EWS/ETS fusion genes induce epithelial and neuroectodermal differentiationin NIH 3T3 fibroblasts

Ewing's sarcoma is the least differentiated member of the peripheral primit ive neuroectodermal (pPNET) tumor family. Chromosomal translocations involv ing the EWS gene and five different Ets family transcription factor genes c reate fusion genes encoding aberrant transcription factors and are implicat ed in the vast majority of Ewing's sarcoma cases. Here, NIH 3T3 fibroblasts were infected with control (tk-neo or RAS) and two different EWS/ETS-expre ssing retroviruses. In vitro studies of established polyclonal lines expres sing the two EWS/ETS genes, either EWS/FLI1 or EWS/ETV1, showed induction o f cytokeratin 15 gene expression. Both fusion genes also caused characteris tic gross morphologic, histologic, and ultrastructural changes in NIH 3T3 c ells when transformed cell lines were injected into CB-17-scid mice. Native NIH 3T3 cells with a spindled cell morphology were converted to polygonal cells with high nucleo-cytoplasmic ratios that continued to express abundan t cytokeratin. Extracellular collagen deposition was abolished, rough endop lasmic reticulum was markedly diminished, and rudimentary cell-cell attachm ents appeared. Most strikingly, neurosecretory-type dense core granules lik e those seen in pPNET were now evident. This murine model, created in mesen chyme-derived NIH 3T3 cells, demonstrated new characteristics of both neuro ectodermal and epithelial differentiation and resembled small round cell tu mors microscopically.