Targeted degradation of USP7 in solid cancer cells reveals distinct effects of deubiquitinase degraders and inhibitors

Abstract

Proteolysis-targeting chimeras (PROTACs) co-op the ubiquitin system for targeted protein degradation, creating opportunities to interrogate cellular functions of proteins through “chemical knockdown”. However, matched pairs of protein degraders and inhibitors, that possess high specificity and chemical complementarity, for individual components of the ubiquitin system have remained scarce. This includes reagents to modulate activity and abundance of deubiquitinases (DUBs). Here, using an integrated chemical biology approach, we explore cellular functions of the DUB USP7 as a case study by comparing inhibition and degradation in melanoma and pancreatic cancer cells. Through the synthesis of a degrader library, we identify and characterize potent USP7 PROTACs for each cancer type. Proteomic and cellular analyses reveal that selective USP7 degradation modulates both shared and distinct protein sets across both cancers without affecting cell growth. In contrast, prolonged inhibitor treatment induces USP7-independent proteomic and metabolic dysregulation, highlighting important caveats for the cellular use of hydroxypiperidine-based USP7 inhibitors. Collectively, our work provides a comprehensively characterized chemical toolbox to distinguish on-target phenotypes which will aid the understanding of USP7 in malignant diseases. More broadly, our data emphasize the importance of increased specificity via PROTAC-mediated degradation and the potential of this modality to elucidate cell-line specific functions of DUBs.