Aggregate formation of mutant protein kinase C gamma found in spinocerebellar ataxia type 14 impairs ubiquitin-proteasome system and induces endoplasmic reticulum stress

Eur J Neurosci. 2007 Dec;26(11):3126-40. doi: 10.1111/j.1460-9568.2007.05933.x. Epub 2007 Nov 14.


Several causal missense mutations in protein kinase C gamma (gamma PKC) gene have been found in spinocerebellar ataxia type 14 (SCA14), an autosomal dominant neurodegenerative disease. We previously demonstrated that mutant gamma PKC found in SCA14 is susceptible to two types of aggregation, cytoplasmic dot-like and perinuclear massive aggregation, and causes cell death in Chinese hamster ovary cells. Long-term time-lapse imaging revealed that firstly accumulated dot-like aggregation of mutant gamma PKC-green fluorescent protein (GFP) gradually formed perinuclear massive aggregations, followed by cell death. However, it remains unclear how aggregate formation of mutant gamma PKC causes cell death. In the present study, we examined whether these mutant aggregations affect the ubiquitin-proteasome system (UPS) and endoplasmic reticular (ER) stress. Two mutant gamma PKC-GFPs (S119P and G128D) were strongly ubiquitinated, and dot-like aggregations of these mutants were ubiquitin-positive and colocalized with proteasome 20S. Furthermore, proteasome activity in cells with aggregates, especially massive ones, was significantly decreased. Aggregate formation of mutant gamma PKC-GFP induced phosphorylation of PERK (PKR-like ER kinase) and nuclear expression of CHOP (C/EBP homologous protein), hallmarks of ER stress and subsequently activated caspase-3. These results indicate that aggregate formation of mutant gamma PKC found in SCA14 impairs UPS and induces ER stress, leading to apoptotic cell death.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Aspartic Acid / genetics
  • CHO Cells / metabolism
  • CHO Cells / ultrastructure
  • Caspases / metabolism
  • Cell Death / physiology
  • Cricetinae
  • Cricetulus
  • Endoplasmic Reticulum / pathology*
  • Glycine / genetics
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Humans
  • Immunoprecipitation / methods
  • Mutation / physiology*
  • Proline / genetics
  • Proteasome Endopeptidase Complex / metabolism*
  • Protein Kinase C / genetics*
  • Protein Processing, Post-Translational / physiology
  • Serine / genetics
  • Stress, Physiological / pathology*
  • Time Factors
  • Transfection / methods
  • Ubiquitin / physiology*


  • Ubiquitin
  • Green Fluorescent Proteins
  • Aspartic Acid
  • Serine
  • Proline
  • protein kinase C gamma
  • Protein Kinase C
  • Caspases
  • Proteasome Endopeptidase Complex
  • Glycine