USP14

USP14 (ubiquitin-specific protease 14) is a proteasome-associated deubiquitinating enzyme that regulates ubiquitin-dependent protein turnover by reversibly interacting with the 26S proteasome and removing ubiquitin chains from proteasome-bound substrates^[1][2]. Mechanistically, USP14 functions as a major regulator of proteasome activity, where proteasome binding markedly enhances its catalytic activity and enables control of substrate processing, ubiquitin recycling, and proteostasis pathways^[1][3]. Through its deubiquitinating activity, USP14 can trim ubiquitin chains before irreversible substrate commitment, thereby influencing the efficiency of proteasomal degradation and cellular protein quality control^[2][4]. These functions connect USP14 to biological processes that depend on balanced protein homeostasis, including autophagy-proteasome crosstalk, where impaired USP14 activity has been associated with reduced autophagic flux and altered autophagosome-lysosome fusion in experimental systems^[5]. In disease-related studies, elevated USP14 expression has been linked to tumor progression and poor clinical outcomes in several cancers, while pharmacological or genetic USP14 inhibition reduces viability of malignant cells and promotes accumulation of polyubiquitinated proteins and proteotoxic stress^[6][7]. Compared with the related proteasomal deubiquitinases UCH37/UCHL5 and PSMD14/RPN11, USP14 is distinguished by its reversible proteasome association and substrate-editing activity prior to degradation commitment rather than degradation-coupled deubiquitination^[2][4][8]. For experimental applications, selective USP14 inhibitors such as IU1 and dual USP14/UCHL5 inhibitors including b-AP15 and VLX1570 have been widely used to investigate proteasome regulation, protein degradation mechanisms, and therapeutic vulnerabilities associated with proteostasis dysfunction^[9][10].