| Chromosomal abnormalities are frequently associated with human neoplasia. The Ewing's Family of Tumors display characteristic chromosomal translocations resulting in the fusion of the ews gene to one of five ets family members (fli1, erg, fev, etv1, or e1af). The most common gene fusion occurs between ews and fli1, which appears in as much as 85% of cases. In all of the fusions, a similar amino terminal region of EWS is attached to a homologous carboxyl terminal portion of an ETS protein containing a highly conserved ETS DNA binding domain. Due to these similarities, as well as equivalent clinical presentations, all of the EWS/ETS fusions are thought to effect tumorigenesis in similar manners.; The primary oncogenic mode of these proteins appears to be through the alteration of normal gene regulation. EWS/ETS proteins can function as aberrant transcription factors, coupling a novel transcriptional regulatory domain in EWS to the ETS DBD of the ETS protein. The fusions have been observed in both biological and biochemical assays to alter the abundance of specific gene transcripts. The fusion proteins may also act as altered splicing factors through the disruption of wild-type EWS, which displays attributes of a splicing factor. Together, these tumor-associated fusion proteins appear to affect multiple levels of gene expression.; With little variation, EWS/ETS fusions contain at least the first seven exons of ews and the ninth exon of fli1 (or equivalent for the other ets genes). These regions contain an amino terminal EWS activation domain, the ETS DNA binding domain, and a degenerate carboxyl terminal domain. In experimental assays using a heterologous NIH 3T3 cell line, the carboxyl terminal domain, which is the most divergent region of the EWS/ETS proteins, is found to play a significant role in determining the repertoire of target genes transcriptionally modulated by EWS/FLI1, and displays a critical role in oncogenesis. Surprisingly, the highly conserved ETS DNA binding domain of EWS/FLI1 is not entirely indispensable for increasing the tumorigenic potential of NIH 3T3 cells. In human tumor-derived cell lines, however, the DNA binding domain does demonstrate a crucial role. These results support a model in which EWS/ETS proteins induce multiple oncogenic signals that likely cooperate to generate unregulated cellular growth.; Critical for establishing the significance of the functions of the EWS/ETS proteins is the identification of biologically important target genes. We have implemented novel methods of identification in order to isolate transcriptionally regulated EWS/ETS target sequences. Through the use of subtractive cloning strategies and microarray technology, we have identified a number of interesting genes including the potential cell cycle regulators e2-c and pim3. It is hoped that through further investigation of these and other target genes that we may be able to learn more about the downstream effects of EWS/ETS translocations. |
