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Purpose: We report a novel analytic method, named intercohort co-analysis or Ican, which aids in the discovery of genes with predictive value for the progression or outcome of diseases from small-size cohorts. We tested this premise in Ewing's sarcoma (ES), a highly metastatic cancer of bone and soft tissues that lacks validated molecular metastasis and prognostic indicators.Experimental Design: To uncover genes significantly expressed in ES patient subsets, we first determined a nonarbitrary gene expression significance cutoff based on expression levels in validated expressing and nonexpressing tissues. We next searched for genes that were consistently significantly expressed in several ES cohort and cell line datasets. Significantly expressed genes were independently validated by quantitative reverse transcription-PCR in an additional ES cohort.Results: Analysis of ES cohorts revealed marked intercohort gene expression variability. After filtering out the intercohort variability, CXCR4 and CXCR7 were found to be consistently associated with specific ES subsets. Pairwise analyses showed CXCR4 to correlate with ES metastases, and CXCR4 and CXCR7 to patient survival, but not with several other clinicopathological variables.Conclusion: Ican is a powerful novel method to identifying genes consistently associated with particular disease states in cancers for which large cohorts are not available, currently the case of most cancers. We report for the first time that high CXCR4 expression preferentially associates with metastatic ES, and that of CXCR7 with poor patient survival. Clin Cancer Res; 16(14); 3769–78. ©2010 AACR.

Supplementary Data from Intercohort Gene Expression Co-Analysis Reveals Chemokine Receptors as Prognostic Indicators in Ewing's Sarcoma

Supplementary Figure Legend 1, Table Legends 1-6 from Hypoxia Modulates EWS-FLI1 Transcriptional Signature and Enhances the Malignant Properties of Ewing's Sarcoma Cells In vitro

Supplementary Figure 1 from Hypoxia Modulates EWS-FLI1 Transcriptional Signature and Enhances the Malignant Properties of Ewing's Sarcoma Cells In vitro

Supplementary Table 7 from Hypoxia Modulates EWS-FLI1 Transcriptional Signature and Enhances the Malignant Properties of Ewing's Sarcoma Cells In vitro

Supplementary Table 9 from Hypoxia Modulates EWS-FLI1 Transcriptional Signature and Enhances the Malignant Properties of Ewing's Sarcoma Cells In vitro

Hypoxia is an important condition in the tumor cell microenvironment and approximately 1% to 1.5% of the genome is transcriptionally responsive to hypoxia with hypoxia-inducible factor-1 (HIF-1) as a major mediator of transcriptional activation. Tumor hypoxia is associated with a more aggressive phenotype of many cancers in adults, but data on pediatric tumors are scarce. Because, by immunohistochemistry, HIF-1α expression was readily detectable in 18 of 28 primary Ewing's sarcoma family tumors (ESFT), a group of highly malignant bone-associated tumors in children and young adults, we studied the effect of hypoxia on ESFT cell lines in vitro. Intriguingly, we found that EWS-FLI1 protein expression, which characterizes ESFT, is upregulated by hypoxia in a HIF-1α–dependent manner. Hypoxia modulated the EWS-FLI1 transcriptional signature relative to normoxic conditions. Both synergistic as well as antagonistic transcriptional effects of EWS-FLI1 and of hypoxia were observed. Consistent with alterations in the expression of metastasis-related genes, hypoxia stimulated the invasiveness and soft agar colony formation of ESFT cells in vitro. Our data represent the first transcriptome analysis of hypoxic ESFT cells and identify hypoxia as an important microenvironmental factor modulating EWS-FLI1 expression and target gene activity with far-reaching consequences for the malignant properties of ESFT. Cancer Res; 70(10); 4015–23. ©2010 AACR.

Supplementary Tables 1-6 from Hypoxia Modulates EWS-FLI1 Transcriptional Signature and Enhances the Malignant Properties of Ewing's Sarcoma Cells In vitro

Supplementary Table 8b from Hypoxia Modulates EWS-FLI1 Transcriptional Signature and Enhances the Malignant Properties of Ewing's Sarcoma Cells In vitro

Ewing sarcoma (EwS) is a highly metastatic bone cancer characterized by the ETS fusion oncoprotein EWS-FLI1. EwS cells are phenotypically highly plastic and switch between functionally distinct cell states dependent on EWS-FLI1 fluctuations. Whereas EWS-FLI1high cells proliferate, EWS-FLI1low cells are migratory and invasive. Recently, we reported activation of MRTFB and TEAD, effectors of RhoA and Hippo signalling, upon low EWS-FLI1, orchestrating key steps of the EwS migratory gene expression program. TEAD and its co-activators YAP and TAZ are commonly overexpressed in cancer, providing attractive therapeutic targets. We find TAZ levels to increase in the migratory EWS-FLI1low state and to associate with adverse prognosis in EwS patients. We tested the effects of the potent YAP/TAZ/TEAD complex inhibitor verteporfin on EwS cell migration in vitro and on metastasis in vivo. Verteporfin suppressed expression of EWS-FLI1 regulated cytoskeletal genes involved in actin signalling to the extracellular matrix, effectively blocked F-actin and focal-adhesion assembly and inhibited EwS cell migration at submicromolar concentrations. In a mouse EwS xenograft model, verteporfin treatment reduced relapses at the surgical site and delayed lung metastasis. These data suggest that YAP/TAZ pathway inhibition may prevent EwS cell dissemination and metastasis, justifying further preclinical development of YAP/TAZ inhibitors for EwS treatment.

Adult Schwann cells (SCs) possess an inherent plastic potential. This plasticity allows SCs to acquire repair-specific functions essential for peripheral nerve regeneration. Here, we investigate whether stromal SCs in benign-behaving peripheral neuroblastic tumors adopt a similar cellular state. We profile ganglioneuromas and neuroblastomas, rich and poor in SC stroma, respectively, and peripheral nerves after injury, rich in repair SCs. Indeed, stromal SCs in ganglioneuromas and repair SCs share the expression of nerve repair-associated genes. Neuroblastoma cells, derived from aggressive tumors, respond to primary repair-related SCs and their secretome with increased neuronal differentiation and reduced proliferation. Within the pool of secreted stromal and repair SC factors, we identify EGFL8, a matricellular protein with so far undescribed function, to act as neuritogen and to rewire cellular signaling by activating kinases involved in neurogenesis. In summary, we report that human SCs undergo a similar adaptive response in two patho-physiologically distinct situations, peripheral nerve injury and tumor development., Schwann cells (SCs) can acquire a repair phenotype following nerve injury. Here, the authors show that stromal SCs in ganglioneuromas express nerve-repair genes. Importantly, neuroblastoma cells respond to repair-related SCs increasing neuronal differentiation and reducing proliferation via EGFL8.

Langerhans cell histiocytosis (LCH) is a MAPK pathway-driven disease characterized by the accumulation of CD1a+langerin+ cells of unknown origin. We have previously reported that the Notch signaling pathway is active in LCH lesions and that the Notch ligand Jagged2 (JAG2) induces CD1a and langerin expression in monocytes in vitro. Here we show that Notch signaling induces monocytes to acquire an LCH gene signature and that Notch inhibition suppresses the LCH phenotype. In contrast, while also CD1c+ dendritic cells or IL-4-stimulated CD14+ monocytes acquire CD1a and langerin positivity in culture, their gene expression profiles and surface phenotypes are more different from primary LCH cells. We propose a model where CD14+ monocytes serve as LCH cell precursor and JAG2-mediated activation of the Notch signaling pathway initiates a differentiation of monocytes toward LCH cells in selected niches and thereby contributes to LCH pathogenesis. This study aims to identify the cell of origin of Langerhans Cell Histiocytosis and the molecular mechanisms of its pathogenesis.

Ewing sarcoma (EwS) is an aggressive pediatric bone cancer in need of more effective therapies than currently available. Most research into novel targeted therapeutic approaches is focused on the fusion oncogene EWSR1-FLI1, which is the genetic hallmark of this disease. In this study, a broad range of 3,325 experimental compounds, among them FDA approved drugs and natural products, were screened for their effect on EwS cell viability depending on EWS-FLI1 expression. In a network-based approach we integrated the results from drug perturbation screens and RNA sequencing, comparing EWS-FLI1-high (normal expression) with EWS-FLI1-low (knockdown) conditions, revealing novel interactions between compounds and EWS-FLI1 associated biological processes. The top candidate list of druggable EWS-FLI1 targets included genes involved in translation, histone modification, microtubule structure, topoisomerase activity as well as apoptosis regulation. We confirmed our in silico results using viability and apoptosis assays, underlining the applicability of our integrative and systemic approach. We identified differential sensitivities of Ewing sarcoma cells to BCL-2 family inhibitors dependent on the EWS-FLI1 regulome including altered MCL-1 expression and subcellular localization. This study facilitates the selection of effective targeted approaches for future combinatorial therapies of patients suffering from Ewing sarcoma.

Ewing sarcoma (EWS) is a paediatric bone cancer with high metastatic potential. Cellular plasticity resulting from dynamic cytoskeletal reorganization, typically regulated via the Rho pathway, is a prerequisite for metastasis initiation. Here, we interrogated the role of the Ewing sarcoma driver oncogene EWS-FLI1 in cytoskeletal reprogramming. We report that EWS-FLI1 strongly represses the activity of the Rho-F-actin signal pathway transcriptional effector MRTFB, affecting the expression of a large number of EWS-FLI1-anticorrelated genes including structural and regulatory cytoskeletal genes. Consistent with this finding, chromatin immunoprecipitation sequencing (ChIP-seq) revealed strong overlaps in myocardin-related transcription factor B (MRTFB) and EWS-FLI1 chromatin occupation, especially for EWS-FLI1-anticorrelated genes. Binding of the transcriptional co-activator Yes-associated protein (YAP)-1, enrichment of TEAD-binding motifs in these shared genomic binding regions and overlapping transcriptional footprints of MRTFB and TEAD factors led us to propose synergy between MRTFB and the YAP/TEAD complex in the regulation of EWS-FLI1-anticorrelated genes. We propose that EWS-FLI1 suppresses the Rho-actin pathway by perturbation of a MRTFB/YAP-1/TEAD transcriptional module, which directly affects the actin-autoregulatory feedback loop. As spontaneous fluctuations in EWS-FLI1 levels of Ewing sarcoma cells in vitro and in vivo, associated with a switch between a proliferative, non-migratory EWS-FLI1-high and a non-proliferative highly migratory EWS-FLI1-low state, were recently described, our data provide a mechanistic basis for the underlying EWS-FLI1-dependent reversible cytoskeletal reprogramming of Ewing sarcoma cells.

T-cell acute lymphoblastic leukemia (T-ALL) is an aggressive hematological disease in which multiple genetic abnormalities cooperate in the malignant transformation of T-lymphoid progenitors. Although in pediatric T-ALL, CDKN1B deletions occur in about 12% of the cases and represent one of the most frequent copy number alterations, neither their association with other genetic alterations nor the clinical characteristics of these patients have been determined yet. In this study, we show that loss of CDKN1B increased the prevalence of cell cycle regulator defects in immature T-ALL, usually only ascribed to CDKN2A/B deletions, and that CDKN1B deletions frequently coincide with expression of MEF2C, considered as one of the driving oncogenes in immature early T-cell precursor (ETP) ALL. However, MEF2C-dysregulation was only partially associated with the immunophenotypic characteristics used to define ETP-ALL. Furthermore, MEF2C expression levels were significantly associated with or may even be predictive of the response to glucocorticoid treatment.

A translocation leading to the formation of an oncogenic EWS-ETS fusion protein defines Ewing sarcoma. The most frequent gene fusion, present in 85 percent of Ewing sarcomas, is EWS-FLI1. Here, a high-throughput RNA interference screen was performed to identify genes whose function is critical for EWS-FLI1 driven cell viability. In total, 6781 genes were targeted by siRNA molecules and the screen was performed both in presence and absence of doxycycline-inducible expression of the EWS-FLI1 shRNA in A673/TR/shEF Ewing sarcoma cells. The Leucine rich repeats and WD repeat Domain containing 1 (LRWD1) targeting siRNA pool was the strongest hit reducing cell viability only in EWS-FLI1 expressing Ewing sarcoma cells. LRWD1 had been previously described as a testis specific gene with only limited information on its function. Analysis of LRWD1 mRNA levels in patient samples indicated that high expression associated with poor overall survival in Ewing sarcoma. Gene ontology analysis of LRWD1 co-expressed genes in Ewing tumors revealed association with DNA replication and analysis of differentially expressed genes in LRWD1 depleted Ewing sarcoma cells indicated a role in connective tissue development and cellular morphogenesis. Moreover, EWS-FLI1 repressed genes with repressive H3K27me3 chromatin marks were highly enriched among LRWD1 target genes in A673/TR/shEF Ewing sarcoma cells, suggesting that LRWD1 contributes to EWS-FLI1 driven transcriptional regulation. Taken together, we have identified LRWD1 as a novel regulator of EWS-FLI1 driven cell viability in A673/TR/shEF Ewing sarcoma cells, shown association between high LRWD1 mRNA expression and aggressive disease and identified processes by which LRWD1 may promote oncogenesis in Ewing sarcoma.

Since publication of the article, the authors became aware that Figure 6(A,D) contained errors in the bands and loading controls. The newly compiled Figure 6A and 6D is given below.

Poor prognosis and frequent relapses are major challenges for patients with high-risk neuroblastoma (NB), especially when tumors show MYCN amplification. High-dose chemotherapy triggers apoptosis, necrosis and senescence, a cellular stress response leading to permanent proliferative arrest and a typical senescence-associated secretome (SASP). SASP components reinforce growth-arrest and act immune-stimulatory, while others are tumor-promoting. We evaluated whether metronomic, i.e. long-term, repetitive low-dose, drug treatment induces senescence in vitro and in vivo. And importantly, by using the secretome as a discriminator for beneficial versus adverse effects of senescence, drugs with a tumor-inhibiting SASP were identified. We demonstrate that metronomic application of chemotherapeutic drugs induces therapy-induced senescence, characterized by cell cycle arrest, p21WAF/CIP1 up-regulation and DNA double-strand breaks selectively in MYCN-amplified NB. Low-dose topotecan (TPT) was identified as an inducer of a favorable SASP while lacking NFKB1/p50 activation. In contrast, Bromo-deoxy-uridine induced senescent NB-cells secret a tumor-promoting SASP in a NFKB1/p50-dependent manner. Importantly, TPT-treated senescent tumor cells act growth-inhibitory in a dose-dependent manner on non-senescent tumor cells and MYCN expression is significantly reduced in vitro and in vivo. Furthermore, in a mouse xenotransplant-model for MYCN-amplified NB metronomic TPT leads to senescence selectively in tumor cells, complete or partial remission, prolonged survival and a favorable SASP. This new mode-of-action of metronomic TPT treatment, i.e. promoting a tumor-inhibiting type of senescence in MYCN-amplified tumors, is clinically relevant as metronomic regimens are increasingly implemented in therapy protocols of various cancer entities and are considered as a feasible maintenance treatment option with moderate adverse event profiles.

The ETV6/RUNX1 gene fusion defines the largest genetic subgroup of childhood ALL with overall rapid treatment response. However, up to 15% of cases relapse. Because an impaired glucocorticoid pathway is implicated in disease recurrence we studied the impact of genetic alterations by SNP array analysis in 31 relapsed cases. In 58% of samples, we found deletions in various glucocorticoid signaling pathway-associated genes, but only NR3C1 and ETV6 deletions prevailed in minimal residual disease poor responding and subsequently relapsing cases (p

P53 suppresses tumour growth via its diverse cellular activities, including induction of apoptosis, cell cycle arrest, differentiation and senescence (Vousden and Lu, 2002). Most of these effects reflect the transactivation of a number of genes by p53 acting as a transcription factor, but p53 also activates mitochondrial-dependent apoptotic pathways that are independent of p53 transcriptional activity (Green and Kroemer, 2009). Activation of p53 leads to apoptosis through either the death receptor pathway or the mitochondrial pathway (Selivanova, 2004). In the mitochondrial apoptotic pathway, p53 induces several genes including Bax, APAF-1, Puma and Noxa (Miyashita and Reed, 1995; Burns and El-Deiry, 1999; Lowe and Lin, 2000; Nakano and Vousden, 2001; Robles et al, 2001). TP53 mutations may be associated with an aggressive phenotype and poor prognosis, and some p53 mutants counteract the effects of anticancer agents that attack tumours (Bunz et al, 1999; Poeta et al, 2007). Given the high frequency of p53 mutations in human tumours, reactivation of the p53 pathway has been widely proposed as beneficial for cancer therapy (Selivanova, 2010). In addition, several reported structural studies have shown that mutant p53 core domain unfolding is reversible and, as mutant p53 is expressed at high levels in many tumours, it therefore serves as a potential target for novel cancer therapy (Lambert et al, 2010). Its reactivation will restore p53-dependent apoptosis, among others, resulting in efficient eradication of tumour cells (Tovar et al, 2006). Wild-type p53 can be induced by small organic molecules such as nutlin-3 inhibiting the p53/MDM2 interaction (Vassilev et al, 2004). PRIMA-1 (p53 reactivation and induction of massive apoptosis) and its potent methylated analog, APR-246/PRIMA-1Met, are small molecules that have the ability to convert mt-p53 to an active conformation, thereby restoring its sequence-specific DNA binding and transcriptional activation (Bykov et al, 2002b). It was reported that PRIMA-1 induces cell death through multiple pathways encompassing transcription-dependent and -independent signaling (Chipuk et al, 2003). In vitro and in vivo studies have shown that p53 reactivating small molecules are less toxic to normal cells than to cancer cells and have no significant adverse or genotoxic effects (Stuhmer et al, 2005; Tovar et al, 2006). Although about half of all human malignancies harbour dysfunctional, mutated p53 proteins, approximately 90% of all ES retain wild-type p53, and the downstream DNA damage cell cycle checkpoints and p53 pathways remain functionally intact (de Kovar et al, 1993; Alava et al, 2000; Kovar et al, 2003b; Huang et al, 2005). Exposure of ES cells to Nutlin-3a, a small organic molecule known to reactivate wild-type 53, resulted in a robust apoptotic phenotype that required the presence of wild-type p53 but did not affect the growth of mutant p53 expressing cells (Pishas et al, 2011). TP53 mutation alone rates high among variables, including p16/p14ARF alteration and tumour stage, predicting poorer overall survival in Ewing sarcoma (de Alava et al, 2000; Lopez-Guerrero et al, 2011). Multivariate analysis identified alterations of TP53 as an adverse prognostic factor defining a subset of ES with highly aggressive behaviour and poor chemoresponse (Huang et al, 2005). Therefore, novel treatment options specifically targeting mutant p53 are highly warranted. There is a prospective COG (Children's Oncology Group, USA) study ongoing to validate a retrospective study which strongly suggested that mutant p53 ES constitutes a particularly bad prognostic group (ClinicalTrials.gov identifier: NCT00898053). If data from the retrospective study is confirmed, this would strongly support the need for novel mutant p53 targeting therapeutic strategies in ES. In this study, we investigated whether the small pharmacological molecule APR-246 is able to reactivate mutant p53 in Ewing sarcoma cells in order to drive tumour cells into apoptosis. Using Ewing sarcoma patients' derived cell lines, we show that APR-246 is able to induce apoptosis to variable degrees independent of the p53 status. We observed that cell lines with similar p53 mutations as well as cell lines established from the same patient at different stages of the disease all exhibited variable responses to the drug. To interrogate the molecular basis for the differential responses to APR-246, we performed comparative transcriptomic analysis on the three STA-ET-7 cell lines established from the same patient. Data analysed revealed genes annotating to p53 and apoptosis pathways whose expression varies between the more APR-246-sensitive and the less APR-246-sensitive cell lines. We propose, therefore, that APR-246 will not be a suitable candidate to consider for targeting p53 mutant Ewing sarcoma.

Ewing sarcoma (ES) is the second most frequent childhood bone cancer driven by the EWS/FLI1 (EF) fusion protein. Genetically defined ES models are needed to understand how EF expression changes bone precursor cell differentiation, how ES arises and through which mechanisms of inhibition it can be targeted. We used mesenchymal Prx1-directed conditional EF expression in mice to study bone development and to establish a reliable sarcoma model. EF expression arrested early chondrocyte and osteoblast differentiation due to changed signaling pathways such as hedgehog, WNT or growth factor signaling. Mesenchymal stem cells (MSCs) expressing EF showed high self-renewal capacity and maintained an undifferentiated state despite high apoptosis. Blocking apoptosis through enforced BCL2 family member expression in MSCs promoted efficient and rapid sarcoma formation when transplanted to immunocompromised mice. Mechanistically, high BCL2 family member and CDK4, but low P53 and INK4A protein expression synergized in Ewing-like sarcoma development. Functionally, knockdown of Mcl1 or Cdk4 or their combined pharmacologic inhibition resulted in growth arrest and apoptosis in both established human ES cell lines and EF-transformed mouse MSCs. Combinatorial targeting of survival and cell cycle progression pathways could counteract this aggressive childhood cancer.

Notch can act as an oncogene or as a tumour suppressor and thus can either promote or inhibit tumour cell growth. To establish Notch status in Ewing's sarcoma family of tumours (ESFT), we investigated the Notch pathway by gene expression profiling meta-analysis or immunohistochemistry in samples obtained from 96 and 24 ESFT patients, respectively. We found that although Notch receptors were highly expressed, Notch did not appear to be active, as evidenced by the absence of Notch receptors in cell nuclei. In contrast, we show that Notch receptors known to be active in colon adenocarcinoma, hepatocarcinoma, and pancreatic carcinoma stain cell nuclei in these tumours. High expression of the Notch effector HES1 transcription factor, usually used as a surrogate marker for active Notch, was also restricted to outside of the nucleus in the majority of ESFT, and analysis of HES1 gene targets indicated HES1 to be transcriptionally inactive. Neither forced activation nor pharmacological or genetic blocking of Notch affected HES1 expression in ESFT cells, indicating HES1 expression to be uncoupled from the Notch pathway. Additional functional studies in ESFT cell lines confirmed Notch to be switched off. Finally, unlike experiments in which HES1 expression was modulated, experimental activation of Notch in ESFT cell lines via several means blocked cell proliferation and reduced their clonogenic potential in soft agar. These indicate that HES1 is uncoupled from Notch in ESFT, that EWS-FLI1-mediated inhibition of Notch contributes to ESFT aggressive cell growth, and support a role for Notch in ESFT tumour suppression, at least partly through the Notch effector HEY1.

Approximately 25% of childhood acute lymphoblastic leukemias carry the ETV6/RUNX1 fusion gene. Despite their excellent initial treatment response, up to 20% of patients relapse. To gain insight into the relapse mechanisms, we analyzed single nucleotide polymorphism arrays for DNA copy number aberrations (CNAs) in 18 matched diagnosis and relapse leukemias. CNAs were more abundant at relapse than at diagnosis (mean 12.5 vs 7.5 per case; P = .01) with 5.3 shared on average. Their patterns revealed a direct clonal relationship with exclusively new aberrations at relapse in only 21.4%, whereas 78.6% shared a common ancestor and subsequently acquired distinct CNA. Moreover, we identified recurrent, mainly nonoverlapping deletions associated with glucocorticoid-mediated apoptosis targeting the Bcl2 modifying factor (BMF) (n = 3), glucocorticoid receptor NR3C1 (n = 4), and components of the mismatch repair pathways (n = 3). Fluorescence in situ hybridization screening of additional 24 relapsed and 72 nonrelapsed ETV6/RUNX1-positive cases demonstrated that BMF deletions were significantly more common in relapse cases (16.6% vs 2.8%; P = .02). Unlike BMF deletions, which were always already present at diagnosis, NR3C1 and mismatch repair aberrations prevailed at relapse. They were all associated with leukemias, which poorly responded to treatment. These findings implicate glucocorticoid-associated drug resistance in ETV6/RUNX1-positive relapse pathogenesis and therefore might help to guide future therapies.

Reversible transitions from a proliferative to a nonproliferative but highly migratory and invasive phenotype, widely known as epithelial-to-mesenchymal transition (EMT), is a prerequisite for wound healing and organ development but also a hallmark of cancer. Recently, phenotypic changes resembling EMT were described to occur in Ewing sarcoma upon modulation of expression of the driver oncogene EWS-FLI1. Evidence was provided for the presence of highly migratory EWS-FLI1-low cells in Ewing sarcoma cell lines as well as in about 20% of primary tumors at low frequency (Franzetti et al., 2017). Importantly, when injected into the tail vein of immunosuppressed mice, EWS-FLI1-low cells were more likely to result in lung metastases than EWS-FLI1-high cells upon re-expression of the oncogene. In our study, we identified a mechanism for the cytoskeletal reprograming underlying EWS-FLI1 dose-dependent phenotypic transitions in Ewing sarcoma. We provide evidence for EWS-FLI1 blocking access of the transcriptional coactivators MRTFB and TAZ to the YAP/TEAD transcription factor complex on enhancers of EWS-FLI1 anti-correlated genes. Upon modulation of EWS-FLI1 expression, TEADs get activated downstream of Rho signaling through recruitment of MRTFB/YAP/TAZ, leading to the expression of key cytoskeletal components and regulators involved in the reorganization of the actin cytoskeleton. Based on these findings, we hypothesized that small-molecule inhibitors of the YAP/TAZ/TEAD pathway should interfere with the migratory phenotype of EWS-FLI1-low cells. In fact, the YAP/TAZ inhibitor verteporfin (Visudyne®), which is clinically used as a photosensitive drug in the treatment of age-related macular degeneration, was able to block Ewing sarcoma cell migration at low nanomolar concentrations without affecting tumor cell proliferation. These results suggest that YAP/TAZ inhibitors may be considered as a promising add-on to conventional combination treatments to prohibit tumor cell dissemination and metastasis. Citation Format: Anna M. Katschnig, Maximilian O. Kauer, Raphaela Schwentner, Eleni M. Tomazou, Dave N.T. Aryee, Heinrich Kovar. Targeting EWS-FLI1 dose-dependent epithelial-to-mesenchymal transition [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr A02.

Background: Poor prognosis and frequent relapses are major challenges for patients with high-risk neuroblastoma (NB), especially when tumors show MYCN amplification. High-dose chemotherapy triggers apoptosis, necrosis, and senescence, a cellular stress response leading to permanent proliferative arrest and a typical senescence-associated secretome (SASP). SASP components reinforce growth arrest and act in an immune-stimulatory fashion, while others are tumor promoting. Studies on low-dose long-term, i.e., metronomic, treatment schedules have demonstrated effects on the tumor microenvironment, but have not comprehensively analyzed cellular responses in tumor cells. Methods and Results: We evaluated efficacy and mode of action of low-dose metronomic treatment schedules in in vitro and in vivo NB models. Importantly, by using the secretome as a discriminator for beneficial versus adverse effects of senescence, drugs with a tumor-inhibiting SASP were identified. Our preclinical work has demonstrated that low-dose long-term topotecan (TPT) treatment (0.1 mg/kg/d, i.p., daily over 15 weeks) improves survival in mouse NB xenografts and leads to long-term cure in 40% of mice. TPT induces a tumor-inhibiting type of senescence, accompanied by changes in the tumor transcriptome and secretome, specifically in MYCN-amplified NB cells. As senescent NB cells showed a reduced MYCN copy number and strongly downregulated MYCN expression, we investigated the mechanism of MYCN inactivation. This showed that upon senescence MYCN is epigenetically silenced and gene copies are recruited to the nuclear periphery where changes in the nuclear lamina composition take place. Conclusion: This new mode of action of metronomic TPT treatment, i.e., promoting a tumor-inhibiting type of senescence selectively in MYCN-amplified neuroblastoma, is clinically relevant as metronomic regimens are increasingly implemented in therapy protocols of various cancer entities and are considered as a feasible maintenance treatment option with moderate adverse event profiles. Citation Format: Sabine Taschner-Mandl, Teresa Gerber, Magdalena Schwarz, Johanna Blaha, Maximilian Kauer, Florian Kromp, Nelli Frank, Fikret Rifatbegovic, Tamara Weiss, Ruth Ladenstein, Martin Hohenegger, Inge M. Ambros, Peter F. Ambros. Metronomic topotecan causes MYCN inactivation and impedes tumor growth selectively in MYCN-amplified neuroblastoma cells in vitro and in vivo by therapy-induced senescence [abstract]. In: Proceedings of the AACR Special Conference: Pediatric Cancer Research: From Basic Science to the Clinic; 2017 Dec 3-6; Atlanta, Georgia. Philadelphia (PA): AACR; Cancer Res 2018;78(19 Suppl):Abstract nr A17.

Beta-catenin (CTNNB) fulfills different functions depending on its subcellular localization. At the membrane it is involved in homotypic cell adhesion. In the nucleus it acts as a transcriptional co-activator, while cytoplasmic CTNNB sequesters and stabilizes the transcriptional co-activator TAZ and prohibits its nuclear translocation. The most extensively characterized CTNNB function is that of a nuclear effector of canonical Wnt signaling, binding and activating TCF/LEF family transcription factors and leading to upregulation of master regulators of epithelial-to-mesenchymal transition. In Ewing sarcoma (EwS), the presence of the driver fusion oncogene EWS-FLI1 renders canonical Wnt signaling unresponsive to Wnts. The exact mechanism of EWS-FLI1 mediated suppression of this signaling pathway is still elusive, but may involve downregulation of the beta-catenin partner transcription factor TCF7L2. In the absence of Wnt/CTNNB/TCF signaling we still find nuclear localization of CTNNB in EwS cells, and demonstrate sensitivity of the tumor cells to the CTNNB targeting cell-permeable oxazole compound iCRT3, suggesting an essential TCF independent role of beta-catenin for EwS survival. The regulation of CTNNB stability is complex and involves phosphorylation and the activity of a multi-protein cytoplasmic destruction complex containing Axin, APC , GSK3B and other proteins. Here, we identify involvement of lysine specific demethylase KDM1A (LSD1) in EWS-FLI1 dependent nuclear CTNNB stabilization. We describe a mechanism, by which EWS-FLI1 directly activates expression of the ubiquitin specific protease USP1 leading to KDM1A post-translational stabilization and ultimately CTNNB nuclear accumulation. Consequently, knockdown of EWS-FLI1 resulted in modulation of USP1, depletion of KDM1A protein, activation of the LSD1 target and negative Wnt signaling regulator DKK1, and cytoplasmic sequestration of CTNNB. Strikingly, in presence of EWS-FLI1, genetic or pharmacologic inhibition of either USP1 or LSD1, or forced DKK1 expression, led to CTNNB degradation. As we find upregulation of TAZ upon EWS-FLI1 knockdown and loss of CTNNB upon modulation of TAZ by siRNA, we speculate that TAZ may be involved in CTNNB cytoplasmic stabilization in absence of EWS-FLI1, while LSD1 is required for nuclear stabilization in presence of the fusion oncogene. These findings indicate complex CTNNB regulation in EwS, orchestrated by EWS-FLI1, and suggest USP1, KDM1A and CTNNB as potential therapeutic targets in EwS. Citation Format: Jozef Ban, Dave N. Aryee, Anna M. Katschnig, Raphaela Schwentner, Maximilian O. Kauer, Heinrich Kovar. EWS-FLI1 orchestrates beta-catenin regulation by a mechanism involving post-translational KDM1A stabilization [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4459.

Purpose: We report a novel analytic method, named intercohort co-analysis or Ican, which aids in the discovery of genes with predictive value for the progression or outcome of diseases from small-size cohorts. We tested this premise in Ewing's sarcoma (ES), a highly metastatic cancer of bone and soft tissues that lacks validated molecular metastasis and prognostic indicators. Experimental Design: To uncover genes significantly expressed in ES patient subsets, we first determined a nonarbitrary gene expression significance cutoff based on expression levels in validated expressing and nonexpressing tissues. We next searched for genes that were consistently significantly expressed in several ES cohort and cell line datasets. Significantly expressed genes were independently validated by quantitative reverse transcription-PCR in an additional ES cohort. Results: Analysis of ES cohorts revealed marked intercohort gene expression variability. After filtering out the intercohort variability, CXCR4 and CXCR7 were found to be consistently associated with specific ES subsets. Pairwise analyses showed CXCR4 to correlate with ES metastases, and CXCR4 and CXCR7 to patient survival, but not with several other clinicopathological variables. Conclusion: Ican is a powerful novel method to identifying genes consistently associated with particular disease states in cancers for which large cohorts are not available, currently the case of most cancers. We report for the first time that high CXCR4 expression preferentially associates with metastatic ES, and that of CXCR7 with poor patient survival. Clin Cancer Res; 16(14); 3769–78. ©2010 AACR.

PAX5-JAK2 has recently been identified as a novel recurrent fusion gene in B-cell precursor acute lymphoblastic leukemia, but the function of the encoded chimeric protein has not yet been characterized in detail. Herein we show that the PAX5-JAK2 chimera, which consists of the DNA-binding paired domain of PAX5 and the active kinase domain of JAK2, is a nuclear protein that has the ability to bind to wild-type PAX5 target loci. Moreover, our data provide compelling evidence that PAX5-JAK2 functions as a nuclear catalytically active kinase that autophosphorylates and in turn phosphorylates and activates downstream signal transducers and activators of transcription (STATs) in an apparently noncanonical mode. The chimeric protein also enables cytokine-independent growth of Ba/F3 cells and therefore possesses transforming potential. Importantly, the kinase activity of PAX5-JAK2 can be efficiently blocked by JAK2 inhibitors, rendering it a potential target for therapeutic intervention. Together, our data show that PAX5-JAK2 simultaneously deregulates the PAX5 downstream transcriptional program and activates the Janus kinase-STAT signaling cascade and thus, by interfering with these two important pathways, may promote leukemogenesis.

Ewing Sarcoma (EwS) is an aggressive pediatric bone tumor driven by the aberrant fusion-oncogene EWS-FLI1, which deregulates hundreds of genes by either activation (EWS-FLI1-correlated genes) or repression (EWS-FLI1-anticorrelated genes). Several EWS-FLI1-anticorrelated genes are involved in cytoskeletal processes and typically regulated by Rho/F-actin signaling. The Rho pathway is a crucial regulator of cell movement and cellular plasticity. Given the fact that EwS cells are highly prone to metastasize we were interested in studying a potential EWS-FLI1-mediated deregulation of Rho signaling. Activation of Rho triggers G- to F-actin polymerization thereby enabling nuclear translocation of the myocardin-related transcription factors MRTFA (MKL-1) and MRTFB (MKL-2). MRTFs typically serve as transcriptional co-activators of the transcription factor SRF regulating several cytoskeletal key players. We used the A673/TR/shEF cell line, harboring a doxycycline inducible sh-EWS-FLI1 plasmid, to interrogate the role of MRTFA/B in the EwS gene regulatory network upon EWS-FLI1-high and -low conditions. Strikingly, MRTFB transcriptional activity was overall repressed by EWS-FLI1. Furthermore, knockdown of MRTFB under EWS-FLI1-low conditions antagonized the re-activation of EWS-FLI1-anticorrelated genes. ChIP-seq revealed a strong overlap of MRTFB and EWS-FLI1 chromatin binding. MRTFB binding was significantly enriched in distal (enhancer) regions of EWS-FLI1-anticorrelated genes, especially upon EWS-FLI1-low conditions. Of note, an overrepresentation of TEAD motifs, but not SRF binding motifs, was observed in these regions suggesting a potential involvement of TEAD transcription factors in the regulation of the MRTFB/EWS-FLI1 reciprocally regulated targets. In line with this finding, target genes of the mechano sensitive YAP/TAZ/TEAD pathway (CTGF, CYR61, SERPINE1) were found among the MRTFB-bound EWS-FLI1-anticorrelated genes. Genome-wide expression profiling upon combined knockdown of EWS-FLI1 and all four TEADs confirmed that TEAD regulates EWS-FLI1 target genes antagonistically. ChIP-qPCR for selected genes validated this finding demonstrating increased TEAD binding to shared MRTFB/EWS-FLI1 target genes upon decreased EWS-FLI1 occupation. Our data suggest that MRTFB/YAP-1/TEAD directly regulate EWS-FLI1-anticorrelated targets. Since, in addition, EWS-FLI1 is known to indirectly perturb F-actin polymerization, we propose a model of dual EWS-FLI1 driven MRTFB/YAP-1/TEAD perturbation by direct and indirect mechanisms downstream of Rho/F-actin signaling. Citation Format: Anna M. Katschnig, Maximilian O. Kauer, Raphaela Schwentner, Eleni M. Tomazou, Markus Linder, Cornelia N. Mutz, Javier Alonso, Dave N. Aryee, Heinrich Kovar. EWS-FLI1 represses Rho-actin signaling via MRTFB/YAP-1/TEAD perturbation in Ewing Sarcoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3508. doi:10.1158/1538-7445.AM2017-3508

Adenoviruses encode a set of highly abundant microRNAs (mivaRNAs), which are generated by Dicer-mediated cleavage of the larger noncoding virus-associated RNAs (VA RNAs) I and II. We performed deep RNA sequencing to thoroughly investigate the relative abundance of individual single strands of mivaRNA isoforms in human A549 cells lytically infected with human adenovirus 5 (Ad5) at physiologically relevant multiplicities of infection (MOIs). In addition, we investigated their relative abundance in the endogenous RNA-induced silencing complexes (RISCs). The occupation of endogenous RISCs by mivaRNAs turned out to be pronounced but not as dominant as previously inferred from experiments with AGO2-overexpressing cells infected at high MOIs. In parallel, levels of RISC-incorporated mRNAs were investigated as well. Analysis of mRNAs enriched in RISCs in Ad5-infected cells revealed that only mRNAs with complementarity to the seed sequences of mivaRNAs derived from VA RNAI but not VA RNAII were overrepresented among them, indicating that only mivaRNAs derived from VA RNAI are likely to contribute substantially to the posttranscriptional downregulation of host gene expression. Furthermore, to generate a comprehensive picture of the entire transcriptome/targetome in lytically infected cells, we determined changes in cellular miRNA levels in both total RNA and RISC RNA as well, and bioinformatical analysis of mRNAs of total RNA/RISC fractions revealed a general, genome-wide trend toward detargeting of cellular mRNAs upon infection. Lastly, we identified the direct targets of both single strands of a VA RNAI-derived mivaRNA that constituted one of the two most abundant isoforms in RISCs of lytically infected A549 cells. IMPORTANCE Viral and cellular miRNAs have been recognized as important players in virus-host interactions. This work provides the currently most comprehensive picture of the entire mRNA/miRNA transcriptome and of the complete RISC targetome during lytic adenovirus infection and thus represents the basis for a deeper understanding of the interplay between the virus and the cellular RNA interference machinery. Our data suggest that, at least in the model system that was employed, lytic infection by Ad5 is accompanied by a measurable global net detargeting effect on cellular mRNAs, and analysis of RISC-associated viral small RNAs revealed that the VA RNAs are the only source of virus-encoded miRNAs. Moreover, this work allows to assess the power of individual viral miRNAs to regulate cellular gene expression and provides a list of proven and putative direct targets of these miRNAs, which is of importance, given the fact that information about validated targets of adenovirus-encoded miRNAs is scarce.

Deregulated E2F transcription factor activity occurs in the vast majority of human tumors and has been solidly implicated in disturbances of cell cycle control, proliferation, and apoptosis. Aberrant E2F regulatory activity is often caused by impairment of control through pRB function, but little is known about the interplay of other oncoproteins with E2F. Here we show that ETS transcription factor fusions resulting from disease driving rearrangements in Ewing sarcoma (ES) and prostate cancer (PC) are one such class of oncoproteins. We performed an integrative study of genome-wide DNA-binding and transcription data in EWSR1/FLI1 expressing ES and TMPRSS2/ERG containing PC cells. Supported by promoter activity and mutation analyses, we demonstrate that a large fraction of E2F3 target genes are synergistically coregulated by these aberrant ETS proteins. We propose that the oncogenic effect of ETS fusion oncoproteins is in part mediated by the disruptive effect of the E2F–ETS interaction on cell cycle control. Additionally, a detailed analysis of the regulatory targets of the characteristic EWSR1/FLI1 fusion in ES identifies two functionally distinct gene sets. While synergistic regulation in concert with E2F in the promoter of target genes has a generally activating effect, EWSR1/FLI1 binding independent of E2F3 is predominantly associated with repressed differentiation genes. Thus, EWSR1/FLI1 appears to promote oncogenesis by simultaneously promoting cell proliferation and perturbing differentiation.

Ewing sarcoma (ES) is the second most frequent childhood bone cancer driven by the EWS/FLI1 (EF) fusion protein. Genetically defined ES models are needed to understand how EF expression changes bone precursor cell differentiation, how ES arises and through which mechanisms of inhibition it can be targeted. We used mesenchymal Prx1-directed conditional EF expression in mice to study bone development and to establish a reliable sarcoma model. EF expression arrested early chondrocyte and osteoblast differentiation due to changed signaling pathways such as hedgehog, WNT or growth factor signaling. Mesenchymal stem cells (MSCs) expressing EF showed high self-renewal capacity and maintained an undifferentiated state despite high apoptosis. Blocking apoptosis through enforced BCL2 family member expression in MSCs promoted efficient and rapid sarcoma formation when transplanted to immunocompromised mice. Mechanistically, high BCL2 family member and CDK4, but low P53 and INK4A protein expression synergized in Ewing-like sarcoma development. Functionally, knockdown of Mcl1 or Cdk4 or their combined pharmacologic inhibition resulted in growth arrest and apoptosis in both established human ES cell lines and EF-transformed mouse MSCs. Combinatorial targeting of survival and cell cycle progression pathways could counteract this aggressive childhood cancer.

Ewing Sarcoma (ES) is the second most common bone cancer in children and adolescents with a high metastatic potential. Tumor development is driven by the specific t(11;22)(q24;q12) chromosomal translocation resulting in the generation of the chimeric transcription factor EWS-FLI1. NAD is a key metabolite of energy metabolism being involved in cellular redox reactions, DNA repair, and in the maintenance of genomic stability serving as a donor of ADP-ribose. This study describes targeting NAMPT (nicotinamide phosphoribosyltransferase), the rate-limiting enzyme in salvage generation of NAD, by FK866 in ES cells. Using FK866 has been proposed as a treatment option for various inflammatory diseases as well as cancer, rendering ES cells with high NAMPT expression especially susceptible to FK866-induced cytotoxicity. Here we report that NAMPT inhibition in ES cells leads to exhaustive NAD depletion, followed by a delayed reduction of ATP levels and concomitantly to apoptosis-mediated cell death. These effects can be reversed by nicotinic acid, a substrate for the NAD salvage generation. However, the use of a doxycycline-inducible shRNA against EWS-FLI1 revealed that the cytotoxic activity of NAMPT inhibition is significantly lowered in the absence of EWS-FLI1. EWS-FLI1-low ES cells have higher viability and lower rates of apoptosis throughout inhibitor treatment compared to cells with high EWS-FLI1 expression. Additionally, changes in mitochondrial respiration and glycolytic rate can be observed when comparing untreated versus EWS-FLI1 knockdown ES cells after NAMPT inhibition. Interestingly, loss of EWS-FLI1 leads to elevated NAD levels and results in alteration of RNA expression of some enzymes involved in the NAD synthesis pathway. These results might explain the high susceptibility of Ewing Sarcoma cells to FK866 treatment. Taken together, our data reveal evidence of an important role of the NAMPT-mediated NAD salvage pathway in the energy homeostasis of ES cells and suggests NAMPT inhibition as a potential new treatment approach for Ewing Sarcoma in combination with standard therapies. Supported by the Austrian Science fund, grant I1225-B19; and the Research Manitoba and CancerCare Manitoba Foundation. Citation Format: Cornelia N. Mutz, Raphaela Schwentner, Eric Bouchard, Edgard M. Mejia, Anna M. Katschnig, Maximilian O. Kauer, Dave N.T. Aryee, Antje Garten, Versha Banerji, Heinrich Kovar. Targeting NAMPT in Ewing's sarcoma cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1045.

Ewing Sarcoma (ES) is an aggressive pediatric bone tumor with a high tendency to metastasize. The primary genetic aberration responsible for ES pathogenesis is EWS-FLI1, a chimeric gene, derived from the chromosomal translocation t(11;22)(q24;q12). EWS-FLI1 encodes an aberrant ETS transcription factor. However, due to its lack of enzymatic activity and intrinsically disordered structure it has yet not been successfully targeted. EWS-FLI1 is prone to rapidly engage in protein-protein complexes, enhancing its oncogenic activity. It has been reported to be involved in interactions with regulators of the basal transcriptional machinery, RNA processing and DNA repair. Furthermore, it has been shown that, similar to the ternary complex factors (TCF) SAP1a and ELK1, EWS-FLI1 is able to form a complex with the global transcriptional regulator Serum Response Factor (SRF) on ETS containing promoter elements. SRF binds to CArG motifs in serum response elements (SRE) and requires a transcriptional co-activator, which is commonly provided upstream via the Rho- or the Ras-axis. Upon serum induced Rho activation, polymerization of globular (G-) actin into filamentous (F-) actin takes place, thereby releasing the G-actin bound myocardin-related transcription factors A and B (MRTFA/B) to translocate to the nucleus and concertedly with SRF regulate transcription of target genes. Binding of MRTFs to SRF is mutually exclusive and competed by TCFs, which are activated downstream of Ras, and require presence of an ETS motif adjacent to CArG. In this study we aim to investigate a potential competition of EWS-FLI1 with MRTFs, which might uncouple SRF dependent transcription from upstream G-protein linked regulation and hence interfere with processes such as proliferation, migration and differentiation. To address this question, we performed gene expression profiling in A673 and SKNMC ES cell lines where we combined EWS-FLI1 knockdown with MRTFA/B knockdown under serum starved and serum induced (SI) conditions. We found that transcriptional activity of MRTFA/B is largely repressed by EWS-FLI1 and that upon combined knockdown conditions, EWS-FLI1 transcriptional effects are rescued by MRTFA/B. To further elucidate the underlying mechanisms of EWS-FLI1 and MRTFA/B gene regulation, we performed chromatin immunoprecipitation combined with massive parallel sequencing (ChIP-seq) of MRTFA, MRTFB, SRF and EWS-FLI1 in A673 ES cells. Preliminary results corroborate EWS-FLI1 and MRTF sharing a large number of target genes and indicate that MRTFA binds to DNA motifs, which are associated with activated and repressive EWS-FLI1 signatures. Ongoing experiments aim at a proteomic understanding of the EWS-FLI1 containing SRF complex as a basis for potential therapeutic intervention. This study was supported by the Liddy Shriver Sarcoma Initiative and the 7th framework program of the European Commission (FP7-259348, “ASSET”). Citation Format: Anna M. Katschnig, Maximilian O. Kauer, Dave N t Aryee, Raphaela Schwentner, Elizabeth Lawlor, Heinrich Kovar. Transcriptional modules involving EWS-FLI1 and SRF in Ewing sarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2028.

Ewing sarcoma is the second most frequent bone cancer in Caucasian children and young adults, but hardly occurs in Africans. It is characterized by a relatively quiet genome with only one highly recurrent chromosomal aberration, a EWS-ETS (predominantly EWS-FLI1) gene rearrangement. The resulting fusion gene encodes for an aberrant ETS transcription factor which drives sarcomagenesis. In a large GWAS study, three Ewing sarcoma susceptibility loci were discovered on chromosomes 1, 10 and 15, but the molecular mechanisms, how these loci affect tumorigenesis, remained largely unknown. By epigenomic mapping, EWS-FLI1 ChIP-seq, and reporter gene assays we found one of the susceptibility loci to localize to an EWS-FLI1 bound enhancer in the intron of a long non-coding antisense RNA, which we termed lncESST1 (Ewing Sarcoma Susceptibility Transcript 1). Deletion of the ETS binding region in the enhancer by CRISPR/Cas9 mediated gene editing lead to a drastic decrease in lncESST1 expression. Modulation of lncESST expression by siRNA or enhancer deletion significantly reduced soft agar colony formation of Ewing sarcoma cells without affecting growth under adherent culture conditions. Detachment of Ewing sarcoma cells from the plastic surface and growth under spheroid culture conditions induced stress granule formation as an immediate response, and a steady increase in lncESST1 expression over a period of at least 72 hours. We report that lncESST1 binds to a stress granule component with which it shares the promoter, and that loss of lncESST1 expression due to enhancer deletion perturbs stress granule formation. Our study therefore unveils a novel mechanism of lncRNA mediated cancer susceptibility. Supported by FWF grant I1225-B19 Citation Format: Dave NT Aryee, Eleni Tomazou, Maximilian Kauer, Thomas Grünewald, Franck Tirode, Olivier Delattre, Heinrich Kovar. A long noncoding RNA-regulating enhancer links Ewing sarcoma susceptibility to stress response. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 973.

MicroRNAs (miRNA) serve to fine-tune gene expression and thus play an important regulatory role in tissue specific gene networks. The identification and validation of miRNA target genes in a given tissue still poses a significant problem since the presence of a seed sequence in the 3′UTR of an mRNA and its expression modulation upon forced ectopic expression of the miRNA do not reliably predict regulation under physiological conditions. The chimeric oncoprotein EWS-FLI1 is the driving pathogenic force in ES. Recently, we reported on the EWS-FLI1 microRNA (miRNA) signature based on knockdown experiments in ES cell lines and on differential expression in primary tumors versus mesenchymal stem cells. Comparison of both datasets revealed the miR17-92 cluster to be the top EWS-FLI1 activated miRNA, which is one of the most potent oncogenic miRNAs. The whole cluster is among the small number of miRNAs down-regulated upon knockdown of EWS-FLI1 in multiple ES cell lines. We now report the use of a combination of AGO2 pull-down experiments by PAR-CLIP - to enrich and sequence RISC-associated RNAs - and of RNAseq upon miRNA depletion by ectopic sponge expression to identify the targetome of miR17-92 in Ewing sarcoma (ES) cells We found a significant enrichment of PAR-CLIP hits for members of the miR-17-92 cluster in the 3′UTRs of genes up-regulated in response to mir-17-92 but not miR9 and 10b specific sponge expression. Among them, we consistently identified known (i.e. CTGF, MXD1, CYLD1) and a multitude of so far unknown targets of the oncomir-1 cluster in ES in three PAR-CLIP experiments. Interestingly, approximately a quarter of these genes annotate to the TGFB/BMP pathway, the majority mapping downstream of SMAD signaling. Gene reporter assays using 3’UTRs of select novel candidate genes showed enhancement of luciferase activity upon transfection of a sponge specific to miR-17-92 and 20a, but not to unrelated miR-9 and 10b. Site directed mutagenesis of seed sequences in these 3’UTR confirmed the direct regulation of these genes by miR17-92. Current research focuses on the functional validation of TGFB pathway modulation by miR17-92. This study provides a paradigmatic approach to the comprehensive definition of the targetome for a defined group of miRNAs under physiological conditions. This study was supported by the 7th framework program of the European Commission (FP7-259348, “ASSET”) and the Austrian Science Fund FWF (24708-B21) Citation Format: Raphaela Schwentner, Maximilian Kauer, David Herrero-Martin, Heinrich Kovar. The role of miR17-92 in the miRegulatory landscape of Ewing sarcoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1918.

Hypoxia is an important condition in the tumor cell microenvironment and approximately 1% to 1.5% of the genome is transcriptionally responsive to hypoxia with hypoxia-inducible factor-1 (HIF-1) as a major mediator of transcriptional activation. Tumor hypoxia is associated with a more aggressive phenotype of many cancers in adults, but data on pediatric tumors are scarce. Because, by immunohistochemistry, HIF-1α expression was readily detectable in 18 of 28 primary Ewing's sarcoma family tumors (ESFT), a group of highly malignant bone-associated tumors in children and young adults, we studied the effect of hypoxia on ESFT cell lines in vitro. Intriguingly, we found that EWS-FLI1 protein expression, which characterizes ESFT, is upregulated by hypoxia in a HIF-1α–dependent manner. Hypoxia modulated the EWS-FLI1 transcriptional signature relative to normoxic conditions. Both synergistic as well as antagonistic transcriptional effects of EWS-FLI1 and of hypoxia were observed. Consistent with alterations in the expression of metastasis-related genes, hypoxia stimulated the invasiveness and soft agar colony formation of ESFT cells in vitro. Our data represent the first transcriptome analysis of hypoxic ESFT cells and identify hypoxia as an important microenvironmental factor modulating EWS-FLI1 expression and target gene activity with far-reaching consequences for the malignant properties of ESFT. Cancer Res; 70(10); 4015–23. ©2010 AACR.

Background EWS-FLI1 is a chimeric ETS transcription factor that is, due to a chromosomal rearrangement, specifically expressed in Ewing's sarcoma family tumors (ESFT) and is thought to initiate the development of the disease. Previous genomic profiling experiments have identified EWS-FLI1–regulated genes and genes that discriminate ESFT from other sarcomas, but so far a comprehensive analysis of EWS-FLI1–dependent molecular functions characterizing this aggressive cancer is lacking. Methodology/Principal Findings In this study, a molecular function map of ESFT was constructed based on an integrative analysis of gene expression profiling experiments following EWS-FLI1 knockdown in a panel of five ESFT cell lines, and on gene expression data from the same platform of 59 primary ESFT. Out of 80 normal tissues tested, mesenchymal progenitor cells (MPC) were found to fit the hypothesis that EWS-FLI1 is the driving transcriptional force in ESFT best and were therefore used as the reference tissue for the construction of the molecular function map. The interrelations of molecular pathways were visualized by measuring the similarity among annotated gene functions by gene sharing. The molecular function map highlighted distinct clusters of activities for EWS-FLI1 regulated genes in ESFT and revealed a striking difference between EWS-FLI1 up- and down-regulated genes: EWS-FLI1 induced genes mainly belong to cell cycle regulation, proliferation, and response to DNA damage, while repressed genes were associated with differentiation and cell communication. Conclusions/Significance This study revealed that EWS-FLI1 combines by distinct molecular mechanisms two important functions of cellular transformation in one protein, growth promotion and differentiation blockage. By taking MPC as a reference tissue, a significant EWS-FLI1 signature was discovered in ESFT that only partially overlapped with previously published EWS-FLI1–dependent gene expression patterns, identifying a series of novel targets for the chimeric protein in ESFT. Our results may guide target selection for future ESFT specific therapies.

The oncogene EWS-FLI1 encodes a chimeric transcription factor expressed in Ewing's sarcoma family tumors (ESFTs). EWS-FLI1 target gene expression is thought to drive ESFT pathogenesis and, therefore, inhibition of EWS-FLI1 activity holds high therapeutic promise. As the activity of many transcription factors is regulated by post-translational modifications, we studied the presence of modifications on EWS-FLI1. The immuno-purified fusion-protein was recognized by an antibody specific for O-linked beta-N-acetylglucosaminylation, and bound readily to a phosphoprotein-specific dye. Inhibition of Ser/Thr-specific phophatases increased EWS-FLI1 molecular weight and reduced its O-GlcNAc content, suggesting that phosphorylation and O-GlcNAcylation of EWS-FLI1 interact dynamically. By mutation analysis, O-GlcNAcylation was delineated to Ser/Thr residues of the amino-terminal EWS transcriptional-activation domain. Metabolic inhibition of the hexosamine biosynthetic pathway abrogated O-GlcNAcylation of EWS-FLI1 and interfered specifically with transcriptional activation of the EWS-FLI1 target Id2. These results suggest that drugs modulating glycosylation of EWS-FLI1 interfere functionally with its activity and might, therefore, constitute promising additions to the current ESFT chemotherapy.

Background Metastases in the bone marrow (BM) in form of disseminated tumor cells (DTCs) are frequent events at diagnosis and also at relapse in high-risk neuroblastoma patients. The frequently highly diluted occurrence of DTCs requires adequate enrichment strategies to enable their detailed characterization. However, to avoid methodical artifacts we tested whether pre-analytical processing steps—including transport duration, temperature and, importantly, tumor cell enrichment techniques—are confounding factors for gene expression analysis in DTCs. Methods LAN-1 neuroblastoma cells were spiked into tumor free BM and/or peripheral blood and: i) kept at room temperature or at 4°C for 24, 48 and 72 hours; ii) frozen down at -80°C and thawed; iii) enriched via magnetic beads. The effect on the gene expression signature of LAN-1 cells was analyzed by qPCR arrays and gene expression microarrays. Results Neither storage at –80°C in DMSO and subsequent thawing nor enrichment of spiked-in neuroblastoma cells changed the expression of the analyzed genes significantly. Whereas storage at 4°C altered the expression of analyzed genes (14.3%) only at the 72h-timepoint in comparison to the 0h-timepoint, storage at room temperature had a much more profound effect on gene expression by affecting 20% at 24h, 26% at 48h and 43% at 72h of the analyzed genes. Conclusion Using neuroblastoma as a model, we show that tumor cell enrichment by magnetic bead separation has virtually no effect on gene expression in DTCs. However, transport time and temperature can influence the expression profile remarkably. Thus, the expression profile of routinely collected BM samples can be analyzed without concern as long as the transport conditions are monitored.

MicroRNAs (miRNA) serve to fine-tune gene expression and thus play an important regulatory role in tissue specific gene networks. The identification and validation of miRNA target genes in a given tissue still poses a significant problem, since the presence of a seed sequence in the 3´UTR of an mRNA and its expression modulation upon forced ectopic expression of the miRNA do not reliably predict regulation under physiological conditions. Here, we used a combination of AGO2 pull-down experiments by PAR-CLIP - to enrich and sequence RISC-associated RNAs - and of RNAseq upon miRNA depletion by ectopic sponge expression, to identify the targetome of miR17-92 in Ewing sarcoma (ES) cells. The chimeric oncoprotein EWS-FLI1 is the driving pathogenic force in ES. As an aberrant ETS transcription factor it directly deregulates a multitude of genes related to proliferation control and differentiation. Recently, we reported on the EWS-FLI1 microRNA (miRNA) signature based on knockdown experiments in ES cell lines and on differential expression in primary tumors versus mesenchymal stem cells. Comparison of both datasets revealed miR20a-3p to be the top EWS-FLI1 activated miRNA. MiR-20a belongs to the miR17-92 cluster, also known as oncomir-1, which is one of the most potent oncogenic miRNAs. The whole cluster is among the small number of miRNAs down-regulated upon knockdown of EWS-FLI1 in multiple ES cell lines. Since feedback loops exists between the E2F transcription factor family and miR-17-92 and between EWS-FLI1 and E2F3, we sought to investigate the role of this miRNA cluster in ES. We found a significant enrichment of PAR-CLIP hits for members of the miR-17-92 cluster, in the 3´UTRs of genes up-regulated in response to mir-17-92 specific sponge expression. Among them we consistently identified known (i.e. CTGF, MXD1, CYLD1) and a multitude of so far unknown targets of the oncomir-1 cluster in ES in three PAR-CLIP experiments. Preliminary experiments using 3′UTRs of select novel candidate genes in gene reporter assays showed up-regulation of luciferase activity upon transfection of a sponge specific to miR-17-92 and 20a, but not to unrelated miR-9 and 10b. Site directed mutagenesis of seed sequences in the 3′UTR of these candidate genes will be used for further validation. This study provides an example for the comprehensive definition of the targetome for a defined group of miRNAs under physiological conditions. This study was supported by the 7th framework program of the European Commission (FP7-259348, “ASSET”) and the Austrian Science Fund FWF (24708-B21) Citation Format: Raphaela Schwentner, David Herrero-Martin, Maximilian Kauer, Heinrich Kovar. Definition of the Ewing sarcoma specific oncomir-1 targetome. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3080. doi:10.1158/1538-7445.AM2015-3080

Ewing Sarcoma (ES) is the second most common bone cancer in children and adolescents with a high metastatic potential. Tumor development is driven by the specific t(11;22)(q24;q12) chromosomal translocation resulting in generation of the chimeric transcription factor EWS-FLI1. Recently, ES has been reported to be exquisitely sensitive to inhibitors of poly(ADP-ribose) polymerase 1 (PARP1). This enzyme uses NAD as substrate and was demonstrated to regulate EWS-FLI1 in a feed-back mechanism. NAD is a key metabolite essential for sustaining cellular energy metabolism. It plays a central role in cellular redox reactions, DNA repair, and in the maintenance of genomic stability serving as a donor of ADP-ribose. The other major mammalian NAD consumer is the deacetylase SIRT1 which we observed to be specifically highly expressed in ES metastases. PARP1 and SIRT1 are crucial for coupling cellular metabolism to transcriptional gene regulation as well as to stress response. Usually, NAD is regenerated from nicotinamide in the NAMPT-dependent salvage pathway or from the reduction of pyruvate via LDHA (Warburg effect), but can also be synthesized de novo from tryptophan. Interestingly, the knockdown of EWS-FLI1 in ES cells comes along with alterations in the expression of multiple enzymes involved in NAD biosynthesis and regeneration, including TDO2, KMO, NMNAT1, NAPRT, NAMPT, and LDHA. We are interrogating the role of EWS-FLI1 mediated modulation of these enzymes and of specific small molecule inhibitors on cellular tryptophan consumption, kynurenine production and intracellular NAD levels of Ewing sarcoma cells. Additionally, we are investigating the functional consequences thereof on constitutive and stress-induced protein poly(ADP)-ribosylation and acetylation. Preliminary results suggest that NAMPT inhibition diminishes PARP1 activity due to low NAD, implying a pivotal role for the regenerative salvage pathway in ES cells. TDO2-dependent tryptophan consumption increases in the absence of the oncogene. These studies aim at a better understanding of factors influencing Ewing sarcoma sensitivity to therapies targeting PARP1 and the NAD metabolome. Citation Format: Cornelia N. Mutz, Raphaela Schwentner, Maximilian O. Kauer, Jozef Ban, Dave N. T. Aryee, Sophie Erhardt, Dietmar Fuchs, Andreas Heitger, Heinrich Kovar. Investigating the NAD metabolome in Ewing Sarcoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1162. doi:10.1158/1538-7445.AM2015-1162

Cell cycle deregulation and enhanced proliferation of cells is one of the hallmarks of oncogenesis. In Ewing Sarcoma, a highly aggressive pediatric cancer, the chimeric transcription factor EWS-FLI1 deregulates cell cycle by targeting several cell cycle regulators including the E2F family of transcription factors. ChIP-seq studies showed a significant overlap of EWS-FLI1 and E2F3/4 binding in Ewing sarcoma cells. We show that EWS-FLI1 is able to directly activate E2F3, followed by the combinatorial binding of EWS-FLI1 and E2F3 on their target genes synergistically activating their transcription. Furthermore we propose a model where EWS-FLI1 directly exchanges repressive E2F4/p130 by E2F3/pRB thereby driving cells into enhanced cell proliferation. However, so far we were unable to experimentally demonstrate a physical interaction of EWS-FLI1 with any E2F or pocket protein. As an alternative approach to the study of functional synergy between EWS-FLI1 and E2F3, we used time resolved RNA and protein expression data as a basis for mathematical modeling of EWS-FLI1 dependent E2F target gene regulation. By Bayesian model selection, we were able to postulate the formation of a complex between EWS-FLI1 and E2F3 as the most likely explanation for the observed ETS/E2F synergy. This study therefore provides an example of how computational systems approaches can complement experimental data in the discovery of disease mechanisms. This study was supported in part by the Austrian Science Fund (FWF), [grant 22328-B09], and by the 7th framework program of the European Commission, [grant 259348] (‘ASSET’). Citation Format: Raphaela Schwentner, Theodore Papamarkou, Maximilian Kauer, Vassilios Stathopoulos, Fan Yang, Sven Bilke, Paul S. Meltzer, Mark Girolami, Heinrich Kovar. Evidence for E2F/EWS-FLI1 oncoprotein synergism using systems biology. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2104. doi:10.1158/1538-7445.AM2015-2104

The pediatric bone cancer Ewing sarcoma (ES) is characterized by the expression of the chimeric transcription factor EWS-FLI1, derived from a chromosomal translocation t(11;22)(q24;q12). The early onset of metastasis in ES leads to poor overall survival and limited treatment options. Remodeling of the actin cytoskeleton is a prerequisite of a tumor cell in order to become metastatic. Previous studies suggest that EWS-FLI1 alters cell morphology and deregulates various cytoskeletal genes. The major point of convergence of extracellular signals influencing cytoskeletal regulation is the Rho pathway. Activation of Rho GTPases promotes polymerization of monomeric G-actin into stress fibers (F-actin) thereby releasing the myocardin-related transcription factor family (MRTF-A, MRTF-B) of transcriptional coactivators. MRTFs translocate to the nucleus and interact with the transcription factor serum response factor (SRF) bound on CArG promoter elements of genes. However, the ternary complex factor (TCF) family, a class of transcriptional coactivators activated downstream of Ras signaling, competes with MRTFs for SRF binding in presence of ets binding sites adjacent to the CArG consensus sequence. The ets-transcription factor EWS-FLI1 has been shown to substitute for TCFs and interact with SRF. We hypothesized that EWS-FLI1 competes with MRTFs for SRF binding and uncouples target gene expression from Rho signaling. In combinatorial knockdown experiments of MRTFA/B and EWS-FLI1 we demonstrate that global changes in gene expression elicited by EWS-FLI1 silencing largely depend on the presence of MRTFs, suggesting that the fusion oncogene prohibits MRTF activity. Using gene expression analysis we identified six different patterns of MRTF/EWS-FLI1 interaction, with predominance of EWS-FLI1 inversely regulating MRTF target genes. Furthermore, we found MRTF transcriptional effects are already present in the absence of serum in A673 ES cells. MRTFB, however, is cytoplasmic under serum starved conditions and translocates to the nucleus only upon serum stimulation unless latrunculin B (LatB), an actin polymerization inhibitor, is added. In contrast, MRTFA is constitutively nuclear even under serum starved conditions or upon LatB treatment indicating that MRTFA might be uncoupled from actin regulation. These findings reveal a previously unknown role of MRTFs and the “CArGome” in EWS-FLI1 driven transcriptional dysregulation. Supported by the Liddy Shriver Sarcoma Initiative. Citation Format: Anna M. Katschnig, Maximilian Kauer, Raphaela Schwentner, Dave N.T Aryee, Elizabeth Lawlor, Heinrich Kovar. An EWS-FLI1/MRTF gene regulatory network in Ewing sarcoma. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2105. doi:10.1158/1538-7445.AM2015-2105