From the Institute of Medical Genetics and Applied Genomics, University of Tübingen, 72076 Tübingen, Germany.
the Center for Rare Diseases, 72076 Tübingen, Germany.
J Biol Chem. 2019 Jan 11;294(2):644-661. doi: 10.1074/jbc.RA118.005801. Epub 2018 Nov 19.
Ataxin-3 is a deubiquitinating enzyme and the affected protein in the neurodegenerative disorder Machado-Joseph disease (MJD). The gene is alternatively spliced, resulting in protein isoforms that differ in the number of ubiquitin-interacting motifs. Additionally, nonsynonymous SNPs in cause amino acid changes in ataxin-3, and one of these polymorphisms introduces a premature stop codon in one isoform. Here, we examined the effects of different ataxin-3 isoforms and of the premature stop codon on ataxin-3's physiological function and on main disease mechanisms. At the physiological level, we show that alternative splicing and the premature stop codon alter ataxin-3 stability and that ataxin-3 isoforms differ in their enzymatic deubiquitination activity, subcellular distribution, and interaction with other proteins. At the pathological level, we found that the expansion of the polyglutamine repeat leads to a stabilization of ataxin-3 and that ataxin-3 isoforms differ in their aggregation properties. Interestingly, we observed a functional interaction between normal and polyglutamine-expanded allelic variants. We found that interactions between different allelic variants modify the physiological and pathophysiological properties of ataxin-3. Our findings indicate that alternative splicing and interactions between different ataxin-3 isoforms affect not only major aspects of ataxin-3 function but also MJD pathogenesis. Our results stress the importance of considering isoforms of disease-causing proteins and their interplay with the normal allelic variant as disease modifiers in MJD and autosomal-dominantly inherited diseases in general.
ataxin-3 是一种去泛素化酶，也是神经退行性疾病 Machado-Joseph 病（MJD）的致病蛋白。该基因存在可变剪接，导致蛋白异构体在泛素相互作用基序的数量上存在差异。此外，ataxin-3 中的非同义 SNPs 导致氨基酸发生变化，其中一种多态性在一个异构体中引入了一个提前终止密码子。在这里，我们研究了不同 ataxin-3 异构体和提前终止密码子对 ataxin-3 生理功能和主要疾病机制的影响。在生理水平上，我们表明可变剪接和提前终止密码子改变了 ataxin-3 的稳定性，并且 ataxin-3 异构体在其酶去泛素化活性、亚细胞分布和与其他蛋白质的相互作用方面存在差异。在病理水平上，我们发现多聚谷氨酰胺重复的扩展导致 ataxin-3 的稳定，并发现 ataxin-3 异构体在其聚集特性方面存在差异。有趣的是，我们观察到正常和多聚谷氨酰胺扩展的 等位基因变体之间存在功能相互作用。我们发现，不同 等位基因变体之间的相互作用改变了 ataxin-3 的生理和病理生理特性。我们的发现表明，可变剪接和不同 ataxin-3 异构体之间的相互作用不仅影响 ataxin-3 功能的主要方面，而且影响 MJD 的发病机制。我们的研究结果表明，考虑致病蛋白的异构体及其与正常等位基因变体的相互作用作为 MJD 和常染色体显性遗传疾病的疾病修饰因子非常重要。
