| Description |
Ewing sarcoma is a highly aggressive pediatric malignancy that is characterized by a chromosomal translocation-derived fusion protein, Ewing sarcoma (EWS)/ Friend leukemia insertion (FLI), EWS/FLI. EWS/FLI is an aberrant transcription factor and its downstream targets contribute to oncogenic transformation in Ewing sarcoma. However, the mechanisms of transcriptional regulation by EWS/FLI and the full complement of direct targets of EWS/FLI were previously unknown. The work documented in this dissertation describes a novel basis for EWS/FLI function in gene activation, and also uncovers a mechanism by which EWS/FLI directly represses a subset of critical targets genes in Ewing sarcoma. Through the identification of direct in vivo targets of EWS/FLI, we made an unexpected discovery that EWS/FLI activates some of its critical target genes, including NR0B1 and GSTM4, by binding to microsatellite repeats. These findings suggest a new paradigm for cancer-relevant gene regulation by EWS/FLI, and perhaps other ETS family members. In addition to the microsatellite repeats, EWS/FLI regulates some of its target genes through the canonical high-affinity consensus E-26 oncogene (ETS) site. We focused on one such target gene, GLI1, and uncovered a novel role for GLI1 and its downstream target, KRT17, in coordinating two cancer-relevant functions: oncogenic transformation and cellular adhesion in Ewing sarcoma. iv The functional relationship between wild-type EWS and the EWS/FLI fusion protein in Ewing sarcoma was largely unknown. Through global transcription profiling and mechanistic studies we demonstrated that EWS and EWS/FLI coregulate a subset of genes in Ewing sarcoma and that EWS functions as a cofactor of the REST transcription factor to repress neuronal differentiation genes. These data suggest that EWS, and consequently EWS/FLI, have transcriptional repressive roles in Ewing sarcoma. We next focused on identifying and characterizing the mechanism underlying EWS/FLI-mediated direct transcriptional repression. We demonstrated that EWS/FLI interacts with the nucleosome remodeling and histone deacetylase (NuRD) corepressor complex to repress critical tumor suppressor genes in Ewing sarcoma. These data identify inhibitors of the NuRD complex components as potentially effective therapeutic agents for the treatment of Ewing sarcoma. Taken together, the work presented in this dissertation advances our molecular understanding of EWS/FLI-mediated gene regulation in Ewing sarcoma. |
