A polypeptide from the junction region sequence of EWS-FLI1 inhibits Ewing's sarcoma cells, interacts with the EWS-FLI1 and partner proteins.

The EWS-FLI1 chimeric protein uniquely expressed in Ewing's sarcoma has an obligate role in its aetiology. In our previous report we showed that ectopic expression of the DNA sequences form the junction region (a.a 251-280) can inhibit Ewing's sarcoma cell growth. In the present report, we introduced a peptide (TAT/NLS/EWS-PEP) comprising of thirty amino acids spanning the junction in conjunction with HIV-1-trans-activating (TAT) and nuclear localization signal sequence (NLS). Peptide uptake and localization studies revealed presence of peptide in ~99% of transduced cells and in the nucleus. Peptide transfection induced cytotoxicity relative to untreated and TAT-NLS peptide treated Ewing's sarcoma cells. The peptide inhibited clonogenicity, cell cycle, bromo-deoxy uridine (BrdU) uptake and invasion capacity of treated cells. The treatment also affected epithelial to mesenchymal transition (EMT) markers and EWS-FLI1 target gene expression levels. Co-immunoprecipitation experiments involving ectopically expressed full-length EWS-FLI1 protein and the peptide revealed an interaction. Additionally, we found that peptide interaction also occurs with the protein-GGAA microsatellite sequences complex known to contain EWS-FLI1. Further, in the pull-down assay, the peptide was found to interact with proteins known to potentially interact with EWS-FLI1. Based on these results we conclude that peptide could be applied in targeting EWS-FLI1 protein.