Skip to main content
Article thumbnail
Location of Repository

The Ubiquitin-Proteasome Reporter GFPu Does Not Accumulate in Neurons of the R6/2 Transgenic Mouse Model of Huntington's Disease

By John S. Bett, Casey Cook, Leonard Petrucelli and Gillian P. Bates


Impairment of the ubiquitin-proteasome system (UPS) has long been considered an attractive hypothesis to explain the selective dysfunction and death of neurons in polyglutamine disorders such as Huntington's disease (HD). The fact that inclusion bodies in HD mouse models and patient brains are rich in ubiquitin and proteasome components suggests that the UPS may be hindered directly or indirectly by inclusion bodies or their misfolded monomeric or oligomeric precursors. However, studies into UPS function in various polyglutamine disease models have yielded conflicting results, suggesting mutant polyglutamine tracts may exert different effects on the UPS depending on protein context, expression level, subcellular localisation and cell-type. To investigate UPS function in a well-characterised mouse model of HD, we have crossed R6/2 HD mice with transgenic UPS reporter mice expressing the GFPu construct. The GFPu construct comprises GFP fused to a constitutive degradation signal (CL-1) that promotes its rapid degradation under conditions of a healthy UPS. Using a combination of immunoblot analysis, fluorescence and immunofluorescence microscopy studies, we found that steady-state GFPu levels were not detectably different between R6/2 and non-R6/2 brain. We observed no correlation between inclusion body formation and GFPu accumulation, suggesting no direct relationship between protein aggregation and global UPS inhibition in R6/2 mice. These findings suggest that while certain branches of the UPS can be impaired by mutant polyglutamine proteins, such proteins do not necessarily cause total blockade of UPS-dependent degradation. It is therefore likely that the relationship between mutant polyglutamine proteins and the UPS is more complex than originally anticipated

Topics: Research Article
Publisher: Public Library of Science
OAI identifier:
Provided by: PubMed Central
Download PDF:
Sorry, we are unable to provide the full text but you may find it at the following location(s):
  • http://www.pubmedcentral.nih.g... (external link)
  • Suggested articles


    1. (2003). A transgenic mouse model of the ubiquitin/proteasome system.
    2. (2002). Aggregate formation inhibits proteasomal degradation of polyglutamine proteins.
    3. (2007). Aggregation and proteasome: the case of elongated polyglutamine aggregation in spinal and bulbar muscular atrophy.
    4. (1997). Aggregation of huntingtin in neuronal intranuclear inclusions and dystrophic neurites in brain.
    5. (2008). Altered histone monoubiquitylation mediated by mutant huntingtin induces transcriptional dysregulation.
    6. (2001). Altered proteasomal function due to the expression of polyglutamine-expanded truncated N-terminal huntingtin induces apoptosis by caspase activation through mitochondrial cytochrome c release.
    7. (2005). Application and analysis of the GFPu family of ubiquitin-proteasome system reporters.
    8. (2003). Are Huntington’s and polyglutamine-based ataxias proteasome storage diseases?
    9. (2001). Centrosome disorganization in fibroblast cultures derived from R6/2 Huntington’s disease (HD) transgenic mice and HD patients.
    10. (2002). Ciechanover A
    11. (2008). Depletion of 26S proteasomes in mouse brain neurons causes neurodegeneration and Lewy-like inclusions resembling human pale bodies.
    12. (2007). Disease-associated prion protein oligomers inhibit the 26S proteasome.
    13. (2004). Eukaryotic proteasomes cannot digest polyglutamine sequences and release them during degradation of polyglutamine-containing proteins.
    14. (2006). Expanded polyglutamines impair synaptic transmission and ubiquitinproteasome system in Caenorhabditis elegans.
    15. (1997). Formation of neuronal intranuclear inclusions underlies the neurological dysfunction in mice transgenic for the HD mutation.
    16. (2004). Generalized brain and skin proteasome inhibition in Huntington’s disease.
    17. (2007). Global changes to the ubiquitin system in Huntington’s disease.
    18. (2005). Global impairment of the ubiquitin-proteasome system by nuclear or cytoplasmic protein aggregates precedes inclusion body formation.
    19. (2006). Histone deacetylase inhibitors as therapeutics for polyglutamine disorders.
    20. (2003). Huntingtin forms toxic NH2-terminal fragment complexes that are promoted by the agedependent decrease in proteasome activity.
    21. (2008). Impaired ubiquitinproteasome system activity in the synapses of Huntington’s disease mice.
    22. (2001). Impairment of the ubiquitinproteasome system by protein aggregation.
    23. (2004). Inefficient degradation of truncated polyglutamine proteins by the proteasome.
    24. (2006). Inhibition of 26S proteasome activity by huntingtin filaments but not inclusion bodies isolated from mouse and human brain.
    25. (2008). Intracellular degradation of misfolded proteins in polyglutamine neurodegenerative diseases. Brain Res Rev.
    26. (2004). Modulating huntingtin half-life alters polyglutamine-dependent aggregate formation and cell toxicity.
    27. (2005). Monitoring of ubiquitindependent proteolysis with green fluorescent protein substrates.
    28. (2005). Neuronal dysfunction in a polyglutamine disease model occurs in the absence of ubiquitin-proteasome UPS Function
    29. (2003). Neuronal induction of the immunoproteasome in Huntington’s disease.
    30. (1996). of the HD gene with an expanded CAG repeat is sufficient to cause a progressive neurological phenotype in transgenic mice.
    31. (2006). Progressive disruption of cellular protein folding in models of polyglutamine diseases.
    32. (2004). Proteasome degrades soluble expanded polyglutamine completely and efficiently.
    33. (2005). Proteasome function is inhibited by polyglutamine-expanded ataxin-1, the SCA1 gene product.
    34. (2006). Proteasome impairment does not contribute to pathogenesis in R6/2 Huntington’s disease mice: exclusion of proteasome activator REGgamma as a therapeutic target.
    35. (2006). Proteasome inhibition and Parkinson’s disease modeling.
    36. (2008). Proteasomes cleave at multiple sites within polyglutamine tracts: activation by PA28gamma(K188E).
    37. (2000). Short-lived green fluorescent proteins for quantifying ubiquitin/proteasome-dependent proteolysis in living cells.
    38. (2009). The polyubiquitin Ubc gene modulates histone H2A monoubiquitylation in the R6/2 mouse model of Huntington’s disease.
    39. (2003). The ubiquitin proteasome system in neurodegenerative diseases: sometimes the chicken, sometimes the egg.

    To submit an update or takedown request for this paper, please submit an Update/Correction/Removal Request.