Using the Ewing's sarcoma fusion gene, EWS-Fli1, to model the earliest steps in oncogenic transformation Free

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While the genetic differences between cancer cells and their normal progenitors are often numerous and complex, a subset of cancers exist which are characterized by chromosomal translocations not found in normal cells. Here, we investigate the potential role of a single genetic change, introduction of the products of a chromosomal translocation, in the origin of cancer. As a model system we have utilized the genetics of Ewing′s sarcoma, a tumor of adolescence that is the second most common bone tumor of childhood. Ewing′s sarcoma is characterized by a pathognomonic chromosomal translocation resulting in fusion of the Ewing′s sarcoma gene (EWS) on chromosome 22 with members of the ets family of transcription factors, usually Fli1 on chromosome 11. The resultant fusion protein, EWS-Fli1, is thought to function as an aberrant transcription factor controlling the expression of genes critical to oncogenic transformation. EWS-Fli1 is present in 85% of Ewing′s sarcomas, and is required for tumor cell growth: loss of fusion protein expression results in death of cancer cell lines. As such, we hypothesized that expression of EWS-Fli1 in non-transformed, primitive cells would recapitulate the early events in oncogenic transformation. As destination cells, we utilized mesenchymal stem cells (MSCs). MSCs are the progenitor cells for multiple cell lineages including bone, fat and cartilage, and, hence, they represent a likely progenitor for mesenchymally-derived tumors. MSCs were transduced with a lentivirus encoding the EWS-Fli1 fusion gene. Expression of EWS-Fli1 in the cells was confirmed by both Western immunoblot and RT-PCR. Interestingly, MSCs expressing EWS-Fli1 exhibit characteristic phenotypic changes, including the extension of neurite-like processes. RNA from EWS-Fli1 expressing and control MSCs was isolated, labeled and applied to an Affymetrix GeneChip for expression analysis. Preliminary results of this expression analysis reveal that EWS-Fli1 induces the expression of a number of genes, including those previously shown to be critical for the propagation of Ewing′s sarcoma, such as IGF-1 and TGF-β. Moreover, expression of other genes known to be involved in cancer (e.g. CXCL-6) and differentiation (e.g. NOV/CCN3) was altered by EWS-Fli1 expression. Thus, expression of EWS-Fli1 in MSCs may provide important information as to the genes critical at the onset of oncogenic transformation. Furthermore, identification of these genes may yield future targets for anti-cancer therapy to attack the earliest cancer cells.