Ubiquitin-binding site 2 of ataxin-3 prevents its proteasomal degradation by interacting with Rad23

Nat Commun. 2014 Aug 21;5:4638. doi: 10.1038/ncomms5638.

Abstract

Polyglutamine repeat expansion in ataxin-3 causes neurodegeneration in the most common dominant ataxia, spinocerebellar ataxia type 3 (SCA3). Since reducing levels of disease proteins improves pathology in animals, we investigated how ataxin-3 is degraded. Here we show that, unlike most proteins, ataxin-3 turnover does not require its ubiquitination, but is regulated by ubiquitin-binding site 2 (UbS2) on its N terminus. Mutating UbS2 decreases ataxin-3 protein levels in cultured mammalian cells and in Drosophila melanogaster by increasing its proteasomal turnover. Ataxin-3 interacts with the proteasome-associated proteins Rad23A/B through UbS2. Knockdown of Rad23 in cultured cells and in Drosophila results in lower levels of ataxin-3 protein. Importantly, reducing Rad23 suppresses ataxin-3-dependent degeneration in flies. We present a mechanism for ubiquitination-independent degradation that is impeded by protein interactions with proteasome-associated factors. We conclude that UbS2 is a potential target through which to enhance ataxin-3 degradation for SCA3 therapy.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Animals, Genetically Modified
  • Ataxin-3 / genetics
  • Ataxin-3 / metabolism*
  • Binding Sites
  • DNA Repair Enzymes / genetics
  • DNA Repair Enzymes / metabolism*
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / metabolism*
  • Drosophila melanogaster / metabolism
  • Gene Knockdown Techniques
  • HeLa Cells
  • Humans
  • Proteasome Endopeptidase Complex / genetics
  • Proteasome Endopeptidase Complex / metabolism
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Ubiquitin / metabolism*
  • Ubiquitination

Substances

  • DNA-Binding Proteins
  • Repressor Proteins
  • Ubiquitin
  • RAD23A protein, human
  • ATXN3 protein, human
  • Ataxin-3
  • Proteasome Endopeptidase Complex
  • DNA Repair Enzymes