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Huda Y. Zoghbi - One of the best experts on this subject based on the ideXlab platform.
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Comparison of an expanded ataxia interactome with patient medical records reveals a relationship between macular degeneration and ataxia
Human molecular genetics, 2010Co-Authors: Juliette J. Kahle, David E. Hill, Natali Gulbahce, Chad A. Shaw, Janghoo Lim, Albert-lászló Barabási, Huda Y. ZoghbiAbstract:Spinocerebellar ataxias 6 and 7 (SCA6 and SCA7) are neurodegenerative disorders caused by expansion of CAG repeats encoding polyglutamine (polyQ) tracts in CACNA1A, the alpha1A subunit of the P/Q-type calcium channel, and Ataxin-7 (ATXN7), a component of a chromatin-remodeling complex, respectively. We hypothesized that finding new protein partners for ATXN7 and CACNA1A would provide insight into the biology of their respective diseases and their relationship to other ataxia-causing proteins. We identified 118 protein interactions for CACNA1A and ATXN7 linking them to other ataxia-causing proteins and the ataxia network. To begin to understand the biological relevance of these protein interactions within the ataxia network, we used OMIM to identify diseases associated with the expanded ataxia network. We then used Medicare patient records to determine if any of these diseases co-occur with hereditary ataxia. We found that patients with ataxia are at 3.03-fold greater risk of these diseases than Medicare patients overall. One of the diseases comorbid with ataxia is macular degeneration (MD). The ataxia network is significantly (P= 7.37 × 10(-5)) enriched for proteins that interact with known MD-causing proteins, forming a MD subnetwork. We found that at least two of the proteins in the MD subnetwork have altered expression in the retina of Ataxin-7(266Q/+) mice suggesting an in vivo functional relationship with ATXN7. Together these data reveal novel protein interactions and suggest potential pathways that can contribute to the pathophysiology of ataxia, MD, and diseases comorbid with ataxia.
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partial loss of Ataxin 1 function contributes to transcriptional dysregulation in spinocerebellar ataxia type 1 pathogenesis
PLOS Genetics, 2010Co-Authors: Juan Crespobarreto, Chad A. Shaw, John D Fryer, Huda Y. ZoghbiAbstract:Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by expansion of a CAG repeat that encodes a polyglutamine tract in Ataxin1 (ATXN1). Molecular and genetic data indicate that SCA1 is mainly caused by a gain-of-function mechanism. However, deletion of wild-type ATXN1 enhances SCA1 pathogenesis, whereas increased levels of an evolutionarily conserved paralog of ATXN1, Ataxin 1-Like, ameliorate it. These data suggest that a partial loss of ATXN1 function contributes to SCA1. To address this possibility, we set out to determine if the SCA1 disease model (Atxn1154Q/+ mice) and the loss of Atxn1 function model (Atxn1−/− mice) share molecular changes that could potentially contribute to SCA1 pathogenesis. To identify transcriptional changes that might result from loss of function of ATXN1 in SCA1, we performed gene expression microarray studies on cerebellar RNA from Atxn1−/− and Atxn1154Q/+ cerebella and uncovered shared gene expression changes. We further show that mild overexpression of Ataxin-1-Like rescues several of the molecular and behavioral defects in Atxn1−/− mice. These results support a model in which Ataxin 1-Like overexpression represses SCA1 pathogenesis by compensating for a partial loss of function of Atxn1. Altogether, these data provide evidence that partial loss of Atxn1 function contributes to SCA1 pathogenesis and raise the possibility that loss-of-function mechanisms contribute to other dominantly inherited neurodegenerative diseases.
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opposing effects of polyglutamine expansion on native protein complexes contribute to sca1
Nature, 2008Co-Authors: Juan Crespobarreto, Paymaan Jafarnejad, David E. Hill, Ronald Richman, Aaron B. Bowman, Huda Y. ZoghbiAbstract:Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by expansion of a glutamine-encoding repeat in Ataxin 1 (ATXN1). In all known polyglutamine diseases, the glutamine expansion confers toxic functions onto the protein; however, the mechanism by which this occurs remains enigmatic, in light of the fact that the mutant protein apparently maintains interactions with its usual partners. Here we show that the expanded polyglutamine tract differentially affects the function of the host protein in the context of different endogenous protein complexes. Polyglutamine expansion in ATXN1 favours the formation of a particular protein complex containing RBM17, contributing to SCA1 neuropathology by means of a gain-of-function mechanism. Concomitantly, polyglutamine expansion attenuates the formation and function of another protein complex containing ATXN1 and capicua, contributing to SCA1 through a partial loss-of-function mechanism. This model provides mechanistic insight into the molecular pathogenesis of SCA1 as well as other polyglutamine diseases. Spinocerebellar ataxia type 1 (SCA1) is an inherited neurodegenerative disease caused by faulty insertion of stretches of glutamines in the Ataxin1 protein. Just how these 'polyglutamine expansions' make a protein neurotoxic — in SCA1 and eight other neurodegenerative diseases including Huntington's — is not clear. Lim et al. now show that the expanded polyglutamine tract can affect Ataxin1 protein function in different ways, depending on the protein partners it associates with. Both loss of function and, more surprisingly, gain of function was observed. Spinocerebellar ataxia type 1 (SCA1) is an inherited neurodegenerative disease caused by expansion of a glutamine-encoding repeat in Ataxin 1. The expanded polyglutamine tract can affect the function of the Ataxin1 protein in different ways, depending on the protein partners Ataxin1 is associated with. This paper shows that polyglutamine expansion in one and the same protein can cause gain of function and loss of function toxicity at the same time.
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dAtaxin-2 Mediates Expanded Ataxin-1-Induced Neurodegeneration in a Drosophila Model of SCA1
PLoS genetics, 2007Co-Authors: Ismael Al-ramahi, Alma M. Perez, Huda Y. Zoghbi, Stefan M. Pulst, Janghoo Lim, Minghang Zhang, Rie D Sørensen, Maria De Haro, Joana Branco, Juan BotasAbstract:Spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of neurodegenerative disorders sharing atrophy of the cerebellum as a common feature. SCA1 and SCA2 are two ataxias caused by expansion of polyglutamine tracts in Ataxin-1 (ATXN1) and Ataxin-2 (ATXN2), respectively, two proteins that are otherwise unrelated. Here, we use a Drosophila model of SCA1 to unveil molecular mechanisms linking Ataxin-1 with Ataxin-2 during SCA1 pathogenesis. We show that wild-type Drosophila Ataxin-2 (dAtx2) is a major genetic modifier of human expanded Ataxin-1 (Ataxin-1[82Q]) toxicity. Increased dAtx2 levels enhance, and more importantly, decreased dAtx2 levels suppress Ataxin-1[82Q]-induced neurodegeneration, thereby ruling out a pathogenic mechanism by depletion of dAtx2. Although Ataxin-2 is normally cytoplasmic and Ataxin-1 nuclear, we show that both dAtx2 and hAtaxin-2 physically interact with Ataxin-1. Furthermore, we show that expanded Ataxin-1 induces intranuclear accumulation of dAtx2/hAtaxin-2 in both Drosophila and SCA1 postmortem neurons. These observations suggest that nuclear accumulation of Ataxin-2 contributes to expanded Ataxin-1-induced toxicity. We tested this hypothesis engineering dAtx2 transgenes with nuclear localization signal (NLS) and nuclear export signal (NES). We find that NLS-dAtx2, but not NES-dAtx2, mimics the neurodegenerative phenotypes caused by Ataxin-1[82Q], including repression of the proneural factor Senseless. Altogether, these findings reveal a previously unknown functional link between neurodegenerative disorders with common clinical features but different etiology.
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The role of LANP and Ataxin 1 in E4F-mediated transcriptional repression
EMBO reports, 2007Co-Authors: Marija Cvetanovic, Huda Y. Zoghbi, Robert J. Rooney, J. García, Nataliya Toporovskaya, Puneet OpalAbstract:The leucine-rich acidic nuclear protein (LANP) belongs to the INHAT family of corepressors that inhibits histone acetyltransferases. The mechanism by which LANP restricts its repression to specific genes is unknown. Here, we report that LANP forms a complex with transcriptional repressor E4F and modulates its activity. As LANP interacts with Ataxin 1—a protein mutated in the neurodegenerative disease spinocerebellar ataxia type 1 (SCA1)—we tested whether Ataxin 1 can alter the E4F–LANP interaction. We show that Ataxin 1 relieves the transcriptional repression induced by the LANP–E4F complex by competing with E4F for LANP. These results provide the first functional link, to our knowledge, between LANP and Ataxin 1, and indicate a potential mechanism for the transcriptional aberrations observed in SCA1.
Harry T Orr - One of the best experts on this subject based on the ideXlab platform.
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RNA association and nucleocytoplasmic shuttling by Ataxin-1.
Journal of cell science, 2005Co-Authors: Stuart Irwin, Harry T Orr, Mark Vandelft, Joanna Graczyk, Deborah Pinchev, Jenny L Howell, Ray TruantAbstract:Spinocerebellar ataxia type 1 (SCA1) is a dominant neurodegenerative disease caused by the expression of mutant Ataxin-1 containing an expanded polyglutamine tract. Ataxin-1 is a nuclear protein that localizes to punctate inclusions similar to neuronal nuclear inclusions seen in many polyglutamine expansion disease proteins. We demonstrate that Ataxin-1 localization to inclusions and inclusion dynamics within the nucleus are RNA and transcription dependent, but not dependent on the polyglutamine tract. Ataxin-1 nuclear inclusions are distinct from other described nuclear bodies but recruit the mRNA export factor, TAP/NXF1, in a manner that is enhanced by cell heat shock. By FRAP protein dynamic studies in live cells, we found that wild-type, but not mutant, Ataxin-1 was capable of nuclear export. These results suggest that the normal role of Ataxin-1 may be in RNA processing, perhaps nuclear RNA export. Thus, nuclear retention of mutant Ataxin-1 may be an important toxic gain of function in SCA1 disease.
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Identification of a novel phosphorylation site in Ataxin-1.
Biochimica et biophysica acta, 2004Co-Authors: Cynthia A. Vierra-green, Huda Y. Zoghbi, Harry T Orr, Deborah A. FerringtonAbstract:Abstract Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disease resulting from an expanded CAG repeat in the SCA1 gene that leads to an expanded polyglutamine tract in the gene product. Previous studies have demonstrated that serine at site 776 is phosphorylated [E.S. Emiamian, M.D. Kaytor, L.A. Duvick, T. Zu, S.K. Tousey, H.Y. Zoghbi, H.B. Clark, H.T. Orr, Serine 776 of Ataxin-1 is critical for polyglutamine-induced disease in SCA1 transgenic mice, Neuron 38 (2003) 375-387.]. Studies of Ataxin-1 S776 and serine mutated to an alanine, A776, have also shown differential protein–protein interactions and reduced neurodegeneration [H.K. Chen, P. Fernandez-Funez, S.F. Acevedo, Y.C. Lam, M.D. Kaytor, M.H. Fernandez, A. Aitken, E.M. Skoulakis, H.T. Orr, J. Botas, H.Y. Zoghbi, Interaction of Akt_phosphorylated Ataxin-1 with 14-3-3 mediates neurodegeneration in spinocerebellar ataxia type 1.]. However, mutation of the site serine 776 to an alanine did not abolish all phosphorylation of the protein Ataxin-1, suggesting the presence of additional phosphorylation sites [E.S. Emiamian, M.D. Kaytor, L.A. Duvick, T. Zu, S.K. Tousey, H.Y. Zoghbi, H.B. Clark, H.T. Orr, Serine 776 of Ataxin-1 is critical for polyglutamine-induced disease in SCA1 transgenic mice, Neuron 38 (2003) 375-387.]. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and mutational analysis demonstrated a novel phosphorylation site at serine 239 of Ataxin-1.
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the spinocerebellar ataxia type 1 protein Ataxin 1 has rna binding activity that is inversely affected by the length of its polyglutamine tract
Human Molecular Genetics, 2001Co-Authors: Shinji Yue, Huda Y. Zoghbi, Heliane G Serra, Harry T OrrAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal dominant neurodegenerative disease caused by the expansion of a polyglutamine tract within the SCA1 product, Ataxin-1. Previously, using transgenic mice, it was demonstrated that in order for a mutant allele of Ataxin-1 to cause disease it must be transported to the nucleus of the neuron. Using an in vitro RNA-binding assay, we demonstrate that Ataxin-1 does bind RNA and that this binding diminishes as the length of its polyglutamine tract increases. These observations suggest that Ataxin-1 plays a role in RNA metabolism and that the expansion of the polyglutamine tract may alter this function.
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Nuclear Localization of the Spinocerebellar Ataxia Type 7 Protein, Ataxin-7
Human molecular genetics, 1999Co-Authors: Michael D Kaytor, Lisa A. Duvick, Pamela J. Skinner, Michael D. Koob, Laura P.w. Ranum, Harry T OrrAbstract:Spinocerebellar ataxia type 7 (SCA7) belongs to a group of neurological disorders caused by a CAG repeat expansion in the coding region of the associated gene. To gain insight into the pathogenesis of SCA7 and possible functions of Ataxin-7, we examined the subcellular localization of Ataxin-7 in transfected COS-1 cells using SCA7 cDNA clones with different CAG repeat tract lengths. In addition to a diffuse distribution throughout the nucleus, Ataxin-7 associated with the nuclear matrix and the nucleolus. The location of the putative SCA7 nuclear localization sequence (NLS) was confirmed by fusing an Ataxin-7 fragment with the normally cytoplasmic protein chicken muscle pyruvate kinase. Mutation of this NLS prevented protein from entering the nucleus. Thus, expanded Ataxin-7 may carry out its pathogenic effects in the nucleus by altering a matrix-associated nuclear structure and/or by disrupting nucleolar function.
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Mutation of the E6-AP Ubiquitin Ligase Reduces Nuclear Inclusion Frequency While Accelerating Polyglutamine-Induced Pathology in SCA1 Mice
Neuron, 1999Co-Authors: Christopher J Cummings, Harry T Orr, Eyal Reinstein, Yaling Sun, Barbara Antalffy, Yong-hui Jiang, Aaron Ciechanover, Arthur L. Beaudet, Huda Y. ZoghbiAbstract:Mutant Ataxin-1, the expanded polyglutamine protein causing spinocerebellar ataxia type 1 (SCA1), aggregates in ubiquitin-positive nuclear inclusions (NI) that alter proteasome distribution in affected SCA1 patient neurons. Here, we observed that Ataxin-1 is degraded by the ubiquitin-proteasome pathway. While Ataxin-1 [2Q] and mutant Ataxin-1 [92Q] are polyubiquitinated equally well in vitro, the mutant form is three times more resistant to degradation. Inhibiting proteasomal degradation promotes Ataxin-1 aggregation in transfected cells. And in mice, Purkinje cells that express mutant Ataxin-1 but not a ubiquitin-protein ligase have significantly fewer NIs. Nonetheless, the Purkinje cell pathology is markedly worse than that of SCA1 mice. Taken together, NIs are not necessary to induce neurodegeneration, but impaired proteasomal degradation of mutant Ataxin-1 may contribute to SCA1 pathogenesis.
Seongman Kang - One of the best experts on this subject based on the ideXlab platform.
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Molecular pathogenesis of spinocerebellar ataxia type 1 disease
Molecules and Cells, 2009Co-Authors: Seongman Kang, Sunghoi HongAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 is associated with an elongated polyglutamine tract in Ataxin-1, the SCA1 gene product. As summarized in this review, recent studies have clarified the molecular mechanisms of SCA1 pathogenesis and provided direction for future therapeutic approaches. The nucleus is the subcellular site where misfolded mutant Ataxin-1 acts to cause SCA1 disease in the cerebellum. The role of these nuclear aggregates is the subject of intensive study. Additional proteins have been identified, whose conformational alterations occurring through interactions with the polyglutamine tract itself or non-polyglutamine regions in Ataxin-1 are the cause of SCA-1 cytotoxicity. Therapeutic hope comes from the observations concerning the reduction of nuclear aggregation and alleviation of the pathogenic phenotype by the application of potent inhibitors and RNA interference.
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The ubiquitin-conjugating enzyme UbcH6 regulates the transcriptional repression activity of the SCA1 gene product Ataxin-1
Biochemical and biophysical research communications, 2008Co-Authors: Soyeon Lee, Sunghoi Hong, Seongman KangAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 is caused by expansion of the polyglutamine tract in the SCA1 gene product, Ataxin-1. We previously reported that the E2 ubiquitin-conjugating enzyme UbcH6 interacts with and ubiquitinates the Ataxin-1 proteins as an E2-substrate cognate pair in the ubiquitin-proteasome system. In the present study, we further investigated whether the function of Ataxin-1 is associated with UbcH6 and found that UbcH6 regulates the transcriptional repression activity of Ataxin-1. The overexpression of UbcH6 reduced the transcriptional repression activity of Ataxin-1. Interestingly, Ataxin-1(30Q) was more affected by the presence of UbcH6 than Ataxin-1(82Q), implying that the length of the polyglutamine tract in Ataxin-1 might be involved in determining the stability of Ataxin-1. The half-life of Ataxin-1(82Q) was longer than that of Ataxin-1(30Q) in the presence of UbcH6. shRNAs targeting UbcH6 enhanced the transcriptional repression activity of Ataxin-1. In addition, the overexpression of UbcH6 reduced the formation of Ataxin-1 aggregates. Our studies demonstrate that UbcH6 modulates the transcriptional repression activity of Ataxin-1 by modulating the degradation of Ataxin-1, suggesting that UbcH6 may have some therapeutic potential in the treatment of SCA1.
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UbcH6 interacts with and ubiquitinates the SCA1 gene product Ataxin-1.
Biochemical and biophysical research communications, 2008Co-Authors: Sunghoi Hong, Soyeon Lee, Ssang-goo Cho, Seongman KangAbstract:UbcH6 is a member of an evolutionally conserved subfamily of E2 ubiquitin-conjugating enzymes. In this study, we report that UbcH6 interacts with and ubiquitinates Ataxin-1, the spinocerebellar ataxia type 1 gene product. UbcH6 was identified as an Ataxin-1-interacting protein using a yeast two-hybrid screen. UbcH6 co-immunoprecipitates and co-localizes with the Ataxin-1 protein in the nucleus. Our binding assays showed that Ataxin-1 interacts with UbcH6 through its AXH domain. Interestingly, UbcH6 could ubiquitinate Ataxin-1 in the absence of an E3 ligase. The expression level of UbcH6 regulated the rate of Ataxin-1 degradation. This study demonstrates that UbcH6 and Ataxin-1 are E2-substrate cognate pairs in the ubiquitin-proteasome system.
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Proteasome function is inhibited by polyglutamine-expanded Ataxin-1, the SCA1 gene product.
Molecules and cells, 2005Co-Authors: Yongjae Park, Sung Jo Kim, Sunghoi Hong, Seongman KangAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder caused by expansion of the polyglutamine tract in the SCA1 gene product, Ataxin-1. Using d2EGFP, a short-lived enhanced green fluorescent protein, we investigated whether polyglutamine-expanded Ataxin-1 affects the function of the proteasome, a cellular multicatalytic protease that degrades most misfolded proteins and regulatory proteins. In Western blot analysis and immunofluorescence experiments, d2EGFP was less degraded in HEK 293T cells transfected with Ataxin-1(82Q) than in cells transfected with lacZ or empty vector controls. To test whether the stability of the d2EGFP protein was due to aggregation of Ataxin-1, we constructed a plasmid carrying Ataxin-1-Delta114, lacking the self-association region (SAR), and examined degradation of the d2EGFP. Both the level of Ataxin-1-Delta114 aggregates and the amount of d2EGFP were drastically reduced in cells containing Ataxin-1-Delta114. Furthermore, d2EGFP localization experiments showed that polyglutamine-expanded Ataxin-1 inhibited the general function of the proteasome activity. Taken together, these results demonstrate that polyglutamine-expanded Ataxin-1 decreases the activity of the proteasome, implying that a disturbance in the ubiquitin-proteasome pathway is directly involved in the development of spinocerebellar ataxia type1.
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USP7, a ubiquitin-specific protease, interacts with Ataxin-1, the SCA1 gene product.
Molecular and cellular neurosciences, 2002Co-Authors: Sunghoi Hong, Sung Jo Kim, Inho Choi, Seongman KangAbstract:Abstract Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 has been known to associate with elongated polyglutamine tract in Ataxin-1, the SCA1 gene product. Using the yeast two-hybrid system, we have found that USP7, a ubiquitin-specific protease, binds to Ataxin-1. Further experiments with deletion mutants indicated that the C-terminal region of Ataxin-1 was essential for the interaction. Liquid β-galactosidase assay and coimmunoprecipitation experiments revealed that the strength of the interaction between USP7 and Ataxin-1 is influenced by the length of the polyglutamine tract in the Ataxin-1; weaker interaction was observed in mutant Ataxin-1 with longer polyglutamine tract and USP7 was not recruited to the mutant Ataxin-1 aggregates in the Purkinje cells of SCA1 transgenic mice. Our results suggest that altered function of the ubiquitin system can be involved in the pathogenesis of spinocerebellar ataxia type 1.
Sunghoi Hong - One of the best experts on this subject based on the ideXlab platform.
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Molecular pathogenesis of spinocerebellar ataxia type 1 disease
Molecules and Cells, 2009Co-Authors: Seongman Kang, Sunghoi HongAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 is associated with an elongated polyglutamine tract in Ataxin-1, the SCA1 gene product. As summarized in this review, recent studies have clarified the molecular mechanisms of SCA1 pathogenesis and provided direction for future therapeutic approaches. The nucleus is the subcellular site where misfolded mutant Ataxin-1 acts to cause SCA1 disease in the cerebellum. The role of these nuclear aggregates is the subject of intensive study. Additional proteins have been identified, whose conformational alterations occurring through interactions with the polyglutamine tract itself or non-polyglutamine regions in Ataxin-1 are the cause of SCA-1 cytotoxicity. Therapeutic hope comes from the observations concerning the reduction of nuclear aggregation and alleviation of the pathogenic phenotype by the application of potent inhibitors and RNA interference.
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The ubiquitin-conjugating enzyme UbcH6 regulates the transcriptional repression activity of the SCA1 gene product Ataxin-1
Biochemical and biophysical research communications, 2008Co-Authors: Soyeon Lee, Sunghoi Hong, Seongman KangAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 is caused by expansion of the polyglutamine tract in the SCA1 gene product, Ataxin-1. We previously reported that the E2 ubiquitin-conjugating enzyme UbcH6 interacts with and ubiquitinates the Ataxin-1 proteins as an E2-substrate cognate pair in the ubiquitin-proteasome system. In the present study, we further investigated whether the function of Ataxin-1 is associated with UbcH6 and found that UbcH6 regulates the transcriptional repression activity of Ataxin-1. The overexpression of UbcH6 reduced the transcriptional repression activity of Ataxin-1. Interestingly, Ataxin-1(30Q) was more affected by the presence of UbcH6 than Ataxin-1(82Q), implying that the length of the polyglutamine tract in Ataxin-1 might be involved in determining the stability of Ataxin-1. The half-life of Ataxin-1(82Q) was longer than that of Ataxin-1(30Q) in the presence of UbcH6. shRNAs targeting UbcH6 enhanced the transcriptional repression activity of Ataxin-1. In addition, the overexpression of UbcH6 reduced the formation of Ataxin-1 aggregates. Our studies demonstrate that UbcH6 modulates the transcriptional repression activity of Ataxin-1 by modulating the degradation of Ataxin-1, suggesting that UbcH6 may have some therapeutic potential in the treatment of SCA1.
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UbcH6 interacts with and ubiquitinates the SCA1 gene product Ataxin-1.
Biochemical and biophysical research communications, 2008Co-Authors: Sunghoi Hong, Soyeon Lee, Ssang-goo Cho, Seongman KangAbstract:UbcH6 is a member of an evolutionally conserved subfamily of E2 ubiquitin-conjugating enzymes. In this study, we report that UbcH6 interacts with and ubiquitinates Ataxin-1, the spinocerebellar ataxia type 1 gene product. UbcH6 was identified as an Ataxin-1-interacting protein using a yeast two-hybrid screen. UbcH6 co-immunoprecipitates and co-localizes with the Ataxin-1 protein in the nucleus. Our binding assays showed that Ataxin-1 interacts with UbcH6 through its AXH domain. Interestingly, UbcH6 could ubiquitinate Ataxin-1 in the absence of an E3 ligase. The expression level of UbcH6 regulated the rate of Ataxin-1 degradation. This study demonstrates that UbcH6 and Ataxin-1 are E2-substrate cognate pairs in the ubiquitin-proteasome system.
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Proteasome function is inhibited by polyglutamine-expanded Ataxin-1, the SCA1 gene product.
Molecules and cells, 2005Co-Authors: Yongjae Park, Sung Jo Kim, Sunghoi Hong, Seongman KangAbstract:Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder caused by expansion of the polyglutamine tract in the SCA1 gene product, Ataxin-1. Using d2EGFP, a short-lived enhanced green fluorescent protein, we investigated whether polyglutamine-expanded Ataxin-1 affects the function of the proteasome, a cellular multicatalytic protease that degrades most misfolded proteins and regulatory proteins. In Western blot analysis and immunofluorescence experiments, d2EGFP was less degraded in HEK 293T cells transfected with Ataxin-1(82Q) than in cells transfected with lacZ or empty vector controls. To test whether the stability of the d2EGFP protein was due to aggregation of Ataxin-1, we constructed a plasmid carrying Ataxin-1-Delta114, lacking the self-association region (SAR), and examined degradation of the d2EGFP. Both the level of Ataxin-1-Delta114 aggregates and the amount of d2EGFP were drastically reduced in cells containing Ataxin-1-Delta114. Furthermore, d2EGFP localization experiments showed that polyglutamine-expanded Ataxin-1 inhibited the general function of the proteasome activity. Taken together, these results demonstrate that polyglutamine-expanded Ataxin-1 decreases the activity of the proteasome, implying that a disturbance in the ubiquitin-proteasome pathway is directly involved in the development of spinocerebellar ataxia type1.
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USP7, a ubiquitin-specific protease, interacts with Ataxin-1, the SCA1 gene product.
Molecular and cellular neurosciences, 2002Co-Authors: Sunghoi Hong, Sung Jo Kim, Inho Choi, Seongman KangAbstract:Abstract Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 has been known to associate with elongated polyglutamine tract in Ataxin-1, the SCA1 gene product. Using the yeast two-hybrid system, we have found that USP7, a ubiquitin-specific protease, binds to Ataxin-1. Further experiments with deletion mutants indicated that the C-terminal region of Ataxin-1 was essential for the interaction. Liquid β-galactosidase assay and coimmunoprecipitation experiments revealed that the strength of the interaction between USP7 and Ataxin-1 is influenced by the length of the polyglutamine tract in the Ataxin-1; weaker interaction was observed in mutant Ataxin-1 with longer polyglutamine tract and USP7 was not recruited to the mutant Ataxin-1 aggregates in the Purkinje cells of SCA1 transgenic mice. Our results suggest that altered function of the ubiquitin system can be involved in the pathogenesis of spinocerebellar ataxia type 1.
Henry L Paulson - One of the best experts on this subject based on the ideXlab platform.
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differential toxicity of Ataxin 3 isoforms in drosophila models of spinocerebellar ataxia type 3
Neurobiology of Disease, 2019Co-Authors: Sean L Johnson, Henry L Paulson, Jessica R. Blount, Wei-ling Tsou, Kozeta Libohova, Bedri Ranxhi, Sokol V. TodiAbstract:Abstract The most commonly inherited dominant ataxia, Spinocerebellar Ataxia Type 3 (SCA3), is caused by a CAG repeat expansion that encodes an abnormally long polyglutamine (polyQ) repeat in the disease protein Ataxin-3, a deubiquitinase. Two major full-length isoforms of Ataxin-3 exist, both of which contain the same N-terminal portion and polyQ repeat, but differ in their C-termini; one (denoted here as isoform 1) contains a motif that binds Ataxin-3's substrate, ubiquitin, whereas the other (denoted here as isoform 2) has a hydrophobic tail. Most SCA3 studies have focused on isoform 1, the predominant version in mammalian brain, yet both isoforms are present in brain and a better understanding of their relative pathogenicity in vivo is needed. We took advantage of the fruit fly, Drosophila melanogaster to model SCA3 and to examine the toxicity of each Ataxin-3 isoform. Our assays reveal isoform 1 to be markedly more toxic than isoform 2 in all fly tissues. Reduced toxicity from isoform 2 is due to much lower protein levels as a result of its expedited degradation. Additional studies indicate that isoform 1 is more aggregation-prone than isoform 2 and that the C-terminus of isoform 2 is critical for its enhanced proteasomal degradation. According to our results, although both full-length, pathogenic Ataxin-3 isoforms are toxic, isoform 1 is likely the primary contributor to SCA3 due to its presence at higher levels. Isoform 2, as a result of rapid degradation that is dictated by its tail, is unlikely to be a key player in this disease. Our findings provide new insight into the biology of this ataxia and the cellular processing of the underlying disease protein.
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valosin containing protein vcp p97 is an activator of wild type Ataxin 3
PLOS ONE, 2012Co-Authors: Mario N Laco, Luisa Cortes, Henry L Paulson, Sue M Travis, Cristina A RegoAbstract: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.
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Valosin-Containing Protein (VCP/p97) Is an Activator of Wild-Type Ataxin-3
PLOS ONE, 2012Co-Authors: Mario N Laco, Luisa Cortes, Henry L Paulson, Sue M Travis, A. Cristina RegoAbstract: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.
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activity and cellular functions of the deubiquitinating enzyme and polyglutamine disease protein Ataxin 3 are regulated by ubiquitination at lysine 117
Journal of Biological Chemistry, 2010Co-Authors: Sokol V. Todi, Jessica R. Blount, Annalisa Pastore, Matthew K Scaglione, Venkatesha Basrur, Kevin P Conlon, Kojo S J Elenitobajohnson, Henry L PaulsonAbstract:Deubiquitinating enzymes (DUbs) play important roles in many ubiquitin-dependent pathways, yet how DUbs themselves are regulated is not well understood. Here, we provide insight into the mechanism by which ubiquitination directly enhances the activity of Ataxin-3, a DUb implicated in protein quality control and the disease protein in the polyglutamine neurodegenerative disorder, Spinocerebellar Ataxia Type 3. We identify Lys-117, which resides near the catalytic triad, as the primary site of ubiquitination in wild type and pathogenic Ataxin-3. Further studies indicate that ubiquitin-dependent activation of Ataxin-3 at Lys-117 is important for its ability to reduce high molecular weight ubiquitinated species in cells. Ubiquitination at Lys-117 also facilitates the ability of Ataxin-3 to induce aggresome formation in cells. Finally, structure-function studies support a model of activation whereby ubiquitination at Lys-117 enhances Ataxin-3 activity independent of the known ubiquitin-binding sites in Ataxin-3, most likely through a direct conformational change in or near the catalytic domain.