Roles of usp1 in ewing sarcoma

Ewing sarcoma is a cancer of bone and soft tissue in children and young adults that is driven by the EWS-ETS fusion transcription factor, most commonly EWS-FLI1. We previously reported that Ewing sarcoma harbors two populations of cells, the CD133^high population displaying higher growth rate and the CD133^low population displaying chemotherapy resistance. We now find that the ubiquitin-specific protease 1 (USP1) is a transcriptional target of the EWS-FLI1 fusion oncoprotein, expressed at high and low levels in the CD133^high and the CD133^low populations, respectively, and determines chemo-sensitivity. We also find that USP1 inhibits cdc42, increases EWS- FLI1 transcriptional output, and simulates Ewing sarcoma growth. We show that chemo-sensitization by USP1 is independent of cdc42. A pharmacological inhibitor of USP1 was able to activate cdc42 and inhibit Ewing sarcoma growth. These results uncover critical roles for USP1 in Ewing sarcoma, which regulates growth and chemosensitivity via distinct mechanisms.

This work was supported by the Owens Medical Research Foundation (to Y.S.), by the National Cancer Institute, the National Institutes of Health (CA202485 and CA283414 to Y.S.), and by the Cancer Prevention and Research Institute of Texas (RP160487, RP160841, and RP190385 to Y.S.).