Dynamic Interaction of USP14 with the Chaperone HSC70 Mediates Crosstalk between the Proteasome, ER Signaling, and Autophagy

Abstract

SummaryUSP14 is a deubiquitinating enzyme associated with the proteasome important for protein degradation. Here we show that upon proteasome inhibition or expression of the mutant W58A-USP14, association of USP14 with the 19S regulatory particle is disrupted. MS-based interactomics revealed an interaction of USP14 with the chaperone, HSC70, in neuroblastoma cells. Proteasome inhibition enhanced binding of USP14 to HSC70, and to XBP1u and IRE1α proteins, demonstrating a role in the unfolded protein response. Striatal neurons expressing mutant huntingtin exhibited reduced USP14 and HSC70 levels, whereas inhibition of HSC70 downregulated USP14. Furthermore, proteasome inhibition or use of the mutant W58A-USP14 facilitated the interaction of USP14 with the autophagy protein, GABARAP. Functionally, overexpression of W58A-USP14 increased GABARAP positive autophagosomes in striatal neurons, and this was abrogated using the HSC70 inhibitor, VER-155008. Modulation of the USP14-HSC70 axis may represent a potential therapeutic target in HD to beneficially influence multiple proteostasis pathways.

Promiscuous Roles of Autophagy and Proteasome in Neurodegenerative Proteinopathies

“…Indeed, very little is known about the effects of an enhanced UPS activity on the autophagy flux and consequent rate of protein degradation. In the context of huntingtin metabolism, recent studies unraveled a role for the deubiquitinase ubiquitin specific peptidase 14 (USP14) as a common denominator mediating a compensatory negative feedback between the two major proteolytic pathways [176][177][178]. On the one hand, UPS activation achieved through USP14 inhibition facilitates the clearance of tau and reduces the amount of its oligomeric forms.…”

“…This may occlude the degradation of large, non-proteasomal substrates. Potential mechanistic insights on the role of UPS14 in the coordinated activities between UPS and autophagy were also provided [178]. In detail, UPS inhibition disrupts the association of USP14 with the P19S regulatory particle of the UPS, while fostering its interaction with either the autophagy protein GABARAP or the heat-shock-related co-chaperonin HSC70 [178].…”

“…Potential mechanistic insights on the role of UPS14 in the coordinated activities between UPS and autophagy were also provided [178]. In detail, UPS inhibition disrupts the association of USP14 with the P19S regulatory particle of the UPS, while fostering its interaction with either the autophagy protein GABARAP or the heat-shock-related co-chaperonin HSC70 [178]. Striatal neurons expressing mutant huntingtin possess reduced USP14 levels, while USP14 overexpression increases GABARAP positive autophagosomes in striatal neurons [178].…”

“…In detail, UPS inhibition disrupts the association of USP14 with the P19S regulatory particle of the UPS, while fostering its interaction with either the autophagy protein GABARAP or the heat-shock-related co-chaperonin HSC70 [178]. Striatal neurons expressing mutant huntingtin possess reduced USP14 levels, while USP14 overexpression increases GABARAP positive autophagosomes in striatal neurons [178]. This suggests that in the presence of mutant huntingtin, low USP14 levels may contribute to UPS activity prevailing over the autophagy pathway, while co-chaperonins and the autophagy pathway may be recruited at later stages when large HT aggregates accumulate in the cell.…”

The Unfolded Protein Response and Autophagy as Drug Targets in Neuropsychiatric Disorders

“…In eukaryotes, XBP1u mRNA can still be translated into a protein with less stability that is rapidly degraded by the ubiquitin-proteasome system (Navon et al, 2010 ). Our recent work showed that proteasome inhibition, stabilizing the protein, resulted in the formation of XBP1u aggresome like induced structures in neuronal cells (Srinivasan et al, 2020 ). The role of these XBP1u structures in neuronal IRE1α signaling remains to be explored.…”