Definition of an Ets1 protein domain required for nuclear localization in cells and DNA-binding activity in vitro

Transcription Factor ETS-1 and Reactive Oxygen Species: Role in Vascular and Renal Injury

The E26 avian erythroblastosis virus transcription factor-1 (ETS-1) is a member of the ETS family and regulates the expression of a variety of genes including growth factors, chemokines and adhesion molecules. Although ETS-1 was discovered as an oncogene, several lines of research show that it is up-regulated by angiotensin II (Ang II) both in the vasculature and the glomerulus. While reactive oxygen species (ROS) are required for Ang II-induced ETS-1 expression, ETS-1 also regulates the expression of p47phox, which is one of the subunits of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and a major source of ROS in the kidney and vasculature. Thus, there appears to be a positive feedback between ETS-1 and ROS. ETS-1 is also upregulated in the kidneys of rats with salt-sensitive hypertension and plays a major role in the development of end-organ injury in this animal model. Activation of the renin angiotensin system is required for the increased ETS-1 expression in these rats, and blockade of ETS-1 or haplodeficiency reduces the severity of kidney injury in these rats. In summary, ETS-1 plays a major role in the development of vascular and renal injury and is a potential target for the development of novel therapeutic strategies to ameliorate end-organ injury in hypertension.

The role of the transcription factor Ets1 in carcinoma

Ets1 belongs to the large family of the ETS domain family of transcription factors and is involved in cancer progression. In most carcinomas, Ets1 expression is linked to poor survival. In breast cancer, Ets1 is primarily expressed in the triple-negative subtype, which is associated with unfavorable prognosis. Ets1 contributes to the acquisition of cancer cell invasiveness, to EMT (epithelial-to-mesenchymal transition), to the development of drug resistance and neo-angiogenesis. The aim of this review is to summarize the current knowledge on the functions of Ets1 in carcinoma progression and on the mechanisms that regulate Ets1 activity in cancer.

The oncogene ERG: a key factor in prostate cancer

ETS-related gene (ERG) is a member of the E-26 transformation-specific (ETS) family of transcription factors with roles in development that include vasculogenesis, angiogenesis, haematopoiesis and bone development. ERG's oncogenic potential is well known because of its involvement in Ewing's sarcoma and leukaemia. However, in the past decade ERG has become highly associated with prostate cancer development, particularly as a result of a gene fusion with the promoter region of the androgen-induced TMPRRSS2 gene. We review ERG's structure and function, and its role in prostate cancer. We discuss potential new therapies that are based on targeting ERG.

Transcription factor avian erythroblastosis virus E26 oncogen homolog-1 is a novel mediator of renal injury in salt-sensitive hypertension

Transcription factor E26 transformation-specific sequence-1 (ETS-1) is a transcription factor that regulates the expression of a variety of genes, including growth factors, chemokines, and adhesion molecules. We recently demonstrated that angiotensin II increases the glomerular expression of ETS-1 and that blockade of ETS-1 ameliorates the profibrotic and proinflammatory effects of angiotensin II. The Dahl salt-sensitive rat is a paradigm of salt-sensitive hypertension associated with local activation of the renin-angiotensin system. In these studies, we determined whether: (1) salt-sensitive hypertension is associated with renal expression of ETS-1 and (2) ETS-1 participates in the development of end-organ injury in salt-sensitive hypertension. Dahl salt-sensitive rats were fed a normal-salt diet (0.5% NaCl diet) or a high-salt diet (4% NaCl) for 4 weeks. Separate groups on high-salt diet received an ETS-1 dominant-negative peptide (10 mg/kg/d), an inactive ETS-1 mutant peptide (10 mg/kg/d), the angiotensin II type 1 receptor blocker candesartan (10 mg/kg/d), or the combination high-salt diet/dominant-negative peptide/angiotensin II type 1 receptor blocker for 4 weeks. High-salt diet rats had a significant increase in the glomerular expression of the phosphorylated ETS-1 that was prevented by angiotensin II type 1 receptor blocker. ETS-1 blockade reduced proteinuria, glomerular injury score, fibronectin expression, urinary transforming growth factor-β excretion, and macrophage infiltration. Angiotensin II type 1 receptor blocker reduced proteinuria, glomerular injury score, and macrophage infiltration, whereas concomitant ETS-1 blockade and angiotensin II type 1 receptor blocker had additive effects and reduced interstitial fibrosis. Our studies demonstrated that salt-sensitive hypertension results in increased glomerular expression of phosphorylated ETS-1 and suggested that ETS-1 plays an important role in the pathogenesis of end-organ injury in salt-sensitive hypertension.

The transcription factor E26 transformation-specific sequence-1 mediates neointima formation in arteriovenous fistula

Hemodialysis vascular access dysfunction contributes to increased morbidity and mortality in hemodialysis patients. Arteriovenous fistula (AVF) is the preferred type of vascular access for hemodialysis but has high rates of dysfunction, in part because of excessive neointima formation. The transcription factor E26 transformation-specific sequence-1 (ETS-1) is a mediator of proinflammatory responses in hypertension and endovascular injury. We examined the role of ETS-1 in the formation of neointima in AVF. Right carotid artery to internal jugular vein fistulas were created in C57BL/6 mice and assigned to treatment with an ETS-1-dominant negative peptide (ETS-DN), an inactive mutant peptide (ETS-MU), or vehicle (n=6 per group). After 7 and 21 days, AVFs or contralateral internal jugular veins were processed for PCR, immunofluorescence, immunohistochemistry, and morphometry. In AVFs, ETS-1 mRNA increased 2.5-fold at 7 days and 4-fold at 21 days. By immunofluorescence, we confirmed increased expression of ETS-1 predominantly in the neointima and overlying endothelium. Similarly, ETS-1 expression increased in human AVFs compared with normal veins. In mice, ETS-DN, but not ETS-MU, reduced neointima formation at days 7 and 21 and reduced the expression of nitric oxide synthase 2, NADPH oxidase (NOX) 2, NOX4, E-selectin, and monocyte chemotactic protein-1. Shear stress increased ETS-1 phosphorylation in human umbilical vein cells in a NOX-dependent manner, demonstrating a role for reactive oxygen species in ETS-1 activation. These results unveil the role of ETS-1 as a mediator of neointima formation in AVF and may result in the development of novel strategies for the treatment of AVF dysfunction.

Nuclear Respiratory Factor 2β (NRF-2β) recruits NRF-2α to the nucleus by binding to importin-α:β via an unusual monopartite-type nuclear localization signal

Nuclear respiratory factor 2 (NRF-2) is a mammalian transcription factor composed of two distinct and unrelated proteins: NRF-2α, which binds to DNA through its Ets domain, and NRF-2β, which contains the transcription activation domain. The activity of NRF-2 in neurons is regulated by nuclear localization; however, the mechanism by which NRF-2 is imported into the nucleus remains unknown. By using in vitro nuclear import assays and immuno-cytofluorescence, we dissect the nuclear import pathways of NRF-2. We show that both NRF-2α and NRF-2β contain intrinsic nuclear localization signals (NLSs): the Ets domain within NRF-2α and the NLS within NRF-2β (amino acids 311/321: EEPPAKRQCIE) that is recognized by importin-α:β. When NRF-2α and NRF-2β form a complex, the nuclear import of NRF-2αβ becomes strictly dependent on the NLS within NRF-2β. Therefore, the nuclear import mechanism of NRF-2 is unique among Ets factors. The NRF-2β NLS contains only two lysine/arginine residues, unlike other known importin-α:β-dependent NLSs. Using ELISA-based binding assays, we show that it is bound by importin-α in almost the same manner and with similar affinity to that of the classical monopartite NLSs, such as c-myc and SV40 T-antigen NLSs. However, the part of the tryptophan array of importin-α that is essential for the recognition of classical monopartite NLSs by generating apolar pockets for the P3 and the P5 lysine/arginine side chains is not required for the recognition of the NRF-2β NLS. We conclude that the NRF-2β NLS is an unusual but is, nevertheless, a bona fide monopartite-type NLS.

Mapping of ESE-1 subdomains required to initiate mammary epithelial cell transformation via a cytoplasmic mechanism

BACKGROUND

The ETS family transcription factor ESE-1 is often overexpressed in human breast cancer. ESE-1 initiates transformation of MCF-12A cells via a non-transcriptional, cytoplasmic process that is mediated by a unique 40-amino acid serine and aspartic acid rich (SAR) subdomain, whereas, ESE-1's nuclear transcriptional property is required to maintain the transformed phenotype of MCF7, ZR-75-1 and T47D breast cancer cells.

RESULTS

To map the minimal functional nuclear localization (NLS) and nuclear export (NES) signals, we fused in-frame putative NLS and NES motifs between GFP and the SAR domain. Using these GFP constructs as reporters of subcellular localization, we mapped a single NLS to six basic amino acids (242 HGKRRR 247) in the AT-hook and two CRM1-dependent NES motifs, one to the pointed domain (NES1: 102 LCNCALEELRL 112) and another to the DNA binding domain (DBD), (NES2: 275 LWEFIRDILI 284). Moreover, analysis of a putative NLS located in the DBD (316 GQKKKNSN 323) by a similar GFP-SAR reporter or by internal deletion of the DBD, revealed this sequence to lack NLS activity. To assess the role of NES2 in regulating ESE-1 subcellular localization and subsequent transformation potency, we site-specifically mutagenized NES2, within full-length GFP-ESE-1 and GFP-NES2-SAR reporter constructs. These studies show that site-specific mutation of NES2 completely abrogates ESE-1 transforming activity. Furthermore, we show that exclusive cytoplasmic targeting of the SAR domain is sufficient to initiate transformation, and we report that an intact SAR domain is required, since block mutagenesis reveals that an intact SAR domain is necessary to maintain its full transforming potency. Finally, using a monoclonal antibody targeting the SAR domain, we demonstrate that the SAR domain contains a region accessible for protein - protein interactions.

CONCLUSIONS

These data highlight that ESE-1 contains NLS and NES signals that play a critical role in regulating its subcellular localization and function, and that an intact SAR domain mediates MEC transformation exclusively in the cytoplasm, via a novel nontranscriptional mechanism, whereby the SAR motif is accessible for ligand and/or protein interactions. These findings are significant, since they provide novel molecular insights into the functions of ETS transcription factors in mammary cell transformation.

The transcription factor ETS-1 mediates proinflammatory responses and neointima formation in carotid artery endoluminal vascular injury

The transcription factor ETS-1 is a critical mediator of vascular inflammation and hypertrophy in hypertension. We tested the hypothesis that ETS-1 is a mediator of proinflammatory responses and neointimal hyperplasia after balloon injury of the carotid artery. For this study, we took advantage of the availability of an ETS-1 dominant-negative (DN) peptide. Sprague-Dawley rats were assigned to treatment with ETS-1 DN, a mutant peptide (ETS-1 MU), or vehicle (Veh) and subjected to balloon injury of the carotid artery. After 2, 24 hours, and 14 days, the rats were euthanized, and both carotid arteries were processed for real-time polymerase chain reaction (2 hours), immunofluorescence and immunohistochemistry (24 hours), and morphometric analysis (14 days). ETS-1 mRNA was up regulated (2.4-fold) in injured carotid arteries. By immunofluorescence, we confirmed increased nuclear expression of ETS-1 24 hours postinjury. The carotid artery mRNA expression of monocyte chemotactic protein-1, cytokine-induced neutrophil chemoattractant-2, P-selectin, E-selectin, vascular cell adhesion molecule, and intercellular adhesion molecule was increased 2 hours after injury. ETS-1 DN but not ETS-1 MU significantly reduced mRNA and protein expression for monocyte chemotactic protein-1, P-selectin, and E-selectin in injured arteries. These changes were accompanied by concomitant reductions in vascular monocyte and leukocyte infiltration. Moreover, treatment with ETS-1 DN but not ETS-1 MU resulted in a 50% reduction in neointima formation at day 14 after balloon injury. This study unveils the role of ETS-1 as a mediator of inflammation and neointima formation in a model of carotid artery balloon injury and may result in the development of novel strategies in the treatment of vascular injury.

Identification of functional domains in TdIF1 and its inhibitory mechanism for TdT activity

TdT interacting factor 1 (TdIF1) was identified as a protein that binds to terminal deoxynucleotidyltransferase (TdT) to negatively regulate TdT activity. TdT is a template-independent DNA polymerase that catalyzes the incorporation of deoxynucleotides to the 3'-hydroxyl end of DNA templates to increase the junctional diversity of immunoglobulin or T-cell receptor (TcR) genes. Here, using bioinformatics analysis, we identified the TdT binding, DNA binding and dimerization regions, and nuclear localization signal (NLS) in TdIF1. TdIF1 bound to double-stranded DNA (dsDNA) through three DNA binding regions: residues 1-75, the AT-hook-like motif (ALM) and the predicted helix-turn-helix (HTH) motif. ALM in TdIF1 preferentially bound to AT-rich DNA regions. NLS was of the bipartite type and overlapped ALM. TdIF1 bound to the Pol beta-like region in TdT and blocked TdT access to DNA ends. In the presence of dsDNA, however, TdIF1 bound to dsDNA to release TdT from the TdIF1/TdT complex and to exhibit TdT activity, implying that active TdT released microenvironmentally concentrates around AT-rich DNA to synthesize DNA.

Curcumin down-regulates Ets-1 and Bcl-2 expression in human endometrial carcinoma HEC-1-A cells

OBJECTIVE

Curcumin has been demonstrated to have an anti-tumor activity but the underlying molecular mechanisms are not fully uncovered. The present study was undertaken to determine the effect of curcumin on the expression of the proto-oncogene Ets-1 and the anti-apoptotic molecule Bcl-2 in human endometrial adenocarcinoma HEC-1-A cells.

METHODS

Confluent HEC-1-A cells were treated with curcumin at various doses for 16 h or at 60 microM for various time points. At the end of the designated treatments, changes in cell morphology, DNA fragmentation and protein contents of Ets-1 and Bcl-2 were determined, respectively, by light microscopy, DNA laddering assay and Western blot analysis. As an initial step towards understanding whether Ets-1 was a possible up-stream regulator of Bcl-2 expression in HEC-1-A cells and if so, whether curcumin could attenuate the Ets-1-induced up-regulation of Bcl-2 expression, cells were transiently transfected with an Ets-1/GFP (Green Fluorescence Protein) fusion construct and the transfectants were treated with 60 microM curcumin for 16 h, followed by whole cell lysate preparation for Western blot analysis of Bcl-2 protein contents.

RESULTS

Curcumin induced apoptosis-like morphological changes and DNA degradation and decreased basal levels of Ets-1 and Bcl-2 protein contents in HEC-1-A cells in a time- and dose-dependent manner. Overexpression of Ets-1 in the cell resulted in an increase in Bcl-2 protein contents and that increase was attenuated by curcumin treatment.

CONCLUSIONS

Curcumin down-regulates Ets-1 and Bcl-2 expression and induces apoptosis in HEC-1-A cells, suggesting a novel molecular mechanism for the anti-tumor activity of curcumin.

The Ets-1 transcription factor is involved in pterygial angiogenesis

Pterygial pathology is characterized by abnormal corneal epithelial proliferation, stromal modulation, matrix degradation and a strong tendency for otherwise absent corneal vascularization. As the proto-oncogene Ets-1 is known to play a key role in angiogenesis and matrix degradation in other tissues, its involvement in corneal vascularization was investigated. Fifteen pterygia representing two groups were studied. Group 1 consisted of five clinically active pterygia, and group 2 consisted of 10 samples of clinically non-active pterygia. (35)S-labelled ets-1 antisense and sense riboprobes were used for in-situ hybridization of Ets-1 transcription factor in all pterygia. The cytoplasm of blood vessel endothelial cells showed strong expression of ets-1 mRNA in all group 1 pterygia. In contrast, no expression of ets-1 was found in group 2 pterygia. Proto-oncogene ets-1 expression has been shown for the first time in the metaplastic pterygium, an eye tissue of unknown pathogenesis.

Regulation of vascular inflammation and remodeling by ETS factors

The ETS (E26 Transformation-specific Sequence) factors are comprised of a family of transcription factors that share a highly conserved DNA binding domain. Although originally described for their role as protooncogenes in the development of several types of human cancer, they have subsequently been shown to regulate a wide variety of biological processes including cellular growth and differentiation under normal and pathological conditions. As transcription factors, they can either function as activators or repressors of gene expression. Several ETS family members are expressed in cells of vascular origin, including endothelial cells and vascular smooth muscle cells, where they regulate the expression of a number of vascular-specific genes. In the past few years, emerging evidence supports a novel role for selected ETS family members in the regulation of vascular inflammation and remodeling. ETS factor expression can be induced by proinflammatory cytokines, growth factors, and vasoactive peptides. Examples of some of the target genes regulated by ETS factors include adhesion molecules, chemokines, and matrix metalloproteinases. Targeted disruption of selected ETS family members such as Ets-1 in mice is associated with marked reductions in the recruitment of inflammatory cells and vascular remodeling in response to systemic administration of the vasoactive peptide angiotensin II. The purpose of this review is to provide an overview of recent advances that have been made in defining a role for selected members of the ETS transcription factor family in the regulation of vascular-specific gene expression, vascular inflammation, and remodeling.

Identification of the nuclear localization motif in the ETV6 (TEL) protein

ETV6, or Translocation-Ets-Leukemia (TEL), is an ETS family transcriptional repressor that is essential for establishing hematopoiesis in neonatal bone marrow, and is frequently a target of chromosomal translocations in human cancer. ETV6 is predominantly a nuclear phosphoprotein that represses transcription by binding directly to the promoters of target genes. The nuclear localization mechanism of ETV6, however, is not well understood. In this report, we provide evidence that a nuclear localization signal (NLS) exists in the C-terminal region of ETV6. ETV6 proteins with mutations outside of amino acids 332-452 localize to the nucleus, whereas proteins with mutations within amino acids 332-452 remain in the cytoplasm. Furthermore, when a fragment of ETV6 comprised of amino acids 332-452 was fused to cytoplasmic beta-galactosidase protein, the fusion protein was able to enter the nucleus. These results strongly indicate that residues 332-452 mediate nuclear localization of ETV6.

Identification of multiple nuclear localization signals in murine Elf3, an ETS transcription factor

We investigated nuclear localization signal (NLS) determinants within the AT-hook and ETS DNA-binding domains of murine Elf3 (mElf3), a member of the subfamily of epithelium-specific ETS transcription factors. Deletion mutants containing the AT-hook, ETS domain or both localized strictly in the nucleus, suggesting that these individual domains contain independent NLS motif(s). Within the AT-hook domain, four basic residues (244KRKR247) were critical for strong NLS activity, and two potent bipartite NLS motifs (236-252 and 249-267) were sufficient for nuclear import of mElf3, although less efficient than the full domain. In addition, one stretch of basic residues (318KKK320) within the ETS domain appears to be essential for mElf3 nuclear localization. Taken together, mElf3 contains multiple NLS motifs, which may function cooperatively to effect efficient nuclear transport.

Ultrastructural study of depolarization-induced translocation of NRF-2 transcription factor in cultured rat visual cortical neurons

Nuclear respiratory factor (NRF)-2 or GA-binding protein is a potential transcriptional, bigenomic coordinator of mitochondrial and nuclear-encoded subunits of cytochrome oxidase genes. It is composed of an alpha subunit that binds DNA and a beta subunit that has the transactivating domain. Previously, we found that the level of NRF-2 paralleled that of cytochrome oxidase under normal and functionally altered states. The goal of our present study was to increase the resolution to the ultrastructural level and to quantify changes before and after depolarizing stimulation. We used a pre-embedding immunogold-silver method for the two subunits of NRF-2 in cultured rat visual cortical neurons. NRF-2alpha and beta were normally located in both the nucleus and the cytoplasm. In the nucleus, both subunits were associated primarily with euchromatin rather than heterochromatin, consistent with active involvement in transcription. In the cytoplasm, they were associated mainly with free ribosomes and occasionally with the Golgi apparatus and the outer membrane of the nuclear envelope. Labelling was not found in the mitochondria, confirming the specificity of the antibodies. Neuronal depolarization by KCl for 5 h induced a six- to seven-fold increase in the nuclear-to-cytoplasmic ratio of both subunits (P < 0.001) without increases in total labelling densities. These results strongly indicate that both NRF-2alpha and NRF-2beta respond to increased neuronal activity by translocating from the cytoplasm to the nucleus, where they engage in transcriptional activation of target genes. Our results also indicate that the cytoplasmic to nuclear movement of transcription factors is a dynamic process induced by neuronal activity.

Mutual repression of transcriptional activation between the ETS-related factor ERG and estrogen receptor

Transcription factors are known to interact with each other to modulate their transcriptional activity. In this study, we found that the transcriptional activity of human Erg (one of the Ets family-transcription factors) was repressed by several nuclear receptors, including human estrogen receptor ERalpha, nonsteroid receptors and orphan receptors. Conversely, Erg inhibited ERalpha-dependent transcription. These reciprocal functional interactions extended to other nuclear receptors such as thyroid hormone and retinoic acid receptors, as well as to Fli1, an ERG-related ETS factor. Although similarly inhibited by overexpression of the orphan nuclear receptors ERR1 and RORalpha, ERG activity was unaffected by either REV-ERBalpha1 or COUP-TFII. The antagonism between ERG and ERalpha did not depend on DNA binding inhibition or direct protein-protein interactions. Repression of ERalpha-dependent transcription required the carboxyterminal and aminoterminal transactivation domains of Erg whereas the carboxyterminal AF-2 domain of ERalpha was necessary for repression of Erg activity. Reciprocal inhibition between Erg and ERalpha was not alleviated by overexpressing CBP, SRC-1 or RIP 140, three nuclear coactivator proteins. A negative cross-talk observed between Erg and ERalpha expands their potential range of regulation and may be relevant in vivo, particularly in endothelial, urogenital and cartilaginous tissues where both factors are expressed.

Epstein-Barr virus LMP1 blocks p16INK4a-RB pathway by promoting nuclear export of E2F4/5

The p16INK4a-RB pathway plays a critical role in preventing inappropriate cell proliferation and is often targeted by viral oncoproteins during immortalization. Latent membrane protein 1 (LMP1) of Epstein-Barr virus (EBV) is often present in EBV-associated proliferative diseases and is critical for the immortalizing and transforming activity of EBV. Unlike other DNA tumor virus oncoproteins, which possess immortalizing activity, LMP1 does not bind to retinoblastoma tumor suppressor protein, but instead blocks the expression of p16INK4a tumor suppressor gene. However, it has been unclear how LMP1 represses the p16INK4a gene expression. Here, we report that LMP1 promotes the CRM1-dependent nuclear export of Ets2, which is an important transcription factor for p16INK4a gene expression, thereby reducing the level of p16INK4a expression. We further demonstrate that LMP1 also blocks the function of E2F4 and E2F5 (E2F4/5) transcription factors through promoting their nuclear export in a CRM1-dependent manner. As E2F4/5 are essential downstream mediators for a p16INK4a-induced cell cycle arrest, these results indicate that the action of LMP1 on nuclear export has two effects on the p16INK4a-RB pathway: (1) repression of p16INK4a expression and (2) blocking the downstream mediator of the p16INK4a-RB pathway. These results reveal a novel activity of LMP1 and increase an understanding of how viral oncoproteins perturb the p16INK4a-RB pathway.

A 27 bp cis-acting sequence is essential for L-type calcium channel alpha(1C) subunit expression in vascular smooth muscle cells

Expression of L-type calcium channels in cardiac myocytes and vascular smooth muscle cells (VSMC) critically regulates the contractile state of these cells. In order to discover the elements in the promoter region of the Ca(v)1.2 gene encoding the vascular/cardiac calcium channel alpha(1C) subunit that are important for the basal gene expression, approximately 2 kb of the 5'-flanking sequence of the Ca(v)1.2 gene has been cloned in our lab. In this study, using various lengths of the 5'-flanking DNA fused with a luciferase gene as a reporter, we have defined a 493-bp fragment of the cis-regulatory DNA which carries the majority of promoter activity in pulmonary artery smooth muscle (PAC1) cells. DNase I footprinting analysis of this 493-bp DNA using nuclear extracts from PAC1 cells revealed a 27-bp DNA sequence that contains a c-Ets like motif (CAGGATGC). Mutation of the Ets-like site and the respective flanking sequence within the DNase I footprinting protection region induced a marked change in the promoter activity in PAC1 cells. Electrophoretic mobility shift assays (EMSA) confirmed the presence of specific binding factor(s) in PAC1 cells' nuclear extracts for this 27-bp DNA. Competition studies with the wild-type and mutated DNA fragments established the importance of the 27 bp DNA sequence for high-affinity binding of the nuclear proteins to the promoter. We conclude that there is a 27 bp region in the promoter of the Ca(v)1.2 gene to which nuclear proteins from VSMC bind and strongly regulate the basal promoter activity.

Expression and evolution studies of ets genes in a primitive coelomate, the polychaete annelid, Hediste (Nereis) diversicolor

The Ets family includes numerous proteins with a highly conserved DNA-binding domain of 85 amino acids named the ETS domain. Phylogenetic analyses from ETS domains revealed that this family could be divided into 13 groups, among them are ETS and ERG. The ets genes are present in the Metazoan kingdom and we have previously characterized the Nd ets and Nd erg genes in the polychaete annelid Hediste diversicolor. Here, we isolated a fragment encoding the ETS domain from Nd Ets, by genomic library screening. By Northern blot analysis, we showed that this gene was transcribed as one major mRNA of 2.6 kb and one minor mRNA of 3.2 kb. By in situ hybridization, we observed that Nd ets was expressed in the intestine and oocytes and that Nd erg was expressed in cellular clumps present in the coelomic cavity, in an area of proliferating cells situated between the last metamere and the pygidium. Finally, we showed that Nd erg shared the expression pattern of Nd ets in oocytes. Molecular modeling studies have revealed that the spatial structure of ETS domain of Nd Ets and Nd Erg was conserved, in comparison to the murine Ets-1 and human Fli-1 proteins, respectively.

Differential regulation of the response to DNA damage in Ewing's sarcoma cells by ETS1 and EWS/FLI-1

Ewing's sarcoma (EWS) cells contain levels of poly(ADP-ribose) polymerase (PARP) significantly higher than other eukaryotic cells. Previously, we cloned the PARP gene promoter region from EWS cells, showed that it contained multiple ETS-binding sites and demonstrated a positive regulation of PARP by ETS1. We now report that, contrary to ETS1, EWS/FLI-1, an aberrant ETS transcription factor present in most EWS cells, is a negative effector of PARP transcription. Because PARP levels have been associated with cellular resistance or sensitivity to genotoxic agents, we studied the effect of modifying PARP levels in EWS cells on their response to DNA damage by modulating the expression of ETS1 or EWS/FLI-1 using antisense methodology. Results show that stable down-regulation of ETS1 increases the resistance of EWS cells to various genotoxic agents, whereas down-regulation of EWS/FLI-1 has pro-apoptotic effects. Because down-regulation EWS/FLI-1 does not dramatically change PARP levels, these results suggest a direct effect for EWS/FLI-1 in the DNA damage response of EWS cells. Since expression of the aberrant fusion proteins by EWS cells is essential for maintaining their neoplastic phenotype, our results suggest that the use of antisense oligonucleotides in combination with chemotherapeutic agents or radiation may be doubly effective by causing both an increase in sensitivity to therapeutic agents and a simultaneous down-regulation, or reversion, of the neoplastic phenotype of EWS cells.

The SAM domain of polyhomeotic, RAE28, and scm mediates specific interactions through conserved residues

The SAM (sterile alpha motif) domain is a 65- to 70-amino acid sequence found in many diverse proteins whose functions range from signal transduction to transcriptional repression. We show that the SAM domain of the Drosophila Polycomb group protein, polyhomeotic (ph), is capable of binding to itself in vitro. We test a number of near relatives of the ph SAM domain from fruit fly, mouse, and yeast and show that all are capable of self-binding. Heterologous interactions are seen among a subset of SAM domains, including ph, Scm, and RAE28. Several conserved amino acid residues were mutated in the ph SAM domain, and the effects on self-binding and heterologous association were demonstrated. L33, L41, and 162 are shown to be important determinants of the binding interface, while W1 and G50 are likely essential for the structure of the domain.

IL-2 and long-term T cell activation induce physical and functional interaction between STAT5 and ETS transcription factors in human T cells

Activation of Stat5 by many cytokines implies that it cannot alone insure the specificity of the regulation of its target genes. We have evidenced a physical and functional interaction between members of two unrelated transcription factor families, Ets-1, Ets-2 and Stat5, which could contribute to the proliferative response to interleukin 2. Competition with GAS- and EBS-specific oligonucleotides and immunoassays with a set of anti-Stat and anti-Ets families revealed that the IL-2-induced Stat5-Ets complex recognizes several GAS motifs identified as target sites for activated Stat5 dimers. Coimmunoprecipitation experiments evidenced that a Stat5/Ets-1/2 complex is formed in vivo in absence of DNA. GST-pull down experiments demonstrated that the C-terminal domain of Ets-1 is sufficient for this interaction in vitro. Cotransfection experiments in Kit225 T cells resulted in cooperative transcriptional activity between both transcription factors in response to a combination of IL-2, PMA and ionomycin. A Stat5-Ets protein complex was the major inducible DNA-binding complex bound to the human IL-2rE GASd/EBSd motif in long-term proliferating normal human T cells activated by CD2 and CD28. These results suggest that the inducible Stat5-Ets protein interaction plays a role in the regulation of gene expression in response to IL-2 in human T lymphocytes.

Constitutive expression of the DNA-binding domain of Ets1 increases endothelial cell adhesion and stimulates their organization into capillary-like structures

We previously reported that the Ets1 transcription factor is expressed in endothelial cells during angiogenesis both in normal and pathological development. We analyse here the effects of the stable expression of an Ets transdominant negative mutant (Ets1-DB), consisting in an Ets1 protein lacking its transactivation domain. A retrovirus containing the Ets1-DB sequence fused to an IRES-Neo sequence was designed and used to infect brain capillary (IBE) and aorta (MAE) mouse endothelial cell lines. Cells expressing this Ets1 mutant were examined for proliferation, migration and adhesion. Consistent changes were observed on cell morphology, with increased spreading and modifications in the organization of the cytoskeleton, and increased cell adhesion. We investigated the ability of endothelial cells to organise into capillary-like structures using three-dimensional gels. On Matrigel, all endothelial cell lines formed a cord-like network within 24 h, with an increased ability of Ets1-DB cells to spread on this substrate. In long term cultures, IBE cells expressing Ets1-DB showed a higher capacity to form branched structures; this effect was potentiated by FGF2. These results demonstrate a role of the Ets transcription factors in the regulation of the adhesive and morphogenetic properties of endothelial cells.

Cloning and expression of the mouse Pse gene encoding a novel Ets family member

Human prostate-specific Ets (hPSE) is a novel Ets transcription factor and is exclusively expressed in human prostate glandular epithelium. To explore the role of PSE, we cloned the mouse Pse (mPse) and examined its pattern of expression. A sequence analysis indicated that mPse contains a conserved carboxy-terminal ETS DNA-binding domain and central Pointed domain, and the overall amino acid sequence shares 86% identity with that of hPSE. The ETS DNA-binding domain is highly conserved between human and mouse (98.8% sequence identity) and is similar to Drosophila dets4 (76.7% identity), but not similar to other Ets factors. A Northern blotting analysis revealed that mPse shows organ-specific expression. An in situ hybridization analysis of the prostate and intestine showed that mPse transcripts were present in their epithelial cells. mPse transactivates the promoter of the MASPIN gene in transient transfection assay. These results suggest that mPse encodes a novel Ets family member and is expressed in epithelial cells of restricted organs.

Regulation of the human poly(ADP-ribose) polymerase promoter by the ETS transcription factor

Ewing's sarcoma (EWS) cells accumulate elevated steady-state levels of poly (ADP-ribose) polymerase (PARP) mRNA and protein. To understand the molecular mechanisms underlying PARP upregulation, we cloned and analysed the 5'-flanking region of the PARP gene from EWS cells. Nucleotide sequence analysis demonstrated no variations in the PARP promoter region in EWS cells. The PARP promoter encompasses multiple binding motifs for the ETS transcription factor. We have also observed that there is a coordinated up-regulation of the expression of both PARP and ETS1, relative to cells of other human tumor types expressing lower levels of PARP. Transient co-expression of ETS1 in EWS cells resulted in a strong enhancement of PARP-promoter activity. The participation of ETS in the regulation of PARP gene expression was further demonstrated in EWS cells stably transfected with Ets1 antisense cDNA constructs. Antisense-mediated down-regulation of endogenous ETS1 resulted in the inhibition of PARP expression in EWS cells, and sensitized these cells to ionizing radiation. These data provide support for ETS regulation of PARP expression levels, and implicate ETS transcription factors in the radiation response of EWS cells.

The expression of a novel, epithelium-specific ets transcription factor is restricted to the most differentiated layers in the epidermis

Ets proteins have been implicated in the regulation of gene expression during a variety of biological processes, including growth control, differentiation, development and transformation. More than 35 related proteins containing the 'ets domain' have now been found which specifically interact with DNA sequences encompassing the core tetranucleotide GGAA. Although ets responsive genes have been identified in the epidermis, little is known about their distribution and function in this tissue. We have now demonstrated that epidermis and cultured epidermal keratinocytes synthesize numerous ets proteins. The expression of some of these proteins is regulated as a function of differentiation. Among these is a novel ets transcription factor with a dual DNA-binding specificity, which we have called jen. The expression of jen is not only epithelial specific, but it is the only ets protein so far described, and one of the very few transcription factors whose expression is restricted to the most differentiated epidermal layers. We show that two epidermal marker genes whose expression coincides with that of jen are transregulated by this protein in a complex mode which involves interactions with other transcriptional regulators such as Sp1 and AP1.

Specific binding of the ETS-domain protein to the interferon-stimulated response element

Interferon (IFN) activation of genes bearing an IFN-stimulated response element (ISRE) is regulated through binding of IFN-stimulated gene factors (ISGF) to the ISRE found in many IFN-stimulated genes. Using a multimerized human 2-5A synthetase ISRE as probe, we screened lambda gt11 expression libraries for cDNA encoding ISRE-binding activity and isolated a clone for murine proto-oncogene ets-1. The Ets-1 protein binds to the 2-5A synthetase ISRE at a site that also binds ISGF3, a multicomponent factor whose ISRE binding correlates with IFN-induced activation of transcription from ISRE-containing promoters. IFN-induced ISGF3 complex formation on the ISRE can be inhibited by specific Ets-1 antibody. Coexpression of Ets-1 represses ISRE-dependent reporter activity, suggesting that one or more members of the Ets protein family may negatively regulate transcriptional activity mediated by the 2-5A synthetase ISRE.

Functional domains of transcription factor hGABP beta1/E4TF1-53 required for nuclear localization and transcription activation

Transcription factor E4TF1 is the human homolog of GABP and has been renamed hGABP (human GABP). hGABP is composed of two types of subunits; hGABP beta1/E4TF1-53 and the ets-related protein hGABP alpha/E4TF1-60. Both bind together to form an (alpha)2(beta1)2 heterotetrameric complex on DNA and activate transcription at specific promoters in vitro. Tetramer formation depends on two regions of hGABP beta1; the N-terminal region containing the Notch/ankyrin-type repeats is necessary for binding to hGABP alpha and the C-terminal region is necessary for homodimerization. In this report, we constructed various deletion mutants of hGABP beta1 in order to delimit the functional regions required for nuclear localization and transcription activity. We found that hGABP beta1 localization in the nucleus is dependent on a region located between amino acids 243 and 330 and that the presence of hGABP beta1 influences the efficiency of hGABP alpha transport into the nucleus. Next, we demonstrated that the hGABP complex composed of alpha and beta1 subunits activates transcription from the adenovirus early 4 promoter in vivo. This transcription activation needs the C-terminal region of hGABP beta1 and is consistent with results obtained with the in vitro assay. Furthermore, site-directed mutagenesis analysis of the C-terminal region reveals that the alpha-helix structure and the leucine residues are important for formation of a heterotetrameric complex with hGABP alpha in vitro and for transcription activation in vivo. These results suggest that hGABP beta1 stimulates transcription as part of a heterotetrameric complex with hGABP alpha in vivo.

Tissue-specific activity of the gammac chain gene promoter depends upon an Ets binding site and is regulated by GA-binding protein

The gammac chain is a subunit of multiple cytokine receptors (interleukin (IL)-2, IL-4, IL-7, IL-9, and IL-15), the expression of which is restricted to hematopoietic lineages. A defect in gammac leads to the X-linked severe combined immunodeficiency characterized by a block in T cell differentiation. In order to better characterize the human gammac promoter and define the minimal tissue-specific promoter region, progressive 5'-deletion constructs of a segment extending 1053 base pairs upstream of the major transcription start site were generated and tested for promoter activity in various hematopoietic and nonhematopoietic cell types. The -1053/+34 construct allowed promoter activity only in cells of hematopoietic origin, and tissue specificity was conserved in all other constructs tested. The region downstream of -90 appeared critical for basal promoter activity. It contains two potential Ets binding sites conserved in the murine gammac promoter gene, one of which was found essential for functional promoter activity as determined by mutational analysis. The functional Ets binding site was found to bind Ets family proteins, principally GA-binding protein and Elf-1 and could be transactivated by GABPalpha and -beta synergistically. These results indicate that, as already reported for the IL2Rbeta promoter, GA-binding protein is an essential component of gammac basal promoter activity. Although GABP expression is not restricted to the hematopoietic lineage, its interaction with other specific factors may contribute to the tissue-specific expression of the gammac gene.

Increased T-cell apoptosis and terminal B-cell differentiation induced by inactivation of the Ets-1 proto-oncogene

The Ets-1 proto-oncogene is a member of a transcription factor family characterized by homology to the v-ets oncogene. In adult mice, Ets-1 is expressed predominantly in lymphoid cells where it has been implicated in regulating transcription of lymphocyte-specific genes. Following T-cell activation, the specific DNA binding activity of Ets-1 is inactivated by transient phosphorylation, suggesting a function in the transition from the resting to activated state. Ets-1 has also been suggested to cooperate with the AP-1 transcription factor complex to mediate cellular growth factor responses. Here we show, by using RAG-2-deficient blastocyst complementation, that Ets-1 deficiency has dramatic, but different, effects on development and function of T- and B-lineage cells. Ets-1-deficient T cells were present in reduced numbers and were highly susceptible to cell death in vitro. In contrast, Ets-1-deficient B cells were present in normal numbers but a large proportion were IgM plasma cells. Our data demonstrate that Ets-1 is essential for maintenance of the normal pool of resting T- and B-lineage cells.

Xl-fli, the Xenopus homologue of the fli-1 gene, is expressed during embryogenesis in a restricted pattern evocative of neural crest cell distribution

The Xenopus laevis fli cDNA, belonging to the ets family of transcription factors, was isolated from a library prepared from unfertilized eggs. It encodes a polypeptide with extensive homology to murine and human Fli proteins. The long 3'-untranslated region contains five nuclear polyadenylation signals and three cytoplasmic polyadenylation elements, as well as many A/T rich elements. Two polyadenylated transcripts appear at the early neurula and accumulate up to the tadpole stage. In situ hybridization reveals an expression in territories invaded by neural crest cells. In the head region, fli is expressed in the peri-ocular zone, in the branchial buds and at the level of the brain floor. In the trunk, a metamerized expression is detected in the dorsum. At a lower level, the tailbud and the peri-cardiac region also appear positive.

Expression of C-ETS1 in early chick embryo mesoderm: relationship to the hemangioblastic lineage

In situ hybridization was used to detect the expression of the c-ets1 protooncogene during formation of the germ layers in the chick blastodisc. c-ets1 transcripts were present during the gastrulation process, i.e. when the mesodermal cells invaginated. The expression became down-regulated in lateral plate and the dorsal part of the somites while an intense signal was retained in the intermediate cell mass. When vasculogenesis started, c-ets1 transcripts labelled blood islands and endothelial cells. Before the mesoderm split, transcripts were present over the whole layer, more abundant however on its ventral side in contact with the endoderm. After the mesoderm split, silver grains became distributed asymmetrically: splanchnopleural mesoderm expressed c-ets1 messengers all over while expression in the somatopleural mesoderm was restricted to a few profiles corresponding to small endothelial cell groups. This asymmetrical distribution of c-ets1 transcripts is in agreement with our previous experimental findings establishing the different potentialities of the two mesodermal layers regarding hemopoiesis, vasculogenesis and angiogenesis processes.

The c-ets-1 proto-oncogenes in Xenopus laevis: expression during oogenesis and embryogenesis

We previously reported the cloning and sequencing of two cDNAs derived from the Xenopus laevis ets-1 gene (Stiegler et al., 1990). The Xl-ets-1a cDNA encodes a polypeptide highly homologous to known ets-1 proteins. The 3'-UTR contains two AATAAA polyadenylation signals together with three copies of the TTTTTAT sequence thought to confer a maturation-specific polyadenylation and implicated in the deadenylation of dormant mRNAs. Several transcripts with maternal characteristics were detected in oogenesis and early embryogenesis. A marked augmentation of the major transcript in the poly(A)+ fraction was detected at fertilization. Ets-1 transcripts were observed at constant levels during the cleavage stages but decreased abruptly at gastrulation, to reappear from neurulation to late embryogenesis. The possible contribution of 3'-UTR sequence elements to this behavior is discussed.

The Ets family of transcription factors

Interest in the Ets proteins has grown enormously over the last decade. The v-ets oncogene was originally discovered as part of a fusion protein expressed by a transforming retrovirus (avian E26), and later shown to be transduced from a cellular gene. About 30 related proteins have now been found in species ranging from flies to humans, that resemble the vEts protein in the so-called 'ets domain'. The ets domain has been shown to be a DNA-binding domain, that specifically interacts with sequences containing the common core trinucleotide GGA. Furthermore, it is involved in protein-protein interactions with co-factors that help determine its biological activity. Many of the Ets-related proteins have been shown to be transcription activators, like other nuclear oncoproteins and anti-oncoproteins (Jun, Fos, Myb, Myc, Rel, p53, etc.). However, Ets-like proteins may have other functions, such as in DNA replication and a general role in transcription activation. Ets proteins have been implicated in regulation of gene expression during a variety of biological processes, including growth control, transformation, T-cell activation, and developmental programs in many organisms. Signals regulating cell growth are transmitted from outside the cell to the nucleus by growth factors and their receptors. G-proteins, kinases and transcription factors. We will discuss how several Ets-related proteins fit into this scheme, and how their activity is regulated both post- and pre-translationally. Loss of normal control is often associated with conversion to an oncoprotein. vEts has been shown to have different properties from its progenitor, which might explain how it has become oncogenic. Oncogene-related products have been implicated in the control of various developmental processes. Evidence is accumulating for a role for Ets family members in Drosophila development, Xenopus oocyte maturation, lymphocyte differentiation, and viral infectious cycles. An ultimate hope in studying transformation by oncoproteins is to understand how cells become cancerous in humans, which would lead to more effective treatments. vEts induces erythroblastosis in chicken. Cellular Ets-family proteins can be activated by proviral insertion in mice and, most interestingly, by chromosome translocation in humans. We are at the beginning of understanding the multiple facets of regulation of Ets activity. Future work on the Ets family promises to provide important insights into both normal control of growth and differentiation, and deregulation in illness.

Characterization and uses of monoclonal antibody derived against DNA binding domain of the ets family of genes

A monoclonal antibody recognizing ets proteins from a variety of species has been developed. This antibody recognizes ets1, ets2, erg, and other related proteins. It has a high affinity for the ets1 protein. The epitope for the pan ets mAb consists of about 13 amino acids. This antibody can be used to isolate and characterize new members of ets gene family derived from a c-DNA expression library, as well as to identify other "ets motif" binding proteins.

Sequence-specific interaction of the Ets1 protein with the long terminal repeat of the human T-lymphotropic virus type I

We recently demonstrated that members of the c-ets proto-oncogene family, Ets1 and Ets2, are sequence-specific transcriptional activators of the human T-lymphotropic virus type I (HTLV-I) long terminal repeat (LTR). We now report that the HTLV-I LTR contains two distinct Ets1-responsive regions, ERR-1 and ERR-2. Expression of Ets1 with reporter plasmids containing ERR-1 or ERR-2 upstream of a basal promoter resulted in an increase in transcriptional activity. By gel mobility shift assay, the interaction of Ets1 with the downstream ERR-1-binding region was found to be more stable than its interaction with the upstream ERR-2 region. By DNase I footprint, gel mobility shift, and methylation interference analyses, ERR-1 was found to contain two Ets1 binding sites, ERE-A and ERE-B. A recombinant Ets1 protein was found to bind with higher affinity to ERE-A than to ERE-B. Binding of Ets1 to these sites appears to result in a specific and sequential protection of a 37-nucleotide sequence of the HTLV-I LTR from -154 to -118. In view of the high-level expression of Ets1 in lymphoid cells, the c-ets proto-oncogenes encode transcription factors which could play an important role in both basal and Tax1-mediated HTLV-I transcription.

Transcriptional regulation of interferon-stimulated genes

Interferons (IFN) stimulate the expression of a number of genes following interaction with specific high-affinity plasma membrane receptors. The products of these genes either singly or coordinately mediate the antiviral, growth inhibitory or immunoregulatory activities attributed to IFN. While the gene products in some cases have been well characterized, other IFN-regulated genes encode proteins whose functions have yet to be elucidated. A feature common to all IFN-stimulated genes characterized thus far is the presence of a DNA element which constitutes an IFN-responsive enhancer, usually present in the 5' upstream region of the genes. This element, termed interferon-stimulated response element (ISRE) binds a nuclear factor(s) translocated from the cytoplasm to the nucleus following IFN-receptor-triggered signal transduction. The binding of these factors to the ISRE represents the initiating event in stimulating RNA-polymerase-II-mediated transcription from IFN-responsive genes. Depending on the nature of the cells responding to IFN and the genes involved, induced transcription may be prolonged or rapidly terminated. The rapid termination of transcription is dependent in some cases on IFN-induced protein synthesis and also involves factor binding to the ISRE. Recent progress in detailing these events will be discussed including IFN-receptor interactions, signal-transduction pathways, comparing and contrasting IFN-regulated genes and elucidation of IFN-regulated factors.

Signal transduction and transcriptional regulation of interferon-alpha-stimulated genes

Interferon-alpha (IFN-alpha) stimulates the expression of a number of genes in a pathway that begins with binding to specific high-affinity plasma membrane receptors. All IFN-alpha-stimulated genes cloned thus far are characterized by the presence of a DNA element, termed Interferon-Stimulated Response Element (ISRE), usually in the 5' upstream region of the genes. The ISRE binds a nuclear factor(s) following IFN-receptor triggered signal transduction and provides a convenient assay for the rapid phase of IFN-alpha signal transduction. This phase utilizes a phospholipase A2-generated second messenger which modulates ISRE-binding factors. Expression cloning has resulted in the identification of two specific ISRE-binding proteins that are candidates as signal recipients. Further advances in our understanding of the molecular mechanisms of IFN action may come through the use of yeast genetics. The human p68 kinase expressed in yeast has a growth inhibitory phenotype and provides a useful alternative system for analyzing components of the IFN-stimulated pathways.

Fusion of the nuclear oncoproteins v-Myb and v-Ets is required for the leukemogenicity of E26 virus

The highly leukemogenic avian retrovirus E26 expresses the two transcriptional activator-type oncogenes v-myb and v-ets as a nuclear fusion protein. Previous studies have shown that both oncogenes cooperate in the transformation of erythroid cells in vitro and that the phenotypes of transformed cells differ, depending on whether the oncogenes are coexpressed as separate proteins or as a fusion protein. Here we show that virus constructs encoding either v-Myb or v-Ets as their only oncoprotein are nonleukemogenic and that constructs coexpressing nonfused v-Myb and v-Ets proteins appear to be weakly leukemogenic. Surprisingly, leukemic animals injected with the latter contain highly leukemogenic variant viruses that exhibit internal deletions in their genome, resulting in the synthesis of novel Myb-Ets fusion proteins. These results show that v-Myb and v-Ets must be fused to cause leukemia and establish a new mechanism of oncogene activation and cooperation.

Nuclear oncogenes

Ample evidence has accumulated in recent years to establish that most, if not all, nuclear proto-oncogenes are in fact sequence-specific DNA-binding proteins that modulate gene expression. Their synthesis or activity is modulated by extracellular signals or by cross talk between different classes of transcription factors.

The c-ets proto-oncogenes encode transcription factors that cooperate with c-Fos and c-Jun for transcriptional activation

Cell transformation by oncogenes leads to changes in gene expression. A key event in this process seems to be activation of the transcription factors AP-1 and PEA 3. Their synergistic activities are required for efficient activation of transcription from different promoters by many different oncogenes, serum growth factors and the tumour promoter TPA. We show here that the products of the ets-1 and -2 proto-oncogenes, whose biological function was previously unknown, are transcription factors that activate transcription through the PEA 3 motif. The p68c-ets-1 protein specifically binds to DNA and contains a transcriptional activation domain. The ets-like gene family therefore seems to encode a new family of transcription factors, apparently unrelated to other transcription factors. The p68c-ets-1 protein cooperates with c-Fos and c-Jun (components of AP-1) for activation of transcription from the oncogene-responsive domain of the polyoma enhancer, indicating that combined activity of all three oncoproteins could be involved in the response of cells to growth stimuli.