A TEF-1 binding motif that interacts with a placental protein is important for the transcriptional activity of the hCS-B enhancer

CCAAT-enhancer-binding protein β (C/EBPβ) and downstream human placental growth hormone genes are targets for dysregulation in pregnancies complicated by maternal obesity

Human chorionic somatomammotropin (CS) and placental growth hormone variant (GH-V) act as metabolic adaptors in response to maternal insulin resistance, which occurs in "normal" pregnancy. Maternal obesity can exacerbate this "resistance," suggesting that CS, GH-V, or transcription factors that regulate their production might be targets. The human CS genes, hCS-A and hCS-B, flank the GH-V gene. A significant decrease in pre-term placental CS/GH-V RNA levels was observed in transgenic mice containing the CS/GH-V genes in a model of high fat diet (HFD)-induced maternal obesity. Similarly, a decrease in CS/GH-V RNA levels was detected in term placentas from obese (body mass index (BMI) ≥ 35 kg/m(2)) versus lean (BMI 20-25 kg/m(2)) women. A specific decrease in transcription factor CCAAT-enhancer-binding protein β (C/EBPβ) RNA levels was also seen with obesity; C/EBPβ is required for mouse placenta development and is expressed, like CS and GH-V, in syncytiotrophoblasts. Binding of C/EBPβ to the CS gene downstream enhancer regions, which by virtue of their position distally flank the GH-V gene, was reduced in placenta chromatin from mice on a HFD and in obese women; a corresponding decrease in RNA polymerase II associated with CS/GH-V promoters was also observed. Detection of decreased endogenous CS/GH-V RNA levels in human placental tumor cells treated with C/EBPβ siRNA is consistent with a direct effect. These data provide evidence for CS/GH-V dysregulation in acute HFD-induced obesity in mouse pregnancy and chronic obesity in human pregnancy and implicate C/EBPβ, a factor associated with CS regulation and placental development.

Transcription cofactor Vgl-2 is required for skeletal muscle differentiation

TEF-1 transcription factors regulate gene expression in skeletal muscle but are not muscle-specific. Instead, TEF-1 factors rely on the muscle-specific cofactor Vestigial-like 2 (Vgl-2), a protein related to Drosophila vestigial. Previously, we showed that Vgl-2 promotes skeletal muscle differentiation and activates muscle-specific promoters. However, the mechanism whereby Vgl-2 regulates TEF-1 factors and the requirement for Vgl-2 for muscle-specific gene expression were not known. In Drosophila, vestigial alters DNA binding specificity of the TEF-1 homolog scalloped to drive wing and flight muscle-specific gene expression. Here, gel mobility shift assays show that Vgl-2 differentially affects DNA binding of different TEF-1 factors. Using an antisense morpholino, we blocked the expression of Vgl-2 and a muscle-specific gene in the myogenic C2C12 cell line and in chick embryos by electroporation. These results demonstrate that Vgl-2 is required for muscle gene expression, in part by switching DNA binding of TEF-1 factors during muscle differentiation.

Vgl-4, a Novel Member of the Vestigial-like Family of Transcription Cofactors, Regulates α1-Adrenergic Activation of Gene Expression in Cardiac Myocytes

Cardiac and skeletal muscle genes are regulated by the transcriptional enhancer factor (TEF-1) family of transcription factors. In skeletal muscle, TEF-1 factors interact with a skeletal muscle-specific cofactor called Vestigial-like 2 (Vgl-2) that is related to the Drosophila protein Vestigial. Here, we characterize Vgl-4, the only member of the Vestigial-like family expressed in the heart. Unlike other members of the Vgl family that have a single TEF-1 interaction domain called the tondu (TDU) motif, Vgl-4 has two TDU motifs in its carboxyl-terminal domain. Like other Vgl factors, Vgl-4 physically interacts with TEF-1 in an immunoprecipitation assay. Vgl-4 functionally interacts with TEF-1 and also with myocyte enhancer factor 2 in a mammalian two-hybrid assay. Overexpression of Vgl-4 in cardiac myocytes interfered with the basal expression and alpha1-adrenergic receptor-dependent activation of a TEF-1-dependent skeletal alpha-actin promoter. In cardiac myocytes cultured in serum and in serum-free medium, a myc-tagged Vgl-4 protein was located in the nucleus and cytoplasm but was exported from the nucleus when cells were treated with alpha1-adrenergic receptor agonist. A chimeric nuclear-retained Vgl-4 protein inhibited alpha1-adrenergic receptor-dependent activation. In contrast, deletion of the TDU motifs of Vgl-4 prevented Vgl-4 nuclear localization, relieved Vgl-4 interference of basal activity, and enhanced alpha1-adrenergic up-regulation of the skeletal alpha-actin promoter. Nuclear export of Vgl-4 is dependent on the nuclear exportin CRM-1. These results suggest that Vgl-4 modulates the activity of TEF-1 factors and counteracts alpha1-adrenergic activation of gene expression in cardiac myocytes.

Transcription enhancer factor-5 and a GATA-like protein determine placental-specific expression of the Type I human 3beta-hydroxysteroid dehydrogenase gene, HSD3B1

The enzyme 3beta-hydroxysteroid dehydrogenase/isomerase (3betaHSD) is required for the biosynthesis of all active steroid hormones. It exists as multiple isoforms in humans and rodents, each a product of a distinct gene. Two isoforms, 3betaHSD I and II, are expressed in a tissue-specific manner in humans. 3betaHSD I is the only isoform expressed in the placenta, where it is required for the biosynthesis of progesterone and thus essential for the maintenance of pregnancy. We recently identified two transcription factors, activating protein-2gamma (AP-2gamma) and the homeodomain protein, distaless-3 (Dlx-3), that are expressed in both human and mouse trophoblast cells that were shown to be required for trophoblast-specific expression of the orthologous murine 3betaHSD, 3betaHSD VI. Although we identified specific binding sites for AP-2gamma and Dlx-3 in the distal promoter of the human 3betaHSD I gene, HSD3B1, it was found that these transcription factors were not involved in determining placental-specific expression of human 3betaHSD I. Instead, a 53-bp placental-specific enhancer element located between -2570 and -2518 of the HSD3B1 promoter was identified. Within this 53-bp element, two potential placental transcription factor binding sites were found. EMSAs with a 20-bp oligonucleotide containing these two potential placental-specific binding sites identified one of the binding sites specific for the transcription enhancer factor (TEF)-5, which is highly expressed in human placenta and in placental choriocarcinoma-derived JEG-3 cells and the other overlapping binding site, specific for a GATA-like protein. Site-specific mutations in either the TEF-5 binding site or in the GATA binding site, each resulted in complete loss of enhancer activity. The data indicate that TEF-5 and the GATA-like protein act in a coordinate manner to determine the placental-specific expression of the human 3betaHSD I enzyme and therefore are critical for placental progesterone production required for the maintenance of pregnancy.

Mammalian vestigial-like 2, a cofactor of TEF-1 and MEF2 transcription factors that promotes skeletal muscle differentiation

Expression of many skeletal muscle-specific genes depends on TEF-1 (transcription enhancer factor-1) and MEF2 transcription factors. In Drosophila, the TEF-1 homolog Scalloped interacts with the cofactor Vestigial to drive differentiation of the wing and indirect flight muscles. Here, we identify three mammalian vestigial-like genes, Vgl-1, Vgl-2, and Vgl-3, that share homology in a TEF-1 interaction domain. Vgl-1 and Vgl-3 transcripts are enriched in the placenta, whereas Vgl-2 is expressed in the differentiating somites and branchial arches during embryogenesis and is skeletal muscle-specific in the adult. During muscle differentiation, Vgl-2 mRNA levels increase and Vgl-2 protein translocates from the cytoplasm to the nucleus. In situ hybridization revealed co-expression of Vgl-2 with myogenin in the differentiating muscle of embryonic myotomes but not in newly formed somites prior to muscle differentiation. Like Vgl-1, Vgl-2 interacts with TEF-1. In addition, we show that Vgl-2 interacts with MEF2 in a mammalian two-hybrid assay and that Vgl-2 selectively binds to MEF2 in vitro. Co-expression of Vgl-2 with MEF2 markedly co-activates an MEF2-dependent promoter through its MEF2 element. Overexpression of Vgl-2 in MyoD-transfected 10T(1/2) cells markedly increased myosin heavy chain expression, a marker of terminal muscle differentiation. These results identify Vgl-2 as an important new component of the myogenic program.

TEF-1 transcription factors regulate activity of the mouse mammary tumor virus LTR

The mouse mammary tumor virus long terminal repeat (LTR) is a potent transcriptional enhancer. We identified several putative binding sites for the TEF-1 family of transcription factors (TEF-1, RTEF-1, DTEF-1, and ETF) in the proximal negative regulatory element of the LTR. Gel mobility shift assays revealed strong TEF-1 factor binding to one site using nuclear extracts from CV-1 cells and from the human breast cancer cell line MCF-7. Mutation of this site increased basal activity of the LTR. In transient transfection assays, TEF-1 squelched the basal LTR activity and completely abrogated the response to the glucocorticoid dexamethasone. RTEF-1 and DTEF-1 had little effect on the basal activity, whereas ETF activated the LTR. These TEF-1 factors also interfered with the response to dexamethasone. Taken together, our results reveal an important new role for TEF-1 factors in regulating MMTV LTR activity and suggest that TEF-1 factors might participate in mammary tumorigenesis.

Cooperative binding of TEF-1 to repeated GGAATG-related consensus elements with restricted spatial separation and orientation

The human transcriptional enhancer factor (TEF) family includes TEF-1, TEF-3, TEF-4, and TEF-5. The TEFs share a highly conserved 68-amino acid TEA/ATTS DNA-binding domain, which binds to SV40 GT-IIC (GGAATG), SphI (AGTATG), SphII (AGCATG), and muscle-specific M-CAT (GGTATG) enhansons. We determined the optimal DNA-binding consensus sequence for TEF-1. Using a purified GST-TEF-1 fusion protein and a random pool of synthetic oligonucleotides, 31 independent clones were obtained after six rounds of binding site selection. DNA sequences analysis revealed that 16 clones contained direct repeats with a 3-bp spacer (DR3), and 15 clones contained a single binding site. The predominate consensus half-site was GGAATG (67%), and the other elements were of the form G(A)GA(T/C)ATG. The TEF-1 bound to the DR3 as a dimer in a cooperative manner. Cooperative binding was dependent on the spacing and orientation of the half-sites and was inhibited by deoxycholate treatment, providing evidence that protein-protein interactions were involved. The data suggest that TEF dimerization is important for its ability to modulate gene transcription.

Human placental TEF-5 transactivates the human chorionic somatomammotropin gene enhancer

Human chorionic somatomammotropin (hCS) gene expression in the placenta is controlled by an enhancer (CSEn) containing SV40-related GT-IIC and SphI/SphII enhansons. These enhancers are controlled by members of the transcription enhancer factor-1 (TEF-1) family. Recently TEF-5, whose mRNA is abundant in placenta, was shown to bind cooperatively to a unique, tandemly repeated element in CSEn2, suggesting that TEF-5 regulates CSEn activity. However, expression of TEF-5 using a cDNA lacking the 5'-untranslated region and containing a modified translation initiation site was not accompanied by CSEn activation. Using nested, degenerate PCR primers corresponding to conserved TEF domains, several novel TEF-1-related cDNAs have been cloned from a human placental cDNA library. The open reading frame of one 3033-bp clone was identical to TEF-5 and contained 300- and 1423-bp 5'- and 3'-untranslated regions, respectively. The in vitro generated approximately 53-kDa TEF-5 polypeptide binds specifically to GT-IIC and SphI/SphII oligonucleotides. Overexpression of TEF-5 in BeWo cells using the intact 3033-bp cDNA transactivates the hCS and SV40 enhancers and artificial enhancers comprised of tandemly repeated GT-IIC enhansons, but not OCT enhansons. The data demonstrate that TEF-5 is a transactivator that is likely involved in the transactivation of CSEn enhancer function. Further, the data suggest that elements within the untranslated regions, initiation site, or both control TEF-5 expression in ways that influence its transactivation function.

Poly(ADP-ribose) polymerase binds with transcription enhancer factor 1 to MCAT1 elements to regulate muscle-specific transcription

Striated muscle-specific expression of the cardiac troponin T (cTNT) gene is mediated through two MCAT elements that act via binding of transcription enhancer factor 1 (TEF-1) to the MCAT core motifs and binding of an auxiliary protein to nucleotides flanking the 5' side of the core motif. Using DNA-protein and protein-protein binding experiments, we identified a 140-kDa polypeptide that bound both the muscle-specific flanking sequences of the most distal MCAT1 element and TEF-1. Screening of an expression library with the MCAT1 element yielded a cDNA encoding a truncated form of poly(ADP-ribose) polymerase (PARP). Endogenous PARP from embryonic tissue nuclear extracts migrated as a 140-kDa protein. Recombinant full-length PARP preferentially bound the wild-type MCAT1 element and was shown to physically interact with TEF-1. In addition, endogenous TEF-1 could be coimmunoprecipitated with PARP from extracts of primary skeletal muscle cells. Recombinant PARP was able to ADP-ribosylate TEF-1 in vitro. Inhibition of the enzymatic activity of PARP repressed expression of an MCAT1-dependent reporter in transiently transfected primary muscle cells. Together, these data implicate PARP as the auxiliary protein that binds with TEF-1 to the MCAT1 element to provide muscle-specific gene transcription.

Differential expression of the TEF family of transcription factors in the murine placenta and during differentiation of primary human trophoblasts in vitro

We describe the molecular cloning of murine (m) Transcriptional Enhancer Factor (TEF)-5 belonging to the TEF family of transcription factors. We show that mTEF-5 is specifically expressed in trophoblast giant cells and other extra-embryonic structures at early stages of development. At later stages, mTEF-5 is specifically expressed in the labyrinthine region of the placenta and in several embryonic tissues. We further show that the other mTEFs are differentially expressed in extraembryonic structures and in the mature placenta. Interestingly, human (h)TEF-5 is specifically expressed in the differentiated syncytiotrophoblast of the human term placenta and its expression is upregulated during the differentiation of cytotrophoblasts to syncytiotrophoblast in vitro, whereas that of hTEF-1 is down-regulated. Together with previous results describing hTEF-binding sites in the human placental lactogen-B gene enhancer, these novel observations support a role for hTEF-5 in the regulation of this gene. We further propose that the hTEF factors may play a more general role in placental gene regulation and development.

Human TEF-5 is preferentially expressed in placenta and binds to multiple functional elements of the human chorionic somatomammotropin-B gene enhancer

We report the cloning of a cDNA encoding the human transcription factor hTEF-5, containing the TEA/ATTS DNA binding domain and related to the TEF family of transcription factors. hTEF-5 is expressed in skeletal and cardiac muscle, but the strongest expression is observed in the placenta and in placenta-derived JEG-3 choriocarcinoma cells. In correlation with its placental expression, we show that hTEF-5 binds to several functional enhansons of the human chorionic somatomammotropin (hCS)-B gene enhancer. We define a novel functional element in this enhancer comprising tandemly repeated sites to which hTEF-5 binds cooperatively. In the corresponding region of the hCS-A enhancer, which is known to be inactive, this element is inactivated by a naturally occurring single base mutation that disrupts hTEF-5 binding. We further show that the binding of the previously described placental protein f/chorionic somatomammotropin enhancer factor-1 to TEF-binding sites is disrupted by monoclonal antibodies directed against the TEA domain and that this factor is a proteolytic degradation product of the TEF factors. These results strongly suggest that hTEF-5 regulates the activity of the hCS-B gene enhancer.

The enhancers of the human placental lactogen B, A, and L genes: progressive activation during in vitro trophoblast differentiation and importance of the DF-3 element in determining their respective activities

The hCS-A and hCS-B genes encoding human chorionic somatomammotropin and the related hCS-L gene are very similar in their coding and flanking sequences. For each of these genes, downstream enhancers, varying in strength, have been identified with the help of cytotrophoblast-derived JEG-3 cells, which do not express the hCS genes. Here we study the activity of the hCS enhancers in human syncytiotrophoblast in primary culture, which naturally expresses the hCS genes. We show that the activity of the hCS-B gene enhancer is mediated by two elements, DF-3 and DF-4, whereas the hCS-L and hCS-A gene enhancers display weaker activity due to mutations in their respective DF-3 sites. Replacement of the hCS-B DF-3 site with the homologous hCS-A sequence causes hCS-B enhancer activity to decrease. Primary cytotrophoblasts differentiate in culture to form the syncytiotrophoblast. We show that during this process the production of hCS progressively increases and that concomitantly all three hCS enhancers are progressively activated. A targeted mutation in the 3' part of the DF-4 element abolishes the binding of a protein present only in syncytiotrophoblast extracts and inactivates the DF-4 element. Thus, a direct correlation exists between the appearance of this syncytiotrophoblast-specific protein and hCS enhancer activity. This primary culture model proves useful in studying the regulation of the hCS genes.

A novel family of developmentally regulated mammalian transcription factors containing the TEA/ATTS DNA binding domain

We describe the molecular cloning of two novel human and murine transcription factors containing the TEA/ATTS DNA binding domain and related to transcriptional enhancer factor-1 (TEF-1). These factors bind to the consensus TEA/ATTS cognate binding site exemplified by the GT-IIC and Sph enhansons of the SV40 enhancer but differ in their ability to bind cooperatively to tandemly repeated sites. The human TEFs are differentially expressed in cultured cell lines and the mouse (m)TEFs are differentially expressed in embryonic and extra-embryonic tissues in early post-implantation embryos. Strikingly, at later stages of embryogenesis, mTEF-3 is specifically expressed in skeletal muscle precursors, whereas mTEF-1 is expressed not only in developing skeletal muscle but also in the myocardium. Together with previous data, these results point to important, partially redundant, roles for these TEF proteins in myogenesis and cardiogenesis. In addition, mTEF-1 is strongly coexpressed with mTEF-4 in mitotic neuroblasts, while accentuated mTEF-4 expression is also observed in the gut and the nephrogenic region of the kidney. These observations suggest additional roles for the TEF proteins in central nervous system development and organogenesis.

The role of transcription enhancer factor-1 (TEF-1) related proteins in the formation of M-CAT binding complexes in muscle and non-muscle tissues

M-CAT sites are required for the activity of many promoters in cardiac and skeletal muscle. M-CAT binding activity is muscle-enriched, but is found in many tissues and is immunologically related to the HeLa transcription enhancer factor-1 (TEF-1). TEF-1-related cDNAs (RTEF-1) have been cloned from chick heart. RTEF-1 mRNA is muscle-enriched, consistent with a role for RTEF-1 in the regulation of muscle-specific gene expression. Here, we have examined the tissue distribution of TEF-1-related proteins and of M-CAT binding activity by Western analysis and mobility shift polyacrylamide gel electrophoresis. TEF-1-related proteins of 57, 54 and 52 kDa were found in most tissues with the highest levels in muscle tissues. All of these TEF-1-related proteins bound M-CAT DNA and the 57- and 54-kDa TEF-1-related polypeptides were phosphorylated. Proteolytic digestion mapping showed that the 54-kDa TEF-1-related polypeptide is encoded by a different gene than the 52- and 57-kDa TEF-1-related polypeptides. A comparison of the migration and proteolytic digestion of the 54-kDa TEF-1-related polypeptide with proteins encoded by the cloned RTEF-1 cDNAs showed that the 54-kDa TEF-1-related polypeptide is encoded by RTEF-1A. High resolution mobility shift polyacrylamide gel electrophoresis showed multiple M-CAT binding activities in tissues. All of these activities contained TEF-1-related proteins. One protein-M-CAT DNA complex was muscle-enriched and was up-regulated upon differentiation of a skeletal muscle cell line. This complex contained the 54-kDa TEF-1-related polypeptide. Therefore, RTEF1-A protein is a component of a muscle-enriched transcription complex that forms on M-CAT sites and may play a key role in the regulation of transcription in muscle.