title: Aggregation of Polyglutamine-expanded Ataxin 7 Protein Specifically Sequesters Ubiquitin-specific Protease 22 and Deteriorates Its Deubiquitinating Function in the Spt-Ada-Gcn5-Acetyltransferase (SAGA) Complex.
abstract: Human ataxin 7 (Atx7) is a component of the deubiquitination module (DUBm) in the Spt-Ada-Gcn5-acetyltransferase (SAGA) complex for transcriptional regulation, and expansion of its polyglutamine (polyQ) tract leads to spinocerebellar ataxia type 7. However, how polyQ expansion of Atx7 affects DUBm function remains elusive. We investigated the effects of polyQ-expanded Atx7 on ubiquitin-specific protease (USP22), an interacting partner of Atx7 functioning in deubiquitination of histone H2B. The results showed that the inclusions or aggregates formed by polyQ-expanded Atx7 specifically sequester USP22 through their interactions mediated by the N-terminal zinc finger domain of Atx7. The mutation of the zinc finger domain in Atx7 that disrupts its interaction with USP22 dramatically abolishes sequestration of USP22. Moreover, polyQ expansion of Atx7 decreases the deubiquitinating activity of USP22 and, consequently, increases the level of monoubiquitinated H2B. Therefore, we propose that polyQ-expanded Atx7 forms insoluble aggregates that sequester USP22 into a catalytically inactive state, and then the impaired DUBm loses the function to deubiquitinate monoubiquitinated histone H2B or H2A. This may result in dysfunction of the SAGA complex and transcriptional dysregulation in spinocerebellar ataxia type 7 disease.
authors.affiliation: From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. 320 Yue-Yang Road, Shanghai 200031, China.
authors.forename: Hui
authors.initials: H
authors.lastname: Yang
authors.affiliation: From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. 320 Yue-Yang Road, Shanghai 200031, China.
authors.forename: Shuai
authors.initials: S
authors.lastname: Liu
authors.affiliation: From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. 320 Yue-Yang Road, Shanghai 200031, China.
authors.forename: Wen-Tian
authors.initials: WT
authors.lastname: He
authors.affiliation: From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. 320 Yue-Yang Road, Shanghai 200031, China.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhao
authors.affiliation: From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. 320 Yue-Yang Road, Shanghai 200031, China.
authors.forename: Lei-Lei
authors.initials: LL
authors.lastname: Jiang
authors.affiliation: From the State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. 320 Yue-Yang Road, Shanghai 200031, China hyhu@sibcb.ac.cn.
authors.forename: Hong-Yu
authors.initials: HY
authors.lastname: Hu
mesh_terms: D000067719:Ataxin-7 / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D015153:Blotting, Western; D057809:HEK293 Cells; D006367:HeLa Cells; D051548:Histone Acetyltransferases / Q000378:metabolism*; D006657:Histones / Q000378:metabolism; D006801:Humans; D008856:Microscopy, Fluorescence; D009097:Multienzyme Complexes / Q000378:metabolism*; D009154:Mutation; D010455:Peptides / Q000235:genetics; D066329:Protein Aggregates; D011485:Protein Binding; D020754:Spinocerebellar Ataxias / Q000235:genetics / Q000378:metabolism; D013869:Thiolester Hydrolases / Q000235:genetics / Q000378:metabolism*; D019680:Trinucleotide Repeat Expansion / Q000235:genetics; D043222:Ubiquitin Thiolesterase; D054875:Ubiquitination; D016335:Zinc Fingers / Q000235:genetics
chemical_list: D000067719:Ataxin-7; D006657:Histones; D009097:Multienzyme Complexes; D010455:Peptides; D066329:Protein Aggregates; C097188:polyglutamine; D051548:Histone Acetyltransferases; D013869:Thiolester Hydrolases; D043222:Ubiquitin Thiolesterase; C527170:Usp22 protein, human
keywords: DUB module; SAGA complex; USP22; aggregation; ataxin 7; deubiquitylation (deubiquitination); polyglutamine; protein-protein interaction; sequestration; zinc finger