title: Molecular clearance of ataxin-3 is regulated by a mammalian E4.
abstract: Insoluble aggregates of polyglutamine-containing proteins are usually conjugated with ubiquitin in neurons of individuals with polyglutamine diseases. We now show that ataxin-3, in which the abnormal expansion of a polyglutamine tract is responsible for spinocerebellar ataxia type 3 (SCA3), undergoes ubiquitylation and degradation by the proteasome. Mammalian E4B (UFD2a), a ubiquitin chain assembly factor (E4), copurified with the polyubiquitylation activity for ataxin-3. E4B interacted with, and thereby mediated polyubiquitylation of, ataxin-3. Expression of E4B promoted degradation of a pathological form of ataxin-3. In contrast, a dominant-negative mutant of E4B inhibited degradation of this form of ataxin-3, resulting in the formation of intracellular aggregates. In a Drosophila model of SCA3, expression of E4B suppressed the neurodegeneration induced by an ataxin-3 mutant. These observations suggest that E4 is a rate-limiting factor in the degradation of pathological forms of ataxin-3, and that targeted expression of E4B is a potential gene therapy for SCA3.
authors.affiliation: Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
authors.forename: Masaki
authors.initials: M
authors.lastname: Matsumoto
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Yada
authors.forename: Shigetsugu
authors.initials: S
authors.lastname: Hatakeyama
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Ishimoto
authors.forename: Teiichi
authors.initials: T
authors.lastname: Tanimura
authors.forename: Shoji
authors.initials: S
authors.lastname: Tsuji
authors.forename: Akira
authors.initials: A
authors.lastname: Kakizuka
authors.forename: Masatoshi
authors.initials: M
authors.lastname: Kitagawa
authors.forename: Keiichi I
authors.initials: KI
authors.lastname: Nakayama
mesh_terms: D000818:Animals; D030801:Animals, Genetically Modified; D000067699:Ataxin-3; D002460:Cell Line; D002524:Cerebellar Ataxia / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster; D006801:Humans; D051379:Mice; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D025801:Ubiquitin / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*
chemical_list: D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; D025801:Ubiquitin; C471292:Ube4b protein, mouse; D044767:Ubiquitin-Protein Ligases; C092341:ATXN3 protein, human; D000067699:Ataxin-3; C511594:Atxn3 protein, mouse