USF1 and USF2 mediate inhibition of human trophoblast differentiation and CYP19 gene expression by Mash-2 and hypoxia

CYP19A1 Expression Is Controlled by mRNA Stability of the Upstream Transcription Factor AP-2γ in Placental JEG3 Cells

CYP19A1 encodes aromatase, which converts testosterone to estrogen, and is induced during placental maturation. To elucidate the molecular mechanism underlying this function, histone methylation was analyzed using the placental cytotrophoblast cell line, JEG3. Treatment of JEG3 cells with 3-deazaneplanocin A, an inhibitor of several methyltransferases, resulted in increased CYP19A1 expression, accompanied by removal of the repressive mark H3K27me3 from the CYP19A1 promoter. However, this increase was not observed in cells treated with GSK126, another specific inhibitor for H3K27me3 methylation. Expression of TFAP2C, which encodes AP-2γ, a transcription factor that regulates CYP19A1, was also elevated on 3-deazaneplanocin A treatment. Interestingly, TFAP2C messenger RNA (mRNA) was readily degraded in JEG3 cells but protected from degradation in the presence of 3-deazaneplanocin A. TFAP2C mRNA contained N6-methyladenosines, which were reduced on drug treatment. These observations indicate that the TFAP2C mRNA undergoes adenosine methylation and rapid degradation, whereas 3-deazaneplanocin A suppresses methylation, resulting in an increase in AP-2γ levels. We conclude that the increase in AP-2γ expression via stabilization of the TFAP2C mRNA is likely to underlie the increased CYP19A1 expression.

USF2-mediated upregulation of TXNRD1 contributes to hepatocellular carcinoma progression by activating Akt/mTOR signaling

Thioredoxin reductase 1 (TXNRD1) is one of the major redox regulators in mammalian cells, which has been reported to be involved in tumorigenesis. However, its roles and regulatory mechanism underlying the progression of HCC remains poorly understood. In this study, we demonstrated that TXNRD1 was significantly upregulated in HCC tumor tissues and correlated with poor survival in HCC patients. Functional studies indicated TXNRD1 knockdown substantially suppressed HCC cell proliferation and metastasis both in vitro and in vivo, and its overexpression showed opposite effects. Mechanistically, TXNRD1 attenuated the interaction between Trx1 and PTEN which resulting in acceleration of PTEN degradation, thereby activated Akt/mTOR signaling and its target genes which conferred to elevated HCC cell mobility and metastasis. Moreover, USF2 was identified as a transcriptional suppressor of TXNRD1, which directly interacted with two E-box sites in TXNRD1 promoter. USF2 functioned as tumor suppressor through the downstream repression of TXNRD1. Further clinical data revealed negative co-expression correlations between USF2 and TXNRD1. In conclusion, our findings reveal that USF2-mediated upregulation of TXNRD1 contributes to hepatocellular carcinoma progression by activating Akt/mTOR signaling.

Decorin–induced, preeclampsia-associated microRNA-512-3p restrains extravillous trophoblast functions by targeting USF2/PPP3R1 axis

Decorin (DCN) is a leucine-rich proteoglycan produced by chorionic villus mesenchymal cells anddecidual cells during human pregnancy. Studies from our laboratory demonstrated that decidua-derived DCN restrains multiple trophoblast functions including proliferation, migration, invasion andendovascular differentiation, mediated by DCN-binding to multiple tyrosine kinase receptors; expressed by the trophoblast. Furthermore, DCN was shown to be selectively over-produced by thedecidua in preeclampsia (PE) subjects and elevated in the second trimester maternal plasma in PE, before the appearance of clinical signs, presenting as a predictive biomarker for PE. Micro (mi)RNAs are single-stranded non-coding RNAs (17–25 nucleotides) that typically downregulate target genes by repressing translation or facilitating degradation of mRNAs. The human; placenta expresses many miRNAs, some of which are exclusively expressed by the trophoblast. Many; of these miRNAs are dysregulated in PE-associated placentas and some appear in the maternal blood as PE biomarkers. However, little is known about their contribution to the pathogenesis of PE, a multi-factorial disease associated with a hypo-invasive placenta. The objective of the present study was to examine whether exposure of extravillous trophoblast (EVT) to DCN affects expression of specific miRNAs, and to test the role of these miRNAs in altering EVT functions. We identified miR-512-3p, as one of the DCN-induced miRNAs, also upregulated in PE placentas. It was shown to be elevated in ectopic DCN-over-expressing or exogenous DCN-treated first trimester human trophoblast cell line HTR-8/SVneo. Use of miRNA-mimics and inhibitors revealed that miR-512-3p compromised trophoblast migration, invasion and VEGF-dependent endovascular differentiation. Finally, Protein Phosphatase 3 Regulatory Subunit B, Alpha (PPP3R1), a known target of miR-512-3p, was paradoxically elevated in miR-512-3p-overexpressing trophoblast and PE-associated placentas. Using Enrichr, a tool that consists of both a validated user-submitted gene list and a search engine for transcription factors, we found that PPP3R1 elevation resulted from the miRNA binding to and targeting Upstream Transcription Factor 2 (USF2) which targeted PPP3R1. These findings reveal a novel aspect of pathogenesis of PE and biomarker potentials of this miRNA in PE.

NRF2 Serves a Critical Role in Regulation of Immune Checkpoint Proteins (ICPs) During Trophoblast Differentiation

Using cultured human trophoblast stem cells (hTSCs), mid-gestation human trophoblasts in primary culture, and gene-targeted mice, we tested the hypothesis that the multinucleated syncytiotrophoblast (SynT) serves a critical role in pregnancy maintenance through production of key immune modulators/checkpoint proteins (ICPs) under control of the O2-regulated transcription factor, NRF2/NFE2L2. These ICPs potentially act at the maternal-fetal interface to protect the hemiallogeneic fetus from rejection by the maternal immune system. Using cultured hTSCs, we observed that several ICPs involved in the induction and maintenance of immune tolerance were markedly upregulated during differentiation of cytotrophoblasts (CytTs) to SynT. These included HMOX1, kynurenine receptor, aryl hydrocarbon receptor, PD-L1, and GDF15. Intriguingly, NRF2, C/EBPβ, and PPARγ were markedly induced when CytTs fused to form SynT in a 20% O2 environment. Notably, when hTSCs were cultured in a hypoxic (2% O2) environment, SynT fusion and the differentiation-associated induction of NRF2, C/EBPβ, aromatase (CYP19A1; SynT differentiation marker), and ICPs were blocked. NRF2 knockdown also prevented induction of aromatase, C/EBPβ and the previously mentioned ICPs. Chromatin immunoprecipitation-quantitative PCR revealed that temporal induction of the ICPs in hTSCs and mid-gestation human trophoblasts cultured in 20% O2 was associated with increased binding of endogenous NRF2 to putative response elements within their promoters. Moreover, placentas of 12.5 days postcoitum mice with a global Nrf2 knockout manifested decreased mRNA expression of C/ebpβ, Pparγ, Hmox1, aryl hydrocarbon receptor, and Nqo1, another direct downstream target of Nrf2, compared with wild-type mice. Collectively, these compelling findings suggest that O2-regulated NRF2 serves as a key regulator of ICP expression during SynT differentiation.

ASCL2 reciprocally controls key trophoblast lineage decisions during hemochorial placenta development

Invasive trophoblast cells are critical to spiral artery remodeling in hemochorial placentation. Insufficient trophoblast cell invasion and vascular remodeling can lead to pregnancy disorders including preeclampsia, preterm birth, and intrauterine growth restriction. Previous studies in mice identified achaete-scute homolog 2 (ASCL2) as essential to extraembryonic development. We hypothesized that ASCL2 is a critical and conserved regulator of invasive trophoblast cell lineage development. In contrast to the mouse, the rat possesses deep intrauterine trophoblast cell invasion and spiral artery remodeling similar to human placentation. In this study, we investigated invasive/extravillous trophoblast (EVT) cell differentiation using human trophoblast stem (TS) cells and a loss-of-function mutant Ascl2 rat model. ASCL2 transcripts are expressed in the EVT column and junctional zone, which represent tissue sources of invasive trophoblast progenitor cells within human and rat placentation sites, respectively. Differentiation of human TS cells into EVT cells resulted in significant up-regulation of ASCL2 and several other transcripts indicative of EVT cell differentiation. Disruption of ASCL2 impaired EVT cell differentiation, as indicated by cell morphology and transcript profiles. RNA sequencing analysis of ASCL2-deficient trophoblast cells identified both down-regulation of EVT cell-associated transcripts and up-regulation of syncytiotrophoblast-associated transcripts, indicative of dual activating and repressing functions. ASCL2 deficiency in the rat impacted placental morphogenesis, resulting in junctional zone dysgenesis and failed intrauterine trophoblast cell invasion. ASCL2 acts as a critical and conserved regulator of invasive trophoblast cell lineage development and a modulator of the syncytiotrophoblast lineage.

Uteroplacental Circulation in Normal Pregnancy and Preeclampsia: Functional Adaptation and Maladaptation

Uteroplacental blood flow increases as pregnancy advances. Adequate supply of nutrients and oxygen carried by uteroplacental blood flow is essential for the well-being of the mother and growth/development of the fetus. The uteroplacental hemodynamic change is accomplished primarily through uterine vascular adaptation, involving hormonal regulation of myogenic tone, vasoreactivity, release of vasoactive factors and others, in addition to the remodeling of spiral arteries. In preeclampsia, hormonal and angiogenic imbalance, proinflammatory cytokines and autoantibodies cause dysfunction of both endothelium and vascular smooth muscle cells of the uteroplacental vasculature. Consequently, the vascular dysfunction leads to increased vascular resistance and reduced blood flow in the uteroplacental circulation. In this article, the (mal)adaptation of uteroplacental vascular function in normal pregnancy and preeclampsia and underlying mechanisms are reviewed.

Elucidating evolutionarily conserved mechanisms of diapause regulation using an in silico approach

Embryonic diapause is an enigmatic phenomenon that appears in diverse species. Although regulatory mechanisms have been established, there is much to be discovered. Herein, we have made the first comprehensive attempt to elucidate diapause regulatory mechanisms using a computational approach. We found transcription factors unique to promoters of genes in diapause species. From pathway analysis and STRING PPI networks, the signaling pathways regulated by these unique transcription factors were identified. The pathways were then consolidated into a model to combine various known mechanisms of diapause regulation. This work also highlighted certain transcription factors that may act as 'master transcription factors' to regulate the phenomenon. Promoter analysis further suggested evidence for independent evolution for some of regulatory elements involved in diapause.

Placental transcriptome profile of women with sickle cell disease reveals differentially expressed genes involved in migration, trophoblast differentiation and inflammation

Sickle cell disease (SCD) is a group of disorders whose common characteristic is the presence of hemoglobin (Hb) S in erythrocytes. The main consequence of this abnormality is vaso-occlusion, which can affect almost all organs including the placenta. This study aimed to evaluate the gene expression profile in placentas of women with SCD by means of total RNA sequencing. For this, we proposed a case-control study, with three groups of pregnant women: HbSS (n = 10), HbSC (n = 14) and HbAA (n = 21). The results showed differences in expression in a number of genes such as NOS2 (fold change, FC = 4.52), HLAG (FC = 5.56), ASCL2 (FC = 3.61), CXCL10 (FC = -3.66) and IL1R2 (FC = 3.92) for the HbSC group and S100A8 (FC = -3.82), CPXM2 (FC = 4.57), CXCL10 (FC = -4.59), CXCL11 (FC = -3.72) and CAMP (FC = -4.55) for the HbSS group. Differentially expressed genes are mainly associated with migration, trophoblast differentiation and inflammation. The causes leading to altered gene expression in placentas of sickle cell patients are not fully understood, but the presence of intravascular hemolysis and vaso-occlusion, with cycles of ischemia and reperfusion, may contribute to the emergence of an environment which can be very harmful for placental physiology, altering the nutrient supply and metabolic exchange for fetal growth.

Influence of Estrogens on Uterine Vascular Adaptation in Normal and Preeclamptic Pregnancies

During pregnancy, the maternal cardiovascular system undergoes significant changes, including increased heart rate, cardiac output, plasma volume, and uteroplacental blood flow (UPBF) that are required for a successful pregnancy outcome. The increased UPBF is secondary to profound circumferential growth that extends from the downstream small spiral arteries to the upstream conduit main uterine artery. Although some of the mechanisms underlying uterine vascular remodeling are, in part, known, the factors that drive the remodeling are less clear. That higher circulating levels of estrogens are positively correlated with gestational uterine vascular remodeling suggests their involvement in this process. Estrogens binding to the estrogen receptors expressed in cytotrophoblast cells and in the uterine artery wall stimulate an outward hypertrophic remodeling of uterine vasculature. In preeclampsia, generally lower concentrations of estrogens limit the proper uterine remodeling, thereby reducing UPBF increases and restricting the growth of the fetus. This review aims to report estrogenic regulation of the maternal uterine circulatory adaptation in physiological and pathological pregnancy that favors vasodilation, and to consider the underlying molecular mechanisms by which estrogens regulate uteroplacental hemodynamics.

Distinct enhancer signatures in the mouse gastrula delineate progressive cell fate continuum during embryo development

Primary germ layers have the potential to form all tissues in the mature organism, and their formation during gastrulation requires precise epigenetic modulation of both proximal and distal regulatory elements. Previous studies indicated that spatial and temporal patterns of gene expression in the gastrula predispose individual regions to distinct cell fates. However, the underlying epigenetic mechanisms remain largely unexplored. Here, we profile the spatiotemporal landscape of the epigenome and transcriptome of the mouse gastrula. We reveal the asynchronous dynamics of proximal chromatin states during germ layer formation as well as unique gastrula-specific epigenomic features of regulatory elements, which have strong usage turnover dynamics and clear germ layer-specific signatures. Importantly, we also find that enhancers around organogenetic genes, which are weakly expressed at the gastrulation stage, are frequently pre-marked by histone H3 lysine 27 acetylation (H3K27ac) in the gastrula. By using the transgenic mice and genome editing system, we demonstrate that a pre-marked enhancer, which is located in the intron of a brain-specific gene 2510009E07Rik, exhibits specific enhancer activity in the ectoderm and future brain tissue, and also executes important function during mouse neural differentiation. Taken together, our study provides the comprehensive epigenetic information for embryonic patterning during mouse gastrulation, demonstrates the importance of gastrula pre-marked enhancers in regulating the correct development of the mouse embryo, and thus broadens the current understanding of mammalian embryonic development and related diseases.

Human Trophoblast Differentiation Is Associated With Profound Gene Regulatory and Epigenetic Changes

Defective placental implantation and vascularization with accompanying hypoxia contribute to preeclampsia (PE), a leading cause of maternal and neonatal morbidity and mortality. Genetic and epigenetic mechanisms underlying differentiation of proliferative cytotrophoblasts (CytTs) to multinucleated syncytiotrophoblast (SynT) are incompletely defined. The SynT performs key functions in nutrient and gas exchange, hormone production, and protection of the fetus from rejection by the maternal immune system. In this study, we used chromatin immunoprecipitation sequencing of midgestation human trophoblasts before CytT and after SynT differentiation in primary culture to analyze changes in binding of RNA polymerase II (Pol II) and of active and repressive histone marks during SynT differentiation. Our findings reveal that increased Pol II binding to promoters of a subset of genes during trophoblast differentiation was closely correlated with active histone marks. This gene set was enriched in those controlling immune response and immune modulation, including interferon-induced tetratricopeptide repeat and placenta-specific glycoprotein gene family members. By contrast, genes downregulated during SynT differentiation included proinflammatory transcription factors ERG1, cFOS, and cJUN, as well as members of the NR4A orphan nuclear receptor subfamily, NUR77, NURR1, and NOR1. Downregulation of proinflammatory transcription factors upon SynT differentiation was associated with decreased promoter enrichment of endogenous H3K27Ac and H3K9Ac and enhanced binding of H3K9me3 and histone deacetylase 1. However, promoter enrichment of H3K27me3 was low in both CytT and SynT and was not altered with changes in gene expression. These findings provide important insight into mechanisms underlying human trophoblast differentiation and may identify therapeutic targets for placental disorders, such as PE.

Aromatase as a target for treating endometriosis

Endometriosis is a common gynecological disease that causes various clinical symptoms, such as chronic pelvic pain, dysmenorrhea and infertility, seriously affecting women's health and their quality of life. The symptoms and endometriotic lesions are relieved, in many cases, after menopause, when estrogen levels are lowered. Therefore, endometriosis is considered to be estrogen-dependent. Aromatase, the enzyme responsible for the last step of estrogen biosynthesis converting testosterone and androgen to estrogen, was previously reported to be more abundant in endometriotic tissues than in the normal endometrium, leading to an increased local estrogen concentration. Therefore, aromatase is considered a key therapeutic target for regulating local estrogen biosynthesis in endometriosis. A more complete understanding of the mechanisms that modulate aromatase and its activity is required to develop novel estrogen-targeted therapies for endometriosis. In this review article, we outline the current understanding of the pathological processes involved in estrogen production in endometriosis and propose novel strategies to treat this disorder.

Abnormal steroidogenesis and aromatase activity in preeclampsia

INTRODUCTION

Estrogens and progesterone play critical roles in angiogenesis and vasodilation. Moreover, placental aromatase deficiency is detected in women with preeclampsia (PE) at delivery. We hypothesized that abnormal steroidogenesis occurs much earlier than typical PE diagnosis. Thus, we investigated whether the circulating steroid profile was already disturbed at 24-29 weeks of gestation in women with subsequent PE, and compared the profile with that of women with "placental" small gestational age (SGA) without PE.

METHODS

We selected nulliparous women (n = 90) from the MOMA trial, including women with PE (n = 25), SGA (n = 25), and controls (NP; n = 40), for plasma steroid profiling by gas chromatography/mass spectrometry and to measure placental growth factor and soluble fms-like tyrosine kinase-1. Placental aromatase expression was evaluated in a new set of women.

RESULTS

Compared with that of controls, the women with PE had a significantly lower estrone/androstenedione ratio, and exhibited a decreasing trend for estradiol and estrone levels. Lower estriol levels were observed in the SGA group compared to the NP group. Compared with that of controls, the women with PE and SGA had significantly higher levels of 20α-dihydroprogesterone (20α-DHP) and 20α-DHP/progesterone ratios. Pregnenolone sulfate levels were lower in the PE group than in the NP and SGA groups. Decreased expression of aromatase was observed in the PE group compared to the control group.

DISCUSSION

Preeclampsia appears to be characterized by specific steroidogenesis dysregulation long before PE diagnosis, highlighting potential new biomarkers of PE.

Hypoxia and Placental Development

Hemochorial placentation is orchestrated through highly regulated temporal and spatial decisions governing the fate of trophoblast stem/progenitor cells. Trophoblast cell acquisition of specializations facilitating invasion and uterine spiral artery remodeling is a labile process, sensitive to the environment, and represents a process that is vulnerable to dysmorphogenesis in pathologic states. Hypoxia is a signal guiding placental development, and molecular mechanisms directing cellular adaptations to low oxygen tension are integral to trophoblast cell differentiation and placentation. Hypoxia can also be used as an experimental tool to investigate regulatory processes controlling hemochorial placentation. These developmental processes are conserved in mouse, rat, and human placentation. Consequently, elements of these developmental events can be modeled and hypotheses tested in trophoblast stem cells and in genetically manipulated rodents. Hypoxia is also a consequence of a failed placenta, yielding pathologies that can adversely affect maternal adjustments to pregnancy, fetal health, and susceptibility to adult disease. The capacity of the placenta for adaptation to environmental challenges highlights the importance of its plasticity in safeguarding a healthy pregnancy. Birth Defects Research 109:1309-1329, 2017.© 2017 Wiley Periodicals, Inc.

From Pregnancy to Preeclampsia: A Key Role for Estrogens

Preeclampsia (PE) results in placental dysfunction and is one of the primary causes of maternal and fetal mortality and morbidity. During pregnancy, estrogen is produced primarily in the placenta by conversion of androgen precursors originating from maternal and fetal adrenal glands. These processes lead to increased plasma estrogen concentrations compared with levels in nonpregnant women. Aberrant production of estrogens could play a key role in PE symptoms because they are exclusively produced by the placenta and they promote angiogenesis and vasodilation. Previous assessments of estrogen synthesis during PE yielded conflicting results, possibly because of the lack of specificity of the assays. However, with the introduction of reliable analytical protocols using liquid chromatography/mass spectrometry or gas chromatography/mass spectrometry, more recent studies suggest a marked decrease in estradiol levels in PE. The aim of this review is to summarize current knowledge of estrogen synthesis, regulation in the placenta, and biological effects during pregnancy and PE. Moreover, this review highlights the links among the occurrence of PE, estrogen biosynthesis, angiogenic factors, and cardiovascular risk factors. A close link between estrogen dysregulation and PE occurrence might validate estrogen levels as a biomarker but could also reveal a potential approach for prevention or cure of PE.

Genetic recapitulation of human pre-eclampsia risk during convergent evolution of reduced placental invasiveness in eutherian mammals

The relationship between phenotypic variation arising through individual development and phenotypic variation arising through diversification of species has long been a central question in evolutionary biology. Among humans, reduced placental invasion into endometrial tissues is associated with diseases of pregnancy, especially pre-eclampsia, and reduced placental invasiveness has also evolved, convergently, in at least 10 lineages of eutherian mammals. We tested the hypothesis that a common genetic basis underlies both reduced placental invasion arising through a developmental process in human placental disease and reduced placental invasion found as a derived trait in the diversification of Euarchontoglires (rodents, lagomorphs, tree shrews, colugos and primates). Based on whole-genome analyses across 18 taxa, we identified 1254 genes as having evolved adaptively across all three lineages exhibiting independent evolutionary transitions towards reduced placental invasion. These genes showed strong evidence of enrichment for associations with pre-eclampsia, based on genetic-association studies, gene-expression analyses and gene ontology. We further used in silico prediction to identify a subset of 199 genes that are likely targets of natural selection during transitions in placental invasiveness and which are predicted to also underlie human placental disorders. Our results indicate that abnormal ontogenies can recapitulate major phylogenetic shifts in mammalian evolution, identify new candidate genes for involvement in pre-eclampsia, imply that study of species with less-invasive placentation will provide useful insights into the regulation of placental invasion and pre-eclampsia, and recommend a novel comparative functional-evolutionary approach to the study of genetically based human disease and mammalian diversification.

OVO-like 1 regulates progenitor cell fate in human trophoblast development

Epithelial barrier integrity is dependent on progenitor cells that either divide to replenish themselves or differentiate into a specialized epithelium. This paradigm exists in human placenta, where cytotrophoblast cells either propagate or undergo a unique differentiation program: fusion into an overlying syncytiotrophoblast. Syncytiotrophoblast is the primary barrier regulating the exchange of nutrients and gases between maternal and fetal blood and is the principal site for synthesizing hormones vital for human pregnancy. How trophoblast cells regulate their differentiation into a syncytium is not well understood. In this study, we show that the transcription factor OVO-like 1 (OVOL1), a homolog of Drosophila ovo, regulates the transition from progenitor to differentiated trophoblast cells. OVOL1 is expressed in human placenta and was robustly induced following stimulation of trophoblast differentiation. Disruption of OVOL1 abrogated cytotrophoblast fusion and inhibited the expression of a broad set of genes required for trophoblast cell fusion and hormonogenesis. OVOL1 was required to suppress genes that maintain cytotrophoblast cells in a progenitor state, including MYC, ID1, TP63, and ASCL2, and bound specifically to regions upstream of each of these genes. Our results reveal an important function of OVOL1 as a regulator of trophoblast progenitor cell fate during human trophoblast development.

Evidence for microRNA-mediated regulation of steroidogenesis by hypoxia

Environmental hypoxia can occur in both natural and occupational environments. Over the recent years, the ability of hypoxia to cause endocrine disruption via perturbations in steroid synthesis (steroidogenesis) has become increasingly clear. To further understand the molecular mechanism underlying hypoxia-induced endocrine disruption, the steroid-producing human cell line H295R was used to identify microRNAs (miRNAs) affecting steroidogenic gene expression under hypoxia. Hypoxic treatment of H295R cells resulted in the downregulation of seven steroidogenic genes and one of these, CYP19A1 (aromatase), was shown to be regulated by the transcription factor hypoxia-inducible factor-1 (HIF-1). Using bioinformatic and luciferase reporter analyses, miR-98 was identified to be a CYP19A1-targeting miRNA from a subset of HIF-1-inducible miRNAs. Gain- and loss-of-function analysis suggested that under hypoxia, the increased expression of miR-98 led to the downregulation of CYP19A1 mRNA and protein expression and that it may have contributed to a reduction in estradiol (E2) production. Intriguingly, luciferase reporter assays using deletion constructs of a proximal 5′-flanking region of miR-98 did not reveal a hypoxia-responsive element (HRE)-containing promoter. Overall, this study provided evidence for the role of miRNAs in regulating steroidogenesis and novel insights into the molecular mechanisms of hypoxia-induced endocrine disruption.

Sexually-dimorphic targeting of functionally-related genes in COPD

BACKGROUND

There is growing evidence that many diseases develop, progress, and respond to therapy differently in men and women. This variability may manifest as a result of sex-specific structures in gene regulatory networks that influence how those networks operate. However, there are few methods to identify and characterize differences in network structure, slowing progress in understanding mechanisms driving sexual dimorphism.

RESULTS

Here we apply an integrative network inference method, PANDA (Passing Attributes between Networks for Data Assimilation), to model sex-specific networks in blood and sputum samples from subjects with Chronic Obstructive Pulmonary Disease (COPD). We used a jack-knifing approach to build an ensemble of likely networks for each sex. By adapting statistical methods to compare these network ensembles, we were able to identify strong differential-targeting patterns associated with functionally-related sets of genes, including those involved in mitochondrial function and energy metabolism. Network analysis also identified several potential sex- and disease-specific transcriptional regulators of these pathways.

CONCLUSIONS

Network analysis yielded insight into potential mechanisms driving sexual dimorphism in COPD that were not evident from gene expression analysis alone. We believe our ensemble approach to network analysis provides a principled way to capture sex-specific regulatory relationships and could be applied to identify differences in gene regulatory patterns in a wide variety of diseases and contexts.

Upstream stimulatory factors 1 and 2 mediate the transcription of angiotensin II binding and inhibitory protein

The angiotensin II type 1 receptor (AT1R)-associated protein (ATRAP/Agtrap) promotes constitutive internalization of the AT1R so as to specifically inhibit the pathological activation of its downstream signaling yet preserve the base-line physiological signaling activity of the AT1R. Thus, tissue-specific regulation of Agtrap expression is relevant to the pathophysiology of cardiovascular and renal disease. However, the regulatory mechanism of Agtrap gene expression has not yet been fully elucidated. In this study, we show that the proximal promoter region from −150 to +72 of the mouse Agtrap promoter, which contains the X-box, E-box, and GC-box consensus motifs, is able to elicit substantial transcription of the Agtrap gene. Among these binding motifs, we showed that the E-box specifically binds upstream stimulatory factor (Usf) 1 and Usf2, which are known E-box-binding transcription factors. It is indicated that the E-box-Usf1/Usf2 binding regulates Agtrap expression because of the following: 1) mutation of the E-box to prevent Usf1/Usf2 binding reduces Agtrap promoter activity; 2) knockdown of Usf1 or Usf2 affects both endogenous Agtrap mRNA and Agtrap protein expression, and 3) the decrease in Agtrap mRNA expression in the afflicted kidney by unilateral ureteral obstruction is accompanied by changes in Usf1 and Usf2 mRNA. Furthermore, the results of siRNA transfection in mouse distal convoluted tubule cells and those of unilateral ureteral obstruction in the afflicted mouse kidney suggest that Usf1 decreases but Usf2 increases the Agtrap gene expression by binding to the E-box. The results also demonstrate a functional E-box-USF1/USF2 interaction in the human AGTRAP promoter, thereby suggesting that a strategy of modulating the E-box-USF1/USF2 binding has novel therapeutic potential.

The c-Myc-regulated microRNA-17~92 (miR-17~92) and miR-106a~363 clusters target hCYP19A1 and hGCM1 to inhibit human trophoblast differentiation

Mononuclear cytotrophoblasts of the human placenta proliferate rapidly, subsequently fuse, and differentiate to form multinucleated syncytiotrophoblast with induction of aromatase (hCYP19A1) and chorionic gonadotropin (hCGβ) expression. Using microarray analysis, we identified members of the miR-17~92 cluster and its paralogs, miR-106a~363 and miR-106b~25, that are significantly downregulated upon syncytiotrophoblast differentiation. Interestingly, miR-19b and miR-106a directly targeted hCYP19A1 expression, while miR-19b also targeted human GCM1 (hGCM1), a transcription factor critical for mouse labyrinthine trophoblast development. Overexpression of these microRNAs (miRNAs) impaired syncytiotrophoblast differentiation. hGCM1 knockdown decreased hCYP19A1 and hCGβ expression, substantiating its important role in human trophoblast differentiation. Expression of the c-Myc proto-oncogene was increased in proliferating cytotrophoblasts compared to that in differentiated syncytiotrophoblast. Moreover, c-Myc overexpression upregulated miR-17~92 and inhibited hCYP19A1 and hCGβ expression. Binding of endogenous c-Myc to genomic regions upstream of the miR-17~92 and miR-106a~363 clusters in cytotrophoblasts dramatically decreased upon syncytiotrophoblast differentiation. Intriguingly, we observed higher levels of miR-106a and -19b and lower aromatase and hGCM1 expression in placentas from preeclamptic women than in placentas from gestation-matched normotensive women. Our findings reveal that c-Myc-regulated members of the miR-17~92 and miR-106a~363 clusters inhibit trophoblast differentiation by repressing hGCM1 and hCYP19A1 and suggest that aberrant regulation of these miRNAs may contribute to the pathogenesis of preeclampsia.

Gene targeting in primary human trophoblasts

Studies in primary human trophoblasts provide critical insights into placental function in normal and complicated pregnancies. Mechanistic studies in these cells require experimental tools to modulate gene expression. Lipid-based methods to transfect primary trophoblasts are fairly simple to use and allow for the efficient delivery of nucleic acids, but potential toxic effects limit these methods. Viral vectors are versatile transfection tools of native trophoblastic or foreign cDNAs, providing high transfection efficiency, low toxicity and stable DNA integration into the trophoblast genome. RNA interference (RNAi), using small interfering RNA (siRNA) or microRNA, constitutes a powerful approach to silence trophoblast genes. However, off-target effects, such as regulation of unintended complementary transcripts, inflammatory responses and saturation of the endogenous RNAi machinery, are significant concerns. Strategies to minimize off-target effects include using multiple individual siRNAs, elimination of pro-inflammatory sequences in the siRNA construct and chemical modification of a nucleotide in the guide strand or of the ribose moiety. Tools for efficient gene targeting in primary human trophoblasts are currently available, albeit not yet extensively validated. These methods are critical for exploring the function of human trophoblast genes and may provide a foundation for the future application of gene therapy that targets placental trophoblasts.

DNA demethylation and USF regulate the meiosis-specific expression of the mouse Miwi

Miwi, a member of the Argonaute family, is required for initiating spermiogenesis; however, the mechanisms that regulate the expression of the Miwi gene remain unknown. By mutation analysis and transgenic models, we identified a 303 bp proximal promoter region of the mouse Miwi gene, which controls specific expression from midpachytene spermatocytes to round spermatids during meiosis. We characterized the binding sites of transcription factors NF-Y (Nuclear Factor Y) and USF (Upstream Stimulatory Factor) within the core promoter and found that both factors specifically bind to and activate the Miwi promoter. Methylation profiling of three CpG islands within the proximal promoter reveals a markedly inverse correlation between the methylation status of the CpG islands and germ cell type–specific expression of Miwi. CpG methylation at the USF–binding site within the E2 box in the promoter inhibits the binding of USF. Transgenic Miwi-EGFP and endogenous Miwi reveal a subcellular co-localization pattern in the germ cells of the Miwi-EGFP transgenic mouse. Furthermore, the DNA methylation profile of the Miwi promoter–driven transgene is consistent with that of the endogenous Miwi promoter, indicating that Miwi transgene is epigenetically modified through methylation in vivo to ensure its spatio-temporal expression. Our findings suggest that USF controls Miwi expression from midpachytene spermatocytes to round spermatids through methylation-mediated regulation. This work identifies an epigenetic regulation mechanism for the spatio-temporal expression of mouse Miwi during spermatogenesis.

Germ cell differentiation is a key process in the formation of functional spermatozoa. Despite the wealth of information about gene expression patterns and regulations important for this process, it is not clear how spatio-temporal expression of the key factor Miwi during spermatogenesis is controlled. We have characterized the functional promoter of the mouse Miwi gene. Transgenic mice harboring EGFP under the Miwi core promoter containing just the functional CCAAT box and E2 box were generated and demonstrated that it can direct germ cell–specific expression. We further identified the transcription factors NF-Y and USF1/2 as activators of Miwi gene expression, through their binding to the CCAAT box and E-box/E2 site of the Miwi promoter, respectively. A CpG dinucleotide just located within the USF binding site is responsible for mediating methylation-dependent silencing of the Miwi gene. Our findings provide new insight into an epigenetic regulation mechanism for the spatio-temporal expression of the mouse Miwi during spermatogenesis.

Estrogen-related receptor gamma (ERRgamma) mediates oxygen-dependent induction of aromatase (CYP19) gene expression during human trophoblast differentiation

Differentiation of human cytotrophoblasts to syncytiotrophoblast and the associated induction of aromatase/hCYP19 gene expression are dependent upon a critical O(2) tension; however, the underlying molecular mechanisms remain undefined. In this study, we provide compelling evidence that expression of the orphan nuclear receptor, estrogen-related receptor γ (ERRγ), is also O(2) dependent, induced during human syncytiotrophoblast differentiation, and plays an obligatory role in the induction of placenta-specific hCYP19I.1 gene expression. Treatment with the selective ERRγ agonist, DY131, or overexpression of ERRγ, stimulated hCYP19 expression in syncytiotrophoblast. Overexpression of ERRγ prevented effects of hypoxia to repress hCYP19 gene expression in cultured trophoblasts. Conversely, small interfering RNA-mediated knockdown of endogenous ERRγ in primary trophoblasts markedly inhibited hCYP19 expression. Promoter and site-directed mutagenesis studies in transfected placental cells identified a nuclear receptor element within placenta-specific hCYP19 promoter I.1 required for ERRγ-stimulated activity. Recruitment of endogenous ERRγ to the nuclear receptor element region in hCYP19 promoter during trophoblast differentiation, assessed by chromatin immunoprecipitation, was prevented by hypoxia. Deferoxamine-induced hypoxia-inducible factor-1α (HIF-1α) levels decreased ERRγ expression, whereas knockdown of endogenous HIF-1α prevented ERRγ suppression by hypoxia. Chromatin immunoprecipitation analysis of trophoblasts cultured in hypoxia revealed recruitment of HIF-1α to one of two putative hypoxia response elements in the ERRγ promoter, providing in vivo evidence of a direct HIF-1α involvement in ERRγ expression. Collectively, these novel findings identify ERRγ as an O(2)-dependent transcription factor and HIF-1α target gene that serves a critical role in the induction of hCYP19 expression during human trophoblast differentiation.

NF-Y and USF1 transcription factor binding to CCAAT-box and E-box elements activates the CP27 promoter

The maintenance and differentiation of embryonic stem cells (ES cells) depends on the regulation of gene expression through the coordinated binding of transcription factors to regulatory promoter elements. One of the genes involved in embryonic development is the chromatin factor CP27. Previously, we have shown that NF-Y interacted with the CP27 proximal promoter CCAAT-box. Here we report that CP27 gene expression in mouse ES cells is controlled by CCAAT and E-box cis-acting regulatory elements and their corresponding transcription factors NF-Y and USF1. Specifically, USF1 interacts with the E-box of the CP27 proximal promoter and NF-Y interacts with the CCAAT-box. NF-Y and USF1 also interacted with each other and activated the CP27 promoter in a synergistic fashion. Together, these studies demonstrate that gene expression of the chromatin factor CP27 is regulated through the interaction of the transcription factors NF-Y and USF1 with the CP27 proximal promoter.

Pre-eclampsia: fitting together the placental, immune and cardiovascular pieces

The success of pregnancy is a result of countless ongoing interactions between the placenta and the maternal immune and cardiovascular systems. Pre-eclampsia is a serious pregnancy complication that arises from multiple potential aberrations in these systems. The pathophysiology of pre-eclampsia is established in the first trimester of pregnancy, when a range of deficiencies in placentation affect the key process of spiral artery remodelling. As pregnancy progresses to the third trimester, inadequate spiral artery remodelling along with multiple haemodynamic, placental and maternal factors converge to activate the maternal immune and cardiovascular systems, events which may in part result from increased shedding of placental debris. As we understand more about the pathophysiology of pre-eclampsia, it is becoming clear that the development of early- and late-onset pre-eclampsia, as well as intrauterine growth restriction (IUGR), does not necessarily arise from the same underlying pathology.

The role of hypoxia in development of the Mammalian embryo

Hypoxia inducible factor (HIF) is a transcription factor that acts in low-oxygen conditions. The cellular response to HIF activation is transcriptional upregulation of a large group of genes. Some target genes promote anaerobic metabolism to reduce oxygen consumption, while others "alleviate" hypoxia by acting non-cell-autonomously to extend and modify the surrounding vasculature. Although hypoxia is often thought of as being a pathological phenomenon, the mammalian embryo in fact develops in a low-oxygen environment, and in this context HIF has additional responsibilities. This review describes how low oxygen and HIF affect gene expression, cell behavior, and ultimately morphogenesis of the embryo and placenta.

Upstream stimulating factors 1 and 2 enhance transcription from the placenta-specific promoter 1.1 of the bovine cyp19 gene

Background

Placenta-derived oestrogens have an impact on the growth and differentiation of the trophoblast, and are involved in processes initiating and facilitating birth. The enzyme that converts androgens into oestrogens, aromatase cytochrome P450 (P450arom), is encoded by the Cyp19 gene. In the placenta of the cow, expression of Cyp19 relies on promoter 1.1 (P1.1). Our recent studies of P1.1 in vitro and in a human trophoblast cell line (Jeg3) revealed that interactions of placental nuclear protein(s) with the E-box element at position -340 are required for full promoter activity. The aim of this work was to identify and characterise the placental E-box (-340)-binding protein(s) (E-BP) as a step towards understanding how the expression of Cyp19 is regulated in the bovine placenta.

Results

The significance of the E-box was confirmed in cultured primary bovine trophoblasts. We enriched the E-BP from placental nuclear extracts using DNA-affinity Dynabeads and showed by Western blot analysis and supershift EMSA experiments that the E-BP is composed of the transcription factors upstream stimulating factor (USF) 1 and USF2. Depletion of the USFs by RNAi and expression of a dominant-negative USF mutant, were both associated with a significant decrease in P1.1-dependent reporter gene expression. Furthermore, scatter plot analysis of P1.1 activity vs. USF binding to the E-box revealed a strong positive correlation between the two parameters.

Conclusion

From these results we conclude that USF1 and USF2 are activators of the bovine placenta-specific promoter P1.1 and thus act in the opposite mode as in the case of the non-orthologous human placenta-specific promoter.

Estrogen receptor alpha (ERalpha) mediates stimulatory effects of estrogen on aromatase (CYP19) gene expression in human placenta

A 246-bp region upstream of placenta-specific exon I.1 of the human aromatase (hCYP19) gene mediates placenta-specific, developmental, and O(2) regulation of expression. In this study, trophoblast differentiation and associated induction of CYP19 expression were prevented when cytotrophoblasts were cultured in phenol red-free medium containing charcoal-stripped serum or with the estrogen receptor (ER) antagonist, ICI 182,780, suggesting a stimulatory role of estrogen/ER. ERalpha protein was expressed in human trophoblasts and increased during syncytiotrophoblast differentiation, whereas ERbeta was undetectable. Mutational analysis revealed that an estrogen response element-like sequence (ERE-LS) at -208 bp is required for inductive effects of estradiol/ERalpha on hCYP19I.1 promoter activity in transfected COS-7 cells. Increased binding of syncytiotrophoblast compared with cytotrophoblast nuclear proteins to the ERE-LS was observed in vitro; however, ERalpha antibodies failed to supershift the complex and in vitro-transcribed/translated ERalpha did not bind. Nonetheless, chromatin immunoprecipitation assays in cultured trophoblasts revealed recruitment of endogenous ERalpha to the -255- to -155-bp region containing the ERE-LS before induction of hCYP19 expression; this was inhibited by ICI 182,780. Chromatin immunoprecipitation also revealed increased acetylated histone H3(K9/14) and decreased methylated histone H3(K9) associated with this region during trophoblast differentiation. These modifications were prevented when trophoblasts were incubated with ICI 182,780, suggesting that ERalpha recruitment to the -255- to -155-bp region promotes histone modifications leading to increased hCYP19 transcription. Thus, during trophoblast differentiation, estrogen/ERalpha exerts a positive feedback role, which promotes permissive histone modifications that are associated with induction of hCYP19 gene transcription.

PPAR-gamma signaling pathway in placental development and function: a potential therapeutic target in the treatment of gestational diseases

BACKGROUND

PPAR-gamma is a target for the treatment of metabolic disorders, as Pioglitazone and Rosiglitazone are already used against type 2 diabetes. Pleiotropic functions, such as antiproliferative and anti-inflammatory effects against several pathological states, including cardiovascular disease and cancer, are currently being explored in clinical studies.

OBJECTIVE

Evidence indicates that PPAR-gamma is expressed in the placenta, playing a crucial role in placental development and function, while PPAR-gamma ligands appear to modulate fetal membrane signals. Thus, in the last few years, the pivotal role of PPAR-gamma in placental biology has been the focus of extensive research, as diabetes appears to be the most common metabolic dysfunction in pregnancy.

METHODS

We aim to present data concerning the expression of PPAR-gamma in animal and human placenta, underlining its significance in normal placental development and several gestational diseases. The effects of PPAR-gamma ligands as modulators of placental biology in normal and certain pathological conditions are also discussed.

RESULTS/CONCLUSION

Current research provides substantial evidence that PPAR-gamma plays a pivotal role in placental biology and may reveal new perspectives in the treatment of gestational diseases.

Oxygen tension directs the differentiation pathway of human cytotrophoblast cells

During placental development, human cytotrophoblast cells can differentiate to either villous syncytiotrophoblast cells or invasive extravillous trophoblast cells. We hypothesize that oxygen tension plays a critical role in determining the pathway of cytotrophoblast differentiation. A highly purified preparation of cytotrophoblast cells from human third trimester placenta was cultured for 5 days in either 20% or 1% oxygen tension. The cells incubated at 20% oxygen formed a syncytium as determined by immunohistochemistry using an anti-desmosomal protein antibody that identifies cell membranes. In addition, the mRNA was markedly induced for syncytin, a glycoprotein shown to be essential for syncytiotrophoblast formation, and for human placental lactogen (hPL), which is a specific marker for syncytiotrophoblast cells. In contrast, the cell incubated at 1% oxygen tension did not fuse by morphologic analysis and did not express syncytin or hPL mRNA. However, these cells expressed abundant amounts of HLA-G, a specific marker for extravillous trophoblast cells, which was not seen in cells incubated at 20% oxygen tension. These results suggest that low oxygen tension directs differentiation along the extravillous trophoblast cell pathway while greater oxygen tension directs differentiation along the villous trophoblast cell pathway.

Mechanisms in the regulation of aromatase in developing ovary and placenta

During human gestation, the placental syncytiotrophoblast develops the capacity to synthesize large amounts of estrogen from C(19)-steroids secreted by the fetal adrenals. The conversion of C(19)-steroids to estrogens is catalyzed by aromatase P450 (P450arom), product of the CYP19 gene. The placenta-specific promoter of the hCYP19 gene lies approximately 100,000 bp upstream of the translation initiation site in exon II. In studies using transgenic mice and transfected human trophoblast cells we have defined a 246-bp region upstream of placenta-specific exon I.1 that mediates placental cell-specific expression. Using transgenic mice, we also observed that as little as 278 bp of DNA flanking the 5'-end of ovary-specific hCYP19 exon IIa was sufficient to target ovary-specific expression. This ovary-specific promoter contains response elements that bind cAMP-response element-binding protein (CREB) and the orphan nuclear receptors SF-1 and LRH-1, which are required for cAMP-mediated stimulation of CYP19 expression in granulosa and luteal cells during the estrous cycle and pregnancy. In this article, we review our studies to define genomic regions and response elements that mediate placenta-specific expression of the hCYP19 gene. The temporal and spatial expression of LRH-1 versus SF-1 in the developing gonad during mouse embryogenesis and in the postnatal ovary also will be considered.

Prolyl-hydroxylase inhibition and HIF activation in osteoblasts promotes an adipocytic phenotype

Bone is a dynamic environment where cells sense and adapt to changes in nutrient and oxygen availability. Conditions associated with hypoxia in bone are also associated with bone loss. In vitro hypoxia (2% oxygen) alters gene expression in osteoblasts and osteocytes and induces cellular changes including the upregulation of hypoxia inducible factor (HIF) levels. Our studies show that osteoblasts respond to hypoxia (2% oxygen) by enhancing expression of genes associated with adipocyte/lipogenesis phenotype (C/EBPbeta, PPARgamma2, and aP2) and by suppressing expression of genes associated with osteoblast differentiation (alkaline phosphatase, AP). Hypoxia increased HIF protein levels, hypoxic response element (HRE) binding, and HRE-reporter activity. We also demonstrate that prolyl-hydroxylases 2 and 3 (PHD2, PHD3), one of the major factors coordinating HIF degradation under normoxic but not hypoxic conditions, are induced in osteoblasts under hypoxic conditions. To further determine the contribution of PHDs and upregulated HIF activity in modulating osteoblast phenotype, we treated osteoblasts with a PHD inhibitor, dimethyloxaloylglycine (DMOG), and maintained cells under normoxic conditions. Similar to hypoxic conditions, HRE reporter activity was increased and adipogenic gene expression was increased while osteoblastic genes were suppressed. Taken together, our findings indicate a role for PHDs and HIFs in the regulation of osteoblast phenotype.

Structure of the bovine VASAP-60/PRKCSH gene, functional analysis of the promoter, and gene expression analysis

Vacuolar system-associated protein-60 (VASAP-60) constitutes the bovine ortholog of the human "protein kinase C substrate 80K-H" (PRKCSH or 80K-H). We characterized the bovine VASAP-60/PRKCSH gene structure and promoter, identified cis-acting elements controlling VASAP-60 expression, searched for mRNA splice variants, and analyzed mRNA expression in ovarian follicles. Expression of VASAP-60 mRNA showed a 2.4-fold increase (P<0.0001) in granulosa cells of dominant follicles compared to small follicles (2-4 mm) or ovulatory follicles, and no mRNA splice variant was identified. The bovine VASAP-60 gene encompasses 12.5 kb and is composed of 18 exons and 17 introns. Primer extension analysis revealed a single transcription initiation site, and the promoter lacks a TATA box. Promoter activity assays were performed with a series of deletion constructs in different bovine cell lines (endometrial epithelial glandular, kidney epithelial and aortic endothelial) to identify cis-acting elements. The -53/+16 bp fragment (+1 = transcription start site) conferred minimal promoter activity whereas activator and repressor elements were located in the -200/-53 bp and -653/-200 bp fragments, respectively. Analysis of cis-acting elements in the -200/-53 bp activation domain revealed by gel shift assays and chromatin immunoprecipitation assay that transcription factor YY1 binds to VASAP-60 promoter. This study is the first to report that VASAP-60 is up-regulated in granulosa cells of dominant follicles, to document the primary structure of the bovine VASAP-60 gene and promoter, and to demonstrate that YY1 binds to the VASAP-60 proximal promoter and may act as a positive transcriptional regulator.

Proteomic analysis of hypoxia-induced responses in the syncytialization of human placental cell line BeWo

Syncytiotrophoblast formation is affected by a number of pathological conditions and suppressed syncytiotrophoblast formation due to hypoxia may play a role in the pathogenesis of preeclampsia. However, the molecular basis of hypoxia-inhibited trophoblast syncytialization is poorly understood. To determine the effect of hypoxia on trophoblast syncytialization, a proteomic analysis was performed in the human cytotrophoblast cell line BeWo using two-dimensional electrophoresis and MALDI-TOF-TOF-MS. Hypoxia induced marked inhibition of BeWo cell fusion and differentiation. The proteomic profiling was established under hypoxia in BeWo cell syncytialization. The results showed that twenty proteins were significantly up-or down-regulated under hypoxia, compared with cells under normoxia. In response to hypoxia, three antioxidants, peroxiredoxin 1, peroxiredoxin 2 and 1-Cys peroxiredoxin, were down-regulated, two proteins involved in glycolysis pathway (malate dehydrogenase and enolase) were up-regulated. The expression of two members of the annexin family (annexin A2 and annexin A5) increased. We also found a decreased expression of 14-3-3 tau protein in hypoxia treated cells. Proteins implied in protein degradation and folding were also identified. The expression of two cytoskeleton components (keratin 1 and beta-actin) was found to be down-regulated. In addition, galectin-3 was up-regulated. These proteins have been implicated in regulating cellular oxidative stress, glycolysis, signal transduction, protein folding and degradation, cell mobility and cytoskeletal structure formation. Western blot analysis revealed that the levels of peroxiredoxin 1 and 14-3-3 tau decreased, whereas the levels of annexin A5 and annexin A2 increased in BeWo cells under hypoxia. These findings provided new insights into the molecular mechanisms in mediating cellular response to hypoxia in trophoblast syncytialization.

Human prolyl-4-hydroxylase alpha(I) transcription is mediated by upstream stimulatory factors

Prolyl-4-hydroxylase alpha(I) (P4Halpha(I)) is the rate-limiting subunit for P4H enzyme activity, which is essential for procollagen hydroxylation and secretion. In the current study, we have characterized the human P4Halpha(I) promoter for transcription factors and DNA elements regulating P4Halpha(I) expression. Using a progressive deletion cloning approach, we have constructed pGL3-P4Halpha(I) recombinant plasmids. We have identified a positive regulatory region at the positions of bp -184 to -97 responsible for approximately 80% of the P4Halpha(I) promoter efficiency. Three E-boxes were located within this region, and the E-box at position bp -135 explains most of the regulatory capacity. Upstream stimulatory factors (USF1/USF2) were shown to bind on the E-box using chromatin immunoprecipitation assay. Suppression of USF1 and/or USF2 using specific short interference RNA resulted in a significant reduction in P4Halpha(I) promoter activity, and overexpressed USF1 or USF2 increased P4Halpha(I) promoter activity significantly. Although transforming growth factor beta1 increased the USF1/USF2-E-box binding and P4Halpha(I) promoter activity, this up-regulatory effect can be largely prevented by USF1/USF2-specific short interference RNA. On the other hand, cigarette smoking extracts, which have been shown to suppress P4Halpha(I) expression, inhibited the binding between the USF1/USF2 and E-box, resulting in a reduced P4Halpha(I) promoter activity. Furthermore, the E-box on the P4Halpha(I) promoter appeared to indiscriminately bind with either USF1 or USF2, with a similar outcome on the promoter efficiency. In conclusion, our study shows that USF1/USF2 plays a critical role in basal P4Halpha(I) expression, and both positive (transforming growth factor beta1) and negative (cigarette smoking extract) regulators appear to influence the USF-E-box interaction and affect P4Halpha(I) expression.

Hypoxia-inducible factors 1alpha and 2alpha regulate trophoblast differentiation

Placental development initially occurs in a low-oxygen (O2) or hypoxic environment. In this report we show that two hypoxia-inducible factors (HIFs), HIF1alpha and HIF2alpha, are essential for determining murine placental cell fates. HIF is a heterodimer composed of HIFalpha and HIFbeta (ARNT) subunits. Placentas from Arnt-/- and Hif1alpha-/- Hif2alpha-/- embryos exhibit defective placental vascularization and aberrant cell fate adoption. HIF regulation of Mash2 promotes spongiotrophoblast differentiation, a prerequisite for trophoblast giant cell differentiation. In the absence of Arnt or Hifalpha, trophoblast stem cells fail to generate these cell types and become labyrinthine trophoblasts instead. Therefore, HIF mediates placental morphogenesis, angiogenesis, and cell fate decisions, demonstrating that O2 tension is a critical regulator of trophoblast lineage determination. This novel genetic approach provides new insights into the role of O2 tension in the development of life-threatening pregnancy-related diseases such as preeclampsia.

Cell type-dependent regulation of the hypoxia-responsive plasminogen activator inhibitor-1 gene by upstream stimulatory factor-2

Transcriptional regulation of the plasminogen activator inhibitor type-1 (PAI-1) gene is an important issue since PAI-1 plays a crucial role in various pathological conditions. The transcription factor USF-2 was shown to be a negative regulator for rat PAI-1 expression, and therefore it was the aim of this study to evaluate the role of USF-2 for human PAI-1 expression. We found in human hepatoma cells (HepG2) that USF-2 induced human PAI-1 expression via two classical E-boxes and the hypoxia-responsive element (HRE) within the promoter. Gel-shift analyses showed that E-box 4 and E-box 5 bound USFs, and although the HRE contributed to the USF-dependent effects, it did not bind them. By contrast, USF-2 inhibited PAI-1 promoter activity in primary rat hepatocytes suggesting that PAI-1 expression depends on either the promoter context or USF activity which might be cell type-specific. Cotransfection of human or rat PAI-1 promoter luciferase constructs with expression vectors for wild-type USF-2 or USF-2 mutants in human HepG2 and rat H4IIE cells as well as in primary rat hepatocytes revealed that the effects of USF on PAI-1 expression depend on the cell type rather than the promoter context and that the USF-specific region domain of USF accounts for the observed cell type-specific effects.

The regulation of trophoblast differentiation by oxygen in the first trimester of pregnancy

In the first trimester of human pregnancy villous cytotrophoblasts are able to differentiate to form either the overlying syncytiotrophoblast layer or, in anchoring villi, extravillous trophoblasts which grow out from the villi and invade into the maternal decidua, acting to both physically attach the placenta to the decidua, and modify the maternal spiral arteries to sustain pregnancy. During the first 10-12 weeks of gestation, extravillous trophoblast plugs block the spiral arteries and prevent maternal blood flow entering the intervillous space, thereby creating an environment of physiological hypoxia in which placental and fetal development occur. As extravillous trophoblasts migrate away from the villus they differentiate from a proliferative to an invasive phenotype. The hypoxic environment of the first trimester is believed to play an important role in the regulation of trophoblast differentiation. However, there is currently a large body of conflicting experimental evidence concerning this topic. This review examines the experimental evidence to date on the role of oxygen in trophoblast differentiation.

O2 enhancement of human trophoblast differentiation and hCYP19 (aromatase) gene expression are mediated by proteasomal degradation of USF1 and USF2

When cultured in 20% O(2), human cytotrophoblasts fuse to form the syncytiotrophoblast with marked induction of hCYP19 (aromatase) gene expression. When cultured in 2% O(2), cytotrophoblast fusion and induced hCYP19 expression are prevented. These effects of hypoxia are mediated by increased expression of mammalian achaete/scute homologue-2 (Mash-2), which increases levels of upstream stimulatory factors 1 and 2 (USF1/2) and their binding as heterodimers to E-boxes surrounding the hCYP19 promoter. In studies to define mechanisms for O(2) regulation of syncytiotrophoblast differentiation, we found that hypoxia and overexpression of Mash-2 markedly increased cyclin B1 levels in cultured trophoblasts and the proportion of cells at the G(2)/M transition. Unlike USF proteins, USF1/2 mRNA levels are unaffected by O(2) tension. To determine whether increased O(2) might enhance proteasomal degradation of USF1/2, human trophoblasts were cultured in 2% or 20% O(2) with or without proteasome inhibitors. In cells cultured in 20% O(2), proteasome inhibitors increased USF1/2 protein levels and blocked spontaneous induction of hCYP19 expression, cell fusion, and differentiation. Like hypoxia, inhibitory effects of proteasome inhibitors on hCYP19 expression were mediated by increased binding of USF1/2 to the E-boxes. In human trophoblast cells cultured in 20% O(2), increased polyubiquitylation of USF1/2 proteins was observed. Thus, early in gestation when the placenta is relatively hypoxic, increased USF1/2 may block trophoblast differentiation and hCYP19 gene expression. In the second trimester, increased O(2) tension promotes proteasomal degradation of USF1/2, resulting in syncytiotrophoblast differentiation and induction of hCYP19 expression.

Regulation of aromatase expression in estrogen-responsive breast and uterine disease: from bench to treatment

A single gene encodes the key enzyme for estrogen biosynthesis termed aromatase, inhibition of which effectively eliminates estrogen production. Aromatase inhibitors successfully treat breast cancer and endometriosis, whereas their roles in endometrial cancer, uterine fibroids, and aromatase excess syndrome are less clear. Ovary, testis, adipose tissue, skin, hypothalamus, and placenta express aromatase normally, whereas breast and endometrial cancers, endometriosis, and uterine fibroids overexpress aromatase and produce local estrogen that exerts paracrine and intracrine effects. Tissue-specific promoters distributed over a 93-kilobase regulatory region upstream of a common coding region alternatively control aromatase expression. A distinct set of transcription factors regulates each promoter in a signaling pathway- and tissue-specific manner. Three mechanisms are responsible for aromatase overexpression in a pathologic tissue versus its normal counterpart. First, cellular composition is altered to increase aromatase-expressing cell types that use distinct promoters (breast cancer). Second, molecular alterations in stromal cells favor binding of transcriptional enhancers versus inhibitors to a normally quiescent aromatase promoter and initiate transcription (breast/endometrial cancer, endometriosis, and uterine fibroids). Third, heterozygous mutations, which cause the aromatase coding region to lie adjacent to constitutively active cryptic promoters that normally transcribe other genes, result in excessive estrogen formation owing to the overexpression of aromatase in many tissues.

Hypoxia-responsive transcription factors

Hypoxia is a common pathophysiological occurrence with a profound impact on the cellular transcriptome. The consequences of hypoxia-induced or hypoxia-repressed gene expression have important implications in disease processes as diverse as tumour development and chronic inflammation. While the hypoxia-inducible factor (HIF-1) plays a major role in controlling the ubiquitous transcriptional response to hypoxia, it is clear that a number of other transcription factors are also activated either directly or indirectly. In this review, we comprehensively discuss the transcription factors that have been reported to be hypoxia-responsive and the signalling mechanisms leading to their activation. Understanding such events will enhance our understanding of cellular oxygen sensing.

Role of upstream stimulatory factor phosphorylation in the regulation of the prostaglandin G/H synthase-2 promoter in granulosa cells

To investigate the role of USF phosphorylation in the regulation of the PGHS-2 promoter in granulosa cells, promoter activity assays were performed in primary cultures of bovine granulosa cells transfected with the chimeric PGHS-2 promoter/luciferase (LUC) construct -149/-2PGHS-2.LUC. Transfections were done in the absence or presence of forskolin; the protein kinase A (PKA) inhibitor H-89; or an expression vector encoding USF1, USF2, the catalytic subunit of PKA (cPKA), or a PKA inhibitor protein (PKI). Electrophoretic mobility shift assays were performed to study USF/DNA interactions using granulosa cell nuclear extracts and a 32P-labeled proximal PGHS-2 promoter fragment containing the E-box element. The results show that forskolin stimulation and cPKA overexpression caused a marked and significant increase in USF-dependent DNA binding and PGHS-2 promoter activities (p < 0.05). In contrast, both activities were decreased by H-89 treatment or PKI overexpression. Reverse transcription-PCR analyses revealed that these treatments had similar effects on endogenous PGHS-2 mRNA levels in granulosa cells. Cotransfection studies with a USF2 mutant lacking N-terminal activation domains (U2Delta1-220) repressed forskolin-, cPKA-, and USF-dependent PGHS-2 promoter activities. Electrophoretic mobility shift assays showed that U2Delta1-220 was able to compete with full-length USF proteins and to saturate the E-box element. Immunoprecipitation/Western blot analyses revealed an increase in the levels of phosphorylated USF1 and USF2 after forskolin treatment, whereas chromatin immunoprecipitation assays showed that binding of USF proteins to the endogenous PGHS-2 promoter was stimulated by forskolin. Site-directed mutagenesis of a consensus PKA phosphorylation site within USF proteins abolished their transactivating capacity. Collectively, these results characterize the role of USF phosphorylation in PGHS-2 expression and identify the phosphorylation-dependent increase in USF binding to the E-box as a putative molecular basis for the increase in PGHS-2 promoter transactivation in granulosa cells.

Transcriptional regulation of aromatase in placenta and ovary

Our goal is to define the cellular and molecular mechanisms for tissue- and cell-specific, developmental and hormonal regulation of the human CYP19 (aromatase P450/P450arom) gene in estrogen-producing cells. In this article, we review studies using transgenic mice and transfected cells to identify genomic regions and response elements that mediate CYP19 expression in placenta and ovary, as well as to define the molecular mechanisms for O2 regulation of differentiation and CYP19 gene expression in human trophoblast cells in culture. We also highlight recent findings regarding LRH-1 versus SF-1 mRNA expression and cellular localization in the mouse ovary during the estrous cycle and various stages of pregnancy. Spatial and temporal expression patterns of mRNAs encoding these orphan nuclear receptors in comparison to those of P450arom and 17alpha-hydroxylase/17,20-lyase mRNAs, suggest an important role of LRH-1 together with SF-1 in ovarian steroidogenesis.

Genomic regions that mediate placental cell-specific and developmental regulation of human Cyp19 (aromatase) gene expression in transgenic mice

The human aromatase (hCYP19) gene is controlled by tissue-specific promoters that lie upstream of tissue-specific first exons. Placenta-specific exon I.1 lies approximately 100,000 bp upstream of exon II. Previously, we observed that genomic sequences within 501 bp upstream of exon I.1 mediate placenta-specific expression. In the present study, transgenic mice were created carrying hCYP19I.1(-246):hGH/hGX, hCYP19I.1(-201):hGH, and hCYP19I.1(-125):hGH fusion genes to further delineate 5'-flanking sequences within 501 bp of exon I.1 that are required to mediate placenta-specific hCYP19 gene expression. As little as 246 bp of hCYP19 exon I.1 5'-flanking sequence was sufficient to direct placenta-specific expression in transgenic mice. By contrast, transgenes containing 201 or 125 bp of exon I.1 5'-flanking DNA were not expressed in mouse placenta. Furthermore, hCYP19I.1(-246):hGX transgene expression was developmentally regulated; expression was observed as early as embryonic d 7.5 (E7.5) in several cells of the trophoblast ectoderm, on E8.5 in some trophoblast giant cells, and by E9.5 in giant cells and the labyrinthine layer. By contrast, expression of the hCYP19I.1(-501):hGH transgene was first observed on E10.5 and was restricted to the labyrinthine layer, which is most analogous to the human syncytiotrophoblast. This suggests the presence of regulatory elements between -501 and -246 bp that may bind inhibitory transcription factors expressed in giant cells. These findings from transgenic experiments together with deletion mapping studies using transfected human placental cells indicate that the concerted interaction of strong placenta-specific enhancers and silencers within this 501-bp region mediate labyrinthine and syncytiotrophoblast-specific CYP19 gene expression.

Upstream stimulatory factors stimulate transcription through E-box motifs in the PF4 gene in megakaryocytes

Platelet factor 4 (PF4) is expressed during megakaryocytic differentiation. We previously demonstrated that the homeodomain proteins (myeloid ecotropic integration site 1 [MEIS1], Pbx-regulating protein 1 [PREP1], and pre-B-cell leukemia transcription factors [PBXs]) bind to the novel regulatory element tandem repeat of MEIS1 binding element [TME] and transactivate the rat PF4 promoter. In the present study, we investigated and identified other TME binding proteins in megakaryocytic HEL cells using mass spectrometry. Among identified proteins, we focused on upstream stimulatory factor (USF1) and USF2 and investigated their effects on the PF4 promoter. USF1 and 2 bound to the E-box motif in the TME and strongly transactivated the PF4 promoter. Furthermore, physiologic bindings of USF1 and 2 to the TME in rat megakaryocytes were demonstrated by the chromatin immunoprecipitation (ChIP) assay. Interestingly, the E-box motif in the TME was conserved in TME-like sequences of both the human and mouse PF4 promoters. USF1 and 2 also bound to the human TME-like sequence and transactivated the human PF4 promoter. Expressions of USF1 and 2 were detected by reverse-transcriptase-polymerase chain reaction (RT-PCR) in the human megakaryocytes derived from CD34+ cells. Thus, these studies demonstrate that the novel TME binding transcription factors, USF1 and 2, transactivate rat and human PF4 promoters and may play an important role in megakaryocytic gene expression.

Molecular Characterization and Role of Bovine Upstream Stimulatory Factor 1 and 2 in the Regulation of the Prostaglandin G/H Synthase-2 Promoter in Granulosa Cells

The transcriptional activation of the prostaglandin G/H synthase-2 (PGHS-2) gene in granulosa cells is required for ovulation. To directly study the ability of upstream stimulatory factor 1 (USF1) and USF2 to trans-activate the bovine PGHS-2 promoter in granulosa cells, USF1 or USF2 expression vectors were cotransfected with the PGHS-2/luciferase (LUC) chimeric construct, -149/-2PGHS-2.LUC. Results revealed that overexpression of USF1 or USF2 caused a marked and significant increase in basal and forskolin-inducible promoter activities (p<0.05), and these effects were dependent on the presence of a consensus E-box cis-element within the promoter fragment. Co-transfections with different N- and C-terminal truncated USF mutants led to significant reductions in promoter activation, as compared with full-length constructs (p<0.05), thus allowing identification of putative bovine USF functional domains. Overexpression of a USF2 truncated mutant lacking the first 220 residues (U2Delta1-220) acted as a dominant negative mutant and blocked endogenous and USF-stimulated PGHS-2 promoter activation. Interestingly, transfections with U2Delta1-220 blocked the forskolin-dependent induction of PGHS-2 mRNA in granulosa cells, whereas transfections with full-length USF2 increased PGHS-2 transcript levels. Immunoblot analyses confirmed overexpression of full-length and truncated USF proteins, and electrophoretic mobility shift assays (EMSAs) and supershift EMSAs established that the observed effects were dependent on specific interactions between USF proteins and the consensus E-box cis-element. Stimulation of cells with forskolin increased, whereas treatment of extracts with phosphatase decreased USF binding activities to the E-box. Thus, this study presents for the first time direct evidence for a role of USF proteins in the regulation of the PGHS-2 promoter in preovulatory granulosa cells.