The Experts below are selected from a list of 4437 Experts worldwide ranked by ideXlab platform
Harry T Orr - One of the best experts on this subject based on the ideXlab platform.
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The Ataxin-1 interactome reveals direct connection with multiple disrupted nuclear transport pathways
'Springer Science and Business Media LLC', 2020Co-Authors: Sunyuan Zhang, Nicholas A. Williamson, Lisa Duvick, Austin Korlin-downs, Praseuth Yang, Harry T Orr, David A Jans, Alexander Lee, Yee-foong Mok, Marie A BogoyevitchAbstract:Patients with spinocerebellar ataxia type 1 express Ataxin-1 with an extended polyglutamine (polyQ) tract that forms distinctive nuclear bodies. Here, the authors characterize the cellular pathways affected by polyQ-Ataxin-1, showing that it disrupts multiple nuclear transport processes
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a native interactor scaffolds and stabilizes toxic Ataxin 1 oligomers in sca1
eLife, 2015Co-Authors: Cristian A Lasagnareeves, Harry T Orr, Maxime W C Rousseaux, Marcos J Guerreromunoz, Jeehye Park, Paymaan Jafarnejad, Ronald Richman, Urmi Sengupta, Alexandra Litvinchuk, Rakez KayedAbstract:Recent studies indicate that soluble oligomers drive pathogenesis in several neurodegenerative proteinopathies, including Alzheimer and Parkinson disease. Curiously, the same conformational antibody recognizes different disease-related oligomers, despite the variations in clinical presentation and brain regions affected, suggesting that the oligomer structure might be responsible for toxicity. We investigated whether polyglutamine-expanded Ataxin-1, the protein that underlies spinocerebellar ataxia type 1, forms toxic oligomers and, if so, what underlies their toxicity. We found that mutant ATXN1 does form oligomers and that oligomer levels correlate with disease progression in the Atxn1(154Q/+) mice. Moreover, oligomeric toxicity, stabilization and seeding require interaction with Capicua, which is expressed at greater ratios with respect to ATXN1 in the cerebellum than in less vulnerable brain regions. Thus, specific interactors, not merely oligomeric structure, drive pathogenesis and contribute to regional vulnerability. Identifying interactors that stabilize toxic oligomeric complexes could answer longstanding questions about the pathogenesis of other proteinopathies.
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a native interactor scaffolds and stabilizes toxic Ataxin 1 oligomers in sca1
eLife, 2015Co-Authors: Cristian A Lasagnareeves, Harry T Orr, Maxime W C Rousseaux, Marcos J Guerreromunoz, Jeehye Park, Paymaan Jafarnejad, Ronald Richman, Urmi Sengupta, Alexandra Litvinchuk, Rakez KayedAbstract:Spinocerebellar ataxia type 1 (SCA1) is a progressive neurodegenerative disease in which damage to the brain regions that control movement results in the gradual loss of coordination and motor skills. The disease is a caused by a mutation in the gene that codes for a protein called Ataxin-1. In healthy individuals this protein contains up to 39 copies of an amino acid called glutamine. However, the mutant gene can encode for 40 or more copies of glutamine, which results in a longer-than-usual Ataxin-1 protein with toxic properties. Within the brain, some of the toxic Ataxin-1 proteins form insoluble deposits, while the rest remain soluble. At first it was assumed that the insoluble deposits were responsible for the neurodegeneration seen in SCA1. However, closer examination revealed that these deposits form mainly in brain regions that do not degenerate, which suggests that they might instead have a protective role. This is consistent with evidence from research into other brain disorders, including Alzheimer's disease, which suggests that the soluble form of the toxic proteins might be causing these diseases. Lasagna-Reeves et al. now provide the first direct evidence that the soluble form of the toxic Ataxin-1 proteins are indeed harmful in a mouse model of SCA1. Experiments reveal that these soluble proteins accumulate in the brain regions that undergo degeneration in SCA1, such as the cerebellum, but not in those regions that remain intact. Moreover, the motor skills and coordination of the mice get worse as the level of soluble toxic Ataxin-1 increases. Lasagna-Reeves et al. go on to show that a protein called capicua stabilizes the toxic Ataxin-1 proteins, which keeps them from forming insoluble deposits. Since capicua is particularly abundant in the cerebellum, this could explain the high levels of toxic Ataxin-1 in this region and why it is vulnerable to degeneration. Future experiments are needed to investigate whether proteins equivalent to capicua might play a similar role in stabilizing toxic proteins in Alzheimer's, Parkinson's and Huntington's diseases, and whether preventing this stabilization could have therapeutic potential.
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regulation of Ataxin 1 phosphorylation and its impact on biology
Methods of Molecular Biology, 2013Co-Authors: Sarita Lagalwar, Harry T OrrAbstract:Ataxin-1 protein expression is found in the cytoplasm and nucleus of Purkinje cells, the primary site of spinocerebellar ataxia type 1 (SCA1). Phosphorylation at S776 occurs in the cytoplasm and stabilizes the protein through interaction with 14-3-3, allowing it to translocate into the nucleus where disease is initiated. Phosphorylation and stabilization are enhanced when the polyglutamine expansion is present. In this chapter, we present a model of neurodegeneration in SCA1 initiated through phosphorylation at S776 by cAMP-dependent protein kinase (PKA) and enhanced by the presence of the polyglutamine expansion. The biological methods used to uncover SCA1 pathogenesis and phosphorylation at S776 are described.
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sca1 phosphorylation a regulator of Ataxin 1 function and pathogenesis
Progress in Neurobiology, 2012Co-Authors: Harry T OrrAbstract:Spinocerebellar ataxia type 1 (SCA1) is one an intriguing set of nine neurodegenerative diseases caused by the expansion of a unstable trinucleotide CAG repeat where the repeat is located within the coding of the affected gene, i.e. the polyglutamine (polyQ) diseases. A gain-of-function mechanism for toxicity in SCA1, like the other polyQ diseases, is thought to have a major role in pathogenesis. Yet, the specific nature of this gain-of-function is a matter of considerable discussion. An issue concerns whether toxicity stems from the native or normal function of the affected protein versus a novel function induced by polyQ expansion. For SCA1 considerable evidence is accumulating that pathology is mediated by a polyQ-induced exaggeration of a native function of the host protein Ataxin-1 (ATXN1) and that phosphorylation of S776 regulates its interaction with other cellular protein and thereby function. In addition, this posttranslational modification modulates toxicity of ATXN1 with an expanded polyglutamine.
Huda Y. Zoghbi - One of the best experts on this subject based on the ideXlab platform.
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structural basis of protein complex formation and reconfiguration by polyglutamine disease protein Ataxin 1 and capicua
Genes & Development, 2013Co-Authors: Eunji Kim, Huda Y. Zoghbi, Jijoon SongAbstract:Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by polyglutamine expansion in Ataxin-1 (ATXN1). ATXN1 binds to the transcriptional repressor Capicua (CIC), and the interaction plays a critical role in SCA1 pathogenesis whereby reducing CIC levels rescues SCA1-like phenotypes in a mouse model. The ATXN1/HBP1 (AXH) domain of ATXN1 mediates its homodimerization as well as the interaction with CIC. Here, we present the crystal structure of ATXN1's AXH domain bound to CIC and show that the binding pocket of the AXH domain to CIC overlaps with the homodimerization pocket of the AXH domain. Thus, the binding to CIC disrupts the homodimerization of ATXN1. Furthermore, the binding of CIC reconfigures the complex to allow another form of dimerization mediated by CIC, showing the intricacy of protein complex formation and reconfiguration by ATXN1 and CIC. Identifying the surfaces mediating the interactions between CIC and ATXN1 reveals a critical role for CIC in the reconfiguration of the AXH dimers and might provide insight into ways to target the ATXN1/CIC interactions to modulate SCA1 pathogenesis.
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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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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, 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.
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duplication of atxn1l suppresses sca1 neuropathology by decreasing incorporation of polyglutamine expanded Ataxin 1 into native complexes
Nature Genetics, 2007Co-Authors: Aaron B Bowman, Harry T Orr, Hung Kai Chen, John D Fryer, Paymaan Jafarnejad, Ronald Richman, Yung C Lam, Rodney C Samaco, Juliette J Kahle, Huda Y. ZoghbiAbstract:Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease caused by expansion of a glutamine tract in Ataxin-1 (ATXN1). SCA1 pathogenesis studies support a model in which the expanded glutamine tract causes toxicity by modulating the normal activities of ATXN1. To explore native interactions that modify the toxicity of ATXN1, we generated a targeted duplication of the mouse Ataxin-1-like (Atxn1l, also known as Boat) locus, a highly conserved paralog of SCA1, and tested the role of this protein in SCA1 pathology. Using a knock-in mouse model of SCA1 that recapitulates the selective neurodegeneration seen in affected individuals, we found that elevated Atxn1l levels suppress neuropathology by displacing mutant Atxn1 from its native complex with Capicua (CIC). Our results provide genetic evidence that the selective neuropathology of SCA1 arises from modulation of a core functional activity of ATXN1, and they underscore the importance of studying the paralogs of genes mutated in neurodegenerative diseases to gain insight into mechanisms of pathogenesis.
Seongman Kang - One of the best experts on this subject based on the ideXlab platform.
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Ataxin 1 regulates epithelial mesenchymal transition of cervical cancer cells
Oncotarget, 2017Co-Authors: Aram Kang, Seongman KangAbstract:// A-Ram Kang 1 , Hyoung-Tae An 1 , Jesang Ko 1 , Seongman Kang 1 1 Division of Life Sciences, College of Life Sciences and Biotechnology, Korea University, Seoul 02841, Korea Correspondence to: Seongman Kang, email: skang@korea.ac.kr Keywords: ATXN1, cervical cancer, epithelial–mesenchymal transition, notch intracellular domain Received: October 31, 2016 Accepted: December 21, 2016 Published: February 14, 2017 ABSTRACT The mutant form of the protein Ataxin-1 (ATXN1) causes the neurodegenerative disease spinocerebellar ataxia type-1. Recently, ATXN1 was reported to enhance E-cadherin expression in the breast cancer cell line MCF-7, suggesting a potential association between ATXN1 and cancer development. In the present study, we discovered a novel mechanism through which ATXN1 regulates the epithelial–mesenchymal transition (EMT) of cancer cells. Hypoxia-induced upregulation of the Notch intracellular domain expression decreased ATXN1 expression via MDM2-associated ubiquitination and degradation. In cervical cancer cells, ATXN1 knockdown induced EMT by directly regulating Snail expression, leading to matrix metalloproteinase activation and the promotion of cell migration and invasion. These findings provide insights into a novel mechanism of tumorigenesis and will facilitate the development of new and more effective therapies for cancer.
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a key lysine residue in the axh domain of Ataxin 1 is essential for its ubiquitylation
Biochimica et Biophysica Acta, 2015Co-Authors: Aram Kang, Sunghoi Hong, Soyeon Lee, Si Hoon Park, Doyoung Choi, Kwang Pyo Kim, Hyun Kyu Song, Seongman KangAbstract:Spinocerebellar ataxia type 1 (SCA1), an autosomal-dominant neurodegenerative disorder, is caused by expansion of the polyglutamine tract within Ataxin-1 (ATXN1). The AXH domain of ATXN1 can mediate neurodegeneration through its interaction with other proteins. We have previously showed that the ubiquitin-conjugating enzyme UbcH6 modulates the transcriptional repression activity of ATXN1 through ubiquitylation. In the present study, we sought to identify sites in the AXH domain that are ubiquitylated by UbcH6. Systematic replacement of each lysine residue in the AXH domain revealed that the lysine at 589 (K589) of ATXN1 is essential for its ubiquitylation by UbcH6. Mass spectrometry studies further confirmed the ubiquitylation site. Interestingly, protein aggregation was significantly enhanced in mutant AXH K589R, implying that the aggregation is strongly associated with the level of ATXN1 expression. Our study may suggest a therapeutic potential of UbcH6 in the treatment of SCA1.
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Ataxin 1 occupies the promoter region of e cadherin in vivo and activates ctbp2 repressed promoter
Biochimica et Biophysica Acta, 2011Co-Authors: Soyeon Lee, Sunghoi Hong, Sungsu Kim, Seongman KangAbstract:Ataxin-1 is a polyglutamine protein of unknown function that is encoded by the ATXN1 gene in humans. To gain insight into the function of Ataxin-1, we sought to identify proteins that interact with Ataxin-1 through yeast two-hybrid screening. In this study, transcriptional corepressor CtBP2 was identified as a protein that interacted with Ataxin-1. CtBP2 and Ataxin-1 colocalized in the nucleus of mammalian cells. Since the E-cadherin promoter is a target of CtBP-mediated repression, the relationship between Ataxin-1 and the E-cadherin promoter was investigated. Chromatin immunoprecipitation assays showed that CtBP2 and Ataxin-1 were recruited to the E-cadherin promoter in mammalian cells. Luciferase assays using E-cadherin promoter reporter constructs revealed that the luciferase activity was enhanced as the level of Ataxin-1 protein expression increased. CtBP2 overexpression decreased E-cadherin expression, but expression of Ataxin-1 inversely increased the mRNA and protein levels of endogenous E-cadherin. Interestingly, siRNA experiments showed that the transcriptional activation of Ataxin-1 was associated with the presence of CtBP2. This study demonstrates that Ataxin-1 occupies the promoter region of E-cadherin in vivo and that Ataxin-1 activates the promoter in a CtBP2-mediated transcriptional regulation manner. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
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sumo 1 interacts with mutant Ataxin 1 and colocalizes to its aggregates in purkinje cells of sca1 transgenic mice
Archives Italiennes De Biologie, 2010Co-Authors: Seongman Kang, Sunghoi HongAbstract:Spinocerebellar ataxia type 1 (SCA1) is one of several progressive neurodegenerative diseases caused by the expanded polyglutamine tract in Ataxin-1, the SCA1 gene product. In SCA1 patients and transgenic mice, the affected neuronal cells contain a large ubiquitin-positive aggregate which is derived from the mutant Ataxin-1. Small ubiquitin-like modifier-1 (SUMO-1) is one of the most intriguing ubiquitin-like modifiers being conjugated to target proteins and modulating a number of cellular pathways. Recent findings that the aggregates from several neurodegenerative diseases are SUMO-1-positive prompted us to examine the implication of SUMO-1 in SCA1 pathogenesis. In our yeast two-hybrid experiments using mutant Ataxin-1 as bait, we identified a SUMO-1 protein that directly binds to Ataxin-1 protein. Interestingly, we found that most of the mutant Ataxin-1-derived aggregates were SUMO-1-positive both in Purkinje cells of SCA1 transgenic mice and in HeLa cells, but not wild-type Ataxin-1 in HeLa cells. In addition, the aggregates in Purkinje cells of SCA1 transgenic mice were positive against both anti-SUMO-1 and anti-ubiquitin antibodies. These results show that the SUMO-1 protein interacts with mutant Ataxin-1 and colocalizes with its aggregates which suggests the involvement of the SUMO-1 system in the pathogenesis of SCA1 disease.
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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.
Annalisa Pastore - One of the best experts on this subject based on the ideXlab platform.
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chemical shift assignment of the Ataxin 1 axh domain in complex with a cic ligand peptide
Biomolecular Nmr Assignments, 2014Co-Authors: Cesira De Chiara, Rajesh P. Menon, Geoff Kelly, John E Mccormick, Annalisa PastoreAbstract:Ataxin-1 is the protein responsible for the genetically-inherited neurodegenerative disease spinocerebellar ataxia type-1 linked to the expansion of a polyglutamine tract within the protein sequence. The AXH domain of Ataxin-1 is essential for the protein to function as a transcriptional co-repressor and mediates the majority of the interactions of Ataxin-1 with cellular partners, mainly transcriptional regulators. One of the best characterized Ataxin-1 functional partners is Capicua (CIC), a transcriptional repressor involved in signalling pathways that regulate mammalian development, tumorigenesis and, through the interaction with Ataxin-1, also neurodegeneration. Complex formation of Ataxin-1 with CIC is important both for the function of the wild-type protein and for pathogenesis as transcriptional disregulation is observed since the early stages of the development of the disease. Here we report the 1H, 13C and 15N backbone and side-chain chemical shift assignments of the human Ataxin-1 AXH domain in complex with a CIC ligand-peptide.
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kaleidoscopic protein protein interactions in the life and death of Ataxin 1 new strategies against protein aggregation
Trends in Neurosciences, 2014Co-Authors: Cesira De Chiara, Annalisa PastoreAbstract:Understanding how proteins protect themselves from aberrant aggregation is of primary interest for understanding basic biology, protein biochemistry, and human disease. We discuss the paradigmatic example of Ataxin-1 (Atx1), the protein responsible for neurodegenerative spinocerebellar ataxia type 1 (SCA1). This disease is part of the increasing family of pathologies caused by protein aggregation and misfolding. We discuss the importance of protein–protein interactions not only in the nonpathological function of Atx1 but also in protecting the protein from aggregation and misfolding. The lessons learned from Atx1 may lead to a more general understanding of the cell's protective strategies against aggregation. The obtained knowledge may suggest a new perspective for designing specific therapeutic strategies for the cure of misfolding diseases.
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mapping the self association domains of Ataxin 1 identification of novel non overlapping motifs
PeerJ, 2014Co-Authors: Rajesh P. Menon, Daniel Soong, Cesira De Chiara, Mark R. Holt, Narayana Anilkumar, Annalisa Pastore, John E MccormickAbstract:The neurodegenerative disease spinocerebellar ataxia type 1 (SCA1) is caused by aggregation and misfolding of the Ataxin-1 protein. While the pathology correlates with mutations that lead to expansion of a polyglutamine tract in the protein, other regions contribute to the aggregation process as also non-expanded Ataxin-1 is intrinsically aggregation-prone and forms nuclear foci in cell. Here, we have used a combined approach based on FRET analysis, confocal microscopy and in vitro techniques to map aggregation-prone regions other than polyglutamine and to establish the importance of dimerization in self-association/foci formation. Identification of aggregation-prone regions other than polyglutamine could greatly help the development of SCA1 treatment more specific than that based on targeting the low complexity polyglutamine region.
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protein protein interactions as a strategy towards protein specific drug design the example of Ataxin 1
PLOS ONE, 2013Co-Authors: Cesira De Chiara, Rajesh P. Menon, Geoff Kelly, Annalisa PastoreAbstract:A main challenge for structural biologists is to understand the mechanisms that discriminate between molecular interactions and determine function. Here, we show how partner recognition of the AXH domain of the transcriptional co-regulator Ataxin-1 is fine-tuned by a subtle balance between self- and hetero-associations. Ataxin-1 is the protein responsible for the hereditary spinocerebellar ataxia type 1, a disease linked to protein aggregation and transcriptional dysregulation. Expansion of a polyglutamine tract is essential for Ataxin-1 aggregation, but the sequence-wise distant AXH domain plays an important aggravating role in the process. The AXH domain is also a key element for non-aberrant function as it intervenes in interactions with multiple protein partners. Previous data have shown that AXH is dimeric in solution and forms a dimer of dimers when crystallized. By solving the structure of a complex of AXH with a peptide from the interacting transcriptional repressor CIC, we show that the dimer interface of AXH is displaced by the new interaction and that, when blocked by the CIC peptide AXH aggregation and misfolding are impaired. This is a unique example in which palindromic self- and hetero-interactions within a sequence with chameleon properties discriminate the partner. We propose a drug design strategy for the treatment of SCA1 that is based on the information gained from the AXH/CIC complex.
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self assembly and conformational heterogeneity of the axh domain of Ataxin 1 an unusual example of a chameleon fold
Biophysical Journal, 2013Co-Authors: Cesira De Chiara, Yu Wai Chen, Martin Rees, Raj P Menon, Kris Pauwels, Ceri Lawrence, Petr V Konarev, Dmitri I Svergun, Stephen R Martin, Annalisa PastoreAbstract:Ataxin-1 is a human protein responsible for spinocerebellar ataxia type 1, a hereditary disease associated with protein aggregation and misfolding. Essential for Ataxin-1 aggregation is the anomalous expansion of a polyglutamine tract near the protein N-terminus, but the sequence-wise distant AXH domain modulates and contributes to the process. The AXH domain is also involved in the nonpathologic functions of the protein, including a variety of intermolecular interactions with other cellular partners. The domain forms a globular dimer in solution and displays a dimer of dimers arrangement in the crystal asymmetric unit. Here, we have characterized the domain further by studying its behavior in the crystal and in solution. We solved two new structures of the domain crystallized under different conditions that confirm an inherent plasticity of the AXH fold. In solution, the domain is present as a complex equilibrium mixture of monomeric, dimeric, and higher molecular weight species. This behavior, together with the tendency of the AXH fold to be trapped in local conformations, and the multiplicity of protomer interfaces, makes the AXH domain an unusual example of a chameleon protein whose properties bear potential relevance for the aggregation properties of Ataxin-1 and thus for disease.
Sunghoi Hong - One of the best experts on this subject based on the ideXlab platform.
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a key lysine residue in the axh domain of Ataxin 1 is essential for its ubiquitylation
Biochimica et Biophysica Acta, 2015Co-Authors: Aram Kang, Sunghoi Hong, Soyeon Lee, Si Hoon Park, Doyoung Choi, Kwang Pyo Kim, Hyun Kyu Song, Seongman KangAbstract:Spinocerebellar ataxia type 1 (SCA1), an autosomal-dominant neurodegenerative disorder, is caused by expansion of the polyglutamine tract within Ataxin-1 (ATXN1). The AXH domain of ATXN1 can mediate neurodegeneration through its interaction with other proteins. We have previously showed that the ubiquitin-conjugating enzyme UbcH6 modulates the transcriptional repression activity of ATXN1 through ubiquitylation. In the present study, we sought to identify sites in the AXH domain that are ubiquitylated by UbcH6. Systematic replacement of each lysine residue in the AXH domain revealed that the lysine at 589 (K589) of ATXN1 is essential for its ubiquitylation by UbcH6. Mass spectrometry studies further confirmed the ubiquitylation site. Interestingly, protein aggregation was significantly enhanced in mutant AXH K589R, implying that the aggregation is strongly associated with the level of ATXN1 expression. Our study may suggest a therapeutic potential of UbcH6 in the treatment of SCA1.
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Ataxin 1 occupies the promoter region of e cadherin in vivo and activates ctbp2 repressed promoter
Biochimica et Biophysica Acta, 2011Co-Authors: Soyeon Lee, Sunghoi Hong, Sungsu Kim, Seongman KangAbstract:Ataxin-1 is a polyglutamine protein of unknown function that is encoded by the ATXN1 gene in humans. To gain insight into the function of Ataxin-1, we sought to identify proteins that interact with Ataxin-1 through yeast two-hybrid screening. In this study, transcriptional corepressor CtBP2 was identified as a protein that interacted with Ataxin-1. CtBP2 and Ataxin-1 colocalized in the nucleus of mammalian cells. Since the E-cadherin promoter is a target of CtBP-mediated repression, the relationship between Ataxin-1 and the E-cadherin promoter was investigated. Chromatin immunoprecipitation assays showed that CtBP2 and Ataxin-1 were recruited to the E-cadherin promoter in mammalian cells. Luciferase assays using E-cadherin promoter reporter constructs revealed that the luciferase activity was enhanced as the level of Ataxin-1 protein expression increased. CtBP2 overexpression decreased E-cadherin expression, but expression of Ataxin-1 inversely increased the mRNA and protein levels of endogenous E-cadherin. Interestingly, siRNA experiments showed that the transcriptional activation of Ataxin-1 was associated with the presence of CtBP2. This study demonstrates that Ataxin-1 occupies the promoter region of E-cadherin in vivo and that Ataxin-1 activates the promoter in a CtBP2-mediated transcriptional regulation manner. This article is part of a Special Issue entitled: 11th European Symposium on Calcium.
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sumo 1 interacts with mutant Ataxin 1 and colocalizes to its aggregates in purkinje cells of sca1 transgenic mice
Archives Italiennes De Biologie, 2010Co-Authors: Seongman Kang, Sunghoi HongAbstract:Spinocerebellar ataxia type 1 (SCA1) is one of several progressive neurodegenerative diseases caused by the expanded polyglutamine tract in Ataxin-1, the SCA1 gene product. In SCA1 patients and transgenic mice, the affected neuronal cells contain a large ubiquitin-positive aggregate which is derived from the mutant Ataxin-1. Small ubiquitin-like modifier-1 (SUMO-1) is one of the most intriguing ubiquitin-like modifiers being conjugated to target proteins and modulating a number of cellular pathways. Recent findings that the aggregates from several neurodegenerative diseases are SUMO-1-positive prompted us to examine the implication of SUMO-1 in SCA1 pathogenesis. In our yeast two-hybrid experiments using mutant Ataxin-1 as bait, we identified a SUMO-1 protein that directly binds to Ataxin-1 protein. Interestingly, we found that most of the mutant Ataxin-1-derived aggregates were SUMO-1-positive both in Purkinje cells of SCA1 transgenic mice and in HeLa cells, but not wild-type Ataxin-1 in HeLa cells. In addition, the aggregates in Purkinje cells of SCA1 transgenic mice were positive against both anti-SUMO-1 and anti-ubiquitin antibodies. These results show that the SUMO-1 protein interacts with mutant Ataxin-1 and colocalizes with its aggregates which suggests the involvement of the SUMO-1 system in the pathogenesis of SCA1 disease.
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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.