Abstract Genes encoding ETS family transcription factors are altered by chromosomal rearrangement in 60-70% of prostate cancers and nearly all Ewing sarcomas. Ewing sarcoma rearrangements result in chimeric fusion of ETS proteins to the RNA-binding protein EWSR1. Prostate cancer rearrangements result in aberrant expression of ETS proteins such as ETV1, ETV4, ETV5 or ERG that can interact with wild-type EWSR1, suggesting common mechanisms between these diseases. Here, we find that ETV1, ETV4, and ETV5 can phenocopy EWSR1::FLI1 in Ewing sarcoma cell lines. However, rescue of EWSR1::FLI1 knockdown by ERG requires an ERG mutant that disrupts interaction with PRC2. This suggests that EWSR1::ERG fusions that drive Ewing sarcoma avoid PRC2 interactions. We then identify an endogenous PRC2/FOXO1 complex and demonstrate that FOXO1 bridges the ERG/PRC2 interaction. AKT-mediated degradation of FOXO1 and subsequent loss of the ERG/PRC2 interaction provides a mechanism for ERG synergy with PTEN deletion in prostate cancer. Implications: These findings indicate that ETS transcription factors that drive prostate cancer and Ewing sarcoma utilize similar mechanisms and thus could be targeted by similar therapeutic approaches.
Downing et al. (2025) studied this question.