MicroRNA expression profiling of Ewing sarcoma cell lines

Ewing’s sarcoma family tumors (ESFT) are the second most common bone malignancy in children and young adults, characterized by the expression of a unique chromosomal translocation, that in 85% of cases lead to the expression of the EWS-FLI-1 fusion protein. ESW-FLI-1 functions as an aberrant transcription factor that can both induce and suppress its target genes. We have recently demonstrated that microRNA (miRNA) 145 is a direct EWS-FLI-1 target implicated in ESFT development. Here, we use global miRNA array profiling to show that ESFT display a distinct miRNA signature characterized by the induction or repression of a limited number of miRNAs, including the oncogenic and tumor suppressor miRNA 17-92 and let-7 families, respectively. We demonstrate that repression of the let-7 family member let-7a may be due to direct binding of EWS-FLI-1 to the let-7a promoter and that it participates in the tumorigenic potential of ESFT cells in vivo. The mechanism whereby let-7a repression enhances ESFT growth is shown to be the induction of its target gene HMGA2, as overexpression of let-7a or repression of HMGA2 blocked ESFT cell tumorigenicity. Consistent with these observations, systemic delivery of synthetic let-7a that restored its expression in tumor cells and decreased HMGA2 expression inhibited ESFT growth in vivo. Our observations provide evidence that deregulation of let-7a target gene expression participates in ESFT development and identify let-7a as a promising new therapeutic target for one of the most aggressive pediatric malignancies. Two Ewing sarcoma cell lines and two samples of human pediatric mesenchymal stem cells are compared to the miRXplore Universal Reference (UR), a defined pool of synthetic microRNAs.