Sequence-specific binding of human Ets-1 to the T cell receptor alpha gene enhancer

Blueprint of human thymopoiesis reveals molecular mechanisms of stage-specific TCR enhancer activation

Cell differentiation is accompanied by epigenetic changes leading to precise lineage definition and cell identity. Here we present a comprehensive resource of epigenomic data of human T cell precursors along with an integrative analysis of other hematopoietic populations. Although T cell commitment is accompanied by large scale epigenetic changes, we observed that the majority of distal regulatory elements are constitutively unmethylated throughout T cell differentiation, irrespective of their activation status. Among these, the TCRA gene enhancer (Eα) is in an open and unmethylated chromatin structure well before activation. Integrative analyses revealed that the HOXA5-9 transcription factors repress the Eα enhancer at early stages of T cell differentiation, while their decommission is required for TCRA locus activation and enforced αβ T lineage differentiation. Remarkably, the HOXA-mediated repression of Eα is paralleled by the ectopic expression of homeodomain-related oncogenes in T cell acute lymphoblastic leukemia. These results highlight an analogous enhancer repression mechanism at play in normal and cancer conditions, but imposing distinct developmental constraints.

TCRα rearrangements identify a subgroup of NKL-deregulated adult T-ALLs associated with favorable outcome

T-cell acute lymphoblastic leukemia (T-ALL) results from leukemic transformation of T-cell precursors arrested at specific differentiation stages, including an 'early-cortical' thymic maturation arrest characterized by expression of cytoplasmic TCRβ but no surface T-cell receptor (TCR) and frequent ectopic expression of the TLX1/3 NK-like homeotic proteins (NKL). We designed a TCRα VJC PCR to identify clonal TCRα rearrangements in 32% of 127 T-ALLs, including 0/52 immature/TCRγδ lineage cases and 41/75 (55%) TCRαβ lineage cases. Amongst the latter, TCRα rearrangements were not identified in 30/54 (56%) of IMβ/pre-αβ early-cortical T-ALLs, of which the majority (21/30) expressed TLX1/3. We reasoned that the remaining T-ALLs might express other NKL proteins, so compared transcript levels of 46 NKL in T-ALL and normal thymic subpopulations. Ectopic overexpression of 10 NKL genes, of which six are unreported in T-ALL (NKX2-3, BARHL1, BARX2, EMX2, LBX2 and MSX2), was detectable in 17/104 (16%) T-ALLs. Virtually all NKL overexpressing T-ALLs were TCRα unrearranged and ectopic NKL transcript expression strongly repressed Eα activity, suggesting that ectopic NKL expression is the major determinant in early-cortical thymic T-ALL maturation arrest. This immunogenetic T-ALL subtype, defined by TCRβ VDJ but no TCRα VJ rearrangement, is associated with a favorable outcome in GRAALL-treated adult T-ALLs.

Dynamic recruitment of Ets1 to both nucleosome-occupied and -depleted enhancer regions mediates a transcriptional program switch during early T-cell differentiation

Ets1 is a sequence-specific transcription factor that plays an important role during hematopoiesis, and is essential for the transition of CD4⁻/CD8⁻ double negative (DN) to CD4⁺/CD8⁺ double positive (DP) thymocytes. Using genome-wide and functional approaches, we investigated the binding properties, transcriptional role and chromatin environment of Ets1 during this transition. We found that while Ets1 binding at distal sites was associated with active genes at both DN and DP stages, its enhancer activity was attained at the DP stage, as reflected by levels of the core transcriptional hallmarks H3K4me1/3, RNA Polymerase II and eRNA. This dual, stage-specific ability reflected a switch from non-T hematopoietic toward T-cell specific gene expression programs during the DN-to-DP transition, as indicated by transcriptome analyses of Ets1^−/− thymic cells. Coincidentally, Ets1 associates more specifically with Runx1 in DN and with TCF1 in DP cells. We also provide evidence that Ets1 predominantly binds distal nucleosome-occupied regions in DN and nucleosome-depleted regions in DP. Finally and importantly, we demonstrate that Ets1 induces chromatin remodeling by displacing H3K4me1-marked nucleosomes. Our results thus provide an original model whereby the ability of a transcription factor to bind nucleosomal DNA changes during differentiation with consequences on its cognate enhancer activity.

The transcription factor ETS1 in lymphomas: friend or foe?

ETS1 is a member of the ETS family of transcription factors, which contains many cancer genes. ETS1 gene is mapped at 11q24.3, a chromosomal region that is often the site of genomic rearrangements in hematological cancers. ETS1 is expressed in a variety of cells, including B and T lymphocytes. ETS1 is important in various biological processes such as development, differentiation, proliferation, apoptosis, migration and tissue remodeling. It acts as an oncogene controlling invasive and angiogenic behavior of malignant cells in multiple human cancers. In particular, ETS1 deregulation has been reported in diffuse large B-cell lymphoma, in Burkitt lymphoma and in Hodgkin lymphoma. Here, we summarize the function of ETS1 in normal cells, with a particular emphasis on lymphocytes, and its possible role as an oncogene or tumor suppressor gene in the different mature B cell lymphomas.

BmEts upregulates promoter activity of lebocin in Bombyx mori

The Ets family protein BmEts is assumed to be implicated in determination of diapause in the embryogenesis of Bombyx mori. In this study, we found that expression of BmEts was increased in the fat body and other tissues of the 5th instar larvae in response to Escherichia coli injection. Cotransfection experiments using a silkworm cell line revealed that overexpression of BmEts significantly elevated the activity of lebocin promoter but not of cecropin B1, cecropin D, attacin, and moricin promoters. Activation of the lebocin promoter by BmEts was dependent on at least two κB elements and the most proximal GGAA/T motif located on the 5'-upstream region. BmEts further synergistically enhanced E. coli or BmRelish1-d2 (active form)-stimulated lebocin promoter activation. Two κB elements were also found to be involved in promoter activation by BmRelish1-d2 and in synergistic promoter activation by BmEts and BmRelish1-d2 in the silkworm cells. Specific binding of recombinant BmEts to the proximal κB element and the most proximal GGAA/T motif and interaction between BmEts and BmRelish1 were also observed. To our knowledge, this is the first report of an Ets family protein directly regulating immune-related genes in invertebrates.

TLX homeodomain oncogenes mediate T cell maturation arrest in T-ALL via interaction with ETS1 and suppression of TCRα gene expression

Acute lymphoblastic leukemias (ALLs) are characterized by multistep oncogenic processes leading to cell-differentiation arrest and proliferation. Specific abrogation of maturation blockage constitutes a promising therapeutic option in cancer, which requires precise understanding of the underlying molecular mechanisms. We show that the cortical thymic maturation arrest in T-lineage ALLs that overexpress TLX1 or TLX3 is due to binding of TLX1/TLX3 to ETS1, leading to repression of T cell receptor (TCR) α enhanceosome activity and blocked TCR-Jα rearrangement. TLX1/TLX3 abrogation or enforced TCRαβ expression leads to TCRα rearrangement and apoptosis. Importantly, the autoextinction of clones carrying TCRα-driven TLX1 expression supports TLX "addiction" in TLX-positive leukemias and provides further rationale for targeted therapy based on disruption of TLX1/TLX3.

Processing ChIP-chip data: from the scanner to the browser

High-density tiling microarrays are increasingly used in combination with chromatin immunoprecipitation (ChIP) assays to delineate the regulation of gene expression. Besides the technical challenges inherent to such complex biological assays, a critical, often daunting issue is the correct interpretation of the sheer amount of raw data generated by utilizing computational methods. Here, we go through the main steps of this intricate process, including optimized chromatin immunoprecipitation on chip (ChIP-chip) data normalization, peak detection, as well as quality control reports. We also describe convenient standalone software suites, including our own, CoCAS, which works on the latest generation of Agilent high-density arrays, allows dye-swap, replicate correlation, and easy connection with genome browsers for results interpretation, or with, e.g., other peak detection algorithms. Overall, the guidelines described herein provide an effective introduction to ChIP-chip technology and analysis.

The transcription factor Ets1 is important for CD4 repression and Runx3 up-regulation during CD8 T cell differentiation in the thymus

The transcription factor Ets1 contributes to the differentiation of CD8 lineage cells in the thymus, but how it does so is not understood. In this study, we demonstrate that Ets1 is required for the proper termination of CD4 expression during the differentiation of major histocompatability class 1 (MHC I)–restricted thymocytes, but not for other events associated with their positive selection, including the initiation of cytotoxic gene expression, corticomedullary migration, or thymus exit. We further show that Ets1 promotes expression of Runx3, a transcription factor important for CD8 T cell differentiation and the cessation of Cd4 gene expression. Enforced Runx3 expression in Ets1-deficient MHC I–restricted thymocytes largely rescued their impaired Cd4 silencing, indicating that Ets1 is not required for Runx3 function. Finally, we document that Ets1 binds at least two evolutionarily conserved regions within the Runx3 gene in vivo, supporting the possibility that Ets1 directly contributes to Runx3 transcription. These findings identify Ets1 as a key player during CD8 lineage differentiation and indicate that it acts, at least in part, by promoting Runx3 expression.

PU.1 regulates TCR expression by modulating GATA-3 activity

The Ets transcription factor PU.1 is a master regulator for the development of multiple lineages during hematopoiesis. The expression pattern of PU.1 is dynamically regulated during early T lineage development in the thymus. We previously revealed that PU.1 delineates heterogeneity of effector Th2 populations. In this study, we further define the function of PU.1 on the Th2 phenotype using mice that specifically lack PU.1 in T cells using an lck-Cre transgene with a conditional Sfpi1 allele (Sfpi1(lck-/-)). Although deletion of PU.1 by the lck-Cre transgene does not affect T cell development, Sfpi1(lck-/-) T cells have a lower activation threshold than wild-type T cells. When TCR engagement is limiting, Sfpi1(lck-/-) T cells cultured in Th2 polarizing conditions secrete higher levels of Th2 cytokines and have greater cytokine homogeneity than wild-type cells. We show that PU.1 modulates the levels of TCR expression in CD4(+) T cells by regulating the DNA-binding activity of GATA-3 and limiting GATA-3 regulation of TCR gene expression. GATA-3-dependent regulation of TCR expression is also observed in Th1 and Th2 cells. In CD4(+) T cells, PU.1 expression segregates into subpopulations of cells that have lower levels of surface TCR, suggesting that PU.1 contributes to the heterogeneity of TCR expression. Thus, we have identified a mechanism whereby increased GATA-3 function in the absence of the antagonizing activity of PU.1 leads to increased TCR expression, a reduced activation threshold, and increased homogeneity in Th2 populations.

Ets-1 proto-oncogene as a potential predictor for poor prognosis of lung adenocarcinoma

The proto-oncogene Ets-1 is a transcription factor that is known to regulate certain matrix metalloproteinases and plasminogen activator, which have been associated with malignant behaviors in solid carcinomas. We hypothesized that Ets-1 expression is also associated with tumor progression and a worse prognosis in lung carcinoma patients. To clarify the role of the Ets-1 proto-oncogene, the expression of Ets-1 in non-small cell lung carcinomas using 156 paraffin-embedded specimens was determined in surgically resected tissue samples. Immunohistochemical staining showed Ets-1 expression in 82 cases of 156 carcinomas (53%): 36 of 52 (69%) squamous cell carcinomas, 41 of 96 (43%) adenocarcinomas, and 5 of 8 (63%) other carcinomas. In adenocarcinomas, a higher proportion of acinar type expressed Ets-1 compared to papillary or alveolar type (p < 0.05). The proportion of adenocarcinoma that expressed Ets-1 increased with poorer histologic differentiation of the adenocarcinoma (p < 0.05). Ets-1 positive adenocarcinomas had a larger mean size than Ets-1 negative adenocarcinomas (p < 0.01). In adenocarcinoma patients, expression of Ets-1 was associated with disease-free (p = 0.09) and overall survivals (p < 0.05) after lung resection. Such relationship was not observed among squamous cell carcinoma patients. Our findings indicate that Ets-1 expression is related to histopathological differentiation, morphogenesis, and tumor progression of lung adenocarcinomas. Ets-1 appears to be a useful predictor of poor prognosis after surgical resection in lung adenocarcinoma patients. Ets-1 expression could be used to evaluate the malignant behaviors of lung adenocarcinomas.

Critical function of Ikaros in controlling Aiolos gene expression

To characterize the regulation of lymphoid Aiolos transcription factor, we have cloned its promoter. Full promoter and nested deletions were expressed in lymphoid and non-lymphoid cell lines. The minimal promoter activity could be considered as a 172bp upstream from the ATG for Jurkat and HEK293 cells and as a 370bp fragment for U937 cells. Moreover, we have mapped the transcription initiation site. Retardation gels showed binding activity for Ikaros, NFkappaB and AP4 transcription factors and mutations in their binding sites abolish Aiolos promoter activity. Chromatin immunoprecipitation assay revealed that Ikaros, NFkappaB and AP4 are bound to Aiolos promoter. The important function of Ikaros and NFkappaB is underlined by their over expression, which results in the trans-activation of the promoter and drives Aiolos expression in cell lines and in freshly isolated B and T cells, while over expression of a dominant negative Ikaros isoform is able to block Aiolos expression.

DNA motifs in human and mouse proximal promoters predict tissue-specific expression

Comprehensive identification of cis-regulatory elements is necessary for accurately reconstructing gene regulatory networks. We studied proximal promoters of human and mouse genes with differential expression across 56 terminally differentiated tissues. Using in silico techniques to discover, evaluate, and model interactions among sequence elements, we systematically identified regulatory modules that distinguish elevated from inhibited expression in the corresponding transcripts. We used these putative regulatory modules to construct a single predictive model for each of the 56 tissues. These predictors distinguish tissue-specific elevated from inhibited expression with statistical significance in 80% of the tissues (45 of 56). The predictors also reveal synergy between cis-regulatory modules and explain large-scale tissue-specific differential expression. For testis and liver, the predictors include computationally predicted motifs. For most other tissues, the predictors reveal synergy between experimentally verified motifs and indicate genes that are regulated by similar tissue-specific machinery. The identification in proximal promoters of cis-regulatory modules with tissue-specific activity lays the groundwork for complete characterization and deciphering of cis-regulatory DNA code in mammalian genomes.

Inhibition of ets, an essential transcription factor for angiogenesis, to prevent the development of abdominal aortic aneurysm in a rat model

The pathophysiology of abdominal aortic aneurysms (AAA) is considered to be complicated. As matrix degradation contributes to the progression of AAA, the destruction and degradation of elastin fibers caused by an increase in matrix metalloproteinases (MMPs) plays a pivotal role in the development of AAA. Although ets, an essential transcription factor for angiogenesis, regulates MMPs, the role of ets in the development of AAA has not yet been clarified. Thus, we evaluated the role of ets in a rat AAA model using a decoy strategy. Transfection of ODN into AAA was performed by transient aortic perfusion of elastase and by wrapping the AAA in a delivery sheet containing decoy ODN. The inhibitory effect of ets decoy ODN on ets binding activity was confirmed by gel mobility shift assay. MMPs expression was decreased in the aorta transfected with ets decoy ODN as compared to scrambled decoy ODN. Also, ultrasound study demonstrated that elastase-induced aneurismal dilation was significantly suppressed by transfection of ets decoy ODN at 4 weeks after treatment as compared to scrambled decoy ODN. Moreover, the destruction of elastin fibers was inhibited in the aorta transfected with ets decoy ODN, accompanied by a reduction of MMPs expression. An inhibitory effect of decoy ODN on MMP expression was confirmed by ex vivo experiments showing that transfection of decoy ODN into an organ culture of human aorta resulted in significant inhibition of the secretion of both MMP-1 and MMP-9. Here, we demonstrated that ets may play a pivotal role in the progression of AAA through the activation of MMPs in a rat model. Ets might be a potential target to develop pharmacotherapy/gene therapy to treat AAA through the inhibition of MMPs.

An Ets element regulates the transcription of the human 2B4 gene in natural killer cells

2B4 (CD244) acts as an activation receptor on human NK cells, whereas it sends inhibitory signals in murine NK cells. A previous study indicated a prominent role for AP-1 in the transcription of 2B4 gene. To further understand the transcriptional regulation we analyzed the upstream positive regulatory region (-1151 to -704) of the 2B4 promoter. We have identified an Ets element that regulates the 2B4 gene transcription in an AP1 dependent manner.

The Ets-1 transcription factor is required for complete pre-T cell receptor function and allelic exclusion at the T cell receptor beta locus

The pre-T cell receptor (TCR) functions as a critical checkpoint during alphabeta T cell development. Signaling through the pre-TCR controls the differentiation of immature CD4(-)CD8(-)CD25(+)CD44(-) [double-negative (DN)3] thymocytes into CD4(+)CD8(+) double-positive (DP) cells through the CD4(-)CD8(-)CD25(-)CD44(-)(DN4) stage. In addition, pre-TCR activity triggers expansion and survival of thymocytes and inhibits TCRbeta gene rearrangement through a process referred to as allelic exclusion. Whereas many proteins involved in the pre-TCR transduction cascade have been identified, little is known about the nuclear factors associated with receptor function. Here, we use gene targeting to inactivate the Ets-1 transcription factor in mice and analyze pre-TCR function in developing Ets-1-deficient (Ets-1(-/-)) thymocytes. We find that inactivation of Ets-1 impairs the development of DN3 into DP thymocytes and induces an elevated rate of cell death in the DN4 subset. This defect appears specific to the alphabeta lineage because gammadelta T cells maturate efficiently. Finally, the percentage of thymocytes coexpressing two different TCRbeta chains is increased in the Ets-1(-/-) background and, in contrast with wild type, forced activation of pre-TCR signaling does not block endogenous TCRbeta gene rearrangement. These data identify Ets-1 as a critical transcription factor for pre-TCR functioning and for allelic exclusion at the TCRbeta locus.

Developmental Activation of the TCR α Enhancer Requires Functional Collaboration among Proteins Bound Inside and Outside the Core Enhancer

The TCR delta enhancer (Edelta) and TCR alpha enhancer (Ealpha) play critical roles in the temporal and lineage-specific control of V(D)J recombination and transcription at the TCR alphadelta locus, working as a developmental switch controlling a transition from TCR delta to TCR alpha activity during thymocyte development. Previous experiments using a transgenic reporter substrate revealed that substitution of the 116-bp minimal Ealpha, denoted Talpha1-Talpha2, for the entire 1.4-kb Ealpha led to a premature activation of V(D)J recombination. This suggested that binding sites outside of Talpha1-Talpha2 are critical for the strict developmental regulation of TCR alpha rearrangement. We have further analyzed Ealpha to better understand the mechanisms responsible for appropriate developmental regulation in vivo. We found that a 275-bp Ealpha fragment, denoted Talpha1-Talpha4, contains all binding sites required for proper developmental regulation in vivo. This suggests that developmentally appropriate enhancer activation results from a functional interaction between factors bound to Talpha1-Talpha2 and Talpha3-Talpha4. In support of this, EMSAs reveal the formation of a large enhanceosome complex that reflects the cooperative assembly of proteins bound to both Talpha1-Talpha2 and Talpha3-Talpha4. Our data suggest that enhanceosome assembly is critical for developmentally appropriate activation of Ealpha in vivo, and that transcription factors, Sp1 and pCREB, may play unique roles in this process.

Transcriptional Regulation of Human CD5: Important Role of Ets Transcription Factors in CD5 Expression in T Cells

CD5 is a surface receptor constitutively expressed on thymocytes and mature T and B-1a cells. CD5 expression is tightly regulated during T and B cell development and activation processes. In this study we shown that the constitutive expression of CD5 on human T cells correlates with the presence of a DNase I-hypersensitive (DH) site at the 5'-flanking region of CD5. Human CD5 is a TATA-less gene for which 5'-RACE analysis shows multiple transcriptional start sites, the most frequent of which locates within an initiator sequence. Luciferase reporter assays indicate that a 282-bp region upstream of the initiation ATG displays full promoter activity in human T cells. Two conserved Ets-binding sites (at positions -239 and -185) were identified as functionally relevant to CD5 expression by site-directed mutagenesis, EMSAs, and cotransfection experiments. A possible contribution of Sp1 (-115 and -95), c-Myb (-177), and AP-1-like (-151) motifs was also detected. Further DH site analyses revealed an inducible DH site 10 kb upstream of the human CD5 gene in both T and B CD5(+) cells. Interestingly, a 140-bp sequence showing high homology with a murine inducible enhancer is found within that site. The data presented indicate that the 5'-flanking region of human CD5 is transcriptionally active in T cells, and that Ets transcription factors in conjunction with other regulatory elements are responsible for constitutive and tissue-specific CD5 expression.

Ets-1 regulates TNF-alpha-induced matrix metalloproteinase-9 and tenascin expression in primary bronchial fibroblasts

Increased subepithelial deposition of extracellular matrix proteins is a key feature in bronchial asthma. Matrix metalloproteinase-9 (MMP-9) is a proteolytic enzyme that degrades the extracellular matrix. Tenascin is an extracellular matrix glycoprotein that is abundant in thickened asthmatic subbasement membrane. The expression of MMP-9 and tenascin reflects disease activity in asthma and airway remodeling. The molecular mechanisms regulating the expression of these proteins remain unknown. Both MMP-9 and tenascin promoters contain an Ets binding site, suggesting control by Ets-1. Thus, we hypothesized that Ets-1 expression is increased in asthma and that it contributed to enhanced MMP-9 and tenascin expression. To test this hypothesis, we determined the expression of Ets-1 in bronchial biopsies obtained from asthmatic subjects and determined the expression of Ets-1, MMP-9, and tenascin by bronchial fibroblasts activated ex vivo. We observed that nuclear extracts from TNF-alpha-activated fibroblasts showed increased Ets-binding activity. In addition, TNF-alpha-activated fibroblasts had increased expression of Ets-1 mRNA and protein, which preceded an increase in MMP-9 and tenascin mRNA. Furthermore, treatment of fibroblasts with Ets-1 antisense oligonucleotides down-regulated TNF-alpha-induced Ets-1, MMP-9, and, to a lesser extent, tenascin protein expression or activity. Taken together, these data demonstrate that TNF-alpha increases MMP-9 and tenascin expression in bronchial fibroblasts via the transcription factor Ets-1, and suggest a role for Ets-1 in airway remodeling in asthma.

Genomic structure around joining segments and constant regions of swine T-cell receptor alpha/delta (TRA/TRD) locus

A complete genomic region of 131.2 kb including the swine T-cell receptor alpha/delta constant region (TRAC/TRDC) and joining segments (TRAJ/TRDJ) was sequenced. The structure of this region was strikingly conserved in comparison to that of human or mouse. All of the 61 TRAJ segments detected in the human genomic sequence were detected in the swine sequence and the sequence of the protein binding site of T early alpha, the sequence of the alpha enhancer element and the conserved sequence block between TRAJ3 and TRAJ4 are highly conserved. Insertion of the repetitive sequences that interspersed after the differentiation of the species in mammals such as short interspersed nucleotide elements is markedly suppressed in comparison to other genomic regions, while the composition of the mammalian-wide interspersed sequences is relatively conserved in human and swine. This observation indicates the existence of a highly selective pressure to conserve this genomic region around TRAJ throughout the evolution of mammals.

C/EBP alpha and Ets protein family members regulate the human myeloid IgA Fc receptor (Fc alpha R, CD89) promoter

Fc alpha R (CD89), the FcR for IgA, is expressed exclusively in myeloid cells, including monocytes/macrophages, neutrophils, and eosinophils, and is thought to mediate IgA-triggered cellular functions in immunity. Here we demonstrate that the Fc alpha R 5'-flanking region from -102 to -64 relative to the ATG translation initiation codon is essential for promoter activity and contains two functional binding motifs for C/EBP and Ets family members at -74 and -92, respectively. EMSAs and cotransfection experiments show that C/EBP alpha acts as a major activator of the Fc alpha R promoter at least in immature myeloid cells. In addition, we found two additional functional targets of C/EBP alpha at -139 and -127. On the other hand, the Fc alpha R Ets binding motif could bind Elf-1 and mediate the trans-activation by cotransfected Elf-1, but a major component of the complex forming on this site appears to be an unidentified Ets-like nuclear protein that is preferentially detected in cells of hemopoietic origin. Furthermore, separation of the C/EBP and Ets binding sites reduces Fc alpha R promoter activity, suggesting some functional interaction between these factors. As the in vivo role of Fc alpha R is still incompletely defined, these findings reveal the features controlling the Fc alpha R promoter in myeloid lineage and provide a foundation for clarifying regulatory mechanisms of Fc alpha R gene expression associated with its potential roles.

Molecular biology of the Ets family of transcription factors

The Ets family of transcription factors characterized by an evolutionarily-conserved DNA-binding domain regulates expression of a variety of viral and cellular genes by binding to a purine-rich GGAA/T core sequence in cooperation with other transcriptional factors and co-factors. Most Ets family proteins are nuclear targets for activation of Ras-MAP kinase signaling pathway and some of them affect proliferation of cells by regulating the immediate early response genes and other growth-related genes. Some of them also regulate apoptosis-related genes. Several Ets family proteins are preferentially expressed in specific cell lineages and are involved in their development and differentiation by increasing the enhancer or promoter activities of the genes encoding growth factor receptors and integrin families specific for the cell lineages. Many Ets family proteins also modulate gene expression through protein-protein interactions with other cellular partners. Deregulated expression or formation of chimeric fusion proteins of Ets family due to proviral insertion or chromosome translocation is associated with leukemias and specific types of solid tumors. Several Ets family proteins also participate in malignancy of tumor cells including invasion and metastasis by activating the transcription of several protease genes and angiogenesis-related genes.

Retinal neuron activity of ETS domain-binding sites in a nicotinic acetylcholine receptor gene cluster enhancer

Nicotinic acetylcholine receptors (nAchRs) mediate amacrine to ganglion cell synaptic transmission in the developing mammalian retina. The clustered neuronal nAchRs subunit genes, alpha 3 and beta 4, are expressed in amacrine and ganglion cells where they are used to assemble functional receptor subtypes. The transcriptional mechanisms underlying expression of these subunits in retina are not yet known but may involve enhancers that are selectively active in retinal neurons. We previously identified a neuron-selective enhancer, beta 43', whose activity in neural cell lines is dependent on ETS domain-binding sites. To determine whether beta 43' is active in retinal neurons that express the alpha 3 and beta 4 genes, we investigated beta 43' activity in primary dissociated rat retinal cultures. We found that beta 43' is selectively active in retinal neurons compared with retinal non-neuronal cells. This activity was derived primarily from amacrine and ganglion neurons, which are the retinal neuron cell types that express the clustered genes. Moreover, beta 43' was selectively active in retinal neurons compared with cerebral cortical neurons suggesting that it is not a pan-neuronal enhancer. ETS factor-binding sites in the enhancer are required for its retinal neuron activity. These findings suggest that ETS factor interactions with beta 43' control retinal neuron expression of certain nAchR subtypes.

High-dose chemoradiotherapy (HDC) in the Ewing family of tumors (EFT)

EFT is defined by the expression of ews/ets fusion genes. The type of the fusion transcript impacts on the clinical biology. EFT requires risk adapted treatment. A risk-adapted treatment is determined by tumor localisation, tumor stage and volume. For metastatic and relapsed disease the pattern of spread and the time of relapse are the determinants of risk stratification. Staging of Ewing tumors has been considerably improved by magnetic resonance imaging and modern isotope scanning techniques. However, the determination of the extent of the metastatic spread in particular number of involved bones remains an unresolved issue. The prognosis for high-risk Ewing tumors has been improved by multimodal and high-dose radio/chemotherapy (HDC). The concepts for high-dose therapy in Ewing tumors are based on dose response and dose intensity relationships. In single agent HDC most experience exists with Melphalan. Several chemotherapeutic agents have been used in combination HDC with or without TBI such as Adriamycin, BCNU, Busulphan, Carboplatin, Cyclophosphamide, Etoposide, Melphalan, Thiotepa Procarbazin and Vincristine. To date, superiority of any high-dose chemotherapy regimen has not been established. However, the clinical biology, the pattern of spread and the time of relapse determine the prognosis of patient who are eligible for HDC. In particular, patients with multifocal bone or bone marrow metastases have a poorer prognosis than patients with lung metastases. In addition, patients with a relapse within 24 months have a poorer prognosis than patients with a relapse later than 24 months after diagnosis. This review will analyze the results of single- and multi-agent chemotherapy with respect to agent combination, dose and risk stratum of patient population. Future therapeutic modalities for the treatment of EFT might encompass immunotherapeutic and genetic strategies including allogeneic stem cell transplantation.

Extinction of expression of the genes encoding haematopoietic cell-restricted transcription factors in T-lymphoma x fibroblast cell hybrids

We previously reported that expression of the T-cell receptor (TCR) alpha and lck genes is extinguished in hybrids between mouse T-lymphoma EL4 cells and mouse fibroblast B82 cells. In the present study, we found that the activities of the TCRalpha minimum enhancer and the lck promoter monitored by the luciferase or chloramphenicol acetyltransferase (CAT) assays were markedly inhibited in the hybrids. Expression of the TCF-1, LEF-1, GATA-3, Ikaros, c-myb and Fli-1 genes, which encode the haematopoietic cell-restricted transcription factors that appear to be responsible for the activities of the enhancer and the promoter, was fully extinguished or markedly suppressed in the hybrids. On the other hand, expression of the transcription factor genes observed in both parental cells, such as the AML1 and c-ets-1 genes, and that of the genes encoding ubiquitously expressed transcription factors, such as the E2A, CREB and c-ets-2 genes, was not significantly suppressed in the hybrids. These results suggest that the genes encoding haematopoietic cell-restricted transcription factors are targets for negative regulation in fibroblastic background and that the repression of these genes may consequently lead to suppression of the promoter and/or enhancer activities of several T-cell-specific structural genes in T-lymphoma x fibroblast cell hybrids.

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.

Ets target genes: past, present and future

Ets is a family of transcription factors present in species ranging from sponges to human. All family members contain an approximately 85 amino acid DNA binding domain, designated the Ets domain. Ets proteins bind to specific purine-rich DNA sequences with a core motif of GGAA/T, and transcriptionally regulate a number of viral and cellular genes. Thus, Ets proteins are an important family of transcription factors that control the expression of genes that are critical for several biological processes, including cellular proliferation, differentiation, development, transformation, and apoptosis. Here, we tabulate genes that are regulated by Ets factors and describe past, present and future strategies for the identification and validation of Ets target genes. Through definition of authentic target genes, we will begin to understand the mechanisms by which Ets factors control normal and abnormal cellular processes.

Renal expression of the Ets-1 proto-oncogene during progression of rat crescentic glomerulonephritis

The ets-1 proto-oncogene is a member of the transcriptional factor family and was identified by homology to the v-ets oncogene. It was recently demonstrated that Ets-1 protein interacts with the promoter region of the genes coding for proteinases, including matrix metalloproteinase-1 (MMP-1), MMP-3, and urokinase-type plasminogen activator, suggesting that it may play an important role in the regulation of MMP expression. The role of the ets-1 proto-oncogene in advanced glomerular diseases, where extracellular matrix accumulation is observed, remains undefined. In this study, the expression of ets-1 mRNA and protein during the progression of rat crescentic glomerulonephritis was examined using immunohistochemical analysis, reverse transcription-PCR, and in situ hybridization. Passive accelerated anti-glomerular basement membrane-induced nephritis was induced in rats by intravenous injection of nephrotoxic serum. Rats were euthanized on day 7, 14, 21, 28, or 42. Immunohistochemical analysis demonstrated significant upregulation of Ets-1 protein expression in glomeruli and the interstitium in anti-glomerular basement membrane-induced nephritis. The numbers of Ets-1-positive cells were increased 8.8-fold on day 21 in glomeruli (1.2+/-0.1 cells/glomerular cross-section, P<0.001) and sixfold on day 28 in the interstitium (21+/-1.3 cells/mm(2), P<0.001), compared with control samples. Ets-1 protein was predominantly localized in glomerular epithelial cells, endothelial cells, and interstitial cells. A small number of vascular endothelial cells, macrophages, and T cells also expressed Ets-1 protein. MMP-3 deposition was upregulated and positive cells in the interstitium often coexpressed Ets-1, whereas only a few glomerular cells were positive for both MMP-3 and Ets-1 protein. The expression of ets-1 mRNA was also markedly increased in diseased kidneys. The distribution of ets-1 mRNA was similar to that of the protein. These results indicate that overexpression of the ets-1 proto-oncogene by phenotypically altered renal cells might be associated with the pathogenesis of rat crescentic glomerulonephritis.

COT kinase proto-oncogene expression in T cells: implication of the JNK/SAPK signal transduction pathway in COT promoter activation

COT/Tpl-2 proto-oncogene encodes a serine/threonine kinase implicated in cellular activation. In this study we have identified the human COT gene promoter region and three different human COT transcripts. These transcripts, with the same initiation site, display heterogeneity in their 5' untranslated regions and in their subcellular localization. Activation of Jurkat T cells with either calcium ionophore or alphaCD3 and a phorbol ester increases the levels of the different COT transcripts. Analysis of the 5' flanking region of the human COT gene reveals a unique transcription initiation site and a TATA element 20 nucleotides upstream. Transient expression of COT promoter constructs containing a reporter gene indicates that the transcriptional activity of the 5' flanking region of the COT gene is regulated by T cell-activating signals. Cotransfection of a dominant negative version of SEK-2 abolishes the inducible transcriptional activity of COT promoter, indicating that the inducible expression of the COT gene by T cell activating signals is mediated by the JNK/SAPK signal transduction pathway. All these data indicate stringent regulation of COT kinase proto-oncogene expression.

Regulation of transcription in the neuronal nicotinic receptor subunit gene cluster by a neuron-selective enhancer and ETS domain factors

Expression of neurotransmitter receptors encoded by the nicotinic acetylcholine receptor (nAchR) subunit gene cluster depends on coexpression of the beta4, alpha3, and alpha5 subunits in certain kinds of neurons. One way in which coexpression might be achieved is through the regulation of promoters in the cluster by neuron-selective enhancers. The beta43' enhancer is located between the beta4 and alpha3 promoters and it directs cell type-specific expression in cell lines. It is not known, however, whether beta43' is active in neurons. Therefore, we assayed beta43' in dissociated rat sympathetic ganglia cultures, which contain nAchR-positive neurons as well as nAchR-negative non-neuronal cells. Reporters controlled by the alpha3 promoter and beta43' were expressed in a neuron-selective manner; greater than 90% and up to 100% of luciferase expression was detected in neurons. Neuron selectivity was maintained when beta43' was placed next to ubiquitously active viral promoters. In contrast, replacing beta43' with the SV40 enhancer eliminated neuron selectivity. The enhancer is composed of at least two separate but functionally interdependent elements, each of which interacts with a different type of ETS domain factor. These findings support a model in which beta43' controls neuronal expression of one or more genes in the cluster through interactions with a combination of ETS factors.

Transcription factors ets1, NF-kappa B, and Sp1 are major determinants of the promoter activity of the human protein kinase CK2alpha gene

CK2alpha is one of two isoforms of protein kinase CK2, a highly conserved, ubiquitous, and vital phosphotransferase whose expression is kept at constant cellular levels and whose dysregulated expression has been linked to malignant diseases. The upstream sequence of the gene coding for human CK2alpha (CSNK1A1, chromosomal location 20p13) has been examined for promoter location and transcription factor interactions using reporter gene assays (luciferase; HeLa cells), site-directed mutagenesis, electrophoretic mobility shift assays, super-shifts, UV cross-linking, Western blotting, and DNA affinity chromatography. Highest promoter activity has been found in a region comprising positions -9 to 46. Factors Sp1, Ets-1, and NF-kappaB have been identified as interaction partners and, by mutation of individual sites and simultaneous mutations of two or more sites, shown to cross-talk to each other. At least two of the factors (Sp1; NF-kappaB) were susceptible to phosphorylation by CK2 holoenzyme, a tetramer composed of two CK2alpha and two regulatory CK2beta proteins, but not by individual CK2alpha. Because the phosphorylation decreases promoter binding and repeated immunoprecipitation reveals presence of "free" CK2beta in cell extracts, it is tempting to speculate that the gene product CK2alpha might readily form CK2 holoenzyme and feed back onto gene transcription. The data represent the first promoter control analysis of a mammalian CK2alpha gene and provide a hypothesis of how the constant expression level of CK2alpha may be achieved.

Functional analysis of the murine TCR beta-chain gene enhancer

The TCR beta-chain gene enhancer activates transcription and V(D)J recombination in immature thymocytes. In this paper we present a systematic analysis of the elements that contribute to the activity of the murine TCR beta enhancer in mature and immature T cell lines. We identified a region containing the beta E4, beta E5, and beta E6 motifs as the essential core of the TCR beta enhancer in pro-T cells. In mature cells, the core enhancer had low activity and required, in addition, either 5' or 3' flanking sequences whose functions may be partially overlapping. Mutation of any of the six protein binding sites located within the beta E4-beta E6 elements essentially abolished enhancer activity, indicating that this core enhancer contained no redundant elements. The beta E4 and beta E6 elements contain binding sites for ETS-domain proteins and the core binding factor. The beta E5 element bound two proteins that could be resolved chromatographically and that were both essential for enhancer activity.

EAP1/Daxx interacts with ETS1 and represses transcriptional activation of ETS1 target genes

ETS1 is a member of the evolutionarily conserved family of ets genes, which are transcription factors that bind to unique DNA sequences, either alone or by association with other proteins. In this study, we have used the yeast two-hybrid system to identify an ETS1 interacting protein. The ETS1 N-terminal amino acid region was used as bait and an interaction was identified with the Daxx protein, referred to as EAP1 (ETS1 Associated Protein 1)/Daxx. This interactin has been shown to exist in yeast and in vitro. EAP1/Daxx and ETS1 are co-localized in the nucleus of mammalian cells. The region in EAP1/Daxx which specifically binds to ETS1 is located within its carboxy terminal 173 amino acid region. The ETS1 interaction region is located within its N-terminal 139 amino acids and is referred as the Daxx Interaction Domain (DID). The DID appears to be conserved in several other ets family members, as well as in other proteins known to interact with Daxx. The EAP1/Daxx interacts with both isoforms of ETS1, p51-ETS1 and p42-ETS1. Interaction of EAP1/Daxx with ETS1 causes the repression of transcriptional activation of the MMP1 and BCL2 genes. The interaction domains of both ETS1 and EAP1/Daxx are required for this repression and deletion of either domain abolishes this activity.

Regulation of rat cytochrome P450C24 (CYP24) gene expression. Evidence for functional cooperation of Ras-activated Ets transcription factors with the vitamin D receptor in 1,25-dihydroxyvitamin D(3)-mediated induction

Transcription of the rat CYP24 gene is induced by 1, 25-dihydroxyvitamin D(3) (1,25-(OH)(2)D(3)) through two vitamin D response elements (VDREs). A functional Ras-dependent Ets-binding site (EBS) was located downstream from the proximal VDRE and was critical to 1,25(OH)(2)D(3)-mediated induction. Cotransfection of Ets-1 and Ets-2 stimulated induction, which was lost when the EBS was mutated. Multiple nuclear-protein complexes from COS-1 cells bound to the EBS in which three complexes were immunologically related to Ets-1. Transcriptional synergy was observed between the proximal VDRE and adjacent EBS as was the attendant formation of a ternary complex between vitamin D receptor- retinoid X receptor (VDR. RXR) and Ets-1. In the absence of 1,25-(OH)(2)D(3) or in the presence of an inactive proximal VDRE, the EBS failed to respond to exogenous Ets-1. However, Ets-1 increased basal expression when cotransfected with a mutant VDR. The inductive action of 1, 25-(OH)(2)D(3) was substantially increased by Ras, which was ablated by mutagenesis of the EBS or by expression of a mutated Ets-1 protein (T38A). EBS contribution to hormone induction was prevented by manumycin A, an inhibitor of Ras farnesylation. A fundamental role was established for transcriptional cooperation between Ras-activated Ets proteins and the VDR.RXR complex in mediating 1, 25-(OH)(2)D(3) action on the CYP24 promoter.

DNase I footprinting of the human interleukin-5 gene promoter

A characteristic feature of allergic asthma is the overexpression of the T helper type 2 (Th2) cytokines interleukin-4 (IL-4), IL-5 and IL-13 by T lymphocytes. Of these cytokines, IL-5 is critical for the growth, survival and recruitment of eosinophils which are thought to be responsible for the tissue damage observed in asthmatic airways. The expression of human IL-5 is primarily regulated at the transcriptional level; however, little is known about the mechanisms that control its transcription. Using nuclear extracts from allergen-specific human T-cell clones we have performed DNase I footprinting of the human IL-5 promoter in order to establish sites occupied by transcription factors. We show footprints covering the conserved lymphokine element 0 ¿(CLE0) -60 to -44 base pairs (bp) and GATA (-73 to -62 bp) elements, which have previously been identified to be important in the regulation of the murine IL-5 promoter. We also describe a footprint covering a considerably extended Octamer binding site (-249 to -217 bp), which encompasses two hitherto unidentified CCAAT/enhancer binding protein consensus binding sites. We have also identified a previously unknown Ets binding site (-274 to -264 bp). These novel data on the regions of the human IL-5 promoter that are bound by transcription factors should allow dissection of the regulatory mechanisms involved in the transcription of IL-5 in the T-helper lymphocytes of asthmatics.

Implication of N-acetylglucosaminyltransferases III and V in cancer: gene regulation and signaling mechanism

N-acetylglucosaminyltransferases III (GnT-III) and V (GnT-V) play a pivotal role in the processing of N-linked glycoproteins, and are highly involved in cancer progression and metastasis. Expression of GnT-III and GnT-V in the liver is enhanced during hepatocarcinogenesis, although they are not expressed in the normal liver. Gene expression of GnT-V is regulated by a transcriptional factor, ets-1, which is involved in angiogenesis and invasion of tumor cells. When the formation of the product of GnT-V, GlcNAc-beta1-6 branches, is inhibited by overexpression of GnT-III, lung metastasis of melanoma cells is suppressed. Modification of glycoprotein receptors such as the receptors for epidermal growth factor and nerve growth factor by GnT-III sense transfection changes an intracellular signaling pathway, which may lead to a variety of biological alterations in tumor cells. In this review, we focus on cancer progression and metastasis in relation to GnT-III and GnT-V.

Regulation of the GnT-V promoter by transcription factor Ets-1 in various cancer cell lines

Although the precise role of oligosaccharides in metastasis is presently unknown, numerous studies suggest that the beta1-6 branching structure of N-linked oligosaccharides plays a role in tumor metastasis. N-Acetylglucosaminyltransferase V (GnT-V), which catalyzes the formation of the beta1-6 branch, therefore appears to play a crucial role in tumor metastasis. Recently, we demonstrated that the expression of the GnT-V gene is regulated by a transcriptional factor, Ets-1 (Kang, R., Saito, H., Ihara, Y., Miyoshi, E., Koyama, N., Sheng, Y., and Taniguchi, N. (1996) J. Biol. Chem. 271, 26706-26712). In this study, we report an investigation of the general requirement for Ets-1 in the expression of GnT-V in cancer cell lines. In 16 cancer cell lines, the levels of GnT-V mRNA were closely correlated with ets-1 expression (r = 0.97; p < 0.0001). An increase in ets-1 levels by transfection of its cDNA led to an enhancement in GnT-V expression in cells that normally expressed low levels of ets-1. In contrast, the transfection of dominant negative ets-1 into cells that express high levels of ets-1 resulted in a decrease in GnT-V expression. Although Ets-1 cooperates with c-Jun in certain gene expressions, this was not the case in the regulation of the GnT-V gene. These results suggest that Ets-1 plays a significant role in regulating the expression of GnT-V in a variety of cancers and might be involved in the potential for malignancy via the action of GnT-V.

The golden hamster aphrodisin gene. Structure, expression in parotid glands of female animals, and comparison with a similar murine gene

The so-called lipocalins are a family of extracellular proteins that are known to typically fulfill tasks as transport proteins for small hydrophobic molecules. However, in the last decade, a large diversity has been described concerning their functions, for example as enzymes, immunomodulators, or proteins involved in coloration and pheromone action. Aphrodisin belongs to those lipocalins, which are of significant importance for the pheromonal stimulation of copulatory behavior in male hamsters. We recently succeeded in characterizing the corresponding cDNA and demonstrated the expression of the aphrodisin gene in the vagina, uterus, and Bartholin's glands of female hamsters. Here we report the structure of the aphrodisin gene and the functionality of its promoter region. We further compare the aphrodisin gene to the related gene for mouse odorant-binding protein 1a, indicating similar functions of their products. As a novelty, we show that the aphrodisin gene, in addition to the above-mentioned tissues, is also expressed in female hamster parotid glands. In contradiction to the results expected, we finally demonstrate that aphrodisin already occurs in vaginal discharge before the female animals reach fertility. These findings may lead to the identification of as yet unknown aphrodisin functions.

Cloning and characterization of GETS-1, a goldfish Ets family member that functions as a transcriptional repressor in muscle

An Ets transcription factor family member, GETS-1, was cloned from a goldfish retina cDNA library. GETS-1 contains a conserved Ets DNA-binding domain at its N-terminus and is most similar to ternary complex factor (TCF) serum-response-factor protein-1a (SAP-1a). GETS-1 is expressed in many tissues, but is enriched in retina and brain. As with the TCFs SAP-1a and ets-related protein (ERP), overexpression of the GETS-1 promoter suppresses nicotinic acetylcholine receptor epsilon-subunit gene expression in cultured muscle cells. A consensus Ets binding site sequence in the promoter of the epsilon-subunit gene is required for GETS-1-mediated repression. GETS-1 repressor activity is abrogated by overexpression of an activated Ras/mitogen-activated protein kinase (MAP kinase) or by mutation of Ser-405, a MAP kinase phosphorylation site in GETS-1. Fusion proteins created between GETS-1 and the Gal4 DNA-binding domain show that, like other TCFs, GETS-1 contains a C-terminal activation domain that is activated by a Ras/MAP kinase signalling cascade. Interestingly, mutation of Ser-405 located within this activation domain abrogated transcriptional activation of the fusion protein.

Fine-mapping of the mouse T lymphocyte fraction (Tlf) locus on chromosome 9: association with autoimmune diabetes

Tlf (T lymphocyte fraction) defines a locus that governs the unusually high fraction of circulating T lymphocytes in the nonobese diabetic (NOD) mouse. We previously mapped Tlf to proximal Chromosome 9 in BC1 mice. Here, Tlf was tine-mapped on Chromosome 9 using 8 markers covering the 43 cM interval from D9Mit90 at 9 cM to D9Mit35 at 52 cM. Markers for diabetic genes on Chromosomes 3, 4, 5, 6, and 17 were also examined for effects on the Tlf phenotype. By both parametric and nonparametric tests. Tlf associated with two areas on Chromosome 9, one with the segment bounded by D9Mit66 (15 cM) and D9Mit2 (17 cM) and a second region near D9Mit71 (29 cM). This linkage pattern was observed both in BC1 and F2 populations. Thus, the Tlf phenotype is possibly governed by two genes on Chromosome 9. An influence by sex on the penetrance of Tlf was evident in that linkage was strongest for female F2 mice and male BC1 mice. One locus controlling the T lymphocyte fraction may be Idd2 since historically a subline of NOD mice with a low T cell fraction showed a low incidence of diabetes. Candidate genes for Tlf are Ets1 and Fli1, proximally and Igif distally.

Developmental regulation of V(D)J recombination at the TCR alpha/delta locus

The T-cell receptor (TCR) alpha/delta locus includes a large number of V, D, J and C gene segments that are used to produce functional TCR delta and TCR alpha chains expressed by distinct subsets of T lymphocytes. V(D)J recombination events within the locus are regulated as a function of developmental stage and cell lineage during T-lymphocyte differentiation in the thymus. The process of V(D)J recombination is regulated by cis-acting elements that modulate the accessibility of chromosomal substrates to the recombinase. Here we evaluate how the assembly of transcription factor complexes onto enhancers, promoters and other regulatory elements within the TCR alpha/delta locus imparts developmental control to VDJ delta and VJ alpha rearrangement events. Furthermore, we develop the notion that within a complex locus such as the TCR alpha/delta locus, highly localized and region-specific control is likely to require an interplay between positive regulatory elements and blocking or boundary elements that restrict the influence of the positive elements to defined regions of the locus.

Transcriptional repression by AML1 and LEF-1 is mediated by the TLE/Groucho corepressors

The mammalian AML/CBFalpha runt domain (RD) transcription factors regulate hematopoiesis and osteoblast differentiation. Like their Drosophila counterparts, most mammalian RD proteins terminate in a common pentapeptide, VWRPY, which serves to recruit the corepressor Groucho (Gro). Using a yeast two-hybrid assay, in vitro association and pull-down experiments, we demonstrate that Gro and its mammalian homolog TLE1 specifically interact with AML1 and AML2. In addition to the VWRPY motif, other C-terminal sequences are required for these interactions with Gro/TLE1. TLE1 inhibits AML1-dependent transactivation of the T cell receptor (TCR) enhancers alpha and beta, which contain functional AML binding sites, in transfected Jurkat T cells. LEF-1 is an additional transcription factor that mediates transactivation of TCR enhancers. LEF-1 and its Drosophila homolog Pangolin (Pan) are involved in the Wnt/Wg signaling pathway through interactions with the coactivator beta-catenin and its highly conserved fly homolog Armadillo (Arm). We show that TLE/Gro interacts with LEF-1 and Pan, and inhibits LEF-1:beta-catenin-dependent transcription. These data indicate that, in addition to their activity as transcriptional activators, AML1 and LEF-1 can act, through recruitment of the corepressor TLE1, as transcriptional repressors in TCR regulation and Wnt/Wg signaling.

Cooperation among multiple transcription factors is required for access to minimal T-cell receptor alpha-enhancer chromatin in vivo

To understand the molecular basis for the dramatic functional synergy between transcription factors that bind to the minimal T-cell receptor alpha enhancer (Ealpha), we analyzed enhancer occupancy in thymocytes of transgenic mice in vivo by genomic footprinting. We found that the formation of a multiprotein complex on this enhancer in vivo results from the occupancy of previously identified sites for CREB/ATF, TCF/LEF, CBF/PEBP2, and Ets factors as well as from the occupancy of two new sites 5' of the CRE site, GC-I (which binds Sp1 in vitro) and GC-II. Significantly, although all sites are occupied on a wild-type Ealpha, all sites are unoccupied on versions of Ealpha with mutations in the TCF/LEF or Ets sites. Previous in vitro experiments demonstrated hierarchical enhancer occupancy with independent binding of LEF-1 and CREB. Our data indicate that the formation of a multiprotein complex on the enhancer in vivo is highly cooperative and that no single Ealpha binding factor can access chromatin in vivo to play a unique initiating role in its assembly. Rather, the simultaneous availability of multiple enhancer binding proteins is required for chromatin disruption and stable binding site occupancy as well as the activation of transcription and V(D)J recombination.

Aging-related deficiency of CD28 expression in CD4+ T cells is associated with the loss of gene-specific nuclear factor binding activity

Changes in T cell populations and concomitant perturbation of T cell effector functions have been postulated to account for many aging-related immune dysfunctions. Here, we report that high frequencies of CD28(null) CD4+ T cells were found in elderly individuals. Because deviations in the function of these unusual CD4+ T cells might be directly related to CD28 deficiency, we examined the molecular basis for the loss of CD28 expression in CD4+ T cells. In reporter gene bioassays, the minimal promoter of the CD28 gene was mapped to the proximal 400 base pairs (bp) of the 5' untranslated region. CD28 deficiency was associated with the loss of two noncompeting binding activities within a 67-bp segment of the minimal promoter. These binding activities were not competed by consensus Ets, Elk, or AP3 motifs that were found within the sequence stretch. The DNA-protein complexes were also not recognized by antibodies to Ets-related transcription factors. Furthermore, introduction of mutations into the 67-bp segment at positions corresponding to the two DNA-protein interaction sites, i.e. nucleotides spanning -206 to -179 and -171 to -148, resulted in the loss of specific nuclear factor binding activities and the abrogation of promoter activity. These observations implicate at least two regulatory motifs in the constitutive expression of CD28. The loss of binding activity of trans-acting factors specific for these sequences may contribute to the accumulation CD4+CD28(null) T cells during aging.

Elf-1 Regulates Basal Expression from the T Cell Antigen Receptor ζ-Chain Gene Promoter

In mature T cells, limited synthesis of the TCR-ζ subunit is primarily responsible for regulating surface expression of TCRs. Transcription of ζ is directed by a complex promoter that includes two potential binding sites for the Ets family of transcription factors at −52 (zEBS1) and −135 (zEBS2). Mutation of these two sites results in a marked reduction of transcription from this promoter. Using electrophoretic mobility shift analysis, Elf-1 was demonstrated to be the Ets family member that binds to these sites. One site, zEBS1, matches the optimal Elf-1 consensus sequence in eight of nine bases, making it the best match of any known mammalian Elf-1 binding site. A role for Elf-1 in TCR-ζ trans-activation was confirmed by ectopic expression of Elf-1 in COS-7 cells. This resulted in an increase in TCR-ζ promoter activity that mapped to zEBS1 and zEBS2. Additional support for the involvement of Elf-1 in TCR-ζ trans-activation derives from the finding that a GAL4-Elf-1 fusion protein trans-activated TCR-ζ promoter constructs that had been modified to contain GAL4 DNA binding sites. These results demonstrate that Elf-1 plays an essential role in the trans-activation of a constitutively expressed T cell-specific gene, and that trans-activation occurs in the context of the native promoter in both lymphoid and nonlymphoid cells. Taken together with the existing literature, these data also suggest that the requirement for inducible factors in Elf-1-mediated trans-activation may decrease as the affinity and number of Elf-1 sites increase.