Relative Structural and Functional Roles of Multiple Deubiquitylating Proteins Associated with Mammalian 26S Proteasome

Abstract

We determined composition and relative roles of deubiquitylating proteins associated with the 26S proteasome in mammalian cells. Three deubiquitylating activities were associated with the 26S proteasome: two from constituent subunits, Rpn11/S13 and Uch37, and one from a reversibly associated protein, Usp14. RNA interference (RNAi) of Rpn11/S13 inhibited cell growth, decreased cellular proteasome activity via disrupted 26S proteasome assembly, and inhibited cellular protein degradation. In contrast, RNAi of Uch37 or Usp14 had no detectable effect on cell growth, proteasome structure or proteolytic capacity, but accelerated cellular protein degradation. RNAi of both Uch37 and Usp14 also had no effect on proteasome structure or proteolytic capacity, but inhibited cellular protein degradation. Thus, proper proteasomal processing of ubiquitylated substrates requires Rpn11 plus either Uch37 or Usp14. Although the latter proteins feature redundant deubiquitylation functions, they also appear to exert noncatalyic effects on proteasome activity that are similar to but independent of one another. These results reveal unexpected functional relationships among multiple deubiquitylating proteins and suggest a model for mammalian 26S proteasome function whereby their concerted action governs proteasome function by linking deubiquitylation to substrate hydrolysis.

Deubiquitylases From Genes to Organism

“…Conversely, retarded deubiquitylation leads to occlusion of substrate binding sites and clogs up the proteasome (291). Only siRNA knockdown of POH1 interferes with proteasome assembly, while depletion of USP14 or UCH37 alone both enhance protein degradation rates, but their combined depletion inhibits proteasomal activity (127). Yeast cells respond to ubiquitin depletion by upregulating the USP14 ortholog Ubp6, which restores ubiquitin levels (85).…”

Role of the ubiquitin–proteasome system in brain ischemia: Friend or foe?

“…Rpn11), or may associate reversibly with the proteasome (e.g. Uch37 and Usp14) (Koulich et al, 2008;Tai et al, 2010;Liu and Jacobson, 2013), but most of them have a cytosolic localization. The overall function of DUBs is to cleave ubiquitinlinked molecules after the C-terminus of the last residue of ubiquitin (Gly76), being essential to: (i) the maintenance of monomeric ubiquitin pool, either by cleaving the ubiquitin precursor or by trimming polyubiquitin chains; (ii) rescue proteins targeted for degradation, allowing the cell to adapt quickly to physiological changes, and (iii) prevent ubiquitinproteasome dependent protein degradation (Guterman and Glickman, 2004;Komander et al, 2009).…”

Regulation of NF-κB activity and inducible nitric oxide synthase by regulatory particle non-ATPase subunit 13 (Rpn13)

“…The 19S regulatory complex is in charge of recognizing, unfolding, deubiquitinating, and threading the substrate into the 20S core for proteolysis (1)(2)(3). The presence of proteasome-associated deubiquitination activity is well recognized, but its role in protein degradation is being actively investigated (4)(5)(6). Deubiquitination can serve to rescue proteins from degradation.…”