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Desmoplastic small round cell tumor is dependent on EWS-WT1

ABSTRACT: Desmoplastic small round cell tumor (DSRCT) is a rare and aggressive soft tissue malignancy. The disease is defined by the oncogenic EWS-WT1 transcription factor. However, the dependence of the tumor on this target has not been well-established and no EWS-WT1 targeted therapy has translated to the clinic. In this report we establish the dependence of DSRCT on EWS-WT1 as well as define a gene signature and a comprehensive list of downstream targets. The selective silencing of EWS-WT1 leads to the marked suppression of proliferation of both JN-DSRCT1 and BER cells. Loss of the fusion protein results in morphologic changes in the cells and eventual cellular apoptosis. RNA sequencing demonstrates large scale gene expression changes attributable to EWS-WT1 with several hundred induced or repressed downstream targets of the fusion. We conclude DSRCT is dependent on the EWS-WT1 transcription factor for cell survival. The presence of EWS-WT1 leads to enrichment of genes involved in aberrant cell differentiation and development as well as those involved in tumor metastasis.

ORGANISM(S): Homo sapiens

PROVIDER: GSE137561 | GEO | 2020/05/04

REPOSITORIES: GEO

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Project description:The t(11;22)(p13;q12) translocation is pathognomonic for the highly aggressive desmoplastic small round cell tumour (DSRCT). The translocation fuses exon 7 of the EWS gene to exon 8 of the WT1 gene (EWS/WT1). Two splice variants of EWS/WT1 exist, arising from the presence (+KTS) or absence (-KTS) of three amino acids: lysine, threonine and serine between zinc fingers 3 and 4. To investigate the oncogenic properties of both isoforms of EWS/WT1, we over-expressed EWS/WT1 in untransformed murine embryonic fibroblasts (MEFs). We demonstrate that neither isoform of EWS/WT1 is sufficient to transform wild type MEFs, however the oncogenic potential of both isoforms is unmasked by the loss of p53. Expression of EWS/WT1 in MEFs lacking at least one allele of p53 resulted in enhanced cell proliferation, clonogenic survival and anchorage-independent growth. In addition EWS/WT1 expression in wild type MEFs attenuated several p53-dependent responses, including cell cycle arrest after irradiation and daunorubicin induced apoptosis. We show that DSRCT commonly have copy number amplification of MDM2 and MDMX, suggesting loss of p53 function in the tumours. Expression of either isoform of EWS/WT1 in MEFs induced characteristic mRNA expression profiles, including up-regulation of canonical Wnt pathway signaling. This was validated in cell lines and in a series of DSCRT, which confirmed canonical Wnt pathway activation in the tumours. We show for the first time that both isoforms of EWS/WT1 have oncogenic potential and that in addition to co-operating with loss of p53 function can also further attenuate p53-mediated responses. In addition we provide the first link between EWS/WT1 and Wnt pathway signaling. These data provide novel insights into the function of the EWS/WT1 fusion protein which characterizes DSCRT. Four independently generated pools of wild type MEFs were infected with tetracycline repressible EWS/WT1+KTS, EWS/WT1-KTS or GFP, selected with hygromycin and protein expression confirmed. Four GFP, four KTS+ and four KTS- samples were hybridized to the Ilumina BeadChip.

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Desmoplastic small round cell tumor is dependent on EWS-WT1

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