EWS/ETS proteins promote expression and regulate function of the homeodomain transcription factor BRN3A.

Ewing's sarcoma family tumors (ESFTs or EFTs) express neuronal markers, which indicates they may originate from cells at least partly committed to neuronal lineage. However, recent publications suggest EFT originates in mesenchymal stem cells, and EWS/ETS fusion proteins characteristic of EFT activate neuronal marker expression to confer a neural phenotype on EFT. Here we show that the neuronal marker BRN3A/POU4F1 is expressed abundantly at the protein level in primary EFT but not in rhabdomyosarcoma and neuroblastoma, and EFT cells exhibit high activity of the BRN3A proximal autoregulatory region. EWS/FLI-1 siRNA reduces BRN3A expression and promoter activity and EWS/ETS proteins are bound to the BRN3A locus, suggesting a direct function for EWS/ETS proteins in control of BRN3A expression. Differentiation-associated and autoregulatory activities of BRN3A are respectively impaired and altered in EFT cells, and EWS/FLI-1 siRNA can restore some BRN3A function. A potentially novel function for BRN3A in EFT cells is identified. These results extend the hypothesis that EWS/ETS proteins induce expression of neuronal markers such as BRN3A in EFT by showing that the function of those same markers may be restricted or controlled in an EWS/ETS-dependent manner.