A direct physical association between ETS and AP-1 transcription factors in normal human T cells

Transcription factors control invasion: AP-1 the first among equals

Metastasis, the aggressive spread of a malignant tumor to distant organs, is a major cause of death in cancer patients. Despite this critical role in cancer outcomes, the molecular mechanisms that control this process are just beginning to be understood. Metastasis is largely dependent upon the ability of tumor cells to invade the barrier formed by the basement membrane and to migrate through neighboring tissues. This review will summarize the evidence that tumor cell invasion is the result of oncogene-mediated signal transduction pathways that control the expression of a specific set of genes that together mediate tumor cell invasion. We focus on the role of the transcription factor AP-1 to both induce the expression of genes that function as invasion effectors and repress other genes that function as invasion suppressors. This identifies AP-1 as a critical regulator of a complex program of gene expression that defines the invasive phenotype.

Site-specific DNA methylation by a complex of PU.1 and Dnmt3a/b

The Ets transcription factor PU.1 is a hematopoietic master regulator essential for the development of myeloid and B-cell lineages. As we previously reported, PU.1 sometimes represses transcription on forming a complex with mSin3A-histone deacetyl transferase-MeCP2. Here, we show an interaction between PU.1 and DNA methyltransferases, DNA methyltransferase (Dnmt)3a and Dnmt3b (Dnmt3s). Glutathione-S-transferase pulldown assay revealed that PU.1 directly interacted with the ATRX domain of Dnmt3s through the ETS domain. Dnmt3s repressed the transcriptional activity of PU.1 on a reporter construct with trimerized PU.1-binding sites. The repression was recovered by addition of 5-aza-deoxycitidine, a DNA methyltransferase inhibitor, but not trichostatin A, a histone deacetylase inhibitor. Bisulfite sequence analysis revealed that several CpG sites in the promoter region neighboring the PU.1-binding sites were methylated when Dnmt3s were coexpressed with PU.1. We also showed that the CpG sites in the p16(INK4A) promoter were methylated by overexpression of PU.1 in NIH3T3 cells, accompanied by a downregulation of p16(INK4A) gene expression. These results suggest that PU.1 may downregulate its target genes through an epigenetic modification such as DNA methylation.

Erm/thyroid transcription factor 1 interactions modulate surfactant protein C transcription

Expression of surfactant protein C (SP-C), which is restricted to alveolar type II epithelial cells of the adult lung, is critically dependent on thyroid transcription factor 1 (TTF-1). In the present study we have demonstrated that Erm, a member of the Ets family of transcription factors, is expressed in the distal lung epithelium during development and is also restricted to alveolar type II cells in the adult. Erm was up-regulated by fibroblast growth factors (FGFs) in culture, and blocking FGF signaling inhibited Erm expression both in vivo and in vitro. The SP-C minimal promoter was found to contain two potential Ets binding sites, and electrophoretic mobility shift assays showed that two 20-bp wild-type oligonucleotides containing the 5'-GGA(A/T)-3' Ets consensus binding motif were shifted by nuclear extracts from MLE15 cells. Co-transfection assays showed that Erm by itself had little effect on SP-C promoter activity but that Erm significantly enhanced TTF-1-mediated SP-C transcription. Mutation of one of the Ets binding sites reduced SP-C transcription to background levels, whereas mutation of the other site resulted in increased SP-C transcription. Protein-protein interactions between Erm and TTF-1 were demonstrated by mammalian two-hybrid assays and by co-immunoprecipitation assays. Mapping studies showed that the Ets domain of Erm and the combined N terminus and homeodomain of TTF-1 were critical for this interaction. Treatment of primary cultures of adult alveolar type II cells with siRNA targeting Erm diminished expression of both Erm and SP-C but had no effect on beta-actin or GAPDH (glyceraldehyde-3-phosphate dehydrogenase). Taken together, these results demonstrate that Erm is involved in SP-C regulation, which results from an interaction with TTF-1.

Makorin RING finger protein 1 (MKRN1) has negative and positive effects on RNA polymerase II-dependent transcription

Through its transcriptional activities, the proto-oncoprotein c-Jun can regulate cellular proliferation, survival, and differentiation. We have established a novel yeast assay that screens for repressors of c-Jun transcriptional activity. This screen led to the identification of a ubiquitously expressed novel RING zinc finger protein, termed Makorin RING zinc finger protein 1 (MKRN1), recently shown to act as an E3 ubiquitin ligase. Overexpression of MKRN1 in mammalian cells inhibited the transcriptional activities of not only c-Jun, but also the nuclear receptors, the androgen receptor, and the retinoic acid receptors. Truncation analysis indicates that both the amino and carboxy termini are required for this transrepression activity. Surprisingly, when fused to the heterologous DNAbinding domain of GAL4, MKRN1 activates, rather than inhibits, a GAL4-responsive reporter plasmid. In addition, truncation of either the amino- or carboxy-terminal half of MKRN1 disrupts its transactivation activity, the same observation that was made on its transrepression activity. These results demonstrate that MKRN1 has transcriptional activity and suggest that its transrepression and transactivation functions are mediated by the same mechanism. Interestingly, disruption of MKRN1's ubiquitin ligase activity does not affect its inhibitory transcriptional activity. Thus, MKRN1 may represent a nuclear protein with multiple nuclear functions, including regulating RNA polymerase II-catalyzed transcription.

Expression of adipose differentiation-related protein (ADRP) is conjointly regulated by PU.1 and AP-1 in macrophages

ADRP is associated with intracellular lipid droplets. We demonstrate the regulatory mechanism for ADRP expression in RAW264.7 macrophages. The ADRP mRNA expression was stimulated by PMA, and synergistically enhanced in association with its protein level in the presence of lipids. A proteasome inhibitor protected the protein from degradation under the lipid-free conditions. One of the possible sites of the PMA action was proved to be an Ets/AP-1 element in the promoter, since mutations of this site reduced the PMA-induced promoter activity, and ligation of this element led to a significant increase in the PMA-responsiveness of homologous or heterologous promoters. Mutations of this site diminished the synergistic effect on the promoter activity induced by PMA and oleic acid, suggesting a possible interaction between this site and the downstream PPARdelta site. EMSA revealed that PU.1 and AP-1 conjointly bound to this site. The juxtaposition of the two sequences was requisite for full activity, since spacer sequences between them decreased the PMA-induced activity. PI3 kinase inhibitor was found to reduce the PMA-induced mRNA expression and promoter activity in parallel with PU.1/AP-1 complex formation on EMSA. From these results, we concluded that the Ets/AP-1 site is an important cis-acting element that regulates the ADRP gene expression in macrophages.

A role for Ets1, synergizing with AP-1 and GATA-3 in the regulation of IL-5 transcription in mouse Th2 lymphocytes

IL-5 is a key regulator of eosinophilic inflammation and is selectively expressed by antigen-activated Th2 lymphocytes. An important role for the proximal AP-1 and GATA sites in regulating IL-5 transcription is generally accepted but the significance of an adjacent Ets/NFAT site has remained unclear. We have investigated its role using the mouse Th2 clone D10.G4.1. Transcription of IL-5 reporter gene plasmids could be induced in D10 cells by phorbol myristate acetate/cyclic adenosine monophosphate (PMA/cAMP) stimulation and significantly further enhanced by activation of the mitogen-activated protein (MAP) kinase pathways. Strong induction of IL-5 mRNA was also induced by PMA/cAMP. Mutagenesis showed that the Ets/NFAT site is of critical importance along with the AP-1 and GATA sites in regulating IL-5 transcription stimulated by PMA/cAMP and MAP kinase activation. Transactivation was used to investigate the transcription factors which could function at the three sites and possible synergistic interactions. AP-1 (c-Fos/c-Jun) strongly induced IL-5 transcription and dominant negative AP-1 constructs confirmed that AP-1 plays an important role in regulating IL-5 expression. Ets1, unlike other members of the Ets/NFAT family, synergized strongly with AP-1 suggesting that Ets1 is the family member which functions at the Ets/NFAT site. AP-1/Ets1 transactivation also stimulated IL-5 mRNA expression. Ets1 binding to the proximal promoter region, demonstrated by chromatin immunoprecipitation, was stimulated by PMA/cAMP. The absolute dependence on the binding sites for Ets1, AP-1 and GATA-3 together with the strong synergy between Ets1 and AP-1 suggest close cooperative interactions between the three transcription factors in the regulation of IL-5 expression in mouse T cells.

Peroxide-inducible Ets-1 mediates platelet-derived growth factor receptor-alpha gene transcription in vascular smooth muscle cells

Platelet-derived growth factor (PDGF) has been implicated in the pathogenesis of vascular occlusive disorders such as atherosclerosis and restenosis in part due to its regulation of smooth muscle cell phenotype. The molecular mechanisms regulating the expression of PDGF-Ralpha, which binds all known dimeric forms of PDGF except PDGF-DD, are poorly understood. Here we demonstrate that the winged helix-turn-helix proto-oncogene Ets-1 controls PDGF-Ralpha transcription and mRNA expression in smooth muscle cells. Mutational analysis, electrophoretic mobility shift assay, and chromatin immunoprecipitation revealed the existence of a reverse Ets binding motif (-45TTCC-42) in the proximal region of the PDGF-Ralpha promoter, which bound both recombinant and endogenous Ets-1. Ets-1-inducible PDGF-Ralpha expression depended on the integrity of both the -45TTCC-42 motif and the -61G10(-52) element, which resides upstream of -45TTCC-42 and mediates Sp1 induction. Hydrogen peroxide (H2O2) at nanomolar concentrations stimulated levels of Ets-1 and increased PDGF-Ralpha transcription and mRNA expression without affecting Sp1 expression. H2O2 activation of the PDGF-Ralpha promoter was abolished by disrupting -45TTCC-42 or -61G10(-52). These studies identify a functional Ets motif in the PDGF-Ralpha promoter that plays a pivotal role in agonist-inducible PDGF-Ralpha transcription.

Characterization of a c-Jun-responsive module in the 5'-flank of the human CYP2J2 gene that regulates transactivation

The human cytochrome P450 2J2 (CYP2J2) generates cytoprotective epoxyeicosatrienoic acids from arachidonic acid. Expression of CYP2J2 is decreased in hypoxia, and the resultant decrease in CYP2J2-derived epoxyeicosanoids may contribute to the pathogenesis of cardiac ischaemia. Recent studies have indicated that AP-1 (activator protein-1) regulates CYP2J2 expression in normoxia and hypoxia. Down-regulation of CYP2J2 in hypoxic HepG2 cells was closely associated with the up-regulation of c-fos and transient transfection analysis demonstrated that c-Fos abolishes the activation of CYP2J2 by the AP-1 protein c-Jun. Deletion of the region between nt -122 and -50 upstream of the start codon in CYP2J2 prevented c-Jun transactivation. In this study we demonstrate that the sequence at -105/-95 is a major regulatory element that binds c-Jun and has a prominent role in CYP2J2 gene transactivation. Mutagenesis of both the -105/-95 region and the previously identified element at -56/-63 was required for complete loss of transactivation by c-Jun; separate mutagenesis of the -105/-95 element or, to a lesser extent, the -56/-63 element resulted in a partial loss of gene activation. In contrast to the behaviour of the -56/-63 element, c-Jun homodimers and c-Fos/c-Jun heterodimers bound to the -105/-95 element. These findings demonstrate that the c-Jun-responsive module between -122 and -50 in the CYP2J2 proximal promoter contains an atypical AP-1 element at -105/-95 that has a major role in c-Jun transactivation and acts in conjunction with the -56/-63 element to regulate expression.

Spatio-temporal expression of immediate early genes in the central nervous system of SJL/J mice

Gene products of immediate early genes (IEGs) interact with specific binding sites in promoter regions of inducible and constitutively expressed genes. Thereby, they control transcription of down-stream targets, like pro- and anti-apoptotic genes and matrix-metalloproteinases (MMPs), known to play an important role in development, plasticity, response to injury and repair of the central nervous system (CNS). A real-time quantitative RT-PCR and immunohistochemical investigation was performed to study mRNA expression levels and protein distribution patterns of IEGs in cerebrum, cerebellum, and spinal cord of SJL/J mice between postnatal weeks 1 and 40. A down-regulation of c-jun, NF-kappaB1, Max, Ets-1, and p53 mRNA, and an up-regulation of c-fos mRNA was noticed. Down-regulations of Ets-1 and p53 were most prominent between week 1 and 3. The prominent role in CNS development for c-jun, Ets-1 and Max was supported by immunohistochemistry. One-week-old mice were strongly positive for all three proteins in cerebral cortex, medulla oblongata, and gray matter of the spinal cord. A high staining intensity was detected in the developing granule cell layer of the cerebellum for c-jun and Ets-1, and in the Purkinje cell layer of the cerebellum for Max. In addition to the general down-regulation of most mRNAs, minor up-regulations of all IEG proteins could be detected in restricted parts of the CNS indicating regional variations and differential expression and translation during development. Apoptosis was demonstrated using immunohistochemistry for active caspase-3. The expression patterns of IEGs might represent the key to understand the balance of proteolytic activities by MMPs, myelination, and the induction of apoptosis during the development of the CNS.

Imaging Erg and Jun transcription factor interaction in living cells using fluorescence resonance energy transfer analyses

Physical interactions between transcription factors play important roles in modulating gene expression. Previous in vitro studies have shown a transcriptional synergy between Erg protein, an Ets family member, and Jun/Fos heterodimer, members of the bZip family, which requires direct Erg-Jun protein interactions. Visualization of protein interactions in living cells is a new challenge in biology. For this purpose, we generated fusion proteins of Erg, Fos, and Jun with yellow and cyan fluorescent proteins, YFP and CFP, respectively. After transient expression in HeLa cells, interactions of the resulting fusion proteins were explored by fluorescence resonance energy transfer microscopy (FRET) in fixed and living cells. FRET between YFP-Erg and CFP-Jun was monitored by using photobleaching FRET and fluorescence lifetime imaging microscopy. Both techniques revealed the occurrence of intermolecular FRET between YFP-Erg and CFP-Jun. This is stressed by loss of FRET with an YFP-Erg version carrying a point mutation in its ETS domain. These results provide evidence for the interaction of Erg and Jun proteins in living cells as a critical prerequisite of their transcriptional synergy, but also for the essential role of the Y371 residue, conserved in most Ets proteins, in this interaction.

The regulation of COUP-TFII gene expression by Ets-1 is enhanced by the steroid receptor co-activators

Recent phenotypic analysis of orphan nuclear receptor chicken ovalbumin upstream promoter-transcription factor II (COUP-TFII) [NR2F2] knockout mice shows that COUP-TFII is involved in the angiogenic process in the developing embryos. Since Ets-1 expression is also correlated with angiogenesis, and both Ets-1 and COUP-TFII mRNA are present in mesenchymal cells, we have sought to determine whether Ets-1 is a potential regulator of COUP-TFII gene expression. For this purpose, we performed transient transfection experiments using a luciferase reporter construct containing the mouse COUP-TFII promoter. We found that the COUP-TFII promoter activity is indeed regulated by Ets-1. We have identified two identical inverted potential ETS-binding sites located 47 nucleotides downstream of the start site. Mutation of both sites reduced the ability of Ets-1 to enhance the COUP-TFII promoter activity. Furthermore, other members of the ETS family such as Ets-2 or ETV1 are also potent regulators of the COUP-TFII promoter. Finally, the induction of the COUP-TFII gene is strongly enhanced by the expression of steroid receptor co-activator factors through a direct interaction with Ets-1. These results indicate that COUP-TFII is a potential downstream target of Ets-1 and it may partially mediate the Ets-1 function in angiogenesis.

Role of Ets-2 in the Regulation of Heme Oxygenase-1 by Endotoxin

Ets proteins play a vital role in the regulation of mammalian immunity, and family members Ets-1 and Ets-2 regulate a variety of genes that participate in the propagation of an inflammatory response. Heme oxygenase (HO)-1, although acutely induced by inflammatory stimuli, has cytoprotective properties and prevents an exaggerated inflammatory response. Ets-1 and Ets-2 both induce HO-1 promoter activity; however, Ets-2 was a more potent transactivator of HO-1 in macrophages. A potent inflammatory mediator, bacterial lipopolysaccharide (LPS), induced Ets-2 at the mRNA and protein level, and this induction preceded the up-regulation of HO-1. To further delineate the role of Ets-2 in regulating HO-1 transcription, we performed HO-1 promoter analysis studies in macrophages. Deletion mutants down to -137/+74 maintained an activity analogous to that of the largest construct, -4045/+74. Further deletion constructs (starting with -117/+74) showed a significant reduction in promoter activity when co-transfected with Ets-2 or exposed to LPS. Promoter sequence analysis revealed two putative Ets binding sites (EBSs) in this region, and mutation of these sites showed that EBS -93, more than EBS -125, was critical for full HO-1 promoter activity. Additional studies showed that EBS -93 binds Ets-2 and that mutation of the DNA binding domain of Ets-2 entirely prevented transactivation of HO-1. Finally, overexpression of a dominant negative form of Ets-2 blunted HO-1 promoter induction by LPS, and kinase inhibitors (PI3K more than JNK) that reduced Ets-2 expression markedly decreased endogenous HO-1 expression. Our data provide evidence that Ets-2 contributes to the up-regulation of HO-1 by the potent inflammatory stimulus LPS in macrophages.

Identification of a single nucleotide polymorphism in the MMP-1 promoter in chondrosarcoma

Matrix metalloproteinases (MMPs) are a group of at least 26 enzymes that facilitate cellular invasion via the degradation of the extracellular matrix. Specifically, the ability to degrade collagen types III and I is important in tumor invasion and metastasis. Over expression of the MMP-1 gene has been shown to correlate with poorer outcome in GI tract and gynecological tumors. This level of expression of this gene has been shown to be significantly increased by the presence of a single nucleotide polymorphism in the MMP-1 promoter sequence as a result of the creation of an ETS binding site. This SNP results from the addition of a single guanine base at -1,607 bp 24. Two chondrosarcoma cell lines and a series of 10 resected chondrosarcoma specimens underwent DNA extraction, purification, polymerase chain reaction, and sequencing. The presence of the single nucleotide polymorphism at -1,607 bp was confirmed within the promoter region for MMP-1 in human chondrosarcoma. Because all three genotypes were found in the clinical samples, the SNP may indeed provide a mechanistic explanation for a more aggressive biologic behavior locally and distally for a subset of chondrosarcomas.

SP100 expression modulates ETS1 transcriptional activity and inhibits cell invasion

The ETS1 transcription factor is a member of the Ets family of conserved sequence-specific DNA-binding proteins. ETS1 has been shown to play important roles in various cellular processes such as proliferation, differentiation, lymphoid development, motility, invasion and angiogenesis. These diverse roles of ETS1 are likely to be dependent on specific protein interactions. To identify proteins that interact with ETS1, a yeast two-hybrid screen was conducted. Here, we describe the functional interaction between SP100 and ETS1. SP100 protein interacts with ETS1 both in vitro and in vivo. SP100 is localized to nuclear bodies and ETS1 expression alters the nuclear body morphology in living cells. SP100 negatively modulates ETS1 transcriptional activation of the MMP1 and uPA promoters in a dose-dependent manner, decreases the expression of these endogenous genes, and reduces ETS1 DNA binding. Expression of SP100 inhibits the invasion of breast cancer cells and is induced by Interferon-alpha, which has been shown to inhibit the invasion of cancer cells. These data demonstrate that SP100 modulates ETS1-dependent biological processes.

Mechanism, detection and clinical significance of the reciprocal translocation t(12;21)(p12;q22) in the children suffering from acute lymphoblastic leukaemia

The t(12;21)(p12;q22) is the most frequent chromosomal rearrangement observed in acute lymphoblastic leukaemia (ALL) and is associated with favourable prognosis and good response to initial treatment. The translocation-Ets-leukaemia (TEL) and AML1 genes are very often involved in chromosomal translocations in haematopoietic malignancies. This review presents the structure, roles of TEL and AML1 genes, and their proteins in haematopoiesis and in leukaemiogenesis as well. Aspects such as: the mechanism of translocation t(12;21)(p12;q22), function of TEL/AML1 fusion gene and chimeric protein, clinical significance of this abnormality and methods allowing to detect this translocation and its transcript are also discussed in this paper.

Direct association between PU.1 and MeCP2 that recruits mSin3A-HDAC complex for PU.1-mediated transcriptional repression

PU.1, a member of the Ets family of transcription factors, is implicated in hematopoietic cell differentiation through its interactions with other transcriptional factors and cofactors. To identify a novel protein(s) binding to PU.1, we carried out affinity purification using a column of Glutathione-Sepharose beads bound to GST-PU.1 fusion protein and isolated several individual proteins using murine erythroleukemia (MEL) cell extracts. Sequence analysis of these proteins revealed that one was MeCP2 a methyl CpG binding protein. GST-pull-down assay and immunoprecipitation assay showed that PU.1 bound directly to MeCP2 via its Ets domain and MeCP2 bound to PU.1 via either its amino terminal domain or trans-repression domain. MeCP2 repressed transcriptional activity of PU.1 on a reporter construct with trimerized PU.1 binding sites. This downregulation was recovered in the presence of histone deacetylase inhibitor, trichostatin A (TSA). MeCP2 was integrated in PU.1-mSin3A-HDAC complex but not in PU.1-CBP complex. Chromatin immunoprecipitation (ChIP) assays showed that PU.1 and MeCP2 were collocated at the PU.1 binding site on the reporter construct and the PU.1 binding site of the intervening sequence 2 (IVS2) region in the intron of the beta-globin gene, which has been proposed to regulate expression of the gene, in undifferentiated MEL cells. The complex disappeared from the region during the course of erythroid differentiation of MEL cells. Our results suggest that MeCP2 acts as a corepressor of PU.1 probably due to facilitating complex formation with mSin3A and HDACs.

The biology of the Ets1 proto-oncogene

The Ets1 proto-oncoprotein is a member of the Ets family of transcription factors that share a unique DNA binding domain, the Ets domain. The DNA binding activity of Ets1 is controlled by kinases and transcription factors. Some transcription factors, such as AML-1, regulate Ets1 by targeting its autoinhibitory module. Others, such as Pax-5, alter Ets1 DNA binding properties. Ets1 harbors two phosphorylation sites, threonine-38 and an array of serines within the exon VII domain. Phosphorylation of threonine-38 by ERK1/2 activates Ets1, whereas phosphorylation of the exon VII domain by CaMKII or MLCK inhibits Ets1 DNA binding activity. Ets1 is expressed by numerous cell types. In haemotopoietic cells, it contributes to the regulation of cellular differentiation. In a variety of other cells, including endothelial cells, vascular smooth muscle cells and epithelial cancer cells, Ets1 promotes invasive behavior. Regulation of MMP1, MMP3, MMP9 and uPA as well as of VEGF and VEGF receptor gene expression has been ascribed to Ets1. In tumors, Ets1 expression is indicative of poorer prognosis.

Characterization and analysis of the proximal Janus kinase 3 promoter

Janus kinase 3 (Jak3) is a nonreceptor tyrosine kinase essential for signaling via cytokine receptors that comprise the common gamma-chain (gammac), i.e., the receptors for IL-2, IL-4, IL-7, IL-9, IL-15, and IL-21. Jak3 is preferentially expressed in hemopoietic cells and is up-regulated upon cell differentiation and activation. Despite the importance of Jak3 in lymphoid development and immune function, the mechanisms that govern its expression have not been defined. To gain insight into this issue, we set out to characterize the Jak3 promoter. The 5'-untranslated region of the Jak3 gene is interrupted by a 3515-bp intron. Upstream of this intron and the transcription initiation site, we identified an approximately 1-kb segment that exhibited lymphoid-specific promoter activity and was responsive to TCR signals. Truncation of this fragment revealed that core promoter activity resided in a 267-bp fragment that contains putative Sp-1, AP-1, Ets, Stat, and other binding sites. Mutation of the AP-1 sites significantly diminished, whereas mutation of the Ets sites abolished, the inducibility of the promoter construct. Chromatin immunoprecipitation assays showed that histone acetylation correlates with mRNA expression and that Ets-1/2 binds this region. Thus, transcription factors that bind these sites, especially Ets family members, are likely to be important regulators of Jak3 expression.

Interplay between proximal and distal promoter elements is required for squamous differentiation marker induction in the bronchial epithelium: role for ESE-1, Sp1, and AP-1 proteins

Overexpression of SPRR1B in bronchial epithelial cells is a marker for early metaplastic changes induced by various toxicants/carcinogens. Previously, we have shown that the transcriptional stimulation of SPRR1B expression by phorbol 12-myristate 13-acetate (PMA) is mainly mediated by a -150/-94 bp enhancer harboring two critical 12-O-tetradecanoylphorbol-13-acetate-responsive elements (TREs) and by Jun.Fra-1 dimers. Here, we show that a region between -54 and -39 bp containing an ETS-binding site (EBS) and a GC box is essential for both basal and PMA-inducible SPRR1B transcription. In vivo footprinting demonstrated binding of transcription factors to these elements. However, unlike enhancer TREs, exposure of cells to PMA did not significantly alter the footprinting pattern at these elements. Mutations that crippled both the EBS and GC box suppressed both basal and PMA-inducible SPRR1B transcription. Consistent with this, overexpression of EBS-binding proteins ESE-1 and ESE-3 significantly stimulated SPRR1B promoter activity. Furthermore, preceding SPRR1B transcription, PMA up-regulated mRNA expression of ETS family members such as ESE-1 and ESE-3. Although ESE-1 synergistically activated c-Jun- and PMA-enhanced SPRR1B transcription, coexpression of Sp1 and ESE-1 showed no synergistic or additive effect on promoter activity, indicating an obligatory role for AP-1 proteins in such regulation. In support of this notion, deletion or mutation of two functional TREs inhibited ESE-1- and Sp1-enhanced promoter activation. Thus, the interaction between ESE-1 and Sp1, and AP-1 proteins that bind to the proximal and distal promoter regions, respectively, play a critical role in the induction of squamous differentiation marker expression in bronchial epithelial cells.

Reciprocal effects of C/EBPalpha and PKCdelta on JunB expression and monocytic differentiation depend upon the C/EBPalpha basic region

Monocytic differentiation of 32DPKCdelta cells in response to activation of protein kinase C delta (PKCdelta) by phorbol 12-myristate 13-acetate (PMA) was inhibited by exogenous CCAAT/enhancer binding protein alpha-estradiol receptor (C/EBPalpha-ER), which impeded morphologic maturation and induction of macrosialin mRNA. Inhibition of monopoiesis was also evident in 32DPKCdelta subclones expressing C/EBPalphaLeu12Val-ER, which cannot dimerize or bind DNA because of mutation of the leucine zipper, C/EBPalphaGZ-ER, in which the leucine zipper has been replaced by the GCN4 zipper, or C/EBPalphaDelta3-8-ER, lacking the C/EBPalpha transactivation domains. In contrast, C/EBPalphaBR3-ER, containing a mutant basic region, did not inhibit monocytic differentiation. C/EBPalpha-ER strongly inhibited endogenous AP-1 DNA-binding. Supershift analysis revealed that the major AP-1 complex contains JunB. Activation of C/EBPalpha-ER specifically reduced endogenous JunB RNA and protein and exogenous JunB levels without affecting endogenous or exogenous c-Jun. The stability of PMA-induced JunB was not affected. Thus, C/EBPalpha-ER suppresses both JunB transcription and posttranscriptional protein generation or induction. PU.1 levels and activity were increased. The Leu12Val, GZ, and Delta3-8 mutants also inhibited JunB expression, whereas the BR3 mutant was ineffective, indicating that inhibition of JunB expression and monocytic differentiation by C/EBPalpha-ER depends upon an interaction mediated by its basic region. Exogenous JunB restored AP-1 DNA-binding but did not prevent inhibition of macrosialin expression by C/EBPalpha-ER, indicating that JunB is not the only target relevant to inhibition of monopoiesis by C/EBPalpha.

EAPII interacts with ETS1 and modulates its transcriptional function

Ets proteins constitute a family of conserved sequence-specific DNA-binding proteins and function as transcription factors. ETS1 plays important roles in differentiation, lymphoid cell development, invasiveness and angiogenesis. Such diverse roles of ETS1 are likely to be dependent on its associated proteins. A yeast two-hybrid screen was conducted and here we describe a novel ETS1 interacting protein designated as ETS1-associated protein II (EAPII). EAPII protein interacts with ETS1 and other Ets proteins (ETS2 and FLI1) both in vitro and in vivo. Indirect immunofluorescence demonstrated that EAPII is predominately localized to the nucleus of mammalian cells. EAPII negatively modulates ETS1 transcriptional activity and attenuates synergistic transactivation by ETS1 and AP-1. Significantly, re-expression of EAPII inhibits the migration of epithelial cancer cells, but does not affect cell viability. Therefore, EAPII is a novel ETS1 modulator that regulates specific aspects of the ETS1 functions.

BATF transgenic mice reveal a role for activator protein-1 in NKT cell development

The importance of regulated AP-1 activity during T cell development was assessed using transgenic mice overexpressing BATF, a basic leucine zipper transcription factor and an AP-1 inhibitor. BATF transgenic animals possess normal thymic cellularity and all major T cell subsets, but show impaired thymocyte proliferation in vitro and no induction of IL-2, IL-4, IL-5, IL-10, and IL-13 expression. Since NKT cells are largely responsible for cytokine production in the thymus, this population was examined by detection of the V alpha 14-J alpha 281 TCR, flow cytometry of NK1.1(+) TCR beta(+) cells, and analysis of cytokine production by heat-stable Ag(low) thymocytes and peripheral NKT cells stimulated in vivo. Results show a severe under-representation of NKT cells in BATF transgenic animals, providing the first evidence that the precise control of AP-1-mediated transcription is critical for the proper emergence of thymus-derived NKT cells in the mouse.

Ets-1 positively regulates Fas ligand transcription via cooperative interactions with Sp1

The FasL/Fas system has been implicated in smooth muscle cell apoptosis and atherosclerotic plaque instability, a process that can lead to plaque rupture, precipitating myocardial infarction and sudden death. The transcriptional mechanisms regulating FasL gene expression in vascular smooth muscle cells are poorly understood. We recently described a novel mechanism mediating inducible FasL gene expression in smooth muscle cells involving the zinc finger transcription factor Sp1 (Kavurma, M. M., Santiago, F. S., Bofocco, E., and Khachigian, L. M. (2001) J. Biol. Chem. 276, 4964-4971). We now show that FasL gene expression is governed by cooperative activation between Sp1 and the Ets family of transcription factors. The overexpression of Ets-1 was sufficient to induce FasL promoter-dependent expression and protein synthesis. Ets-1 activation of the promoter was abrogated either by deletion or mutation of the Sp1 binding site. The overexpression of Ets-1 together with Sp1 produced cooperative activation of the FasL promoter. Sp1 induction of the FasL promoter was abrogated by an Ets-1 mutant lacking the activation domain. Conversely, Ets-1 activation of the promoter was blocked by an Sp1 mutant bearing the DNA-binding domain. The mutation of the (-365)GGAA(-362) element in the FasL promoter abolished Ets-1 activation and attenuated Sp1-inducible gene expression. Immunoprecipitation and supershift experiments revealed that endogenous Ets-1 and Sp1 physically interact and co-occupy this site. Thus, FasL gene expression in vascular smooth muscle cells is mediated by cooperativity between Ets-1 and Sp1.

Correlation of transcriptional repression by p21(SNFT) with changes in DNA.NF-AT complex interactions

p21(SNFT) (21-kDa small nuclear factor isolated from T cells) is a novel human protein of the basic leucine zipper family. The overexpression of p21(SNFT) leads to the significant and specific repression of transcription from the interleukin-2 promoter as well as from several essential activator protein 1 (AP-1)-driven composite promoter elements. One example is the distal nuclear factor of activated T cells (NF-AT)/AP-1 element where the AP-1 (Fos/Jun) basic leucine zipper heterodimer interacts with members of the NF-AT family. p21(SNFT) has been shown to replace Fos in dimerization with Jun on a consensus AP-1 binding site (12-O-tetradecanolyphorbol-13-acetate response element (TRE)) and to interact with Jun and NF-AT at the distal NF-AT/AP-1 enhancer element. A detailed biochemical analysis presented here compares interactions involving p21(SNFT) with those involving Fos. The results demonstrate that a p21(SNFT)/Jun dimer binds a TRE similarly to AP-1 and like AP-1 binds cooperatively with NF-AT at the NF-AT/AP-1 composite element. However, Fos interacts significantly more efficiently than p21(SNFT) with Jun and NF-AT, and the replacement of Fos by p21(SNFT) in the trimolecular complex drastically alters protein-DNA contacts. The data suggest that p21(SNFT) may repress transcriptional activity by inducing a unique conformation in the transcription factor complex.

Accessory elements, flanking DNA sequence, and promoter context play key roles in determining the efficacy of insulin and phorbol ester signaling through the malic enzyme and collagenase-1 AP-1 motifs

Insulin stimulates malic enzyme (ME)-chloramphenicol acetyltransferase (CAT) and collagenase-1-CAT fusion gene expression in H4IIE cells through identical activator protein-1 (AP-1) motifs. In contrast, insulin and phorbol esters only stimulate collagenase-1-CAT and not ME-CAT fusion gene expression in HeLa cells. The experiments in this article were designed to explore the molecular basis for this differential cell type- and gene-specific regulation. The results highlight the influence of three variables, namely promoter context, AP-1 flanking sequence, and accessory elements that modulate insulin and phorbol ester signaling through the AP-1 motif. Thus, fusion gene transfection and proteolytic clipping gel retardation assays suggest that the AP-1 flanking sequence affects the conformation of AP-1 binding to the collagenase-1 and ME AP-1 motifs such that it selectively binds the latter in a fully activated state. However, this influence of ME AP-1 flanking sequence is dependent on promoter context. Thus, the ME AP-1 motif will mediate both an insulin and phorbol ester response in HeLa cells when introduced into either the collagenase-1 promoter or a specific heterologous promoter. But even in the context of the collagenase-1 promoter, the effects of both insulin and phorbol esters, mediated through the ME AP-1 motif are dependent on accessory factors.

Transcriptional regulation of granulocyte and monocyte development

Granulocytes and monocytes develop from a common myeloid progenitor. Early granulopoiesis requires the C/EBPalpha, PU.1, RAR, CBF, and c-Myb transcription factors, and terminal neutrophil differentiation is dependent upon C/EBPepsilon, PU.1, Sp1, CDP, and HoxA10. Monopoiesis can be induced by Maf-B, c-Jun, or Egr-1 and is dependent upon PU.1, Sp1, and ICSBP. Signals eminating from cytokine receptors modulate factor activities but do not determine cell fates. Orchestration of the myeloid developmental program is achieved via cooperative gene regulation, via synergistic and inhibitory protein-protein interactions, via promoter auto-regulation and cross-regulation, via regulation of factor levels, and via induction of cell cycle arrest: For example, c-Myb and C/EBPalpha cooperate to activate the mim-1 and NE promoters, PU.1, C/EBPalpha, and CBF, regulate the NE, MPO, and M-CSF Receptor genes. PU.1:GATA-1 interaction and C/EBP suppression of FOG transcription inhibits erythroid and megakaryocyte gene expression. c-Jun:PU.1, ICSBP:PU.1, and perhaps Maf:Jun complexes induce monocytic genes. PU.1 and C/EBPalpha activate their own promoters, C/EBPalpha rapidly induces PU.1 and C/EBPepsilon RNA expression, and RARalpha activates the C/EBPepsilon promoter. Higher levels of PU.1 are required for monopoiesis than for B-lymphopoiesis, and higher C/EBP levels may favor granulopoiesis over monopoiesis. CBF and c-Myb stimulate proliferation whereas C/EBPalpha induces a G1/S arrest; cell cycle arrest is required for terminal myelopoiesis, perhaps due to expression of p53 or hypo-phosphorylated Rb.

Heat shock factor 1 represses transcription of the IL-1beta gene through physical interaction with the nuclear factor of interleukin 6

Heat shock factor (HSF) 1 is the major heat shock transcription factor that regulates stress-inducible synthesis of heat shock proteins and is also essential in protection against endotoxic shock. Following our previous study, which demonstrated the transcriptional repression of the IL-1beta gene by HSF1 (Cahill, C. M., Waterman, W. R., Xie, Y., Auron, P. E., and Calderwood, S. K. (1996) J. Biol. Chem. 271, 24874-24879), we have examined the mechanisms of transcriptional repression. Our studies show that HSF1 represses the lipopolyliposaccharide-induced transcription of the IL-1beta promoter through direct interaction with the nuclear factor of interleukin 6 (NF-IL6, also known as CCAAT enhancer binding protein (C/EBPbeta), an essential regulator in IL-1beta transcription. We show for the first time that HSF1 binds directly to NF-IL6 in vivo and antagonizes its activity. The HSF1/NF-IL6 interaction involves a sequence of HSF1 containing the trimerization and regulatory domains and the bZip region of NF-IL6. HSF1 has little effect on IL-1beta promoter activity stimulated by the essential monocytic transcription factor Spi.1 but is strongly inhibitory to transcriptional activation by NF-IL6 and to the synergistic activation by NF-IL6 and Spi.1. Because of its ability to bind to specific C/EBP elements in the promoters of multiple genes and its ability to interact with other transcription factors, NF-IL6 is involved in transcriptional regulation of a wide range of genes. Interaction between HSF1 and NF-IL6 could thus be an important mechanism in HSF1 regulation of general gene transcription during endotoxin stress.

When Ets transcription factors meet their partners

Ets proteins are a family of transcription factors that regulate the expression of a myriad of genes in a variety of tissues and cell types. This functional versatility emerges from their interactions with other structurally unrelated transcription factors. Indeed, combinatorial control is a characteristic property of Ets family members, involving interactions between Ets and other key transcriptional factors such as AP1, SRF, and Pax family members. Intriguingly, recent molecular modeling and crystallographic data suggest that not only the ETS DNA-binding domain, but also the DNA recognition helix alpha3, are often directly required for Ets partner's selection. Indeed, while most DNA-binding proteins appear to exploit differences within their DNA recognition helices for sites selection, the Ets proteins exploit differences in their surfaces that interact with other transcription factors, which in turn may modify their DNA-binding properties in a promoter-specific fashion. Taken together, the gene-specific architecture of these unique complexes can mediate the selective control of transcriptional activity.

Inducer-specific enhanceosome formation controls tumor necrosis factor alpha gene expression in T lymphocytes

We present evidence that the inducer-specific regulation of the human tumor necrosis factor alpha (TNF-alpha) gene in T cells involves the assembly of distinct higher-order transcription enhancer complexes (enhanceosomes), which is dependent upon inducer-specific helical phasing relationships between transcription factor binding sites. While ATF-2, c-Jun, and the coactivator proteins CBP/p300 play a central role in TNF-alpha gene activation stimulated by virus infection or intracellular calcium flux, different sets of activators including NFATp, Sp1, and Ets/Elk are recruited to a shared set of transcription factor binding sites depending upon the particular stimulus. Thus, these studies demonstrate that the inducer-specific assembly of unique enhanceosomes is a general mechanism by which a single gene is controlled in response to different extracellular stimuli.

Transcriptional mechanisms regulating myeloid-specific genes

Myeloid blood cells comprise an important component of the immune system. Proper control of both lineage- and stage-specific gene expression is required for normal myeloid cell development and function. In recent years, a relatively small number of critical transcriptional regulators have been identified that serve important roles both in myeloid cell development and regulation of lineage-restricted gene expression in mature myeloid cells. This review summarizes our current understanding of the regulation of lineage- and stage-restricted transcription during myeloid cell differentiation, how critical transcriptional regulators control myeloid cell development, and how perturbations in transcription factor function results in the development of leukemia.

Structural studies of Ets-1/Pax5 complex formation on DNA

Pax5 regulates the B cell-specific expression of the mb-1 gene together with members of the Ets family of transcriptional activators. The Ets proteins on their own bind poorly to the Pax5/Ets binding site, but can be recruited to the site by cooperative interactions with Pax5. The structure of the ETS domain of Ets-1 and the paired domain of Pax5 bound to DNA reveals the molecular details of the selective recruitment of different Ets proteins by Pax5. Comparison with structures of Ets-1 alone bound to both high- and low-affinity DNA sites reveals that Pax5 alters the Ets-1 contacts with DNA. The ability of one protein to alter the DNA sequence-specific contacts of another provides a general mechanism for combinatorial regulation of transcription.

Transcriptional regulation of hemopoiesis

The regulation of blood cell formation, or hemopoiesis, is central to the replenishment of mature effector cells of innate and acquired immune responses. These cells fulfil specific roles in the host defense against invading pathogens, and in the maintenance of homeostasis. The development of hemopoietic cells is under stringent control from extracellular and intracellular stimuli that result in the activation of specific downstream signaling cascades. Ultimately, all signal transduction pathways converge at the level of gene expression where positive and negative modulators of transcription interact to delineate the pattern of gene expression and the overall cellular hemopoietic response. Transcription factors, therefore, represent a nodal point of hemopoietic control through the integration of the various signaling pathways and subsequent modulation of the transcriptional machinery. Transcription factors can act both positively and negatively to regulate the expression of a wide range of hemopoiesis-relevant genes including growth factors and their receptors, other transcription factors, as well as various molecules important for the function of developing cells. The expression of these genes is dependent on the complex interactions between transcription factors, co-regulatory molecules, and specific binding sequences on the DNA. Recent advances in various vertebrate and invertebrate systems emphasize the importance of transcription factors for hemopoiesis control and the evolutionary conservation of several of such mechanisms. In this review we outline some of the key issues frequently identified in studies of the transcriptional regulation of hemopoietic gene expression. In teleosts, we expect that the characterization of several of these transcription factors and their regulatory mechanisms will complement recent advances in a number of fish systems where identification of cytokine and other hemopoiesis-relevant factors are currently under investigation.

Gel-based fluorescence resonance energy transfer (gelFRET) analysis of nucleoprotein complex architecture

A gel-based fluorescence resonance energy transfer (gelFRET) assay was developed for analysis of the architecture of nucleoprotein complexes. gelFRET is based on fluorescence analysis of nucleoprotein complexes separated by polyacrylamide gel electrophoresis. These complexes are separated from free components and nonspecific complexes, enabling fluorescence analysis of complexes containing all components in stoichiometric proportions. gelFRET can be used to investigate the structural organization of nucleoprotein complexes through comparison of the relative efficiencies of energy transfer from donor fluorophores linked to different positions on DNA to an acceptor fluorophore linked to a unique position on the binding protein. We have applied gelFRET to analysis of the orientation of binding by heterodimeric transcription factors. By using Fos-Jun heterodimers as a model system we have identified the structural determinants that control the orientation of heterodimer binding. gelFRET can be applied to studies of a variety of biological processes that influence the proximity of two sites within a complex, such as the assembly of transcription regulatory complexes.

Control of the orientation of Fos-Jun binding and the transcriptional cooperativity of Fos-Jun-NFAT1 complexes

Heterodimeric transcription regulatory proteins can bind to palindromic recognition elements in two opposite orientations. We have developed a gel-based fluorescence resonance energy transfer assay for quantifying heterodimer orientation preferences. Fos-Jun heterodimers bind in opposite orientations to AP-1 sites with different flanking sequences. The effects of individual amino acid and base pair substitutions on heterodimer binding orientation were quantified. Base pairs at positions +/-6 and +/-10 relative to the center of the AP-1 site were the principal determinants of Fos-Jun binding orientation. Amino acid residues of opposite charge adjacent to the basic regions of Fos and Jun had independent effects on heterodimer orientation. Exchange of these amino acid residues between the basic region-leucine zipper domains of Fos and Jun reversed the binding orientation. Heterodimers formed by full-length Fos and Jun exhibited the same changes in binding orientation in response to amino acid and base pair substitutions. The preferred orientation of heterodimer binding affected the stability of Fos-Jun-NFAT1 complexes at composite regulatory elements. Changes in heterodimer orientation preference altered the transcriptional activity and the promoter selectivity of Fos-Jun-NFAT1 complexes. Consequently, the orientation of Fos-Jun binding can influence transcriptional activity by altering cooperative interactions with other transcription regulatory proteins.

AP-1 and Cbfa/runt physically interact and regulate parathyroid hormone-dependent MMP13 expression in osteoblasts through a new osteoblast-specific element 2/AP-1 composite element

The expression of MMP13 (collagenase-3), a member of the matrix metalloproteinase family, is increased in vivo as well as in cultured osteosarcoma cell lines by parathyroid hormone (PTH), a major regulator of calcium homeostasis. Binding sites for AP-1 and Cbfa/Runt transcription factors in close proximity have been identified as cis-acting elements in the murine and rat mmp13 promoter required for PTH-induced expression. The cooperative function of these factors in response to PTH in osteoblastic cells suggests a direct interaction between AP-1 and Cbfa/Runt transcription factors. Here, we demonstrate interaction between c-Jun and c-Fos with Cbfa/Runt proteins. This interaction depends on the leucine zipper of c-Jun or c-Fos and the Runt domain of Cbfa/Runt proteins, respectively. Moreover, c-Fos interacts with the C-terminal part of Cbfa1 and Cbfa2, sharing a conserved transcriptional repression domain. In addition to the distal osteoblast-specific element 2 (OSE2) element in the murine and rat mmp13 promoter, we identified a new proximal OSE2 site overlapping with the TRE motif. Both interaction of Cbfa/Runt proteins with AP-1 and the presence of a functional proximal OSE2 site are required for enhanced transcriptional activity of the mmp13 promoter in transient transfected fibroblasts and in PTH-treated osteosarcoma cells.

Ets1 is a common element in directing transcription of the alpha and beta genes of human protein kinase CK2

Protein kinase CK2 is a conserved and vital Ser/Thr phosphotransferase with various links to malignant diseases, occurring as a tetramer composed of two catalytically active (CK2alpha and/or CK2alpha') and two regulatory subunits (CK2beta). There is balanced availability of CK2alpha and CK2beta transcripts in proliferating and differentiating cultured cells. Examination of the human CK2beta gene for transcriptionally active regions by systematic deletions and reporter gene assays indicates strong promoter activity at positions -42 to 14 and 12 to 72 containing transcription start sites 1 and 2 of the gene (positions +1 and 33), respectively, an upstream and a downstream enhancer activity at positions -241 to -168 and 123 to 677, respectively, and silencer activity at positions -241 to -261. Of the various transcription factor binding motifs present in those regions, Ets1 and CAAT-related motifs turned out to be of particular importance, Ets1 for promoter activation and CAAT-related motifs for enhancer activation. In addition, there are contributions by Sp1. Most strikingly, the Ets1 region representing two adjoining consensus motifs also occurs with complete identity in the recently characterized promoter of the CK2alpha gene [Krehan, A., Ansuini, H., Böcher, O., Grein, S., Wirkner, U. & Pyerin, W. (2001) J. Biol. Chem. 275, 18327-18336], and affects comparably, when assayed in parallel, the promoters of both CK2 genes, both by motif mutations and by Ets1 overexpression. The data strongly support the hypothesis that Ets1 acts as a common regulatory element of the CK2alpha and CK2beta genes involved in directing coordinate transcription and contributing to the balanced availability of transcripts.

Identification of amino acid residues in the ETS transcription factor Erg that mediate Erg-Jun/Fos-DNA ternary complex formation

Jun, Fos, and Ets proteins belong to distinct families of transcription factors that target specific DNA elements often found jointly in gene promoters. Physical and functional interactions between these families play important roles in modulating gene expression. Previous studies have demonstrated a direct interaction between the DNA-binding domains of the two partners. However, the molecular details of the interactions have not been investigated so far. Here we used the known three-dimensional structures of the ETS DNA-binding domain and Jun/Fos heterodimer to model an ETS-Jun/Fos-DNA ternary complex. Docking procedures suggested that certain ETS domain residues in the DNA recognition helix alpha3 interact with the N-terminal basic domain of Jun. To support the model, different Erg ETS domain mutants were obtained by deletion or by single amino acid substitutions and were tested for their ability to mediate DNA binding, Erg-Jun/Fos complex formation, and transcriptional activation. We identified point mutations that affect both the DNA binding properties of Erg and its physical interaction with Jun (R367K), as well as mutations that essentially prevent transcriptional synergy with the Jun/Fos heterodimer (Y371V). These results provide a framework of the ETS/bZIP interaction linked to the manifestation of functional activity in gene regulation.

Close encounters of many kinds: Fos-Jun interactions that mediate transcription regulatory specificity

Fos and Jun family proteins regulate the expression of a myriad of genes in a variety of tissues and cell types. This functional versatility emerges from their interactions with related bZIP proteins and with structurally unrelated transcription factors. These interactions at composite regulatory elements produce nucleoprotein complexes with high sequence-specificity and regulatory selectivity. Several general principles including binding cooperativity and conformational adaptability have emerged from studies of regulatory complexes containing Fos-Jun family proteins. The structural properties of Fos-Jun family proteins including opposite orientations of heterodimer binding and the ability to bend DNA can contribute to the assembly and functions of such complexes. The cooperative recruitment of transcription factors, coactivators and chromatin remodeling factors to promoter and enhancer regions generates multiprotein transcription regulatory complexes with cell- and stimulus-specific transcriptional activities. The gene-specific architecture of these complexes can mediate the selective control of transcriptional activity.

The Ets-transcription factor family in embryonic development: lessons from the amphibian and bird

This chapter reviews the expression and role of Ets-genes during embryogenesis of amphibians and birds. In addition to overlapping expression domains, some of them exhibit cell type-specific expression. Many of them are expressed in migratory cells: neural crest, endothelial, and pronephric duct cells for instance. They are also transcribed in embryonic areas affected by epithelio-mesenchymal transitions. Both processes involve modifications of cellular adhesion. Ets-family genes appear to coordinate changes in the expression of adhesion molecules and degradation of the extracellular matrix upon regulation of matrix metalloproteinases and their specific inhibitors. These functions are essential for physiological processes like tissue remodelling during embryogenesis or wound healing. Unfortunately they also play a harmful role in metastasis. Recent studies in the nervous system showed that Ets-genes contribute to the establishment of a cellular identity. This identity could rely on definite cell-surface determinants, among which cadherins could play an important role. In addition to cell-type specific expression, other factors contribute to the specificity of function of Ets-genes. These genes have a broad specificity of recognition of target sequences in gene promoters, insufficient for accurate control of gene expression. A fine tuning could arise from combinatorial interactions with other Ets- or accessory proteins.

Regulation of Ets function by protein - protein interactions

Ets proteins are a family of transcription factors that share an 85 amino acid conserved DNA binding domain, the ETS domain. Over 25 mammalian Ets family members control important biological processes, including cellular proliferation, differentiation, lymphocyte development and activation, transformation and apoptosis by recognizing the GGA core motif in the promoter or enhancer of their target genes. Protein - protein interactions regulates DNA binding, subcellular localization, target gene selection and transcriptional activity of Ets proteins. Combinatorial control is a characteristic property of Ets family members, involving interaction between Ets and other key transcriptional factors such as AP-1, NFkappaB and Pax family members. Specific domains of Ets proteins interact with many protein motifs such as bHLH, bZipper and Paired domain. Such interactions coordinate cellular processes in response to diverse signals including cytokines, growth factors, antigen and cellular stresses.

Expression and function of Ets transcription factors in mammalian development: a regulatory network

The Ets transcription factor family is involved in a variety of mammalian developmental processes at the cellular, tissue and organ levels. They are implicated in cellular proliferation, differentiation, migration, apoptosis and cell - cell interactions. This article reviews recent studies that demonstrate the integral importance of Ets in the dosage dependent regulation of development. The expression of many Ets genes is associated with mesenchymal - epithelial interactions and changes in extracellular matrix proteins. These inductive processes contribute to tissue remodeling and integrity, particularly during embryonic development. Overlapping as well as unique patterns of Ets expression are evident in developing tissues, including development of the lymphoid and myeloid lineages, brain and central nervous system, bone and mammary gland. Integration of these data will allow the development of predictive models for the regulation of complex developmental processes.

NF-IL6 (C/EBPbeta ) vigorously activates il1b gene expression via a Spi-1 (PU.1) protein-protein tether

Two classes of transcription factors, ETS and bZIP, stand out as key mediators of monocyte commitment and differentiation. The ETS domain factor Spi-1 (also called PU.1) and the bZIP factor NF-IL6 (also called C/EBPbeta) have been shown to be involved in the transcriptional regulation of interleukin-1beta gene (il1b) and other monocyte-specific genes. We now show that these two factors strongly cooperate on the il1b core promoter (-59/+12) in the absence of direct NF-IL6 binding to DNA. Transient transfection assays, using mutated il1b core promoters, showed that the Spi-1, but not the NF-IL6, binding site is absolutely required for functional cooperativity. Furthermore, the NF-IL6 transactivation domain (TAD) is functionally indispensable and more critical than that of Spi-1. Additionally, TAD-deficient NF-IL6 functions as a dominant negative for Spi-1-mediated activation, suggesting the involvement of the bZIP DNA binding domain. This is supported by the demonstration of in vitro interaction between the NF-IL6 bZIP and Spi-1 winged helix-turn-helix (wHTH) DNA binding domains, arguing that NF-IL6 vigorously activates the il1b core promoter via protein-tethered transactivation mediated by Spi-1.

Identification and characterization of a new human ETS-family transcription factor, TEL2, that is expressed in hematopoietic tissues and can associate with TEL1/ETV6

The ETS family of proteins is a large group of transcription factors implicated in many aspects of normal hematopoietic development, as well as oncogenesis. For example, the TEL1/ETV6 (TEL1) gene is required for normal yolk sac angiogenesis, adult bone marrow hematopoiesis, and is rearranged or deleted in numerous leukemias. This report describes the cloning and characterization of a novelETS gene that is highly related to TEL1 and is therefore called TEL2. The TEL2 gene consists of 8 exons spanning approximately 21 kilobases (kb) in human chromosome 6p21. Unlike the ubiquitously expressed TEL1 gene, however,TEL2 appears to be expressed predominantly in hematopoietic tissues. Antibodies raised against the C-terminus of the TEL2 protein were used to show that TEL2 localizes to the nucleus. All ETS proteins can bind DNA via the highly conserved ETS domain, which recognizes a purine-rich DNA sequence with a GGAA core motif. DNA binding assays show that TEL2 can bind the same consensus DNA binding sequence recognized by TEL1/ETV6. Additionally, the TEL2 protein is capable of associating with itself and with TEL1 in doubly transfected Hela cells, and this interaction is mediated through the pointed (PNT) domain of TEL1. The striking similarities ofTEL2 to the oncogenic TEL1, its expression in hematopoietic tissues, and its ability to associate withTEL1 suggest that TEL2 may be an important hematopoietic regulatory protein.

Identification and characterization of a new human ETS-family transcription factor, TEL2, that is expressed in hematopoietic tissues and can associate with TEL1/ETV6

The ETS family of proteins is a large group of transcription factors implicated in many aspects of normal hematopoietic development, as well as oncogenesis. For example, the TEL1/ETV6 (TEL1) gene is required for normal yolk sac angiogenesis, adult bone marrow hematopoiesis, and is rearranged or deleted in numerous leukemias. This report describes the cloning and characterization of a novelETS gene that is highly related to TEL1 and is therefore called TEL2. The TEL2 gene consists of 8 exons spanning approximately 21 kilobases (kb) in human chromosome 6p21. Unlike the ubiquitously expressed TEL1 gene, however,TEL2 appears to be expressed predominantly in hematopoietic tissues. Antibodies raised against the C-terminus of the TEL2 protein were used to show that TEL2 localizes to the nucleus. All ETS proteins can bind DNA via the highly conserved ETS domain, which recognizes a purine-rich DNA sequence with a GGAA core motif. DNA binding assays show that TEL2 can bind the same consensus DNA binding sequence recognized by TEL1/ETV6. Additionally, the TEL2 protein is capable of associating with itself and with TEL1 in doubly transfected Hela cells, and this interaction is mediated through the pointed (PNT) domain of TEL1. The striking similarities ofTEL2 to the oncogenic TEL1, its expression in hematopoietic tissues, and its ability to associate withTEL1 suggest that TEL2 may be an important hematopoietic regulatory protein.

Epstein-barr virus nuclear antigen 3C activates the latent membrane protein 1 promoter in the presence of Epstein-Barr virus nuclear antigen 2 through sequences encompassing an spi-1/Spi-B binding site

The Epstein-Barr virus (EBV) nuclear antigen 3C (EBNA-3C) protein is a transcriptional regulator of viral and cellular genes that is essential for EBV-mediated immortalization of B lymphocytes in vitro. EBNA-3C can inhibit transcription through an association with the cellular DNA-binding protein Jkappa, a function shared by EBNA-3A and EBNA-3B. Here, we report a mechanism by which EBNA-3C can activate transcription from the EBV latent membrane protein 1 (LMP-1) promoter in conjunction with EBNA-2. Jkappa DNA-binding sites were not required for this activation, and a mutant EBNA-3C protein unable to bind Jkappa activated transcription as efficiently as wild-type EBNA-3C, indicating that EBNA-3C can regulate transcription through a mechanism that is independent of Jkappa. Furthermore, activation of the LMP-1 promoter is a unique function of EBNA-3C, not shared by EBNA-3A and EBNA-3B. The DNA element through which EBNA-3C activates the LMP-1 promoter includes a Spi-1/Spi-B binding site, previously characterized as an important EBNA-2 response element. Although this element has considerable homology to mouse immunoglobulin light chain promoter sequences to which the mouse homologue of Spi-1 binds with its dimerization partner IRF4, we demonstrate that the IRF4-like binding sites in the LMP-1 promoter do not play a role in EBNA-3C-mediated activation. Both EBNA-2 and EBNA-3C were required for transcription mediated through a 41-bp region of the LMP-1 promoter encompassing the Spi binding site. However, EBNA-3C had no effect on transcription mediated in conjunction with the EBNA-2 activation domain fused to the GAL4 DNA-binding domain, suggesting that it does not function as an adapter between EBNA-2 and the cellular transcriptional machinery. Like EBNA-2, EBNA-3C bound directly to both Spi-1 and Spi-B in vitro. This interaction was mediated by a region of EBNA-3C encompassing a likely basic leucine zipper (bZIP) domain and the ets domain of Spi-1 or Spi-B, reminiscent of interactions between bZIP and ets domains of other transcription factors that result in their targeting to DNA. There are many examples of regulation of the hematopoietic-specific Spi transcription factors through protein-protein interactions, and a similar regulation by EBNA-3C, in conjunction with EBNA-2, is likely to be an important and unique contribution of EBNA-3C to EBV-mediated immortalization.

Regulation of granulopoiesis by transcription factors and cytokine signals

The development of mature granulocytes from hematopoietic precursor cells is controlled by a myriad of transcription factors which regulate the expression of essential genes, including those encoding growth factors and their receptors, enzymes, adhesion molecules, and transcription factors themselves. In particular, C/EBPalpha, PU.1, CBF, and c-Myb have emerged as critical players during early granulopoiesis. These transcription factors interact with one another as well as other factors to regulate the expression of a variety of genes important in granulocytic lineage commitment. An important goal remains to understand in greater detail how these various factors act in concert with signals emanating from cytokine receptors to influence the various steps of maturation, from the pluripotent hematopoietic stem cell, to a committed myeloid progenitor, to myeloid precursors, and ultimately to mature granulocytes.

MafB is an inducer of monocytic differentiation

The bZip transcription factor MafB is expressed specifically in the myeloid lineage of the hematopoietic system and is up-regulated successively during myeloid differentiation from multipotent progenitors to macrophages. Here we report that this induction reflects an essential role of MafB in early myeloid and monocytic differentiation. We observed that the expression of MafB in transformed chicken hematopoietic precursors dramatically increases the proportion of myeloid colony formation at the expense of multipotent progenitor-type colonies. In addition, the overexpression of MafB in transformed myeloblasts stimulates the rapid formation of macrophages, as judged by morphology, surface marker expression and functional criteria. MafB-induced macrophages exhibit typical levels of phagocytic activity and nitric oxide release after activation by lipopolysaccharide. By contrast, overexpression of the myeloid transcription factor PU.1 in these cells does not induce macrophage differentiation. Furthermore, a dominant-negative allele of MafB inhibits both myeloid colony formation and the differentiation of myeloblasts into macrophages. Taken together, our results indicate that MafB induction is a specific and essential determinant of the monocytic program in hematopoietic cells.

GATA-1 interacts with the myeloid PU.1 transcription factor and represses PU.1-dependent transcription

The GATA-1 transcription factor is capable of suppressing the myeloid gene expression program when ectopically expressed in myeloid cells. We examined the ability of GATA-1 to repress the expression and function of the PU.1 transcription factor, a central regulator of myeloid differentiation. We found that GATA-1 is capable of suppressing the myeloid phenotype without interfering with PU.1 gene expression, but instead was capable of inhibiting the activity of the PU.1 protein in a dose-dependent manner. This inhibition was independent of the ability of GATA-1 to bind DNA, suggesting that it is mediated by protein-protein interaction. We examined the ability of PU.1 to interact with GATA-1 and found a direct interaction between the PU.1 ETS domain and the C-terminal finger region of GATA-1. Replacing the PU.1 ETS domain with the GAL4 DNA-binding domain removed the ability of GATA-1 to inhibit PU.1 activity, indicating that the PU.1 DNA-binding domain, rather than the transactivation domain, is the target for GATA-1–mediated repression. We therefore propose that GATA-1 represses myeloid gene expression, at least in part, through its ability to directly interact with the PU.1 ETS domain and thereby interfere with PU.1 function.

GATA-1 interacts with the myeloid PU.1 transcription factor and represses PU.1-dependent transcription

The GATA-1 transcription factor is capable of suppressing the myeloid gene expression program when ectopically expressed in myeloid cells. We examined the ability of GATA-1 to repress the expression and function of the PU.1 transcription factor, a central regulator of myeloid differentiation. We found that GATA-1 is capable of suppressing the myeloid phenotype without interfering with PU.1 gene expression, but instead was capable of inhibiting the activity of the PU.1 protein in a dose-dependent manner. This inhibition was independent of the ability of GATA-1 to bind DNA, suggesting that it is mediated by protein-protein interaction. We examined the ability of PU.1 to interact with GATA-1 and found a direct interaction between the PU.1 ETS domain and the C-terminal finger region of GATA-1. Replacing the PU.1 ETS domain with the GAL4 DNA-binding domain removed the ability of GATA-1 to inhibit PU.1 activity, indicating that the PU.1 DNA-binding domain, rather than the transactivation domain, is the target for GATA-1–mediated repression. We therefore propose that GATA-1 represses myeloid gene expression, at least in part, through its ability to directly interact with the PU.1 ETS domain and thereby interfere with PU.1 function.

The human NAD+-dependent 15-hydroxyprostaglandin dehydrogenase gene promoter is controlled by Ets and activating protein-1 transcription factors and progesterone

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) is a key catabolic enzyme in the inactivation of PGF2alpha and PGE2 and therefore serves as an important determinant in regulating their local concentrations. To gain insights into the transcriptional regulation of this enzyme, we have isolated 3.5 kb of the 5'-flanking sequence of the human PGDH promoter and characterized its control in hemopoietic cells and cells of myometrial and placental origin. Several potential binding sites for cAMP-responsive element-binding protein (CREB), Ets, and activating protein-1 (AP-1) transcription factors are present within 2368 bp of the 5'-flanking region. This region and deletions thereof were fused to the luciferase reporter gene and used for transient transfection experiments. In Jurkat leukemic T cells, which express PGDH endogenously, the transfected PGDH promoter was strongly induced by phorbol ester. Induction was reversed by coexpression of A-Fos, a dominant negative to AP-1. In primary cultures of myometrial smooth muscle cells (SMC), the Ets family members Ets-1, Ets-2, and PEA3 potently stimulated transcriptional activity of the PGDH promoter. PEA3-mediated activation was partially repressed by A-Fos, suggesting an involvement of AP-1 proteins, which might be conferred by a distal and a proximal Ets/ AP-1 composite element. The distal Ets/AP-1 element is flanked by two CRE-like sequences. Cotransfection of A-CREB, a dominant negative to CREB, inhibited stimulation of PGDH-2368/luc3 by PEA3 in myometrial SMC, whereas treatment with 8-bromo-cAMP moderately enhanced promoter activity. Progesterone is believed to be an important stimulus for PGDH expression in the utero-placental unit, thus contributing to the maintenance of a quiescent uterus during pregnancy. In myometrial SMC, both isoforms of the progesterone receptor, PR-B and PR-A, caused a ligand-dependent activation of PGDH-2368/luc3. Transcriptional activity of PR-B, but not PR-A, was further enhanced by the addition of 8-bromo-cAMP. We could not confirm a recently proposed transcriptional control of PGDH by mineralocorticoid receptor. No effect of mineralocorticoid receptor, in the absence or presence of aldosterone, with or without 8-bromo-cAMP, was observed on PGDH-2368/luc3. Taken together, these findings demonstrate control of the PGDH promoter by multiple pathways and provide evidence for cross-talk among Ets, AP-1, cAMP, and PR-mediated signaling, suggesting complex regulatory mechanisms for the expression of PGDH.