Proteomic Analysis of the EWS-Fli‑1 Interactome Reveals the Role of the Lysosome in EWS-Fli‑1 Turnover

Ewing
sarcoma is a cancer of bone and soft tissue in children that
is characterized by a chromosomal translocation involving EWS and
an Ets family transcription factor, most commonly Fli-1. EWS-Fli-1
fusion accounts for 85% of cases. The growth and survival of Ewing
sarcoma cells are critically dependent on EWS-Fli-1. A large body
of evidence has established that EWS-Fli-1 functions as a DNA-binding
transcription factor that regulates the expression of a number of
genes important for cell proliferation and transformation. However,
little is known about the biochemical properties of the EWS-Fli-1
protein. We undertook a series of proteomic analyses to dissect the
EWS-Fli-1 interactome. Employing a proximity-dependent biotinylation
technique, BioID, we identified cation-independent mannose 6-phosphate
receptor (CIMPR) as a protein located in the vicinity of EWS-Fli-1
within a cell. CIMPR is a cargo that mediates the delivery of lysosomal
hydrolases from the trans-Golgi network to the endosome, which are
subsequently transferred to the lysosomes. Further molecular cell
biological analyses uncovered a role for lysosomes in the turnover
of the EWS-Fli-1 protein. We demonstrate that an mTORC1 active-site
inhibitor, torin 1, which stimulates the TFEB-lysosome pathway, can
induce the degradation of EWS-Fli-1, suggesting a potential therapeutic
approach to target EWS-Fli-1 for degradation.