TEF-1 and MEF2 transcription factors interact to regulate muscle-specific promoters

Non-coding RNAs as regulators of the Hippo pathway in cardiac development and cardiovascular disease

Cardiovascular diseases pose a serious threat to human health. The onset of cardiovascular diseases involves the comprehensive effects of multiple genes and environmental factors, and multiple signaling pathways are involved in regulating the occurrence and development of cardiovascular diseases. The Hippo pathway is a highly conserved signaling pathway involved in the regulation of cell proliferation, apoptosis, and differentiation. Recently, it has been widely studied in the fields of cardiovascular disease, cancer, and cell regeneration. Non-coding RNA (ncRNAs), which are important small molecules for the regulation of gene expression in cells, can directly target genes and have diverse regulatory functions. Recent studies have found that ncRNAs interact with Hippo pathway components to regulate myocardial fibrosis, cardiomyocyte proliferation, apoptosis, and hypertrophy and play an important role in cardiovascular disease. In this review, we describe the mode of action of ncRNAs in regulating the Hippo pathway, provide new ideas for further research, and identify molecules involved in the mechanism of action of ncRNAs and the Hippo pathway as potential therapeutic targets, with the aim of finding new modes of action for the treatment and prevention of cardiovascular diseases.

Single-nucleus chromatin accessibility profiling highlights regulatory mechanisms of coronary artery disease risk

Coronary artery disease (CAD) is a complex inflammatory disease involving genetic influences across cell types. Genome-wide association studies have identified over 200 loci associated with CAD, where the majority of risk variants reside in noncoding DNA sequences impacting cis-regulatory elements. Here, we applied single-nucleus assay for transposase-accessible chromatin with sequencing to profile 28,316 nuclei across coronary artery segments from 41 patients with varying stages of CAD, which revealed 14 distinct cellular clusters. We mapped ~320,000 accessible sites across all cells, identified cell-type-specific elements and transcription factors, and prioritized functional CAD risk variants. We identified elements in smooth muscle cell transition states (for example, fibromyocytes) and functional variants predicted to alter smooth muscle cell- and macrophage-specific regulation of MRAS (3q22) and LIPA (10q23), respectively. We further nominated key driver transcription factors such as PRDM16 and TBX2. Together, this single-nucleus atlas provides a critical step towards interpreting regulatory mechanisms across the continuum of CAD risk.

TAZ exhibits phase separation properties and interacts with Smad7 and β-catenin to repress skeletal myogenesis

Hippo signaling in Drosophila and mammals is prominent in regulating cell proliferation, death and differentiation. Hippo signaling effectors (YAP/TAZ) exhibit crosstalk with transforming growth factor-β (TGF-β)-Smad and Wnt-β-catenin pathways. Previously, we implicated Smad7 and β-catenin in myogenesis. Therefore, we assessed a potential role of TAZ on theSmad7/β-catenin complex in muscle cells. Here, we document functional interactions between Smad7, TAZ and β-catenin in myogenic cells. Ectopic TAZ expression resulted in repression of the muscle-specific creatine kinase muscle (ckm) gene promoter and its corresponding protein level. Depletion of endogenous TAZ enhanced ckm promoter activation. Ectopic TAZ, while potently active on a TEAD reporter (HIP-HOP), repressed myogenin and myod enhancer regions and Myogenin protein level. Additionally, a Wnt/β-catenin readout (TOP flash) demonstrated TAZ inhibition of β-catenin activity. In myoblasts, TAZ is predominantly localized in nuclear speckles, while in differentiation conditions TAZ is hyperphosphorylated at Ser 89 leading to enhanced cytoplasmic sequestration. Finally, live cell imaging indicates that TAZ exhibits properties of liquid-liquid phase separation (LLPS). These observations indicate that TAZ, as an effector of Hippo signaling, supresses the myogenic differentiation machinery.

TEAD family transcription factors in development and disease

The balance between stem cell potency and lineage specification entails the integration of both extrinsic and intrinsic cues, which ultimately influence gene expression through the activity of transcription factors. One example of this is provided by the Hippo signalling pathway, which plays a central role in regulating organ size during development. Hippo pathway activity is mediated by the transcriptional co-factors Yes-associated protein (YAP) and transcriptional co-activator with PDZ-binding motif (TAZ), which interact with TEA domain (TEAD) proteins to regulate gene expression. Although the roles of YAP and TAZ have been intensively studied, the roles played by TEAD proteins are less well understood. Recent studies have begun to address this, revealing that TEADs regulate the balance between progenitor self-renewal and differentiation throughout various stages of development. Furthermore, it is becoming apparent that TEAD proteins interact with other co-factors that influence stem cell biology. This Primer provides an overview of the role of TEAD proteins during development, focusing on their role in Hippo signalling as well as within other developmental, homeostatic and disease contexts.

The NOTCH1-dependent HIF1α/VGLL4/IRF2BP2 oxygen sensing pathway triggers erythropoiesis terminal differentiation

Hypoxia is widely considered as a limiting factor in vertebrate embryonic development, which requires adequate oxygen delivery for efficient energy metabolism, while nowadays some researches have revealed that hypoxia can induce stem cells so as to improve embryonic development. Erythroid differentiation is the oxygen delivery method employed by vertebrates at the very early step of embryo development, however, the mechanism how erythroid progenitor cell was triggered into mature erythrocyte is still not clear. In this study, after detecting the upregulation of vgll4b in response to oxygen levels, we generated vgll4b mutant zebrafish using CRISPR/Cas9, and verified the resulting impaired heme and dysfunctional erythroid terminal differentiation phenotype. Neither the vgll4b-deficient nor the γ-secretase inhibitor IX (DAPT)-adapted zebrafish were able to mediate HIF1α-induced heme generation. In addition, we showed that vgll4b mutant zebrafish were associated with an impaired erythroid phenotype, induced by the downregulation of alas2, which could be rescued by irf2bp2 depletion. Further mechanistic studies revealed that zebrafish VGLL4 sequesters IRF2BP2, thereby inhibiting its repression of alas2 expression and heme biosynthesis. These processes occur primarily via the VGLL4 TDU1 and IRF2BP2 ring finger domains. Our study also indicates that VGLL4 is a key player in the mediation of NOTCH1-dependent HIF1α-regulated erythropoiesis and can be sensitively regulated by oxygen concentrations. On the other hand, VGLL4 is a pivotal regulator of heme biosynthesis and erythroid terminal differentiation, which collectively improve oxygen metabolism.

Activation of Yap1/Taz signaling in ischemic heart disease and dilated cardiomyopathy

Genetic manipulation of key components of the evolutionally conserved Hippo pathway has shown that the precise control of these signaling molecules is critical to cardiac development and response to stresses. However, how this pathway is involved in the progression of cardiac dysfunction in different heart diseases remains unclear. We investigated the expressional levels and subcellular localization of Yap1, Taz, and Tead1 and determined Hippo target gene expression in failing human hearts with ischemic heart disease (IHD) and idiopathic dilated cardiomyopathy (IDC) and mouse desmin-related cardiomyopathy (DES). Our results demonstrated that Yap1, Taz, and Tead1 were significantly increased in failing human and DES hearts compared with the non-failing controls (NFH) or wild type (WT) mouse hearts at both mRNA and protein levels. Interestingly, adult human and mouse hearts had more Taz than Yap1 by mRNA and protein expression and their increases in diseased hearts were proportional and did not change Yap1/Taz ratio. Yap1, Taz, and Tead1 were accumulated in the nuclear fraction and cardiomyocyte nuclei of diseased hearts. The ratio of Yap1 phosphorylated at serine 127 (human) or serine 112 (mouse) to the total Yap1 (pYap1/Yap1) was significantly lower in the nuclear fraction of diseased hearts than that in normal controls. More importantly, Hippo downstream targets Ankrd1, Ctgf, and Cyr61 were transcriptionally elevated in the diseased hearts. These results suggest that Yap1/Taz signaling is activated in human and mouse dysfunctional hearts. Further investigation with relevant animal models will determine whether this pathway is a potential target for preventing and reversing abnormal remodeling during the progression of different cardiac disorders.

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.

IRF2BP2 Reduces Macrophage Inflammation and Susceptibility to Atherosclerosis

RATIONALE

Inflammation impairs macrophage cholesterol clearance from vascular tissues and promotes atherosclerosis. Inflammatory macrophages suppress expression of the transcription cofactor interferon regulatory factor 2-binding protein 2 (IRF2BP2), and genetic variants near IRF2BP2 associate with ischemic heart disease progression in humans.

OBJECTIVES

To test whether IRF2BP2 in macrophages affects atherosclerosis in mice and humans.

METHODS AND RESULTS

We generated mice that delete IRF2BP2 in macrophages. IRF2BP2-deficient macrophages worsened atherosclerosis in irradiated low-density lipoprotein receptor null-recipient mice and in apolipoprotein E null mice. IRF2BP2-deficient macrophages were inflammatory and had impaired cholesterol efflux because of their inability to activate the cholesterol transporter ABCA1 in response to cholesterol loading. Their expression of the anti-inflammatory transcription factor Krüppel-like factor 2 was markedly reduced. Promoter studies revealed that IRF2BP2 is required for MEF2-dependent activation of Krüppel-like factor 2. Importantly, restoring Krüppel-like factor 2 in IRF2BP2-deficient macrophages attenuated M1 inflammatory and rescued M2 anti-inflammatory gene activation and improved the cholesterol efflux deficit by restoring ABCA1 activation in response to cholesterol loading. In a cohort of 1066 angiographic cases and 1011 controls, homozygous carriers of a deletion polymorphism (rs3045215) in the 3' untranslated region sequence of human IRF2BP2 mRNA had a higher risk of coronary artery disease (recessive model, odds ratio [95% confidence interval]=1.560 [1.179-2.065], P=1.73E-03) and had lower IRF2BP2 (and Krüppel-like factor 2) protein levels in peripheral blood mononuclear cells. The effect of this deletion polymorphism to suppress protein expression was confirmed in luciferase reporter studies.

CONCLUSION

Ablation of IRF2BP2 in macrophages worsens atherosclerosis in mice, and a deletion variant that lowers IRF2BP2 expression predisposes to coronary artery disease in humans.

Mef2 interacts with the Notch pathway during adult muscle development in Drosophila melanogaster

Myogenesis of indirect flight muscles (IFMs) in Drosophila melanogaster follows a well-defined cellular developmental scheme. During embryogenesis, a set of cells, the Adult Muscle Precursors (AMPs), are specified. These cells will become proliferating myoblasts during the larval stages which will then give rise to the adult IFMs. Although the cellular aspect of this developmental process is well studied, the molecular biology behind the different stages is still under investigation. In particular, the interactions required during the transition from proliferating myoblasts to differentiated myoblasts ready to fuse to the muscle fiber. It has been previously shown that the Notch pathway is active in proliferating myoblasts, and that this pathway is inhibited in developing muscle fibers. Furthermore, the Myocyte Enhancing Factor 2 (Mef2), Vestigial (Vg) and Scalloped (Sd) transcription factors are necessary for IFM development and that Vg is required for Notch pathway repression in differentiating fibers. Here we examine the interactions between Notch and Mef2 and mechanisms by which the Notch pathway is inhibited during differentiation. We show that Mef2 is capable of inhibiting the Notch pathway in non myogenic cells. A previous screen for Mef2 potential targets identified Delta a component of the Notch pathway. Dl is expressed in Mef2 and Sd-positive developing fibers. Our results show that Mef2 and possibly Sd regulate a Dl enhancer specifically expressed in the developing IFMs and that Mef2 is required for Dl expression in developing IFMs.

Myogenic enhancers regulate expression of the facioscapulohumeral muscular dystrophy-associated DUX4 gene

Facioscapulohumeral muscular dystrophy (FSHD) is linked to epigenetic dysregulation of the chromosome 4q35 D4Z4 macrosatellite. However, this does not account for the tissue specificity of FSHD pathology, which requires stable expression of an alternative full-length mRNA splice form of DUX4 (DUX4-fl) from the D4Z4 array in skeletal muscle. Here, we describe the identification of two enhancers, DUX4 myogenic enhancer 1 (DME1) and DME2 which activate DUX4-fl expression in skeletal myocytes but not fibroblasts. Analysis of the chromatin revealed histone modifications and RNA polymerase II occupancy consistent with DME1 and DME2 being functional enhancers. Chromosome conformation capture analysis confirmed association of DME1 and DME2 with the DUX4 promoter in vivo. The strong interaction between DME2 and the DUX4 promoter in both FSHD and unaffected primary myocytes was greatly reduced in fibroblasts, suggesting a muscle-specific interaction. Nucleosome occupancy and methylome sequencing analysis indicated that in most FSHD myocytes, both enhancers are associated with nucleosomes but have hypomethylated DNA, consistent with a permissive transcriptional state, sporadic occupancy, and the observed DUX4 expression in rare myonuclei. Our data support a model in which these myogenic enhancers associate with the DUX4 promoter in skeletal myocytes and activate transcription when epigenetically derepressed in FSHD, resulting in the pathological misexpression of DUX4-fl.

Essential role of TEA domain transcription factors in the negative regulation of the MYH 7 gene by thyroid hormone and its receptors

MYH7 (also referred to as cardiac myosin heavy chain β) gene expression is known to be repressed by thyroid hormone (T3). However, the molecular mechanism by which T3 inhibits the transcription of its target genes (negative regulation) remains to be clarified, whereas those of transcriptional activation by T3 (positive regulation) have been elucidated in detail. Two MCAT (muscle C, A, and T) sites and an A/T-rich region in the MYH7 gene have been shown to play a critical role in the expression of this gene and are known to be recognized by the TEAD/TEF family of transcription factors (TEADs). Using a reconstitution system with CV-1 cells, which has been utilized in the analysis of positive as well as negative regulation, we demonstrate that both T3 receptor (TR) β1 and α1 inhibit TEAD-dependent activation of the MYH7 promoter in a T3 dose-dependent manner. TRβ1 bound with GC-1, a TRβ-selective T3 analog, also repressed TEAD-induced activity. Although T3-dependent inhibition required the DNA-binding domain (DBD) of TRβ1, it remained after the putative negative T3-responsive elements were mutated. A co-immunoprecipitation study demonstrated the in vivo association of TRβ1 with TEAD-1, and the interaction surfaces were mapped to the DBD of the TRβ1 and TEA domains of TEAD-1, both of which are highly conserved among TRs and TEADs, respectively. The importance of TEADs in MYH7 expression was also validated with RNA interference using rat embryonic cardiomyocyte H9c2 cells. These results indicate that T3-bound TRs interfere with transactivation by TEADs via protein-protein interactions, resulting in the negative regulation of MYH7 promoter activity.

MEF2 is restricted to the male gonad and regulates expression of the orphan nuclear receptor NR4A1

Leydig cell steroidogenesis is controlled by the pituitary gonadotropin LH that activates several signaling pathways, including the Ca(2+)/calmodulin kinase I (CAMKI) pathway. In other tissues, CAMKI regulates the activity of the myocyte enhancer factor 2 (MEF2) transcription factors. MEF2 factors are essential regulators of cell differentiation and organogenesis in numerous tissues but their expression and role in the mammalian gonad had not been explored. Here we show that MEF2 factors are expressed in a sexually dimorphic pattern in the mouse gonad. MEF2 factors are present in the testis throughout development and into adulthood but absent from the ovary. In the testis, MEF2 was localized mainly in the nucleus of both somatic lineages, the supporting Sertoli cells and the steroidogenic Leydig cells. In Leydig cells, MEF2 was found to activate the expression of Nr4a1, a nuclear receptor important for hormone-induced steroidogenesis. In these cells MEF2 also cooperates with forskolin and CAMKI to enhance Nr4a1 promoter activity via two MEF2 elements (-318 and -284 bp). EMSA confirmed direct binding of MEF2 to these elements whereas chromatin immunoprecipitation revealed that MEF2 recruitment to the proximal Nr4a1 promoter was increased following hormonal stimulation. Modulation of endogenous MEF2 protein level (small interfering RNA-mediated knockdown) or MEF2 activity (MEF2-Engrailed active dominant negative) led to a significant decrease in Nr4a1 mRNA levels in Leydig cells. All together, our results identify MEF2 as a novel testis-specific transcription factor, supporting a role for this factor in male sex differentiation and function. MEF2 was also positioned upstream of NR4A1 in a regulatory cascade controlling Leydig cell gene expression.

Investigation of four candidate genes (IGF2, JHDM1A, COPB1 and TEF1) for growth rate and backfat thickness traits on SSC2q in Large White pigs

As important quantitative traits, the growth rate and backfat thickness are controlled by multiple genes. The aim of this investigation was to evaluate the effect of the single and multiple SNPs of four candidate genes (IGF2, JHDM1A, COPB1 and TEF-1) on growth rate and backfat thickness. The four candidate genes were mapped on the p arm of SSC 2, and there are several QTLs, such as average daily gain, backfat thickness, an imprinted QTLs affecting muscle mass and fat deposition have been reported in this region. The polymorphisms of these genes were detected using PCR-RFLP methods, mixed procedure was used to analyze the single marker association with the growth and backfat thickness traits, and the gene-gene combination was investigated using multiple-markers analysis. The single marker association analysis indicated that the IGF2 intron-3 g.3072G > A and the substitution g.93G > A of TEF-1 gene were significantly associated with the age at 100 kg (P < 0.05). The JHDM1A 3′UTR g.224C > G, the c.3096C > T polymorphism of COPB1 gene and the substitution g.93G > A of TEF-1 gene were all significantly associated with the backfat at the shoulder (P < 0.05), backfat at the last rib, backfat at the lumbar, and the average backfat thickness, respectively. The multiple-markers analysis indicated that IGF2 and TEF-1 integrated gene networks for the age at 100 kg. Therefore, we can suggest that the polymorphism of IGF2 and TEF-1 gene could be used in marker-assisted selection for the age at 100 kg in Large White pigs.

The role of taurine on skeletal muscle cell differentiation

Taurine abundantly contained in the skeletal muscle has been considered as one of essential factors for the differentiation and growth of skeletal muscles. The previous studies in the taurine transporter knockout mice showed that deficiency of taurine content in the skeletal muscle caused incomplete muscular developments, morphological abnormalities, and exercise abilities. In fetal and neonatal periods, taurine must be an essential amino acid due to no biosynthesis capacity, and therefore, taurine should be endogenously supplied through placenta and maternal milk. In general cell culture condition, taurine contained in the culture medium is absent or few, and therefore, most of cultured cells are in taurine-deficient condition. In the present study, we confirmed, in cultured mouse differentiable myoblast, taurine treatment significantly enhanced the differentiation to myotube in a dose-dependent manner, while these effects were abrogated by inhibitions of taurine transport and Ca(2+) signaling pathway.The present study suggested that exogenous taurine might play a key role on the mature differentiation/growth of the skeletal muscle during development period through Ca(2+) signaling pathway, and therefore, taurine would contribute the muscle recovery after damages.

Sequencing of mRNA identifies re-expression of fetal splice variants in cardiac hypertrophy

Cardiac hypertrophy has been well-characterized at the level of transcription. During cardiac hypertrophy, genes normally expressed primarily during fetal heart development are re-expressed, and this fetal gene program is believed to be a critical component of the hypertrophic process. Recently, alternative splicing of mRNA transcripts has been shown to be temporally regulated during heart development, leading us to consider whether fetal patterns of splicing also reappear during hypertrophy. We hypothesized that patterns of alternative splicing occurring during heart development are recapitulated during cardiac hypertrophy. Here we present a study of isoform expression during pressure-overload cardiac hypertrophy induced by 10 days of transverse aortic constriction (TAC) in rats and in developing fetal rat hearts compared to sham-operated adult rat hearts, using high-throughput sequencing of poly(A) tail mRNA. We find a striking degree of overlap between the isoforms expressed differentially in fetal and pressure-overloaded hearts compared to control: forty-four percent of the isoforms with significantly altered expression in TAC hearts are also expressed at significantly different levels in fetal hearts compared to control (P<0.001). The isoforms that are shared between hypertrophy and fetal heart development are significantly enriched for genes involved in cytoskeletal organization, RNA processing, developmental processes, and metabolic enzymes. Our data strongly support the concept that mRNA splicing patterns normally associated with heart development recur as part of the hypertrophic response to pressure overload. These findings suggest that cardiac hypertrophy shares post-transcriptional as well as transcriptional regulatory mechanisms with fetal heart development.

Functional effect of mir-27b on myostatin expression: a relationship in Piedmontese cattle with double-muscled phenotype

BACKGROUND

In Piedmontese cattle the double-muscled phenotype is an inherited condition associated to a point mutation in the myostatin (MSTN) gene. The Piedmontese MSTN missense mutation G938A is translated to C313Y myostatin protein. This mutation alters MSTN function as a negative regulator of muscle growth, thereby inducing muscle hypertrophy. MiRNAs could play a role in skeletal muscle hypertrophy modulation by down-regulating gene expression.

RESULTS

After identifying a 3'-UTR consensus sequence of several negative and positive modulator genes involved in the skeletal muscle hypertrophy pathway, such as IGF1, IGF1R, PPP3CA, NFATc1, MEF2C, GSK3b, TEAD1 and MSTN, we screened miRNAs matching to it. This analysis led to the identification of miR-27b, miR-132, miR-186 and miR-199b-5p as possible candidates. We collected samples of longissimus thoracis from twenty Piedmontese and twenty Friesian male bovines. In Piedmontese group miR-27b was up-regulated 7.4-fold (p < 0.05). Further, we report that the level of MSTN mRNA was about 5-fold lower in Piedmontese cattle vs Friesian cattle (p < 0.0001) and that less mature MSTN protein was detected in the Piedmontese one (p < 0.0001). Cotransfection of miR-27b and psi-check2 vector with the luciferase reporter gene linked to the bovine wild-type 3'-UTR of MSTN strongly inhibited the luciferase activity (79%, p < 0.0001).

CONCLUSIONS

These data demonstrate that bovine MSTN is a specific target of miR-27b and that miRNAs contribute to explain additive phenotypic hypertrophy in Piedmontese cattle selected for the MSTN gene mutation, possibly outlining a more precise genetic signature able to elucidate differences in muscle conformation.

Emerging roles of TEAD transcription factors and its coactivators in cancers

TEAD proteins are transcription factors that are crucial for development, but also play a role in cancers. Several developmentally and pathologically important genes are upregulated by TEADs. TEADs have a TEA domain that enables them to bind specific DNA elements and a transactivation domain that enables them to interact with coactivators. TEADs on their own are unable to activate transcription and they require the help of coactivators. Several TEAD-interacting coactivators are known and they can be classified into three groups: (1) YAP and its paralog TAZ; (2) Vgll proteins; and (3) p160s. Accordingly, these coactivators also play a role in development and cancers. Recent studies have shown that TEADs and their coactivators aid in the progression of various cancers, including the difficult to treat glioblastoma, liver and ovarian cancers. They facilitate cancer progression through expression of proliferation promoting genes such as c-myc, survivin, Axl, CTGF and Cyr61. There is also a good correlation between high TEAD or its coactivator expression and poor prognosis in various cancers. Given the fact that TEADs and their coactivators need to work together for a functional outcome, disrupting the interaction between them appears to be a viable option for cancer therapy. Structures of TEAD-coactivator complexes have been elucidated and will facilitate drug design and development.

TEAD1 controls C2C12 cell proliferation and differentiation and regulates three novel target genes

TEAD1 is a transcription factor involved in activation of muscle specific genes, such as the cardiac muscle troponin T gene, skeletal muscle actin, myosin heavy chains genes. Here, we reported that TEAD1 was expressed ubiquitously in different mouse tissues and was up-regulated in differentiation process of the mouse myoblast cell line C2C12. Functional assay revealed that overexpression of TEAD1 gene can arrest the C2C12 cell cycle and promote C2C12 cell differentiation. To understand the physiological role of TEAD1 in muscle development, three new regulated genes of TEAD1, Mrpl21, Ndufa6 and Ccne1, were identified by expression analysis, promoter activity measurement assay. The expression patterns of target genes were detected in the cell differentiation process. The Mrpl21 and Ndufa6 genes were up-regulated in cell differentiation while Ccne1 gene was significantly down-regulated. Overexpression of Mrpl21 and Ndufa6 in C2C12 can up-regulate Myh4 gene expression thus promote C2C12 differentiation, but did not affect cell cycle. Co-overexpression of Ccne1 with Ndufa6 resulted in Myh4 expression decrease and the number of S-phase cells slight increase. Together, our results suggested that TEAD1 may mediate muscle development through its target genes, Mrpl21, Ndufa6 and Ccne1.

Alteration of TEAD1 expression levels confers apoptotic resistance through the transcriptional up-regulation of Livin

Background

TEA domain (TEAD) proteins are highly conserved transcription factors involved in embryonic development and differentiation of various tissues. More recently, emerging evidences for a contribution of these proteins towards apoptosis and cell proliferation regulation have also been proposed. These effects appear to be mediated by the interaction between TEAD and its co-activator Yes-Associated Protein (YAP), the downstream effector of the Hippo tumour suppressor pathway.

Methodology/Principal Findings

We further investigated the mechanisms underlying TEAD-mediated apoptosis regulation and showed that overexpression or RNAi-mediated silencing of the TEAD1 protein is sufficient to protect mammalian cell lines from induced apoptosis, suggesting a proapoptotic function for TEAD1 and a non physiological cytoprotective effect for overexpressed TEAD1. Moreover we show that the apoptotic resistance conferred by altered TEAD1 expression is mediated by the transcriptional up-regulation of Livin, a member of the Inhibitor of Apoptosis Protein (IAP) family. In addition, we show that overexpression of a repressive form of TEAD1 can induce Livin up-regulation, indicating that the effect of TEAD1 on Livin expression is indirect and favoring a model in which TEAD1 activates a repressor of Livin by interacting with a limiting cofactor that gets titrated upon TEAD1 up-regulation. Interestingly, we show that overexpression of a mutated form of TEAD1 (Y421H) implicated in Sveinsson's chorioretinal atrophy that strongly reduces its interaction with YAP as well as its activation, can induce Livin expression and protect cells from induced apoptosis, suggesting that YAP is not the cofactor involved in this process.

Conclusions/Significance

Taken together our data reveal a new, Livin-dependent, apoptotic role for TEAD1 in mammals and provide mechanistic insight downstream of TEAD1 deregulation in cancers.

The role of transcription enhancer factors in cardiovascular biology

The transcriptional enhancer factor (TEF) multigene family is primarily functional in muscle-specific genes through binding to MCAT elements that activate or repress transcription of many genes in response to physiological and pathological stimuli. Among the TEF family, TEF-1, RTEF-1, and DTEF-1 are critical regulators of cardiac and smooth muscle-specific genes during cardiovascular development and cardiac disorders including cardiac hypertrophy. Emerging evidence suggests that in addition to functioning as muscle-specific transcription factors, members of the TEF family may be key mediators of gene expression induced by hypoxia in endothelial cells by virtue of its multidomain organization, potential for post-translational modifications, and interactions with numerous transcription factors, which represent a cell-selective control mediator of nuclear signaling. We review the recent literature demonstrating the involvement of the TEF family of transcription factors in the regulation of differential gene expression in cardiovascular physiology and pathology.

RTEF-1 attenuates blood glucose levels by regulating insulin-like growth factor binding protein-1 in the endothelium

RATIONALE

Related transcriptional enhancer factor-1 (RTEF-1) plays an important role in endothelial cell function by regulating angiogenesis; however, the mechanism underlying the role of RTEF-1 in the endothelium in vivo is not well defined.

OBJECTIVE

We investigated the biological functions of RTEF-1 by disrupting the gene that encodes it in mice endothelium -specific RTEF-1-deficient transgenic mice (RTEF-1(-/-)).

METHODS AND RESULTS

RTEF-1(-/-) mice showed significantly increased blood glucose levels and insulin resistance, accompanied by decreased levels of insulin-like growth factor binding protein-1 (IGFBP-1) mRNA in the endothelium and decreased serum IGFBP-1 levels. Additionally, the RTEF-1(-/-) phenotype was exacerbated when the mice were fed a high-fat diet, which correlated with decreased IGFBP-1 levels. In contrast, vascular endothelial cadherin/RTEF-1-overexpressing(1) transgenic mice (VE-Cad/RTEF1) demonstrated improved glucose clearance and insulin sensitivity in response to a high-fat diet. Furthermore, we demonstrated that RTEF-1 upregulates IGFBP-1 through selective binding and promotion of transcription from the insulin response element site. Insulin prevented RTEF-1 expression and significantly inhibited IGFBP-1 transcription in endothelial cells in a dose-dependent fashion.

CONCLUSIONS

To the best of our knowledge, this is the first report demonstrating that RTEF-1 stimulates promoter activity through an insulin response element and also mediates the effects of insulin on gene expression. These results show that RTEF-1-stimulated IGFBP-1 expression may be central to the mechanism by which RTEF-1 attenuates blood glucose levels. These findings provide the basis for novel insights into the transcriptional regulation of IGFBP-1 and contribute to our understanding of the role of vascular endothelial cells in metabolism.

Myocyte enhancer factor-2 and cardiac muscle gene expression during hibernation in thirteen-lined ground squirrels

Many small mammals turn to hibernation to survive the winter, cycling through bouts of prolonged torpor where metabolic rate and body temperature fall to low levels. Remarkably, hypertrophy is promoted in cardiac muscle to support the stronger contractions needed in the cold. We proposed that altered expression of mRNA/protein levels of myocyte enhancer factor-2 (MEF2A, MEF2C) transcription factors and downstream targets (e.g., desmin, glucose transporter 4, and myomesin 1) would aid cardiac muscle of thirteen-lined ground squirrels (Ictidomys tridecemlineatus) in meeting challenges associated with hibernation. Gene and protein responses were compared over six conditions: control (euthermic animals in a 5 °C cold room), entrance into torpor, short and long torpors, arousal and interbout. Mef2a relative transcript levels were significantly elevated from controls contributing to increases in MEF2A protein levels throughout the torpor-arousal bout. In addition, levels of phosphorylated, activated MEF2A (Thr312) correlated with increases in MEF2A-DNA binding. MEF2C transcript/protein levels were significantly elevated over controls at selected sampling points whereas phosphorylated/activated MEF2C (Ser387) levels rose during torpor and DNA binding was most prominent during entrance into torpor. Some gene targets of MEF2 action were also upregulated. Desmin transcript levels remained constant whereas enhanced protein expression occurred during entrance into torpor. Glut4 transcript levels were enhanced in arousal and protein expression was elevated over all five sampling points during torpor/arousal. Myomesin 1 transcript levels increased between early torpor and early arousal and protein levels increased during entrance and deep torpor. These data provide insights into the changes in gene/protein in expression that help to prepare cardiac muscle for hibernation.

CORECLUST: identification of the conserved CRM grammar together with prediction of gene regulation

Identification of transcriptional regulatory regions and tracing their internal organization are important for understanding the eukaryotic cell machinery. Cis-regulatory modules (CRMs) of higher eukaryotes are believed to possess a regulatory ‘grammar’, or preferred arrangement of binding sites, that is crucial for proper regulation and thus tends to be evolutionarily conserved. Here, we present a method CORECLUST (COnservative REgulatory CLUster STructure) that predicts CRMs based on a set of positional weight matrices. Given regulatory regions of orthologous and/or co-regulated genes, CORECLUST constructs a CRM model by revealing the conserved rules that describe the relative location of binding sites. The constructed model may be consequently used for the genome-wide prediction of similar CRMs, and thus detection of co-regulated genes, and for the investigation of the regulatory grammar of the system. Compared with related methods, CORECLUST shows better performance at identification of CRMs conferring muscle-specific gene expression in vertebrates and early-developmental CRMs in Drosophila.

M-CAT element mediates mechanical stretch-activated transcription of B-type natriuretic peptide via ERK activation

The muscle-CAT (M-CAT) promoter element is found on promoters of most muscle-specific cardiac genes, but its role in cardiac pathology is poorly understood. Here we studied whether the M-CAT element is involved in hypertrophic process activated by mechanical stretch, and identified the intracellular pathways mediating the response. When an in vitro stretch model of cultured neonatal rat cardiomyocytes and luciferase reporter construct driven by rat B-type natriuretic peptide (BNP) promoter were used, mutation of M-CAT element inhibited not only the basal reporter activity (88%), but also the stretch-activated BNP transcription (58%, p < 0.001). Stretch-induced BNP promoter activation was associated with an increase in transcriptional enhancer factor-1 (TEF-1) binding activity after 24 h mechanical stretch (p < 0.05). Inhibition of mitogen-activated protein kinases ERK, JNK, or p38 attenuated stretch-induced BNP activation. Interestingly, as opposed to p38 and JNK, inhibition of ERK had no additional effect on transcriptional activity of BNP promoter harboring the M-CAT mutation, suggesting a pivotal role for ERK in regulating stretch-induced BNP transcription via M-CAT binding site. Finally, immunoprecipitation studies showed that mechanical stretch induced myocyte enhancer factor-2 (MEF-2) binding to TEF-1. These data suggest a central role for M-CAT element in regulation of mechanical stretch-induced hypertrophic response via ERK activation.

Members of the TEAD family of transcription factors regulate the expression of Myf5 in ventral somitic compartments

The transcriptional regulation of the Mrf4/Myf5 locus depends on a multitude of enhancers that, in equilibria with transcription balancing sequences and the promoters, regulate the expression of the two genes throughout embryonic development and in the adult. Transcription in a particular set of muscle progenitors can be driven by the combined outputs of several enhancers that are not able to recapitulate the entire expression pattern in isolation, or by the action of a single enhancer the activity of which in isolation is equivalent to that within the context of the locus. We identified a new enhancer element of this second class, ECR111, which is highly conserved in all vertebrate species and is necessary and sufficient to drive Myf5 expression in ventro-caudal and ventro-rostral somitic compartments in the mouse embryo. EMSA analyses and data obtained from binding-site mutations in transgenic embryos show that a binding site for a TEA Domain (TEAD) transcription factor is essential for the function of this new enhancer, while ChIP assays show that at least two members of the family of transcription factors bind to it in vivo.

TEAD1-dependent expression of the FoxO3a gene in mouse skeletal muscle

Background

TEAD1 (TEA domain family member 1) is constitutively expressed in cardiac and skeletal muscles. It acts as a key molecule of muscle development, and trans-activates multiple target genes involved in cell proliferation and differentiation pathways. However, its target genes in skeletal muscles, regulatory mechanisms and networks are unknown.

Results

In this paper, we have identified 136 target genes regulated directly by TEAD1 in skeletal muscle using integrated analyses of ChIP-on-chip. Most of the targets take part in the cell process, physiology process, biological regulation metabolism and development process. The targets also play an important role in MAPK, mTOR, T cell receptor, JAK-STAT, calcineurin and insulin signaling pathways. TEAD1 regulates foxo3a transcription through binding to the M-CAT element in foxo3a promoter, demonstrated with independent ChIP-PCR, EMSA and luciferase reporter system assay. In addition, results of over-expression and inhibition experiments suggest that foxo3a is positively regulated by TEAD1.

Conclusions

Our present data suggests that TEAD1 plays an important role in the regulation of gene expression and different signaling pathways may co-operate with each other mediated by TEAD1. We have preliminarily concluded that TEAD1 may regulate FoxO3a expression through calcineurin/MEF2/NFAT and IGF-1/PI3K/AKT signaling pathways in skeletal muscles. These findings provide important clues for further analysis of the role of FoxO3a gene in the formation and transformation of skeletal muscle fiber types.

Design and testing of regulatory cassettes for optimal activity in skeletal and cardiac muscles

Gene therapy for muscular dystrophies requires efficient gene delivery to the striated musculature and specific, high-level expression of the therapeutic gene in a physiologically diverse array of muscles. This can be achieved by the use of recombinant adeno-associated virus vectors in conjunction with muscle-specific regulatory cassettes. We have constructed several generations of regulatory cassettes based on the enhancer and promoter of the muscle creatine kinase gene, some of which include heterologous enhancers and individual elements from other muscle genes. Since the relative importance of many control elements varies among different anatomical muscles, we are aiming to tailor these cassettes for high-level expression in cardiac muscle, and in fast and slow skeletal muscles. With the achievement of efficient intravascular gene delivery to isolated limbs, selected muscle groups, and heart in large animal models, the design of cassettes optimized for activity in different muscle types is now a practical goal. In this protocol, we outline the key steps involved in the design of regulatory cassettes for optimal activity in skeletal and cardiac muscle, and testing in mature muscle fiber cultures. The basic principles described here can also be applied to engineering tissue-specific regulatory cassettes for other cell types.

IRF2BP2 is a skeletal and cardiac muscle-enriched ischemia-inducible activator of VEGFA expression

We sought to identify an essential component of the TEAD4/VGLL4 transcription factor complex that controls vascular endothelial growth factor A (VEGFA) expression in muscle. A yeast 2-hybrid screen was used to clone a novel component of the TEAD4 complex from a human heart cDNA library. We identified interferon response factor 2 binding protein 2 (IRF2BP2) and confirmed its presence in the TEAD4/VGLL4 complex in vivo by coimmunoprecipitation and mammalian 2-hybrid assays. Coexpression of IRF2BP2 with TEAD4/VGLL4 or TEAD1 alone potently activated, whereas knockdown of IRF2BP2 reduced, VEGFA expression in C(2)C(12) muscle cells. Thus, IRF2BP2 is required to activate VEGFA expression. In mouse embryos, IRF2BP2 was ubiquitously expressed but became progressively enriched in the fetal heart, skeletal muscles, and lung. Northern blot analysis revealed high levels of IRF2BP2 mRNA in adult human heart and skeletal muscles, but immunoblot analysis showed low levels of IRF2BP2 protein in skeletal muscle, indicating post-transcriptional regulation of IRF2BP2 expression. IRF2BP2 protein levels are markedly increased by ischemia in skeletal and cardiac muscle compared to normoxic controls. IRF2BP2 is a novel ischemia-induced coactivator of VEGFA expression that may contribute to revascularization of ischemic cardiac and skeletal muscles.

TEAD-1 overexpression in the mouse heart promotes an age-dependent heart dysfunction

TEA domain transcription factor-1 (TEAD-1) is essential for proper heart development and is implicated in cardiac specific gene expression and the hypertrophic response of primary cardiomyocytes to hormonal and mechanical stimuli, and its activity increases in the pressure-overloaded hypertrophied rat heart. To investigate whether TEAD-1 is an in vivo modulator of cardiac specific gene expression and hypertrophy, we developed transgenic mice expressing hemagglutinin-tagged TEAD-1 under the control of the muscle creatine kinase promoter. We show that a sustained increase in TEAD-1 protein leads to an age-dependent dysfunction. Magnetic resonance imaging revealed decreases in cardiac output, stroke volume, ejection fraction, and fractional shortening. Isolated TEAD-1 hearts revealed decreased left ventricular power output that correlated with increased betaMyHC protein. Histological analysis showed altered alignment of cardiomyocytes, septal wall thickening, and fibrosis, although electrocardiography displayed a left axis shift of mean electrical axis. Transcripts representing most members of the fetal heart gene program remained elevated from fetal to adult life. Western blot analyses revealed decreases in p-phospholamban, SERCA2a, p-CX43, p-GSK-3alpha/beta, nuclear beta-catenin, GATA4, NFATc3/c4, and increased NCX1, nuclear DYKR1A, and Pur alpha/beta protein. TEAD-1 mice did not display cardiac hypertrophy. TEAD-1 mice do not tolerate stress as they die over a 4-day period after surgical induction of pressure overload. These data provide the first in vivo evidence that increased TEAD-1 can induce characteristics of cardiac remodeling associated with cardiomyopathy and heart failure.

Vestigial-like 2 acts downstream of MyoD activation and is associated with skeletal muscle differentiation in chick myogenesis

The co-factor Vestigial-like 2 (Vgl-2), in association with the Scalloped/Tef/Tead transcription factors, has been identified as a component of the myogenic program in the C2C12 cell line. In order to understand Vgl-2 function in embryonic muscle formation, we analysed Vgl-2 expression and regulation during chick embryonic development. Vgl-2 expression was associated with all known sites of skeletal muscle formation, including those in the head, trunk and limb. Vgl-2 was expressed after the myogenic factor MyoD, regardless of the site of myogenesis. Analysis of Vgl-2 regulation by Notch signalling showed that Vgl-2 expression was down-regulated by Delta1-activated Notch, similarly to the muscle differentiation genes MyoD, Myogenin,Desmin, and Mef2c, while the expression of the muscle progenitor markers such as Myf5, Six1 and FgfR4 was not modified. Moreover, we established that the Myogenic Regulatory Factors (MRFs) associated with skeletal muscle differentiation (MyoD, Myogenin and Mrf4) were sufficient to activate Vgl-2 expression, while Myf5 was not able to do so. The Vgl-2 endogenous expression, the similar regulation of Vgl-2 and that of MyoD and Myogenin by Notch signalling, and the positive regulation of Vgl-2 by these MRFs suggest that Vgl-2 acts downstream of MyoD activation and is associated with the differentiation step in embryonic skeletal myogenesis.

The transcriptional co-activator TAZ interacts differentially with transcriptional enhancer factor-1 (TEF-1) family members

Members of the highly related TEF-1 (transcriptional enhancer factor-1) family (also known as TEAD, for TEF-1, TEC1, ABAA domain) bind to MCAT (muscle C, A and T sites) and A/T-rich sites in promoters active in cardiac, skeletal and smooth muscle, placenta, and neural crest. TEF-1 activity is regulated by interactions with transcriptional co-factors [p160, TONDU (Vgl-1, Vestigial-like protein-1), Vgl-2 and YAP65 (Yes-associated protein 65 kDa)]. The strong transcriptional co-activator YAP65 interacts with all TEF-1 family members, and, since YAP65 is related to TAZ (transcriptional co-activator with PDZ-binding motif), we wanted to determine if TAZ also interacts with members of the TEF-1 family. In the present study, we show by GST (glutathione S-transferase) pull-down assays, by co-immunoprecipitation and by modified mammalian two-hybrid assays that TEF-1 interacts with TAZ in vitro and in vivo. Electrophoretic mobility-shift assays with purified TEF-1 and GST-TAZ fusion protein showed that TAZ interacts with TEF-1 bound to MCAT DNA. TAZ can interact with endogenous TEF-1 proteins, since exogenous TAZ activated MCAT-dependent reporter promoters. Like YAP65, TAZ interacted with all four TEF-1 family members. GST pull-down assays with increasing amounts of [35S]TEF-1 and [35S]RTEF-1 (related TEF-1) showed that TAZ interacts more efficiently with TEF-1 than with RTEF-1. This differential interaction also extended to the interaction of TEF-1 and RTEF-1 with TAZ in vivo, as assayed by a modified mammalian two-hybrid experiment. These data show that differential association of TEF-1 proteins with transcriptional co-activators may regulate the activity of TEF-1 family members.

CpG-depleted promoters harbor tissue-specific transcription factor binding signals--implications for motif overrepresentation analyses

Motif overrepresentation analysis of proximal promoters is a common approach to characterize the regulatory properties of co-expressed sets of genes. Here we show that these approaches perform well on mammalian CpG-depleted promoter sets that regulate expression in terminally differentiated tissues such as liver and heart. In contrast, CpG-rich promoters show very little overrepresentation signal, even when associated with genes that display highly constrained spatiotemporal expression. For instance, while ∼50% of heart specific genes possess CpG-rich promoters we find that the frequently observed enrichment of MEF2-binding sites upstream of heart-specific genes is solely due to contributions from CpG-depleted promoters. Similar results are obtained for all sets of tissue-specific genes indicating that CpG-rich and CpG-depleted promoters differ fundamentally in their distribution of regulatory inputs around the transcription start site. In order not to dilute the respective transcription factor binding signals, the two promoter types should thus be treated as separate sets in any motif overrepresentation analysis.

TEAD1 inhibits prolactin gene expression in cultured human uterine decidual cells

Forced overexpression of TEAD1 in human uterine fibroblast (HUF) and human endometrial stromal cells markedly inhibited prolactin promoter activity in both cell types in a dose-dependent manner, with maximal inhibition of greater than 90%. Conversely, the knockdown of TEAD1 expression in HUF cells with a TEAD1 siRNA resulted in a 75-80% increase in prolactin mRNA levels (p<0.01) compared to control cells exposed to a scrambled nonsense RNA. Mutagenesis of the putative TEAD site inhibited basal promoter activity by about 80%. However, mutagenesis of the TEAD site did not prevent TEAD1-induced inhibition of promoter activity; and the transcription activity of a minimal promoter fragment lacking a putative TEAD binding site was repressed by overexpression of TEAD1. Taken together, these findings suggest that the TEAD binding site on the prolactin promoter is important for the maintenance of basal prolactin promoter activity and that overexpression of TEAD1 has a dominant-negative effect on prolactin promoter activity, probably by interacting directly with other transcription factors.

Alternative requirements for Vestigial, Scalloped, and Dmef2 during muscle differentiation in Drosophila melanogaster

Vertebrate development requires the activity of the myocyte enhancer factor 2 (mef2) gene family for muscle cell specification and subsequent differentiation. Additionally, several muscle-specific functions of MEF2 family proteins require binding additional cofactors including members of the Transcription Enhancing Factor-1 (TEF-1) and Vestigial-like protein families. In Drosophila there is a single mef2 (Dmef2) gene as well single homologues of TEF-1 and vestigial-like, scalloped (sd), and vestigial (vg), respectively. To clarify the role(s) of these factors, we examined the requirements for Vg and Sd during Drosophila muscle specification. We found that both are required for muscle differentiation as loss of sd or vg leads to a reproducible loss of a subset of either cardiac or somatic muscle cells in developing embryos. This muscle requirement for Sd or Vg is cell specific, as ubiquitous overexpression of either or both of these proteins in muscle cells has a deleterious effect on muscle differentiation. Finally, using both in vitro and in vivo binding assays, we determined that Sd, Vg, and Dmef2 can interact directly. Thus, the muscle-specific phenotypes we have associated with Vg or Sd may be a consequence of alternative binding of Vg and/or Sd to Dmef2 forming alternative protein complexes that modify Dmef2 activity.

Porcine TEF1 and RTEF1: molecular characterization and association analyses with growth traits

TEA domain transcription factors play vital roles in myogenesis by binding the M-CAT motif in the promoter of the muscle-specific genes. In the present study, we cloned two porcine TEA domain family genes, TEF1 and RTEF1, and identified two different variants respectively. RT-PCR revealed that the TEF1-a variant was highly expressed and up-regulated with the development of the porcine skeletal muscle, indicating its potential regulatory function for muscle development. Promoter analysis revealed porcine TEF1 was regulated, in a TATA-independent manner, by a specific intact initiator element, and numerous binding motifs of multiple transcription factors, including SP1, CREB/ATF and AREB6. A substitution G93A was identified in the 5'-flanking sequence and used for the linkage mapping of TEF1. Association analyses in a BerkshirexYorkshire F(2) population revealed that the substitution of G93A has a significant effect on average daily gain from birth to weaning (p<0.05) and 16-day weight (p<0.05), and a suggestive effect on loin eye area (p<0.06), average back fat (p<0.07) and lumbar back fat (p<0.08). The association analyses results are in agreement with the gene's localization demonstrated by linkage analysis, SCHP and RH mapping to the QTL region of growth and carcass traits on chromosome 2p14-17.

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.

Factors controlling cardiac myosin-isoform shift during hypertrophy and heart failure

Myosin is a molecular motor, which interacts with actin to convert the energy from ATP hydrolysis into mechanical work. In cardiac myocytes, two myosin isoforms are expressed and their relative distribution changes in different developmental and pathophysiologic conditions of the heart. It has been realized for a long time that a shift in myosin isoforms plays a major role in regulating myocardial contractile activity. With the recent evidence implicating that alteration in myosin isoform ratio may be eventually beneficial for the treatment of a stressed heart, a new interest has developed to find out ways of controlling the myosin isoform shift. This article reviews the published data describing the role of myosin isoforms in the heart and highlighting the importance of various factors shown to influence myosin isofrom shift during physiology and disease states of the heart.

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.

Vestigial-like-2b (VITO-1b) and Tead-3a (Tef-5a) expression in zebrafish skeletal muscle, brain and notochord

The vestigial gene has been shown to control skeletal muscle formation in Drosophila and the related Vestigial-like 2 (Vgl-2) protein plays a similar role in mice. Vgl-family proteins are thought to regulate tissue-specific gene expression by binding to members of the broadly expressed Scalloped/Tef/TEAD transcription factor family. Zebrafish have at least four Vgl genes, including two Vgl-2s, and at least three TEAD genes, including two Tead3s. We describe the cloning and expression of one member from each family in the zebrafish. A novel gene, vgl-2b, with closest homology to mouse and human vgl-2, is expressed transiently in nascent notochord and in muscle fibres as they undergo terminal differentiation during somitogenesis. Muscle cells also express a TEAD-3 homologue, a possible partner of Vgl-2b, during myoblast differentiation and early fibre assembly. Tead-3a is also expressed in rhombomeres, eye and epiphysis regions.

A Sveinsson's chorioretinal atrophy-associated missense mutation in mouse Tead1 affects its interaction with the co-factors YAP and TAZ

Sveinsson's chorioretinal atrophy (SCRA) is an autosomal dominant eye disease characterized by bilateral chorioretinal degeneration. A missense mutation in the gene encoding the transcription factor TEAD1/TEF-1 (Y421H) is genetically linked to SCRA, but the mechanisms of pathology remain unclear. To study the molecular mechanisms underlying SCRA, a missense mutation corresponding to Y421H in human TEAD1 was introduced into mouse Tead1 (Y410H), and a functional analysis of the mutant protein was performed in RPE-J cells. The missense mutation reduced the ability of Tead1 to interact with the co-factors YAP and TAZ, but not with the co-factors Vgl-1, -2, and -3, in a mammalian two-hybrid assay. A GST pull-down assay showed that the direct interaction between Tead1 and YAP or TAZ was lost owing to the mutation. Amino acid substitutions at position 410 of Tead1 revealed the essentiality of this tyrosine residue to the interaction. The Y410H mutation also abolished the transcriptional activity of Tead1 under the co-expression of YAP or TAZ. These results suggest that SCRA pathogenesis may be due to a loss-of-function of TEAD1 affecting the regulation of its target genes.

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.

In Vivo beta-adrenergic activation of atrial natriuretic factor (ANF) reporter expression

Isoproterenol (ISO) infusion increases ANF-mRNA levels and control of ANF expression lies at the level of transcription. In neonatal cardiomyocytes, previous investigations determined that the -125 to -100 region of the rat ANF 5' flanking region contained cis-elements critical for control of ISO induced ANF transcription. However, it is unclear if these same cis-elements regulate ANF transcription in vivo. To examine this question, reporter plasmids containing the ANF 5' flanking/promoter region were injected directly into the left ventricle. Following a recovery period, osmotic pumps were implanted to infuse vehicle or ISO (0.2 or 2.0 mg/kg/d). ISO significantly (p < .05) increased the LV/BW ratio in a dose dependent, but not a time dependent manner. ISO significantly (p < .05) increased ANF reporter expression in both a dose-dependent and time dependent manner. Injections into the midwall of the LV or into the apex did not lead to significant differences in ISO-induced ANF reporter expression. Using site-specific mutations of ANF reporter constructs, comparisons were made of ISO induced ANF transcription in vitro in neonatal cardiomyocytes and in vivo in the adult heart. Cis-elements critical for ISO activation in cultured cardiomyocytes were not essential for the increased expression of the ANF reporters in vivo. The results indicate that distinct differences in ANF transcriptional regulation exist in vivo in the adult heart as compared with neonatal cardiomyocytes, and suggest the recruitment of other signaling pathways beyond adrenergic-receptor mediated pathways.

Transcriptional regulation of tissue-specific genes by the ERK5 mitogen-activated protein kinase

The ERK5 mitogen-activated protein kinase (MAPK) differs from other MAPKs in possessing a potent transcriptional activation domain. ERK5-/- embryos die from angiogenic defects, but the precise physiological role of ERK5 remains poorly understood. To elucidate molecular functions of ERK5 in the development of vasculature and other tissues, we performed gene profile analyses of erk5-/- mouse embryos and erk5-/- fibroblast cells reconstituted with ERK5 or ERK5(1-740), which lacks the transactivation domain. These experiments revealed several potential ERK5 target genes, including a proapoptotic gene bnip3, known angiogenic genes flt1 and lklf (lung Krüppel-like factor), and genes that regulate cardiovascular development. Among these, LKLF, known for its roles in angiogenesis, T-cell quiescence, and survival, was found to be absolutely dependent on ERK5 for expression in endothelial and T cells. We show that ERK5 drives lklf transcription by activating MEF2 transcription factors. Expression of erk5 short hairpin or a dominant-negative form of the ERK5 upstream activator, MEK5, in T cells led to downregulation of LKLF, increased cell size and upregulation of activation markers. Thus, through its kinase and transcriptional activation domains, ERK5 regulates transcriptional responses of cell survival and quiescence critical for angiogenesis and T-cell function.

Adaptation of muscle size and myofascial force transmission: a review and some new experimental results

This paper considers the literature and some new experimental results important for adaptation of muscle fiber cross-sectional area and serial sarcomere number. Two major points emerge: (1) general rules for the regulation of adaptation (for in vivo immobilization, low gravity conditions, synergist ablation, tenotomy and retinaculum trans-section experiments) cannot be derived. As a consequence, paradoxes are reported in the literature. Some paradoxes are resolved by considering the interaction between different levels of organization (e.g. muscle geometrical effects), but others cannot. (2) An inventory of signal transduction pathways affecting rates of muscle protein synthesis and/or degradation reveals controversy concerning the pathways and their relative contributions. A major explanation for the above is not only the inherently limited control of the experimental conditions in vivo, but also of in situ experiments. Culturing of mature single Xenopus muscle fibers at high and low lengths (allowing longitudinal study of adaptation for periods up to 3 months) did not yield major changes in the fiber cross-sectional area or the serial sarcomere number. This is very different from substantial effects (within days) of immobilization in vivo. It is concluded that overall strain does not uniquely regulate muscle fiber size. Force transmission, via pathways other than the myotendinous junctions, may contribute to the discrepancies reported: because of substantial serial heterogeneity of sarcomere lengths within muscle fibers creating local variations in the mechanical stimuli for adaptation. For the single muscle fiber, mechanical signalling is quite different from the in vivo or in vitro condition. Removal of tensile and shear effects of neighboring tissues (even of antagonistic muscle) modifies or removes mechanical stimuli for adaptation. It is concluded that the study of adaptation of muscle size requires an integrative approach taking into account fundamental mechanisms of adaptation, as well as effects of higher levels of organization. More attention should be paid to adaptation of connective tissues within and surrounding the muscle and their effects on muscular properties.

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.

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.