Expression of the ets-1 proto-oncogene in human breast carcinoma: differential expression with histological grading and growth pattern

Glycogen synthase kinase-3 beta (GSK3β)-mediated phosphorylation of ETS1 promotes progression of ovarian carcinoma

ETS1 - an evolutionarily conserved transcription factor involved in the regulation of a number of cellular processes - is overexpressed in several malignancies, including ovarian cancer. Most studies on ETS1 expression have been focused on the transcriptional and RNA levels, with post-translational control mechanisms remaining relatively unexplored in the pathogenesis of malignancies. Here, we show that ETS1 forms a complex with glycogen synthase kinase-3β (GSK3β). Specifically, GSK3β-mediated phosphorylation of ETS1 at threonine 265 and serine 269 promoted protein stability, induced the transcriptional activation of matrix metalloproteinase (MMP)-9, and increased cell migration. In vivo experiments revealed that a GSK3β inhibitor was able to suppress both endogenous ETS1 expression and induction of MMP-9 expression. Upon generation of a specific antibody against phosphorylated ETS1, we demonstrated that phospho-ETS1 immunohistochemical expression in ovarian cancer specimens was correlated with that of MMP-9. Notably, the cumulative overall survival of patients with low phospho-ETS1 histoscores was significantly longer than that of those showing higher scores. We conclude that the GSK3β/ETS1/MMP-9 axis may regulate the biological aggressiveness of ovarian cancer and can serve as a prognostic factor in patients with this malignancy.

Statins affect ETS1-overexpressing triple-negative breast cancer cells by restoring DUSP4 deficiency

We investigated the molecular mechanisms underlying statin-induced growth suppression of triple-negative breast cancer (TNBC) that overexpress the transcription factor ets proto-oncogene 1(ets-1) and downregulate dual specific protein phosphatase 4(dusp4) expression. We examined the gene expression of BC cell lines using the nCounter expression assay, MTT viability assay, cell proliferation assay and Western blot to evaluate the effects of simvastatin. Finally, we performed cell viability testing in TNBC cell line-transfected DUSP4. We demonstrated that ETS1 mRNA and protein were overexpressed in TNBC cells compared with other BC cell lines (P = <0.001) and DUSP4 mRNA was downregulated (P = <0.001). MTT viability assay showed that simvastatin had significant antitumor activity (P = 0.002 in 0.1 μM). In addition, simvastatin could restore dusp4 deficiency and suppress ets-1 expression in TNBC. Lastly, we found that si-DUSP4 RNA transfection overcame the antitumor activity of statins. MAPK pathway inhibitor, U0126 and PI3KCA inhibitor LY294002 also decreased levels of ets-1, phosphor-ERK and phosphor-AKT on Western blot assay. Accordingly, our study indicates that simvastatin potentially affects the activity of transcriptional factors such as ets-1 and dusp4 through the MAPK pathway. In conclusion, statins might be potential candidates for TNBC therapy reducing ets-1 expression via overexpression of dusp4.

MicroRNA-124 inhibits cellular proliferation and invasion by targeting Ets-1 in breast cancer

MicroRNAs (miRNAs) are small non-coding RNAs that, by targeting certain messenger RNAs (mRNAs) for translational repression or cleavage, can regulate the expression of these genes. In addition, miRNAs may also function as oncogenes and tumor-suppressor genes, as the abnormal expression of miRNAs is associated with various human tumors. However, the effects of the expression of miR-124 in breast cancer remain unclear. The present study was conducted to study the expression of miR-124 in breast cancer, paying particular attention to miR-124's relation to the proliferation, invasion, and apoptosis in breast cancer cell MCF-7 and MDA-MB-231. Real-time quantitative RT-PCR (qRT-PCR) was performed to identify miR-124 that was down-regulated in breast cancer tissues. We also showed E26 transformation specific-1 (Ets-1) and miR-124 expression levels in breast cancer tissues that were associated with lymph node metastases. With transfected synthetic miR-124 agomir into MCF-7 and MDA-MB-231, a significant reduction (P < 0.05) in MCF-7 and MDA-MB-231 cell proliferation and colony forming potential was observed after treatment with miR-124. Apoptosis and migration rates were found to be significantly higher in two breast-derived cell lines transfected with a miR-124 agomir (P < 0.05). Luciferase reporter assay and Western blot were used to verify Ets-1 as a potential major target gene of miR-124, and the result showed that miR-124 can bind to putative binding sites within the Ets-1 mRNA 3' untranslated region (UTR) to reduce its expression. Based on these findings, we propose that miR-124 and Ets-1 may serve as a therapeutic agent in breast cancer.

FBI-1 enhances ETS-1 signaling activity and promotes proliferation of human colorectal carcinoma cells

In this study, we investigated a potential regulatory role of FBI-1 in transcription factor activity of ETS-1. The protein interaction was identified between ETS-1 and FBI-1 in lovo cells. The accumulating data showed that FBI-1 promoted the recruitment of ETS-1 to endogenous promoter of its target genes and increase ETS-1 accumulation in the nuclear. Our work also indicated that the FBI-1 enhances ETS-1 transcription factor activity via down-regulating p53-mediated inhibition on ETS-1. Further, FBI-1 plays a role in regulation of colorectal carcinoma cells proliferation. These findings supported that FBI-1 might be a potential molecule target for treating colorectal carcinoma.

Requirement of PEA3 for transcriptional activation of FAK gene in tumor metastasis

Focal adhesion kinase (FAK) is a non-receptor tyrosine kinase critically involved in cancer metastasis. We found an elevation of FAK expression in highly metastatic melanoma B16F10 cells compared with its less metastatic partner B16F1 cells. Down-regulation of the FAK expression by either small interfering RNA or dominant negative FAK (FAK Related Non-Kinase, FRNK) inhibited the B16F10 cell migration in vitro and invasiveness in vivo. The mechanism by which FAK activity is up-regulated in highly metastatic cells remains unclear. In this study, we reported for the first time that one of the Est family proteins, PEA3, is able to transactivate FAK expression through binding to the promoter region of FAK. We identified a PEA3-binding site between nucleotides -170 and +43 in the FAK promoter that was critical for the responsiveness to PEA3. A stronger affinity of PEA3 to this region contributed to the elevation of FAK expression in B16F10 cells. Both in vitro and in vivo knockdown of PEA3 gene successfully mimicked the cell migration and invasiveness as that induced by FAK down-regulation. The activation of the well-known upstream of PEA3, such as epidermal growth factor, JNK, and ERK can also induce FAK expression. Furthermore, in the metastatic human clinic tumor specimens from the patients with human primary oral squamous cell carcinoma, we observed a strong positive correlation among PEA3, FAK, and carcinoma metastasis. Taking together, we hypothesized that PEA3 might play an essential role in the activation of the FAK gene during tumor metastasis.

Ets-1 regulates intracellular glutathione levels: key target for resistant ovarian cancer

Background

Ovarian cancer is characterized by high rates of metastasis and therapeutic resistance. Many chemotherapeutic agents rely on the induction of oxidative stress to cause cancer cell death, thus targeting redox regulation is a promising strategy to overcome drug resistance.

Methods

We have used a tetracycline-inducible Ets-1 overexpression model derived from 2008 ovarian cancer cells in the present study. To examine the role of Ets-1 in glutathione regulation we have measured intracellular reactive oxygen species and glutathione levels, as well as glutathione peroxidase enzyme activity. Glutathione synthesis was limited using transsulfuration or Sx_c^- pathway blocking agents, and glutamate release was measured to confirm Sx_c^- blockade. Cell viability following drug treatment was assessed via crystal violet assay. Oxidative stress was induced through glucose oxidase treatment, which produces hydrogen peroxide by glucose oxidation. The protein expressions of redox-related factors were measured through western blotting.

Results

Overexpression of Ets-1 was associated with decreased intracellular ROS, concomitantly with increased intracellular GSH, GPX antioxidant activity, and Sx_c^- transporter activity. Under basal conditions, inhibition of the transsulfuration pathway resulted in decreased GSH levels and GPX activity in all cell lines, whereas inhibition of Sx_c^- by sulfasalazine decreased GPX activity in Ets-1-expressing cells only. However, under oxidative stress the intracellular GSH levels decreased significantly in correlation with increased Ets-1 expression following sulfasalazine treatment.

Conclusions

In this study we have identified a role for proto-oncogene Ets-1 in the regulation of intracellular glutathione levels, and examined the effects of the anti-inflammatory drug sulfasalazine on glutathione depletion using an ovarian cancer cell model. The findings from this study show that Ets-1 mediates enhanced Sx_c^- activity to increase glutathione levels under oxidative stress, suggesting that Ets-1 could be a promising putative target to enhance conventional therapeutic strategies.

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.

Ets-1 is required for the activation of VEGFR3 during latent Kaposi's sarcoma-associated herpesvirus infection of endothelial cells

Kaposi's sarcoma-associated herpesvirus (KSHV), the etiologic agent of Kaposi's sarcoma (KS), is present in the predominant tumor cells of KS, the spindle cells. Spindle cells express markers of lymphatic endothelium and, interestingly, KSHV infection of blood endothelial cells reprograms them to a lymphatic endothelial cell phenotype. KSHV-induced reprogramming requires the activation of STAT3 and phosphatidylinositol 3 (PI3)/AKT through the activation of cellular receptor gp130. Importantly, KSHV-induced reprogramming is specific to endothelial cells, indicating that there are additional host genes that are differentially regulated during KSHV infection of endothelial cells that contribute to lymphatic reprogramming. We found that the transcription factor Ets-1 is highly expressed in KS spindle cells and is upregulated during KSHV infection of endothelial cells in culture. The KSHV latent vFLIP gene is sufficient to induce Ets-1 expression in an NF-κB-dependent fashion. Ets-1 is required for KSHV-induced expression of VEGFR3, a lymphatic endothelial-cell-specific receptor important for lymphangiogenesis, and Ets-1 activates the promoter of VEGFR3. Ets-1 knockdown does not alter the expression of another lymphatic-specific gene, the podoplanin gene, but does inhibit the expression of VEGFR3 in uninfected lymphatic endothelium, indicating that Ets-1 is a novel cellular regulator of VEGFR3 expression. Knockdown of Ets-1 affects the ability of KSHV-infected cells to display angiogenic phenotypes, indicating that Ets-1 plays a role in KSHV activation of endothelial cells during latent KSHV infection. Thus, Ets-1 is a novel regulator of VEGFR3 and is involved in the induction of angiogenic phenotypes by KSHV.

The level of Ets-1 protein is regulated by poly(ADP-ribose) polymerase-1 (PARP-1) in cancer cells to prevent DNA damage

Ets-1 is a transcription factor that regulates many genes involved in cancer progression and in tumour invasion. It is a poor prognostic marker for breast, lung, colorectal and ovary carcinomas. Here, we identified poly(ADP-ribose) polymerase-1 (PARP-1) as a novel interaction partner of Ets-1. We show that Ets-1 activates, by direct interaction, the catalytic activity of PARP-1 and is then poly(ADP-ribosyl)ated in a DNA-independent manner. The catalytic inhibition of PARP-1 enhanced Ets-1 transcriptional activity and caused its massive accumulation in cell nuclei. Ets-1 expression was correlated with an increase in DNA damage when PARP-1 was inhibited, leading to cancer cell death. Moreover, PARP-1 inhibitors caused only Ets-1-expressing cells to accumulate DNA damage. These results provide new insight into Ets-1 regulation in cancer cells and its link with DNA repair proteins. Furthermore, our findings suggest that PARP-1 inhibitors would be useful in a new therapeutic strategy that specifically targets Ets-1-expressing tumours.

Transcriptional silencing of the ETS1 oncogene contributes to human granulocytic differentiation

BACKGROUND

Ets-1 is a widely expressed transcription factor implicated in several biological processes including hematopoiesis, where it contributes to the regulation of cellular differentiation. The functions of Ets-1 are regulated by transcription factors as well as by phosphorylation events: phosphorylation of threonine 38 activates Ets-1, whereas phosphorylation of a cluster of serines within exon VII reduces DNA binding activity. This study focuses on the role of Ets-1 during granulocytic differentiation of NB4 promyelocytic and HL60 myeloblastic leukemia cell lines induced by all-trans retinoic acid.

DESIGN AND METHODS

Ets-1 expression was measured by real-time reverse transcriptase polymerase chain reaction and western blotting. The role of Ets-1 during all-trans retinoic acid-induced differentiation was analyzed by using a transdominant negative molecule or small interfering RNA.

RESULTS

NB4 and HL60 cell lines expressed high levels of p51 Ets-1, while the splice variant isoform that lacks exon VII (p42) was almost undetectable. The addition of all-trans retinoic acid reduced p51 Ets-1 levels and induced inhibitory phosphorylation of the remaining protein. Expression of Ets-1 was also reduced during dimethylsulfoxide-induced differentiation and during granulocytic differentiation of human CD34(+) hematopoietic progenitor cells but not in NB4.R2 and HL60R cells resistant to all-trans retinoic acid. In line with these observations, transduction of a transdominant negative molecule of Ets-1, which inhibited DNA binding and transcriptional activity of the wild-type Ets-1, significantly increased chemical-induced differentiation. Consistently, Ets-1 knockdown by small interfering RNA increased the number of mature neutrophils upon addition of all-trans retinoic acid. Interestingly, p51 Ets-1 over-expression was frequently observed in CD34(+) hematopoietic progenitor cells derived from patients with acute myeloid leukemia, as compared to its expression in normal CD34(+) cells.

CONCLUSIONS

Our results indicated that a decreased expression of Ets-1 protein generalizes to granulocytic differentiation and may represent a crucial event for granulocytic maturation.

PIASy controls ubiquitination-dependent proteasomal degradation of Ets-1

The ETS transcription factor Ets-1 (E26 transformation-specific-1) plays a critical role in many physiological processes including angiogenesis, haematopoietic development and tumour progression. Its activity can be regulated by post-translational modifications, such as phosphorylation. Recently, we showed that Ets-1 is a target for SUMO (small ubiquitin-like modifier) modification and that PIASy [protein inhibitor of activated STAT (signal transducer and activator of transcription) Y], a specific SUMO-E3 ligase for Ets-1, represses Ets-1-dependent transcription. In the present study, we demonstrated that Ets-1 is degraded by the proteasome and that overexpression of PIASy increased the stability of endogenous and ectopically expressed Ets-1 protein by preventing proteasomal degradation. Moreover, knockdown of the endogenous PIASy expression by RNA interference reduced the protein level of endogenous Ets-1. The proteasome inhibitor MG132 reversed this effect. Deletion analysis showed that the TAD (transcriptional activation domain), which has been identified as the interaction domain with PIASy, was also required for Ets-1 ubiquitination and proteasomal degradation. However, the Ets-1 stabilization by PIASy was not due to reduced ubiquitination of Ets-1. Our results suggested that PIASy controls Ets-1 function, at least in part, by inhibiting Ets-1 protein turnover via the ubiquitin-proteasome system.

Bioinformatic screening of human ESTs for differentially expressed genes in normal and tumor tissues

Background

Owing to the explosion of information generated by human genomics, analysis of publicly available databases can help identify potential candidate genes relevant to the cancerous phenotype. The aim of this study was to scan for such genes by whole-genome in silico subtraction using Expressed Sequence Tag (EST) data.

Methods

Genes differentially expressed in normal versus tumor tissues were identified using a computer-based differential display strategy. Bcl-xL, an anti-apoptotic member of the Bcl-2 family, was selected for confirmation by western blot analysis.

Results

Our genome-wide expression analysis identified a set of genes whose differential expression may be attributed to the genetic alterations associated with tumor formation and malignant growth. We propose complete lists of genes that may serve as targets for projects seeking novel candidates for cancer diagnosis and therapy. Our validation result showed increased protein levels of Bcl-xL in two different liver cancer specimens compared to normal liver. Notably, our EST-based data mining procedure indicated that most of the changes in gene expression observed in cancer cells corresponded to gene inactivation patterns. Chromosomes and chromosomal regions most frequently associated with aberrant expression changes in cancer libraries were also determined.

Conclusion

Through the description of several candidates (including genes encoding extracellular matrix and ribosomal components, cytoskeletal proteins, apoptotic regulators, and novel tissue-specific biomarkers), our study illustrates the utility of in silico transcriptomics to identify tumor cell signatures, tumor-related genes and chromosomal regions frequently associated with aberrant expression in cancer.