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

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.

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.

Related transcriptional enhancer factor 1 increases endothelial-dependent microvascular relaxation and proliferation

OBJECTIVE

Related transcriptional enhancer factor 1 (RTEF-1) is a key transcriptional regulator in endothelial function. In this study, we investigated a possible role for RTEF-1 in the regulation of microvascular relaxation and the underlying mechanism involved. Activation of fibroblast growth factor receptor 1 (FGFR1) by FGFs increases vasodilation, although transcriptional control of the molecular mechanisms underlying FGFR1 is still unclear.

MATERIALS AND METHODS

We demonstrated that RTEF-1 stimulated FGFR1 expression at the transcriptional level, specifically an area including Sp1 elements, as evidenced by promoter assays. Additionally, RTEF-1 increased FGFR1 mRNA and protein expression in vitro and in VE-cadherin-promoted RTEF-1 (VE-Cad/RTEF-1) transgenic mice, whereas RTEF-1 siRNA blocked the upregulation of FGFR1 expression. Furthermore, increased endothelial-dependent microvessel relaxation was observed in the coronary arteries of VE-Cad/RTEF-1 mice, and increased proliferation was observed in RTEF-1-overexpressing cells, both of which correlated to increased FGF/FGFR1 signaling and endothelial nitric oxide synthase (eNOS) upregulation. Our results indicate that RTEF-1 acts as a transcriptional stimulator of FGFR1 and is involved in FGF pathways by increasing microvessel dilatation via eNOS.

CONCLUSIONS

These findings suggest that RTEF-1 plays an important role in FGFR1- stimulated vasodilatation. Understanding the effect of RTEF-1 in microvessel relaxation may provide beneficial knowledge in improving treatments in regards to ischemic vascular disorders.

Transcription factor TEAD4 regulates expression of myogenin and the unfolded protein response genes during C2C12 cell differentiation

The TEAD (1-4) transcription factors comprise the conserved TEA/ATTS DNA-binding domain recognising the MCAT element in the promoters of muscle-specific genes. Despite extensive genetic analysis, the function of TEAD factors in muscle differentiation has proved elusive due to redundancy among the family members. Expression of the TEA/ATTS DNA-binding domain that acts as a dominant negative repressor of TEAD factors in C2C12 myoblasts inhibits their differentiation, whereas selective shRNA knockdown of TEAD4 results in abnormal differentiation characterised by the formation of shortened myotubes. Chromatin immunoprecipitation coupled to array hybridisation shows that TEAD4 occupies 867 promoters including those of myogenic miRNAs. We show that TEAD factors directly induce Myogenin, CDKN1A and Caveolin 3 expression to promote myoblast differentiation. RNA-seq identifies a set of genes whose expression is strongly reduced upon TEAD4 knockdown among which are structural and regulatory proteins and those required for the unfolded protein response. In contrast, TEAD4 represses expression of the growth factor CTGF (connective tissue growth factor) to promote differentiation. Together these results show that TEAD factor activity is essential for normal C2C12 cell differentiation and suggest a role for TEAD4 in regulating expression of the unfolded protein response genes.

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.

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.

The androgen and progesterone receptors regulate distinct gene networks and cellular functions in decidualizing endometrium

Progesterone is indispensable for differentiation of human endometrial stromal cells (HESCs) into decidual cells, a process that critically controls embryo implantation. We now show an important role for androgen receptor (AR) signaling in this differentiation process. Decreased posttranslational modification of the AR by small ubiquitin-like modifier (SUMO)-1 in decidualizing cells accounted for increased responsiveness to androgen. By combining small interfering RNA technology with genome-wide expression profiling, we found that AR and progesterone receptor (PR) regulate the expression of distinct decidual gene networks. Ingenuity pathway analysis implicated a preponderance of AR-induced genes in cytoskeletal organization and cell motility, whereas analysis of AR-repressed genes suggested involvement in cell cycle regulation. Functionally, AR depletion prevented differentiation-dependent stress fiber formation and promoted motility and proliferation of decidualizing cells. In comparison, PR depletion perturbed the expression of many more genes, underscoring the importance of this nuclear receptor in diverse cellular functions. However, several PR-dependent genes encode for signaling intermediates, and knockdown of PR, but not AR, compromised activation of WNT/beta-catenin, TGFbeta/SMAD, and signal transducer and activator of transcription (STAT) pathways in decidualizing cells. Thus, the nonredundant function of the AR in decidualizing HESCs, centered on cytoskeletal organization and cell cycle regulation, implies an important role for androgens in modulating fetal-maternal interactions. Moreover, we show that PR regulates HESC differentiation, at least in part, by reprogramming growth factor and cytokine signal transduction.

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.

Smooth muscle cells and myofibroblasts use distinct transcriptional mechanisms for smooth muscle alpha-actin expression

There has been considerable controversy regarding the lineage relationship between smooth muscle cells (SMCs) and myofibroblasts, because they express a number of common cell-selective markers including smooth muscle (SM) alpha-actin. We have shown previously that MCAT elements within the SM alpha-actin promoter confer differential activity in cultured SMCs versus myofibroblasts. In the present study, to determine the role of MCAT elements in vivo, we generated transgenic mice harboring an SM alpha-actin promoter-enhancer-LacZ reporter gene containing MCAT element mutations and compared transgene expression patterns with wild-type SM alpha-actin promoter-enhancer-LacZ transgenic mice. Results showed no differences in LacZ expression patterns in adult SMC-containing tissues. However, of interest, mutations of MCAT elements selectively abolished transgene expression in myofibroblasts within granulation tissue of skin wounds. In addition, mutations of MCAT elements caused a delay in the induction of transgene expression in SMCs, as well as loss of expression in cardiac and skeletal muscles during embryogenesis. Results of small interfering RNA-induced knockdown experiments showed that RTEF-1 regulated SM alpha-actin transcription in myofibroblasts, but not in differentiated SMCs. Moreover, quantitative chromatin immunoprecipitation assays revealed that RTEF-1 bound to the MCAT element-containing region within the SM alpha-actin promoter in myofibroblasts, whereas transcriptional enhancer factor (TEF)-1 was bound to the same region in differentiated SMCs. These results provide novel evidence that, although both SMCs and myofibroblasts express SM alpha-actin, they use distinct transcriptional control mechanisms for regulating its expression. Results also indicate that the MCAT element-mutated SM alpha-actin promoter-enhancer is a useful tool to direct gene expression selectively in differentiated SMCs.

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.

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.

Characterization of human OATP2B1 (SLCO2B1) gene promoter regulation

PURPOSE

We investigated transcriptional regulation of organic anion transporter OATP2B1 (SLCO2B1) that is expressed in multiple tissues such as liver, small intestine, and others and compared it with that of liver-specific OATPs.

METHODS

The promoter activity was examined by luciferase assay. Specific bindings of transcription factors to the promoter region were examined by gel mobility shift assay using native and mutated nucleotides of the promoter region of OATP2B1.

RESULTS

Deletion-mutation study of the promoter region of OATP2B1 showed that the -59 region that included the Sp1 binding site had basal promoter activity, whereas promoter activities of the further upper region were different between intestine-derived Caco-2 cells and liver-derived HepG2 cells. The association of Sp1 to the promoter region was confirmed by gel shift assay and overexpression of Sp1 in cultured cells. Although the promoter of OATP2B1 has a putative HNF1alpha binding site, overexpression of HNF1alpha did not induce the expression of OATP2B1.

CONCLUSION

Sp1, a transcription factor, was required for constitutive expression of OATP2B1 in liver and small intestine, whereas HNF1alpha, which is involved in the expression of liver-specific OATPs, did not seem to play a role in OATP2B1 expression. Accordingly, it was suggested that the tissue expression profile of OATP2B1 was different from that of other liver-specific OATPs.

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.

Regulation of testis-specific carnitine transporter (octn3) gene by proximal cis-acting elements Sp1 in mice

The mouse octn transporter family consists of three genes, octn1, octn2 and octn3. The gene products octn2 and octn3, which transport carnitine with high affinity, are both expressed in testis, where carnitine is required to maintain sperm cell motility. Here, we focused on the regulatory mechanism of the expression of octn3 in an attempt to determine whether the differential tissue expression profiles of the octn2 and octn3 genes reflect distinct physiological roles of octn2 and octn3. The promoter activity of the octn3 gene was examined by luciferase assay and gel mobility shift assay using the mouse Sertoli cell line TM4 as host cells. Deletion-mutant assay demonstrated that a gene segment of the 5'-untranslated region located at about -500 bp relative to the transcription start site is required for constitutive octn3 transcription. Deletion of the Sp1-binding site within the region resulted in loss of transcriptional activity. In addition, overexpression of Sp1 in TM4 cells led to a further increase of transcription of octn3. These results demonstrated that Sp1-binding sites are necessary and sufficient for constitutive octn3 gene transcription. Furthermore, the expressions of both of octn2 and octn3 genes in TM4 cells were up-regulated by palmitic acid, whereas carnitine increased only the expression of octn2 without any change in octn3 expression. Accordingly, the expressions of octn2 and 3 are regulated by distinct mechanisms, suggesting distinct roles of octn2 and octn3 in carnitine transport.

Molecular and functional analysis of scalloped recessive lethal alleles in Drosophila melanogaster

The Drosophila melanogaster scalloped (sd) gene is a homolog of the human TEF-1 gene and is a member of the TEA/ATTS domain-containing family of transcription factors. In Drosophila, sd is involved in wing development as well as neural development. Herein, data are presented from a molecular analysis of five recessive lethal sd alleles. Only one of these alleles complements a viable allele associated with an sd mutant wing phenotype, suggesting that functions important for wing development are compromised by the noncomplementing alleles. Two of the wing noncomplementing alleles have mutations that help to define a VG-binding domain for the SD protein in vivo, and another noncomplementing allele has a lesion within the TEA DNA-binding domain. The VG-binding domain overlaps with a domain important for viability of the fly, since two of the sd lethal lesions are located there. The fifth lethal affects a yet undefined motif lying just outside the VG-binding domain in the C-terminal direction that affects both wing phenotype and viability. This is the first example linking mutations affecting specific amino acids in the SD protein with phenotypic consequences for the organism.

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.

Molecular and Functional Analysis of scalloped Recessive Lethal Alleles in Drosophila melanogaster

The Drosophila melanogaster scalloped (sd) gene is a homolog of the human TEF-1 gene and is a member of the TEA/ATTS domain-containing family of transcription factors. In Drosophila, sd is involved in wing development as well as neural development. Herein, data are presented from a molecular analysis of five recessive lethal sd alleles. Only one of these alleles complements a viable allele associated with an sd mutant wing phenotype, suggesting that functions important for wing development are compromised by the noncomplementing alleles. Two of the wing noncomplementing alleles have mutations that help to define a VG-binding domain for the SD protein in vivo, and another noncomplementing allele has a lesion within the TEA DNA-binding domain. The VG-binding domain overlaps with a domain important for viability of the fly, since two of the sd lethal lesions are located there. The fifth lethal affects a yet undefined motif lying just outside the VG-binding domain in the C-terminal direction that affects both wing phenotype and viability. This is the first example linking mutations affecting specific amino acids in the SD protein with phenotypic consequences for the organism.

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

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

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

Many muscle-specific genes are regulated by transcriptional enhancer factor-1 (TEF-1), serum response factor (SRF), and myocyte enhancer factor-2 (MEF2) transcription factors. TEF-1 interacts with the MADS domain of SRF and together SRF and TEF-1 co-activate the skeletal alpha-actin promoter. MEF2 factors also contain a MADS domain with 50% amino acid identity to the SRF MADS domain. Because of this sequence divergence, some SRF co-factors do not interact with MEF2. To demonstrate that TEF-1 factors could also interact with MEF2 through its MADS domain, we used co-immunoprecipitation and GST pull-down assays in vitro and a mammalian two-hybrid assay in vivo. The MADS domain was not sufficient for MEF2 interaction with TEF-1, because additional sequences in the activation domains of both proteins were required for in vivo association. The physiological significance of this interaction was also demonstrated by transient transfection assays using muscle-specific promoters. Our results suggest that by their interaction with MEF2 factors, TEF-1 factors can control MEF2-dependent muscle-specific gene expression.