An inhibitor of the proteasomal deubiquitinating enzyme USP14 induces tau elimination in cultured neurons

Abstract

The ubiquitin-proteasome system (UPS) is responsible for most selective protein degradation in eukaryotes and regulates numerous cellular processes, including cell cycle control and protein quality control. A component of this system, the deubiquitinating enzyme USP14, associates with the proteasome where it can rescue substrates from degradation by removal of the ubiquitin tag. We previously found that a small-molecule inhibitor of USP14, known as IU1, can increase the rate of degradation of a subset of proteasome substrates. We report here the synthesis and characterization of 87 variants of IU1, which resulted in the identification of a 10-fold more potent USP14 inhibitor that retains specificity for USP14. The capacity of this compound, IU1-47, to enhance protein degradation in cells was tested using as a reporter the microtubule-associated protein tau, which has been implicated in many neurodegenerative diseases. Using primary neuronal cultures, IU1-47 was found to accelerate the rate of degradation of wild-type tau, the pathological tau mutants P301L and P301S, and the A152T tau variant. We also report that a specific residue in tau, lysine 174, is critical for the IU1-47-mediated tau degradation by the proteasome. Finally, we show that IU1-47 stimulates autophagic flux in primary neurons. In summary, these findings provide a powerful research tool for investigating the complex biology of USP14.

USP 14 inhibition corrects an in vivo model of impaired mitophagy

“…Our study showed no toxicity by IU1, in terms of life span and motor neuron survivability of Drosophila. Other studies also showed no toxicity of IU1 on neuronal population (Boselli et al, 2017;Min et al, 2017). However, while chronic intranasal administration is an option, the blood-brain barrier permeability of the drug is yet to be studied.…”

Meddling with Fate: The Proteasomal Deubiquitinating Enzymes

“…IU1 does not appear to induce the noncatalytic effect [41]; therefore this compound provides one method to discriminate between catalytic and noncatalytic suppression of proteasome activity. Recently a 10-fold more potent variant of IU1, known as IU1-47, has been reported ([110]).…”

The Degradation-promoting Roles of Deubiquitinases Ubp6 and Ubp3 in Cytosolic and ER Protein Quality Control

“…Ubp6 is a peripheral subunit of the proteasome which recycles ubiquitin from substrates prior to proteolysis (Aufderheide et al, 2015;Bashore et al, 2015;Hanna et al, 2006;Hanna et al, 2003). Although UBP6 deletion had been suggested to enhance QC (Boselli et al, 2017;Nielsen et al, 2014;Torres et al, 2010), it in fact compromised the degradation of CytoQC substrate Ste6*c and ΔssPrA ( Figure 1A, 2A and 2B). Meanwhile, it did not delay or accelerate the clearance of any ERQC substrate, CPY*, Ste6* or Sec61-2 ( Figure 1B and 2C -E).…”

“…Ubp3 supports CytoQC under heat stress by suppressing the conjugation of lysine 63 (K63)-linked ubiquitin chains on misfolded proteins and facilitating K48linkage (Fang et al, 2014;Fang et al, 2016;Silva et al, 2015) but its function under the physiological temperature or in other QC pathways is unknown (Oling et al, 2014). Ubp6 was proposed to delay QC because deleting UBP6 reduced the steady-state abundance of some proteins (Boselli et al, 2017;Nielsen et al, 2014;Torres et al, 2010). This hypothesis, however, lacks support from direct assays of degradation kinetics (Dephoure et al, 2014).…”