Inhibition of the transcriptional function of p53 by EWS-Fli1 chimeric protein in Ewing Family Tumors

Noncanonical roles of p53 in cancer stemness and their implications in sarcomas

Impairment of the prominent tumor suppressor p53, well known for its canonical role as the "guardian of the genome", is found in almost half of human cancers. More recently, p53 has been suggested to be a crucial regulator of stemness, orchestrating the differentiation of embryonal and adult stem cells, suppressing reprogramming into induced pluripotent stem cells, or inhibiting cancer stemness (i.e., cancer stem cells, CSCs), which underlies the development of therapy-resistant tumors. This review addresses these noncanonical roles of p53 and their implications in sarcoma initiation and progression. Indeed, dysregulation of p53 family proteins is a common event in sarcomas and is associated with poor survival. Additionally, emerging studies have demonstrated that loss of wild-type p53 activity hinders the terminal differentiation of mesenchymal stem cells and leads to the development of aggressive sarcomas. This review summarizes recent findings on the roles of aberrant p53 in sarcoma development and stemness and further describes therapeutic approaches to restore normal p53 activity as a promising anti-CSC strategy to treat refractory sarcomas.

Intracranial Ewing Sarcoma - A case report

Background:

Intracranial Ewing’s sarcoma (ES) is a rare entity with <15 cases reported in the literature. It belongs to a family of round-cell neuroectodermally derived tumors bearing many similarities to peripheral primitive neuroectodermal tumor (pPNET). There is currently no established treatment protocol. Reported cases are treated with either surgery alone or surgery with adjuvant chemotherapy and radiation.

Case Description:

We describe a case of intracranial left frontal ES in a 19-year-old patient who presented with change in behavior. Diagnosis was unclear based on radiological findings on MRI and CT alone. MRI brain with contrast demonstrated a large extra-axial ovoid heterogeneously enhancing left frontal convexity mass. The patient underwent gross total resection with adjuvant chemotherapy and radiation. No local or systemic recurrence was found at 12 months postoperatively.

Conclusion:

Intracranial ES/pPNET is rare tumor with nonspecific clinical presentation and radiological findings. They are locally invasive. Surgery with adjuvant chemoradiation is the mainstay treatment. Distinction of pPNET and cPNET is important for therapeutic and prognostic purposes.

Targeting the undruggable: exploiting neomorphic features of fusion oncoproteins in childhood sarcomas for innovative therapies

While sarcomas account for approximately 1% of malignant tumors of adults, they are particularly more common in children and adolescents affected by cancer. In contrast to malignancies that occur in later stages of life, childhood tumors, including sarcoma, are characterized by a striking paucity of somatic mutations. However, entity-defining fusion oncogenes acting as the main oncogenic driver mutations are frequently found in pediatric bone and soft-tissue sarcomas such as Ewing sarcoma (EWSR1-FLI1), alveolar rhabdomyosarcoma (PAX3/7-FOXO1), and synovial sarcoma (SS18-SSX1/2/4). Since strong oncogene-dependency has been demonstrated in these entities, direct pharmacological targeting of these fusion oncogenes has been excessively attempted, thus far, with limited success. Despite apparent challenges, our increasing understanding of the neomorphic features of these fusion oncogenes in conjunction with rapid technological advances will likely enable the development of new strategies to therapeutically exploit these neomorphic features and to ultimately turn the "undruggable" into first-line target structures. In this review, we provide a broad overview of the current literature on targeting neomorphic features of fusion oncogenes found in Ewing sarcoma, alveolar rhabdomyosarcoma, and synovial sarcoma, and give a perspective for future developments. Graphical abstract Scheme depicting the different targeting strategies of fusion oncogenes in pediatric fusion-driven sarcomas. Fusion oncogenes can be targeted on their DNA level (1), RNA level (2), protein level (3), and by targeting downstream functions and interaction partners (4).

TP53 in bone and soft tissue sarcomas

Genomic and functional study of existing and emerging sarcoma targets, such as fusion proteins, chromosomal aberrations, reduced tumor suppressor activity, and oncogenic drivers, is broadening our understanding of sarcomagenesis. Among these mechanisms, the tumor suppressor p53 (TP53) plays significant roles in the suppression of bone and soft tissue sarcoma progression. Although mutations in TP53 were thought to be relatively low in sarcomas, modern techniques including whole-genome sequencing have recently illuminated unappreciated alterations in TP53 in osteosarcoma. In addition, oncogenic gain-of-function activities of missense mutant p53 (mutp53) have been reported in sarcomas. Moreover, new targeting strategies for TP53 have been discovered: restoration of wild-type p53 (wtp53) activity through inhibition of TP53 negative regulators, reactivation of the wtp53 activity from mutp53, depletion of mutp53, and targeting of vulnerabilities in cells with TP53 deletions or mutations. These discoveries enable development of novel therapeutic strategies for therapy-resistant sarcomas. We have outlined nine bone and soft tissue sarcomas for which TP53 plays a crucial tumor suppressive role. These include osteosarcoma, Ewing sarcoma, chondrosarcoma, rhabdomyosarcoma (RMS), leiomyosarcoma (LMS), synovial sarcoma, liposarcoma (LPS), angiosarcoma, and undifferentiated pleomorphic sarcoma (UPS).

Cytogenetic characterization of the malignant primitive neuroectodermal SK-PN-DW tumor cell line

Background

The SK-PN-DW cell line was established in 1979 and is commercially available. Despite the use of this cell line as an in vitro model for functional and therapeutic studies of malignant primitive neuroectodermal tumor (PNET), there is a lack of complete information about the genetic alterations that are present at the cytogenetic level. Thus, the current study aimed to characterize the cytogenetic profile of this cell line.

Methods

Routine G-banded chromosome analysis, fluorescence in situ hybridization, and oligonucleotide array comparative genomic hybridization assays were performed to characterize the chromosomal changes in this cell line.

Results

The G-banded karyotype analysis showed that the number of chromosomes in this cell line ranged between 36 and 41. Importantly, all cells displayed a loss of chromosomes Y, 11, 13, and 18. However, some cells showed an additional loss of chromosome 10. Additionally, the observed structural changes indicated: a) unbalanced translocation between chromosomes 1 and 7; b) translocation between chromosomes 11 and 22 at breakpoints 11q24 and 22q12, which is a classical translocation that is associated with Ewing sarcoma; c) a derivative chromosome due to a whole arm translocation between chromosomes 16 and 17 at likely breakpoints 16p10 and 17q10; and d) possible rearrangement in the short arm of chromosome 18. Moreover, a variable number of double minutes were also observed in each metaphase cell. Furthermore, the microarray assay results not only demonstrated genomic-wide chromosomal imbalance in this cell line and precisely placed chromosomal breakpoints on unbalanced, rearranged chromosomes, but also revealed information about subtle chromosomal changes and the chromosomal origin of double minutes. Finally, the fluorescence in situ hybridization assay confirmed the findings of the routine cytogenetic analysis and microarrays.

Conclusion

The accurate determination of the cytogenetic profile of the SK-PN-DW cell line is helpful in enabling the research community to utilize this cell line for future identity and comparability studies, in addition to demonstrating the utility of the complete cytogenetic profile, as a public resource.

Epidermal Growth Factor Receptor Regulation of Ewing Sarcoma Cell Function

OBJECTIVE

Ewing sarcoma (ES) is a type of childhood cancer probably arising from stem mesenchymal or neural crest cells. The epidermal growth factor receptor (EGFR) acts as a driver oncogene in many types of solid tumors. However, its involvement in ES remains poorly understood.

METHODS

Human SK-ES-1 and RD-ES ES cells were treated with EGF, the EGFR inhibitor tyrphostin (AG1478), or phosphoinositide 3-kinase (PI3K) or extracellular-regulated kinase (ERK)/mitogen-activated kinase (MAPK) inhibitors. Cell proliferation survival, cycle, and senescence were analyzed. The protein content of possible targets of EGFR manipulation was measured by Western blot.

RESULTS

Cell proliferation and survival were increased by EGF and inhibited by AG1478. The EGFR inhibitor also altered the cell cycle, inducing arrest in G1 and increasing the sub-G1 population, reduced polyploidy and increased the population of senescent cells. In addition, AG1478 reduced the levels of phosphorylated AKT (p-AKT), ERK, p-ERK, cyclin D1, and brain-derived neurotrophic factor (BDNF), while enhancing p53 levels. Cell proliferation was also impaired by inhibitors of PI3K or ERK, alone or combined with AG1478.

CONCLUSIONS

Our findings reveal novel aspects of EGFR regulation of ES cells and provide early evidence for antitumor activities of EGFR inhibitors in ES.

Intracranial Ewing sarcoma: four pediatric examples

BACKGROUND

Ewing sarcoma typically arises in bone and is unrelated to intraparenchymal small blue cell embryonal central nervous system (CNS) tumors previously designated primitive neuroectodermal tumors (PNETs). When the CNS is impacted, it is usually secondary to local extension from either the epidural space, skull, or intracranial or spinal metastases. Primary examples within the cranial vault are rare, usually dural-based, and are largely case reports in the literature. We detail four pediatric patients with solitary, primary intracranial Ewing sarcoma, all manifesting the archetypal EWRS1 gene rearrangement that confirms diagnosis.

PROCEDURE

Neurosurgical Department records, spanning 21 years (1995-2016), were reviewed to identify patients. Demographics, clinical history, pathological/genetic features, and clinical course were retrieved from the medical record and personal files of the authors.

RESULTS

Four patients, one male and three females, age 5 to 16 years, were identified. One presented in extremis from a large lesion, two with soft tissue masses, and the fourth as an incidental finding after being involved in a motor vehicle collision. Three had clear bony involvement: a 10-year-old girl with a large left temporal lesion had clear origin in the skull, with spiculated calcified striations throughout the mass; a 9-year-old girl presented with a bony left petrous apex mass; and a 16-year-old girl presented with a left temporal mass with extension to the dura and underlying bone erosion. Only the 5-year-old boy had a large left frontoparietal mass traversing the falx with no bony contact. All four tumors manifested the diagnostic EWSR1 mutation and were treated with an Ewing sarcoma regimen. Outcomes were variable, with one patient showing progressive metastatic disease and death 3 years after presentation, one patient with disease-free survival 10.5 years after completion of therapy, and one alive and well at the completion of therapy 1 year after diagnosis. One patient completed therapy recently with post-therapy scans showing no evidence of disease.

CONCLUSION

Testing for the EWSR1 mutation confirms the diagnosis of Ewing sarcoma and excludes other types of embryonal CNS tumors. Long-term disease-free survival is possible with adherence to the appropriate therapeutic regimen after gross surgical resection.

EWSR1/ELF5 induces acute myeloid leukemia by inhibiting p53/p21 pathway

The Ewing sarcoma breakpoint region 1 (EWSR1) gene is known to fuse with various partner genes to promote the development of the Ewing sarcoma family of tumors and other sarcomas. In contrast, the association of EWSR1 chimeric fusion genes with leukemia has rarely been reported. We identified a novel EWSR1‐associated chimeric fusion gene in a patient with acute myeloid leukemia harboring 46, XY, t (11; 22) (p13; q12) karyotype abnormality. The patient was refractory to intensified chemotherapy including hematopoietic stem cell transplantation. Total RNA paired‐end sequencing identified a novel chimeric fusion gene as EWSR1/ELF5, a member of the E26 transformation‐specific transcription factor family. Transduction of EWSR1/ELF5 to NIH3T3 cells induced transformation by attenuating with the p53/p21‐dependent pathway. The injection of EWSR1/ELF5‐transduced NIH3T3 cells into NSG‐SCID mice systematically induced the development of tumors in vivo. These results revealed the oncogenic potency of EWSR1/ELF5.

The cell cycle regulator CCDC6 is a key target of RNA-binding protein EWS

Genetic translocation of EWSR1 to ETS transcription factor coding region is considered as primary cause for Ewing sarcoma. Previous studies focused on the biology of chimeric transcription factors formed due to this translocation. However, the physiological consequences of heterozygous EWSR1 loss in these tumors have largely remained elusive. Previously, we have identified various mRNAs bound to EWS using PAR-CLIP. In this study, we demonstrate CCDC6, a known cell cycle regulator protein, as a novel target regulated by EWS. siRNA mediated down regulation of EWS caused an elevated apoptosis in cells in a CCDC6-dependant manner. This effect was rescued upon re-expression of CCDC6. This study provides evidence for a novel functional link through which wild-type EWS operates in a target-dependant manner in Ewing sarcoma.

RUNX3 facilitates growth of Ewing sarcoma cells

Ewing sarcoma is an aggressive pediatric small round cell tumor that predominantly occurs in bone. Approximately 85% of Ewing sarcomas harbor the EWS/FLI fusion protein, which arises from a chromosomal translocation, t(11:22)(q24:q12). EWS/FLI interacts with numerous lineage-essential transcription factors to maintain mesenchymal progenitors in an undifferentiated state. We previously showed that EWS/FLI binds the osteogenic transcription factor RUNX2 and prevents osteoblast differentiation. In this study, we investigated the role of another Runt-domain protein, RUNX3, in Ewing sarcoma. RUNX3 participates in mesenchymal-derived bone formation and is a context dependent tumor suppressor and oncogene. RUNX3 was detected in all Ewing sarcoma cells examined, whereas RUNX2 was detected in only 73% of specimens. Like RUNX2, RUNX3 binds to EWS/FLI via its Runt domain. EWS/FLI prevented RUNX3 from activating the transcription of a RUNX-responsive reporter, p6OSE2. Stable suppression of RUNX3 expression in the Ewing sarcoma cell line A673 delayed colony growth in anchorage independent soft agar assays and reversed expression of EWS/FLI-responsive genes. These results demonstrate an important role for RUNX3 in Ewing sarcoma.

Targeted polytherapy in small cell sarcoma and its association with doxorubicin

A paradigm shift has occurred in the last decade from chemotherapy to targeted therapy for the management of many patients with advanced sarcoma. This work identifies a combination of targeted agents and doxorubicin that are effective against small cell sarcoma cell lines. Three small cell sarcoma cell lines were studied: RD18 (rhabdomyosarcoma), A204 (undifferentiated sarcoma) and TC 71 (Ewing's sarcoma). Each cell line was exposed to increasing concentrations of vorinostat (HDAC inhibitor), 17-DMAG (HSP90 inhibitor), abacavir (anti-telomerase) or sorafenib (tyrosine kinase inhibitor) alone, combined with one another, or combined with doxorubicin. Cell viability, cell cycle analysis and apoptosis were assessed by MTS assay, propidium iodide-Annexin V staining, and caspase 3/7 activity, respectively. The Chou and Talalay combination index (CI) was used to determine whether the effects were additive (CI = 1), synergistic (CI < 1) or antagonistic (CI > 1). In monotherapy, targeted agents achieved 30-90% reductions in viability, with the exception of abacavir. Dual-targeted combination therapies with vorinostat, sorafenib and 17-DMAG demonstrated synergy. Abacavir was antagonistic with every other drug and was not further studied. Both vorinostat and 17-DMAG synergized with doxorubicin, achieving 60% cell killing compared to 12% with doxorubicin alone. No synergy was observed for sorafenib with doxorubicin. The triple therapy vorinostat, 17-DMAG and doxorubicin did not show synergy, but increased the subG1 population at 24H, from 30% to 70% compared to monotherapies with an increase in apoptosis. This work provides evidence of synergy of combinations of vorinostat, 17-DMAG and sorafenib in small cell sarcoma. In addition to doxorubicin, these combinations enhance doxorubicin cytotoxicity at therapeutically relevant concentrations.

The ets transcription factor Fli-1 in development, cancer and disease

Friend Leukemia Virus Induced erythroleukemia-1 (Fli-1), an ETS transcription factor, was isolated a quarter century ago through a retrovirus mutagenesis screen. Fli-1 has since been recognized to play critical roles in normal development and homeostasis. For example, it transcriptionally regulates genes that drive normal hematopoiesis and vasculogenesis. Indeed, Fli-1 is one of 10 key regulators of hematopoietic stem/progenitor cell maintenance and differentiation. Aberrant expression of Fli-1 also underlies a number of virally induced leukemias, including Friend virus-induced erythroleukemia and various types of human cancers, and it is the target of chromosomal translocations in childhood Ewing’s sarcoma. Abnormal expression of Fli-1 is important in the aetiology of auto-immune diseases such as Systemic Lupus Erythematosus (SLE) and Systemic Sclerosis (SSc). These studies establish Fli-1 as a strong candidate for drug development. Despite difficulties in targeting transcription factors, recent studies identified small molecule inhibitors for Fli-1. Here we review past and ongoing research on Fli-1 with emphasis on its mechanistic function in autoimmune disease and malignant transformation. The significance of identifying Fli-1 inhibitors and their clinical applications for treatment of disease and cancer with deregulated Fli-1 expression are discussed.

Anti-Epileptic Drug Targets Ewing Sarcoma

Ewing Sarcoma (ES) is a rare form of bone cancer that most commonly affects children and adolescents. Chromosomal translocations are fundamental to the development of Ewing Sarcoma, linked to the changes in gene expression affecting transcription factors. Histone acetyl transferases (HATs) and histone deacetylases (HDACs) regulate transcription by modifying acetylation of both histones and transcription factors. Despite the use of multimodal therapeutic approaches current therapies are associated with significant short and long-term side effects. Hence, new therapeutic approaches are needed. In this study, we show that ERG/EWS-ERG, inhibits transcriptional activation properties of RXRα. These results suggest that ERG/EWS-ERG/EWS-Fli-1 may target transcriptional co-activators and transcriptional repressors and thereby regulate RXRα transcriptional activity. To understand the molecular mechanism of action, how the fusion protein targets nuclear receptor function, and to provide a clue for the cancer health disparity seen in Ewing Sarcoma, we hypothesized that the aberrant fusion protein, EWS-ERG/EWS-Fli-1 regulates HDACs-mediated repressor complex and inhibits the binding of transcriptional activator complex causing transcriptional repression of RXRα activity. Since it is known that HDACs regulate nuclear receptors, we proposed that HDAC inhibitor, valproic acid (VPA), an anti-epileptic drug, may reverse the inhibitory properties of EWS-ERG/EWS-Fli-1 oncoprotein on RXRα transcriptional activity and might therefore be used as therapeutic agent in ES. We demonstrate that VPA reverses the inhibitory effect of EWSERG/EWS-Fli-1 on RXRα transcriptional activity and also inhibits the cell growth. Furthermore, VPA induces apoptosis and restored the expression of RXRα target genes RARβ, CRABPII and p21 activity and repressed the expression of aberrant fusion proteins, EWS-ERG and EWS-Fli-1 in Ewing Sarcoma cells. Thus, therapeutic regulation of transcriptional repressor properties of EWS-ERG/EWS-Fli-1 with an anti-epileptic drug with a promising new potential might have a profound impact on prevention, management and treatment of Ewing Sarcoma. Therapeutic use of VPA in minority patients may help reduce the health disparity.

High-resolution genome-wide copy-number analyses identify localized copy-number alterations in Ewing sarcoma

Ewing sarcoma family tumors are aggressive sarcomas of childhood and adolescence with continuing poor outcomes. Decades of research on the characteristics of the often solitary-known oncogenic-genomic aberration in Ewing sarcoma family tumors, namely a TET-ETS fusion, have provided little advancement in the understanding of the molecular pathogenesis of Ewing sarcoma or treatment thereof. In this study, the high-resolution single-nucleotide polymorphism technology was used to identify additional/secondary copy-number alterations (CNAs) in Ewing sarcoma that might elucidate the aggressive biology of this sarcoma. We compared paired constitutional and tumor DNA samples. Commonly known genomic alterations including gain of 1q and chromosome 8 were the most frequently detected changes in this study. In addition, deletions and loss of heterozygosity were identified in 10q, 11p, and 17p. Furthermore, tumor-specific CNAs were identified not only in genes previously known to be of interest, including CDKN2A, but also in genes not previously associated with Ewing sarcoma, including SOX6 and PTEN. Selected array-based findings were confirmed by fluorescence in situ hybridization, immunohistochemical studies, or sequencing. The results highlight an unexpected level of cytogenetic complexity associated with several of the samples, 2 of which contained TP53 mutations. In summary, our high-resolution genome-wide copy-number data identify several novel CNAs associated with Ewing sarcoma, which are promising targets for novel therapeutic strategies in this aggressive sarcoma.

p53 and hepatoma-derived growth factor expression and their clinicopathological association with Ewing family tumour

PURPOSE

To investigate p53 and hepatoma-derived growth factor (HDGF) expression and their association with clinicopathological features of Ewing family tumour (EFT).

EXPERIMENTAL DESIGN

A total of 108 cases of EFT were retrospectively analysed. p53 and HDGF expression were detected using immunohistochemistry, and the relationships between p53 expression and HDGF expression and clinicopathological features of EFT were analysed. Kaplan-Meier curves were applied to estimate overall survival, log-rank test was used to assess prognostic relevance of p53 expression with overall survival and Cox regression model was performed to evaluate HRs.

RESULTS

p53 expression and high HDGF expression was found in 17 (15.7%) and 55 (50.9%) patients, respectively. p53 expression was significantly associated with metastatic stage at initial diagnosis (p=0.007) and tumour venous/nerve invasion (p=0.023). A significant positive correlation was found between p53 expression and HDGF expression in EFT (p=0.022). p53 expression was an independent prognostic factor for overall survival of patients with EFT (p<0.001). Patients with p53-positive/high HDGF expression had a significantly shorter overall survival than those with p53-positive/low HDGF expression or p53-negative/high HDGF expression or p53-negative/low HDGF expression. We first constructed a novel molecular staging system by combining p53 expression and HDGF expression, which significantly improved prognostic stratification for patients with EFT.

CONCLUSIONS

p53 expression was an independent prognostic factor for patients with EFT. Combining p53 expression and HDGF expression significantly improved prognostic stratification for patients with EFT.

Children's Oncology Group's 2013 blueprint for research: bone tumors

In the US, approximately 650 children are diagnosed with osteosarcoma and Ewing sarcoma (ES) each year. Five-year survival ranges from 65% to 75% for localized disease and <30% for patients with metastases. Recent findings include interval-compressed five drug chemotherapy improves survival with localized ES. In osteosarcoma a large international trial investigating the addition of ifosfamide/etoposide or interferon to standard therapy has completed accrual. For ES an ongoing trial explores the addition of cyclophosphamide/topotecan to interval-compressed chemotherapy. Trials planned by the Children's Oncology Group will investigate new target(s) including IGF-1R and mTOR in ES, and RANKL and GD2 in osteosarcoma.

Potential molecular targets for Ewing's sarcoma therapy

Ewing's sarcoma (ES) is a highly malignant tumor of children and young adults. Modern therapy for Ewing's sarcoma combines high-dose chemotherapy for systemic control of disease, with advanced surgical and/or radiation therapeutic approaches for local control. Despite optimal management, the cure rate for localized disease is only approximately 70%, whereas the cure rate for metastatic disease at presentation is less than 30%. Patients who experience long-term disease-free survival are at risk for significant side-effects of therapy, including infertility, limb dysfunction and an increased risk for second malignancies. The identification of new targets for innovative therapeutic approaches is, therefore, strongly needed for its treatment. Many new pharmaceutical agents have been tested in early phases of clinical trials in ES patients who have recurrent disease. While some agents led to partial response or stable disease, the percentages of drugs eliciting responses or causing an overall effect have been minimal. Furthermore, of the new pharmaceuticals being introduced to clinical practice, the most effective agents also have dose-limiting toxicities. Novel approaches are needed to minimize non-specific toxicity, both for patients with recurrence and at diagnosis. This report presents an overview of the potential molecular targets in ES and highlights the possibility that they may serve as therapeutic targets for the disease. Although additional investigations are required before most of these approaches can be assessed in the clinic, they provide a great deal of hope for patients with Ewing's sarcoma.

miR-125b develops chemoresistance in Ewing sarcoma/primitive neuroectodermal tumor

Background

Diverse functions of microRNAs (miRNAs), including effects on tumorigenesis, proliferation, and differentiation, have been reported, and several miRNAs have also been demonstrated to play an important role in apoptosis. In this study, we investigated the possible role that miRNAs may play in the development of chemoresistance in Ewing sarcoma/primitive neuroectodermal tumor (EWS).

Methods

We screened doxorubicin (Dox)-resistant EWS cells to identify any distinct miRNA sequences that may regulate the chemoresistance of EWS cells. The effects of miRNAs were evaluated using a chemosensitivity assay. The possible target genes of the miRNAs were predicted using a web-based prediction program.

Results

We found miR-125b to be upregulated in two different Dox-resistant EWS cell lines. The upregulation of miR-125b was also confirmed in the EWS tumors having survived chemotherapy regimen which includes doxorubicin. When miR-125b was knocked down in EWS cells, both the Dox-resistant and parental cells showed an enhanced sensitivity to doxorubicin, which was associated with the upregulation of the pro-apoptotic molecules, p53 and Bak. Inversely, the overexpression of miR-125b in parental EWS cells resulted in enhanced drug resistance, not only to doxorubicin, but also to etoposide and vincristine.

Conclusions

Our findings suggest that miR-125b may play a role in the development of chemoresistance in EWS by suppressing the expression of the apoptotic mediators, such as p53 and Bak.

Molecular detection and targeting of EWSR1 fusion transcripts in soft tissue tumors

Soft tissue tumors are a heterogeneous group of tumors, traditionally classified according to morphology and histogenesis. Molecular classification divides sarcomas into two main categories: (a) sarcomas with specific genetic alterations and (b) sarcomas showing multiple complex karyotypic abnormalities without any specific pattern. Most chromosomal alterations are represented by translocations which are increasingly detected. The identification of fusion transcripts, in fact, not only support the diagnosis but also provides the basis for the development of new therapeutic strategies aimed at blocking aberrant activity of the chimeric proteins. One of the genes most susceptible to breakage/translocation in soft tissue tumors is represented by Ewing sarcoma breakpoint region 1 (EWSR1). This gene has a large number of fusion partners, mainly associated with the pathogenesis of Ewing's sarcoma but with other soft tissue tumors too. In this review, we illustrate the characteristics of this gene/protein, both in normal cellular physiology and in carcinogenesis. We describe the different fusion partners of EWSR1, the molecular pathways in which is involved and the main molecular biology techniques for the identification of fusion transcripts and for their inhibition.

Targeted therapy in Ewing sarcoma

Despite marked improvement in the prognosis of patients with nonmetastatic Ewing sarcoma (ES), the outcome for patients with recurrent or metastatic disease remains poor. Insight into key biologic processes in ES could provide new therapeutic targets. The particular biologic feature of ES, the fusion of the EWS gene with a member of the ETS family of genes, is present in >95% of cases. The EWS-ETS chimeric protein leads to aberrant transcription that promotes tumor initiation and propagation via prosurvival and antiapoptotic pathways. Recent research has identified cooperating mutations important for ES tumorigenesis. This paper provides a summary of the latest research in ES and discusses potential novel targets for therapy.

Impairment of p53 acetylation by EWS-Fli1 chimeric protein in Ewing family tumors

The chromosomal translocation t(11;22)(q24;q12) yields the EWS-Fli1 fusion gene, which contributes to the development of Ewing Family Tumors (EFTs). Previous studies have shown the ability of EWS-Fli1 chimeric protein to silence p53 activity. Here we demonstrate that the introduction of EWS-Fli1 significantly inhibited p300-mediated acetylation of p53 at Lys-382 and depletion of EWS-Fli1 protein by small interfering RNAs (siRNA) in EFTs cells facilitated it in response to DNA damage. Furthermore, the deacetylation of p53 by EWS-Fli1 suppressed its transcriptional activity and enhanced mdm2-mediated p53 degradation. On the other hand, immunoprecipitation study shows that N-terminal region of EWS-Fli1 associated with histone deacetylase 1 (HDAC1) to forms a complex with p53. Knockdown of HDAC1, but not HDAC2 or HDAC3 protein restored the expression of p53 Lys-382 in EFTs cells. Overexpression of HDAC1 also significantly inhibited p53 transcriptional activity. Pharmacologic inhibitor of HDAC, trichostatin A (TSA) promoted p53-p300 interaction and recruitment of p53 Lys-382 to promoter regions of its target genes p21 and Puma, consequently inducing apoptosis and stabilizing the acetylation of p53 at Lys-382 together with the upregulation of p21 and Puma, which were impaired in EFTs cells after the knockdown of p53 expression. Our data indicate EWS-Fli1 might deacetylate p53 to inhibit its transcriptional function and protein stability via the recruitment of HDAC1. These results might elucidate a novel molecular mechanism about the abrogation of p53 pathway by EWS-Fli1 in EFTs pathogenesis.

A zebrafish transgenic model of Ewing's sarcoma reveals conserved mediators of EWS-FLI1 tumorigenesis

Ewing’s sarcoma, a malignant bone tumor of children and young adults, is a member of the small-round-blue-cell tumor family. Ewing’s sarcoma family tumors (ESFTs), which include peripheral primitive neuroectodermal tumors (PNETs), are characterized by chromosomal translocations that generate fusions between the EWS gene and ETS-family transcription factors, most commonly FLI1. The EWS-FLI1 fusion oncoprotein represents an attractive therapeutic target for treatment of Ewing’s sarcoma. The cell of origin of ESFT and the molecular mechanisms by which EWS-FLI1 mediates tumorigenesis remain unknown, and few animal models of Ewing’s sarcoma exist. Here, we report the use of zebrafish as a vertebrate model of EWS-FLI1 function and tumorigenesis. Mosaic expression of the human EWS-FLI1 fusion protein in zebrafish caused the development of tumors with histology strongly resembling that of human Ewing’s sarcoma. The incidence of tumors increased in a p53 mutant background, suggesting that the p53 pathway suppresses EWS-FLI1-driven tumorigenesis. Gene expression profiling of the zebrafish tumors defined a set of genes that might be regulated by EWS-FLI1, including the zebrafish ortholog of a crucial EWS-FLI1 target gene in humans. Stable zebrafish transgenic lines expressing EWS-FLI1 under the control of the heat-shock promoter exhibit altered embryonic development and defective convergence and extension, suggesting that EWS-FLI1 interacts with conserved developmental pathways. These results indicate that functional targets of EWS-FLI1 that mediate tumorigenesis are conserved from zebrafish to human and provide a novel context in which to study the function of this fusion oncogene.

Modeling sarcomagenesis using multipotent mesenchymal stem cells

Because of their unique properties, multipotent mesenchymal stem cells (MSCs) represent one of the most promising adult stem cells being used worldwide in a wide array of clinical applications. Overall, compelling evidence supports the long-term safety of ex vivo expanded human MSCs, which do not seem to transform spontaneously. However, experimental data reveal a link between MSCs and cancer, and MSCs have been reported to inhibit or promote tumor growth depending on yet undefined conditions. Interestingly, solid evidence based on transgenic mice and genetic intervention of MSCs has placed these cells as the most likely cell of origin for certain sarcomas. This research area is being increasingly explored to develop accurate MSC-based models of sarcomagenesis, which will be undoubtedly valuable in providing a better understanding about the etiology and pathogenesis of mesenchymal cancer, eventually leading to the development of more specific therapies directed against the sarcoma-initiating cell. Unfortunately, still little is known about the mechanisms underlying MSC transformation and further studies are required to develop bona fide sarcoma models based on human MSCs. Here, we comprehensively review the existing MSC-based models of sarcoma and discuss the most common mechanisms leading to tumoral transformation of MSCs and sarcomagenesis.

Dr. Jekyll and Mr. Hyde: The Two Faces of the FUS/EWS/TAF15 Protein Family

FUS, EWS, and TAF15 form the FET family of RNA-binding proteins whose genes are found rearranged with various transcription factor genes predominantly in sarcomas and in rare hematopoietic and epithelial cancers. The resulting fusion gene products have attracted considerable interest as diagnostic and promising therapeutic targets. So far, oncogenic FET fusion proteins have been regarded as strong transcription factors that aberrantly activate or repress target genes of their DNA-binding fusion partners. However, the role of the transactivating domain in the context of the normal FET proteins is poorly defined, and, therefore, our knowledge on how FET aberrations impact on tumor biology is incomplete. Since we believe that a full understanding of aberrant FET protein function can only arise from looking at both sides of the coin, the good and the evil, this paper summarizes evidence for the central function of FET proteins in bridging RNA transcription, processing, transport, and DNA repair.

Targeting the p53 Pathway in Ewing Sarcoma

The p53 tumour suppressor plays a pivotal role in the prevention of oncogenic transformation. Cancers frequently evade the potent antitumour surveillance mechanisms of p53 through mutation of the TP53 gene, with approximately 50% of all human malignancies expressing dysfunctional, mutated p53 proteins. Interestingly, genetic lesions in the TP53 gene are only observed in 10% of Ewing Sarcomas, with the majority of these sarcomas expressing a functional wild-type p53. In addition, the p53 downstream signaling pathways and DNA-damage cell cycle checkpoints remain functionally intact in these sarcomas. This paper summarizes recent insights into the functional capabilities and regulation of p53 in Ewing Sarcoma, with a particular focus on the cross-talk between p53 and the EWS-FLI1 gene rearrangement frequently associated with this disease. The development of several activators of p53 is discussed, with recent evidence demonstrating the potential of small molecule p53 activators as a promising systemic therapeutic approach for the treatment of Ewing Sarcomas with wild-type p53.

EWS-FLI1 inhibits TNFalpha-induced NFkappaB-dependent transcription in Ewing sarcoma cells

Ewing sarcoma is primarily caused by a t(11;22) chromosomal translocation encoding the EWS-FLI1 fusion protein. To exert its oncogenic function, EWS-FLI1 acts as an aberrant transcription factor, broadly altering the gene expression profile of tumor cells. Nuclear factor-kappaB (NFkappaB) is a tightly regulated transcription factor controlling cell survival, proliferation and differentiation, as well as tumorigenesis. NFkappaB activity is very low in unstimulated Ewing sarcoma cells, but can be induced in response to tumor necrosis factor (TNF). We wondered whether NFkappaB activity could be modulated by EWS-FLI1 in Ewing sarcoma. Using a knockdown approach in Ewing sarcoma cells, we demonstrated that EWS-FLI1 has no influence on NFkappaB basal activity, but impairs TNF-induced NFkappaB-driven transcription, at least in part through inhibition of NFkappaB binding to DNA. We detected an in vivo physical interaction between the fusion protein and NFkappaB p65, which could mediate these effects. Our findings suggest that, besides directly controlling the activity of its primary target promoters, EWS-FLI1 can also indirectly influence gene expression in tumor cells by modulating the activity of key transcription factors such as NFkappaB.