FUS/ERG gene fusions in Ewing's tumors

Ewing's tumors are rare pediatric neoplasms that are characterized by specific chromosomal translocations and gene rearrangements. All of the fusion genes reported to date in Ewing's tumors juxtapose the EWS gene at 22q12 to an ETS-related gene, the most common of which are FLI1 at 11q24 and ERG at 21q22. We present here four cases of Ewing's tumor, which showed no evidence of a EWS gene rearrangement, but instead contained translocations involving 16p11 and 21q22. A rearrangement involving the same chromosome bands, t(16;21)(p11;q22), is found in rare cases of acute myeloid leukemia and fuses the FUS gene at 16p11 to the ERG gene at 21q22. In two of our Ewing's tumor cases, we were able to show at the sequence level that the translocation between chromosomes 16 and 21 similarly results in a FUS/ERG fusion. In one case, exons 1-5 and most of exon 6 of FUS were fused in-frame to exon 9 of ERG; in the other case, FUS exons 1-7 were fused in-frame to ERG exons 8-9. The functional fusion transcript is expected to be expressed from the der(21)t(16;21) derivative. In the two other t(16;21)-positive Ewing's cases, we performed bacterial artificial chromosome fluorescence in situ hybridization analysis on metaphases and interphase nuclei to demonstrate colocalization of bacterial artificial chromosomes containing FUS and ERG genes, also highly suggestive of fusion gene formation. These represent the first four cases where FUS, rather than EWS, is rearranged with an ETS-family transcription factor in Ewing's tumors. Our data provide additional evidence that the transactivation domains of the TET family of RNA-binding proteins (such as EWS and FUS) are interchangeable, and suggests a novel mechanism of oncogenesis in Ewing's tumors.