The orphan receptor ARP-1/COUP-TFII, a member of the chicken ovalbumin upstream promoter transcription factor (COUP-TF) subfamily of nuclear receptors, strongly represses transcriptional activity of numerous genes, including several apolipoprotein-encoding genes. Recently it has been demonstrated that the mechanism by which COUP-TFs reduce transcriptional activity involves active repression and transrepression. To map the domains of ARP-1/COUP-TFII required for repressor activity, a detailed deletion analysis of the protein was performed. Chimeric proteins in which various segments of the ARP-1/COUP-TFII carboxy terminus were fused to the GAL4 DNA binding domain were used to characterize its active repression domain. The smallest segment confering active repressor activity to a heterologous DNA binding domain was found to comprise residues 210 to 414. This domain encompasses the region of ARP-1/COUP-TFII corresponding to helices 3 to 12 in the recently published crystal structure of other members of the nuclear receptor superfamily. It includes the AF-2 AD core domain formed by helix 12 but not the hinge region, which is essential for interaction with a corepressor in the case of the thyroid hormone and retinoic acid receptor. Attachment of the nuclear localization signal from the simian virus 40 large T antigen (Flu tag) to the amino terminus of ARP-1/COUP-TFII abolished its ability to bind to DNA without affecting its repressor activity. By using a series of Flu-tagged mutants, the domains required for transrepressor activity of the protein were mapped. They include the DNA binding domain and the segment spanning residues 193 to 399. Transcriptional activity induced by liver-enriched transactivators such as hepatocyte nuclear factor 3 (HNF-3), C/EBP, or HNF-4 was repressed by ARP-1/COUP-TFII independent of the presence of its cognate binding site, while basal transcription or transcriptional activity induced by ATF or Sp1 was not perturbed by the protein. In conclusion, our results demonstrate that the domains of ARP-1/COUP-TFII required for active repression and transrepression do not coincide. Moreover, they strongly suggest that transrepression is the predominant mechanism underlying repressor activity of ARP-1/COUP-TFII. This mechanism most likely involves interaction of the protein with one or several transcriptional coactivator proteins which are employed by various liver-enriched transactivators but not by ubiquitous factors such as Sp1 or ATF.
The Oct-3/4 transcription factor is a member of the POU family of transcription factors and, as such, probably plays a crucial role in mammalian embryogenesis and differentiation. It is expressed in the earliest stages of embryogenesis and repressed in subsequent stages. Similarly, Oct-3/4 is expressed in embryonal carcinoma (EC) cells and is repressed in retinoic acid (RA)-differentiated EC cells. Previously we have shown that the Oct-3/4 promoter harbors an RA-responsive element, RAREoct, which functions in EC cells as a binding site for positive regulators of transcription and in RA-differentiated EC cells as a binding site for positive regulators of transcription and in RA-differentiated EC cells as a binding site for negative regulators. Our present results demonstrate that in P19 and RA-treated P19 cells, the orphan receptors ARP-1/COUP-TFII and EAR-3/COUP-TFI repress Oct-3/4 promoter activity through the RAREoct site in a dose-dependent manner. While the N-terminal region of the ARP-1/COUP-TFII receptor is dispensable for this repression, the C-terminal domain harbors the silencing region. Interestingly, three different RA receptor:retinoid X receptor (RAR:RXR) heterodimers, RAR alpha:RXR alpha, RAR beta:RXR alpha, and RAR beta:RXR beta, specifically bind and activate Oct-3/4 promoter through the RAREoct site in a ligand-dependent manner. We have shown that antagonism between ARP-1/COUP-TFII or EAR-3/COUP-TFI and the RAR:RXR heterodimers and their intracellular balance modulate Oct-3/4 expression. Oct-3/4 transcriptional repression by the orphan receptors can be overcome by increasing amounts of RAR:RXR heterodimers. Conversely, activation of Oct-3/4 promoter by RAR:RXR heterodimers was completely abolished by EAR-3/COUP-TFI and by ARP-1/COUP-TFII. The orphan receptors bind the RAREoct site with a much higher affinity than the RAR:RXR heterodimers. This high binding affinity provides ARP-1/COUP-TFII and EAR-3/COUP-TFI with the ability to compete with and even displace RAR:RXR from the RAREoct site and subsequently to actively silence the Oct-3/4 promoter. We have shown that RA treatment of EC cells results in up-regulation of ARP-1/COUP-TFII and EAR-3/COUP-TFI expression. Most interestingly, in RA-treated EC cells, the kinetics of Oct-3/4 repression inversely correlates with the kinetics of ARP-1/COUP-TFII and EAR-3/COUP-TFI activation. These findings are in accordance with the suggestion that these orphan receptors participate in controlling a network of transcription factors, among which Oct-3/4 is included, which may establish the pattern of normal gene expression during development.
Pancreatic islet beta cell differentiation and function are dependent upon a group of transcription factors that maintain the expression of key genes and suppress others. Knockout mice with the heterozygous deletion of the gene for chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) or the complete disruption of the gene for hepatocyte nuclear factor 4α (HNF4α) in pancreatic beta cells have similar insulin secretion defects, leading us to hypothesize that there is transcriptional cross talk between these two nuclear receptors. Here, we demonstrate specific HNF4α activation of a reporter plasmid containing the COUP-TFII gene promoter region in transfected pancreatic beta cells. The stable association of the endogenous HNF4α with a region of the COUP-TFII gene promoter that contains a direct repeat 1 (DR-1) binding site was revealed by chromatin immunoprecipitation. Mutation experiments showed that this DR-1 site is essential for HNF4α transactivation of COUP-TFII. The dominant negative suppression of HNF4α function decreased endogenous COUP-TFII expression, and the specific inactivation of COUP-TFII by small interfering RNA caused HNF4α mRNA levels in 832/13 INS-1 cells to decrease. This positive regulation of HNF4α by COUP-TFII was confirmed by the adenovirus-mediated overexpression of human COUP-TFII (hCOUP-TFII), which increased HNF4α mRNA levels in 832/13 INS-1 cells and in mouse pancreatic islets. Finally, hCOUP-TFII overexpression showed that there is direct COUP-TFII autorepression, as COUP-TFII occupies the proximal DR-1 binding site of its own gene in vivo. Therefore, COUP-TFII may contribute to the control of insulin secretion through the complex HNF4α/maturity-onset diabetes of the young 1 (MODY1) transcription factor network operating in beta cells.
The orphan nuclear receptor COUP-TFII plays an undefined role in breast cancer. Previously we reported lower COUP-TFII expression in tamoxifen/endocrine- resistant versus sensitive breast cancer cell lines. The identification of COUP-TFII-interacting proteins will help to elucidate its mechanism of action as a transcriptional regulator in breast cancer.
FLAG-affinity purification and multidimensional protein identification technology (MudPIT) identified nucleolin among the proteins interacting with COUP-TFII in MCF-7 tamoxifen-sensitive breast cancer cells. Interaction of COUP-TFII and nucleolin was confirmed by coimmunoprecipitation of endogenous proteins in MCF-7 and T47D breast cancer cells. In vitro studies revealed that COUP-TFII interacts with the C-terminal arginine-glycine repeat (RGG) domain of nucleolin. Functional interaction between COUP-TFII and nucleolin was indicated by studies showing that siRNA knockdown of nucleolin and an oligonucleotide aptamer that targets nucleolin, AS1411, inhibited endogenous COUP-TFII-stimulated RARB2 expression in MCF-7 and T47D cells. Chromatin immunoprecipitation revealed COUP-TFII occupancy of the RARB2 promoter was increased by all-trans retinoic acid (atRA). RARβ2 regulated gene RRIG1 was increased by atRA and COUP-TFII transfection and inhibited by siCOUP-TFII. Immunohistochemical staining of breast tumor microarrays showed nuclear COUP-TFII and nucleolin staining was correlated in invasive ductal carcinomas. COUP-TFII staining correlated with ERα, SRC-1, AIB1, Pea3, MMP2, and phospho-Src and was reduced with increased tumor grade.
Our data indicate that nucleolin plays a coregulatory role in transcriptional regulation of the tumor suppressor RARB2 by COUP-TFII.
Ucp3 is an integral protein of the inner mitochondrial membrane with a role in lipid metabolism preventing deleterious effects of fatty acids in states of high lipid oxidation. Ucp3 is expressed in brown adipose tissue and skeletal muscle and controlled by a transcription factor complex including PPARalpha, MyoD and the histone acetyltransferase p300. Several studies have demonstrated interaction of these factors with chicken ovalbumin upstream promoter transcription factor II (Coup-TFII). This nuclear receptor is involved in organogenesis and other developmental processes including skeletal muscle development, but also co-regulates a number of metabolic genes. In this study we in silico analyzed the upstream region of Ucp3 of the Djungarian hamster Phodopus sungorus and identified several putative response elements for Coup-TFII. We therefore investigated whether Coup-TFII is a further player in the transcriptional control of the Ucp3 gene in rodents.
By quantitative PCR we demonstrated a positive correlation of Coup-TFII and Ucp3 mRNA expression in skeletal muscle and brown adipose tissue in response to food deprivation and cold exposure, respectively. In reporter gene assays Coup-TFII enhanced transactivation of the Ucp3 promoter conveyed by MyoD, PPARalpha, RXRalpha and/or p300. Using deletions and mutated constructs, we identified a Coup-TFII enhancer element 816–840 bp upstream of the transcriptional start site. Binding of Coup-TFII to this upstream enhancer was confirmed in electrophoretic mobility shift and supershift assays.
Transcriptional regulation of the Coup-TFII gene in response to starvation and cold exposure seems to be the regulatory mechanism of Ucp3 mRNA expression in brown adipose and skeletal muscle tissue determining the final appropriate rate of transcript synthesis. These findings add a crucial component to the complex transcriptional machinery controlling expression of Ucp3. Given the substantial evidence for a function of Ucp3 in lipid metabolism, Coup-TFII may not only be a negative regulator of glucose responsive genes but also transactivate genes involved in lipid metabolism.
vHNF1 (also termed HNF1 beta) is a member of the hepatocyte nuclear fa ctor 1 (HNF1; also termed HNF1 alpha) family of homeodomain-containing transcription factors that interact with a sequence motif found in the regulatory regions of a large number of genes expressed mainly in the liver. It has been suggested that vHNF1 plays a role in early differentiation of specialized epithelia of several endoderm- and mesoderm-derived organs, with HNF1 playing a role in later stages. In support of this idea, expression of vHNF1 but not HNF1 is induced upon treatment of the embryonal carcinoma cell line F9 with retinoic acid. We have cloned and analyzed the vHNF1 promoter to gain a better understanding of the regulation of vHNF1 expression and how it relates to the expression of HNF1. We have identified five sites of DNA-protein interaction within the first 260 bp upstream of the transcription start site, which involve at least three different families of transcription factors. Two sites, a distal DR-1 motif and a proximal octamer motif, are the most important for promoter activity. The DR-1 motif interacts with several members of the steroid hormone receptor superfamily including HNF4, COUP-TFI/Ear3, COUP-TFII/Arp1, and RAR alpha/RXR alpha heterodimers. The vHNF1 promoter is transactivated by COUP-TFI/Ear3 and COUP-TFII/Arp1 and, unlike the HNF1 promoter, is virtually unaffected by HNF4. Interestingly, the proximal octamer site and not the DR-1 site is required for COUP-TFI/Ear3 and COUP-TFII/Arp1 transactivation of the vHNF1 promoter. COUP-TFI/Ear3 does not bind directly to this proximal octamer site. We present evidence of an interaction between COUP-TFI/Ear3 and the octamer-binding proteins in vitro and in the cell, suggesting that COUP-TFI and COUP-TFII activate the vHNF1 promoter via an indirect mechanism.
Progesterone and estrogen are critical regulators of uterine receptivity. To facilitate uterine remodeling for embryo attachment, estrogen activity in the uterine epithelia is attenuated by progesterone; however, the molecular mechanism by which this occurs is poorly defined. COUP-TFII (chicken ovalbumin upstream promoter transcription factor II; also known as NR2F2), a member of the nuclear receptor superfamily, is highly expressed in the uterine stroma and its expression is regulated by the progesterone–Indian hedgehog–Patched signaling axis that emanates from the epithelium. To further assess COUP-TFII uterine function, a conditional COUP-TFII knockout mouse was generated. This mutant mouse is infertile due to implantation failure, in which both embryo attachment and uterine decidualization are impaired. Using this animal model, we have identified a novel genetic pathway in which BMP2 lies downstream of COUP-TFII. Epithelial progesterone-induced Indian hedgehog regulates stromal COUP-TFII, which in turn controls BMP2 to allow decidualization to manifest in vivo. Interestingly, enhanced epithelial estrogen activity, which impedes maturation of the receptive uterus, was clearly observed in the absence of stromal-derived COUP-TFII. This finding is consistent with the notion that progesterone exerts its control of implantation through uterine epithelial-stromal cross-talk and reveals that stromal-derived COUP-TFII is an essential mediator of this complex cross-communication pathway. This finding also provides a new signaling paradigm for steroid hormone regulation in female reproductive biology, with attendant implications for furthering our understanding of the molecular mechanisms that underlie dysregulation of hormonal signaling in such human reproductive disorders as endometriosis and endometrial cancer.
Pregnancy is established and maintained through a series of precisely choreographed cellular and molecular events that are controlled by two sex hormones, estrogen and progesterone. Both hormones exert their actions through their distinct nuclear receptors. During the peri-implantation period, estrogen activity is attenuated by progesterone to facilitate epithelial remodeling and embryo attachment, but the detailed molecular mechanism of how this process is achieved remains largely undefined. COUP-TFII (chicken ovalbumin upstream promoter transcription factor II; also known as NR2F2), a member of the nuclear receptor superfamily, is highly expressed in the uterine stroma, and its expression is controlled by progesterone–Indian hedgehog–Patched signaling from the epithelium to the stroma. To assess the uterine function of COUP-TFII, uterine-specific COUP-TFII knockout mice were generated. These mutant mice are infertile due to failure of implantation. We identified a novel genetic pathway in which the epithelial Ihh regulates the stroma COUP-TFII to control BMP2 and regulates decidualization. Interestingly, enhanced epithelial estrogen activity, which impedes the maturation of receptive uterus, was clearly noted in the absence of COUP-TFII. This finding reveals that COUP-TFII plays a critical role in maintaining the balance between estrogen and progesterone activities to establish proper implantation. This finding also provides new insights into women's health care associated with uncontrolled estrogen activity, such as breast cancer and endometriosis.
The formation of various tissues requires close communication between two groups of cells, epithelial and mesenchymal cells. COUP-TFs are transcription factors which have been shown to have functions in embryonic development. COUP-TFI is expressed mainly in the nervous system, and its targeted deletion leads to defects in the central and peripheral nervous systems. COUP-TFII is highly expressed in the mesenchymal component of the developing organs. A null mutation of COUP-TFII results in the malformation of the heart and blood vessels. From their expression pattern, we proposed that COUP-TFs regulate paracrine signals important for mesenchymal cell-epithelial cell interactions. In order to identify genes regulated by COUP-TF in this process, a rat urogenital mesenchymal cell line was stably transfected with a COUP-TFI expression vector. We found that NGFI-A, a gene with important functions in brain, organ, and vasculature development, has elevated mRNA and protein levels upon overexpression of COUP-TFI in these cells. A study of the promoter region of this gene identified a COUP-TF-responsive element between positions −64 and −46. Surprisingly, this region includes binding sites for members of the Sp1 family of transcription factors but no COUP-TF binding site. Mutations that abolish the Sp1 binding activity also impair the transactivation of the NGFI-A promoter by COUP-TF. Two regions of the COUP-TF molecule are shown to be important for NGFI-A activation: the DNA binding domain and the extreme C terminus of the putative ligand binding domain. The C-terminal region is likely to be important for interaction with coactivators. In fact, the coactivators p300 and steroid receptor activator 1 can enhance the transactivation of the NGFI-A promoter induced by COUP-TFI. Finally, we demonstrated that COUP-TF can directly interact with Sp1. Taken together, these results suggest that NGFI-A is a target gene for COUP-TFs and that the Sp1 family of transcription factors mediates its regulation by COUP-TFs.
Chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an orphan nuclear receptor that regulates many key biological processes, including organ development and cell fate determination. Although the biological functions of COUP-TFII have been studied extensively, little is known about what regulates its gene expression, especially the role of inducible extracellular factors in triggering it. Here we report that COUP-TFII expression is regulated specifically by fibroblast growth factor 2 (FGF2), which mediates activation of the MEK1/2 pathway in mesenchymal lineage C3H10T1/2 cells. Although FGF2 treatment increased cell proliferation, the induction of COUP-TFII expression was dispensable. Instead, FGF2-primed cells in which COUP-TFII expression was induced showed a low potential for osteoblast differentiation, as evidenced by decreases in alkaline phosphatase activity and osteogenic marker gene expression. Reducing COUP-TFII by U0126 or siRNA against COUP-TFII prevented the anti-osteogenic effect of FGF2, indicating that COUP-TFII plays a key role in the FGF2-mediated determination of osteoblast differentiation capability. This report is the first to suggest that FGF2 is an extracellular inducer of COUP-TFII expression and may suppress the osteogenic potential of mesenchymal cells by inducing COUP-TFII expression prior to the onset of osteogenic differentiation.
COUP-TF II is an orphan nuclear receptor that has no known ligand in the 'classical sense'. COUP-TF interacts with the corepressors N-CoR, SMRT and RIP13, and silences transcription by active repression and trans-repression. Forced expression of the orphan nuclear receptor COUP-TF II in mouse C2 myogenic cells has been demonstrated to inhibit morphological differentiation, and to repress the expression of: (i) the myoD gene family which encodes myogenic basic helix-loop-helix (bHLH) proteins; and (ii) the cell cycle regulator, p21(Waf-1/Cip-1). In the present study, we show that COUP-TF II efficiently inhibits the myoD -mediated myogenic conversion of pluripotential C3H10T1/2 cells by post-transcriptional mechanisms. Furthermore, repression of MyoD-dependent transcription by COUP-TF II occurs in the absence of the nuclear receptor cognate binding motif. The inhibition of MyoD-mediated trans-activation involves the direct binding of the DNA binding domain/C-region and hinge/D-regions [i.e. amino acid (aa) residues 78-213] of COUP-TF II to the N-terminal activation domain of MyoD. Over-expression of the cofactor p300, which functions as a coactivator of myoD-mediated transcription, alleviated repression by COUP-TF II. Further binding analysis demonstrated that COUP-TF II interacted with the N-terminal 149 aa residues of p300 which encoded the receptor interaction domain of the coactivator. Finally we observed that COUP-TF II, MyoD and p300 interact in a competitive manner, and that increasing amounts of COUP-TF II have the ability to reduce the interaction between myoD and p300 invitro. The experiments presented herein suggest thatCOUP-TF II post-transcriptionally regulates myoD activity/function, and that crosstalk between orphan nuclear receptors and the myogenic bHLH proteins has functional consequences for differentiation.
Chicken ovalbumin upstream promoter transcription factors (COUP-TFs) strongly inhibit transcriptional activation mediated by nuclear hormone receptors, including hepatocyte nuclear factor 4 (HNF-4). COUP-TFs repress HNF-4-dependent gene expression by competition with HNF-4 for common binding sites found in several regulatory regions. Here we show that promoters, such as the HNF-1 promoter, which are recognized by HNF-4 but not by COUP-TFs are activated by COUP-TFI and COUP-TFII in conjunction with HNF-4 more than 100-fold above basal levels, as opposed to about 8-fold activation by HNF-4 alone. This enhancement was strictly dependent on an intact HNF-4 E domain. In vitro and in vivo evidence suggests that COUP-TFs enhance HNF-4 activity by a mechanism that involves their physical interaction with the amino acid 227 to 271 region of HNF-4. Our results indicate that in certain promoters, COUP-TFs act as auxiliary cofactors for HNF-4, orienting the HNF-4 activation domain in a more efficient configuration to achieve enhanced transcriptional activity. These findings provide new insights into the regulatory functions of COUP-TFs, suggesting their involvement in the initial activation and subsequent high-level expression of hepatic regulators, as well as in the positive and negative modulation of downstream target genes.
Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII; also known as NR2F2), is an orphan nuclear receptor of the steroid/thyroid hormone receptor superfamily. COUP-TFII-null mice die during the early embryonic development due to angiogenesis and cardiovascular defects. To circumvent the early embryonic lethality and investigate the physiological function of COUP-TFII, we knocked out COUP-TFII gene in a time-specific manner by using a tamoxifen inducible Cre recombinase. The ablation of COUP-TFII during pre-pubertal stages of male development results in infertility, hypogonadism and spermatogenetic arrest. Homozygous adult male mutants are defective in testosterone synthesis, and administration of testosterone could largely rescue the mutant defects. Notably, the rescued results also provide the evidence that the major function of adult Leydig cell is to synthesize testosterone. Further phenotypic analysis reveals that Leydig cell differentiation is arrested at the progenitor cell stage in the testes of null mice. The failure of testosterone to resumption of Leydig cell maturation in the null mice indicates that COUP-TFII itself is essential for this process. In addition, we identify that COUP-TFII plays roles in progenitor Leydig cell formation and early testis organogenesis, as demonstrated by the ablation of COUP-TFII at E18.5. On the other hand, when COUP-TFII is deleted in the adult stage after Leydig cells are well differentiated, there are no obvious defects in reproduction and Leydig cell function. Taken together, these results indicate that COUP-TFII plays a major role in differentiation, but not the maintenance of Leydig cells.
The chicken ovalbumin upstream promoter transcription factors (COUP-TFs), members of the nuclear receptor superfamily, consist of two highly homologous subtypes, COUP-TFI (EAR-3, NR2F1) and COUP-TFII (ARP-1, NR2F2). They are referred to as orphan receptors because the COUP-TF ligands have yet to be identified. Since the discovery of COUP-TFs in 1986, extensive studies have demonstrated their crucial functions in a variety of developmental processes, such as organogenesis, angiogenesis, and metabolic homeostasis. Recently, emerging evidence has highlighted that COUP-TFs, specifically COUP-TFII, play important roles in tumorigenesis. In this review, we will discuss the critical functions of COUP-TFII in the development of the tumor microenvironment, the progression of various cancers, and its underlying mechanisms.
nuclear receptor; COUP-TFII; tumorigenesis; prostate cancer; breast cancer
The orphan receptors COUP-TF (chicken ovalbumin upstream promoter transcription factor) I and II are members of the nuclear receptor superfamily that play distinct and critical roles in vertebrate organogenesis. The involvement of COUP-TFs in cancer development has recently been suggested by several studies but remains poorly understood.
MCF-7 breast cancer cells overexpressing COUP-TFI and human breast tumors were used to investigate the role of COUP-TFI in the regulation of CXCL12/CXCR4 signaling axis in relation to cell growth and migration. We used Immunofluorescence, western-blot, RT-PCR, Formaldehyde-assisted Isolation of Regulatory Elements (FAIRE) assays, as well as cell proliferation and migration assays.
Previously, we showed that COUP-TFI expression is enhanced in breast cancer compared to normal tissue. Here, we report that the CXCL12/CXCR4 signaling pathway, a crucial pathway in cell growth and migration, is an endogenous target of COUP-TFI in breast cancer cells. The overexpression of COUP-TFI in MCF-7 cells inhibits the expression of the chemokine CXCL12 and markedly enhances the expression of its receptor, CXCR4. Our results demonstrate that the modification of CXCL12/CXCR4 expression by COUP-TFI is mediated by the activation of epithelial growth factor (EGF) and the EGF receptor. Furthermore, we provide evidence that these effects of COUP-TFI increase the growth and motility of MCF-7 cells in response to CXCL12. Cell migration toward a CXCL12 gradient was inhibited by AMD3100, a specific antagonist of CXCR4, or in the presence of excess CXCL12 in the cell culture medium. The expression profiles of CXCR4, CXCR7, CXCL12, and COUP-TFI mRNA in 82 breast tumors and control non-tumor samples were measured using real-time PCR. CXCR4 expression was found to be significantly increased in the tumors and correlated with the tumor grade, whereas the expression of CXCL12 was significantly decreased in the tumors compared with the healthy samples. Significantly higher COUP-TFI mRNA expression was also detected in grade 1 tumors.
Together, our mechanistic in vitro assays and in vivo results suggest that a reduction in chemokine CXCL12 expression, with an enhancement of CXCR4 expression, provoked by COUP-TFI, could be associated with an increase in the invasive potential of breast cancer cells.
COUP-TF; CXCL12 signaling; Estrogen receptor; Cell migration; Breast cancer
The rainbow trout estrogen receptor (rtER) is a positively autoregulated gene in liver cells. In a previous report, we showed that upregulation is mediated by an estrogen response element (ERE) located in the proximal promoter of the gene and that a half binding site for nuclear receptors (5'-TGACCT-3') located 15 bp upstream of the ERE is involved in the magnitude of the estrogen response. We now report that the human orphan receptor COUP-TF and a COUP-TF-like protein from trout liver are able to bind to the consensus half-site. When cotransfected with the rtER gene proximal promoter, COUP-TF had no regulatory functions on its own. Interestingly, COUP-TF enhanced rtER transactivation properties in the presence of estradiol in a dose-dependent manner when cotransfected with the rtER gene promoter. Unliganded retinoid receptor heterodimers had the same helper function as COUP-TF in the presence of estradiol but were switched to repressors when the ligand all-trans-retinoic acid was added. Mutation of the consensus half-site only slightly reduced COUP-TF helper function, suggesting that it actually results from a complex mechanism that probably involves both DNA binding of COUP-TF to the promoter and protein-protein interaction with another transcription factor bound to the promoter. Nevertheless, a DNA-binding-defective mutant of COUP-TF was also defective in ER helper function. Competition footprinting analysis suggested that COUP-TF actually establishes contacts with the consensus upstream half-site and the downstream ERE half-site that would form a DR-24-like response element. Interaction of COUP-TF with the DR-24 element was confirmed in footprinting assays by using nuclear extracts from Saccharomyces cerevisiae expressing COUP-TF. Finally, interaction of COUP-TF with mutants of the rtER gene promoter showed that COUP-TF recognizes the ERE when the upstream half-site is mutated. These data show that COUP-TF may activate transcription through interaction with other nuclear receptors. This cross-talk between liganded nuclear receptors and orphan receptors is likely to modulate the spectrum of action of a particular ligand-receptor complex and may participate in the cell-type specificity of the ligand effect.
Osteoblasts and adipocytes are differentiated from common mesenchymal stem cells (MSCs) in processes which are tightly controlled by various growth factors, signaling molecules, transcriptional factors and microRNAs. Recently, chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) was identified as a critical regulator of MSC fate. In the present study, we aimed to identify some microRNAs (miR), which target COUP-TFII, and to determine the effects on MSCs fate. During osteoblastic or adipocytic differentiation from MSCs lineage cells, miR-194 expression was found to be reversal. In the cultures of mesenchymal C3H10T1/2 and primary bone marrow stromal cells, osteogenic stimuli increased miR-194 expression with accompanying decreases in COUP-TFII expression, whereas adipogenic stimuli reduced miR-194 expression with accompanying increases in COUP-TFII expression. A luciferase assay with COUP-TFII 3′-untranslated region (UTR) reporter plasmid, including the miR-194 binding sequences, showed that the introduction of miR-194 reduced the luciferase activity. However, it did not affect the activity of mutated COUP-TFII 3′-UTR reporter. Enforced expression of miR-194 significantly enhanced osteoblast differentiation, but inhibited adipocyte differentiation by decreasing COUP-TFII mRNA and protein levels. In contrast, inhibition of the endogenous miR-194 reduced matrix mineralization in the MSCs cultures, promoting the formation of lipid droplets by rescuing COUP-TFII expression. Furthermore, overexpression of COUP-TFII reversed the effects of miR-194 on the cell fates. Taken together, our results showed that miR-194 acts as a critical regulator of COUP-TFII, and can determinate the fate of MSCs to differentiate into osteoblasts and adipocytes. This suggests that miR-194 and COUP-TFII may be good target molecules for controlling bone and metabolic diseases.
The nuclear receptor chicken ovalbumin upstream promoter transcription factor II (COUP-TFII) is an important coordinator of glucose homeostasis. We report, for the first time, a unique differential regulation of its expression by the nutritional status in the mouse hypothalamus compared to peripheral tissues.
Using hyperinsulinemic-euglycemic clamps and insulinopenic mice, we show that insulin upregulates its expression in the hypothalamus. Immunofluorescence studies demonstrate that COUP-TFII gene expression is restricted to a subpopulation of ventromedial hypothalamic neurons expressing the melanocortin receptor. In GT1-7 hypothalamic cells, the MC4-R agonist MTII leads to a dose dependant increase of COUP-TFII gene expression secondarily to a local increase in cAMP concentrations. Transfection experiments, using a COUP-TFII promoter containing a functional cAMP responsive element, suggest a direct transcriptional activation by cAMP. Finally, we show that the fed state or intracerebroventricular injections of MTII in mice induce an increased hypothalamic COUP-TFII expression associated with a decreased hepatic and pancreatic COUP-TFII expression.
These observations strongly suggest that hypothalamic COUP-TFII gene expression could be a central integrator of insulin and melanocortin signaling pathway within the ventromedial hypothalamus. COUP-TFII could play a crucial role in brain integration of circulating signal of hunger and satiety involved in energy balance regulation.
The chicken ovalbumin upstream promoter transcription factor II, COUP-TFII, is a member of the Orphan nuclear receptor transcription factor family. Genetic ablation of COUP-TFII results in early embryonic lethality and demonstrates that this gene is required for cardiac and vascular development. Expression of COUP-TFII persists throughout postnatal life in various tissues including the female reproductive tract. However, the physiological function of COUP-TFII in female reproduction has not been extensively analyzed. Here, we provide phenotypic evidences that haploinsufficiency of COUP-TFII in mice demonstrates an important role of COUP-TFII for normal female reproduction. COUP-TFII +/− females show significantly reduced fecundity, irregular estrus cycles, delayed puberty and retarded postnatal growth. Analysis of the reduced fertility revealed that although ovarian function was normal with respect to ovulation, the ovaries have reduced ability to synthesize progesterone in response to exogenous gonadotropins. This reduction is due to the reduction of the expression of steroidogenic enzymes important for P4 synthesis and the reduction of vascularization in COUP-TFII heterozygotes. Analysis of uterine function demonstrated a reduced response to an experimentally induced decidual cell reaction indicating that the ability of the uterus to support embryo implantation was reduced. Taken together, our data shows global impact of gene dosage effects of COUP-TFII on female postnatal life and indicates requirement of COUP-TFII in normal female reproduction, in particular for uterine endometrial functions during the peri-implantation period.
Identification of bona fide direct nuclear receptor gene targets has been challenging but essential for understanding regulation of organismal physiological processes.
We describe a methodology to identify transcription factor binding sites and target genes in vivo by intersecting microarray data, computational binding site queries, and evolutionary conservation. We provide detailed experimental validation of each step and, as a proof of principle, utilize the methodology to identify novel direct targets of the orphan nuclear receptor NR2F1 (COUP-TFI). The first step involved validation of microarray gene expression profiles obtained from wild-type and COUP-TFI−/− inner ear tissues. Secondly, we developed a bioinformatic tool to search for COUP-TFI DNA binding sites in genomes, using a classification-type Hidden Markov Model trained with 49 published COUP-TF response elements. We next obtained a ranked list of candidate in vivo direct COUP-TFI targets by integrating the microarray and bioinformatics analyses according to the degree of binding site evolutionary conservation and microarray statistical significance. Lastly, as proof-of-concept, 5 specific genes were validated for direct regulation. For example, the fatty acid binding protein 7 (Fabp7) gene is a direct COUP-TFI target in vivo because: i) we identified 2 conserved COUP-TFI binding sites in the Fabp7 promoter; ii) Fapb7 transcript and protein levels are significantly reduced in COUP-TFI−/− tissues and in MEFs; iii) chromatin immunoprecipitation demonstrates that COUP-TFI is recruited to the Fabp7 promoter in vitro and in vivo and iv) it is associated with active chromatin having increased H3K9 acetylation and enrichment for CBP and SRC-1 binding in the newborn brain.
We have developed and validated a methodology to identify in vivo direct nuclear receptor target genes. This bioinformatics tool can be modified to scan for response elements of transcription factors, cis-regulatory modules, or any flexible DNA pattern.
The vitamin hormone retinoic acid (RA) regulates many complex biological programs. The hormonal signals are mediated at the level of transcription by multiple nuclear receptors. These receptors belong to the steroid/thyroid hormone receptor superfamily that also includes a large number of orphan receptors whose biological roles have not yet been determined. Although much has been learned in recent years about RA receptor (RAR) functions, little is known about how specific RA response programs are restricted to certain tissues and cell types during development and in the adult. It has been recently shown that RAR activities are regulated by retinoid X receptors (RXR) through heterodimer formation. In an effort to isolate and further characterize nuclear receptors that modulate RAR and/or RXR activities, we have screened cDNA libraries by using a RXR alpha cDNA probe. Two clones, COUP alpha and COUP beta, identical and closely related to the orphan receptor COUP-TF, were obtained. We show that COUP proteins dramatically inhibit retinoid receptor activities on certain response elements that are activated by RAR/RXR heterodimers or RXR homodimers. COUP alpha and -beta bind strongly to these response elements, including a palindromic thyroid hormone response element and a direct repeat RA response element as well as an RXR-specific response element. In addition, we found that the previously identified COUP-TF binding site in the ovalbumin gene functions in vitro as an RA response element that is repressed in the presence of COUP. Our data suggest that the COUP receptors are a novel class of RAR and RXR regulators that can restrict RA signaling to certain elements. The COUP orphan receptors may thus play an important role in cell- or tissue-specific repression of subsets of RA-sensitive programs during development and in the adult.
Reproductive disorders that are common/increasing in prevalence in human males may arise because of deficient androgen production/action during a fetal ‘masculinization programming window’. We identify a potentially important role for Chicken Ovalbumin Upstream Promoter-Transcription Factor II (COUP-TFII) in Leydig cell (LC) steroidogenesis that may partly explain this. In rats, fetal LC size and intratesticular testosterone (ITT) increased ∼3-fold between e15.5-e21.5 which associated with a progressive decrease in the percentage of LC expressing COUP-TFII. Exposure of fetuses to dibutyl phthalate (DBP), which induces masculinization disorders, dose-dependently prevented the age-related decrease in LC COUP-TFII expression and the normal increases in LC size and ITT. We show that nuclear COUP-TFII expression in fetal rat LC relates inversely to LC expression of steroidogenic factor-1 (SF-1)-dependent genes (StAR, Cyp11a1, Cyp17a1) with overlapping binding sites for SF-1 and COUP-TFII in their promoter regions, but does not affect an SF-1 dependent LC gene (3β-HSD) without overlapping sites. We also show that once COUP-TFII expression in LC has switched off, it is re-induced by DBP exposure, coincident with suppression of ITT. Furthermore, other treatments that reduce fetal ITT in rats (dexamethasone, diethylstilbestrol (DES)) also maintain/induce LC nuclear expression of COUP-TFII. In contrast to rats, in mice DBP neither causes persistence of fetal LC COUP-TFII nor reduces ITT, whereas DES-exposure of mice maintains COUP-TFII expression in fetal LC and decreases ITT, as in rats. These findings suggest that lifting of repression by COUP-TFII may be an important mechanism that promotes increased testosterone production by fetal LC to drive masculinization. As we also show an age-related decline in expression of COUP-TFII in human fetal LC, this mechanism may also be functional in humans, and its susceptibility to disruption by environmental chemicals, stress and pregnancy hormones could explain the origin of some human male reproductive disorders.
Retinoic acid (RA) is a positive regulator of P19 cell differentiation. Silencing of pre-B cell leukemia transcription factors (PBXs) expression in P19 cells (AS cells) results in a failure of these cells to differentiate to endodermal cells upon RA treatment. Chicken Ovalbumin Upstream Promoter Transcription Factor I (COUP-TFI) is an orphan member of the steroid-thyroid hormone superfamily. RA treatment of wild type P19 cells results in a dramatic increase in the expression of COUP-TFI however COUP-TFI mRNA levels fail to be elevated upon RA treatment of AS cells indicating that PBX expression is required for elevation in COUP-TFI expression. To study the role of COUP-TFI during RA-dependent differentiation of P19 cells, AS cells that inducibly express various levels of COUP-TFI were prepared. Exogenous expression of COUP-TFI in AS cells, in a dose-dependent fashion, leads to growth inhibition, modest cell cycle disruption and early apoptosis. Furthermore, AS cells can overcome the blockage in RA-dependent differentiation to endodermal cells when either pharmacological levels of COUP-TFI are expressed or a combination of both the expression of physiological levels of COUP-TFI and RA treatment. Additionally, the mRNA level of several pluripotency associated genes including OCT-4, DAX-1 and SF-1 in the COUP-TFI expressing AS cells are reduced. Moreover, analysis of the expression of primary RA response genes indicates that COUP-TFI is involved in the regulatory modulation of the expression of at least two genes, CYP26A1 and HoxA1. These studies demonstrate that COUP-TFI functions as a physiologically relevant regulator during RA-mediated endodermal differentiation of P19 cells.
COUP-TFI; COUP-TFII; retinoic acid; P19 cells
Retinoic acid receptor β (RARβ) plays a critical role in mediating the anticancer effects of retinoids. Expression of RARβ is highly induced by retinoic acid (RA) through a RA response element (βRARE) that is activated by heterodimers of RARs and retinoid X receptors (RXRs). However, RARβ induction is often lost in cancer cells despite expression of RARs and RXRs. In this study, we provide evidence that orphan receptor COUP-TF is required for induction of RARβ expression, growth inhibition, and apoptosis by RA in cancer cells. Expression of COUP-TF correlates with RARβ induction in a variety of cancer cell lines. In addition, stable expression of COUP-TF in COUP-TF-negative cancer cells restores induction of RARβ expression, growth inhibition, and apoptosis by RA, whereas inhibition of COUP-TF by expression of COUP-TF antisense RNA represses the RA effects. In a transient transfection assay, COUP-TF strongly induced transcriptional activity of the RARβ promoter in a RA- and RARα-dependent manner. By mutation analysis, we demonstrate that the effect of COUP-TF requires its binding to a DR-8 element present in the RARβ promoter. The binding of COUP-TF to the DR-8 element synergistically increases the RA-dependent RARα transactivation function by enhancing the interaction of RARα with its coactivator CREB binding protein. These results demonstrate that COUP-TF, by serving as an accessory protein for RARα to induce RARβ expression, plays a critical role in regulating the anticancer activities of retinoids.
Cone photopigments, known as opsins, are pivotal elements and the first detection module employed in color vision. In mice, cone photoreceptors are distributed throughout the retina, and S- and M-opsins have unique expression patterns in the retina with a gradient along the dorsoventral axis; however, the mechanisms regulating the spatial patterning of cone opsin expression have not been well documented. The purpose of this study was to define the mechanisms regulating the spatial patterning of cone opsin expression. By analyzing knockouts for bone morphogenetic protein (BMP) signaling, we found an essential role for BMP in forming cone opsin expression patterns in the retina; however, BMP signaling is activated only transiently in the dorsal half of the retina during early retinal development. Thus, BMP is not likely to play a direct role in opsin gene expression, which starts at a later stage of retinal development. We identified the chicken ovalbumin upstream promoter-transcription factor (COUP-TF) nuclear receptor as a link between BMP and opsin expression. BMP signaling is essential for the correct dorsoventral spatial expression of COUP-TFI and -TFII. Through gain- and loss-of-function analyses, we found that both COUP-TFI and -TFII are required to suppress S-opsin expression in the dorsal retina but that only COUP-TFI plays an essential role in suppressing M-opsin expression in the ventral retina. Based on these findings, we propose a new molecular cascade involving BMP and COUP-TFs that conveys dorsoventral information to direct the expression of cone opsins during retinal development.
BMP signal; mouse retina; nuclear receptor; S-opsin; M-opsin; photoreceptor
The lymphatic system plays a key role in tissue fluid homeostasis. Lymphatic dysfunction contributes to the pathogenesis of many human diseases, including lymphedema and tumor metastasis. However, the mechanisms regulating lymphangiogenesis remain largely unknown. Here, we show that COUP-TFII (also known as Nr2f2), an orphan member of the nuclear receptor superfamily, mediates both developmental and pathological lymphangiogenesis in mice. Conditional ablation of COUP-TFII at an early embryonic stage resulted in failed formation of pre-lymphatic ECs (pre-LECs) and lymphatic vessels. COUP-TFII deficiency at a late developmental stage resulted in loss of LEC identity, gain of blood EC fate, and impaired lymphatic vessel sprouting. siRNA-mediated downregulation of COUP-TFII in cultured primary human LECs demonstrated that the maintenance of lymphatic identity and VEGF-C–induced lymphangiogenic activity, including cell proliferation and migration, are COUP-TFII–dependent and cell-autonomous processes. COUP-TFII enhanced the pro-lymphangiogenic actions of VEGF-C, at least in part by directly stimulating expression of neuropilin-2, a coreceptor for VEGF-C. In addition, COUP-TFII inactivation in a mammary gland mouse tumor model resulted in inhibition of tumor lymphangiogenesis, suggesting that COUP-TFII also regulates neo-lymphangiogenesis in the adult. Thus, COUP-TFII is a critical factor that controls lymphangiogenesis in embryonic development and tumorigenesis in adults.