A cell-specific factor represses stimulation of transcription in vitro by transcriptional enhancer factor 1

A TEAD1/p65 complex regulates the eutherian-conserved MnSOD intronic enhancer, eRNA transcription and the innate immune response

Manganese superoxide dismutase (MnSOD), a critical anti-oxidant enzyme, detoxifies the mitochondrial-derived reactive oxygen species, superoxide, elicited through normal respiration or the inflammatory response. Proinflammatory stimuli induce MnSOD gene expression through a eutherian-conserved, intronic enhancer element. We identified two prototypic enhancer binding proteins, TEAD1 and p65, that when co-expressed induce MnSOD expression comparable to pro-inflammatory stimuli. TEAD1 causes the nuclear sequestration of p65 leading to a novel TEAD1/p65 complex that associates with the intronic enhancer and is necessary for cytokine induction of MnSOD. Unlike typical NF-κB-responsive genes, the induction of MnSOD does not involve p50. Beyond MnSOD, the TEAD1/p65 complex regulates a subset of genes controlling the innate immune response that were previously viewed as solely NF-κB-dependent. We also identified an enhancer-derived RNA (eRNA) that is induced by either proinflammatory stimuli or the TEAD1/p65 complex, potentially linking the intronic enhancer to intra- and interchromosomal gene regulation through the inducible eRNA.

Transcriptional enhancer factor 1 (TEF-1/TEAD1) mediates activation of IFITM3 gene by BRGl

The interferon inducible transmembrane (IFITM) proteins mediate several cellular processes such as homotypic cell adhesion functions of interferons (IFNs) and cellular anti-proliferative activities. We show that the BAF complex-mediated induction of IFITM3 is dependent on binding of the transcriptional enhancer factor 1 (TEF-1/TEAD1) to the M-CAT like elements of its promoter. TEF-1 knock-down reduced the BAF complex-mediated activation of IFITM3 promoter. In the absence of the BAF complex, TEF-1 is repressive to IFITM3 expression. The regulation of IFITM3 by TEF-1 demonstrates that TEF-1 dependent regulation is more widespread than its previously established role in the expression of muscle specific genes.

VITO-1 is an essential cofactor of TEF1-dependent muscle-specific gene regulation

The expression of several muscle-specific genes is partially or completely regulated by MCAT elements, which bind members of the TEF family of transcription factors. TEF1 itself is unable to activate reporter plasmids bearing TEF1-binding sites, suggesting that additional bridging or co-activating factors are necessary to allow interaction of TEF1 with the transcriptional machinery. In addition, none of the known TEF genes are exclusively expressed in the cardiac or skeletal muscle lineage to account for the muscle-specific expression of MCAT-dependent genes. Here we describe that VITO-1, a new SID (scalloped interaction domain)-containing protein, binds to TEF1 in vitro and strongly stimulates transcription of a MCAT reporter plasmid together with TEF-1. Since VITO-1 is predominantly expressed in the skeletal muscle lineage, it might serve as an essential transcriptional intermediary factor to promote muscle-specific expression via MCAT cis-regulatory elements. Although VITO-1 alone is not sufficient to initiate myogenic conversion of 10T1/2 fibroblastic cells, it enhanced MyoD-mediated myogenic conversion. In addition, interference with VITO-1 expression by siRNA attenuated differentiation of C2C12 muscle cells and MyoD-dependent myogenesis in 10T1/2 cells. We conclude that VITO-1 is a crucial new cofactor of the muscle regulatory programme.

Transcription enhancer factor 1 interacts with a basic helix-loop-helix zipper protein, Max, for positive regulation of cardiac alpha-myosin heavy-chain gene expression

The M-CAT binding factor transcription enhancer factor 1 (TEF-1) has been implicated in the regulation of several cardiac and skeletal muscle genes. Previously, we identified an E-box-M-CAT hybrid (EM) motif that is responsible for the basal and cyclic AMP-inducible expression of the rat cardiac alpha-myosin heavy chain (alpha-MHC) gene in cardiac myocytes. In this study, we report that two factors, TEF-1 and a basic helix-loop-helix leucine zipper protein, Max, bind to the alpha-MHC EM motif. We also found that Max was a part of the cardiac troponin T M-CAT-TEF-1 complex even when the DNA template did not contain an apparent E-box binding site. In the protein-protein interaction assay, a stable association of Max with TEF-1 was observed when glutathione S-transferase (GST)-TEF-1 or GST-Max was used to pull down in vitro-translated Max or TEF-1, respectively. In addition, Max was coimmunoprecipitated with TEF-1, thus documenting an in vivo TEF-1-Max interaction. In the transient transcription assay, overexpression of either Max or TEF-1 resulted a mild activation of the alpha-MHC-chloramphenicol acetyltransferase (CAT) reporter gene at lower concentrations and repression of this gene at higher concentrations. However, when Max and TEF-1 expression plasmids were transfected together, the repression mediated by a single expression plasmid was alleviated and a three- to fourfold transactivation of the alpha-MHC-CAT reporter gene was observed. This effect was abolished once the EM motif in the promoter-reporter construct was mutated, thus suggesting that the synergistic transactivation function of the TEF-1-Max heterotypic complex is mediated through binding of the complex to the EM motif. These results demonstrate a novel association between Max and TEF-1 and indicate a positive cooperation between these two factors in alpha-MHC gene regulation.

Transcription factor TFIIB and the vitamin D receptor cooperatively activate ligand-dependent transcription

The active metabolite of vitamin D, 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], regulates gene transcription through binding to the vitamin D receptor (VDR), a member of the nuclear hormone receptor superfamily. Sequence-specific transcription factors, including nuclear hormone receptors, are thought to interact with the basal transcription complex to regulate transcription. In glutathione S-transferase fusion-based protein-protein binding assays we found that VDR specifically binds to TFIIB, a component of the basal complex, and that the interaction requires select domains of each protein. To assess the functional significance of this interaction, transfection assays were performed with a 1,25(OH)2D3-responsive reporter construct. In P19 embryonal carcinoma cells cotransfection of VDR and TFIIB cooperatively activated reporter transcription, while each factor alone gave very low to no activation. This activation was dependent on 1,25(OH)2D3 and the dose of TFIIB and VDR transfected, demonstrating that a nuclear hormone receptor functionally interacts with TFIIB in vivo. In contrast, transfection of NIH 3T3 cells generated strong reporter activation by 1,25(OH)2D3 in the presence of VDR alone, and cotransfection of TFIIB led to specific dose-dependent repression of reporter activity. Taken together, these results indicate that TFIIB-nuclear hormone receptor interaction plays a critical role in ligand-dependent transcription, which is apparently modulated by a cell-type-specific accessory factor.