The HeLa cell protein TEF-1 binds specifically and cooperatively to two SV40 enhancer motifs of unrelated sequence

Assembling a Hippo: the evolutionary emergence of an animal developmental signaling pathway

Decades of work in developmental genetics has given us a deep mechanistic understanding of the fundamental signaling pathways underlying animal development. However, little is known about how these pathways emerged and changed over evolutionary time. Here, we review our current understanding of the evolutionary emergence of the Hippo pathway, a conserved signaling pathway that regulates tissue size in animals. This pathway has deep evolutionary roots, emerging piece by piece in the unicellular ancestors of animals, with a complete core pathway predating the origin of animals. Recent functional studies in close unicellular relatives of animals and early-branching animals suggest an ancestral function of the Hippo pathway in cytoskeletal regulation, which was subsequently co-opted to regulate proliferation and animal tissue size.

Optimized reporters for multiplexed detection of transcription factor activity

In any given cell type, dozens of transcription factors (TFs) act in concert to control the activity of the genome by binding to specific DNA sequences in regulatory elements. Despite their considerable importance in determining cell identity and their pivotal role in numerous disorders, we currently lack simple tools to directly measure the activity of many TFs in parallel. Massively parallel reporter assays (MPRAs) allow the detection of TF activities in a multiplexed fashion; however, we lack basic understanding to rationally design sensitive reporters for many TFs. Here, we use an MPRA to systematically optimize transcriptional reporters for 86 TFs and evaluate the specificity of all reporters across a wide array of TF perturbation conditions. We thus identified critical TF reporter design features and obtained highly sensitive and specific reporters for 60 TFs, many of which outperform available reporters. The resulting collection of "prime" TF reporters can be used to uncover TF regulatory networks and to illuminate signaling pathways.

HIGHLIGHTS

Systematic design and optimization of transcriptional reporters for 86 TFsCharacterization of TF-specific reporter design optimization rulesEvaluation of reporter TF-specificity across a wide array of TF perturbationsIdentification of a collection of 60 "prime" TF reporters with optimized performance.

The YAP1/TAZ-TEAD transcriptional network regulates gene expression at neuromuscular junctions in skeletal muscle fibers

We examined YAP1/TAZ-TEAD signaling pathway activity at neuromuscular junctions (NMJs) of skeletal muscle fibers in adult mice. Our investigations revealed that muscle-specific knockouts of Yap1 or Taz, or both, demonstrate that these transcriptional coactivators regulate synaptic gene expression, the number and morphology of NMJs, and synaptic nuclei. Yap1 or Taz single knockout mice display reduced grip strength, fragmentation of NMJs, and accumulation of synaptic nuclei. Yap1/Taz muscle-specific double knockout mice do not survive beyond birth and possess almost no NMJs, the few detectable show severely impaired morphology and are organized in widened endplate bands; and with motor nerve endings being mostly absent. Myogenic gene expression is significantly impaired in the denervated muscles of knockout mice. We found that Tead1 and Tead4 transcription rates were increased upon incubation of control primary myotubes with AGRN-conditioned medium. Reduced AGRN-dependent acetylcholine receptor clustering and synaptic gene transcription were observed in differentiated primary Tead1 and Tead4 knockout myotubes. In silico analysis of previously reported genomic occupancy sites of TEAD1/4 revealed evolutionary conserved regions of potential TEAD binding motifs in key synaptic genes, the relevance of which was functionally confirmed by reporter assays. Collectively, our data suggest a role for YAP1/TAZ-TEAD1/TEAD4 signaling, particularly through TAZ-TEAD4, in regulating synaptic gene expression and acetylcholine receptor clustering at NMJs.

YAP1 and WWTR1 expression inversely correlates with neuroendocrine markers in Merkel cell carcinoma

BackgroundMerkel cell carcinoma (MCC) is an aggressive neuroendocrine (NE) skin cancer caused by severe UV-induced mutations or expression of Merkel cell polyomavirus (MCPyV) large and small T antigens (LT and ST). Despite deep genetic differences between MCPyV-positive and -negative subtypes, current clinical diagnostic markers are indistinguishable, and the expression profile of MCC tumors is, to our knowledge, unexplored.MethodsHere, we leveraged bulk and single-cell RNA-Seq of patient-derived tumor biopsies and cell lines to explore the underlying transcriptional environment of MCC.ResultsStrikingly, MCC samples could be separated into transcriptional subtypes that were independent of MCPyV status. Instead, we observed an inverse correlation between a NE gene signature and the Hippo pathway transcription factors Yes1-associated transcriptional regulator (YAP1) and WW domain-containing transcriptional regulator 1 (WWTR1). This inverse correlation was broadly present at the transcript and protein levels in the tumor biopsies as well as in established and patient-derived cell lines. Mechanistically, expression of YAP1 or WWTR1 in a MCPyV-positive MCC cell line induced cell-cycle arrest at least in part through TEA domain-dependent (TEAD-dependent) transcriptional repression of MCPyV LT.ConclusionThese findings identify what we believe to be a previously unrecognized heterogeneity in NE gene expression within MCC and support a model of YAP1/WWTR1 silencing as essential for the development of MCPyV-positive MCC.FundingUS Public Health Service grants R35CA232128, P01CA203655, and P30CA06516.

The transcription factor TEAD4 enhances lung adenocarcinoma progression through enhancing PKM2 mediated glycolysis

Lung adenocarcinoma (LUAD) is a deadly disease with a hallmark of aberrant metabolism. TEA domain 4 (TEAD4) is involved in the progression of several forms of cancer including LUAD. However, the role of TEAD4 in LUAD glucose metabolism is rarely reported as well as its potential mechanisms. Pyruvate kinase isozymes M2 (PKM2), the key regulatory enzymes in glycolysis, was predicted to be a target for TEAD4 by bioinformatics analysis. Thus, we aimed to explore whether TEAD4/PKM2 axis was related to LUAD glucose metabolism and malignant phenotype. The expression level of TEAD4 and PKM2 was measured by quantitative real-time PCR and Western blot. Luciferase reporter assay were employed to verify the effect of TEAD4 on PKM2 promoter as well as TEAD4/PKM2 axis on reporter activity of hypoxia inducible factor-1α (HIF-1α). Glycolysis was investigated according to glucose consumption, lactate production and the extracellular acidification rate. The present study indicated that TEAD4 and PKM2 were upregulated in LUAD and closely related to prognosis. Mechanistic investigations identified that TEAD4 played a key role as a transcription factor and promoted PKM2 transcription and expression, which further altered the reporter activity of HIF-1α and upregulated HIF-1α-targeted glycolytic genes glucose transporter-1 and hexokinase II. Functional assays revealed that TEAD4 and PKM2 affected glycolytic and 2-DG blocked the positive function of TEAD4 and PKM2 on glycolytic. Besides, TEAD4/PKM2 axis affects LUAD cell viability, apoptosis, migration, and invasion. Together, these data provided evidence that both TEAD4 and PKM2 were poor prognosticator. Targeting TEAD4/PKM2 axis might be an effective therapeutic strategy for LUAD.

Exploring TEAD2 as a drug target for therapeutic intervention of cancer: A multi-computational case study

Transcriptional enhanced associate domain (TEAD) is a family of transcription factors that plays a significant role during embryonic developmental processes, and its dysregulation is responsible for tumour progression. TEAD is considered as druggable targets in various diseases, namely cancer, cardiovascular diseases and neurodegenerative disorders. Previous structural studies revealed the importance of the central hydrophobic pocket of TEAD as a potential target for small-molecule inhibitors and demonstrated flufenamic acid (FLU) (a COX-2 enzyme inhibitor) to bind and inhibit TEAD2 functions. However, to date, no drug candidates that bind specifically to TEAD2 with high selectivity and efficacy have been developed or proposed. Within this framework, we present here a case study where we have identified potential TEAD2 inhibitor candidates by integrating multiple computational approaches. Among the candidates, the top two ranked compounds ZINC95969481 (LG1) which is a fused pyrazole derivative and ZINC05203789 (LG2), a fluorene derivative resulted in much favourable binding energy scores than the reference ligand, FLU. The drug likeliness of the best compounds was also evaluated in silico to ensure the bioavailability of these compounds particularly LG1 as compared to FLU thus providing a strong rationale for their development as leads against TEAD. Molecular dynamics simulations results highlighted the role of key residues contributing to favourable interactions in TEAD2-LG1 complex with much favourable interaction and binding free energy values with respect to the reference compound. Altogether, this study provides a starting platform to be more exploited by future experimental research towards the development of inhibitors against TEAD, a persuasive strategy for therapeutic intervention in cancer treatment.

A novel isoform of Homeodomain-interacting protein kinase-2 promotes YAP/TEAD transcriptional activity in NSCLC cells

Homeodomain-interacting protein kinase-2 (HIPK2) can either promote or inhibit transcription depending on cellular context. In this study, we show that a new HIPK2 isoform increases TEAD reporter activity in NSCLC cells. We detected HIPK2 copy number gain in 5/6 (83.3%) NSCLC cell lines. In NSCLC patients with high HIPK2 mRNA expression in the Human Protein Atlas, the five-year survival rate is significantly lower than in patients with low expression (38% vs 47%; p = 0.047). We also found that 70/78 (89.7%) of NSCLC tissues have moderate to strong expression of the N-terminal HIPK2 protein. We detected and cloned a novel HIPK2 isoform 3 and found that its forced overexpression promotes TEAD reporter activity in NSCLC cells. Expressing HIPK2 isoform 3_K228A kinase-dead plasmid failed to increase TEAD reporter activity in NSCLC cells. Next, we showed that two siRNAs targeting HIPK2 decreased HIPK2 isoform 3 and YAP protein levels in NSCLC cells. Degradation of the YAP protein was accelerated after HIPK2 knockdown in NSCLC cells. Inhibition of HIPK2 isoform 3 decreased the mRNA expression of YAP downstream gene CTGF. The specific HIPK2 kinase inhibitor TBID decreased TEAD reporter activity, reduced cancer side populations, and inhibited tumorsphere formation of NSCLC cells. In summary, this study indicates that HIPK2 isoform 3, the main HIPK2 isoform expressed in NSCLC, promotes YAP/TEAD transcriptional activity in NSCLC cells. Our results suggest that HIPK2 isoform 3 may be a potential therapeutic target for NSCLC.

The Transcriptional Cofactor VGLL1 Drives Transcription of Human Papillomavirus Early Genes via TEAD1

The TEAD family of transcription factors requires associating cofactors to induce gene expression. TEAD1 is known to activate the early promoter of human papillomavirus (HPV), but the precise mechanisms of TEAD1-mediated transactivation of the HPV promoter, including its relevant cofactors, remain unexplored. Here, we reveal that VGLL1, a TEAD-interacting cofactor, contributes to HPV early gene expression. Knockdown of VGLL1 and/or TEAD1 led to a decrease in viral early gene expression in human cervical keratinocytes and cervical cancer cell lines. We identified 11 TEAD1 target sites in the HPV16 long control region (LCR) by in vitro DNA pulldown assays; 8 of these sites contributed to the transcriptional activation of the early promoter in luciferase reporter assays. VGLL1 bound to the HPV16 LCR via its interaction with TEAD1 both in vitro and in vivo Furthermore, introducing HPV16 and HPV18 whole genomes into primary human keratinocytes led to increased levels of VGLL1, due in part to the upregulation of TEADs. These results suggest that multiple VGLL1/TEAD1 complexes are recruited to the LCR to support the efficient transcription of HPV early genes.IMPORTANCE Although a number of transcription factors have been reported to be involved in HPV gene expression, little is known about the cofactors that support HPV transcription. In this study, we demonstrate that the transcriptional cofactor VGLL1 plays a prominent role in HPV early gene expression, dependent on its association with the transcription factor TEAD1. Whereas TEAD1 is ubiquitously expressed in a variety of tissues, VGLL1 displays tissue-specific expression and is implicated in the development and differentiation of epithelial lineage tissues, where HPV gene expression occurs. Our results suggest that VGLL1 may contribute to the epithelial specificity of HPV gene expression, providing new insights into the mechanisms that regulate HPV infection. Further, VGLL1 is also critical for the growth of cervical cancer cells and may represent a novel therapeutic target for HPV-associated cancers.

YAP/TAZ functions and their regulation at a glance

YAP and TAZ proteins are transcriptional coactivators encoded by paralogous genes, which shuttle between the cytoplasm and the nucleus in response to multiple inputs, including the Hippo pathway. In the nucleus, they pair with DNA-binding factors of the TEAD family to regulate gene expression. Nuclear YAP/TAZ promote cell proliferation, organ overgrowth, survival to stress and dedifferentiation of post-mitotic cells into their respective tissue progenitors. YAP/TAZ are required for growth of embryonic tissues, wound healing and organ regeneration, where they are activated by cell-intrinsic and extrinsic cues. Surprisingly, this activity is dispensable in many adult self-renewing tissues, where YAP/TAZ are constantly kept in check. YAP/TAZ lay at the center of a complex regulatory network including cell-autonomous factors but also cell- and tissue-level structural features such as the mechanical properties of the cell microenvironment, the establishment of cell-cell junctions and of basolateral tissue polarity. Enhanced levels and activity of YAP/TAZ are observed in many cancers, where they sustain tumor growth, drug resistance and malignancy. In this Cell Science at a Glance article and the accompanying poster, we review the biological functions of YAP/TAZ and their regulatory mechanisms, and highlight their position at the center of a complex signaling network.

Dual function of VGLL4 in muscle regeneration

VGLL4 has previously been identified as a negative regulator of YAP. Here we show that VGLL4 regulates muscle regeneration in both YAP-dependent and YAP-independent manners at different stages. Knockout of VGLL4 in mice leads to smaller myofiber size and defective muscle contraction force. Furthermore, our studies reveal that knockout of VGLL4 results in increased muscle satellite cells proliferation and impaired myoblast differentiation, which ultimately leads to delayed muscle regeneration. Mechanistically, the results show that VGLL4 works as a conventional repressor of YAP at the proliferation stage of muscle regeneration. At the differentiation stage, VGLL4 acts as a co-activator of TEAD4 to promote MyoG transactivation and facilitate the initiation of differentiation in a YAP-independent manner. Moreover, VGLL4 stabilizes the protein-protein interactions between MyoD and TEAD4 to achieve efficient MyoG transactivation. Our findings define the dual roles of VGLL4 in regulating muscle regeneration at different stages and may open novel therapeutic perspectives for muscle regeneration.

Regulation of the Hippo Pathway Transcription Factor TEAD

The TEAD transcription factor family is best known for transcriptional output of the Hippo signaling pathway and has been implicated in processes such as development, cell growth and proliferation, tissue homeostasis, and regeneration. Our understanding of the functional importance of TEADs has increased dramatically since its initial discovery three decades ago. The majority of our knowledge of TEADs is in the context of Hippo signaling as nuclear DNA-binding proteins passively activated by Yes-associated protein (YAP) and transcriptional activator with PDZ-binding domain (TAZ), transcription coactivators downstream of the Hippo pathway. However, recent studies suggest that TEAD itself is actively regulated. Here, we highlight evidence demonstrating Hippo-independent regulation of TEADs and the potential impacts these studies may have on new cancer therapeutics.

The Hippo signaling pathway provides novel anti-cancer drug targets

The Hippo signaling pathway plays a crucial role in cell proliferation, apoptosis, differentiation, and development. Major effectors of the Hippo signaling pathway include the transcriptional co-activators Yes-associated protein 1 (YAP) and WW domain-containing transcription regulator protein 1 (TAZ). The transcriptional activities of YAP and TAZ are affected by interactions with proteins from many diverse signaling pathways as well as responses to the external environment. High YAP and TAZ activity has been observed in many cancer types, and functional dysregulation of Hippo signaling enhances the oncogenic properties of YAP and TAZ and promotes cancer development. Many biological elements, including mechanical strain on the cell, cell polarity/adhesion molecules, other signaling pathways (e.g., G-protein-coupled receptor, epidermal growth factor receptor, Wnt, Notch, and transforming growth factor β/bone morphogenic protein), and cellular metabolic status, can promote oncogenesis through synergistic association with components of the Hippo signaling pathway. Here, we review the signaling networks that interact with the Hippo signaling pathway and discuss the potential of using drugs that inhibit YAP and TAZ activity for cancer therapy.

Regulation of localization and function of the transcriptional co-activator YAP by angiomotin

The Hippo-YAP pathway is a central regulator of cell contact inhibition, proliferation and death. There are conflicting reports regarding the role of Angiomotin (Amot) in regulating this pathway. While some studies suggest a YAP-inhibitory function other studies indicate Amot is required for YAP activity. Here, we describe an Amot-dependent complex comprised of Amot, YAP and Merlin. The phosphorylation of Amot at Serine 176 shifts localization of this complex to the plasma membrane, where it associates with the tight-junction proteins Pals1/PATJ and E-cadherin. Conversely, hypophosphorylated Amot shifts localization of the complex to the nucleus, where it facilitates the association of YAP and TEAD, induces transcriptional activation of YAP target genes and promotes YAP-dependent cell proliferation. We propose that phosphorylation of Amot^S176 is a critical post-translational modification that suppresses YAP’s ability to promote cell proliferation and tumorigenesis by altering the subcellular localization of an essential YAP co-factor.

DOI:http://dx.doi.org/10.7554/eLife.23966.001

Cells in animals and other multi-cellular organisms need to know when and where they should grow and divide. Individual cells communicate with their surrounding environment and each other via signaling pathways such as the Hippo-YAP pathway, which stimulates cells to grow and therefore influences the size of organs. When the Hippo part of the pathway is active it causes a protein known as YAP to move out of a compartment in the cell called the nucleus. Inside the nucleus, YAP helps to activate genes that promote cell growth. If the Hippo pathway can no longer respond to cues from the environment, YAP becomes over-active and can contribute to the development of various cancers. Therefore researchers are trying to better understand how it is regulated.

Many signals both from inside and outside the cell influence YAP activity. For example, some signals block YAP from entering the nucleus, whereas others cause YAP to be broken down entirely. Several studies have recently identified a signal protein called angiomotin as a regulator of YAP. However, the studies provide conflicting reports as to whether angiomotin promotes or inhibits cell growth.

Like many other proteins, angiomotin can be tagged with a small molecule called a phosphate group that can alter its activity. Moleirinho, Hoxha et al. studied human cells containing versions of angiomotin that mimic different forms of the protein with or without the phosphate. The experiments indicate that when a phosphate is attached at a particular position (known as serine 176), angiomotin predominantly interacts with YAP and another protein called Merlin at the cell surface. On the other hand, when angiomotin does not have a phosphate attached to it, all three proteins can move into the nucleus, where YAP is able to activate genes and promote cell growth.

Overall, these findings indicate that adding a phosphate group to angiomotin can act as a switch to regulate where in the cell it and YAP are found and thus, whether YAP is active. Future experiments will investigate which enzymes add the phosphate group to serine 176, and when they are able to do so.

DOI:http://dx.doi.org/10.7554/eLife.23966.002

DNA-binding mechanism of the Hippo pathway transcription factor TEAD4

TEA domain (TEAD) family transcription factors are key regulators in development, tissue homeostasis and cancer progression. TEAD4 acts as a critical downstream effector of the evolutionarily conserved Hippo signaling pathway. The well-studied oncogenic protein YAP forms a complex with TEAD4 to regulate gene transcription; so does the tumor suppressor VGLL4. Although it is known that TEAD proteins can bind promoter regions of target genes through the TEA domain, the specific and detailed mechanism of DNA recognition by the TEA domain remains partially understood. Here, we report the crystal structure of TEAD4 TEA domain in complex with a muscle-CAT DNA element. The structure revealed extensive interactions between the TEA domain and the DNA duplex involving both the major and minor grooves of DNA helix. The DNA recognition helix, α3 helix, determines the specificity of the TEA domain binding to DNA sequence. Structure-guided biochemical analysis identified two major binding sites on the interface of the TEA domain-DNA complex. Mutation of TEAD4 at either site substantially decreases its occupancy on the promoter region of target genes, and largely impaired YAP-induced TEAD4 transactivation and target gene transcription, leading to inhibition of growth and colony formation of gastric cancer cell HGC-27. Collectively, our work provides a structural basis for understanding the regulatory mechanism of TEAD-mediated gene transcription.

TEAD transcription factors are required for normal primary myoblast differentiation in vitro and muscle regeneration in vivo

The TEAD family of transcription factors (TEAD1-4) bind the MCAT element in the regulatory elements of both growth promoting and myogenic differentiation genes. Defining TEAD transcription factor function in myogenesis has proved elusive due to overlapping expression of family members and their functional redundancy. We show that silencing of either Tead1, Tead2 or Tead4 did not effect primary myoblast (PM) differentiation, but that their simultaneous knockdown strongly impaired differentiation. In contrast, Tead1 or Tead4 silencing impaired C2C12 differentiation showing their different contributions in PMs and C2C12 cells. Chromatin immunoprecipitation identified enhancers associated with myogenic genes bound by combinations of Tead4, Myod1 or Myog. Tead4 regulated distinct gene sets in C2C12 cells and PMs involving both activation of the myogenic program and repression of growth and signaling pathways. ChIP-seq from mature mouse muscle fibres in vivo identified a set of highly transcribed muscle cell-identity genes and sites bound by Tead1 and Tead4. Although inactivation of Tead4 in mature muscle fibres caused no obvious phenotype under normal conditions, notexin-induced muscle regeneration was delayed in Tead4 mutants suggesting an important role in myogenic differentiation in vivo. By combining knockdown in cell models in vitro with Tead4 inactivation in muscle in vivo, we provide the first comprehensive description of the specific and redundant roles of Tead factors in myogenic differentiation.

Muscle contraction is required to maintain the pool of muscle progenitors via YAP and NOTCH during fetal myogenesis

The importance of mechanical activity in the regulation of muscle progenitors during chick development has not been investigated. We show that immobilization decreases NOTCH activity and mimics a NOTCH loss-of-function phenotype, a reduction in the number of muscle progenitors and increased differentiation. Ligand-induced NOTCH activation prevents the reduction of muscle progenitors and the increase of differentiation upon immobilization. Inhibition of NOTCH ligand activity in muscle fibers suffices to reduce the progenitor pool. Furthermore, immobilization reduces the activity of the transcriptional co-activator YAP and the expression of the NOTCH ligand JAG2 in muscle fibers. YAP forced-activity in muscle fibers prevents the decrease of JAG2 expression and the number of PAX7+ cells in immobilization conditions. Our results identify a novel mechanism acting downstream of muscle contraction, where YAP activates JAG2 expression in muscle fibers, which in turn regulates the pool of fetal muscle progenitors via NOTCH in a non-cell-autonomous manner.

DOI:http://dx.doi.org/10.7554/eLife.15593.001

Skeletal muscle is attached to the skeleton and allows the body to move. Making a new muscle, or repairing an existing one, relies on stem cells that are present inside muscles. A major goal of skeletal muscle research is to understand the signals that regulate the abilities of muscle stem cells to divide and give rise to more stem cells or to become muscle cells. Molecular signals are known to regulate the numbers of stem cells in the muscle. Skeletal muscles become larger if they are exercised, but it is not clear if mechanical forces generated by muscle contractions directly affect the number of muscle stem cells.

The NOTCH signaling pathway contributes to maintaining the population of stem cells in muscles by forcing the stem cells to divide and preventing them from becoming muscle cells. Here, Esteves de Lima et al. investigated whether muscle contraction regulates NOTCH signaling during muscle formation in chick fetuses.

The experiments show that muscle contraction stimulates the activity of a protein called YAP in muscle cells, which in turn, activates a gene in the NOTCH signaling pathway known as JAG2. This increases NOTCH signaling activity in the neighboring stem cells and maintains the number of stem cells in the muscle. The next step following this work will be to establish if this mechanism also operates during muscle formation and regeneration in other animals such as mice and zebrafish.

DOI:http://dx.doi.org/10.7554/eLife.15593.002

An evolutionary, structural and functional overview of the mammalian TEAD1 and TEAD2 transcription factors

TEAD proteins constitute a family of highly conserved transcription factors, characterized by a DNA-binding domain called the TEA domain and a protein-binding domain that permits association with transcriptional co-activators. TEAD proteins are unable to induce transcription on their own. They have to interact with transcriptional cofactors to do so. Once TEADs bind their co-activators, the different complexes formed are known to regulate the expression of genes that are crucial for embryonic development, important for organ formation (heart, muscles), and involved in cell death and proliferation. In the first part of this review we describe what is known of the structure of TEAD proteins. We then focus on two members of the family: TEAD1 and TEAD2. First the different transcriptional cofactors are described. These proteins can be classified in three categories: i), cofactors regulating chromatin conformation, ii), cofactors able to bind DNA, and iii), transcriptional cofactors without DNA binding domain. Finally we discuss the recent findings that identified TEAD1 and 2 and its coactivators involved in cancer progression.

A Potential Structural Switch for Regulating DNA-Binding by TEAD Transcription Factors

TEA domain (TEAD) transcription factors are essential for the normal development of eukaryotes and are the downstream effectors of the Hippo tumor suppressor pathway. Whereas our earlier work established the three-dimensional structure of the highly conserved DNA-binding domain using solution NMR spectroscopy, the structural basis for regulating the DNA-binding activity remains unknown. Here, we present the X-ray crystallographic structure and activity of a TEAD mutant containing a truncated L1 loop, ΔL1 TEAD DBD. Unexpectedly, the three-dimensional structure of the ΔL1 TEAD DBD reveals a helix-swapped homodimer wherein helix 1 is swapped between monomers. Furthermore, each three-helix bundle in the domain-swapped dimer is a structural homolog of MYB-like domains. Our investigations of the DNA-binding activity reveal that although the formation of the three-helix bundle by the ΔL1 TEAD DBD is sufficient for binding to an isolated M-CAT-like DNA element, multimeric forms are deficient for cooperative binding to tandemly duplicated elements, indicating that the L1 loop contributes to the DNA-binding activity of TEAD. These results suggest that switching between monomeric and domain-swapped forms may regulate DNA selectivity of TEAD proteins.

The Hippo signal transduction network for exercise physiologists

The ubiquitous transcriptional coactivators Yap (gene symbol Yap1) and Taz (gene symbol Wwtr1) regulate gene expression mainly by coactivating the Tead transcription factors. Being at the center of the Hippo signaling network, Yap and Taz are regulated by the Hippo kinase cassette and additionally by a plethora of exercise-associated signals and signaling modules. These include mechanotransduction, the AKT-mTORC1 network, the SMAD transcription factors, hypoxia, glucose homeostasis, AMPK, adrenaline/epinephrine and angiotensin II through G protein-coupled receptors, and IL-6. Consequently, exercise should alter Hippo signaling in several organs to mediate at least some aspects of the organ-specific adaptations to exercise. Indeed, Tead1 overexpression in muscle fibers has been shown to promote a fast-to-slow fiber type switch, whereas Yap in muscle fibers and cardiomyocytes promotes skeletal muscle hypertrophy and cardiomyocyte adaptations, respectively. Finally, genome-wide association studies in humans have linked the Hippo pathway members LATS2, TEAD1, YAP1, VGLL2, VGLL3, and VGLL4 to body height, which is a key factor in sports.

YAP1 Exerts Its Transcriptional Control via TEAD-Mediated Activation of Enhancers

YAP1 is a major effector of the Hippo pathway and a well-established oncogene. Elevated YAP1 activity due to mutations in Hippo pathway components or YAP1 amplification is observed in several types of human cancers. Here we investigated its genomic binding landscape in YAP1-activated cancer cells, as well as in non-transformed cells. We demonstrate that TEAD transcription factors mediate YAP1 chromatin-binding genome-wide, further explaining their dominant role as primary mediators of YAP1-transcriptional activity. Moreover, we show that YAP1 largely exerts its transcriptional control via distal enhancers that are marked by H3K27 acetylation and that YAP1 is necessary for this chromatin mark at bound enhancers and the activity of the associated genes. This work establishes YAP1-mediated transcriptional regulation at distal enhancers and provides an expanded set of target genes resulting in a fundamental source to study YAP1 function in a normal and cancer setting.

The YAP1/Hippo signaling pathway is a key regulator of organ size and tissue homeostasis, and its dysregulation is linked to cancer development. Elevated activity of YAP1, a transcriptional coactivator and well-established oncogene has been reported to occur in human cancers. Comprehensive identification of YAP1 regulated genes and its mode of action will be of high importance to uncover YAP1 biology that could be exploited for a therapeutic intervention. To this end, we performed genome-wide analyses to identify YAP1 occupied sites in cancer cell lines representing different YAP1/Hippo pathway tumor etiologies and in non-transformed fibroblasts. Our data demonstrate that YAP1 activity is mediated predominantly via TEAD transcription factors supporting the importance of TEADs as main mediators of YAP1-coactivator activity. We further show that YAP1 and TEAD1 exert their transcriptional control via binding to enhancers, leading to characteristic chromatin changes and distal activation of genes. By linking enhancers to genes, we provide a list of novel YAP1 target genes in an oncogenic setting that we show can readily be exploited in tumor classification and provides a foundation for further investigations.

c-Abl antagonizes the YAP oncogenic function

YES-associated protein (YAP) is a central transcription coactivator that functions as an oncogene in a number of experimental systems. However, under DNA damage, YAP activates pro-apoptotic genes in conjunction with p73. This program switching is mediated by c-Abl (Abelson murine leukemia viral oncogene) via phosphorylation of YAP at the Y357 residue (pY357). YAP as an oncogene coactivates the TEAD (transcriptional enhancer activator domain) family transcription factors. Here we asked whether c-Abl regulates the YAP-TEAD functional module. We found that DNA damage, through c-Abl activation, specifically depressed YAP-TEAD-induced transcription. Remarkably, c-Abl counteracts YAP-induced transformation by interfering with the YAP-TEAD transcriptional program. c-Abl induced TEAD1 phosphorylation, but the YAP-TEAD complex remained unaffected. In contrast, TEAD coactivation was compromised by phosphomimetic YAP Y357E mutation but not Y357F, as demonstrated at the level of reporter genes and endogenous TEAD target genes. Furthermore, YAP Y357E also severely compromised the role of YAP in cell transformation, migration, anchorage-independent growth, and epithelial-to-mesenchymal transition (EMT) in human mammary MCF10A cells. These results suggest that YAP pY357 lost TEAD transcription activation function. Our results demonstrate that YAP pY357 inactivates YAP oncogenic function and establish a role for YAP Y357 phosphorylation in cell-fate decision.

The Hippo signal transduction network in skeletal and cardiac muscle

The discovery of the Hippo pathway can be traced back to two areas of research. Genetic screens in fruit flies led to the identification of the Hippo pathway kinases and scaffolding proteins that function together to suppress cell proliferation and tumor growth. Independent research, often in the context of muscle biology, described Tead (TEA domain) transcription factors, which bind CATTCC DNA motifs to regulate gene expression. These two research areas were joined by the finding that the Hippo pathway regulates the activity of Tead transcription factors mainly through phosphorylation of the transcriptional coactivators Yap and Taz, which bind to and activate Teads. Additionally, many other signal transduction proteins crosstalk to members of the Hippo pathway forming a Hippo signal transduction network. We discuss evidence that the Hippo signal transduction network plays important roles in myogenesis, regeneration, muscular dystrophy, and rhabdomyosarcoma in skeletal muscle, as well as in myogenesis, organ size control, and regeneration of the heart. Understanding the role of Hippo kinases in skeletal and heart muscle physiology could have important implications for translational research.

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.

Establishment of transgenic lines to monitor and manipulate Yap/Taz-Tead activity in zebrafish reveals both evolutionarily conserved and divergent functions of the Hippo pathway

To investigate the role of Hippo pathway signaling during vertebrate development transgenic zebrafish lines were generated and validated to dynamically monitor and manipulate Yap/Taz-Tead activity. Spatial and temporal analysis of Yap/Taz-Tead activity suggested the importance of Hippo signaling during cardiac precursor migration and other developmental processes. When the transcriptional co-activators, Yap and Taz were restricted from interacting with DNA-binding Tead transcription factors through expression of a dominant negative transgene, cardiac precursors failed to migrate completely to the midline resulting in strong cardia bifida. Yap/Taz-Tead activity reporters also allowed us to investigate upstream and downstream factors known to regulate Hippo signaling output in Drosophila. While Crumbs mutations in Drosophila eye disc epithelia increase nuclear translocation and activity of Yorkie (the fly homolog of Yap/Taz), zebrafish crb2a mutants lacked nuclear Yap positive cells and down-regulated Yap/Taz-Tead activity reporters in the eye epithelia, despite the loss of apical-basal cell polarity in those cells. However, as an example of evolutionary conservation, the Tondu-domain containing protein Vestigial-like 4b (Vgll4b) was found to down-regulate endogenous Yap/Taz-Tead activity in the retinal pigment epithelium, similar to Drosophila Tgi in imaginal discs. In conclusion, the Yap/Taz-Tead activity reporters revealed the dynamics of Yap/Taz-Tead signaling and novel insights into Hippo pathway regulation for vertebrates. These studies highlight the utility of this transgenic tool-suite for ongoing analysis into the mechanisms of Hippo pathway regulation and the consequences of signaling output.

Identification of a classical bipartite nuclear localization signal in the Drosophila TEA/ATTS protein scalloped

Drosophila melanogaster wing development has been shown to rely on the activity of a complex of two proteins, Scalloped (Sd) and Vestigial (Vg). Within this complex, Sd is known to provide DNA binding though its TEA/ATTS domain, while Vg modulates this binding and provides transcriptional activation through N- and C-terminal activation domains. There is also evidence that Sd is required for the nuclear translocation of Vg. Indeed, a candidate sequence which shows consensus to the bipartite family of nuclear localization signals (NLSs) has been identified within Sd previously, though it is not known if it is functional, or if additional unpredicted signals that mediate nuclear transport exist within the protein. By expressing various enhanced green fluorescent protein (eGFP) tagged constructs within Drosophila S2 cells, we demonstrate that this NLS is indeed functional and necessary for the proper nuclear localization of Sd. Additionally, the region containing the NLS is critical for the wildtype function of ectopically expressed Sd, in the context of wing development. Using site-directed mutagenesis, we have identified a group of five amino acids within this NLS which is critical for its function, as well as another group of two which is of lesser importance. Together with data that suggests that this sequence mediates interactions with Importin-α3, we conclude that the identified NLS is likely a classical bipartite signal. Further dissection of Sd has also revealed that a large portion of the C-terminal domain of the protein is required its proper nuclear localization. Finally, a Leptomycin B (LB) sensitive signal which appears to facilitate nuclear export is identified, raising the possibility that Sd also contains a nuclear export signal (NES).

Reexamining the DNA target selectivity of Scalloped

Selector proteins are transcription factors that coordinate the formation and identity of organs and appendages. The proper formation of these tissues requires the selector proteins to regulate the expression of a large set of genes. Many selector proteins are involved in regulating multiple developmental processes, yet it is not completely clear how they are able to activate different sets of genes in a tissue-specific manner. An association with cofactors is thought to be one method by which enhancer selectivity is achieved. During wing development the selector protein Scalloped (SD) interacts with the cofactor Vestigial (VG). This interaction leads to the activation of a specific set of downstream wing genes. Herein, data are presented indicating that the switch in binding selectivity is likely achieved by VG altering the general affinity that the SD protein has for DNA. The decreased affinity for DNA is compensated for by the fact that the VG protein forms a complex containing two SD proteins. These two properties ensure that the SD–VG complex is able to bind only to enhancers that have two consecutive binding sites. Furthermore, data are presented that indicate that the function of the two terminal domains of the VG protein is not restricted to activating transcription and promoting the recruitment of two SD proteins.

Genome-wide analysis of POU3F2/BRN2 promoter occupancy in human melanoma cells reveals Kitl as a novel regulated target gene

POU3F2 is a POU-Homeodomain transcription factor expressed in neurons and melanoma cells. In melanoma lesions, cells expressing high levels of POU3F2 show enhanced invasive and metastatic capacity that can in part be explained by repression of Micropthalmia-associated Transcription Factor (MITF) expression via POU3F2 binding to its promoter. To identify other POU3F2 target genes that may be involved in modulating the properties of melanoma cells, we performed ChIP-chip experiments in 501Mel melanoma cells. 2108 binding loci located in the regulatory regions of 1700 potential target genes were identified. Bioinformatic and experimental assays showed the presence of known POU3F2-binding motifs, but also many AT-rich sequences with only partial similarity to the known motifs at the occupied loci. Functional analysis indicates that POU3F2 regulates the stem cell factor (Kit ligand, Kitl) promoter via a cluster of four closely spaced binding sites located in the proximal promoter. Our results suggest that POU3F2 may regulate the properties of melanoma cells via autocrine KIT ligand signalling.

Mammalian Tead proteins regulate cell proliferation and contact inhibition as transcriptional mediators of Hippo signaling

Regulation of organ size is important for development and tissue homeostasis. In Drosophila, Hippo signaling controls organ size by regulating the activity of a TEAD transcription factor, Scalloped, through modulation of its co-activator protein Yki. Here, we show that mouse Tead proteins regulate cell proliferation by mediating Hippo signaling. In NIH3T3 cells, cell density and Hippo signaling regulated the activity of endogenous Tead proteins by modulating nuclear localization of a Yki homolog, Yap1, and the resulting change in Tead activity altered cell proliferation. Tead2-VP16 mimicked Yap1 overexpression, including increased cell proliferation, reduced cell death, promotion of EMT, lack of cell contact inhibition and promotion of tumor formation. Growth-promoting activities of various Yap1 mutants correlated with their Tead-co-activator activities. Tead2-VP16 and Yap1 regulated largely overlapping sets of genes. However, only a few of the Tead/Yap1-regulated genes in NIH3T3 cells were affected in Tead1(-/-);Tead2(-/-) or Yap1(-/-) embryos. Most of the previously identified Yap1-regulated genes were not affected in NIH3T3 cells or mutant mice. In embryos, levels of nuclear Yap1 and Tead1 varied depending on cell type. Strong nuclear accumulation of Yap1 and Tead1 were seen in myocardium, correlating with requirements of Tead1 for proliferation. However, their distribution did not always correlate with proliferation. Taken together, mammalian Tead proteins regulate cell proliferation and contact inhibition as a transcriptional mediator of Hippo signaling, but the mechanisms by which Tead/Yap1 regulate cell proliferation differ depending on the cell type, and Tead, Yap1 and Hippo signaling may play multiple roles in mouse embryos.

Transcription enhancer factor 3 (TEF3) mediates the expression of Down syndrome candidate region 1 isoform 1 (DSCR1-1L) in endothelial cells

The Down syndrome candidate region 1 gene (DSCR1) can be expressed as four isoforms, one of which is the well-studied isoform 4 (DSCR1-4) that is induced by VEGF-A(165) to provide a negative feedback loop in the VEGF-A(165)-induced angiogenesis. We reported previously that another DSCR1 isoform, DSCR1-1L, was also up-regulated by VEGF-A(165) in cultured endothelial cells and in several in vivo models of pathological angiogenesis and that different from DSCR1-4, DSCR1-1L overexpression alone induced cultured endothelial cell proliferation and promoted angiogenesis in Matrigel assays. It was reported recently that tumor growth was greatly repressed in DSCR1 knock-out mice. Although DSCR1-4 transcription was primarily regulated by NFAT, the mechanism regulating DSCR1-1L expression was still unknown. We developed human DSCR1-1L promoter-driven luciferase system and found that deletion of a putative conserved M-CAT site located 1426-bp upstream of the translation start site blunted promoter activity. We further showed that knockdown of TEF3, not other members of TEF family inhibited VEGF-A(165)-induced DSCR1-1L expression. We also demonstrated that TEF3 directly interacted with the putative M-CAT site in the DSCR1-1L promoter in vitro and in vivo. Finally, overexpression of TEF3 isoform 1, not isoform 3, in HUVEC was sufficient to induce DSCR1-1L expression even in the absence of VEGF-A(165) stimulation. Taken together, we elucidated a novel function of transcriptional factor TEF3. TEF3 was required for DSCR1-1L expression through binding to the M-CAT site in its promoter and could be an attractive target for anti-angiogenesis therapy.

Redundant roles of Tead1 and Tead2 in notochord development and the regulation of cell proliferation and survival

Four members of the TEAD/TEF family of transcription factors are expressed widely in mouse embryos and adult tissues. Although in vitro studies have suggested various roles for TEAD proteins, their in vivo functions remain poorly understood. Here we examined the role of Tead genes by generating mouse mutants for Tead1 and Tead2. Tead2(-/-) mice appeared normal, but Tead1(-/-); Tead2(-/-) embryos died at embryonic day 9.5 (E9.5) with severe growth defects and morphological abnormalities. At E8.5, Tead1(-/-); Tead2(-/-) embryos were already small and lacked characteristic structures such as a closed neural tube, a notochord, and somites. Despite these overt abnormalities, differentiation and patterning of the neural plate and endoderm were relatively normal. In contrast, the paraxial mesoderm and lateral plate mesoderm were displaced laterally, and a differentiated notochord was not maintained. These abnormalities and defects in yolk sac vasculature organization resemble those of mutants for Yap, which encodes a coactivator of TEAD proteins. Moreover, we demonstrated genetic interactions between Tead1 and Tead2 and Yap. Finally, Tead1(-/-); Tead2(-/-) embryos showed reduced cell proliferation and increased apoptosis. These results suggest that Tead1 and Tead2 are functionally redundant, use YAP as a major coactivator, and support notochord maintenance as well as cell proliferation and survival in mouse development.

Transcriptional regulation of phosphatidylcholine biosynthesis

Phosphatidylcholine biosynthesis in animal cells is primarily regulated by the rapid translocation of CTP:phosphocholine cytidylyltransferase alpha between a soluble form that is inactive and a membrane-associated form that is activated. Until less than 10 years ago there was no information on the transcriptional regulation of phosphatidylcholine biosynthesis. Research has identified the transcription factors Sp1, Rb, TEF4, Ets-1 and E2F as enhancing the expression of the cytidylyltransferase and Net as a factor that represses cytidylyltransferase expression. Key transcription factors involved in cholesterol or fatty acid metabolism (SREBPs, LXRs, PPARs) do not have a major role in transcriptional regulation of the cytidylyltransferase. Rather than being linked to cholesterol or energy metabolism, regulation of the cytidylyltransferase is linked to the cell cycle, cell growth and differentiation. Transcriptional regulation of phospholipid biosynthesis is more elegantly understood in yeast and involves responses to inositol, choline and zinc in the culture medium.

MCAT elements and the TEF-1 family of transcription factors in muscle development and disease

MCAT elements are located in the promoter-enhancer regions of cardiac, smooth, and skeletal muscle-specific genes including cardiac troponin T, beta-myosin heavy chain, smooth muscle alpha-actin, and skeletal alpha-actin, and play a key role in the regulation of these genes during muscle development and disease. The binding factors of MCAT elements are members of the transcriptional enhancer factor-1 (TEF-1) family. However, it has not been fully understood how these transcription factors confer cell-specific expression in muscle, because their expression patterns are relatively broad. Results of recent studies revealed multiple mechanisms whereby TEF-1 family members control MCAT element-dependent muscle-specific gene expression, including posttranslational modifications of TEF-1 family members, the presence of muscle-selective TEF-1 cofactors, and cell-selective control of TEF-1 accessibility to MCAT elements. In addition, of particular interest, recent studies regarding MCAT element-dependent transcription of the myocardin gene and the smooth muscle alpha-actin gene in muscle provide evidence for the transcriptional diversity among distinct cell types and subtypes. This article summarizes the role of MCAT elements and the TEF-1 family of transcription factors in muscle development and disease, and reviews recent progress in our understanding of the transcriptional regulatory mechanisms involved in MCAT element-dependent muscle-specific gene expression.

High Cancer-Specific Expression of Mesothelin (MSLN) Is Attributable to an Upstream Enhancer Containing a Transcription Enhancer Factor–Dependent MCAT Motif

Identification of genes with cancer-specific overexpression offers the potential to efficiently discover cancer-specific activities in an unbiased manner. We apply this paradigm to study mesothelin (MSLN) overexpression, a nearly ubiquitous, diagnostically and therapeutically useful characteristic of pancreatic cancer. We identified an 18-bp upstream enhancer, termed CanScript, strongly activating transcription from an otherwise weak tissue-nonspecific promoter and operating selectively in cells having aberrantly elevated cancer-specific MSLN transcription. Introducing mutations into CanScript showed two functionally distinct sites: an Sp1-like site and an MCAT element. Gel retardation and chromatin immunoprecipitation assays showed the MCAT element to be bound by transcription enhancer factor (TEF)-1 (TEAD1) in vitro and in vivo. The presence of TEF-1 was required for MSLN protein overexpression as determined by TEF-1 knockdown experiments. The cancer specificity seemed to be provided by a putative limiting cofactor of TEF-1 that could be outcompeted by exogenous TEF-1 only in a MSLN-overexpressing cell line. A CanScript concatemer offered enhanced activity. These results identify a TEF family member as a major regulator of MSLN overexpression, a fundamental characteristic of pancreatic and other cancers, perhaps due to an upstream and highly frequent aberrant cellular activity. The CanScript sequence represents a modular element for cancer-specific targeting, potentially suitable for nearly a third of human malignancies.

Transcription factor TEAD2 is involved in neural tube closure

TEAD2, one of the first transcription factors expressed at the beginning of mammalian development, appears to be required during neural development. For example, Tead2 expression is greatest in the dorsal neural crest where it appears to regulate expression of Pax3, a gene essential for brain development. Consistent with this hypothesis, we found that inactivation of the Tead2 gene in mice significantly increased the risk of exencephaly (a defect in neural tube closure). However, none of the embryos exhibited spina bifida, the major phenotype of Pax3 nullizygous embryos, and expression of Pax3 in E11.5 Tead2 nullizygous embryos was normal. Thus, Tead2 plays a role in neural tube closure that is independent of its putative role in Pax3 regulation. In addition, the risk of exencephaly was greatest with Tead2 nullizygous females, and could be suppressed either by folic acid or pifithrin-alpha. These results reveal a maternal genetic contribution to neural tube closure, and suggest that Tead2-deficient mice provide a model for anencephaly, a common human birth defect that can be prevented by folic acid.

Insights into transcription enhancer factor 1 (TEF-1) activity from the solution structure of the TEA domain

Transcription enhancer factor 1 is essential for cardiac, skeletal, and smooth muscle development and uses its N-terminal TEA domain (TEAD) to bind M-CAT elements. Here, we present the first structure of TEAD and show that it is a three-helix bundle with a homeodomain fold. Structural data reveal how TEAD binds DNA. Using structure-function correlations, we find that the L1 loop is essential for cooperative loading of TEAD molecules on to tandemly duplicated M-CAT sites. Furthermore, using a microarray chip-based assay, we establish that known binding sites of the full-length protein are only a subset of DNA elements recognized by TEAD. Our results provide a model for understanding the regulation of genome-wide gene expression during development by TEA/ATTS family of transcription factors.

Myocardin is a direct transcriptional target of Mef2, Tead and Foxo proteins during cardiovascular development

Myocardin is a transcriptional co-activator of serum response factor (Srf), which is a key regulator of the expression of smooth and cardiac muscle genes. Consistent with its role in regulating cardiovascular development, myocardin is the earliest known marker specific to both the cardiac and smooth muscle lineages during embryogenesis. To understand how the expression of this early transcriptional regulator is initiated and maintained, we scanned 90 kb of genomic DNA encompassing the myocardin gene for cis-regulatory elements capable of directing myocardin transcription in cardiac and smooth muscle lineages in vivo. Here, we describe an enhancer that controls cardiovascular expression of the mouse myocardin gene during mouse embryogenesis and adulthood. Activity of this enhancer in the heart and vascular system requires the combined actions of the Mef2 and Foxo transcription factors. In addition, the Tead transcription factor is required specifically for enhancer activation in neural-crest-derived smooth muscle cells and dorsal aorta. Notably, myocardin also regulates its own enhancer, but in contrast to the majority of myocardin target genes, which are dependent on Srf, myocardin acts through Mef2 to control its enhancer. These findings reveal an Srf-independent mechanism for smooth and cardiac muscle-restricted transcription and provide insight into the regulatory mechanisms responsible for establishing the smooth and cardiac muscle phenotypes during development.

Divergent transcriptional enhancer factor-1 regulates the cardiac troponin T promoter

MCAT elements are essential for cardiac gene expression during development. Avian transcriptional enhancer factor-1 (TEF-1) proteins are muscle-enriched and contribute to MCAT binding activities. However, direct activation of MCAT-driven promoters by TEF-1-related proteins has not been uniformly achieved. Divergent TEF (DTEF)-1 is a unique member of the TEF-1 multigene family with abundant transcripts in the heart but not in skeletal muscle. Herein we show that DTEF-1 proteins are highly expressed in the heart. Protein expression is activated at very early stages of chick embryogenesis (Hamburger-Hamilton stage 4, 16–18 h), after which DTEF-1 becomes abundant in the sinus venosus and is expressed in the trabeculated ventricular myocardium and ventricular outflow tracts. By chromatin immunoprecipitation, DTEF-1 interacts with the cardiac troponin T (cTnT) promoter in vivo. DTEF-1 also interacts with MEF- 2 by coimmunoprecipitation and independently or cooperatively (with MEF-2) trans-activates the cTnT promoter. DTEF-1 isoforms do not activate the cTnT promoter in fibroblasts or skeletal muscle. DTEF-1 expression occurs very early in chick embryogenesis (16–18 h), preceding sarcomeric protein expression, and it activates cardiac promoters. As such, DTEF-1 may be an early marker of the myocardial phenotype. DTEF-1 trans-activates the cTnT promoter in a tissue-specific fashion independent of AT-rich, MEF-2, or GATA sites. The observed spatial pattern suggests decreasing levels of expression from the cardiac inlet to the ventricular outflow tracts, which may mark a cardiogenic or differentiation pathway that parallels the direction of flow through the developing chick heart.

Fgfr4 is required for effective muscle regeneration in vivo. Delineation of a MyoD-Tead2-Fgfr4 transcriptional pathway

Fgfr4 has been shown to be important for appropriate muscle development in chick limb buds; however, Fgfr4 null mice show no phenotype. Here, we show that staged induction of muscle regeneration in Fgfr4 null mice becomes highly abnormal at the time point when Fgfr4 is normally expressed. By 7 days of regeneration, differentiation of myotubes became poorly coordinated and delayed by both histology and embryonic myosin heavy chain staining. By 14 days much of the muscle was replaced by fat and calcifications. To begin to dissect the molecular pathways involving Fgfr4, we queried the promoter sequences for transcriptional factor binding sites and tested candidate regulators in a 27-time point regeneration series. The Fgfr4 promoter region contained a Tead protein binding site (M-CAT 5'-CATTCCT-3'), and Tead2 showed induction during regeneration commensurate with Fgfr4 regulation. Co-transfection of Tead2 and Fgfr4 promoter reporter constructs into C2C12 myotubes showed Tead2 to activate Fgfr4, and mutation of the M-CAT motif in the Fgfr4 promoter abolished these effects. Immunostaining for Tead2 showed timed expression in myotube nuclei consistent with the mRNA data. Query of the expression timing and genomic sequences of Tead2 suggested direct regulation by MyoD, and consistent with this, MyoD directly bound to two strong E-boxes in the first intron of Tead2 by chromatin immunoprecipitation assay. Moreover, co-transfection of MyoD and Tead2 intron reporter constructs into 10T1/2 cells activated reporter activity in a dose-dependent manner. This activation was greatly reduced when the two E-boxes were mutated. Our data suggest a novel MyoD-Tead2-Fgfr4 pathway important for effective muscle regeneration.

Tead proteins activate the Foxa2 enhancer in the node in cooperation with a second factor

The cell population and the activity of the organizer change during the course of development. We addressed the mechanism of mouse node development via an analysis of the node/notochord enhancer (NE) of Foxa2. We first identified the core element (CE) of the enhancer, which in multimeric form drives gene expression in the node. The CE was activated in Wnt/β-catenin-treated P19 cells with a time lag, and this activation was dependent on two separate sequence motifs within the CE. These same motifs were also required for enhancer activity in transgenic embryos. We identified the Tead family of transcription factors as binding proteins for the 3′motif. Teads and their co-factor YAP65 activated the CE in P19 cells, and binding of Tead to CE was essential for enhancer activity. Inhibition of Tead activity by repressor-modified Tead compromised NE enhancer activation and notochord development in transgenic mouse embryos. Furthermore, manipulation of Tead activity in zebrafish embryos led to altered expression of foxa2 in the embryonic shield. These results suggest that Tead activates the Foxa2 enhancer core element in the mouse node in cooperation with a second factor that binds to the 5′ element, and that a similar mechanism also operates in the zebrafish shield.

Identification of minimal enhancer elements sufficient for Pax3 expression in neural crest and implication of Tead2 as a regulator of Pax3

Pax3 is a transcription factor that is required by Pre-migratory neural crest cells give rise to the peripheral nervous system, melanocytes, some vascular smooth muscle, and numerous other derivatives. These cells require the transcription factor Pax3, and both mice and humans with Pax3 deficiency exhibit neural crest-related developmental defects. Pax3 is also expressed in the dorsal neural tube, and by myogenic progenitors in the presomitic mesoderm and the hypaxial somites. Molecular pathways that regulate Pax3expression in the roof plate probably represent early upstream signals in neural crest induction. We have identified an enhancer region in the Pax3 genomic locus that is sufficient to recapitulate expression in neural crest precursors in transgenic mice. We show that Tead2, a member of the Tead box family of transcription factors, binds to a neural crest enhancer and activates Pax3 expression. Tead2, and its co-activator YAP65, are co-expressed with Pax3 in the dorsal neural tube, and mutation of the Tead2 binding site in the context of Pax3 transgenic constructs abolishes neural expression. In addition, a Tead2-Engrailed fusion protein is able to repress retinoic acid-induced Pax3 expression in P19 cells and in vivo. These results suggest that Tead2 is an endogenous activator of Pax3 in neural crest.

Combinatorial control of smooth muscle-specific gene expression

Alterations in the differentiated state of vascular smooth muscle cells (SMCs) are known to play a key role in vascular diseases, yet the mechanisms controlling SMC differentiation are still poorly understand. In this review, we discuss our present knowledge of control of SMC differentiation at the transcriptional level, pointing out some common themes, important paradigms, and unresolved issues in SMC-specific gene regulation. We focus primarily on the serum response factor-CArG box-dependent pathway, because it has been shown to play a critical role in regulation of multiple SMC marker genes. However, we also highlight several other important regulatory elements, such as a transforming growth factor beta control element, E-boxes, and MCAT motifs. We present evidence in support of the notion that SMC-specific gene regulation is not controlled by a few SMC-specific transcription factors but rather by complex combinatorial interactions between multiple general and tissue-specific proteins. Finally, we discuss the implications of chromatin remodeling on SMC differentiation.

A TEF-1-element is required for activation of the promoter of pseudorabies virus glycoprotein X gene by IE180

The pseudorabies virus (PRV) immediate-early regulatory protein IE180 is able to transactivate the viral early and late genes. Using chloramphenicol acetyltransferase (CAT) assay, we investigated the transactivation function of IE180 to the promoter of PRV glycoprotein X (gX) gene, and our results showed that IE180 could significantly increase the expression of CAT gene which was under the control of gX promoter. To further identify the activation domains of IE180 protein that interact with the gX promoter sequences, various truncated mutants of IE180 gene and gX promoter gene were constructed and analyzed by CAT and gel retardation assay. Results revealed that the N-terminal amino acid residues from 133 to 736 of IE180 could interact with the binding site of transcriptional enhancer factor-1 (TEF-1) that resides in the gX promoter. Formation of protein-DNA complexes between the IE180 protein and the TEF-1 element of the gX promoter was observed using electrophoretic mobility shift assay (EMSA) as well as Southwestern blot analysis. These results indicated that a direct interaction occurred between IE180 and the TEF-1 element; and this interaction was abolished if the TEF-1 element was mutated. The association of IE180 with the TEF-1 element was further confirmed by the supershift of EMSA complexes using IE180 specific antibody. Taken together, our results suggested that formation of a complex between the IE180 protein and TEF-1 element in the gX promoter region was involved in the transcriptional regulation of the gX gene.

Mouse DTEF-1 (ETFR-1, TEF-5) is a transcriptional activator in alpha 1-adrenergic agonist-stimulated cardiac myocytes

alpha(1)-Adrenergic signaling in cardiac myocytes activates the skeletal muscle alpha-actin gene through an MCAT cis-element, the binding site of the transcriptional enhancer factor-1 (TEF-1) family of transcription factors. TEF-1 accounts for more than 85% of the MCAT binding activity in neonatal rat cardiac myocytes. Other TEF-1 family members account for the rest. Although TEF-1 itself has little effect on the alpha(1)-adrenergic activation of skeletal muscle alpha-actin, the related factor RTEF-1 augments the response and is a target of alpha(1)-adrenergic signaling. Here, we examined another TEF-1 family member expressed in cardiac muscle, DTEF-1, and observed that it also augmented the alpha(1)-adrenergic response of skeletal muscle alpha-actin. A DTEF-1 peptide-specific antibody revealed that endogenous DTEF-1 accounts for up to 5% of the MCAT binding activity in neonatal rat cardiac myocytes. A TEF-1/DTEF-1 chimera suggests that alpha(1)-adrenergic signaling modulates DTEF-1 function. Orthophosphate labeling and immunoprecipitation of an epitope-tagged DTEF-1 showed that DTEF-1 is phosphorylated in vivo. alpha(1)-Adrenergic stimulation increased while phosphatase treatment lowered the MCAT binding by DTEF-1 and the endogenous non-TEF-1 MCAT-binding factor. In contrast, alpha(1)-adrenergic stimulation did not alter, and phosphatase treatment increased, MCAT binding of TEF-1 and RTEF-1. Taken together, these results suggest that DTEF-1 is a target for alpha(1)-adrenergic activation of the skeletal muscle alpha-actin gene in neonatal rat cardiac myocytes.

Cryptic MCAT enhancer regulation in fibroblasts and smooth muscle cells. Suppression of TEF-1 mediated activation by the single-stranded DNA-binding proteins, Pur alpha, Pur beta, and MSY1

An asymmetric polypurine-polypyrimidine cis-element located in the 5' region of the mouse vascular smooth muscle alpha-actin gene serves as a binding site for multiple proteins with specific affinity for either single- or double-stranded DNA. Here, we test the hypothesis that single-stranded DNA-binding proteins are responsible for preventing a cryptic MCAT enhancer centered within this element from cooperating with a nearby serum response factor-interacting CArG motif to trans-activate the minimal promoter in fibroblasts and smooth muscle cells. DNA binding studies revealed that the core MCAT sequence mediates binding of transcription enhancer factor-1 to the double-stranded polypurine-polypyrimidine element while flanking nucleotides account for interaction of Pur alpha and Pur beta with the purine-rich strand and MSY1 with the complementary pyrimidine-rich strand. Mutations that selectively impaired high affinity single-stranded DNA binding by fibroblast or smooth muscle cell-derived Pur alpha, Pur beta, and MSY1 in vitro, released the cryptic MCAT enhancer from repression in transfected cells. Additional experiments indicated that Pur alpha, Pur beta, and MSY1 also interact specifically, albeit weakly, with double-stranded DNA and with transcription enhancer factor-1. These results are consistent with two plausible models of cryptic MCAT enhancer regulation by Pur alpha, Pur beta, and MSY1 involving either competitive single-stranded DNA binding or masking of MCAT-bound transcription enhancer factor-1.

Binding of the Vestigial co-factor switches the DNA-target selectivity of the Scalloped selector protein

The formation and identity of organs and appendages are regulated by specific selector genes that encode transcription factors that regulate potentially large sets of target genes. The DNA-binding domains of selector proteins often exhibit relatively low DNA-binding specificity in vitro. It is not understood how the target selectivity of most selector proteins is determined in vivo. The Scalloped selector protein controls wing development in Drosophila by regulating the expression of numerous target genes and forming a complex with the Vestigial protein. We show that binding of Vestigial to Scalloped switches the DNA-binding selectivity of Scalloped. Two conserved domains of the Vestigial protein that are not required for Scalloped binding in solution are required for the formation of the heterotetrameric Vestigial-Scalloped complex on DNA. We suggest that Vestigial affects the conformation of Scalloped to create a wing cell-specific DNA-binding selectivity. The modification of selector protein DNA-binding specificity by co-factors appears to be a general mechanism for regulating their target selectivity in vivo.

SAGA is an essential in vivo target of the yeast acidic activator Gal4p

Despite major advances in characterizing the eukaryotic transcriptional machinery, the function of promoter-specific transcriptional activators (activators) is still not understood. For example, in no case have the direct in vivo targets of a transcriptional activator been unambiguously identified, nor has it been resolved whether activators have a single essential target or multiple redundant targets. Here we address these issues for the prototype acidic activator yeast Gal4p. Gal4p binds to the upstream activating sequence (UAS) of GAL1 and several other GAL genes and stimulates transcription in the presence of galactose. Previous studies have shown that GAL1 transcription is dependent on the yeast SAGA (Spt/Ada/GCN5/acetyltransferase) complex. Using formaldehyde-based in vivo cross-linking, we show that the Gal4p activation domain recruits SAGA to the GAL1 UAS. If SAGA is not recruited to the UAS, the preinitiation complex (PIC) fails to assemble at the GAL1 core promoter, and transcription does not occur. SAGA, but not other transcription components, is also recruited by the Gal4p activation domain to a plasmid containing minimal Gal4p-binding sites. Recruitment of SAGA by Gal4p and stimulation of PIC assembly is dependent on several SAGA subunits but not the SAGA histone acetyl-transferase (HAT) GCN5. Based on these and other results, we conclude that SAGA is an essential target of Gal4p that, following recruitment to the UAS, facilitates PIC assembly and transcription.

Novel cell lines promote the discovery of genes involved in early heart development

Clonal cell lines representing early cardiomyocytes would provide valuable reagents for the dissection of the genetic program of early cardiogenesis. Here we describe the establishment and characterization of cell lines from the hearts of transgenic mice and embryos with SV40 large T antigen expressed in the heart-forming region. Ultrastructure analysis by transmission electron microscopy showed the primitive, precontractile nature of the resulting cells, with the absence of myofilaments, Z lines, and intercalated disks. Immunohistochemistry, RT-PCR, Northern blots, and oligonucleotide microarrays were used to determine the expression levels of thousands of genes in the 1H and ECL-2 cell lines. The resulting gene-expression profiles showed the transcription of early cardiomyocyte genes such as Nkx2.5, GATA4, Tbx5, dHAND, cardiac troponin C, and SM22-alpha. Furthermore, many genes not previously implicated in early cardiac development were expressed. Two of these genes, Hic-5, a possible negative regulator of muscle differentiation, and the transcription enhancing factor TEF-5 were selected and shown by in situ hybridizations to be expressed in the early developing heart. The results show that the 1H and ECL-2 cell lines can be used to discover novel genes expressed in the early cardiomyocyte.

An E-box motif residing in the exon/intron 1 junction regulates both transcriptional activation and splicing of the human norepinephrine transporter gene

The norepinephrine transporter (NET) is responsible for the rapid NaCl-dependent uptake of norepinephrine into presynaptic noradrenergic nerve endings. Recently, we have characterized the structural organization of the 5' upstream promoter region of the human NET (hNET) gene. A new intron of 476 base pairs was found in the middle of the 5'-untranslated leader sequence and was shown to robustly enhance the promoter activity. Here, we show that the first hNET intron enhances both the homologous hNET and the heterologous thymidine kinase promoter activities in an orientation- and position-dependent manner. The first hNET intron exhibited a similar promoter-enhancing effect in both SK-N-BE(2)C (NET-positive) and HeLa (NET-negative) cell lines, showing that its function is not cell-specific. Transient transfection assays of a series of deletional constructs show that the first hNET intron contains subdomains with either positive or negative regulatory functions. Furthermore, DNase I footprinting analysis demonstrated that the 5' side of the intron, encompassing the splice donor site, is prominently protected by nuclear proteins isolated from both SK-N-BE(2)C and HeLa cells. The protected nucleotide sequence contains a consensus E-box motif, known to regulate diverse eukaryotic genes, which overlaps with the splice donor site of the first intron. We demonstrate that two basic helix-loop-helix proteins, upstream stimulatory factors 1 and 2, are major proteins interacting at this site and that the E-box is at least in part responsible for the promoter-enhancing activity of the first intron. Furthermore, site-directed mutagenesis of the splice donor site of the first intron affects both correct splicing and transcriptional activity. Taken together, our results indicate that a cis-element residing at the first exon/intron junction, encompassing an E-box motif, has a unique dual role in basal transcriptional activation and splicing of hNET mRNA.

TEAD/TEF transcription factors utilize the activation domain of YAP65, a Src/Yes-associated protein localized in the cytoplasm

Mammals express four highly conserved TEAD/TEF transcription factors that bind the same DNA sequence, but serve different functions during development. TEAD-2/TEF-4 protein purified from mouse cells was associated predominantly with a novel TEAD-binding domain at the amino terminus of YAP65, a powerful transcriptional coactivator. YAP65 interacted specifically with the carboxyl terminus of all four TEAD proteins. Both this interaction and sequence-specific DNA binding by TEAD were required for transcriptional activation in mouse cells. Expression of YAP in lymphocytic cells that normally do not support TEAD-dependent transcription (e.g., MPC11) resulted in up to 300-fold induction of TEAD activity. Conversely, TEAD overexpression squelched YAP activity. Therefore, the carboxy-terminal acidic activation domain in YAP is the transcriptional activation domain for TEAD transcription factors. However, whereas TEAD was concentrated in the nucleus, excess YAP65 accumulated in the cytoplasm as a complex with the cytoplasmic localization protein, 14-3-3. Because TEAD-dependent transcription was limited by YAP65, and YAP65 also binds Src/Yes protein tyrosine kinases, we propose that YAP65 regulates TEAD-dependent transcription in response to mitogenic signals.