Elevated expression of Ets2 or distinct portions of Ets2 can reverse Ras-mediated cellular transformation

CIP/KIP and INK4 families as hostages of oncogenic signaling

CIP/KIP and INK4 families of Cyclin-dependent kinase inhibitors (CKIs) are well-established cell cycle regulatory proteins whose canonical function is binding to Cyclin-CDK complexes and altering their function. Initial experiments showed that these proteins negatively regulate cell cycle progression and thus are tumor suppressors in the context of molecular oncology. However, expanded research into the functions of these proteins showed that most of them have non-canonical functions, both cell cycle-dependent and independent, and can even act as tumor enhancers depending on their posttranslational modifications, subcellular localization, and cell state context. This review aims to provide an overview of canonical as well as non-canonical functions of CIP/KIP and INK4 families of CKIs, discuss the potential avenues to promote their tumor suppressor functions instead of tumor enhancing ones, and how they could be utilized to design improved treatment regimens for cancer patients.

A genetic variation in microRNA target site of ETS2 is associated with clinical outcomes of paclitaxel-cisplatin chemotherapy in non-small cell lung cancer

The present study was performed to investigate the association of single nucleotide polymorphisms (SNPs) located in the miRNA target sites with the clinical outcomes of first line paclitaxel-cisplatin chemotherapy in advanced NSCLC. Eighty SNPs in miRNA binding sites of cancer related genes selected from 18,500 miRNA:target bindings in crosslinking, ligation, and sequencing of hybrids (CLASH) data were investigated in 379 advanced NSCLC patients using a sequenom mass spectrometry-based genotype assay. qRT-PCR and luciferase assay were conducted to examine functional relevance of potentially functional SNPs in miRNA binding sites. Of the 80 SNPs analyzed, 16 SNPs were significantly associated with the clinical outcomes after chemotherapy. Among these, ANAPC1 rs3814026C>T, ETS2 rs461155A>G, SORBS1 rs7081076C>A and POLR2A rs2071504C>T could predict both chemotherapy response and survival. Notably, ETS2 rs461155A>G was significantly associated with decreased ETS2 mRNA expression in both tumor and paired normal lung tissues (Ptrend = 4 × 10⁻⁷, and 3 × 10⁻⁴, respectively). Consistently, a decreased expression of the reporter gene for the G allele of rs461155 compared with the A allele was observed by luciferase assay. These findings suggest that the four SNPs, especially ETS2 rs461155A>G, could be used as biomarkers predicting the clinical outcomes of NSCLC patients treated with first-line paclitaxel-cisplatin chemotherapy.

Intrinsically active variants of Erk oncogenically transform cells and disclose unexpected autophosphorylation capability that is independent of TEY phosphorylation

The receptor-tyrosine kinase (RTK)/Ras/Raf pathway is an essential cascade for mediating growth factor signaling. It is abnormally overactive in almost all human cancers. The downstream targets of the pathway are members of the extracellular regulated kinases (Erk1/2) family, suggesting that this family is a mediator of the oncogenic capability of the cascade. Although all oncogenic mutations in the pathway result in strong activation of Erks, activating mutations in Erks themselves were not reported in cancers. Here we used spontaneously active Erk variants to check whether Erk's activity per se is sufficient for oncogenic transformation. We show that Erk1(R84S) is an oncoprotein, as NIH3T3 cells that express it form foci in tissue culture plates, colonies in soft agar, and tumors in nude mice. We further show that Erk1(R84S) and Erk2(R65S) are intrinsically active due to an unusual autophosphorylation activity they acquire. They autophosphorylate the activatory TEY motif and also other residues, including the critical residue Thr-207 (in Erk1)/Thr-188 (in Erk2). Strikingly, Erk2(R65S) efficiently autophosphorylates its Thr-188 even when dually mutated in the TEY motif. Thus this study shows that Erk1 can be considered a proto-oncogene and that Erk molecules possess unusual autoregulatory properties, some of them independent of TEY phosphorylation.

ETS family transcriptional regulators drive chromatin dynamics and malignancy in squamous cell carcinomas

Tumor-initiating stem cells (SCs) exhibit distinct patterns of transcription factors and gene expression compared to healthy counterparts. Here, we show that dramatic shifts in large open-chromatin domain (super-enhancer) landscapes underlie these differences and reflect tumor microenvironment. By in vivo super-enhancer and transcriptional profiling, we uncover a dynamic cancer-specific epigenetic network selectively enriched for binding motifs of a transcription factor cohort expressed in squamous cell carcinoma SCs (SCC-SCs). Many of their genes, including Ets2 and Elk3, are themselves regulated by SCC-SC super-enhancers suggesting a cooperative feed-forward loop. Malignant progression requires these genes, whose knockdown severely impairs tumor growth and prohibits progression from benign papillomas to SCCs. ETS2-deficiency disrupts the SCC-SC super-enhancer landscape and downstream cancer genes while ETS2-overactivation in epidermal-SCs induces hyperproliferation and SCC super-enhancer-associated genes Fos, Junb and Klf5. Together, our findings unearth an essential regulatory network required for the SCC-SC chromatin landscape and unveil its importance in malignant progression.

DOI:http://dx.doi.org/10.7554/eLife.10870.001

Many cancers contain a mixture of different types of cells. Of these, cells known as cancer stem cells can form new tumours and drive the growth and spread of the cancer around the body. A central question is how cancer stem cells differ from healthy adult stem cells. Recent evidence suggests that, in addition to having genetic mutations, cancer stem cells live in a very different environment to other cells within the tumour. This 'microenvironment'also has a major impact on how these cells behave compared to normal stem cells. Together, the genetic and environmental differences profoundly change the way genes are expressed in the cancer cells.

In 2013, a group of researchers identified regions of DNA called super-enhancers. These regions are long stretches of DNA that proteins called transcription factors can interact with to coordinate the expression of nearby genes to alter the production of certain proteins. Super-enhancers contain several transcription factor-binding sites that are close to each other with the different sites being associated with transcription factors that are only active in specific types of cells. Furthermore, super-enhancers are often self-regulatory, meaning that the binding of transcription factors to a super-enhancer can lead to an increase in the expression of the genes that encode the same transcription factors.

Yang, Schramek et al. have now identified the super-enhancers in a skin cancer called squamous cell carcinoma and showed that they differ dramatically from the super-enhancers of normal skin stem cells. Their experiments show that the active super-enhancers in cancer stem cells are associated with a very different set of genes that are highly and often specifically expressed in cancer stem cells. In the cancer stem cells, a transcription factor called ETS2 binds to the super-enhancers and reprograms the expression of genes to promote the development of cancer. Yang, Schramek et al. also show that over-active ETS2 is a major driver of squamous cell carcinoma. Furthermore, ETS2 also increases the expression of genes that cause inflammation and promote the growth of cancers.

Yang, Schramek et al.’s findings reveal a new regulatory network that governs the expression of genes involved in cancer. Furthermore, the experiments show that high levels of ETS2 are linked with poor outcomes for patients with head and neck squamous cell carcinoma, which is one of the most life-threatening cancers world-wide. In the future, these findings might lead to the development of new therapies to treat these cancers.

DOI:http://dx.doi.org/10.7554/eLife.10870.002

Ets-1 global gene expression profile reveals associations with metabolism and oxidative stress in ovarian and breast cancers

Background

The Ets-1 proto-oncogene is frequently upregulated in cancer cells, with known involvement in cancer angiogenesis, metastasis, and more recently energy metabolism. In this study we have performed various bioinformatic analyses on existing microarray data to further clarify the role of Ets-1 in ovarian cancer, and validated these results with functional assays.

Methods

Functional pathway analyses were conducted on existing microarray data comparing 2008 and 2008-Ets1 ovarian cancer cells. Methods included over-representation analysis, functional class scoring and pathway topology, and network representations were visualized in Cytoscape. Oxidative stress regulation was examined in ovarian cancer cells by measuring protein expression and enzyme activity of glutathione peroxidases, as well as intracellular reactive oxygen species using dichlorofluorescin fluorescence. A stable Ets-1 knockdown MDA-MB-231 cell line was created using short hairpin RNA, and glycolytic dependence of these cells was measured following treatment with 2-deoxy-D-glucose and Hoechst nuclear staining to determine cell number. High-resolution respirometry was performed to measure changes in basal oxygen flux between MDA-MB-231 cells and MDA-Ets1KD variants.

Results

Enrichments in oxidoreductase activity and various metabolic pathways were observed upon integration of the different analyses, suggesting that Ets-1 is important in their regulation. As oxidative stress is closely associated with these pathways, we functionally validated our observations by showing that Ets-1 overexpression resulted in decreased reactive oxygen species with increased glutathione peroxidase expression and activity, thereby regulating cellular oxidative stress. To extend our findings to another cancer type, we developed an Ets-1 knockdown breast cancer cell model, which displayed decreased glycolytic dependence and increased oxygen consumption following Ets-1 knockdown confirming our earlier findings.

Conclusions

Collectively, this study confirms the important role of Ets-1 in the regulation of cancer energy metabolism in ovarian and breast cancers. Furthermore, Ets-1 is a key regulator of oxidative stress in ovarian cancer cells by mediating alterations in glutathione antioxidant capacity.

ETS2 mediated tumor suppressive function and MET oncogene inhibition in human non-small cell lung cancer

PURPOSE

The ETS2 transcription factor is an evolutionarily conserved gene that is deregulated in cancer. We analyzed the transcriptome of lung adenocarcinomas and normal lung tissue by expression profiling and found that ETS2 was significantly downregulated in adenocarcinomas. In this study, we probed the yet unknown functional role of ETS2 in lung cancer pathogenesis.

EXPERIMENTAL DESIGN

Lung adenocarcinomas (n = 80) and normal lung tissues (n = 30) were profiled using the Affymetrix Human Gene 1.0 ST platform. Immunohistochemical (IHC) analysis was conducted to determine ETS2 protein expression in non-small cell lung cancer (NSCLC) histologic tissue specimens (n = 201). Patient clinical outcome, based on ETS2 IHC expression, was statistically assessed using the log-rank and Kaplan-Meier tests. RNA interference and overexpression strategies were used to assess the effects of ETS2 expression on the transcriptome and on various malignant phenotypes.

RESULTS

ETS2 expression was significantly reduced in lung adenocarcinomas compared with normal lung (P < 0.001). Low ETS2 IHC expression was a significant predictor of shorter time to recurrence in NSCLC (P = 0.009, HR = 1.89) and adenocarcinoma (P = 0.03, HR = 1.86). Moreover, ETS2 was found to significantly inhibit lung cancer cell growth, migration, and invasion (P < 0.05), and microarray and pathways analysis revealed significant (P < 0.001) activation of the HGF pathway following ETS2 knockdown. In addition, ETS2 was found to suppress MET phosphorylation and knockdown of MET expression significantly attenuated (P < 0.05) cell invasion mediated by ETS2-specific siRNA. Furthermore, knockdown of ETS2 augmented HGF-induced MET phosphorylation, cell migration, and invasion.

CONCLUSION(S)

Our findings point to a tumor suppressor role for ETS2 in human NSCLC pathogenesis through inhibition of the MET proto-oncogene.

Cellular senescence and tumor suppressor gene p16

Cellular senescence is an irreversible arrest of cell growth. Biochemical and morphological changes occur during cellular senescence, including the formation of a unique cellular morphology such as flattened cytoplasm. Function of mitochondria, endoplasmic reticulum and lysosomes are affected resulting in the inhibition of lysosomal and proteosomal pathways. Cellular senescence can be triggered by a number of factors including, aging, DNA damage, oncogene activation and oxidative stress. While the molecular mechanism of senescence involves p16 and p53 tumor suppressor genes and telomere shortening, this review is focused on the mechanism of p16 control. The p16-mediated senescence acts through the retinoblastoma (Rb) pathway inhibiting the action of the cyclin dependant kinases leading to G1 cell cycle arrest. Rb is maintained in a hypophosphorylated state resulting in the inhibition of transcription factor E2F1. Regulation of p16 expression is complex and involves epigenetic control and multiple transcription factors. PRC1 (Pombe repressor complex (1) and PRC2 (Pombe repressor complex (2) proteins and histone deacetylases play an important role in the promoter hypermethylation for suppressing p16 expression. While transcription factors YY1 and Id1 suppress p16 expression, transcription factors CTCF, Sp1 and Ets family members activate p16 transcription. Senescence occurs with the inactivation of suppressor elements leading to the enhanced expression of p16.

A gene on the HER2 amplicon, C35, is an oncogene in breast cancer whose actions are prevented by inhibition of Syk

Background:

C35 is a 12 kDa membrane-anchored protein endogenously over-expressed in many invasive breast cancers. C35 (C17orf37) is located on the HER2 amplicon, between HER2 and GRB7. The function of over-expressed C35 in invasive breast cancer is unknown.

Methods:

Tissue microarrays containing 122 primary human breast cancer specimens were used to examine the association of C35 with HER2 expression. Cell lines over-expressing C35 were generated and tested for evidence of cell transformation in vitro.

Results:

In primary breast cancers high levels of C35 mRNA expression were associated with HER2 gene amplification. High levels of C35 protein expression were associated with hallmarks of transformation, such as, colony growth in soft agar, invasion into collagen matrix and formation of large acinar structures in three-dimensional (3D) cell cultures. The transformed phenotype was also associated with characteristics of epithelial to mesenchymal transition, such as adoption of spindle cell morphology and down-regulation of epithelial markers, such as E-cadherin and keratin-8. Furthermore, C35-induced transformation in 3D cell cultures was dependent on Syk kinase, a downstream mediator of signalling from the immunoreceptor tyrosine-based activation motif, which is present in C35.

Conclusion:

C35 functions as an oncogene in breast cancer cell lines. Drug targeting of C35 or Syk kinase might be helpful in treating a subset of patients with HER2-amplified breast cancers.

Aspects of digestive tract tumors in Down syndrome: a literature review

The purpose of this study was to describe the digestive neoplasms found in persons with Down syndrome. Due to intellectual disability, persons with Down syndrome do not convey their symptoms and pain, leading to delayed diagnosis and potentially worse outcome. It is thus important to know which organs are at risk for tumors and possible tumor risk factors. In a review of the literature, we found 13 benign tumors and 127 cancers in 1 fetus, 8 children, and 131 adults with Down syndrome. The review suggests a decreased incidence of digestive cancer, however, with a possible increased incidence of neoplasms of the pancreas and gallbladder. The distribution of cancers is distinct from that in the general population and that in persons with other intellectual disabilities who share the same life conditions, suggesting that constitutional protective factors exist. This review may allow a more specific, adapted medical follow-up for persons with Down syndrome and could help to elucidate the oncogenesis of digestive neoplasms.

Cooperative DNA binding with AP-1 proteins is required for transformation by EWS-Ets fusion proteins

A key molecular event in the genesis of Ewing's sarcoma is the consistent presence of chromosomal translocations that result in the formation of proteins in which the amino terminus of EWS is fused to the carboxyl terminus, including the DNA binding domain, of one of five different Ets family proteins. These fusion proteins function as deregulated transcription factors, resulting in aberrant control of gene expression. Recent data indicate that some EWS-Ets target promoters, including the uridine phosphorylase (UPP) promoter, harbor tandem binding sites for Ets and AP-1 proteins. Here we show that those Ets family proteins that participate in Ewing's sarcoma, including Fli1, ERG, and ETV1, cooperatively bind these tandem elements with Fos-Jun while other Ets family members do not. Analysis of this cooperativity in vitro shows that (i) many different spatial arrangements of the Ets and AP-1 sites support cooperative binding, (ii) the bZIP motifs of Fos and Jun are sufficient to support this cooperativity, and (iii) both the Ets domain and carboxy-terminal sequences of Fli1 are important for cooperative DNA binding. EWS-Fli1 activates the expression of UPP mRNA, is directly bound to the UPP promoter, and transforms 3T3 fibroblasts; in contrast, a C-terminally truncated mutant form of EWS-Fli1 that cannot cooperatively bind DNA with Fos-Jun is defective in all of these properties. The results show that the ability of EWS-Ets proteins to cooperatively bind DNA with Fos-Jun is critical to the biologic activities of these proteins. The results have implications for understanding the pathogenesis of Ewing's sarcoma. In addition, they may be relevant to the mechanisms of Ras-dependent activation of genes that harbor tandem Ets and AP-1 binding sites.

Capsaicin-induced inactivation of sensory neurons promotes a more aggressive gene expression phenotype in breast cancer cells

Capsaicin-induced inactivation of sensory neurons has been reported to enhance metastasis of a murine breast cancer cell line, specifically enhancing myocardial metastases. Here we characterized changes in gene expression patterns in primary tumors which developed in capsaicin-treated vs. control mice. We identified a small cohort of genes (17) which all showed significant decreases in expression levels. All of the identified genes have been linked to cell growth, differentiation, and/or cancer progression. Three representative genes, Caspase-7 (an executor of apoptosis), ADAM-10 (A Disintegrin and Metalloprotease), and Elk-3 (a transcriptional repressor of the ternary factor subfamily of the Ets factors) were further investigated. All three showed dramatic downregulation at the protein level in primary tumors from capsaicin-treated animals compared with control (vehicle-treated) animals, and their expression was also lost in cell culture. Elk-3 and Caspase-7 were not expressed in vitro in cultured cell lines, suggesting that their expression was induced by the tumor microenvironment. Loss of Caspase-7 expression can be expected to result in loss of function of apoptotic pathways. At first glance, loss of ADAM-10 expression would be expected to result in decreased invasive capability, due to loss of matrix metalloprotease activity. However, just the opposite appears to be true. We found that ADAM-10 actually hydrolyzes Substance P. Specifically ADAM-10 produces the same growth-inhibitory products from Substance P (i.e., SP (1-7)) that Neprilysin does, so that loss of ADAM-10 expression actually results in loss of production of growth inhibitory peptides from Substance P. Similarly, ADAM-10 also efficiently hydrolyzes Calcitonin Gene-Related Peptide, which may act in concert with Substance P. Finally, overactivity of Ets transcriptional suppressor functions has been linked to inhibition of tumorigenesis (e.g., Erf and Mef), and in addition loss of Elk-3 expression might also be be linked to tumorigenesis via loss of its putative anti-inflammatory activities. There is anecdotal evidence in the literature to indicate that the rest of the down-regulated genes may also contribute to development of a more aggressive phenotype in this breast cancer model.

Novel role for PDEF in epithelial cell migration and invasion

Cell migration and invasion are two critical cellular processes that are often deregulated during tumorigenesis. To identify factors that contribute to oncogenic progression by stimulating cell migration, we conducted a powerful retroviral based migration screen using an MCF7 cDNA library and the immortalized human breast epithelial cell line MCF-10A. We identified prostate derived Ets factor (PDEF), an Ets transcription factor that is overexpressed in both prostate and breast carcinoma, as a candidate promigratory gene from this screen. Whereas PDEF induced limited motility of MCF-10A cells, coexpression of PDEF with the receptor tyrosine kinases (RTK) ErbB2 and colony-stimulating factor receptor (CSF-1R)/CSF-1 significantly enhanced MCF-10A motility. Furthermore, cells coexpressing PDEF with either ErbB2 or CSF-1R/CSF-1 induced a dramatic invasive phenotype in three-dimensional cultures. Constitutive activation of the extracellular signal-regulated kinase (ERK) pathway also enhanced PDEF-induced motility and invasion, suggesting that activation of the ERK/mitogen-activated protein kinase by ErbB2 and CSF-1R/CSF-1 can cooperate with PDEF to promote motility and invasion. Furthermore, PDEF promoted anchorage-independent growth of ErbB2 and CSF-1R/CSF-1-expressing cells. Using laser capture microdissection, we also found that PDEF mRNA is overexpressed in breast tumor epithelia throughout tumor progression. Taken together, these findings suggest that the transcription factor PDEF may play an important role in breast tumorigenesis and that PDEF overexpression may be particularly significant in tumors that exhibit activation of oncogenic RTKs such as ErbB2 and CSF-1R.

c-Myb and members of the c-Ets family of transcription factors act as molecular switches to mediate opposite steroid regulation of the human glucocorticoid receptor 1A promoter

Steroid auto-regulation of the human glucocorticoid receptor (hGR) 1A promoter in lymphoblast cells resides largely in two DNA elements (footprints 11 and 12). We show here that c-Myb and c-Ets family members (Ets-1/2, PU.1, and Spi-B) control hGR 1A promoter regulation in T- and B-lymphoblast cells. Two T-lymphoblast lines, CEM-C7 and Jurkat, contain high levels of c-Myb and low levels of PU.1, whereas the opposite is true in IM-9 B-lymphoblasts. In Jurkat cells, overexpression of c-Ets-1, c-Ets-2, or PU.1 effectively represses dexamethasone-mediated up-regulation of an hGR 1A promoter-luciferase reporter gene, as do dominant negative c-Myb (c-Myb DNA-binding domain) or Ets proteins (Ets-2 DNA-binding domain). Overexpression of c-Myb in IM-9 cells confers hormone-dependent up-regulation to the hGR 1A promoter reporter gene. Chromatin immunoprecipitation assays show that hormone treatment causes the recruitment of hGR and c-Myb to the hGR 1A promoter in CEM-C7 cells, whereas hGR and PU.1 are recruited to this promoter in IM-9 cells. These observations suggest that the specific transcription factor that binds to footprint 12, when hGR binds to the adjacent footprint 11, determines the direction of hGR 1A promoter auto-regulation. This leads to a "molecular switch" model for auto-regulation of the hGR 1A promoter.

ETS transcription factors and their emerging roles in human cancer

Cancer can be defined as a genetic disease, resulting as a consequence of multiple events associated with initiation, promotion and metastatic growth. Cancer results from the loss of control of cellular homeostasis. Cell homeostasis is the result of the balance between proliferation and cell death, while cellular transformation can be viewed as a loss of relationship between these events. Oncogenes and tumour suppressor genes act as modulators of cell proliferation, while the balance of apoptotic and anti-apoptotic genes controls cell death. All cancer cells acquire similar sets of functional capacities: (1) independence from mitogenic/growth signals; (2) loss of sensitivity to "anti-growth" signals; (3) evade apoptosis; (4) Neo-angiogenic conversion; (5) release from senescence; and (6) invasiveness and metastasis. One of the goals of molecular biology is to elucidate the mechanisms that contribute to the development and progression of cancer. Such understanding of the molecular basis of cancer will provide new possibilities for: (1) earlier detection as well as better diagnosis and staging of disease with detection of minimal residual disease recurrences and evaluation of response to therapy; (2) prevention; and (3) novel treatment strategies. We feel that increased understanding of ETS-regulated biological pathways will directly impact these areas. ETS proteins are transcription factors that activate or repress the expression of genes that are involved in various biological processes, including cellular proliferation, differentiation, development, transformation and apoptosis. Identification of target genes that are regulated by a specific transcription factor is one of the most critical areas in understanding the molecular mechanisms that control transcription. Furthermore, identification of target gene promoters for normal and oncogenic transcription factors provides insight into the regulation of genes that are involved in control of normal cell growth, and differentiation, as well as provide information critical to understanding cancer development. This review will highlight the current understanding of ETS genes and their role in cancer.

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

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

Despite WT1 binding sites in the promoter region of human and mouse nucleoporin glycoprotein 210, WT1 does not influence expression of GP210

Background

Glycoprotein 210 (GP210) is a transmembrane component of the nuclear pore complex of metazoans, with a short carboxyterminus protruding towards the cytoplasm. Its function is unknown, but it is considered to be a major structural component of metazoan nuclear pores. Yet, our previous findings showed pronounced differences in expression levels in embryonic mouse tissues and cell lines. In order to identify factors regulating GP210, the genomic organization of human GP210 was analyzed in silico.

Results

The human gene was mapped to chromosome 3 and consists of 40 exons spread over 102 kb. The deduced 1887 amino acid showed a high degree of alignment homology to previously reported orthologues. Experimentally we defined two transcription initiation sites, 18 and 29 bp upstream of the ATG start codon. The promoter region is characterized by a CpG island and several consensus binding motifs for gene regulatory transcription factors, including clustered sites associated with Sp1 and the Wilms' tumor suppressor gene zinc finger protein (WT1). In addition, distal to the translation start we found a (GT)n repetitive sequence, an element known for its ability to bind WT1. Homologies for these motifs could be identified in the corresponding mouse genomic region. However, experimental tetracycline dependent induction of WT1 in SAOS osteosarcoma cells did not influence GP210 transcription.

Conclusion

Although mouse GP210 was identified as an early response gene during induced metanephric kidney development, and WT1 binding sites were identified in the promoter region of the human GP210 gene, experimental modulation of WT1 expression did not influence expression of GP210. Therefore, WT1 is probably not regulating GP210 expression. Instead, we suggest that the identified Sp binding sites are involved.

SP100 expression modulates ETS1 transcriptional activity and inhibits cell invasion

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

Unique and selective effects of five Ets family members, Elf3, Ets1, Ets2, PEA3, and PU.1, on the promoter of the type II transforming growth factor-beta receptor gene

Previous studies have shown that the promoter of the type II TGF-beta receptor gene (TbetaR-II) is strongly stimulated by Elf3, a member of the Ets transcription factor family. The TbetaR-II gene behaves as a tumor suppressor and it is expressed in nearly all cell types, whereas Elf3 is expressed primarily in epithelial cells. Hence, the TbetaR-II gene is likely to be regulated by other Ets proteins in nonepithelial cells. In this study, we examined the effects of four other Ets family members (Ets1, Ets2, PEA3, and PU.1) on TbetaR-II promoter/reporter constructs that contain the two essential ets sites of this gene. These studies employed F9 embryonal carcinoma cells and their differentiated cells, because transcription of the TbetaR-II gene increases after F9 cells differentiate. Here we demonstrate that Ets2, which is expressed in F9-differentiated cells along with Elf3, does not stimulate or bind to the TbetaR-II promoter in these cells. In contrast, PEA3 stimulates the TbetaR-II promoter in F9-differentiated cells, but it inhibits this promoter in F9 cells. Thus, the effects of PEA3 on the TbetaR-II promoter are cell context-dependent. We also show that the effects of Elf3 are cell context-dependent. Elf3 strongly stimulates the TbetaR-II promoter in F9-differentiated cells, but not in F9 cells. In contrast to Elf3 and PEA3, Ets1 strongly stimulates this promoter in both F9 cells and F9-differentiated cells. Finally, we show that PU.1 exerts little or no effect on the activity of the TbetaR-II promoter. Together, our findings indicate that Elf3 is not the only Ets protein capable of stimulating the TbetaR-II promoter. Importantly, our findings also indicate that each of the five Ets proteins influences the TbetaR-II promoter in a unique manner because of important differences in their biochemical properties or their patterns of cellular expression.

Changes in the expression of many Ets family transcription factors and of potential target genes in normal mammary tissue and tumors

Interfering with Ets transcription factor function reverses multiple aspects of the transformed phenotype of mouse or human tumor cells. However, the unknown number of individual Ets factors expressed in any cellular context and the similar DNA binding specificities of Ets family members complicates the identification of those that mediate transformation. By utilizing quantitative PCR assays for 25 mouse Ets factors, we analyzed the expression of essentially the entire Ets family in normal mammary tissue, mammary-related cell lines, and mammary tumors. In normal mammary tissue, 24 Ets factors were expressed. Even clonal derived cell lines expressed 14-20 Ets members. The most abundant Ets factor mRNAs measured in normal mammary tissue were Elk4, Elf1, and Ets2. Subtractive analysis of mammary tissue identified which Ets factors were predominantly expressed in the myeloid/lymphoid or epithelial cell compartments. Comparison of Ets factor expression in normal mammary tissue and mammary tumors identified significantly elevated expression of Pse/PDEF, Ese2/Elf5, Ese3/Ehf, TEL/Etv6, and Elf2/NERF in mammary tumors and confirmed previously reported alterations in expression of Ese1/Elf3 and the PEA3 subfamily. Expression of 13 Ets target genes, implicated in various aspects of tumor progression, was also analyzed. Altered expression of particular Ets target genes was significantly correlated with particular Ets factors (e.g. maspin and Ese2), suggesting specific in vivo regulatory roles. Together, this comprehensive analysis revealed unexpectedly diverse Ets family gene expression, characterized novel Ets factor changes in mammary tumors, and implicated specific Ets factors in the regulation of multiple genes involved in mammary tumor progression.

Ets2-dependent stromal regulation of mouse mammary tumors

The Ets2 transcription factor is regulated by mitogen-activated protein (MAP) kinase phosphorylation of a single threonine residue. We generated by gene targeting a single codon mutation in Ets2 substituting Ala for the critical Thr-72 phosphorylation site (Ets2A72), to investigate the importance of MAP kinase activation of Ets2 in embryo and tumor development. Ets2(A72/A72) mice are viable and develop normally. However, combining the Ets2A72 allele with a deletion mutant of Ets2 results in lethality at E11.5 and shows that Ets2A72 is a hypomorphic allele. Mammary tumors caused by transgenic polyomavirus middle T antigen, activated Neu(Erbb2), or the combination of Neu and transgenic VEGF (Neu; VEGF-25) were all restricted in Ets2(A72/A72) females. The Ets2(A72/A72) restriction on Neu; VEGF-25 tumor growth was associated with increased p21Cip1 expression. The size of tumors transplanted into fat pads of mice with Ets2 targeted alleles was correlated directly with Ets2 activity and fewer stromal cells expressing matrix metalloproteinase 9 (MMP-9). Decreased MMP-3 and MMP-9 mRNAs were confirmed in Ets2(A72/A72) macrophages. Activation of Ets2 at Thr-72 acts in the stroma, downstream of vascular endothelial growth factor production, in part through the regulation of macrophage proteases to support the progression of Neu- and polyomavirus middle-T-initiated mammary tumors.

Ets2 is not required for Ras or Neu/ErbB-2 mediated cellular transformation in vitro

Ets2 is a widely expressed Ets family transcription factor which is activated by Ras signaling and has been reported to transform fibroblasts. Expression of a dominant inhibitory Ets2 construct consisting of just the Ets2 DNA binding domain (Ets2DBD), reverses Ras transformation of NIH3T3 cells and the transformed characteristics of several human tumor cells. However, the Ets2DBD may interfere with multiple Ets family members. We have now utilized cell lines with a disrupted ets2 gene to determine whether Ets2 is required to mediate oncogenic signaling. Expression of the Ets2DBD in an Ets2-deficient cell line dramatically inhibited Ets-dependent (but not AP-1-dependent) reporter gene expression, revealing that the Ets2DBD does inhibit additional Ets family members. The transformation efficiency of Ets2-deficient cell lines by oncogenic Ras or Neu/ErbB-2 was similar to that of control cells in several in vitro assays, and was not enhanced by re-expression of Ets2. Finally, overexpression of Ets2 was not sufficient to induce focus formation in NIH3T3 cells, nor to enhance transformation by oncogenic Ras. Thus, Ets2 is not an essential mediator of Ras or Neu/ErbB-2 transformation in these cells. Our results illustrate the importance of utilizing specific approaches for analyzing the function of individual members of large gene families.

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.

Ets2 and protein kinase C epsilon are important regulators of parathyroid hormone-related protein expression in MCF-7 breast cancer cells

Parathyroid hormone-related protein (PTHrP) promotes the metastatic potential and proliferation of breast cancer cells, and acts anti-apoptotically. In invasive MDA-MB-231 breast cancer cells, transforming growth factor beta-regulated PTHrP synthesis is mediated by an Ets1/Smad3-dependent activation of the PTHrP P3 promoter. In the present study, we studied the regulation of PTHrP expression in non-invasive, Ets1-deficient and transforming growth factor beta-resistant MCF-7 cells. We found PMA to be a strong stimulator of P3-dependent PTHrP expression in MCF-7 cells. Mitogen-activated protein kinase (MAPK)/extracellular-signal-regulated kinase (ERK) kinase 1 (MEK-1)/ERK1/2 inhibitor PD98059 interfered with this activity. Promoter studies revealed that the PMA effect depended on the Ets and stimulating protein-1 (Sp1)-binding sites. Of several Ets factors tested, Ets2, but not Ese-1, Elf-1 or Ets1, supported the PMA-dependent increase in promoter activity. PD98059 and a threonine to alanine mutation of the ERK1/2-responsive Ets2 phosphorylation site at position 72 inhibited the Ets2/PMA effect. Activated protein kinase C (PKC) epsilon could mimic PMA by stimulating the P3 promoter alone or in co-operation with Ets2 in an MEK-1/ERK1/2-dependent manner. Activated PKC alpha, although capable of co-operating with Ets2, failed to induce transcription from the P3 promoter on its own. The Ets2/PKalpha synergistic effect was neither sensitive to PD98059 nor to Thr(72)/Ala(72) mutation. PMA neither increased the expression of Sp1 nor modulated the transcriptional activity of Sp1. However, it induced the displacement of a yet unknown factor from the Sp1-binding site, which may result in Sp1 recruitment to the promoter. Our results suggest an ERK1/2-dependent Ets2/PKC epsilon synergism to be involved in PTHrP expression in MCF-7 breast cancer cells.

Dominant negative form of signal-regulatory protein-alpha (SIRPalpha /SHPS-1) inhibits tumor necrosis factor-mediated apoptosis by activation of NF-kappa B

Genetic suppressor element (GSE) methodology was applied to identify new genes controlling cell response to tumor necrosis factor (TNF). A retroviral library of randomly fragmented normalized cDNA from mouse fibroblasts was screened for GSEs capable of protecting NIH3T3 cells from TNF-induced apoptosis. The most abundant among isolated GSEs represented a fragment of cDNA encoding the C-terminal cytoplasmic region of the immunoglobulin family inhibitory receptor, SHPS-1 (mouse homologue of human SIRPalpha). Ectopic expression of this fragment (both from human and mouse versions) increased the NF-kappaB-dependent transcription in three cell lines tested; this effect could be reduced by the expression of full-length SIRPalpha, suggesting that the isolated GSE acts through a dominant negative mechanism. GSE-mediated activation of NF-kappaB depended on the presence of serum, was abrogated by wortmannin, and was associated with phosphorylation of PKB/Akt, suggesting that Akt mediates it. These data indicate that SIRPalpha/SHPS-1 is involved in negative regulation of NF-kappaB signaling.

The epithelial-specific ETS transcription factor ESX/ESE-1/Elf-3 modulates breast cancer-associated gene expression

Several members of the ETS family of transcription factors contribute to tumorigenesis in many different tissues, including breast epithelium. The ESX gene is an epithelial-specific Ets member that is particularly relevant to breast cancer. ESX is amplified in early breast cancers, it is overexpressed in human breast ductal carcinoma in situ, and there may be a positive feedback loop between the HER2/neu proto-oncogene and ESX. Despite this progress in our understanding of ESX, its ability to regulate tumor-related gene expression and to modulate breast cell survival, remain unknown. Here we show that HA-ESX stimulates the collagenase and HER2/neu promoters, but fails to activate an intact stromelysin promoter. However, HA-ESX activates, in a dose-dependent manner, a heterologous promoter containing eight copies of the Ets binding site derived from the stromelysin gene (p8Xpal-CAT). Analysis of the ability of constructs encoding nine Ets family members to activate the HER2/neu promoter revealed three patterns of gene activation: (1) no effect or repressed promoter activity (Elk-1 and NET); (2) intermediate activity (ER81, GABP, ESX, and HA-Ets-2); and, (3) maximal activity (Ets-1, VP-16-Ets-1, and EHF). Based on these observations, we also determined whether ESX is capable of conferring a survival phenotype upon immortalized, but nontransformed and ESX negative MCF-12A human breast cells. Using a colony formation assay, we found that HA-ESX and HA-Ets-2, mediated MCF-12A cell survival rates that approached those generated by oncogenic V12 Ras, whereas empty vector resulted in negligible colony formation. By contrast, in immortalized and transformed T47D breast cancer cells, which express both HER2/neu and ESX, we found that antisense and dominant-negative HA-ESX inhibited T47D colony formation, whereas control vector allowed formation of many colonies. These results are significant because they show that HA-ESX is able to differentially activate several malignancy-associated gene promoters, and that ESX expression is required for cellular survival of nontransformed MCF-12A and transformed T47D human mammary cells.

Ras signalling on the endoplasmic reticulum and the Golgi

Current models evoke the plasma membrane (PM) as the exclusive platform from which Ras regulates signalling. We developed a fluorescent probe that reports where and when Ras is activated in living cells. We show that oncogenic H-Ras and N-Ras engage Raf-1 on the Golgi and that endogenous Ras and unpalmitoylated H-Ras are activated in response to mitogens on the Golgi and endoplasmic reticulum (ER), respectively. We also demonstrate that H-Ras that is restricted to the ER can activate the Erk pathway and transform fibroblasts, and that Ras localized on different membrane compartments differentially engages various signalling pathways. Thus, Ras signalling is not limited to the PM, but also proceeds on the endomembrane.

Ets-2 is induced by oxidative stress and sensitizes cells to H(2)O(2)-induced apoptosis: implications for Down's syndrome

An elevated production of hydrogen peroxide mediates the increased rate of apoptosis of cells derived from individuals with Down's syndrome. The mechanism via which this occurs is unknown. Here we show that Ets-2, a transcription factor located on human chromosome 21 and already overexpressed in multiple tissues in Down syndrome (DS, trisomy 21), is induced by low concentrations of hydrogen peroxide. Moreover, cells with an imbalance in the antioxidant enzymes SOD-1/GPX-1, such as occurs in DS through the overexpression of the chromosome 21 gene SOD-1, also results in increased Ets-2 expression. The increase in Ets-2 expression is dependent on mRNA transcription. Importantly, we further demonstrate that 3T3 fibroblasts that overexpress Ets-2 are sensitized to hydrogen peroxide-induced apoptosis. These data implicate Ets-2 in the regulation of oxidant-induced apoptosis and provide a possible rationale for both the (5- to 7-) fold increase in Ets-2 protein level in DS tissues, above the expected gene dosage of 1.5-fold, and the elevated rate of apoptosis in DS cells.

The epithelium-specific ETS protein EHF/ESE-3 is a context-dependent transcriptional repressor downstream of MAPK signaling cascades

Exon trapping and cDNA selection procedures were used to search for novel genes at human chromosome 11p13, a region previously associated with loss of heterozygosity in epithelial carcinomas. Using these approaches, we found the ESE-2 and ESE-3 genes, coding for ETS domain-containing transcription factors. These genes lie in close proximity to the catalase gene within a approximately 200-kilobase genomic interval. ESE-3 mRNA is widely expressed in human tissues with high epithelial content, and immunohistochemical analysis with a newly generated monoclonal antibody revealed that ESE-3 is a nuclear protein expressed exclusively in differentiated epithelial cells and that it is absent in the epithelial carcinomas tested. In transient transfections, ESE-3 behaves as a repressor of the Ras- or phorbol ester-induced transcriptional activation of a subset of promoters that contain ETS and AP-1 binding sites. ESE-3-mediated repression is sequence- and context-dependent and depends both on the presence of high affinity ESE-3 binding sites in combination with AP-1 cis-elements and the arrangement of these sites within a given promoter. We propose that ESE-3 might be an important determinant in the control of epithelial differentiation, as a modulator of the nuclear response to mitogen-activated protein kinase signaling cascades.

Opposing effects of Ets and Id proteins on p16INK4a expression during cellular senescence

The p16INK4a cyclin-dependent kinase inhibitor is implicated in replicative senescence, the state of permanent growth arrest provoked by cumulative cell divisions or as a response to constitutive Ras-Raf-MEK signalling in somatic cells. Some contribution to senescence presumably underlies the importance of p16INK4a as a tumour suppressor but the mechanisms regulating its expression in these different contexts remain unknown. Here we demonstrate a role for the Ets1 and Ets2 transcription factors based on their ability to activate the p16INK4a promoter through an ETS-binding site and their patterns of expression during the lifespan of human diploid fibroblasts. The induction of p16INK4a by Ets2, which is abundant in young human diploid fibroblasts, is potentiated by signalling through the Ras-Raf-MEK kinase cascade and inhibited by a direct interaction with the helix-loop-helix protein Id1 (ref. 11). In senescent cells, where the Ets2 levels and MEK signalling decline, the marked increase in p16INK4a expression is consistent with the reciprocal reduction of Id1 and accumulation of Ets1.

Proteins of the ETS family with transcriptional repressor activity

ETS proteins form one of the largest families of signal-dependent transcriptional regulators, mediating cellular proliferation, differentiation and tumorigenesis. Most of the known ETS proteins have been shown to activate transcription. However, four ETS proteins (YAN, ERF, NET and TEL) can act as transcriptional repressors. In three cases (ERF, NET and TEL) distinct repression domains have been identified and there are indications that NET and TEL may mediate transcription via Histone Deacetylase recruitment. All four proteins appear to be regulated by MAPKs, though for YAN and ERF this regulation seems to be restricted to ERKs. YAN, ERF and TEL have been implicated in cellular proliferation although there are indications suggesting a possible involvement of YAN and TEL in differentiation as well. Other ETS-domain proteins have been shown to repress transcription in a context specific manner, and there are suggestions that the ETS DNA-binding domain may act as a transcriptional repressor. Transcriptional repression by ETS domain proteins adds an other level in the orchestrated regulation by this diverse family of transcription factors that often recognize similar if not identical binding sites on DNA and are believed to regulate critical genes in a variety of biological processes. Definitive assessment of the importance of this novel regulatory level will require the identification of ETS proteins target genes and the further analysis of transcriptional control and biological function of these proteins in defined pathways.

The p38 pathway provides negative feedback for Ras proliferative signaling

Ras activates three mitogen-activated protein kinases (MAPKs) including ERK, JNK, and p38. Whereas the essential roles of ERK and JNK in Ras signaling has been established, the contribution of p38 remains unclear. Here we demonstrate that the p38 pathway functions as a negative regulator of Ras proliferative signaling via a feedback mechanism. Oncogenic Ras activated p38 and two p38-activated protein kinases, MAPK-activated protein kinase 2 (MK2) and p38-related/activated protein kinase (PRAK). MK2 and PRAK in turn suppressed Ras-induced gene expression and cell proliferation, whereas two mutant PRAKs, unresponsive to Ras, had little effect. Moreover, the constitutive p38 activator MKK6 also suppressed Ras activity in a p38-dependent manner whereas arsenite, a potent chemical inducer of p38, inhibited proliferation only in a tumor cell line that required Ras activity. MEK was required for Ras stimulation of the p38 pathway. The p38 pathway inhibited Ras activity by blocking activation of JNK, without effect upon ERK, as evidenced by the fact that PRAK-mediated suppression of Ras-induced cell proliferation was reversed by coexpression of JNKK2 or JNK1. These studies thus establish a negative feedback mechanism by which Ras proliferative activity is regulated via signaling integrations of MAPK pathways.

Altered Ets transcription factor activity in prostate tumor cells inhibits anchorage-independent growth, survival, and invasiveness

The Ets family of transcription factors are important downstream targets in cellular transformation, as altering Ets activity has been found to reverse the transformed phenotype of Ras transformed mouse fibroblasts and of several human tumor cell lines. To determine whether Ets factors are important targets in the largely uncharacterized aberrant signaling in prostate cancer, we have altered Ets activity in the prostate tumor cell line PPC-1, by stable expression of either full-length Ets2, or a dominant inhibitor of Ets activity, the Ets2 DNA binding domain (Ets2DBD). Analysis of multiple independent clonal cell lines revealed that expression of either Ets2 or the Ets2DBD inhibited the anchorage-independent growth of PPC-1 cells up to 20-fold. In contrast to our previous findings with Ras-transformed NIH3T3 cells, PPC-1 cell lines expressing either Ets2 or the EtsDBD exhibited slower attached cell growth, increased Ets-dependent gene expression, and up to a 10-fold increase in apoptotic cell death. The p21cip gene was identified as a potential target of altered Ets signaling. Interestingly, the two distinct Ets2 constructs had strikingly different effects on in vitro invasiveness. Expression of the Ets2DBD almost completely blocked PPC-1 cell invasion through Matrigel, whereas over-expression of full-length Ets2 did not inhibit invasion. Overall, these results demonstrate that the balance of Ets factor activity can regulate multiple aspects of the transformed phenotype of PPC-1 prostate tumor cells, including anchorage-independent growth, survival, and invasiveness.

Tel induces a G1 arrest and suppresses Ras-induced transformation

The Tel gene is a major target of translocations in leukemia and loss of heterozygosity is regularly observed for the non-translocated allele, thus supporting the notion that Tel is a tumor suppressor. Most tumor suppressors influence cellular proliferation, differentiation and cell death and thereby prevent oncogenic transformation and genetic instability. We found that overexpression of Tel retards proliferation of many cell types, primary cells and immortalized cells, by inducing a G1 arrest. Tel's block of cellular proliferation is rescued by high seeding densities. Furthermore, Tel suppressed Ras-mediated colony growth in soft agar and tumor formation in nude mice. The Pointed and DNA binding (DB) domains of Tel were required for all Tel-induced phenotypes.

TEL, a putative tumor suppressor, modulates cell growth and cell morphology of ras-transformed cells while repressing the transcription of stromelysin-1

TEL is a member of the ETS family of transcription factors that interacts with the mSin3 and SMRT corepressors to regulate transcription. TEL is biallelically disrupted in acute leukemia, and loss of heterozygosity at the TEL locus has been observed in various cancers. Here we show that expression of TEL in Ras-transformed NIH 3T3 cells inhibits cell growth in soft agar and in normal cultures. Unexpectedly, cells expressing both Ras and TEL grew as aggregates. To begin to explain the morphology of Ras-plus TEL-expressing cells, we demonstrated that the endogenous matrix metalloproteinase stromelysin-1 was repressed by TEL. TEL bound sequences in the stromelysin-1 promoter and repressed the promoter in transient-expression assays, suggesting that it is a direct target for TEL-mediated regulation. Mutants of TEL that removed a binding site for the mSin3A corepressor but retained the ETS domain failed to repress stromelysin-1. When BB-94, a matrix metalloproteinase inhibitor, was added to the culture medium of Ras-expressing cells, it caused a cell aggregation phenotype similar to that caused by TEL expression. In addition, TEL inhibited the invasiveness of Ras-transformed cells in vitro and in vivo. Our results suggest that TEL acts as a tumor suppressor, in part, by transcriptional repression of stromelysin-1.

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.

Transcriptional repressor ERF is a Ras/mitogen-activated protein kinase target that regulates cellular proliferation

A limited number of transcription factors have been suggested to be regulated directly by Erks within the Ras/mitogen-activated protein kinase signaling pathway. In this paper we demonstrate that ERF, a ubiquitously expressed transcriptional repressor that belongs to the Ets family, is physically associated with and phosphorylated in vitro and in vivo by Erks. This phosphorylation determines the ERF subcellular localization. Upon mitogenic stimulation, ERF is immediately phosphorylated and exported to the cytoplasm. The export is blocked by specific Erk inhibitors and is abolished when residues undergoing phosphorylation are mutated to alanine. Upon growth factor deprivation, ERF is rapidly dephosphorylated and transported back into the nucleus. Phosphorylation-defective ERF mutations suppress Ras-induced tumorigenicity and arrest the cells at the G0/G1 phase of the cell cycle. Our findings strongly suggest that ERF may be important in the control of cellular proliferation during the G0/G1 transition and that it may be one of the effectors in the mammalian Ras signaling pathway.