Ets Binding Sites Research Articles

Incorporation of a Histone Demethylase, JARID1B, in a Novel ETS-E Box DNA-Binding Complex in Murine Erythroid Progenitors.

Abstract 2335The TAL1/SCL gene, originally discovered from its involvement by a recurrent chromosomal translocation in T-cell acute lymphoblastic leukemia, is important for hematopoietic stem cell and progenitor function and is essential for hematopoietic and vascular development. A member of the basic helix-loop-helix family of transcription factors, TAL1 binds a DNA sequence motif, CANNTG, termed the E box. We and others recently identified a novel TAL1-containing DNA-binding complex that includes an ETS protein, ELF2 (also known as NERF) in erythroid cells, and recognizes a bipartite sequence element containing an adjacent ETS binding site and E box. Our work showed this complex also contains proteins common to other TAL1 DNA-binding complexes described, including a LIM domain protein, LMO2 in erythroid cells, the LIM domain binding protein Ldb1, and putative single-stranded DNA-binding proteins SSBP2 and SSBP3. As both ELF2 and histone demethylase JARID1A, and later the related JARID1B, were identified using the same methodology (yeast two-hybrid analysis) to interact with LMO2, and multiple peptides derived from Jarid1b were identified by mass spectrometry analysis of highly purified Tal1-containing complexes from murine erythroleukemia (MEL) cells, we investigated whether JARID1B was present in the TAL1- and ELF2-containing complex. First, co-immunoprecipitation analysis identified Jarid1b in Tal1- or Elf2-containing immune precipitates and Tal1 in Jarid1b-containing immune precipitates from MEL cell extracts. Further, chromatin immunoprecipitation (ChIP) and re-ChIP analysis showed that Elf2 and Jarid1b co-occupied a region in the fourth intron of the Ssbp3 gene in MEL cells, previously demonstrated to be a physiologic target of the Tal1/Elf2 complex. Finally, knockdown of Elf2 and Jarid1b in MEL cells produced the same phenotype, decreased cellular proliferation. These results suggest a role for the JARID type histone demethylase JARID1B, and by inference histone demethylation, in the function of the ETS-E box DNA-binding complex and in proliferation of late-stage murine erythroid progenitors. Disclosures:No relevant conflicts of interest to declare.

Genome-Wide Analysis of NOTCH1, ETS Family Factors, and RUNX1 Binding in Human T Lymphoblastic Leukemia Cells Reveals Distinct Regulatory Elements

Abstract 1277NOTCH1 regulates gene expression by forming transcription activation complexes with the DNA-binding factor RBPJ and gain-of-function NOTCH1 mutations are common in human and murine T lymphoblastic leukemia/lymphoma (T-LL). Via ChIP-seq studies of T-LL cells with constitutive Notch activation, we previously showed that NOTCH1/RBPJ binding sites in T-LL genomes are highly enriched for motifs corresponding to Ets factors and Runx factors. In this study, we determined the relationship of NOTCH1, RBPJ, ETS1, GABPA and RUNX1 binding sites in human T-LL cells by performing ChIP-Seq for each of these factors, as well as the chromatin marks H3K4me1, H3K4me3, and H3K27me3, and aligning the resulting sequences to human genome reference hg19 using programs available through Cistrome. Peak calling was performed with MACS2, and motif analysis was performed using SeqPos, which relies on JASPAR, TRANSFAC, Protein Binding Microarray (PBM), Yeast-1-hybrid (y1h), and human protein-DNA interaction (hPDI) databases to find known motifs and can also perform de novo motif discovery. Our analysis showed even more pervasive overlap of NOTCH1/RBPJ binding with ETS1/GABPA and RUNX1 factor binding than was predicted by motif analysis, in part due to binding of Ets factors and RUNX1 to non-canonical sequences. Heat-map analysis with K-means clustering on NOTCH1 binding regions identified three major classes of RBPJ/NOTCH1: class 1, characterized by high NOTCH/RBPJ signals, binding of the cofactors ZNF143, ETS1 and GABPA, high H3K4me3 signals, localization to promoters, and binding motifs for ZNF143; class 2, characterized by low NOTCH/RBPJ signals, binding of the cofactors ETS1, GABPA and RUNX1, high H3K4me3 signals, and Ets factor and CREB binding motifs; and class 3, characterized by high NOTCH/RBPJ signals, binding of RUNX1 and ETS1 cofactors, high H3K4me1 signals, intergenic localization (consistent with enhancers), and motifs for RUNX factors, ETS factors, and RBPJ. Of note, the nearest binding sites to the most responsive NOTCH1 target genes (defined as >2 fold stimulation when NOTCH1 was activated following release of gamma-secretase inhibitor (GSI) blockade by drug washout) were preferentially associated with Class 3 sites. Furthermore, shRNA knockdown of Ets factors and RUNX1 in T-LL cell lines induced apoptosis and reduced cell proliferation, implicating these factors in maintenance of T-LL growth and survival. Combination of knockdown of either Ets factors or RUNX1 with GSI treatment resulted in more severe phenotype in terms of apoptosis and cell growth compared to the knockdown or GSI treatment alone. In summary, our studies represent a step forward towards genome-wide understanding of how Notch works in concerts with other transcription factors to regulate the transcriptome of T-LL cells. Disclosures:No relevant conflicts of interest to declare.

Spi-1, Fli-1 and Fli-3 (miR-17-92) Oncogenes Contribute to a Single Oncogenic Network Controlling Cell Proliferation in Friend Erythroleukemia

Clonal erythroleukemia developing in susceptible mice infected by Friend virus complex are associated with highly recurrent proviral insertions at one of three loci called Spi-1, Fli-1 or Fli-3, leading to deregulated expression of oncogenic Spi-1 or Fli-1 transcription factors or miR-17-92 miRNA cluster, respectively. Deregulated expression of each of these three oncogenes has been independently shown to contribute to cell proliferation of erythroleukemic clones. Previous studies showed a close relationship between Spi-1 and Fli-1, which belong to the same ETS family, Spi-1 activating fli-1 gene, and both Spi-1 and Fli-1 activating multiple common target genes involved in ribosome biogenesis. In this study, we demonstrated that Spi-1 and Fli-1 are also involved in direct miR-17-92 transcriptional activation through their binding to a conserved ETS binding site in its promoter. Moreover, we demonstrated that physiological re-expression of exogenous miR-17 and miR-20a are able to partially rescue the proliferation loss induced by Fli-1 knock-down and identified HBP1 as a target of these miRNA in erythroleukemic cells. These results establish that three of the most recurrently activated oncogenes in Friend erythroleukemia are actually involved in a same oncogenic network controlling cell proliferation. The putative contribution of a similar ETS-miR-17-92 network module in other normal or pathological proliferative contexts is discussed.

Intergenic region between TATA-box binding protein and proteasome subunit C3 genes of Medaka function as the bidirectional promoter in vitro and in vivo

In the genome of eukaryotic organisms, each protein-coding gene has the unique promoter in the 5′-flanking region, and the direction of the promoter is usually controlled unidirectional. In this study, we revealed that the intergenic region between TATA-box binding protein (tbp) and proteasome subunit C3 (psmc3) genes in Medaka functions as bidirectional promoter in vitro and in vivo. The tbp and psmc3 genes were allocated as a head-to-head configuration with a 719bp intergenic region. A comparative analysis of gene arrangement surrounding loci of tbp in vertebrates also illustrated that it was unique in Acanthopterygii lineage. The transcription activities were about 1.2 times for tbp direction and 0.7 times for psmc3 direction against that of SV40 promoter in Medaka fibroblasts, respectively. A dual fluorescent reporter assay directly showed that the bidirectional promoter could express two divergent genes concurrently without disruption of RNA polymerase II elongation. In addition, an analysis of sequential deletion of this promoter suggested that the ETS binding site was necessary for maximum expression of downstream gene, and only the ETS binding site was shared from fish to mammals. In mammals, high correlation with CpG islands was observed in such bidirectional promoters, no association was found in the tbp/psmc3 bidirectional promoter in Medaka. These results suggest that molecular machineries of fish bidirectional promoter may be somehow different from those of mammals but the cis-acting element for binding ETS transcription factors is essential for divergent gene expression.

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

IntroductionThe 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.MethodsPromoter 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).ResultsPromoter 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.ConclusionsThese 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.

Transcriptional Regulation of the Endothelial Cell-specific Receptor, Robo4

Roundabout4 (Robo4) is a transmembrane receptor that belongs to the Robo family of neural cell adhesion molecules. Robo4 has been shown to play a role in endothelial cell (EC) migration, proliferation, angiogenesis, and stabilizing the vasculature. Robo4 is expressed specifically in ECs in the developing embryo, placenta, tumors, and normal tissues. The goal of our study is to understand the mechanism for Robo4 gene expression. In the previous study we demonstrated that EC-specific Robo4 gene expression was regulated by the 3-kb Robo4 promoter in the 5'-flanking region of the human Robo4 gene. In vitro studies demonstrated that the Robo4 promoter is activated by the transcription factors GA-binding protein (GABP) and SP1 through the ETS binding site at -119 and the 2 SP1 binding sites at -42 and -153, respectively. The functional relevance of these sites was confirmed by in vivo reporter gene assays using Hprt locus knock in mice. In addition to the regulation mechanism by transcription factors, our recent study implicated that epigenetic modification of the promoter contributes to the Robo4 gene expression. Here I will discuss the regulation mechanism of Robo4 gene expression by transcription factors and epigenetic control.

Transcriptional Regulation of Mouse PXR Gene: An Interplay of Transregulatory Factors

Pregnane X Receptor (PXR) is an important ligand-activated nuclear receptor functioning as a ‘master regulator’ of expression of phase I, phase II drug metabolizing enzymes, and members of the drug transporters. PXR is primarily expressed in hepatic tissues and to lesser extent in other non-hepatic tissues both in human and in mice. Although its expression profile is well studied but little is known about the regulatory mechanisms that govern PXR gene expression in these cells. In the present study, we have cloned and characterized over 5 kb (−4963 to +54) region lying upstream of mouse PXR transcription start site. Promoter-reporter assays revealed that the proximal promoter region of up to 1 kb is sufficient to support the expression of PXR in the mouse liver cell lines. It was evident that the 500 bp proximal promoter region contains active binding sites for Ets, Tcf, Ikarose and nuclear factor families of transcription factors. Electrophoretic mobility shift assays demonstrated that the minimal region of 134 bp PXR promoter was able to bind Ets-1 and β-catenin proteins. This result was further confirmed by chromatin immunoprecipitation analysis. In summary, the present study identified a promoter region of mouse PXR gene and the transregulatory factors responsible for PXR promoter activity. The results presented herein are expected to provide important cues to gain further insight into the regulatory mechanisms of PXR function.

ETS1 regulates the expression of ATXN2

Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominant disorder caused by the expansion of a CAG tract in the ATXN2 gene. The SCA2 phenotype is characterized by cerebellar ataxia, neuropathy and slow saccades. SCA2 foreshortens life span and is currently without symptomatic or disease-modifying treatments. Identifying function-specific therapeutics for SCA2 is problematic due to the limited knowledge of ATXN2 function. As SCA2 is likely caused by a gain-of-toxic or gain-of-normal function like other polyglutamine disorders, targeting ATXN2 expression may represent a valid therapeutic approach. This study characterized aspects of ATXN2 expression control using an ATXN2 promoter-luciferase (luc) reporter construct. We verified the fidelity of construct expression by generating transgenic mice expressing the reporter construct. High reporter expression was seen in the cerebellum and olfactory bulb in vivo but there was relatively low expression in other tissues, similar to the expression of endogenous ataxin-2. We verified the second of two possible start codons as the functional start codon in ATXN2. By evaluating deletions in the ATXN2 promoter, we identified an E-twenty six (ETS)-binding site required for ATXN2 expression. We verified that endogenous ETS1 interacted with the ATXN2 promoter by an electromobility supershift assay and chromatin immunoprecipitation polymerase chain reaction. ETS1 overexpression increased ATXN2-luc (ATXN2-luciferase) as well as endogenous ATXN2 expression. Deletion of the putative ETS1-binding site abrogated the effects on the expression of ATXN2-luc. A dominant negative ETS1 and an ETS1 short-hairpin RNA both reduced ATXN2-luc expression. Our study broadens the understanding on the transcriptional control of ATXN2 and reveals specific regulatory features of the ATXN2 promoter that can be exploited therapeutically.

Core Transcriptional Regulatory Circuit Controlled by the TAL1 Complex in Human T Cell Acute Lymphoblastic Leukemia

The oncogenic transcription factor TAL1/SCL is aberrantly expressed in over 40% of cases of human Tcell acute lymphoblastic leukemia (T-ALL), emphasizing its importance in the molecular pathogenesis of T-ALL. Here we identify the core transcriptional regulatory circuit controlled by TAL1 and its regulatory partners HEB, E2A, LMO1/2, GATA3, and RUNX1. We show that TAL1 forms a positive interconnected autoregulatory loop with GATA3 and RUNX1 and that the TAL1 complex directly activates the MYB oncogene, forming a positive feed-forward regulatory loop that reinforces and stabilizes the TAL1-regulated oncogenic program. One of the critical downstream targets in this circuitry is the TRIB2 gene, which is oppositely regulated by TAL1 and E2A/HEB and is essential for the survival of T-ALL cells.

The PP2A-Aβ Gene is Regulated by Multiple Transcriptional Factors Including Ets-1, SP1/SP3, and RXRα /β

Protein phosphatase-2A (PP-2A) is a major serine/threonine phosphatase abundantly expressed in eukaryotes. PP-2A is a heterotrimer that contains a 65 kD scaffold A subunit, a 36 kD catalytic C subunit, and a regulatory B subunit of variable isoforms ranging from 54-130 kDs. The scaffold subunits, PP2A-Aα/β, act as platforms for both the C and B subunits to bind, and thus are key structural components for PP-2A activity. Mutations in both genes encoding PP2A-Aα and PP2A-Aβ lead to carcinogenesis and likely other human diseases. Our previous work showed that the gene coding for PP2A-Aα is positively regulated by multiple transcription factors including Ets-1, CREB, and AP-2α but negatively regulated by SP-1/SP-3. In the present study, we have functionally dissected the promoter of the mouse PP2A-Aβ gene. Our results demonstrate that three major cis-elements, including the binding sites for Ets-1, SP1/SP3, and RXRα/β, are present in the proximal promoter of the mouse PP2A-Aβ gene. Gel mobility shifting assays reveal that Ets-1, SP1/SP3, and RXRα/β all bind to PP2A-Aβ gene promoter. In vitro mutagenesis and reporter gene activity assays demonstrate that while Ets-1 displays negative regulation, SP1/SP3 and RXRα/β positively regulate the promoter of the PP2A-Aβ gene. Co-expression of the cDNAs encoding Ets-1, SP1/SP3, or RXRα/β and the luciferase reporter gene driven by PP2A-Aβ promoter further confirm their control over the PP2A-Aβ promoter. Finally, ChIP assays demonstrate that Ets-1, SP1/SP3, and RXRα/β can all bind to the PP2A-Aβ gene promoter. Together, our results reveal that multiple transcription factors regulate the PP2A-Aβ gene. Moreover, our results provide important information explaining why PP2A-Aα and PP2A-Aβ display distinct expression levels.

Aberrant expression of the neuronal-specific protein DCDC2 promotes malignant phenotypes and is associated with prostate cancer progression

By integrating gene profiling and immunohistochemical data with functional experiments in cell lines in this study we show for the first time that doublecortin (DCX) domain containing 2 (DCDC2), a protein belonging to the DCX family and involved in neuronal cell migration, is aberrantly expressed in prostate tumors whereas absent in normal prostate. Furthermore, in patients treated with radical prostatectomy, high levels of DCDC2 RNA were significantly associated with increased biochemical relapse (LogRank Mantel-Cox=0.012). Mechanistically, we found that the ETS transcription factor ESE3/EHF, which is expressed in normal prostate and frequently lost in prostate tumors, maintained DCDC2 repressed by binding to a novel identified ETS binding site in the gene promoter. Consistently, in prostate tumors and in cellular models of gain and loss of ESE3/EHF, the expression of DCDC2 and ESE3/EHF were inversely correlated. In prostate cancer cells, DCDC2 colocalized with microtubules and promoted cell migration and resistance to the microtubule-targeting drug taxol. Collectively, this study establishes DCDC2 as a novel ESE3/EHF oncogenic target in prostate cancer. These findings may be relevant for the clinical management of prostate cancer as DCDC2 may signal tumors more prone to relapse and resistant to taxol treatment.

Initial deployment of the cardiogenic gene regulatory network in the basal chordate, Ciona intestinalis

The complex, partially redundant gene regulatory architecture underlying vertebrate heart formation has been difficult to characterize. Here, we dissect the primary cardiac gene regulatory network in the invertebrate chordate, Ciona intestinalis. The Ciona heart progenitor lineage is first specified by Fibroblast Growth Factor/Map Kinase (FGF/MapK) activation of the transcription factor Ets1/2 (Ets). Through microarray analysis of sorted heart progenitor cells, we identified the complete set of primary genes upregulated by FGF/Ets shortly after heart progenitor emergence. Combinatorial sequence analysis of these co-regulated genes generated a hypothetical regulatory code consisting of Ets binding sites associated with a specific co-motif, ATTA. Through extensive reporter analysis, we confirmed the functional importance of the ATTA co-motif in primary heart progenitor gene regulation. We then used the Ets/ATTA combination motif to successfully predict a number of additional heart progenitor gene regulatory elements, including an intronic element driving expression of the core conserved cardiac transcription factor, GATAa. This work significantly advances our understanding of the Ciona heart gene network. Furthermore, this work has begun to elucidate the precise regulatory architecture underlying the conserved, primary role of FGF/Ets in chordate heart lineage specification.

The Ets-1 transcription factor is required for Stat1-mediated T-bet expression and IgG2a class switching in mouse B cells

AbstractIn response to antigens and cytokines, mouse B cells undergo class-switch recombination (CSR) and differentiate into Ig-secreting cells. T-bet, a T-box transcription factor that is up-regulated in lymphocytes by IFN-γ or IL-27, was shown to regulate CSR to IgG2a after T cell–independent B-cell stimulations. However, the molecular mechanisms controlling this process remain unclear. In the present study, we show that inactivation of the Ets-1 transcription factor results in a severe decrease in IgG2a secretion in vivo and in vitro. No T-bet expression was observed in Ets-1–deficient (Ets-1−/−) B cells stimulated with IFN-γ and lipopolysaccharide, and forced expression of T-bet in these cells rescued IgG2a secretion. Furthermore, we identified a transcriptional enhancer in the T-bet locus with an activity in B cells that relies on ETS-binding sites. After IFN-γ stimulation of Ets-1−/− B cells, activated Stat1, which forms a complex with Ets-1 in wild-type cells, no longer binds to the T-bet enhancer or promotes histone modifications at this site. These results demonstrate that Ets-1 is critical for IgG2a CSR and acts as an essential cofactor for Stat1 in the regulation of T-bet expression in B cells.

AP-1 and NF-κB regulate osteopontin gene expression in anti-CD40 treated B cells (161.16)

Abstract Osteopontin (OPN) is a glycoprotein that is implicated in many physiological and pathological processes. Elevated levels of OPN are linked to autoimmunity and cancer and correlate with disease progression. In the immune system, macrophages, dendritic cells, T and B cells express OPN. The regulatory elements involved in B cell OPN expression are poorly understood. Our objective is to determine the regulatory elements critical for OPN expression in B cells. B cells express OPN when stimulated with anti-Ig post treatment with IL-4 or CD40L. To determine the regulatory elements, we made four overlapping OPN promoter-luciferase constructs extending from -2000bp to +80bp. We then transfected 1C10 (anti-CD40 antibody) treated and anti-Ig stimulated primary murine B cells with the OPN promoter constructs. We saw an increase in luciferase activity in the promoter construct containing binding sites for AP-1, Ets and Runx2. Significantly, mutagenesis of the AP-1 site abrogated this increase in luciferase activity. To investigate the role of NF-κB in OPN expression, we used an NF-κB inhibitor to evaluate OPN expression in B cells stimulated with anti-Ig post treatment with1C10. NF-κB inhibition reduced OPN transcript expression in these cells. In conclusion, preliminary data indicate that AP-1 and NF-κB play a role in OPN expression in anti-CD40 treated B cells.

Abstract 2198: A functional ETS/E2F module in cancers expressing ETS fusion genes

Abstract Ewing's sarcoma (ESFT) is a highly aggressive pediatric cancer characterized by the chimeric ETS transcription factor EWS-FLI1 as a result of a chromosomal translocation. By whole genome gene expression and ChIP-seq analyses we obtained evidence that EWS-FLI1 directly binds to 50% of E2F target genes in ESFT. Furthermore, several E2F factors were themselves found to be directly regulated by EWS-FLI1. Therefore, we studied the functional interaction of EWS-FLI1 with E2F. Ten arbitrarily chosen EWS-FLI1/E2F candidate targets including E2F3, RAD51, and ATAD2 were chosen for an in-depth promoter activity study by luciferase reporter gene assays in combination with mutation analysis of transcription factor binding motifs. By ChIP-PCR we confirmed direct EWS-FLI1 promoter binding, and observed decreased reporter activity for all ten studied promoters upon knockdown of EWS-FLI1 by RNAi. Furthermore, the study of promoter occupancy by different E2F family members revealed that silencing of EWS-FLI1 results in the exchange of EWS-FLI1 induced, activating E2F3 by constitutively expressed repressive E2F4 on the promoters of there jointly regulated target genes. Importantly, testing E2F3 promoter occupancy on wildtype and ETS motif mutated promoter constructs in ESFT cell lines revealed that binding of E2F3 to its target promoters is dependent on an intact ETS binding site. Mutation of the ETS motif resulted in reduced binding of E2F3. These data are consistent with a model in which EWS-FLI1 actively recruits an activating E2F factor thereby replacing a repressing E2F factor and in which EWS-FLI1 binding is essential for E2F binding. Strikingly, the functional E2F/ETS transcriptional module detected in ESFT for the chimeric ETS factor EWS-FLI1 was found to be also relevant to TMPRSS2-ERG expressing prostate cancer cells, but not active in HeLa cells. Supported by grants from the Austrian Science Fund (P22328-B09), and the European Comission (EU-FP7 STREP 259348). R. Schwentner is a recipient of a DOC-fFORTE-fellowship of the Austrian Academy of Sciences. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2198. doi:1538-7445.AM2012-2198

Mutant p53 cooperates with ETS2 to promote etoposide resistance

Mutant p53 (mtp53) promotes chemotherapy resistance through multiple mechanisms, including disabling proapoptotic proteins and regulating gene expression. Comparison of genome wide analysis of mtp53 binding revealed that the ETS-binding site motif (EBS) is prevalent within predicted mtp53-binding sites. We demonstrate that mtp53 regulates gene expression through EBS in promoters and that ETS2 mediates the interaction with this motif. Importantly, we identified TDP2, a 5'-tyrosyl DNA phosphodiesterase involved in the repair of DNA damage caused by etoposide, as a transcriptional target of mtp53. We demonstrate that suppression of TDP2 sensitizes mtp53-expressing cells to etoposide and that mtp53 and TDP2 are frequently overexpressed in human lung cancer; thus, our analysis identifies a potentially "druggable" component of mtp53's gain-of-function activity.

The Transcription Factor Erg Controls Endothelial Cell Quiescence by Repressing Activity of Nuclear Factor (NF)-κB p65

The interaction of transcription factors with specific DNA sequences is critical for activation of gene expression programs. In endothelial cells (EC), the transcription factor NF-κB is important in the switch from quiescence to activation, and is tightly controlled to avoid excessive inflammation and organ damage. Here we describe a novel mechanism that controls the activation of NF-κB in EC. The transcription factor Erg, the most highly expressed ETS member in resting EC, controls quiescence by repressing proinflammatory gene expression. Focusing on intercellular adhesion molecule 1(ICAM)-1 as a model, we identify two ETS binding sites (EBS -118 and -181) within the ICAM-1 promoter required for Erg-mediated repression. We show that Erg binds to both EBS -118 and EBS -181, the latter located within the NF-κB binding site. Interestingly, inhibition of Erg expression in quiescent EC results in increased NF-κB-dependent ICAM-1 expression, indicating that Erg represses basal NF-κB activity. Erg prevents NF-κB p65 from binding to the ICAM-1 promoter, suggesting a direct mechanism of interference. Gene set enrichment analysis of transcriptome profiles of Erg and NF-κB-dependent genes, together with chromatin immunoprecipitation (ChIP) studies, reveals that this mechanism is common to other proinflammatory genes, including cIAP-2 and IL-8. These results identify a role for Erg as a gatekeeper controlling vascular inflammation, thus providing an important barrier to protect against inappropriate endothelial activation.

Squelching of ETS2 Transactivation by POU5F1 Silences the Human Chorionic Gonadotropin CGA Subunit Gene in Human Choriocarcinoma and Embryonic Stem Cells

The subunit genes encoding human chorionic gonadotropin, CGA, and CGB, are up-regulated in human trophoblast. However, they are effectively silenced in choriocarcinoma cells by ectopically expressed POU domain class 5 transcription factor 1 (POU5F1). Here we show that POU5F1 represses activity of the CGA promoter through its interactions with ETS2, a transcription factor required for both placental development and human chorionic gonadotropin subunit gene expression, by forming a complex that precludes ETS2 from interacting with the CGA promoter. Mutation of a POU5F1 binding site proximal to the ETS2 binding site does not alter the ability of POU5F1 to act as a repressor but causes a drop in basal promoter activity due to overlap with the binding site for DLX3. DLX3 has only a modest ability to raise basal CGA promoter activity, but its coexpression with ETS2 can up-regulate it 100-fold or more. The two factors form a complex, and both must bind to the promoter for the combination to be transcriptionally effective, a synergy compromised by POU5F1. Similarly, in human embryonic stem cells, which express ETS2 but not CGA, ETS2 does not occupy its binding site on the CGA promoter but is found instead as a soluble complex with POU5F1. When human embryonic stem cells differentiate in response to bone morphogenetic protein-4 and concentrations of POU5F1 fall and hCG and DLX3 rise, ETS2 then occupies its binding site on the CGA promoter. Hence, a squelching mechanism underpins the transcriptional silencing of CGA by POU5F1 and could have general relevance to how pluripotency is maintained and how the trophoblast lineage emerges from pluripotent precursor cells.

EGF activates TTP expression by activation of ELK-1 and EGR-1 transcription factors

BackgroundTristetraprolin (TTP) is a key mediator of processes such as inflammation resolution, the inhibition of autoimmunity and in cancer. It carries out this role by the binding and degradation of mRNA transcripts, thereby decreasing their half-life. Transcripts modulated by TTP encode proteins such as cytokines, pro-inflammatory agents and immediate-early response proteins. TTP can also modulate neoplastic phenotypes in many cancers. TTP is induced and functionally regulated by a spectrum of both pro- and anti-inflammatory cytokines, mitogens and drugs in a MAPK-dependent manner. So far the contribution of p38 MAPK to the regulation of TTP expression and function has been best described.ResultsOur results demonstrate the induction of the gene coding TTP (ZFP36) by EGF through the ERK1/2-dependent pathway and implicates the transcription factor ELK-1 in this process. We show that ELK-1 regulates ZFP36 expression by two mechanisms: by binding the ZFP36 promoter directly through ETS-binding site (+ 883 to +905 bp) and by inducing expression of EGR-1, which in turn increases ZFP36 expression through sequences located between -111 and -103 bp.ConclusionsEGF activates TTP expression via ELK-1 and EGR-1 transcription factors.

Effect of phorbol 12‐myristate 13‐acetate activated signaling pathways on 1α, 25 dihydroxyvitamin D3 Regulated Human 25‐hydroxyvitamin D3 24‐hydroxylase Gene Expression in Differentiated Caco‐2 Cells

Phorbol-12-myristate-13-acetate (PMA), a protein kinase C(PKC) activator, can modulate 1α, 25 dihydroxyvitamin D(3) (1,25(OH)(2)D(3))-induced expression of the 24-hydroxylase (CYP24A1) gene but this has not been studied in differentiated enterocytes, a primary 1,25(OH)(2) D(3) target cell. We found that in differentiated Caco-2 cells, an established model of the mature absorptive epithelial cell, PMA significantly enhanced 1,25(OH)(2)D(3)-induced human CYP24A1 (hCYP24A1) mRNA accumulation and hCYP24A1 promoter-luciferase reporter gene activation by 150%. Reporter gene studies further identified the region between -298 and +74 bp in the hCYP24A1 promoter as critical for the PMA enhancing effect and chromatin immunoprecipitation (ChIP) analysis showed that PMA enhanced 1,25(OH)(2)D(3)-induced binding of vitamin D receptor to this region. PMA can activate PKC, ERK1/2, and p38 MAP kinases and inhibition of these signaling pathways reduced both 1,25(OH)(2)D(3)-induced hCYP24A1 gene transcription and the enhancing effect of PMA. The PMA enhancing effect on 1,25(OH)(2)D(3) action was evident in a minimal promoter with three osteocalcin VDREs and was reduced after mutation of a putative vitamin D stimulatory site in the hCYP24A1 promoter. In contrast, mutation of a Ets binding site (EBS) in the hCYP24A1 promoter had no impact on 1,25(OH)(2)D(3) action or the PMA enhancing effect. These data suggest that in the differentiated enterocyte PMA-induced activation of several signaling pathways contribute to 1,25(OH)(2)D(3)-induced hCYP24A1 gene expression through multiple regulatory motifs within the proximal hCYP24A1 promoter.