IU1

IU1 is a potent and selective small-molecule inhibitor of Usp14, a proteasome-associated deubiquitinating enzyme in habiting the degradation of ubiquitin-protein conjugates, with the inhibition constant IC₅₀ ranging from 4 to 5 μM. Structural analysis reveals IU1 is an active-site-directed thiol protease inhibitor that binds to the activated form of Usp14 preventing it docking on the proteasome in a rapid but reversible manner. According to the results of previous studies, it has shown that IU1 failed to inhibit Usp14 in the absence of proteasomes as well as eight deubiquitinating enzymes (DUBs) of human origin and Ub-AMC hrolysis by proteasomes lacking Usp14.

Reference

Byung-Hoon Lee, Min Jae Lee, Soyeon Park, Dong-Chan Oh, Suzanne Elsasser, Ping-Chung Chen, Carlos Gartner, Nevena Dimova, John Hanna, Steven P. Gygi, Scott M. Wilson, Randall W. King and Daniel Finley. Enhancement of proteasome activity by a small-molecule inhibitor of Usp14. Nature. 2010; 467(7312): 179-184

USP14 inhibitor IU1 prevents ventilator-induced lung injury in rats.[Pubmed:25198582]

Cell Mol Biol (Noisy-le-grand). 2014 Sep 7;60(2):50-4.

The pathophysiology of ventilator-induced lung injury (VILI) involves multiple mechanisms including inflammation. USP14 removes the ubiquitin chain of I-kappaB, therefore inducing I-kappaB degradation and increasing cytokine release. The purpose of this study was to examine the protecting roles and mechanisms of USP14 inhibitor on I-kappaB expression and lung injury induced by high tidal volume ventilation in normal rat lung. Male Sprague-Dawley rats were divided into follows: Two ventilation modalities were used: rats in Groups LD (low volume + DMSO) and LI (low volume + IU1) received ventilation with a tidal volume of 8 ml/kg, while the rats in Groups HD (high volume + DMSO) and HI (high volume + IU1) were ventilated with a tidal volume of 40 ml/kg. The levels of lung wet-to-dry weight ratio were used as indicators of water metabolism in lung tissue; the detection of inflammatory cytokines in bronchoalveolar lavage (BAL) fluid was used to indicate inflammatory response, while lung injury was assessed by injury score and morphological changes under light microscope. The USP14 and I-kappaB protein level was measured in lung tissue by Western blot. Our results indicated that administration of IU1 alleviated ventilator-induced lung injury which was accompanied by reduced MPO activity, wet-to-dry weight ratio, lower TNF-alpha, IL-1beta, IL-6 and IL-8 levels and increased I-kappaB expression in lung tissue. IU1 could significantly alleviate ventilator-induced rat lung injury by attenuate intrapulmonary inflammatory response.

Enhancement of proteasome activity by a small-molecule inhibitor of USP14.[Pubmed:20829789]

Nature. 2010 Sep 9;467(7312):179-84.

Proteasomes, the primary mediators of ubiquitin-protein conjugate degradation, are regulated through complex and poorly understood mechanisms. Here we show that USP14, a proteasome-associated deubiquitinating enzyme, can inhibit the degradation of ubiquitin-protein conjugates both in vitro and in cells. A catalytically inactive variant of USP14 has reduced inhibitory activity, indicating that inhibition is mediated by trimming of the ubiquitin chain on the substrate. A high-throughput screen identified a selective small-molecule inhibitor of the deubiquitinating activity of human USP14. Treatment of cultured cells with this compound enhanced degradation of several proteasome substrates that have been implicated in neurodegenerative disease. USP14 inhibition accelerated the degradation of oxidized proteins and enhanced resistance to oxidative stress. Enhancement of proteasome activity through inhibition of USP14 may offer a strategy to reduce the levels of aberrant proteins in cells under proteotoxic stress.

Trimming of ubiquitin chains by proteasome-associated deubiquitinating enzymes.[Pubmed:20823120]

Mol Cell Proteomics. 2011 May;10(5):R110.003871.

The proteasome generally recognizes substrate via its multiubiquitin chain followed by ATP-dependent unfolding and translocation of the substrate from the regulatory particle into the proteolytic core particle to be degraded. Substrate-bound ubiquitin groups are for the most part not delivered to the core particle and broken down together with substrate but instead recovered as intact free ubiquitin and ubiquitin chains. Substrate deubiquitination on the proteasome is mediated by three distinct deubiquitinating enzymes associated with the regulatory particle: RPN11, UCH37, and USP14. RPN11 cleaves at the base of the ubiquitin chain where it is linked to the substrate, whereas UCH37 and apparently USP14 mediate a stepwise removal of ubiquitin from the substrate by disassembling the chain from its distal tip. In contrast to UCH37 and USP14, RPN11 shows degradation-coupled activity; RPN11-mediated deubiquitination is apparently delayed until the proteasome is committed to degrade the substrate. Accordingly, RPN11-mediated deubiquitination promotes substrate degradation. In contrast, removal of ubiquitin prior to commitment could antagonize substrate degradation by promoting substrate dissociation from the proteasome. Emerging evidence suggests that USP14 and UCH37 can both suppress substrate degradation in this way. One line of study has shown that small molecule USP14 inhibitors can enhance proteasome function in cells, which is consistent with this model. Enhancing protein degradation could potentially have therapeutic applications for diseases involving toxic proteins that are proteasome substrates. However, the responsiveness of substrates to inhibition of proteasomal deubiquitinating enzymes may vary substantially. This substrate specificity and its mechanistic basis should be addressed in future studies.