UBQLN2 Mediates Autophagy-Independent Protein Aggregate Clearance by the Proteasome

Cell. 2016 Aug 11;166(4):935-949. doi: 10.1016/j.cell.2016.07.001. Epub 2016 Jul 28.

Abstract

Clearance of misfolded and aggregated proteins is central to cell survival. Here, we describe a new pathway for maintaining protein homeostasis mediated by the proteasome shuttle factor UBQLN2. The 26S proteasome degrades polyubiquitylated substrates by recognizing them through stoichiometrically bound ubiquitin receptors, but substrates are also delivered by reversibly bound shuttles. We aimed to determine why these parallel delivery mechanisms exist and found that UBQLN2 acts with the HSP70-HSP110 disaggregase machinery to clear protein aggregates via the 26S proteasome. UBQLN2 recognizes client-bound HSP70 and links it to the proteasome to allow for the degradation of aggregated and misfolded proteins. We further show that this process is active in the cell nucleus, where another system for aggregate clearance, autophagy, does not act. Finally, we found that mutations in UBQLN2, which lead to neurodegeneration in humans, are defective in chaperone binding, impair aggregate clearance, and cause cognitive deficits in mice.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Adaptor Proteins, Vesicular Transport / metabolism*
  • Animals
  • Autophagy*
  • Autophagy-Related Proteins
  • Brain / metabolism
  • Brain / pathology
  • Disease Models, Animal
  • Gene Knock-In Techniques
  • HSP70 Heat-Shock Proteins / metabolism
  • Huntingtin Protein / metabolism
  • Male
  • Mice
  • Neurodegenerative Diseases / metabolism*
  • Neurodegenerative Diseases / pathology
  • Proteasome Endopeptidase Complex / metabolism*
  • Protein Aggregates
  • Protein Folding
  • Proteolysis

Substances

  • Adaptor Proteins, Signal Transducing
  • Adaptor Proteins, Vesicular Transport
  • Autophagy-Related Proteins
  • HSP70 Heat-Shock Proteins
  • Htt protein, mouse
  • Huntingtin Protein
  • Protein Aggregates
  • UBQLN2 protein, mouse
  • Proteasome Endopeptidase Complex