Understanding EWS/FLI-Mediated Regulation of Cyclin A in Ewing's Sarcoma

Ewing’s sarcoma is highly aggressive, undifferentiated tumor of the bone found in children and adolescents. It has previously been shown that the majority of cases harbor a chromosomal translocation, fusing the transcriptional activation domain of EWS with the DNA-binding domain of FLI.  This results in the fusion protein EWS/FLI, which acts as an aberrant transcription factor necessary for the oncogenic phenotype.  One part of its function in the disease process is to modulate the cell cycle.  Specifically, it has been shown by a number of groups to up-regulate the expression of cyclin A.  However, it does not appear that cyclin A is a direct transcriptional target of EWS/FLI, suggesting that an indirect mechanism is involved.  In order to understand how EWS/FLI modulates its expression, full-length and deletion mutants of the cyclin A promoter were cloned upstream of luciferase, which were then used in a reporter assay to determine what regulatory element(s) are involved in this process.  We predict that EWS/FLI impinges on one or more transcription factors shown to bind the cyclin A promoter to regulate its expression indirectly.  We believe that the regulation of cyclin A plays a vital role in the modulation of cell cycle by EWS/FLI and is necessary for the oncogenic phenotype.