Ras-mediated phosphorylation of a conserved threonine residue enhances the transactivation activities of c-Ets1 and c-Ets2

Molecular mechanisms of ETS transcription factor-mediated tumorigenesis

The E26 transformation-specific (ETS) family of transcription factors is critical for development, differentiation, proliferation and also has a role in apoptosis and tissue remodeling. Changes in expression of ETS proteins therefore have a significant impact on normal physiology of the cell. Transcriptional consequences of ETS protein deregulation by overexpression, gene fusion, and modulation by RAS/MAPK signaling are linked to alterations in normal cell functions, and lead to unlimited increased proliferation, sustained angiogenesis, invasion and metastasis. Existing data show that ETS proteins control pathways in epithelial cells as well as stromal compartments, and the crosstalk between the two is essential for normal development and cancer. In this review, we have focused on ETS factors with a known contribution in cancer development. Instead of focusing on a prototype, we address cancer associated ETS proteins and have highlighted the diverse mechanisms by which they affect carcinogenesis. Finally, we discuss strategies for ETS factor targeting as a potential means for cancer therapeutics.

Depletion of ERK2 but not ERK1 abrogates oncogenic Ras-induced senescence

In response to oncogenic activation, cells initially undergo proliferation followed by an irreversible growth arrest called oncogene-induced senescence (OIS), an endogenous defense mechanism against tumorigenesis. Oncogenic activation of ERK1/2 is essential for both the initial phase of cellular proliferation as well as subsequent premature senescence, but little is known about the specific contribution of ERK1 versus 2 to OIS. Here we show that depletion of ERK2 but not ERK1 by shRNA knockdown in MEFs leads to continuous proliferation bypassing senescence even in the presence of oncogenic HRAS(V12). Upon depletion of ERK2, induction of both p19(Arf) and p16(Ink4a) was significantly compromised after oncogenic HRAS(V12) expression, attenuating activation of the key tumor suppressors p53 and pRb. Here we demonstrate that ERK2 but not ERK1 indirectly regulates p19(Arf) and p16(Ink4a) both at the transcriptional and translational level. Oncogenic Ras expression after ERK2 knockdown downregulates Fra-1 and c-Jun, components of the activator protein-1 (AP-1) heterodimer essential for transactivation of p19(Arf). Similarly we show a significant decrease in the activation of p38 MAPK and ETS family members which are involved in the induction of p16(Ink4a). The role of ERK2 in translational regulation is observed by the lack of tuberin (TSC2) and p70 ribosomal S6 kinase 1 (p70S6K1) phosphorylation, components of the mTOR pathway, which enhances p19(Arf) mRNA translation during oncogenic Ras-induced senescence. These observations suggest that ERK2 but not ERK1 contributes to upregulation of p19(Arf) and p16(Ink4a) in a transcription- and translation-dependent manner during oncogenic Ras-induced senescence. Taken together, our data indicate that ERK2 is the key ERK isoform mediating the senescence signaling pathway downstream of oncogenic Ras.

Induction of p38δ expression plays an essential role in oncogenic ras-induced senescence

Oncogene-induced senescence is a stable proliferative arrest that serves as a tumor-suppressing defense mechanism. p38 mitogen-activated protein kinase (MAPK) has been implicated in oncogene-induced senescence and tumor suppression. However, the specific role of each of the four p38 isoforms in oncogene-induced senescence is not fully understood. Here, we demonstrate that p38δ mediates oncogene-induced senescence through a p53- and p16(INK4A)-independent mechanism. Instead, evidence suggests a link between p38δ and the DNA damage pathways. Moreover, we have discovered a novel mechanism that enhances the expression of p38δ during senescence. In this mechanism, oncogenic ras induces the Raf-1-MEK-extracellular signal-regulated kinase (ERK) pathway, which, in turn, activates the AP-1 and Ets transcription factors that are bound to the p38δ promoter, leading to increased transcription of p38δ. These findings indicate that induction of the prosenescent function of p38δ by oncogenic ras is achieved through 2 mechanisms, transcriptional activation by the Raf-1-MEK-ERK-AP-1/Ets pathway, which increases the cellular concentration of the p38δ protein, and posttranslational modification by MKK3/6, which stimulates the enzymatic activity of p38δ. In addition, these studies identify the AP-1 and Ets transcription factors as novel signaling components in the senescence-inducing pathway.

24-Hydroxylase in cancer: impact on vitamin D-based anticancer therapeutics

The active vitamin D hormone 1,25-dihydroxyvitamin D3 (1,25(OH)2D3) plays a major role in regulating calcium homeostasis and bone mineralization. 1,25(OH)2D3 also modulates cellular proliferation and differentiation in a variety of cell types. 24-Hydroxylase, encoded by the CYP24A1 gene, is the key enzyme which converts 1,25(OH)2D3 to less active calcitroic acid. Nearly all cell types express 24-hydroxylase, the highest activity being observed in the kidney. There is increasing evidence linking the incidence and prognosis of certain cancers to low serum 25(OH)D3 levels and high expression of vitamin D 24-hydroxylase, supporting the idea that elevated CYP24A1 expression may stimulate degradation of vitamin D metabolites including 25(OH)D3 and 1,25(OH)2D3. The over expression of CYP24A1 in cancer cells may be a factor affecting 1,25(OH)2D3 bioavailability and anti-proliferative activity pre-clinically and clinically. The combination of 1,25(OH)2D3 with CYP24A1 inhibitors enhances 1,25(OH)2D3 mediated signaling and anti-proliferative effects and may be useful in overcoming effects of aberrant CYP24A1 expression. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

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.

The Rho-GEF Trio regulates a novel pro-inflammatory pathway through the transcription factor Ets2

Inflammation is characterized by endothelium that highly expresses numerous adhesion molecules to trigger leukocyte extravasation. Central to this event is increased gene transcription. Small Rho-GTPases not only control the actin cytoskeleton, but are also implicated in gene regulation. However, in inflammation, it is not clear how this is regulated. Here, we show that the guanine-nucleotide exchange factor Trio expression is increased upon inflammatory stimuli in endothelium. Additionally, increased Trio expression was found in the vessel wall of rheumatoid arthritis patients. Trio silencing impaired VCAM-1 expression. Finally, we excluded that Trio-controlled VCAM-1 expression used the classical NFκB or MAP-kinase pathways, but rather acts on the transcriptional level by increasing phosphorylation and nuclear translocalization of Ets2. These data implicate Trio in regulating inflammation and provide novel targets for therapeutic purposes to treat inflammatory diseases such as rheumatoid arthritis.

Modulation of Ets-1 expression in B lymphocytes is dependent on the antigen receptor-mediated activation signals and cell cycle status

In this report, we tested the hypothesis that Ets-1 transcription factor is modulated at the mRNA level during B cell antigen receptor (BCR)-induced cell-signalling events. Quiescent B cells express high levels of Ets-1 mRNA. Stimulation through the BCR results in time-dependent inhibition of Ets-1 mRNA expression in primary splenic B cells with maximal inhibition observed by 16-h post-stimulation. Inhibition of Ets-1 expression is specific to antigen receptor but not CD40-mediated activation. Antigen receptor-induced inhibition of Ets-1 mRNA can be mimicked by phorbol myristate acetate (PMA) and/or ionomycin. PMA but not ionomycin-induced inhibition of Ets-1 expression is rescued by the inhibitors of protein kinase C and MEK. Extended time-course analysis revealed a time-dependent cyclical pattern in the re-expression of Ets-1 mRNA. While resting cells revealed maximal Ets-1 mRNA expression, activation events that induced exit from G(0) /G(1) or cells blocked in early S phase exhibited decreased Ets-1 mRNA levels. Interestingly, cells arrested at late G2 or M phase of the cell cycle failed to down modulate Ets-1 mRNA expression. Overexpression of Ets-1 in 70Z/3 B cell line caused abnormal accumulation of cells in S phase associated with increased cyclin A expression. Consistent with a requirement for Ets-1 in BCR-induced cell cycle entry, splenic B cells from mice deficient in Ets-1 showed defective antigen receptor-induced DNA synthesis and S phase entry. These results suggest a critical role for Ets-1 regulation during B cell activation and cell cycle entry.

Review of Ets1 structure, function, and roles in immunity

The Ets1 transcription factor is a member of the Ets gene family and is highly conserved throughout evolution. Ets1 is known to regulate a number of important biological processes in normal cells and in tumors. In particular, Ets1 has been associated with regulation of immune cell function and with an aggressive behavior in tumors that express it at high levels. Here we review and summarize the general features of Ets1 and describe its roles in immunity and autoimmunity, with a focus on its roles in B lymphocytes. We also review evidence that suggests that Ets1 may play a role in malignant transformation of hematopoietic malignancies including B cell malignancies.

Ras/MAPK signaling modulates VEGFR-3 expression through Ets-mediated p300 recruitment and histone acetylation on the Vegfr3 gene in lymphatic endothelial cells

Modulation of VEGFR-3 expression is important for altering lymphatic endothelial cell (LEC) characteristics during the lymphangiogenic processes that occur under developmental, physiological, and pathological conditions. However, the mechanisms underlying the modulation of Vegfr3 gene expression remain largely unknown. Using genetically engineered mice and LECs, we demonstrated previously that Ras signaling is involved not only in VEGFR-3-induced signal transduction but also in Vegfr3 gene expression. Here, we investigated the roles of the transcription factor Ets and the histone acetyltransferase p300 in LECs in Ras-mediated transcriptional regulation of Vegfr3. Ras activates Ets proteins via MAPK-induced phosphorylation. Ets knockdown, similar to Ras knockdown, resulted in a decrease in both Vegfr3 transcript levels and acetylated histone H3 on the Vegfr3 gene. Vegfr3 knockdown results in altered LEC phenotypes, such as aberrant cell proliferation and network formation, and Ets knockdown led to milder but similar phenotypic changes. We identified evolutionarily conserved, non-coding regulatory elements within the Vegfr3 gene that harbor Ets-binding motifs and have enhancer activities in LECs. Chromatin immunoprecipitation (ChIP) assays revealed that acetylated histone H3 on the regulatory elements of the Vegfr3 gene was decreased following Ras and Ets knockdown, and that activated Ets proteins, together with p300, were associated with these regulatory elements, consistent with a reduction in Vegfr3 gene expression in p300-knockdown LECs. Our findings demonstrate a link between Ras signaling and Ets- and p300-mediated transcriptional regulation of Vegfr3, and provide a potential mechanism by which VEGFR-3 expression levels may be modulated during lymphangiogenesis.

The microRNA miR-199a-5p down-regulation switches on wound angiogenesis by derepressing the v-ets erythroblastosis virus E26 oncogene homolog 1-matrix metalloproteinase-1 pathway

miR-199a-5p plays a critical role in controlling cardiomyocyte survival. However, its significance in endothelial cell biology remains ambiguous. Here, we report the first evidence that miR-199a-5p negatively regulates angiogenic responses by directly targeting v-ets erythroblastosis virus E26 oncogene homolog 1 (Ets-1). Induction of miR-199a-5p in human dermal microvascular endothelial cells (HMECs) blocked angiogenic response in Matrigel® culture, whereas miR-199a-5p-deprived cells exhibited enhanced angiogenesis in vitro. Bioinformatics prediction and miR target reporter assay recognized Ets-1 as a novel direct target of miR-199a-5p. Delivery of miR-199a-5p blocked Ets-1 expression in HMECs, whereas knockdown endogenous miR-199a-5p induced Ets-1 expression. Matrix metalloproteinase 1 (MMP-1), one of the Ets-1 downstream mediators, was negatively regulated by miR-199a-5p. Overexpression of Ets-1 not only rescued miR-199a-5p-dependent anti-angiogenic effects but also reversed miR-199a-5p-induced loss of MMP-1 expression. Similarly, Ets-1 knockdown blunted angiogenic response and induction of MMP-1 in miR-199a-5p-deprived HMECs. Examination of cutaneous wound dermal tissue revealed a significant down-regulation of miR-199a-5p expression, which was associated with induction of Ets-1 and MMP-1. Mice carrying homozygous deletions in the Ets-1 gene exhibited blunted wound blood flow and reduced abundance of endothelial cells. Impaired wound angiogenesis was associated with compromised wound closure, insufficient granulation tissue formation, and blunted induction of MMP-1. Thus, down-regulation of miR-199a-5p is involved in the induction of wound angiogenesis through derepressing of the Ets-1-MMP1 pathway.

Ets-1 regulates radial glia formation during vertebrate embryogenesis

Radial glia cells are the first distinguishable glial population derived from neural epithelial cells and serve as guides for migrating neurons and as neural progenitor cells in the developing brain. Despite their functional importance during neural development, the determination and differentiation of these cells remains poorly understood at the molecular level. Ets-1 and Ets-2, Ets (E26 transformation-specific) transcription factors, are vertebrate homologues of Drosophila pointed, which is expressed in a subset of glia cells and promotes different aspects of Drosophila glia cell differentiation. However, it remains unsolved that the function of Ets genes is conserved in vertebrate glia development. Here we report that Ets-1 but not Ets-2 is necessary for Xenopus radial glia formation and the activity of Ets-1 is sufficient for radial glia formation prior to neural tube closure. Furthermore, we show that Ras-MAPK (mitogen activated protein kinase) signaling, which acts as an upstream activator of Ets-1 in other biological processes, also regulates radial glia formation. A mutant form of Ets-1, which is not responsive to Ras-MAPK signaling, inhibits radial glia formation promoted by Ras-MAPK signaling. Together, our results show that Ets-1 activated by Ras-MAPK signaling promotes radial glia formation during Xenopus embryogenesis.

Serum protein N-glycan alterations of diethylnitrosamine-induced hepatocellular carcinoma mice and their evolution after inhibition of the placental growth factor

Placental growth factor (PlGF) inhibition produced promising results in reducing tumor burden in a diethylnitrosamine (DEN)-induced mouse model for hepatocellular carcinoma (HCC). The aim of this study was to non-invasively assess the improved histology by performing a serum glycomic analysis. To elucidate the molecular mechanism underlying the observed glycomic effects, we investigated the transcription and expression of E26 transformation-specific sequence 1 (Ets-1), a transcription factor essential for the glycomic and angiogenic changes in malignant transformation, including its different phosphorylated forms that result from activation of the MAP kinase and a Ca(2+)-dependent pathway. In addition, three Ets-1-dependent glycosyltransferase genes, Mgat4a, Mgat4b, and Mgat5, were also evaluated. HCC was induced in mice by weekly injections with DEN for 16, 20, 25, and 30 w. In the treatment study, mice were injected with DEN for 25 w and subsequently treated with PlGF antibodies (5D11D4) for 5 w. Finally, PlGF-/- mice were injected with DEN for 20, 25, and 30 w. Serum N-glycans were analyzed with DNA sequencer-assisted fluorophore-assisted capillary electrophoresis and compared with histology. Maximum altered N-glycan phenotype was reached after 20 w of DEN-injections, i.e., when the first neoplastic lesions started to appear. 5D11D4-treatment improved the glycomic phenotype in that 7 of the 11 altered glycans tended to normalize. The PlGF-/- mice also showed a normalization trend, although not to the same extent of the treatment group. Number of Ets1, Mgat4a, Mgat4b, and Mgat5 transcripts increased considerably in DEN-injected mice, however, a non-significant decrease was observed after 5D11D4-treatment. On the protein level, 5D11D4-treatment had a prominent effect on the MAP kinase pathway with a significant p38 activation, yet independent of Ets-1 function.

Ets-1 is a transcriptional mediator of oncogenic nitric oxide signaling in estrogen receptor-negative breast cancer

Introduction

The Ets-1 transcription factor is a candidate breast cancer oncogene that regulates the expression of genes involved in tumor progression and metastasis. Ets-1 signaling has also been linked to the development of a basal-like breast cancer phenotype. We recently described a nitric oxide (NO)-induced gene signature that is associated with poor disease outcome in estrogen receptor-negative (ER-) breast cancer and contains both stem cell-like and basal-like components. Thus, we examined the role of Ets-1 in NO signaling and NO-induced phenotypes in ER- human breast cancer cells.

Methods

Promoter region analyses were performed on genes upregulated in inducible nitric oxide synthase (NOS2) high expressing tumors for Ets-binding sites. In vitro mechanisms were examined in human basal-like breast cancer cells lines. NO signaling effects were studied using either forced NOS2 expression or the use of a chemical NO-donor, diethlylenetriamine NONOate (DETANO).

Results

Promoter region analysis of genes that are up-regulated in human ER-negative breast tumors with high NOS2 expression revealed that the Ets-binding sequence is the only common promoter element present in all of these genes, indicating that Ets-1 is the key transcriptional factor down-stream of oncogenic NOS2-signaling. Accordingly, both forced NOS2 over-expression and exposure to NO-donors resulted in significant Ets-1 transcriptional activation in ER- breast cancer cells. Functional studies showed that NO activated Ets-1 transcriptional activity via a Ras/MEK/ERK signaling pathway by a mechanism that involved Ras S-nitrosylation. RNA knock-down of Ets-1 suppressed NO-induced expression of selected basal-like breast cancer markers such as P-cadherin, S100A8, IL-8 and αβ-crystallin. Additionally, Ets-1 knock-down reduced NO-mediated cellular proliferation, matrix metalloproteinase and cathepsin B activities, as well as matrigel invasion.

Conclusions

These data show that Ets-1 is a key transcriptional mediator of oncogenic NO signaling that promotes the development of an aggressive disease phenotype in ER- breast cancer in an Ets-1 and Ras-dependent manner, providing novel clues of how NOS2 expression in human breast tumors is functionally linked to poor patient survival.

Ets-1 transcription is required in tissue factor driven microvessel formation and stabilization

Tissue factor (TF) has well-recognized roles as initiator of blood coagulation as well as an intracellular signaling receptor. TF signaling regulates gene transcription and protein translation. Recently, we have shown that TF-induced mature neovessel formation is ultimately driven by CCL2 expression. However, the signaling process induced by TF to promote microvessel formation remains to be determined. This study was designed with the objective to investigate the mechanisms involved in TF-induced neovessel formation. Here, we have identified that Ets-1 expression is a downstream effector of TF signaling. TF-siRNA induced a highly significant reduction in Ets-1 expression levels and in Ets-1/DNA binding while inducing abrogation of microvessel formation. Activation of Ets-1 rescued the effect of TF inhibition and restored microvessel formation confirming the critical role of Ets-1 in TF-induced angiogenesis. VE-cadherin expression, a key regulator of endothelial intercellular junctions, and an Ets-1 target molecule was dependent of TF-inhibition. We show that TF signals through ERK1/2 to activate Ets-1 and induce CCL2 gene expression by binding to its promoter region. We conclude that endothelial cell TF signals through ERK1/2 and Ets-1 to trigger microvessel formation.

Inhibitory effects of the transcription factor Ets-1 on the expression of type I collagen in TGF-β1-stimulated renal epithelial cells

Extracellular matrix (ECM) production and epithelial-mesenchymal transition (EMT) are important for phenotypic conversion in normal development and disease states such as tissue fibrosis. Transforming growth factor-β1 (TGFβ1) is one of the most potent inducers of ECM proteins, and its role in the pathogenesis of fibrosis is well established. Ets family is involved in a diverse array of biologic functions including cellular growth, migration, and differentiation. In the present study, we investigated whether Ets-1 has a role in ECM production and EMT in human renal tubuloepithelial cells (HKC cells). TGFβ1 treatment increases Ets-1 expression and nuclear translocation in the HKC cells. Overexpression of recombinant Ets-1 suppressed transcription of α2(I) collagen (COL1A2) and type I collagen production in the TGFβ1-activated HKC cells. From the experiments using specific inhibitors against Smad3 or mitogen-activated protein (MAP) kinase pathways, Ets-1 has an inhibitory role for COL1A2 transcription and the p38 MAPK pathway participates in the negative contribution of Ets-1 in TGFβ1/Smad3-activated renal cells.

The SAM domain of human TEL2 can abrogate transcriptional output from TEL1 (ETV-6) and ETS1/ETS2

Regulation of gene expression downstream of the Receptor Tyrosine Kinase signaling pathway in Drosophila relies on a transcriptional effector network featuring two conserved Ets family proteins, Yan and Pointed, known as TEL1 (ETV6) and ETS1/ETS2, respectively, in mammals. As in Drosophila, both TEL1 and ETS1/ETS2 operate as Ras pathway transcriptional effectors and misregulated activity of either factor has been implicated in many human leukemias and solid tumors. Providing essential regulation to the Drosophila network, direct interactions with the SAM domain protein Mae attenuate both Yan-mediated repression and PointedP2-mediated transcriptional activation. Given the critical contributions of Mae to the Drosophila circuitry, we investigated whether the human Ets factors TEL1 and ETS1/ETS2 could be subject to analogous regulation. Here we demonstrate that the SAM domain of human TEL2 can inhibit the transcriptional activities of ETS1/2 and TEL1. Drosophila Mae can also attenuate human ETS1/ETS2 function, suggesting there could be cross-species conservation of underlying mechanism. In contrast, Mae is not an effective inhibitor of TEL1, suggesting the mode of TEL2SAM-mediated inhibition of TEL1 may be distinct from how Drosophila Mae antagonizes Yan. Together our results reveal both further similarities and new differences between the mammalian and Drosophila networks and more broadly suggest that SAM domain-mediated interactions could provide an effective mechanism for modulating output from the TEL1 and ETS1/2 oncogenes.

EBV-encoded LMP1 upregulates Igκ 3'enhancer activity and Igκ expression in nasopharyngeal cancer cells by activating the Ets-1 through ERKs signaling

Accumulating evidence indicates that epithelial cancer cells, including nasopharyngeal carcinoma (NPC) cells, express immunoglobulins (Igs). We previously found that the expression of the kappa light chain protein in NPC cells can be upregulated by the EBV-encoded latent membrane protein 1 (LMP1). In the present study, we used NPC cell lines as models and found that LMP1-augmented kappa production corresponds with elevations in ERKs phosphorylation. PD98059 attenuates LMP1-induced ERKs phosphorylation resulting in decreased expression of the kappa light chain. ERK-specific small interfering RNA blunts LMP1-induced kappa light chain gene expression. Luciferase reporter assays demonstrate that immunoglobulin κ 3′ enhancer (3′E_κ) is active in Igκ-expressing NPC cells and LMP1 upregulates the activity of 3′E_κ in NPC cells. Moreover, mutation analysis of the PU binding site in 3′E_κ and inhibition of the MEK/ERKs pathway by PD98059 indicate that the PU site is functional and LMP1-enhanced 3′E_κ activity is partly regulated by this site. PD98059 treatment also leads to a concentration-dependent inhibition of LMP1-induced Ets-1 expression and phosphorylation, which corresponds with a dose-dependent attenuation of LMP1-induced ERK phosphorylation and kappa light chain expression. Suppression of endogenous Ets-1 by small interfering RNA is accompanied by a decrease of Ig kappa light chain expression. Gel shift assays using nuclear extracts of NPC cells indicate that the transcription factor Ets-1 is recruited by LMP1 to the PU motif within 3′E_κin vitro. ChIP assays further demonstrate Ets-1 binding to the PU motif of 3′E_κ in cells. These results suggest that LMP1 upregulates 3′E_κ activity and kappa gene expression by activating the Ets-1 transcription factor through the ERKs signaling pathway. Our studies provide evidence for a novel regulatory mechanism of kappa expression, by which virus-encoded proteins activate the kappa 3′ enhancer through activating transcription factors in non-B epithelial cancer cells.

The transcription factor ETS-1 regulates angiotensin II-stimulated fibronectin production in mesangial cells

Angiotensin II (ANG II) produced as result of activation of the renin-angiotensin system (RAS) plays a critical role in the pathogenesis of chronic kidney disease via its hemodynamic effects on the renal microcirculation as well as by its nonhemodynamic actions including the production of extracellular matrix proteins such as fibronectin, a multifunctional extracellular matrix protein that plays a major role in cell adhesion and migration as well as in the development of glomerulosclerosis. ETS-1 is an important transcription factor essential for normal kidney development and glomerular integrity. We previously showed that ANG II increases ETS-1 expression and is required for fibronectin production in mesangial cells. In these studies, we determined that ANG II induces phosphorylation of ETS-1 via activation of the type 1 ANG II receptor and that Erk1/2 and Akt/PKB phosphorylation are required for these effects. In addition, we characterized the role of ETS-1 on the transcriptional activation of fibronectin production in mesangial cells. We determined that ETS-1 directly activates the fibronectin promoter and by utilizing gel shift assays and chromatin immunoprecipitation assays identified two different ETS-1 binding sites that promote the transcriptional activation of fibronectin in response to ANG II. In addition, we identified the essential role of CREB and its coactivator p300 on the transcriptional activation of fibronectin by ETS-1. These studies unveil novel mechanisms involved in RAS-induced production of the extracellular matrix protein fibronectin in mesangial cells and establish the role of the transcription factor ETS-1 as a direct mediator of these effects.

c-Jun and Ets2 proteins regulate expression of spleen tyrosine kinase in T cells

Effector T cells and T cells from patients with systemic lupus erythematosus (SLE) express increased levels of the spleen tyrosine kinase (Syk). Syk binds to the T cell receptor (TCR)-CD3 complex and transduces the TCR-mediated signal in the cell more efficiently than the canonical CD3ζ chain. The reasons for the increased expression of Syk are unclear. In the present study, we found that Syk is regulated by the transcription factor c-Jun in cooperation with Ets2. c-Jun and Ets2 bound to the SYK promoter in close proximity and increased the promoter activity in a specific manner. Disruption of c-Jun and Ets2 expression by siRNA resulted in decreased expression of Syk. Overexpression of c-Jun but not Ets2 resulted in increase in Syk protein. c-Jun and Ets2 co-immunoprecipitated and had an additive effect on Syk expression. c-Jun-driven SYK promoter activation showed a similar pattern in B cells; however, as expected, basal promoter activity was much higher in B cells as compared with T cells. Overexpression of c-Jun led to increase in intracytoplasmic calcium flux following TCR stimulation. Moreover, we found that SLE T cells had increased levels of c-Jun at baseline and phosphorylated c-Jun upon activation. Finally, disruption of c-Jun and Ets2 in SLE T cells resulted in a decrease in calcium flux upon TCR stimulation. In conclusion, c-Jun in cooperation with Ets2 increases the expression of Syk and contributes to Syk-mediated heightened calcium responses in SLE T cells.

Role for Ets-2(Thr-72) transcription factor in stage-specific thymocyte development and survival

Interference of Ras signaling deregulates thymocyte development in mouse models. However, the role of Ets-2, a transcription factor that is phosphorylated on a critical threonine residue (Thr-72) by the Ras/MAPK pathway in thymocyte development, has not been defined. Transgenic mice overexpressing a phosphomutant Ets-2 (T72A) in the thymus displayed reduced thymus size associated with a 60-80% reduction in thymocyte populations. The transgenic mice exhibited a 20-fold increase in a c-Kit(+) CD4(+) CD8(+) CD3(-) population and a 5-fold increase in a unique CD5(low) population associated with a partial developmental block at the DN2-DN3 stage of thymocytes. Transgenic thymocytes exhibited increased apoptosis, and overexpression of Bcl-2 rescued the hypocellularity and associated thymocyte developmental block in double transgenic mice. The observed defects in these mice are not dependent on Ets-1 expression. These studies implicate for the first time a stage-specific Ets-1-independent regulatory role for Ets-2 in early thymocyte development and survival.

Constitutive activation of the ETS-1-miR-222 circuitry in metastatic melanoma

MicroRNAs-221 and -222 are highly upregulated in several solid tumors, including melanomas. We demonstrate that the proto-oncogene ETS-1, involved in the pathogenesis of cancers of different origin, is a transcriptional regulator of miR-222 by direct binding to its promoter region. Differently from 293FT cells or early stage melanomas, where unphosphorylated ETS-1 represses miR-222 transcription, in metastatic melanoma the constitutively Thr-38 phosphorylated fraction of ETS-1 induces miR-222. Despite its stepwise decreased expression along with melanoma progression, the oncogenic activity of ETS-1 relies on its RAS/RAF/ERK-dependent phosphorylation status more than on its total amount. To close the loop, we demonstrate ETS-1 as a direct target of miR-222, but not miR-221, showing the novel option of their uncoupled functions. In addition, a spatial redistribution of ETS-1 protein from the nucleus to the cytoplasm is also evidenced in advanced melanoma cells. Finally, in vivo studies confirmed the contribution of miR-222 to the increased invasive potential obtained by ETS- silencing.

Regulation of endothelial cell development by ETS transcription factors

The ETS family of transcription factors plays an essential role in controlling endothelial gene expression. Multiple members of the ETS family are expressed in the developing endothelium and evidence suggests that the proteins function, to some extent, redundantly. However, recent studies have demonstrated a crucial non-redundant role for ETV2, as a primary player in specification and differentiation of the endothelial lineage. Here, we review the contribution of ETS factors, and their partner proteins, to the regulation of embryonic vascular development.

Paradoxical action of growth factors: antiproliferative and proapoptotic signaling by HGF/c-MET

Hepatocyte growth factor (HGF)/mesenchymal-epithelial transition factor (c-MET) signaling is usually associated with the promotion of cellular growth and often with progression of tumors. Nevertheless, under certain conditions HGF can also act as an antiproliferative and proapoptotic factor and can sensitize various cancer cells, treated with anticancer drugs, to apoptosis. Not only HGF but also its various truncated forms as well as intracellular fragments of its membrane receptor, c-MET, may act as antiproliferative and proapoptotic factors toward various cells. This review focuses on different mechanisms responsible for such paradoxical action of the known typical growth factor. It also points toward the possibilities of usage of this information in anticancer therapy.

Transcription factor ets-2 plays an important role in the pathogenesis of pulmonary fibrosis

Ets-2 is a ubiquitous transcription factor activated after phosphorylation at threonine-72. Previous studies highlighted the importance of phosphorylated ets-2 in lung inflammation and extracellular matrix remodeling, two pathways involved in pulmonary fibrosis. We hypothesized that phosphorylated ets-2 played an important role in pulmonary fibrosis, and we sought to determine the role of ets-2 in its pathogenesis. We challenged ets-2 (A72/A72) transgenic mice (harboring a mutated form of ets-2 at phosphorylation site threonine-72) and ets-2 (wild-type/wild-type [WT/WT]) control mice with sequential intraperitoneal injections of bleomycin, followed by quantitative measurements of lung fibrosis and inflammation and primary cell in vitro assays. Concentrations of phosphorylated ets-2 were detected via the single and dual immunohistochemical staining of murine lungs and lung sections from patients with idiopathic pulmonary fibrosis. Ets-2 (A72/A72) mice were protected from bleomycin-induced pulmonary fibrosis, compared with ets-2 (WT/WT) mice. This protection was characterized by decreased lung pathological abnormalities and the fibrotic gene expression of Type I collagen, Type III collagen, α-smooth muscle actin, and connective tissue growth factor. Immunohistochemical staining of lung sections from bleomycin-treated ets-2 (WT/WT) mice and from patients with idiopathic pulmonary fibrosis demonstrated increased staining of phosphorylated ets-2 that colocalized with Type I collagen expression and to fibroblastic foci. Lastly, primary lung fibroblasts from ets-2 (A72/A72) mice exhibited decreased expression of Type I collagen in response to stimulation with TGF-β, compared with fibroblasts from ets-2 (WT/WT) mice. These data indicate the importance of phosphorylated ets-2 in the pathogenesis of pulmonary fibrosis through the expression of Type I collagen and (myo)fibroblast activation.

Mutant K-Ras increases GSK-3β gene expression via an ETS-p300 transcriptional complex in pancreatic cancer

Glycogen synthase kinase-3 beta (GSK-3β) is overexpressed in a number of human malignancies and has been shown to contribute to tumor cell proliferation and survival. Although regulation of GSK-3β activity has been extensively studied, the mechanisms governing GSK-3β gene expression are still unknown. Using pancreatic cancer as a model, we find that constitutively active Ras signaling increases GSK-3β gene expression via the canonical mitogen-activated protein kinase signaling pathway. Analysis of the mechanism revealed that K-Ras regulates the expression of this kinase through two highly conserved E-twenty six (ETS) binding elements within the proximal region. Furthermore, we demonstrate that mutant K-Ras enhances ETS2 loading onto the promoter, and ETS requires its transcriptional activity to increase GSK-3β gene transcription in pancreatic cancer cells. Lastly, we show that ETS2 cooperates with p300 histone acetyltransferase to remodel chromatin and promote GSK-3β expression. Taken together, these results provide a general mechanism for increased expression of GSK-3β in pancreatic cancer and perhaps other cancers, where Ras signaling is deregulated.

ETS1 mediates MEK1/2-dependent overexpression of cancerous inhibitor of protein phosphatase 2A (CIP2A) in human cancer cells

EGFR-MEK-ERK signaling pathway has an established role in promoting malignant growth and disease progression in human cancers. Therefore identification of transcriptional targets mediating the oncogenic effects of the EGFR-MEK-ERK pathway would be highly relevant. Cancerous inhibitor of protein phosphatase 2A (CIP2A) is a recently characterized human oncoprotein. CIP2A promotes malignant cell growth and is over expressed at high frequency (40–80%) in most of the human cancer types. However, the mechanisms inducing its expression in cancer still remain largely unexplored. Here we present systematic analysis of contribution of potential gene regulatory mechanisms for high CIP2A expression in cancer. Our data shows that evolutionary conserved CpG islands at the proximal CIP2A promoter are not methylated both in normal and cancer cells. Furthermore, sequencing of the active CIP2A promoter region from altogether seven normal and malignant cell types did not reveal any sequence alterations that would increase CIP2A expression specifically in cancer cells. However, treatment of cancer cells with various signaling pathway inhibitors revealed that CIP2A mRNA expression was sensitive to inhibition of EGFR activity as well as inhibition or activation of MEK-ERK pathway. Moreover, MEK1/2-specific siRNAs decreased CIP2A protein expression. Series of CIP2A promoter-luciferase constructs were created to identify proximal −27 to −107 promoter region responsible for MEK-dependent stimulation of CIP2A expression. Additional mutagenesis and chromatin immunoprecipitation experiments revealed ETS1 as the transcription factor mediating stimulation of CIP2A expression through EGFR-MEK pathway. Thus, ETS1 is probably mediating high CIP2A expression in human cancers with increased EGFR-MEK1/2-ERK pathway activity. These results also suggest that in addition to its established role in invasion and angiogenesis, ETS1 may support malignant cellular growth via regulation of CIP2A expression and protein phosphatase 2A inhibition.

Ets1 blocks terminal differentiation of keratinocytes and induces expression of matrix metalloproteases and innate immune mediators

The transcription factor Ets1 is normally expressed in the proliferative layer of stratified epithelium, but expression of Ets1 is significantly upregulated in squamous cell carcinomas. How elevated levels of Ets1 impact tumor initiation and progression is not well understood. To determine the biological consequences of overexpression of Ets1, we developed a transgenic mouse model that allows induction of Ets1 expression in keratinocytes of stratified epithelium in a regulatable fashion. Induction of Ets1 during embryonic development results in a dramatic alteration in epidermal structure and function by suppressing the expression of multiple stratum corneum constituents, while at the same time inducing expression of EGF ligands, AP1 transcription factors and matrix metalloproteases. Interestingly, expression of certain immune-related genes, including defensins, chemokines and cytokines was increased as well, suggesting a possible role for immune dysregulation in the promotion of squamous dysplasia. Experiments using cultured mouse keratinocytes indicate that Ets1 can induce expression of some of these mediators in a cell-intrinsic fashion. Collectively, our data reveal that elevated expression of Ets1 has a much broader array of pro-tumorigenic effects on epithelial cells than previously appreciated.

miR-200b targets Ets-1 and is down-regulated by hypoxia to induce angiogenic response of endothelial cells

The miR-200 family plays a crucial role in epithelial to mesenchymal transition via controlling cell migration and polarity. We hypothesized that miR-200b, one miR-200 family member, could regulate angiogenic responses via modulating endothelial cell migration. Delivery of the miR-200b mimic in human microvascular endothelial cells (HMECs) suppressed the angiogenic response, whereas miR-200b-depleted HMECs exhibited elevated angiogenesis in vitro, as evidenced by Matrigel® tube formation and cell migration. Using in silico studies, miR target reporter assay, and Western blot analysis revealed that v-ets erythroblastosis virus E26 oncogene homolog 1 (Ets-1), a crucial angiogenesis-related transcription factor, serves as a novel direct target of miR-200b. Knocking down endogenous Ets-1 simulated an anti-angiogenic response of the miR-200b mimic-transfected cells. Certain Ets-1-associated genes, namely matrix metalloproteinase 1 and vascular endothelial growth factor receptor 2, were negatively regulated by miR-200b. Overexpression of Ets-1 rescued miR-200b-dependent impairment in angiogenic response and suppression of Ets-1-associated gene expression. Both hypoxia as well as HIF-1α stabilization inhibited miR-200b expression and elevated Ets-1 expression. Experiments to identify how miR-200b modulates angiogenesis under a low oxygen environment illustrated that hypoxia-induced miR-200b down-regulation de-repressed Ets-1 expression to promote angiogenesis. This study provides the first evidence that hypoxia-sensitive miR-200b is involved in induction of angiogenesis via directly targeting Ets-1 in HMECs.

Discovering causal signaling pathways through gene-expression patterns

High-throughput gene-expression studies result in lists of differentially expressed genes. Most current meta-analyses of these gene lists include searching for significant membership of the translated proteins in various signaling pathways. However, such membership enrichment algorithms do not provide insight into which pathways caused the genes to be differentially expressed in the first place. Here, we present an intuitive approach for discovering upstream signaling pathways responsible for regulating these differentially expressed genes. We identify consistently regulated signature genes specific for signal transduction pathways from a panel of single-pathway perturbation experiments. An algorithm that detects overrepresentation of these signature genes in a gene group of interest is used to infer the signaling pathway responsible for regulation. We expose our novel resource and algorithm through a web server called SPEED: Signaling Pathway Enrichment using Experimental Data sets. SPEED can be freely accessed at http://speed.sys-bio.net/.

Ras signaling requires dynamic properties of Ets1 for phosphorylation-enhanced binding to coactivator CBP

Ras/MAPK signaling is often aberrantly activated in human cancers. The downstream effectors are transcription factors, including those encoded by the ETS gene family. Using cell-based assays and biophysical measurements, we have determined the mechanism by which Ras/MAPK signaling affects the function of Ets1 via phosphorylation of Thr38 and Ser41. These ERK2 phosphoacceptors lie within the unstructured N-terminal region of Ets1, immediately adjacent to the PNT domain. NMR spectroscopic analyses demonstrated that the PNT domain is a four-helix bundle (H2-H5), resembling the SAM domain, appended with two additional helices (H0-H1). Phosphorylation shifted a conformational equilibrium, displacing the dynamic helix H0 from the core bundle. The affinity of Ets1 for the TAZ1 (or CH1) domain of the coactivator CBP was enhanced 34-fold by phosphorylation, and this binding was sensitive to ionic strength. NMR-monitored titration experiments mapped the interaction surfaces of the TAZ1 domain and Ets1, the latter encompassing both the phosphoacceptors and PNT domain. Charge complementarity of these surfaces indicate that electrostatic forces act in concert with a conformational equilibrium to mediate phosphorylation effects. We conclude that the dynamic helical elements of Ets1, appended to a conserved structural core, constitute a phospho-switch that directs Ras/MAPK signaling to downstream changes in gene expression. This detailed structural and mechanistic information will guide strategies for targeting ETS proteins in human disease.

Ets1 is required for proper migration and differentiation of the cardiac neural crest

Defects in cardiac neural crest lead to congenital heart disease through failure of cardiac outflow tract and ventricular septation. In this report, we demonstrate a previously unappreciated role for the transcription factor Ets1 in the regulation of cardiac neural crest development. When bred onto a C57BL/6 genetic background, Ets1(-/-) mice have a nearly complete perinatal lethality. Histologic examination of Ets1(-/-) embryos revealed a membranous ventricular septal defect and an abnormal nodule of cartilage within the heart. Lineage-tracing experiments in Ets1(-/-) mice demonstrated that cells of the neural crest lineage form this cartilage nodule and do not complete their migration to the proximal aspects of the outflow tract endocardial cushions, resulting in the failure of membranous interventricular septum formation. Given previous studies demonstrating that the MEK/ERK pathway directly regulates Ets1 activity, we cultured embryonic hearts in the presence of the MEK inhibitor U0126 and found that U0126 induced intra-cardiac cartilage formation, suggesting the involvement of a MEK/ERK/Ets1 pathway in blocking chondrocyte differentiation of cardiac neural crest. Taken together, these results demonstrate that Ets1 is required to direct the proper migration and differentiation of cardiac neural crest in the formation of the interventricular septum, and therefore could play a role in the etiology of human congenital heart disease.

A review of post-translational modifications and subcellular localization of Ets transcription factors: possible connection with cancer and involvement in the hypoxic response

Post-translational modifications and subcellular localizations modulate transcription factors, generating a code that is deciphered into an activity. We describe our current understanding of these processes for Ets factors, which have recently been recognized for their importance in various biological processes. We present the global picture for the family, and then focus on particular aspects related to cancer and hypoxia. The analysis of Post-translational modification and cellular localization is only beginning to enter the age of "omic," high content, systems biology. Our snap-shots of particularly active fields point to the directions in which new techniques will be needed, in our search for a more complete description of regulatory pathways.

DNA-dependent protein kinase is a novel interaction partner for Ets-1 isoforms

The Ets-1 transcription factor plays an important role in various physiological and pathological processes. These diverse roles of Ets-1 are likely to depend on its interaction partner proteins. We used our previously developed, recombinant biotinylated Ets-1 that conserves native Ets-1 properties to identify new interaction partners. Here, based on results from streptavidin pull-down assays, mass spectrometry and co-immunoprecipitation, we report a novel interaction partner for Ets-1 isoforms: a heterotrimeric complex of DNA-dependent protein kinase (DNA-PK), made up of Ku70, Ku86, and DNA-PK catalytic subunit (DNA-PKcs). Kinase assays performed in vitro showed that DNA-PK phosphorylates the Ets-1 protein. Furthermore, we demonstrated that Ku86, but not Ku70 or DNA-PKcs, down-regulated the transcriptional activity of Ets-1 when analysed using a reporter gene assay. These results illustrate how detecting novel molecular interactions may provide new clues for understanding the diverse functions of Ets-1.

Antigen-induced Erk1/2 activation regulates Ets-1-mediated sensitization of CD8+ T cells for IL-12 responses

The presence of IL-12 during antigen stimulation instructs naive CD8+ T cells for long-term effector responses, but their mechanisms of collaboration are not understood completely. Herein, we report that CD8+ T cells (OT-I T cells) stimulated with antigen for a longer duration show enhanced sensitization to IL-12 as a result of Erk1/2-dependent, increased Ets-1 phosphorylation and subsequent increases in IL-12Rbeta2 expression. Correspondingly, naive OT-I T cells stimulated by antigen for a longer duration in the presence of IL-12, irrespective of frequency of APCs, show robust effector maturation and mount long-term antigen-recall responses upon adoptive transfer. These results identify the role of antigen strength-dependent Erk1/2 activation for Ets-1-mediated collaboration with IL-12 in CD8+ T cells.

Data recovery and integration from public databases uncovers transformation-specific transcriptional downregulation of cAMP-PKA pathway-encoding genes

BACKGROUND

The integration of data from multiple genome-wide assays is essential for understanding dynamic spatio-temporal interactions within cells. Such integration, which leads to a more complete view of cellular processes, offers the opportunity to rationalize better the high amount of "omics" data freely available in several public databases.In particular, integration of microarray-derived transcriptome data with other high-throughput analyses (genomic and mutational analysis, promoter analysis) may allow us to unravel transcriptional regulatory networks under a variety of physio-pathological situations, such as the alteration in the cross-talk between signal transduction pathways in transformed cells.

RESULTS

Here we sequentially apply web-based and statistical tools to a case study: the role of oncogenic activation of different signal transduction pathways in the transcriptional regulation of genes encoding proteins involved in the cAMP-PKA pathway. To this end, we first re-analyzed available genome-wide expression data for genes encoding proteins of the downstream branch of the PKA pathway in normal tissues and human tumor cell lines. Then, in order to identify mutation-dependent transcriptional signatures, we classified cancer cells as a function of their mutational state. The results of such procedure were used as a starting point to analyze the structure of PKA pathway-encoding genes promoters, leading to identification of specific combinations of transcription factor binding sites, which are neatly consistent with available experimental data and help to clarify the relation between gene expression, transcriptional factors and oncogenes in our case study.

CONCLUSIONS

Genome-wide, large-scale "omics" experimental technologies give different, complementary perspectives on the structure and regulatory properties of complex systems. Even the relatively simple, integrated workflow presented here offers opportunities not only for filtering data noise intrinsic in high throughput data, but also to progressively extract novel information that would have remained hidden otherwise. In fact we have been able to detect a strong transcriptional repression of genes encoding proteins of cAMP/PKA pathway in cancer cells of different genetic origins. The basic workflow presented herein may be easily extended by incorporating other tools and can be applied even by researchers with poor bioinformatics skills.

Id1 is down-regulated by hepatocyte growth factor via ERK-dependent and ERK-independent signaling pathways, leading to increased expression of p16INK4a in hepatoma cells

Hepatocyte growth factor (HGF) inhibits the proliferation of several tumor cell lines and tumor growth in vivo. We showed previously that HGF induces cell cycle arrest at G1 in a human hepatoma cell line, HepG2, by up-regulating the expression of p16INK4a through strong activation of extracellular signal-regulated kinase (ERK). However, although essential, the activation was not sufficient for the up-regulation of p16. In this study, we examined regulatory mechanisms of p16 expression through a transcription factor, Ets, which has been shown previously to bind to the promoter. The treatment of HepG2 cells with HGF induced ERK-dependent phosphorylation of Ets, which leads to its activation, before the up-regulation of p16, suggesting that another factor suppresses Ets activity. We found that HGF reduces the amount of Id1, which is a dominant-negative inhibitor of Ets, leading to a decrease in Ets associated with Id1. Id1 was down-regulated via transcriptional regulation not via the ubiquitin-proteasome-mediated pathway. Inhibition of the HGF-induced high-intensity ERK activity had a modest effect on the Id1 down-regulation, and inhibition of the phosphatidylinositol 3-kinase pathway had no effect, showing that Id1 is regulated by ERK-dependent and -independent pathways other than the phosphatidylinositol 3-kinase pathway. Exogenously expressed Id1 suppressed the up-regulation of p16 by HGF and the antiproliferative effect of HGF. Knockdown of Id1 significantly enhanced the activity of the p16 promoter coordinately with the activation of ERK. Our results indicated that down-regulation of Id1 plays a key role in the inhibitory effect of HGF on cell proliferation and provides a molecular basis for cancer therapy with HGF.

Ets1 and Ets2 are required for endothelial cell survival during embryonic angiogenesis

The ras/Raf/Mek/Erk pathway plays a central role in coordinating endothelial cell activities during angiogenesis. Transcription factors Ets1 and Ets2 are targets of ras/Erk signaling pathways that have been implicated in endothelial cell function in vitro, but their precise role in vascular formation and function in vivo remains ill-defined. In this work, mutation of both Ets1 and Ets2 resulted in embryonic lethality at midgestation, with striking defects in vascular branching having been observed. The action of these factors was endothelial cell autonomous as demonstrated using Cre/loxP technology. Analysis of Ets1/Ets2 target genes in isolated embryonic endothelial cells demonstrated down-regulation of Mmp9, Bcl-X(L), and cIAP2 in double mutants versus controls, and chromatin immunoprecipitation revealed that both Ets1 and Ets2 were loaded at target promoters. Consistent with these observations, endothelial cell apoptosis was significantly increased both in vivo and in vitro when both Ets1 and Ets2 were mutated. These results establish essential and overlapping functions for Ets1 and Ets2 in coordinating endothelial cell functions with survival during embryonic angiogenesis.

Regulatory effect of extracellular signal-regulated kinases (ERK) on type I collagen synthesis in human dermal fibroblasts stimulated by IL-4 and IL-13

Synthesis of collagen is up-regulated by pro-fibrogenic growth factors and cytokines such as TGF-beta 1, IL-4, and IL-13 binding to their corresponding cell membrane receptors of fibroblasts. The ERK pathway is an important MAPK signaling pathway that is involved in regulating cell function. The aim of our studies was to examine effects of IL-4 and IL-13 on the ERK signaling pathway and its function in regulating type I collagen gene expression in human fibroblasts. We found that human dermal fibroblasts treated with IL-4 and IL-13 exhibited an increase in the activated ERK1/2 pathway. As well, pro-fibrogenic cytokines increased the promoter activity of type I collagen, and this activity decreased with cells that were co-transfected with dominant negative plasmids of ERK1 and 2. RT-PCR confirmed that collagen transcript levels decreased when cells were transfected with dn ERK1 and 2 and then further stimulated with IL-4 and IL-13. These results were also mirrored with collagen secretion assays. In addition, we studied the role for transcription factor Elk-1 known to be activated via the ERK pathway. Dominant negative Elk-1 showed inhibition of collagen promoter activity in fibroblasts transfected with full collagen type I promoter or two fragments which contain the Elk-1 binding site. Our results suggest that the modulation of collagen gene expression may occur via the ERK pathway and is mediated by Elk-1.

Correlated motions and interactions at the onset of the DNA-induced partial unfolding of Ets-1

The binding of the Ets-1 transcription factor to its target DNA sequence is characterized by a highly unusual conformational change consisting of the unfolding of inhibitory helix 1 (HI-1). To probe the interactions that lead to this unfolding, we performed molecular dynamics simulations of the folded states of apo-Ets-1 and the Ets-1-DNA complex. The simulations showed large differences in correlated motions between helix 4 (H4) and HI-1. In apo-Ets-1, H4 and HI-1 moved in-phase and stabilized each other by hydrogen bonding and macrodipolar interactions, whereas in the DNA-bound state, the motion was out-of-phase, with a disruption of the stabilizing interactions. This change in motion was due to hydrogen-bonding interactions between helix 1 (H1) and the DNA. The dipolar energy between H1 and H4 was modulated by hydrogen bonds between H1 and DNA, and, in accordance with experiments, elimination of the hydrogen bonds increased the stability of HI-1. The simulations confirm that the hydrogen bonds between H1 and DNA act as a conformational switch and show that the presence of DNA is communicated from H1 to H4, destabilizing HI-1. The calculations reveal a critical role for correlated motions at the onset of the DNA-induced unfolding.

Effects of MAPK signaling on 1,25-dihydroxyvitamin D-mediated CYP24 gene expression in the enterocyte-like cell line, Caco-2

We examined the role of the extracellular signal regulated kinases (ERK) in 1,25-dihydroxyvitamin D (1,25(OH)(2)D(3))-induced gene expression in the differentiated Caco-2 cells. 1,25(OH)(2)D(3)-regulated expression of the 25-hydroxyvitamin D, 24-hydroxylase (CYP24) gene (both natural gene and promoter construct) was strongly modulated by altering ERK activity (i.e., reduced by MEK inhibitors and dominant negative (dn) ERK1 and ERK2, activated by epidermal growth factor) but ERK inhibition had no effect on 1,25(OH)(2)D(3)-regulated expression of the transient receptor potential cation channel, subfamily V, member 6 (TRPV6). ERK5-mediated phosphorylation of the transcription factor Ets-1 enhanced 1,25(OH)(2)D(3)-mediated CYP24 gene transcription in proliferating but not differentiated Caco-2 cells due to reduced levels of ERK5 and Ets-1 (total and phosphoprotein levels) in differentiated cells. MEK inhibition reduced 1,25(OH)(2)D(3)-induced 3X-VDRE promoter activity but had no impact on the association of vitamin D receptor (VDR) with chromatin suggesting a role for co-activator recruitment in ERK-modulation of vitamin D-regulated CYP24 gene activation. Chromatin immunoprecipitation assays revealed that the ERK1/2 target, mediator 1 (MED1), is recruited to the CYP24, but not the TRPV6, promoter following 1,25(OH)(2)D(3) treatment. MED1 phosphorylation was sensitive to activators and inhibitors of the ERK1/2 signaling and MED1 siRNA reduced 1,25(OH)(2)D(3)-regulated human CYP24 promoter activity. This suggests ERK1/2 signaling enhances 1,25(OH)(2)D(3) effects on the CYP24 promoter by MED1-mediated events. Our data show that there are both promoter-specific and cell stage-specific roles for the ERK signaling pathway on 1,25(OH)(2)D(3)-mediated gene induction in enterocyte-like Caco-2 cells.

The adaptor protein of the anaphase promoting complex Cdh1 is essential in maintaining replicative lifespan and in learning and memory

The anaphase promoting complex (APC) or cyclosome is a multisubunit E3 ubiquitin ligase. Cdc20 (fizzy (fzy)) or p55CDC, and Cdh1 (Hct1, srw1 or fizzy-related 1 (fzr1)) encode two adaptor proteins that bring substrates to the APC. Both APC-Cdc20 and APC-Cdh1 have been implicated in the control of mitosis through mediating ubiquitination of mitotic regulators, such as cyclin B1 and securin. However, the importance of Cdh1 function in vivo and whether its function is redundant with that of Cdc20 are unclear. Here we have analysed mice lacking Cdh1. We show that Cdh1 is essential for placental development and that its deficiency causes early lethality. Cdhl-deficient mouse embryonic fibroblasts (MEFs) entered replicative senescence prematurely because of stabilization of Ets2 and subsequent activation of p6(Ink4a) expression. These results have uncovered an unexpected role of the APC in maintaining replicative lifespan of MEFs. Further, Cdh1 heterozygous mice show defects in late-phase long-term potentiation (L-LTP) in the hippocampus and are deficient in contextual fear-conditioning, suggesting that Cdh1 has a role in learning and memory.

The function of APC/CCdh1 in cell cycle and beyond

The anaphase promoting complex/cyclosome (APC/C) is a multi-subunit E3 ubiquitin ligase playing essential functions in mitosis. It is conserved from yeast to human and relies on two adaptor proteins, Cdc20 and Cdh1, to bring in substrates. Both APCCdc20 and APCCdh1 are implicated in the control of mitosis through mediating ubiquitination and degradation of important mitotic regulators such as cyclin B1, securin, and Plk1. In addition, APCCdh1 is thought to prevent premature S phase entry by limiting the accumulation of mitotic cyclins in G1 and to regulate processes unrelated to cell cycle. In this review, we will summarize our current understanding of APCCdh1 function in cell cycle and beyond.

Epiregulin expression by Ets-1 and ERK signaling pathway in Ki-ras-transformed cells

Epiregulin belongs to the epidermal growth factor family, binds to the epidermal growth factor receptor, and its expression is upregulated in various cancer cells, but the regulatory mechanism is unclear. We investigated the regulatory mechanism of epiregulin expression in Ki-ras-transformed cancer cells. In 267B1/Ki-ras cells, the RAF/MEK/ERK pathway was constitutively activated, epiregulin was up-regulated, and the expression and phosphorylation of Ets-1 were augmented. The inhibition of ERK by PD98059 decreased epiregulin and Ets-1 expression and suppressed the growth of 267B1/Ki-ras cells. A chromatin immunoprecipitation assay demonstrated that Ets-1 was bound to human epiregulin promoter, and this binding was abolished by PD98059. Silencing of Ets-1 by RNA interference decreased cellular epiregulin transcript expression. We suggest that the Ki-ras mutation in 267B1 prostate cells constitutively activates the RAF/MEK/ERK pathway and induces the activation of the Ets-1 transcription factor, ultimately leading to the increased expression of epiregulin.

Hepatitis B virus-induced hFGL2 transcription is dependent on c-Ets-2 and MAPK signal pathway

Fibrinogen-like protein 2 (FGL2)/fibroleukin plays a pivotal role in the pathogenesis of experimental and human fulminant and chronic viral hepatitis. To define the transcription factor(s) and upstream signal transduction pathways involved in the transcription of human FGL2 (hFGL2) in response to hepatitis B (HB) virus, hepatitis B core (HBc), hepatitis B virus S protein (HBs), or hepatitis B virus X protein (HBx) protein, expression plasmids were cotransfected with an hFGL2 promoter luciferase reporter construct into Chinese hamster ovary and HepG2 cells, respectively. HBc and HBx proteins, but not HBs protein, enhanced hFGL2 transcription in both cell lines. A strong regulatory region from -712 to -568 (relative to the transcriptional starting site) was shown to be responsible for hFGL2 gene transcription in response to both HBc and HBx proteins. c-Ets-2 was shown to be translocated to the nucleus in association with hFGL2 expression in response to both HBc and HBx proteins. Short hairpin RNA (shRNA) interference of c-Ets-2 expression inhibited hFGL2 gene transcription by 64.8 and 60.0% in response to HBc and HBx, respectively. c-Ets-2 protein was highly expressed in peripheral blood mononuclear cells from patients with severe chronic hepatitis B (CHB) in contrast to patients with mild CHB. Increased phosphorylation of ERK and JNK was detected in peripheral blood mononuclear cells from patients with severe CHB. ERK inhibitor PD098059 or ERK shRNA abolished the nuclear c-Ets-2 DNA binding activity and hFGL2 induction in response to HBc, whereas JNK inhibitor SP600125 or JNK shRNA abolished the nuclear c-Ets-2 DNA binding activity and hFGL2 induction in response to HBx. In conclusion, HBc and HBx proteins enhance transcription of hFGL2 through c-Ets-2 dependent on MAPK signal pathways.