The role of the EWS/WT1 fusion protein in the pathogenesis of desmoplastic small round cell tumor

Abstract

© 2012 Dr. Pratiti BandopadhayayDesmoplastic small round cell tumor (DSRCT) is an aggressive tumor characterised by the t(11;22) translocation which results in the fusion of exons 1-VII of the Ewing’s sarcoma gene (EWS) to exons VIII-X of the Wilms tumor gene (WT1). Little is understood in regards to the role of the fusion protein in the pathogenesis of this tumor. Two splice variants of the fusion protein are described, which result in the insertion (+KTS) or absence (-KTS) of a three amino acid sequence in the WT1 zinc binding fingers. Using inducible lentiviral expression vectors, EWS/WT1 was expressed in primary murine embryonic fibroblasts (MEFs) derived from E14.5 embryos of C57BL6 or p53 knock-out mice. EWS/WT1-KTS or EWS/WT1+KTS were insufficient to transform wild type MEFs, however in p53 knock-out MEFs both isoforms of EWS/WT1 were able to transform the cells. Primary MEFs expressing EWS/WT1-KTS or EWS/WT1+KTS demonstrated attenuated p53 mediated responses. Microarray analysis demonstrated different expression profiles of cells expressing EWS/WT1 compared to eGFP controls and pathway analysis shows differential expression of genes involved Wnt signaling. Analysis of a series of DSRCT samples revealed both transcripts of EWS/WT1 are present with the EWS/WT1+KTS transcript being more abundant. There was no evidence of p53 mutations in exons five to eight however there was a high incidence of MDM2/MDM4 amplification in a series of 15 tumors examined, representing a mechanism by which p53 function may be suppressed in the tumours. -catenin immunohistochemistry in the tumors revealed nuclear immunoreactivity of -catenin, suggesting up-regulation of Wnt signaling and this was validated with real time PCR. These results provide novel insights into the oncogenic properties of EWS/WT1