1 (MSK1) could be a potential druggable target. Using the breast cancer cell line T47D, we show that estrogens (E2) and progestins activate MSK1, which forms a complex with the corresponding hormone receptor. Inhibition of MSK1 activity with H89 or its depletion by MSK1 short hairpin RNAs (shRNAs) specifically abrogates cell proliferation in response to E2 or progestins without affecting serum-induced cell proliferation. MSK1 activity is required for the transition from the G1- to the S-phase of the cell cycle and inhibition of MSK1 compromises both estradiol- and progestin-dependent induction of cell cycle genes. ChIP-seq experiments identified binding of MSK1 to progesterone receptor-binding sites associated with hormone-responsive genes. MSK1 recruitment to epigenetically defined enhancer regions supports the need of MSK1 as a chromatin remodeler in hormone-dependent regulation of gene transcription. In agreement with this interpretation, expression of a histone H3 mutated at S10 eliminates the hormonal effect on cell proliferation and on induction of relevant target genes. Finally, we show that E2- or progestin-dependent growth of T47D cells xenografted in immunodefficient mice is inhibited by depletion of MSK1, indicating that our findings are not restricted to cultured cells, and that MSK1 plays an important role for hormone-dependent breast cancer growth in a more physiological context.

Chronic estradiol treatment reduces platelet responses and protects mice from thromboembolism through the hematopoietic estrogen receptor α

Although estrogens are known to have a deleterious effect on the venous thrombosis risk and a preventive action on the development of arterial atheroma, their effect on platelet function in vivo remains unclear. Here, we demonstrate that a chronic high physiologic level of estradiol (E2) in mice leads to a marked decrease in platelet responsiveness ex vivo and in vivo compared with ovariectomized controls. E2 treatment led to increased bleeding time and a resistance to thromboembolism. Hematopoietic chimera mice harboring a selective deletion of estrogen receptors (ERs) α or β were used to demonstrate that the effects of E2 were exclusively because of hematopoietic ERα. Within ERα the activation function-1 domain was not required for resistance to thromboembolism, as was previously shown for atheroprotection. This domain is mandatory for E2-mediated reproductive function and suggests that this role is controlled independently. Differential proteomics indicated that E2 treatment modulated the expression of platelet proteins including β1 tubulin and a few other proteins that may impact platelet production and activation. Overall, these data demonstrate a previously unrecognized role for E2 in regulating the platelet proteome and platelet function, and point to new potential antithrombotic and vasculoprotective therapeutic strategies.

Ex-vivo expansion of red blood cells: how real for transfusion in humans?

Blood transfusion is indispensable for modern medicine. In developed countries, the blood supply is adequate and safe but blood for alloimmunized patients is often unavailable. Concerns are increasing that donations may become inadequate in the future as the population ages prompting a search for alternative transfusion products. Improvements in culture conditions and proof-of-principle studies in animal models have suggested that ex-vivo expanded red cells may represent such a product. Compared to other cell therapies transfusion poses the unique challenge of requiring great cell doses (2.5×10(12) cells vs 10(7) cells). Although production of such cell numbers is theoretically possible, current technologies generate red cells in numbers sufficient only for safety studies. It is conceived that by the time these studies will be completed, technical barriers to mass cell production will have been eliminated making transfusion with ex-vivo generated red cells a reality.

Cell signaling pathways for the regulation of GATA4 transcription factor: Implications for cell growth and apoptosis

GATA4 is a member of the GATA family of zinc finger transcription factor, which regulates gene transcription by binding to GATA elements. GATA4 was originally discovered as a regulator of cardiac development and subsequently identified as a major regulator of adult cardiac hypertrophy. GATA4 regulates gene expression of various genes, which are involved in cardiac development and cardiac hypertrophy and heart failure. In addition to the heart, GATA4 plays important roles in the reproductive system, gastrointestinal system, respiratory system and cancer. Positive and negative regulations of GATA4 therefore are important components of biologic functions. The activation of GATA4 occurs via various cell signaling events. Earlier studies have identified protein-protein interactions of GATA4 with other factors. The discovery of interactions of GATA4 with nuclear factor for activated T cells (NFAT) revealed the importance of calcium signaling in the activation of GATA4. GATA4 can also be phosphorylated by mitogen activated protein kinases and protein kinase A. Lysine modifications also occur on the GATA4 molecule including acetylation and sumoylation. Both reactive oxygen-dependent and -independent antioxidant-sensitive pathways for GATA4 activation have also been demonstrated. The GATA4 activity is also regulated by modulating the level of GATA4 expression via transcriptional as well as translational mechanisms. This work summarizes the current understanding of regulatory mechanisms for modulating GATA4 activity.

Phosphorylation of Estrogen Receptor α at serine 118 directs recruitment of promoter complexes and gene-specific transcription

Phosphorylation of estrogen receptor α (ERα) is important for receptor function, although the role of specific ERα phosphorylation sites in ERα-mediated transcription remains to be fully evaluated. Transcriptional activation by ERα involves dynamic, coordinate interactions with coregulators at promoter enhancer elements to effect gene expression. To determine whether ERα phosphorylation affects recruitment of unique protein complexes at gene-specific promoters, changes in ERα Ser118 phosphorylation were assessed for effects on receptor and coregulator recruitment and transcription of ERα-regulated genes. Chromatin immunoprecipitation assays to measure promoter association found a 17β-estradiol (E2)-dependent recruitment of ERα at 150 min to ERα-regulated promoters, whereas ERα phosphorylated at Ser118 was dissociated from promoters after E2 treatment. Mutation of Ser118 to alanine (S118A) altered unliganded and ligand-induced association of ERα and p160 coregulators with ERα target promoters when compared with wild-type (WT)-ERα transfection. S118A and WT-ERα exhibited a similar level of recruitment to the estrogen response element-driven pS2 promoter and induced pS2 mRNA after E2 treatment. Although WT-ERα was recruited to c-myc and cyclin D1 promoters after E2 treatment and induced mRNA expression, S118A exhibited reduced interaction with c-myc and cyclin D1 promoters, and E2 did not induce c-myc and cyclin D1 mRNA. In addition, S118A resulted in increased recruitment of steroid receptor coactivator-1, glucocorticoid receptor interacting protein-1, and activated in breast cancer-1 to pS2, c-myc, and cyclin D1 irrespective of the presence of E2. Together, these data indicate that site specific phosphorylation of ERα directs gene-specific recruitment of ERα and transcriptional coregulators to ERα target gene promoters.

Global analysis of estrogen receptor beta binding to breast cancer cell genome reveals an extensive interplay with estrogen receptor alpha for target gene regulation

Background

Estrogen receptors alpha (ERα) and beta (ERβ) are transcription factors (TFs) that mediate estrogen signaling and define the hormone-responsive phenotype of breast cancer (BC). The two receptors can be found co-expressed and play specific, often opposite, roles, with ERβ being able to modulate the effects of ERα on gene transcription and cell proliferation. ERβ is frequently lost in BC, where its presence generally correlates with a better prognosis of the disease. The identification of the genomic targets of ERβ in hormone-responsive BC cells is thus a critical step to elucidate the roles of this receptor in estrogen signaling and tumor cell biology.

Results

Expression of full-length ERβ in hormone-responsive, ERα-positive MCF-7 cells resulted in a marked reduction in cell proliferation in response to estrogen and marked effects on the cell transcriptome. By ChIP-Seq we identified 9702 ERβ and 6024 ERα binding sites in estrogen-stimulated cells, comprising sites occupied by either ERβ, ERα or both ER subtypes. A search for TF binding matrices revealed that the majority of the binding sites identified comprise one or more Estrogen Response Element and the remaining show binding matrixes for other TFs known to mediate ER interaction with chromatin by tethering, including AP2, E2F and SP1. Of 921 genes differentially regulated by estrogen in ERβ+ vs ERβ- cells, 424 showed one or more ERβ site within 10 kb. These putative primary ERβ target genes control cell proliferation, death, differentiation, motility and adhesion, signal transduction and transcription, key cellular processes that might explain the biological and clinical phenotype of tumors expressing this ER subtype. ERβ binding in close proximity of several miRNA genes and in the mitochondrial genome, suggests the possible involvement of this receptor in small non-coding RNA biogenesis and mitochondrial genome functions.

Conclusions

Results indicate that the vast majority of the genomic targets of ERβ can bind also ERα, suggesting that the overall action of ERβ on the genome of hormone-responsive BC cells depends mainly on the relative concentration of both ERs in the cell.

Gastrin increases its own synthesis in gastrointestinal cancer cells via the CCK2 receptor

The involvement of the gastrointestinal hormone gastrin in the development of gastrointestinal cancer is highly controversial. Here we demonstrate a positive-feedback loop whereby gastrin, acting via the CCK2 receptor, increases its own expression. Such an autocrine loop has not previously been reported for any other gastrointestinal hormone. Gastrin promoter activation was dependent on the MAP kinase pathway and did not involve Sp1 binding sites or epidermal growth factor receptor transactivation. As the treatment of gastrointestinal cancer cells with amidated gastrin led to increased expression of non-amidated gastrins, the positive-feedback loop may contribute to the sustained increase in circulating gastrins observed in colorectal cancer patients.

Estrogen receptor alpha regulates retinaldehyde dehydrogenase 1 expression in rat anterior pituitary cells

Retinoic acid (RA) plays a critical role in embryonic development, growth, and reproduction. RA is synthesized from retinoids via oxidation processes, and the oxidation of retinal to RA is catalyzed by the retinaldehyde dehydrogenases (RALDHs). We previously reported that RALDH1 mRNA was expressed in the anterior pituitary glands of adult rats and suppressed by administration of 17beta-estradiol in vivo. However, little is known about the mechanism regulating pituitary RALDH1 expression. In order to characterize the mechanism of estrogen-induced RALDH1 reduction, we examined the effect of 17beta-estradiol on the regulation of pituitary RALDH1 gene expression and protein production both in vivo and in vitro. Using quantitative real-time PCR and immunoblot analysis, we found that levels of RALDH1 gene expression and protein production markedly decreased after 1-week treatment with 17beta-estradiol in male rats. In immunohistochemical analysis, RALDH1-immunoreaction was observed in prolactin cells and folliculo-stellate cells. In 17beta-estradiol-treated rats, RALDH1-immunoreactivity was lower in prolactin cells, but not in folliculo-stellate cells. Treatment of isolated anterior pituitary cells with 17beta-estradiol (10(-14) - 10(-8) M) decreased expression of RALDH1 mRNA in a dose-dependent manner. Estradiol-induced suppression of RALDH1 expression was completely blocked by the estrogen receptor (ER) antagonist ICI 182, 780. The ERalpha-selective agonist propylpyrazole triol (10(-8) M) mimicked the effect of 17beta-estradiol on RALDH1 expression, but the ERbeta-selective agonist diarylpropionitrile (10(-8) M) did not. These results strongly suggest that RALDH1 mRNA expression is suppressed by 17beta-estradiol through ERalpha, and that estrogen regulates the expression of RALDH1 and production of RA in the anterior pituitary gland.

Detection of ERalpha-SRC-1 interactions using bioluminescent resonance energy transfer

Bioluminescent Resonance Energy Transfer is a naturally occurring phenomenon that can be exploited to explore protein-protein interactions in real-time in intact cells and cellular extracts. It detects energy transferred between a bioluminescent donor enzyme (Renilla luciferase) fusion protein and a fluorescent (GFP(2), a mutant of Green Fluorescent Protein) acceptor fusion protein. Optimal detection of BRET(2) energy transfer relies on the distance and orientation generated by the fusion proteins. This chapter describes in detail the BRET(2) assay as it is used to examine the physical interaction between the nuclear receptor ERalpha and the transcriptional coactivator SRC-1. Description of methods include selection of donor and acceptor combinations, fusion construct generation and validation, cell culture and transfection, individual fluorescence and luminescence detection, BRET(2) detection, and data analysis.

DNA-binding ability of NF-kappaB is affected differently by ERalpha and ERbeta and its activation results in inhibition of estrogen responsiveness

Estrogenic effects involve interactions between estrogen receptors (ERs), response elements, and nuclear proteins. It is hypothesized that interaction between ER and NF-kappa B may affect the regulation of responsive genes. Electrophoretic mobility shift assay (EMSA) was performed to assess if the interaction of ERs and NF- kappaB affect their respective DNA-binding activities, and alkaline phosphatase assay was done to evaluate estrogenic activity. EMSA revealed that ERs inhibit DNA-binding of p50 and p65, whereas p50 did not impair ER alpha binding. Stimulation with estradiol inhibited DNA binding of NF-kappaB in ERalpha-transfected endometrial stromal cells (ESCs). Moreover, activation of NF-kappaB significantly decreased estrogen responsiveness of Ishikawa cells and ERalpha-transfected ESC. Our results suggest that ERs downregulate NF-kappaB-dependent gene activation by directly preventing DNA binding. However, NF-kappaB-mediated inhibition of ER-dependent gene activation may be carried out indirectly rather than through a direct inhibition of ER-DNA binding. These findings offer new insight into the specific role of ERalpha and could eventually help in developing therapeutics for endometriosis.

Hematological changes associated with egg production: estrogen dependence and repeatability

The `cost of reproduction' (i.e. the trade-off between current reproduction and future fecundity and/or survival) is a central concept in life history theory, yet we still know very little about the physiological mechanisms underlying such costs. Recently it has been recognized that reproduction itself or the regulatory (hormonal) mechanisms underlying reproduction might result in `costs' (cf. resource-allocation based mechanisms). As one example,it has been suggested that the decrease in hematocrit observed during egg production in birds might be due to antagonistic pleiotropic effects of estrogens. This could generate costs of reproduction by reducing oxygen-carrying capacity during subsequent aerobically demanding stages such as chick-provisioning. Here we show that the reduction in hematocrit during egg-laying is dependent on receptor-mediated actions of endogenous estrogens:blocking estrogen receptors using the anti-estrogen tamoxifen reduces the decrease in hematocrit during egg production in female zebra finches(Taeniopygia guttata) such that hematocrit at the 1-egg stage is not significantly different than pre-breeding, baseline values. We also show that both pre-breeding hematocrit and the decrease in hematocrit associated with egg production are repeatable, and that females with the highest pre-breeding hematocrit values tend to show the largest decreases in hematocrit during egg production. We suggest that hematological changes during egg production are a good candidate mechanism for a regulatory-network based trade-off involving antagonistic pleiotropic effects of estrogens, which otherwise have essential reproductive functions.

Epigenetic regulation of normal and malignant hematopoiesis

The molecular processes governing hematopoiesis involve the interplay between lineage-specific transcription factors and a series of epigenetic tags, including DNA methylation and covalent histone tail modifications, such as acetylation, methylation, phosphorylation, SUMOylation and ubiquitylation. These post-translational modifications, which collectively constitute the 'histone code', are capable of affecting chromatin structure and gene transcription and are catalysed by opposing families of enzymes, allowing the developmental potential of hematopoietic stem cells to be dynamically regulated. The essential role of these enzymes in regulating normal blood development is highlighted by the finding that members from all families of chromatin regulators are targets for dysregulation in many hematological malignancies, and that patterns of histone modification are globally affected in cancer as well as the regulatory regions of specific oncogenes and tumor suppressors. The discovery that these epigenetic marks can be reversed by compounds targeting aberrant transcription factor/co-activator/co-repressor interactions and histone-modifying activities, provides the basis for an exciting field in which the epigenome of cancer cells may be manipulated with potential therapeutic benefits.

Mechanisms of primary and secondary estrogen target gene regulation in breast cancer cells

Estrogen receptors (ERs), which mediate the proliferative action of estrogens in breast cancer cells, are ligand-dependent transcription factors that regulate expression of their primary target genes through several mechanisms. In addition to direct binding to cognate DNA sequences, ERs can be recruited to DNA through other transcription factors (tethering), or affect gene transcription through modulation of signaling cascades by non-genomic mechanisms of action. To better characterize the mechanisms of gene regulation by estrogens, we have identified more than 700 putative primary and about 1300 putative secondary target genes of estradiol in MCF-7 cells through microarray analysis performed in the presence or absence of the translation inhibitor cycloheximide. Although siRNA-mediated inhibition of ERalpha expression antagonized the effects of estradiol on up- and down-regulated primary target genes, estrogen response elements (EREs) were enriched only in the vicinity of up-regulated genes. Binding sites for several other transcription factors, including proteins known to tether ERalpha, were enriched in up- and/or down-regulated primary targets. Secondary estrogen targets were particularly enriched in sites for E2F family members, several of which were transcriptionally regulated by estradiol, consistent with a major role of these factors in mediating the effects of estrogens on gene expression and cellular growth.

Determining the transrepression activity of xenoestrogen on nuclear factor-kappa B in Cos-1 cells by estrogen receptor-alpha

Functional assays have been used to define the estrogenicity of xenoestrogens in cotransfection studies employing estrogen receptors in various cell lines. It is known that estrogen is able to affect transcription from other nuclear transcription factors, especially the nuclear factor-kappa B (NF-kappa B). The ability of selected xenoestrogens (methoxychlor [MXC], dieldrin, and o',p'-DDT) to transrepress the NF-kappa B-mediated transcription in Cos-1 cells was evaluated by cotransfection of human estrogen receptor-alpha (hERalpha). These xenoestrogens have been described as comparably potent xenoestrogens, whereas their relative binding activity (RBA) has been relegated to a lower order as compare to estrogen. The two NF-kappa B response element-containing SV40 promoter and -242/+54 cytomegalovirus (CMV)-expressing firefly luciferase (2 x NRE-PV-Luc and 2 x NRE-CMV-Luc, respectively) were transfected into Cos-1 cells with pRL-tk, expressing the renilla luciferase as internal control. The estrogen receptor was expressed from cytomegalovirus major immediate early promoter (CMV-MIEP) (CMV5-hERalpha). Treatment with 1 nM estrogen (E(2)) (26.2%), 5 nM E(2) (41.4%; p < .05), and xenoestrogens (methoxychlor [1 nM: 29.6%, p < .05; 10 nM: 22.6%), dieldrin [1 nM: 10.3%; 10 nM: 36.06%, p < .05], and o',p'-DDT [1 nM: 17.0%; 10 nM: 7.15%]) repressed transcription from 2 x NREX-PV-Luc. The antiestrogen, ICI 182,780, failed to antagonize the effects of xenoestrogens. The effects of xenoestrogens in transrepression of NF-kappa B by ERalpha were similar when 2 x NRE-CMV-Luc was employed as reporter. Statistically significant (p < .01) repression by 1 nM E(2) (69.2%), 5 nM E(2) (69.1%), 1 nM o',p'-DDT (51.4%), 1 nM dieldrin (47.3%), and 1 nM MXC (73.3%) were observed. The effect of these xenoestrogens without ERalpha cotransfection on 2 x NRE-PV-Luc- and 2 x NRE-CMV-Luc-mediated NF-kappa B transcription was not affected by the treatment alone. It is concluded that xenoestrogens, like estrogens, are capable of producing transrepression of NF-kappa B by hERalpha.

Positive Cross-Regulatory Loop Ties GATA-3 to Estrogen Receptor α Expression in Breast Cancer

The transcription factor GATA-3 is required for normal mammary gland development, and its expression is highly correlated with estrogen receptor alpha (ER alpha) in human breast tumors. However, the functional role of GATA-3 in ER alpha-positive breast cancers is yet to be established. Here, we show that GATA-3 is required for estradiol stimulation of cell cycle progression in breast cancer cells. The role of GATA-3 in estradiol signaling requires the direct positive regulation of the expression of the ER alpha gene itself by GATA-3. GATA-3 binds to two cis-regulatory elements located within the ER alpha gene, and this is required for RNA polymerase II recruitment to ER alpha promoters. Reciprocally, ER alpha directly stimulates the transcription of the GATA-3 gene, indicating that these two factors are involved in a positive cross-regulatory loop. Moreover, GATA-3 and ER alpha regulate their own expression in breast cancer cells. Hence, this transcriptional coregulatory mechanism accounts for the robust coexpression of GATA-3 and ER alpha in human breast cancers. In addition, these results highlight the crucial role of GATA-3 for the response of ER alpha-positive breast cancers to estradiol. Moreover, they identify GATA-3 as a critical component of the master cell-type-specific transcriptional network including ER alpha and FoxA1 that dictates the phenotype of hormone-dependent breast cancer.

Estrogen-induced and TAFII30-mediated gene repression by direct recruitment of the estrogen receptor and co-repressors to the core promoter and its reversal by tamoxifen

Estradiol (E2) acts through the estrogen receptor (ER) to downregulate many genes, and tamoxifen (Tam) largely reverses this repression but the underlying mechanisms are unclear. Repression of the folate receptor (FR)-alpha P4 core promoter by ER is enhanced by E2 and reversed by Tam. This effect was unaffected by inhibition of new protein synthesis and required the E/F and the DNA-binding domains of ER without direct binding of ER to DNA. The repression by E2/ER was not specific for either Sp1 or TATA elements but was loosely selective for the initiator and flanking sequence. Insertion of a response element or a relatively strong Sp1 cluster to recruit ER upstream of the core promoters caused a switch to activation by E2/ER that was inhibited by Tam. In nuclear extracts, association of ER with a biotinylated core promoter fragment was promoted by E2 but Tam blocked this effect. Repression/de-repression of the P4 promoter and endogenous FR-alpha expression by E2/Tam required SMRT and/or NCoR. ER associated with the chromosomal P4 promoter and SMRT and NCoR associated with it in an ER-dependent manner; these associations were favored by E2 but disrupted by Tam, in the short term, without changes in ER expression. TAFII30 was required for optimal P4 promoter activity and for the repressive association of ER. E2 may thus maintain a low transcriptional status of genes by favoring direct TAFII30-dependent association of ER with the core promoter in a co-repressor complex containing SMRT and/or NCoR; this repression is overridden in target genes containing an upstream element that strongly recruits ER. In addition to suppressing the activation of classical E2 target genes, Tam may upregulate genes by passively dissociating the ER co-repressor complex.

GATA3 protein as a MUC1 transcriptional regulator in breast cancer cells

Introduction

Recent studies have demonstrated that members of the GATA-binding protein (GATA) family (GATA4 and GATA5) might have pivotal roles in the transcriptional upregulation of mucin genes (MUC2, MUC3 and MUC4) in gastrointestinal epithelium. The zinc-finger GATA3 transcription factor has been reported to be involved in the growth control and differentiation of breast epithelial cells. In SAGE (serial analysis of gene expression) studies we observed an intriguing significant correlation between GATA3 and MUC1 mRNA expression in breast carcinomas. We therefore designed the present study to elucidate whether MUC1 expression is regulated by GATA3 in breast cancer cells.

Methods

Promoter sequence analysis of the MUC1 gene identified six GATA cis consensus elements in the 5' flanking region (GATA1, GATA3 and four GATA-like sequences). Chromatin immunoprecipitation and electrophoretic mobility-shift assays were employed to study the presence of a functional GATA3-binding site. GATA3 and MUC1 expression was analyzed in vitro with a GATA3 knockdown assay. Furthermore, expression of GATA3 and MUC1 genes was analyzed by real-time RT-PCR and immunohistochemistry on breast cancer-specific tissue microarrays.

Results

We confirmed the presence of a functional GATA3-binding site on the MUC1 promoter region in the MCF7 cell line. We determined that GATA3 knockdown assays led to a decrease in MUC1 protein expression in MCF7 and T47D cells. In addition, we detected a statistically significant correlation in expression between GATA3 and MUC1 genes at the mRNA and protein levels both in normal breast epithelium and in breast carcinomas (p = 0.01). GATA3 expression was also highly associated with estrogen receptor and progesterone receptor status (p = 0.0001) and tumor grade (p = 0.004) in breast carcinomas.

Conclusion

Our study provides evidence indicating that GATA3 is probably a mediator for the transcriptional upregulation of MUC1 expression in some breast cancers.

Essential role of GATA2 in the negative regulation of thyrotropin beta gene by thyroid hormone and its receptors

Previously we reported that the negative regulation of the TSHbeta gene by T(3) and its receptor [thyroid hormone receptor (TR)] is observed in CV1 cells when GATA2 and Pit1 are introduced. Using this system, we further studied the mechanism of TSHbeta inhibition. The negative regulatory element (NRE), which had been reported to mediate T(3)-bound TR (T(3)-TR)-dependent inhibition, is dispensable, because deletion or mutation of NRE did not impair suppression. The reporter construct, TSHbeta-D4-chloramphenicol acetyltransferase, which possesses only the binding sites for Pit1 and GATA2, was activated by GATA2 alone, and this transactivation was specifically inhibited by T(3)-TR. The Zn finger region of GATA2 interacts with the DNA-binding domain of TR in a T(3)-independent manner. The suppression by T(3)-TR was impaired by overexpression of a dominant-negative type TR-associated protein (TRAP) 220, an N- and C-terminal deletion construct, indicating the participation of TRAP220. Chromatin immunoprecipitation assays with a thyrotroph cell line, TalphaT1, revealed that T(3) treatment recruited histone deacetylase 3, reduced the acetylation of histone H4, and caused the dissociation of TRAP220 within 15-30 min. The reduction of histone H4 acetylation was transient, whereas the dissociation of TRAP220 persisted for a longer period. In the negative regulation of the TSHbeta gene by T(3)-TR we report that 1) GATA2 is the major transcriptional activator of the TSHbeta gene, 2) the putative NRE previously reported is not required, 3) TR-DNA-binding domain directly interacts with the Zn finger region of GATA2, and 4) histone deacetylation and TRAP220 dissociation are important.

17 beta-estradiol modifies nitric oxide-sensitive guanylyl cyclase expression and down-regulates its activity in rat anterior pituitary gland

Previous studies showed that 17 beta-estradiol (17 beta-E2) regulates the nitric oxide (NO)/soluble guanylyl cyclase (sGC)/cGMP pathway in many tissues. Evidence from our laboratory indicates that 17 beta-E2 disrupts the inhibitory effect of NO on prolactin release, decreasing sGC activity and affecting the cGMP pathway in anterior pituitary gland of adult ovariectomized and estrogenized rats. To ascertain the mechanisms by which 17 beta-E2 affects sGC activity, we investigated the in vivo and in vitro effects of 17 beta-E2 on sGC protein and mRNA expression in anterior pituitary gland from immature female rats. In the present work, we showed that 17 beta-E2 acute treatment exerted opposite effects on the two sGC subunits, increasing alpha1 and decreasing beta1 subunit protein and mRNA expression. This action on sGC protein expression was maximal 6-9 h after 17 beta-E2 administration. 17beta-E2 also caused the same effect on mRNA expression at earlier times. Concomitantly, 17 beta-E2 dramatically decreased sGC activity 6 and 9 h after injection. These effects were specific of 17 beta-E2, because they were not observed with the administration of other steroids such as progesterone and 17 alpha-estradiol. This inhibitory action of 17beta-E2 on sGC also required the activation of estrogen receptor (ER), because treatment with the pure ER antagonist ICI 182,780 completely blocked 17 beta-E2 action. 17 beta-E2 acute treatment caused the same effects on pituitary cells in culture. These results suggest that 17 beta-E2 exerts an acute inhibitory effect on sGC in anterior pituitary gland by down-regulating sGC beta 1 subunit and sGC activity in a specific, ER-dependent manner.

MED220/thyroid receptor-associated protein 220 functions as a transcriptional coactivator with Pit-1 and GATA-2 on the thyrotropin-beta promoter in thyrotropes

Mediator (MED) 220/thyroid receptor-associated protein (TRAP) 220 is a transcriptional mediator that interacts with liganded thyroid/steroid hormone receptors. MED220 haploinsufficient heterozygotes exhibited hypothyroidism and reduced TSHbeta transcripts, suggesting a specific function for TSHbeta transcription. We previously demonstrated that Pit-1 and GATA-2 can bind to a composite element within the proximal TSHbeta promoter and synergistically activate transcription. We detected MED220 expression in TtT-97 thyrotropes by Northern and Western blot analysis. Cotransfections in CV-1 cells showed that Pit-1, GATA-2, or MED220 alone did not markedly stimulate the TSHbeta promoter. However, Pit-1 plus GATA-2 resulted in an 10-fold activation, demonstrating synergistic cooperativity. Titration of MED220 resulted in a further dose-dependent stimulation up to 25-fold that was promoter specific. Glutathione-S-transferase interaction studies showed that MED220 or GATA-2 each bound the homeodomain of Pit-1, whereas MED220 interacted independently with each zinc finger of GATA-2 but not with either terminus. MED220 interacted with GATA-2 and Pit-1 over a broad region of its N terminus. These regions of interaction were also important for maximal function. Coimmunoprecipitation confirmed that all three factors can interact in thyrotropes and chromatin immunoprecipitation demonstrated in vivo occupancy on the proximal TSHbeta promoter. Thus, the TSHbeta gene is maximally activated by a combination of three thyrotrope transcription factors that act via both protein-DNA and protein-protein interactions.

Cloning and functional analysis of promoters of three GnRH genes in a cichlid

Mechanisms regulating gonadotropin-releasing hormone (GnRH) types, a key molecule for reproductive physiology, remain unclear. In the present study, we cloned the promoters of GnRH1, GnRH2, and GnRH3 genes in the tilapia, Oreochromis niloticus; and found putative binding sites for glucocorticoid receptors, Sp1, C/EBP, GATA, and Oct-1, but not for androgen receptors in all three GnRH promoters using computer analysis. The presence of binding sites for progesterone receptors in GnRH1, estrogen receptors in GnRH1 and GnRH2, and thyroid hormone receptors in GnRH1 and GnRH3 suggests direct action of steroid hormones on GnRH types. Our observation of SOX and LINE-like sequences exclusively in GnRH1, COUP in GnRH2, and retinoid X receptors in GnRH3 suggests their role in sexual differentiation, midbrain segmentation, and visual cue integration, respectively. Thus, the characteristic binding sites for nuclear receptors and transcription factors support the notion that each GnRH type is regulated differently and has distinct physiological roles.

GATA-3 expression as a predictor of hormone response in breast cancer

BACKGROUND

Expression of estrogen receptor-alpha (ERalpha) as determined by immunohistochemistry of tumor tissue is currently the most clinically useful test to predict hormone responsiveness of breast cancer. Thirty percent of ERalpha-positive breast cancers do not respond to hormonal therapy. GATA-3 is a transcription factor that is expressed in association with ERalpha and there is evidence that GATA factors influence response to estrogen. In this pilot study, we investigated whether GATA-3 expression is associated with hormone response in breast cancer.

STUDY DESIGN

Breast cancer tissue was stained for GATA-3 expression by immunohistochemistry in ERalpha-positive cancers from 28 patients, 14 of whom were defined as hormone unresponsive (cases) and 14 of whom were age-matched controls with hormone-responsive, ERalpha-positive cancers (controls).

RESULTS

Comparing cases and controls, there were no differences in expression of ERalpha; progesterone receptor, ErbB2; or tumor grade. Using 20% nuclear staining to characterize tumors as GATA-3 positive or GATA-3 negative, 6 of 14 (43%) cancers in the hormone-unresponsive group and none of the controls were classified as GATA-3 negative (odds ratio, 8.2; 95% confidence interval, 1.2-infinity; p = 0.031). Using different cut points to characterize GATA-3 positivity yielded very similar results, indicating a positive association between lack of GATA-3 expression and lack of response to hormonal therapy.

CONCLUSIONS

The study suggests that analyzing ERalpha-positive breast tumors for GATA-3 using immunohistochemistry might improve prediction of hormone responsiveness. The association between GATA-3 expression and hormone response suggests that GATA-3 may play a role in mechanisms controlling response to estrogen.

Embryonic stem cells: prospects for developmental biology and cell therapy

Stem cells represent natural units of embryonic development and tissue regeneration. Embryonic stem (ES) cells, in particular, possess a nearly unlimited self-renewal capacity and developmental potential to differentiate into virtually any cell type of an organism. Mouse ES cells, which are established as permanent cell lines from early embryos, can be regarded as a versatile biological system that has led to major advances in cell and developmental biology. Human ES cell lines, which have recently been derived, may additionally serve as an unlimited source of cells for regenerative medicine. Before therapeutic applications can be realized, important problems must be resolved. Ethical issues surround the derivation of human ES cells from in vitro fertilized blastocysts. Current techniques for directed differentiation into somatic cell populations remain inefficient and yield heterogeneous cell populations. Transplanted ES cell progeny may not function normally in organs, might retain tumorigenic potential, and could be rejected immunologically. The number of human ES cell lines available for research may also be insufficient to adequately determine their therapeutic potential. Recent molecular and cellular advances with mouse ES cells, however, portend the successful use of these cells in therapeutics. This review therefore focuses both on mouse and human ES cells with respect to in vitro propagation and differentiation as well as their use in basic cell and developmental biology and toxicology and presents prospects for human ES cells in tissue regeneration and transplantation.

Mechanisms of estrogen receptor signaling: convergence of genomic and nongenomic actions on target genes

Estrogen receptors (ERs) act by regulating transcriptional processes. The classical mechanism of ER action involves estrogen binding to receptors in the nucleus, after which the receptors dimerize and bind to specific response elements known as estrogen response elements (EREs) located in the promoters of target genes. However, ERs can also regulate gene expression without directly binding to DNA. This occurs through protein-protein interactions with other DNA-binding transcription factors in the nucleus. In addition, membrane-associated ERs mediate nongenomic actions of estrogens, which can lead both to altered functions of proteins in the cytoplasm and to regulation of gene expression. The latter two mechanisms of ER action enable a broader range of genes to be regulated than the range that can be regulated by the classical mechanism of ER action alone. This review surveys our knowledge about the molecular mechanism by which ERs regulate the expression of genes that do not contain EREs, and it gives examples of the ways in which the genomic and nongenomic actions of ERs on target genes converge. Genomic and nongenomic actions of ERs that do not depend on EREs influence the physiology of many target tissues, and thus, increasing our understanding of the molecular mechanisms behind these actions is highly relevant for the development of novel drugs that target specific receptor actions.

GATA1 in normal and malignant hematopoiesis

In the late 1980s, several research groups independently discovered the founding member of the GATA family of transcription factors, GATA-1. Each group had evidence that GATA-1 played an important role in erythroid gene expression, but little did they know that it would turn out to be a key regulator of development of not only red blood cells, but of several other hematopoietic cell types as well. Furthermore, few would have guessed that missense mutations in GATA1 would cause inherited blood disorders, while acquired mutations would be found associated with essentially all cases of acute megakaryoblastic leukemia (AMKL) in children with Down syndrome (DS). With respect to the latter disorder, the presence of a GATA1 mutation is now arguably the defining feature of this leukemia. In this review, I will summarize our current knowledge of the role of GATA-1 in normal development, and discuss how mutations in GATA1 lead to abnormal and malignant hematopoiesis.

Tumour necrosis factor and PI3-kinase control oestrogen receptor alpha protein level and its transrepression function

Oestrogen receptor alpha (ERα) is an oestrogen-activated transcription factor, which regulates proliferation and differentiation of mammary epithelial cells by activating or repressing gene expression. ERα is a critical prognostic indicator and a therapeutic target for breast cancer. Patients with tumours that express higher level of ERα have better prognosis than patients with tumours that are ERα negative or express lower level of ERα. Better prognosis in ERα-positive patients is believed to be due to repression of proinvasive gene expression by ERα. Oestrogen receptor alpha represses gene expression by transrepressing the activity of the transcription factors such as nuclear factor-kappaB or by inducing the expression of transcriptional suppressors such as MTA3. In this report, we show that ERα transrepresses the expression of the proinvasive gene interleukin 6 (IL-6) in ERα-negative MDA-MB-231 breast cancer cells stably overexpressing ERα. Using these cells as well as ERα-positive MCF-7 and ZR-75-1 cells, we show that tumour necrosis factor alpha (TNFα) and the phosphatidylinositol-3-kinase (PI3-kinase) modulate transrepression function of ERα by reducing its stability. From these results, we propose that TNFα expression or PI3-kinase activation lead to reduced levels of ERα protein in cancer cells and corresponding loss of transrepression function and acquisition of an invasive phenotype.

Regulation of cardiac myocyte apoptosis by the GATA-4 transcription factor

Apoptosis of cardiac muscle cells plays important roles in the development of various heart diseases including myocardial infarction and anthracycline-induced cardiomyopathy. Understanding the regulatory mechanisms of cardiac myocyte apoptosis and survival is important for establishing therapeutic strategies against heart disease. Our recent experiments demonstrate that the GATA-4 transcription factor not only mediates cardiac hypertrophy, but also regulates apoptosis and survival of adult cardiac muscle cells. Apoptosis induced by anthracyclines is associated with decreased expression of GATA-4, while the restoration of GATA-4 levels via ectopic expression attenuated the apoptosis. Survival factors of cardiac myocytes such as hepatocyte growth factor and endothelin-1 activate GATA-4, and this signal transduction mechanism at least in part serves to protect the heart against oxidative stress.

Interaction between hex and GATA transcription factors in vascular endothelial cells inhibits flk-1/KDR-mediated vascular endothelial growth factor signaling

Recent evidence supports a role for GATA transcription factors as important signal intermediates in differentiated endothelial cells. The goal of this study was to identify proteins that interact with endothelial-derived GATA transcription factors. Using yeast two-hybrid screening, we identified hematopoietically expressed homeobox (Hex) as a GATA-binding partner in endothelial cells. The physical association between Hex and GATA was confirmed with immunoprecipitation in cultured cells. Hex overexpression resulted in decreased flk-1/KDR expression, both at the level of the promoter and the endogenous gene, and attenuated vascular endothelial growth factor-mediated tube formation in primary endothelial cell cultures. In electrophoretic mobility shift assays, Hex inhibited the binding of GATA-2 to the flk-1/KDR 5'-untranslated region GATA motif. Finally, in RNase protection assays, transforming growth factor beta1, which has been previously shown to decrease flk-1 expression by interfering with GATA binding activity, was shown to increase Hex expression in endothelial cells. Taken together, the present study provides evidence for a novel association between Hex and GATA and suggests that transforming growth factor beta-mediated repression of flk-1/KDR and vascular endothelial growth factor signaling involves the inducible formation of inhibitory Hex-GATA complexes.

Thrombin and phenotypic modulation of the endothelium

Thrombin signaling in the endothelium is linked to multiple phenotypic changes, including alterations in permeability, vasomotor tone, and leukocyte trafficking. The thrombin signal is transduced, at least in part, at the level of gene transcription. In this review, we focus on the role of thrombin signaling and transcriptional networks in mediating downstream gene expression and endothelial phenotype. In addition, we report the results of DNA microarrays in control and thrombin-treated endothelial cells. We conclude that (1) thrombin induces the upregulation and downregulation of multiple genes in the endothelium, (2) thrombin-mediated gene expression involves a multitude of transcription factors, and (3) future breakthroughs in the field will depend on a better understanding of the spatial and temporal dynamics of these transcriptional networks.

Testosterone metabolism, dose-response relationships and receptor polymorphisms: selected pharmacological/toxicological considerations on benefits versus risks of testosterone therapy in men

In this review selected toxicological problems related to testosterone therapy in hypogonadal men are discussed. Applying "classical" pharmacological/toxicological findings (e.g. animal studies on short- and long-term toxicity) to clinical situations is not very helpful. Molecular biological knowledge and especially evaluation of epidemiological studies, as well as intervention studies, on testosterone therapy in hypogonadal men are more useful. Potential risks include overdosage for lifestyle reasons, e.g. excessive muscle building and reduction of visceral obesity, when erythrocytosis occurs concomitantly. Modern galenic formulations of testosterone administration (e.g. transdermal gel, suitable testosterone esters for intramuscular application and newer oral preparations) avoid supraphysiological serum concentrations, therefore significantly reducing the toxicological risk. A hypothetical model of the toxicological risks of testosterone therapy is given that is based on the influence of testosterone metabolism (aromatization vs. reduction) of the respective parameter/target chosen. Finally, the great influence of polymorphisms of the androgen receptor on the assessment of toxicological risk and on the individualization of androgen therapy is shown. Already existing national, continental and international guidelines or recommendations for the testosterone therapy should be harmonized.

Growth factor signaling for cardioprotection against oxidative stress-induced apoptosis

The heart is subjected to oxidative stress during various clinical situations, such as ischemia-reperfusion injury and anthracycline chemotherapy. The loss of cardiac myocytes is the major problem in heart failure; thus, it is important to protect cardiac myocytes against cell death. Various growth factors, including insulin like growth factor, hepatocyte growth factor, endothelin-1, fibroblast growth factor, and transforming growth factor, have been shown to protect the heart against oxidative stress. The mechanism of growth factor-mediated cardioprotection may involve the attenuation of cardiac myocyte apoptosis. The present article summarizes the current knowledge on the molecular mechanisms of growth factor-mediated antiapoptotic signaling in cardiac myocytes. Insulin-like growth factor-1 activates phosphatidylinositol 3' -kinase and extracellular signal-regulated kinase pathways. Recent data showed that GATA-4 might be an important mediator of cardiac myocyte survival by endothelin-1 and hepatocyte growth factor. These growth factors, as well as mediators of growth factor-signaling, may be useful in therapeutic strategies against oxidative stress-induced cardiac injury.

An activator protein 1-like motif mediates 17beta-estradiol repression of gonadotropin-releasing hormone receptor promoter via an estrogen receptor alpha-dependent mechanism in ovarian and breast cancer cells

Although it is recognized that estrogen is one of the most important regulators of GnRH receptor (GnRHR) gene expression, the mechanism underlying the regulation at the transcriptional level is unknown. In the present study, we demonstrated that 17beta-estradiol (E2) repressed human GnRHR promoter via an activator protein 1-like motif and estrogen receptor-alpha, of which the DNA-binding domain and the ligand-binding domain were indispensable for the repression. Interestingly, the same cis-acting motif was also found to be important for both the basal activity and phorbol 12-myristate 13-acetate responsiveness of the GnRHR promoter. EMSAs indicated that multiple transcription factors including c-Jun and c-Fos bound to the activator protein 1-like site and that their DNA binding activity was not significantly affected by E2 treatment. In addition, we demonstrated that the E2 repression could be antagonized by phorbol 12-myristate 13-acetate, which stimulated c-Jun phosphorylation on serine 63, a process that is a prerequisite for recruitment of the transcriptional coactivator cAMP response element binding protein (CREB)-binding protein (CBP). Concomitantly, we found that overexpression of CBP could reverse the suppression in a dose-dependent manner. Taken together, our data indicate that E2-activated estrogen receptor-alpha represses human GnRHR gene transcription via an indirect mechanism involving CBP and possibly other transcriptional regulators.

Stress-induced activation of GATA-4 in cardiac muscle cells

GATA-4 regulates gene transcription in the heart. This study examined whether GATA-4 is influenced by stress-induced signaling events. Treatment of HL-1 cardiac muscle cells with mercury results in the induction of apoptosis that is blocked by overexpression of catalase. Similar to daunorubicin (DNR), mercury causes downregulation of GATA-4 mRNA expression. However, mercury is less effective in inducing apoptosis compared to DNR. Analyses of GATA-4 protein expression and activity reveal that mercury initially enhances the GATA-4 DNA-binding activity, before subsequent downregulation of GATA-4 expression. The mercury-induced GATA-4 activation is associated with a phosphorylation of GATA-4, which appears to occur via the MEK/ERK pathway. The level of phosphorylated GATA-4 is more slowly decreased by mercury or actinomycin D, compared to unphosphorylated GATA-4, suggesting that phosphorylated GATA-4 is more resistant to cellular degradation. Consistent with a previous finding that GATA-4 phosphorylation induces cell survival, mercury decreases cell death induced by DNR. These results suggest that cardiac muscle cells respond to mercury stress by eliciting MEK/ERK signaling to form phosphorylated GATA-4 that is more resistant to cellular degradation and induce cell survival.

Thrombin stimulation of vascular adhesion molecule-1 in endothelial cells is mediated by protein kinase C (PKC)-delta-NF-kappa B and PKC-zeta-GATA signaling pathways

We recently demonstrated that thrombin induces the expression of vascular adhesion molecule-1 (VCAM-1) in endothelial cells by an NF-kappaB- and GATA-dependent mechanism. In the present study, we describe the signaling pathways that mediate this response. Thrombin stimulation of the VCAM-1 gene and promoter in human umbilical vein endothelial cells was inhibited by preincubation with the phosphatidylinositol 3-kinase inhibitor, LY294002, the protein kinase C (PKC)-delta inhibitor, rottlerin, a PKC-zeta peptide inhibitor, or by overexpression of dominant negative (DN)-PKC-zeta. In electrophoretic mobility shift assays, thrombin-mediated induction of NF-kappaB p65 binding to two NF-kappaB motifs in the upstream promoter region of VCAM-1 was blocked by LY294002 and rottlerin, whereas the inducible binding of GATA-2 to a tandem GATA motif was inhibited by LY294002 and the PKC-zeta peptide inhibitor. In co-transfection assays, thrombin stimulation of a minimal promoter containing multimerized VCAM-1 NF-kappaB sites was inhibited by DN-PKC-delta but not DN-PKC-zeta. In contrast, thrombin-mediated transactivation of a minimal promoter containing tandem VCAM-1 GATA motifs was inhibited by DN-PKC-zeta but not DN-PKC-delta. Finally, thrombin failed to induce VCAM-1 expression in vascular smooth muscle cells. Taken together, these data suggest that the endothelial cell-specific effect of thrombin on VCAM-1 expression involves the coordinate activity of PKC-delta-NF-kappaB and PKC-zeta-GATA signaling pathways.

Hepatocyte growth factor induces GATA-4 phosphorylation and cell survival in cardiac muscle cells

Hepatocyte growth factor (HGF) is released in response to myocardial infarction and may play a role in regulating cardiac remodeling. Recently, HGF was found to inhibit the apoptosis of cardiac muscle cells. Because GATA-4 can induce cell survival, the effects of HGF on GATA-4 activity were investigated. Treatment of HL-1 cells or primary adult rat cardiac myocytes with HGF, at concentrations that can be detected in the human serum after myocardial infarction, rapidly enhances GATA-4 DNA-binding activity. The enhanced DNA-binding activity is associated with the phosphorylation of GATA-4. HGF-induced phosphorylation and activation of GATA-4 is abolished by MEK inhibitors or the mutation of the ERK phosphorylation site (S105A), suggesting that HGF activates GATA-4 via MEK-ERK pathway-dependent phosphorylation. HGF enhances the expression of anti-apoptotic Bcl-x(L), and this is blocked by dominant negative mutants of MEK or GATA-4. Forced expression of wild-type GATA-4, but not the GATA-4 mutant (S105A) increases the expression of Bcl-x(L). Furthermore, expression of the GATA-4 mutant (S105A) suppresses HGF-mediated protection of cells against daunorubicin-induced apoptosis. These results demonstrate that HGF protects cardiac muscle cells against apoptosis via a signaling pathway involving MEK/ERK-dependent phosphorylation of GATA-4.

Anthracycline-induced suppression of GATA-4 transcription factor: implication in the regulation of cardiac myocyte apoptosis

Anthracyclines are effective cancer chemotherapeutic agents but can induce serious cardiotoxicity. Understanding the mechanism of cardiac damage by these agents will help in development of better therapeutic strategies against cancer. The GATA-4 transcription factor is an important regulator of cardiac muscle cells. The present study demonstrates that anthracyclines can down-regulate GATA-4 activity. Treatment of HL-1 cardiac muscle cells or isolated adult rat ventricular myocytes with anthracyclines such as daunorubicin and doxorubicin decreased the level of GATA-4 DNA-binding activity. The mechanism of decreased GATA-4 activity acts at the level of the GATA-4 gene, because anthracyclines caused significantly decreased levels of GATA-4 protein and mRNA. The rate of decline in GATA-4 transcript levels in the presence of actinomycin D was unaltered by anthracyclines, indicating that these agents may affect directly GATA-4 gene transcription. To determine whether decreased GATA-4 levels are functionally related to cardiac muscle cell death that can be induced by anthracyclines, the ability of ectopic GATA factors to rescue anthracycline-induced apoptosis was tested. Adenovirus-mediated expression of either GATA-4 or GATA-6 was sufficient to attenuate the incidence of apoptosis. Furthermore, suppression of GATA-4 DNA-binding activity by a dominant negative mutant of GATA-4 induced the apoptosis. These results suggest that the mechanism of anthracycline-induced cardiotoxicity may involve the down-regulation of GATA-4 and the induction of apoptosis.

Mutations in the estrogen receptor DNA-binding domain discriminate between the classical mechanism of action and cross-talk with Stat5b and activating protein 1 (AP-1)

Estrogen receptors (ERs) efficiently potentiate the transcriptional activity of prolactin-activated Stat5b through a mechanism that involves the ER DNA-binding domain (DBD) and the hinge domain. We have identified residues within the DBD of ER that are critical for the functional interaction of ER with Stat5b. We show that disruption of the second zinc finger structure abrogated cross-talk between ER and Stat5b, while the structure of the first zinc finger was not important. Furthermore, we confirm that intact DNA binding activity was not required for potentiation of Stat5b activity and that the dimerization of ER did not seem to be involved. Ligand-bound ERs also modulated activating protein 1-dependent transcription, and our data demonstrate that both zinc finger structures of the ER DBD are important for an intact response. We show that introduction of various point mutations within the DBD altered the response of the receptor to 17beta-estradiol and to the estrogen antagonists 4-hydroxytamoxifen and ICI 182,870 on the collagenase promoter. These findings provide new insights into the mechanisms by which ERs act in cross-talk with non-related transcription factors.