title: The Toxic Effects of Pathogenic Ataxin-3 Variants in a Yeast Cellular Model.
abstract: Ataxin-3 (AT3) is a deubiquitinating enzyme that triggers an inherited neurodegenerative disorder, spinocerebellar ataxia type 3, when its polyglutamine (polyQ) stretch close to the C-terminus exceeds a critical length. AT3 variants carrying the expanded polyQ are prone to associate with each other into amyloid toxic aggregates, which are responsible for neuronal death with ensuing neurodegeneration. We employed Saccharomyces cerevisiae as a eukaryotic cellular model to better clarify the mechanism by which AT3 triggers the disease. We expressed three variants: one normal (Q26), one expanded (Q85) and one truncated for a region lying from the beginning of its polyQ stretch to the end of the protein (291Δ). We found that the expression of the expanded form caused reduction in viability, accumulation of reactive oxygen species, imbalance of the antioxidant defense system and loss in cell membrane integrity, leading to necrotic death. The truncated variant also exerted a qualitatively similar, albeit milder, effect on cell growth and cytotoxicity, which points to the involvement of also non-polyQ regions in cytotoxicity. Guanidine hydrochloride, a well-known inhibitor of the chaperone Hsp104, almost completely restored wild-type survival rate of both 291Δ- and Q85-expressing strains. This suggests that AT3 aggregation and toxicity is mediated by prion forms of yeast proteins, as this chaperone plays a key role in their propagation.
authors.affiliation: Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy.
authors.forename: Marcella
authors.initials: M
authors.lastname: Bonanomi
authors.affiliation: Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy.
authors.forename: Cristina
authors.initials: C
authors.lastname: Visentin
authors.affiliation: Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy.
authors.forename: Gaetano
authors.initials: G
authors.lastname: Invernizzi
authors.affiliation: Department of Biotechnologies and Biosciences, University of Milano-Bicocca, Milan, Italy; Milan Center of Neuroscience (NeuroMI), Milan, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Tortora
authors.affiliation: Milan Center of Neuroscience (NeuroMI), Milan, Italy; Department of Statistics and Quantitative Methods, University of Milano-Bicocca, Milan, Italy.
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: Regonesi
mesh_terms: D000975:Antioxidants / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D000067699:Ataxin-3 / Q000633:toxicity*; D019791:Guanidine / Q000494:pharmacology; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D018832:Molecular Chaperones / Q000378:metabolism; D050505:Mutant Proteins / Q000633:toxicity*; D018384:Oxidative Stress / Q000187:drug effects; D011419:Propidium / Q000378:metabolism; D066329:Protein Aggregates / Q000187:drug effects; D012441:Saccharomyces cerevisiae / Q000187:drug effects / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D012995:Solubility
chemical_list: D000975:Antioxidants; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D050505:Mutant Proteins; D066329:Protein Aggregates; D029701:Saccharomyces cerevisiae Proteins; C070972:HsP104 protein, S cerevisiae; D011419:Propidium; D012967:Sodium Dodecyl Sulfate; D000067699:Ataxin-3; D019791:Guanidine