title: Valosin-containing protein (VCP/p97) is an activator of wild-type ataxin-3.
abstract: Alterations in the ubiquitin-proteasome system (UPS) have been reported in several neurodegenerative disorders characterized by protein misfolding and aggregation, including the polylgutamine diseases. Machado-Joseph disease (MJD) or Spinocerebellar Ataxia type 3 is caused by a polyglutamine-encoding CAG expansion in the ATXN3 gene, which encodes a 42 kDa deubiquitinating enzyme (DUB), ataxin-3. We investigated ataxin-3 deubiquitinating activity and the functional relevance of ataxin-3 interactions with two proteins previously described to interact with ataxin-3, hHR23A and valosin-containing protein (VCP/p97). We confirmed ataxin-3 affinity for both hHR23A and VCP/p97. hHR23A and ataxin-3 were shown to co-localize in discrete nuclear foci, while VCP/p97 was primarily cytoplasmic. hHR23A and VCP/p97 recombinant proteins were added, separately or together, to normal and expanded ataxin-3 in in vitro deubiquitination assays to evaluate their influence on ataxin-3 activity. VCP/p97 was shown to be an activator specifically of wild-type ataxin-3, exhibiting no effect on expanded ataxin-3, In contrast, we observed no significant alterations in ataxin-3 enzyme kinetics or substrate preference in the presence of hHR23A alone or in combination with VCP. Based on our results we propose a model where ataxin-3 normally functions with its interactors to specify the cellular fate of ubiquitinated proteins.
authors.affiliation: Center for Neuroscience and Cell Biology, University of Coimbra, Coimbra, Portugal.
authors.forename: Mário N
authors.initials: MN
authors.lastname: Laço
authors.forename: Luisa
authors.initials: L
authors.lastname: Cortes
authors.forename: Sue M
authors.initials: SM
authors.lastname: Travis
authors.forename: Henry L
authors.initials: HL
authors.lastname: Paulson
authors.forename: A Cristina
authors.initials: AC
authors.lastname: Rego
mesh_terms: D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D000067699:Ataxin-3; D019556:COS Cells; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002522:Chlorocebus aethiops; D045643:DNA Repair Enzymes / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D006867:Hydrolases / Q000378:metabolism; D007700:Kinetics; D008954:Models, Biological; D050505:Mutant Proteins / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D009687:Nuclear Proteins / Q000378:metabolism*; D010447:Peptide Hydrolases / Q000378:metabolism; D011485:Protein Binding; D012097:Repressor Proteins / Q000378:metabolism*; D013379:Substrate Specificity; D019680:Trinucleotide Repeat Expansion; D025801:Ubiquitin / Q000378:metabolism; D000074405:Valosin Containing Protein
chemical_list: D018797:Cell Cycle Proteins; D004268:DNA-Binding Proteins; D050505:Mutant Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D025801:Ubiquitin; C086985:RAD23A protein, human; D006867:Hydrolases; D010447:Peptide Hydrolases; C092341:ATXN3 protein, human; D000067699:Ataxin-3; D000251:Adenosine Triphosphatases; C000614178:VCP protein, human; D000074405:Valosin Containing Protein; D045643:DNA Repair Enzymes