Matsumoto Masaki, Yada Masayoshi, Hatakeyama Shigetsugu, Ishimoto Hiroshi, Tanimura Teiichi, Tsuji Shoji, Kakizuka Akira, Kitagawa Masatoshi, Nakayama Keiichi I
Department of Molecular and Cellular Biology, Medical Institute of Bioregulation, Kyushu University, Fukuoka, Japan.
EMBO J. 2004 Feb 11;23(3):659-69. doi: 10.1038/sj.emboj.7600081. Epub 2004 Jan 29.
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.
在患有多聚谷氨酰胺疾病的个体的神经元中，含多聚谷氨酰胺的蛋白质的不溶性聚集体通常与泛素结合。我们现在表明，ataxin-3（其多聚谷氨酰胺序列的异常扩展导致3型脊髓小脑共济失调（SCA3））会发生泛素化并被蛋白酶体降解。哺乳动物E4B（UFD2a），一种泛素链组装因子（E4），与ataxin-3的多泛素化活性共纯化。E4B与ataxin-3相互作用，从而介导其多泛素化。E4B的表达促进了ataxin-3病理形式的降解。相反，E4B的显性负性突变体抑制了这种形式的ataxin-3的降解，导致细胞内聚集体的形成。在SCA3的果蝇模型中，E4B的表达抑制了由ataxin-3突变体诱导的神经变性。这些观察结果表明，E4是ataxin-3病理形式降解的限速因子，并且E4B的靶向表达是SCA3的一种潜在基因疗法。
