EWS-FLI1 fusion protein up-regulates critical genes in neural crest development and is responsible for the observed phenotype of Ewing's family of tumors

EWS-FLI1 induces developmental abnormalities and accelerates sarcoma formation in a transgenic mouse model

Ewing's sarcoma is characterized by the t(11;22)(q24:q12) reciprocal translocation. To study the effects of the fusion gene EWS-FLI1 on development and tumor formation, a transgenic mouse model was created. A strategy of conditional expression was used to limit the potentially deleterious effects of EWS-FLI1 to certain tissues. In the absence of Cre recombinase, EWS-FLI1 was not expressed in the EWS-FLI1 transgenic mice, and they had a normal phenotype. When crossed to the Prx1-Cre transgenic mouse, which expresses Cre recombinase in the primitive mesenchymal cells of the embryonic limb bud, the EF mice were noted to have a number of developmental defects of the limbs. These included shortening of the limbs, muscle atrophy, cartilage dysplasia, and immature bone. By itself, EWS-FLI1 did not induce the formation of tumors in the EF transgenic mice. However, in the setting of p53 deletion, EWS-FLI1 accelerated the formation of sarcomas from a median time of 50 to 21 weeks. Furthermore, EWS-FLI1 altered the type of tumor that formed. Conditional deletion of p53 in mesenchymal cells (Prx1-Cre p53(lox/lox)) produced osteosarcomas as the predominant tumor. The presence of EWS-FLI1 shifted the tumor phenotype to a poorly differentiated sarcoma. The results taken together suggest that EWS-FLI1 inhibits normal limb development and accelerates the formation of poorly differentiated sarcomas.

Histone deacetylase inhibitors induce growth arrest, apoptosis, and differentiation in clear cell sarcoma models

Clear cell sarcoma is an aggressive malignancy occurring most commonly in the distal extremities of young adults, characterized by t(12;22)(q13;q12) creating the chimeric fusion oncoprotein EWS-ATF1. We assessed growth inhibition and differentiation effects of histone deacetylase inhibitors MS-275 and romidepsin (depsipeptide, FK228) on clear cell sarcoma cells and evaluated drug sensitivity among related translocation-associated sarcomas and other cell models. Three clear cell sarcoma cell lines, seven other sarcomas, six nonsarcoma malignant cell lines, and two nonneoplastic mesenchymal cell models were treated with MS-275 or romidepsin. Growth inhibition was assayed by monolayer 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Induction of cell cycle arrest and apoptosis were assessed by propidium iodide/Annexin V flow cytometry in monolayer and spheroid cultures and by immunoblotting analysis. Expression levels of key genes involved in mesenchymal differentiation and of EWS-ATF1 were measured by quantitative real-time PCR in clear cell sarcoma cells treated with histone deacetylase inhibitors. MS-275 and romidepsin inhibited growth in clear cell sarcoma cells by inducing cell cycle arrest and apoptosis in a time- and dose-dependent manner. Sarcomas showed greater sensitivity than other tumor types, with clear cell sarcomas most sensitive of all, whereas nonmalignant mesenchymal cells were highly resistant. MS-275 at 1 micromol/L and romidepsin at 1 nmol/L induced histone H3 acetylation, cell cycle arrest, apoptosis, and differentiation in clear cell sarcoma cells within 24 hours. Histone deacetylase inhibitors increased expression of SOX9, MYOD1, and PPARG and decreased EWS-ATF1 expression in clear cell sarcoma cells. Histone deacetylase inhibitors show promising preclinical activity in multiple clear cell sarcoma models.

EWS-FLI1 causes neuroepithelial defects and abrogates emigration of neural crest stem cells

The most frequently occurring chromosomal translocation that gives rise to the Ewing's sarcoma family of tumors (ESFT) is the chimeric fusion gene EWS-FLI1 that encodes an oncogenic protein composed of the N terminus of EWS and the C terminus of FLI1. Although the genetic basis of ESFT is fairly well understood, its putative cellular origin remains to be determined. Previous work has proposed that neural crest progenitor cells may be the causative cell type responsible for ESFT. However, surprisingly little is known about the expression pattern or role of either wild-type EWS or wild-type FLI1 in this cell population during early embryonic development. Using the developing chick embryo as a model system, we identified EWS expression in emigrating and migratory neural crest stem cells, whereas FLI1 transcripts were found to be absent in these populations and were restricted to developing endothelial cells. By ectopically expressing EWS-FLI1 or wild-type FLI1 in the developing embryo, we have been able to study the cellular transformations that ensue in the context of an in vivo model system. Our results reveal that misexpression of the chimeric EWS-FLI1 fusion gene, or wild-type FLI1, in the developing neural crest stem cell population leads to significant aberrations in neural crest development. An intriguing possibility is that misexpression of the EWS-FLI1 oncogene in neural crest-derived stem cells may be an initiating event in ESFT genesis.

EWS-FLI-1 expression triggers a Ewing's sarcoma initiation program in primary human mesenchymal stem cells

Ewing's sarcoma family tumors (ESFT) express the EWS-FLI-1 fusion gene generated by the chromosomal translocation t(11;22)(q24;q12). Expression of the EWS-FLI-1 fusion protein in a permissive cellular environment is believed to play a key role in ESFT pathogenesis. However, EWS-FLI-1 induces growth arrest or apoptosis in differentiated primary cells, and the identity of permissive primary human cells that can support its expression and function has until now remained elusive. Here we show that expression of EWS-FLI-1 in human mesenchymal stem cells (hMSC) is not only stably maintained without inhibiting proliferation but also induces a gene expression profile bearing striking similarity to that of ESFT, including genes that are among the highest ESFT discriminators. Expression of EWS-FLI-1 in hMSCs may recapitulate the initial steps of Ewing's sarcoma development, allowing identification of genes that play an important role early in its pathogenesis. Among relevant candidate transcripts induced by EWS-FLI-1 in hMSCs, we found the polycomb group gene EZH2, which we show to play a critical role in Ewing's sarcoma growth. These observations are consistent with our recent findings using mouse mesenchymal progenitor cells and provide compelling evidence that hMSCs are candidate cells of origin of ESFT.

Inducible expression of chimeric EWS/ETS proteins confers Ewing's family tumor-like phenotypes to human mesenchymal progenitor cells

Ewing's family tumor (EFT) is a rare pediatric tumor of unclear origin that occurs in bone and soft tissue. Specific chromosomal translocations found in EFT cause EWS to fuse to a subset of ets transcription factor genes (ETS), generating chimeric EWS/ETS proteins. These proteins are believed to play a crucial role in the onset and progression of EFT. However, the mechanisms responsible for the EWS/ETS-mediated onset remain unclear. Here we report the establishment of a tetracycline-controlled EWS/ETS-inducible system in human bone marrow-derived mesenchymal progenitor cells (MPCs). Ectopic expression of both EWS/FLI1 and EWS/ERG proteins resulted in a dramatic change of morphology, i.e., from a mesenchymal spindle shape to a small round-to-polygonal cell, one of the characteristics of EFT. EWS/ETS also induced immunophenotypic changes in MPCs, including the disappearance of the mesenchyme-positive markers CD10 and CD13 and the up-regulation of the EFT-positive markers CD54, CD99, CD117, and CD271. Furthermore, a prominent shift from the gene expression profile of MPCs to that of EFT was observed in the presence of EWS/ETS. Together with the observation that EWS/ETS enhances the ability of cells to invade Matrigel, these results suggest that EWS/ETS proteins contribute to alterations of cellular features and confer an EFT-like phenotype to human MPCs.

The sensitivity of the Ewing's sarcoma family of tumours to fenretinide-induced cell death is increased by EWS-Fli1-dependent modulation of p38MAPK activity

The Ewing's sarcoma family of tumours (ESFT) are small round cell tumours characterized by the non-random EWS-ETS gene rearrangements. We have previously demonstrated that ESFT are highly sensitive to fenretinide-induced death, effected in part through a reactive oxygen species (ROS)-dependent pathway. Here, we demonstrate for the first time that the sensitivity of ESFT cells to fenretinide-induced cell death is decreased following downregulation of the oncogenic fusion protein EWS-Fli1; siRNA targeting EWS-Fli1 attenuated fenretinide-induced cell death in cell lines expressing EWS-Fli1, but not EWS-ERG. This decrease in cell death was independent of the level of ROS produced following exposure to fenretinide, but was effected through EWS-Fli1-dependent modulation of p38(MAPK) activity. Furthermore, inhibition of p38(MAPK) activity and knockdown of EWS-Fli1 reduced fenretinide-induced mitochondrial permeabilization, cytochrome c release, caspase and PARP cleavage, consistent with the hypothesis that p38(MAPK) is critical for activation of the death cascade by fenretinide in ESFT cells. These data demonstrate that expression of EWS-Fli1 enhances fenretinide-induced cell death in ESFT and that this is effected at least in part through modulation of p38(MAPK) activity.

EWS/FLI1 Regulates Tumor Angiogenesis in Ewing's Sarcoma via Suppression of Thrombospondins

Suppression of the expression of antiangiogenic factors has been closely associated with multiple malignancies. Thrombospondins 1 and 2 are members of a family of angiogenic inhibitors that are regulated by several oncogenes. In this study, we investigate the role of thrombospondins in Ewing's sarcoma and their regulation by EWS/ETS fusion oncoproteins. We show that the EWS/FLI1 fusion suppresses the expression of thrombospondins in both NIH3T3 fibroblasts and Ewing's sarcoma tumor-derived cell lines. This regulation depends on an intact EWS/FLI1 DNA-binding domain and may involve direct interactions between EWS/FLI1 and thrombospondin promoter regions. Forced expression of thrombospondins in Ewing's sarcoma cell lines inhibited the rate of tumor formation in vivo and markedly decreased the number of microvessels present in the tumors. These findings suggest that thrombospondins play a biologically significant role in tumor vascularization in Ewing's sarcoma and suggest potential therapeutic strategies for future therapeutic intervention.

Mesenchymal stem cell features of Ewing tumors

The cellular origin of Ewing tumor (ET), a tumor of bone or soft tissues characterized by specific fusions between EWS and ETS genes, is highly debated. Through gene expression analysis comparing ETs with a variety of normal tissues, we show that the profiles of different EWS-FLI1-silenced Ewing cell lines converge toward that of mesenchymal stem cells (MSC). Moreover, upon EWS-FLI1 silencing, two different Ewing cell lines can differentiate along the adipogenic lineage when incubated in appropriate differentiation cocktails. In addition, Ewing cells can also differentiate along the osteogenic lineage upon long-term inhibition of EWS-FLI1. These in silico and experimental data strongly suggest that the inhibition of EWS-FLI1 may allow Ewing cells to recover the phenotype of their MSC progenitor.

EWS/FLI-1 oncoprotein subtypes impose different requirements for transformation and metastatic activity in a murine model

Ewing sarcoma/primitive neuroectodermal tumors (EWS/PNET) are characterized by specific chromosomal translocations most often generating a chimeric EWS/FLI-1 gene. Depending on the number of juxtaposed exons assembled, several fusion types have been described with different incidences and prognoses. To assess the impact of each fusion type on the specific phenotypic, tumorigenic, and metastatic features of EWS/PNET, we developed an amenable system using a murine mesenchymal multipotent C3H10T1/2 cell line. Upon transduction of EWS/FLI-1, cells acquired dramatic morphological changes in vitro, including a smaller size and "neurite-like" membrane elongations. Chimeric fusion proteins conferred oncogenic properties in vitro, including anchorage-independent growth and an increased rate of proliferation. Furthermore, EWS/FLI-1 expression blocked mineralization, with concomitant repression of osteoblastic genes, and induced a dramatic repression of the adipocytic differentiation program. Moreover, EWS/FLI-1 promoted an aberrant neural phenotype by the de novo expression of specific neural genes. The intramuscular injection of transduced cells led to tumor development and the induction of overt osteolytic lesions. Analogously, to what was observed in human tumors, type 2 EWS/FLI-1 cells formed primary tumors in immunodeficient mice with a higher incidence and a lower latency than cells bearing types 1 and 3 fusions. By contrast, cells expressing types 2 and 3 fusions showed specific metastatic activity with a higher number of macroscopic metastases in soft tissues and osteolytic lesions in the limbs as compared to type-1-expressing cells. Therefore, the structure of each oncoprotein strongly influenced its tumorigenicity and metastagenicity. Thus, this model provides a basis for understanding the genetic determinants involved in Ewing tumor development and metastatic activity and represents a cellular system to analyze other oncoproteins involved in human sarcomagenesis.

Cholecystokinin Down-Regulation by RNA Interference Impairs Ewing Tumor Growth

PURPOSE

Tumors of the Ewing family are characterized by chromosomal translocations that yield chimeric transcription factors, such as EWS/FLI1, which regulate the expression of specific genes that contribute to the malignant phenotype. In the present study, we show that cholecystokinin (CCK) is a new target of the EWS/FLI1 oncoprotein and assess its functional role in Ewing tumor pathogenesis.

EXPERIMENTAL DESIGN

Relevant EWS/FLI1 targets were identified using a combination of cell systems with inducible EWS/FLI1 expression, Ewing tumors and cell lines, microarrays, and RNA interference with doxycycline-inducible small hairpin RNA (shRNA) vectors. A doxycycline-inducible CCK-shRNA vector was stably transfected in A673 and SK-PN-DW Ewing cell lines to assess the role of CCK in cell proliferation and tumor growth.

RESULTS

Microarray analysis revealed that CCK was up-regulated by EWS/FLI1 in HeLa cells. CCK was overexpressed in Ewing tumors as compared with other pediatric malignancies such as rhabdomyosarcoma and neuroblastoma, with levels close to those detected in normal tissues expressing the highest levels of CCK. Furthermore, EWS/FLI1 knockdown in A673 and SK-PN-DW Ewing cells using two different doxycycline-inducible EWS/FLI1-specific shRNA vectors down-regulated CCK mRNA expression and diminished the levels of secreted CCK, showing that CCK is a EWS/FLI1 specific target gene in Ewing cells. A doxycycline-inducible CCK-specific shRNA vector successfully down-regulated CCK expression, reduced the levels of secreted CCK in Ewing cell lines, and inhibited cell growth and proliferation in vitro and in vivo. Finally, we show that Ewing cell lines and tumors express CCK receptors and that the growth inhibition produced by CCK silencing can be rescued by culturing the cells with medium containing CCK.

CONCLUSIONS

Our data support the hypothesis that CCK acts as an autocrine growth factor stimulating the proliferation of Ewing cells and suggest that therapies targeting CCK could be promising in the treatment of Ewing tumors.

The Biology of Ewing sarcoma

Sarcomas account for less than 10% of all human malignancies that are believed to originate from as yet poorly defined mesenchymal progenitor cells. They constitute some of the most aggressive adult and childhood cancers in that they have a high metastatic proclivity and are typically refractory to conventional chemo- and radiation therapy. Ewing's sarcoma is a member of Ewing's family tumors (ESFT) and the second most common solid bone and soft tissue malignancy of children and young adults. It is associated in 85% of cases with the t(11;22)(q24:q12) chromosomal translocation that generates fusion of the 5' segment of the EWS gene with the 3' segment of the ETS family gene FLI-1. The resulting EWS-FLI-1 fusion protein is believed to behave as an aberrant transcriptional activator that contributes to ESFT development by altering the expression of its target genes in a permissive cellular environment. Although ESFTs are among the best studied sarcomas, the mechanisms involved in EWS-FLI-1-induced transformation require further elucidation and the primary cells from which ESFTs originate need to be identified. This review will highlight some of the most recent discoveries in the field of Ewing sarcoma biology and origins.

Novel approaches for the management of patients with Ewing sarcoma

The concepts of tailored therapy according to genetic profiling and response based on minimal residual disease evaluation during therapy are attracting increasing interest in modern clinical oncology. Children with acute lymphoblastic leukemia are being stratified to various treatment arms with different intensities according to the genetic characteristics of their leukemia and their response to therapy as measured by real-time polymerase chain reaction. Our ability to quickly identify patients with Ewing sarcoma who have a poor prognosis, and to offer them aggressive therapeutic modalities, such as stem cell transplantation, may result in an improved cure rate. Based on the knowledge gained by gene expression profiling and gene silencing techniques we can expect the emergence of new specific drugs that will target malignant cells without causing damage to normal tissue, resulting in improved cancer therapy.

Caveolin-1 (CAV1) is a target of EWS/FLI-1 and a key determinant of the oncogenic phenotype and tumorigenicity of Ewing's sarcoma cells

Tumors of the Ewing's sarcoma family (ESFT), such as Ewing's sarcoma (EWS) and primitive neuroectodermal tumors (PNET), are highly aggressive malignancies predominantly affecting children and young adults. ESFT express chimeric transcription factors encoded by hybrid genes fusing the EWS gene with several ETS genes, most commonly FLI-1. EWS/FLI-1 proteins are responsible for the malignant phenotype of ESFT, but only few of their transcriptional targets are known. Using antisense and short hairpin RNA-mediated gene expression knockdown, array analyses, chromatin immunoprecipitation methods, and reexpression studies, we show that caveolin-1 (CAV1) is a new direct target of EWS/FLI-1 that is overexpressed in ESFT cell lines and tumor specimens and is necessary for ESFT tumorigenesis. CAV1 knockdown led to up-regulation of Snail and the concomitant loss of E-cadherin expression. Consistently, loss of CAV1 expression inhibited the anchorage-independent growth of EWS cells and markedly reduced the growth of EWS cell-derived tumors in nude mice xenografts, indicating that CAV1 promotes the malignant phenotype in EWS carcinogenesis. Reexpression of CAV1 or E-cadherin in CAV1 knockdown EWS cells rescued the oncogenic phenotype of the original EWS cells, showing that the CAV1/Snail/E-cadherin pathway plays a central role in the expression of the oncogenic transformation functions of EWS/FLI-1. Overall, these data identify CAV1 as a key determinant of the tumorigenicity of ESFT and imply that targeting CAV1 may allow the development of new molecular therapeutic strategies for ESFT patients.

NR0B1 Is Required for the Oncogenic Phenotype Mediated by EWS/FLI in Ewing's Sarcoma

A number of solid tumors, such as alveolar rhabdomyosarcoma, synovial sarcoma, and myxoid liposarcoma, are associated with recurrent translocation events that encode fusion proteins. Ewing's sarcoma is a pediatric tumor that serves as a prototype for this tumor class. Ewing's sarcomas usually harbor the (11;22)(q24;q12) translocation. The t(11;22) encodes the EWS/FLI fusion oncoprotein. EWS/FLI functions as an aberrant transcription factor, but the key target genes that are involved in oncogenesis are largely unknown. Although some target genes have been defined, many of these have been identified in heterologous model systems with uncertain relevance to the human disease. To understand the function of EWS/FLI and its targets in a more clinically relevant system, we used retroviral-mediated RNAi to "knock-down" the fusion protein in patient-derived Ewing's sarcoma cell lines. By combining transcriptional profiling data from three of these lines, we identified a conserved transcriptional response to EWS/FLI. The gene that was most reproducibly up-regulated by EWS/FLI was NR0B1. NR0B1 is a developmentally important orphan nuclear receptor with no previously defined role in oncogenesis. We validated NR0B1 as an EWS/FLI-dysregulated gene and confirmed its expression in primary human tumor samples. Functional studies revealed that ongoing NR0B1 expression is required for the transformed phenotype of Ewing's sarcoma. These studies define a new role for NR0B1 in oncogenic transformation and emphasize the utility of analyzing the function of EWS/FLI in Ewing's sarcoma cells.

Identification of a PAX-FKHR gene expression signature that defines molecular classes and determines the prognosis of alveolar rhabdomyosarcomas

Alveolar rhabdomyosarcomas (ARMS) are aggressive soft-tissue sarcomas affecting children and young adults. Most ARMS tumors express the PAX3-FKHR or PAX7-FKHR (PAX-FKHR) fusion genes resulting from the t(2;13) or t(1;13) chromosomal translocations, respectively. However, up to 25% of ARMS tumors are fusion negative, making it unclear whether ARMS represent a single disease or multiple clinical and biological entities with a common phenotype. To test to what extent PAX-FKHR determine class and behavior of ARMS, we used oligonucleotide microarray expression profiling on 139 primary rhabdomyosarcoma tumors and an in vitro model. We found that ARMS tumors expressing either PAX-FKHR gene share a common expression profile distinct from fusion-negative ARMS and from the other rhabdomyosarcoma variants. We also observed that PAX-FKHR expression above a minimum level is necessary for the detection of this expression profile. Using an ectopic PAX3-FKHR and PAX7-FKHR expression model, we identified an expression signature regulated by PAX-FKHR that is specific to PAX-FKHR-positive ARMS tumors. Data mining for functional annotations of signature genes suggested a role for PAX-FKHR in regulating ARMS proliferation and differentiation. Cox regression modeling identified a subset of genes within the PAX-FKHR expression signature that segregated ARMS patients into three risk groups with 5-year overall survival estimates of 7%, 48%, and 93%. These prognostic classes were independent of conventional clinical risk factors. Our results show that PAX-FKHR dictate a specific expression signature that helps define the molecular phenotype of PAX-FKHR-positive ARMS tumors and, because it is linked with disease outcome in ARMS patients, determine tumor behavior.

Antisense oligonucleotide nanocapsules efficiently inhibit EWS-Fli1 expression in a Ewing's sarcoma model

The cytogenetic abnormality of Ewing's sarcoma is related to the presence of a balanced t(11;22) translocation expressing the EWS-Fli1 chimeric fusion protein. Oligonucleotides (ODNs) are specific compounds that inhibit gene expression at the transcriptional level. They possess a poor bioavailability and are degraded by nucleases very rapidly. Therefore, there is a strong need for the development of ODN drug delivery systems. In the present study, polyisobutylcyanoacrylate nanocapsules entrapping ODNs in their aqueous core were prepared, with high encapsulation yield (99%). Previous studies have demonstrated that such complexes were able to inhibit tumor growth in mice. Nevertheless, no information was available about their mode of action at the cellular level. The aim of this study was to investigate the efficacy of these ODN nanocapsules on cultured tumor cells. We found that nanocapsules were capable of protecting ODN against degradation. Using confocal microscopy, we observed that cell uptake and nuclear accumulation of ODNs were importantly enhanced when ODNs were associated with these nanocapsules. Consequently, a specific cellular growth inhibition and suppression of EWSFli1 fusion gene expression was noticed. In conclusion, it was demonstrated that nanocapsules as nonviral vectors show great potential for the delivery of ODNs to cells.

The myxoid/round cell liposarcoma fusion oncogene FUS-DDIT3 and the normal DDIT3 induce a liposarcoma phenotype in transfected human fibrosarcoma cells

Myxoid/round cell liposarcoma (MLS/RCLS) is the most common subtype of liposarcoma. Most MLS/RCLS carry a t(12;16) translocation, resulting in a FUS-DDIT3 fusion gene. We investigated the role of the FUS-DDIT3 fusion in the development of MLS/RCLS in FUS-DDIT3- and DDIT3-transfected human HT1080 sarcoma cells. Cells expressing FUS-DDIT3 and DDIT3 grew as liposarcomas in severe combined immunodeficient mice and exhibited a capillary network morphology that was similar to networks of MLS/RCLS. Microarray-based comparison of HT1080, the transfected cells, and an MLS/RCLS-derived cell line showed that the FUS-DDIT3- and DDIT3-transfected variants shifted toward an MLS/RCLS-like expression pattern. DDIT3-transfected cells responded in vitro to adipogenic factors by accumulation of fat and transformation to a lipoblast-like morphology. In conclusion, because the fusion oncogene FUS-DDIT3 and the normal DDIT3 induce a liposarcoma phenotype when expressed in a primitive sarcoma cell line, MLS/RCLS may develop from cell types other than preadipocytes. This may explain the preferential occurrence of MLS/RCLS in nonadipose tissues. In addition, development of lipoblasts and the typical MLS/RCLS capillary network could be an effect of the DDIT3 transcription factor partner of the fusion oncogene.

Suppression of KCMF1 by constitutive high CD99 expression is involved in the migratory ability of Ewing's sarcoma cells

High CD99 expression levels and rearrangements of the EWS gene with ETS transcription factor genes characterize the Ewing's sarcoma family of tumors (ESFT). CD99 is a cell surface glycoprotein whose engagement has been implicated in cell proliferation as well as upregulation and transport of several transmembrane proteins in hematopoietic cells. In ESFT, antibody ligation of CD99 induces fast homotypic cell aggregation and cell death although its functional role in these processes remains largely unknown. Here, using an RNAi approach, we studied for the first time the consequences of modulated CD99 expression in six different ESFT cell lines, representing the most frequent variant forms of EWS gene rearrangement. CD99 suppression resulted in growth inhibition and reduced migration of ESFT cells. Among genes whose expression changes in response to CD99 modulation, the potassium-channel modulatory factor KCMF1 was consistently upregulated. In a series of 22 primary ESFT, KCMF1 expression levels inversely correlated with CD99 abundancy. Cells forced to express ectopic KCMF1 showed a similar reduction in migratory ability as CD99 silenced ESFT cells. Our results suggest that in ESFT, high CD99 expression levels contribute to the malignant properties of ESFT by promoting growth and migration of tumor cells and identify KCMF1 as a potential metastasis suppressor gene downregulated by high constitutive CD99 expression in ESFT.

Ewing's sarcoma: general insights from a rare model

Ewing's sarcoma is characterized by the presence of fusion oncoproteins involving EWSR1 and an ETS gene, most commonly FLI1. In this issue of Cancer Cell, Smith et al. have combined RNA interference with expression profiling to study the pattern of gene expression downstream of the most common of these fusions, EWS/FLI. Using this strategy, Smith et al. have identified a homeobox gene, NKX2.2, which is both highly expressed in Ewing's sarcoma and essential for the transforming activity of EWS/FLI.

Expression profiling of EWS/FLI identifies NKX2.2 as a critical target gene in Ewing's sarcoma

Our understanding of Ewing's sarcoma development mediated by the EWS/FLI fusion protein has been limited by a lack of knowledge regarding the tumor cell of origin. To circumvent this, we analyzed the function of EWS/FLI in Ewing's sarcoma itself. By combining retroviral-mediated RNA interference with reexpression studies, we show that ongoing EWS/FLI expression is required for the tumorigenic phenotype of Ewing's sarcoma. We used this system to define the full complement of EWS/FLI-regulated genes in Ewing's sarcoma. Functional analysis revealed that NKX2.2 is an EWS/FLI-regulated gene that is necessary for oncogenic transformation in this tumor. Thus, we developed a highly validated transcriptional profile for the EWS/FLI fusion protein and identified a critical target gene in Ewing's sarcoma development.

The role of microarray technologies in the study of soft tissue tumours

Array technologies (gene array, tissue microarray and others) are being used in a growing number of research projects involving soft tissue tumours. Gene array techniques allow for measurements of RNA expression levels or gene copy number changes for a large number of genes in a single specimen. A complementary technique, tissue microarrays, allows for the measurement of expression of a single gene in a large number of specimens. These techniques and similar ones have created a fundamentally new approach to the investigation of soft tissue tumours. This review addresses some of the advantages, problems, and solutions to those problems that come with these technologies.

The orphan nuclear receptor DAX1 is up-regulated by the EWS/FLI1 oncoprotein and is highly expressed in Ewing tumors

The Ewing family of tumors harbors chromosomal translocations that join the N-terminal region of the EWS gene with the C-terminal region of several transcription factors of the ETS family, mainly FLI1, resulting in chimeric transcription factors that play a pivotal role in the pathogenesis of Ewing tumors. To identify downstream targets of the EWS/FLI1 fusion protein, we established 293 cells expressing constitutively either the chimeric EWS/FLI1 or wild type FLI1 proteins and used cDNA arrays to identify genes differentially regulated by EWS/FLI1. DAX1 (NR0B1), an unusual orphan nuclear receptor involved in gonadal development, sex determination and steroidogenesis, showed a consistent up-regulation by EWS/FLI1 oncoprotein, but not by wild type FLI1. Specific induction of DAX1 by EWS/FLI1 was confirmed in two independent cell systems with inducible expression of EWS/FLI1. We also analyzed the expression of DAX1 in Ewing tumors and derived cell lines, as well as in other nonrelated small round cell tumors. DAX1 was expressed in all Ewing tumor specimens analyzed, and in seven out of eight Ewing tumor cell lines, but not in any neuroblastoma or embryonal rhabdomyosarcoma. Furthermore, silencing of EWS/FLI1 by RNA interference in a Ewing tumor cell line markedly reduced the levels of DAX1 mRNA and protein, confirming that DAX1 up-regulation is dependent upon EWS/FLI1 expression. The high levels of DAX1 found in Ewing tumors and its potent transcriptional repressor activity suggest that the oncogenic effect of EWS/FLI1 may be mediated, at least in part, by the up-regulation of DAX1 expression.