Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI, USA.
Department of Pharmacology, Wayne State University School of Medicine, Detroit, MI, USA; Department of Neurology, Wayne State University School of Medicine, Detroit, MI, USA.
Neurobiol Dis. 2018 Aug;116:78-92. doi: 10.1016/j.nbd.2018.04.013. Epub 2018 Apr 26.
Among the nine dominantly inherited, age-dependent neurodegenerative diseases caused by abnormal expansion in the polyglutamine (polyQ) repeat of otherwise unrelated proteins is Spinocerebellar Ataxia Type 3 (SCA3). SCA3 is caused by polyQ expansion in the deubiquitinase (DUB), ataxin-3. Molecular sequelae related to SCA3 remain unclear. Here, we sought to understand the role of protein context in SCA3 by focusing on the interaction between this DUB and Valosin-Containing Protein (VCP). VCP is bound directly by ataxin-3 through an arginine-rich area preceding the polyQ repeat. We examined the importance of this interaction in ataxin-3-dependent degeneration in Drosophila melanogaster. Our assays with new isogenic fly lines expressing pathogenic ataxin-3 with an intact or mutated VCP-binding site show that disrupting the ataxin-3-VCP interaction delays the aggregation of the toxic protein in vivo. Importantly, early on flies that express pathogenic ataxin-3 with a mutated VCP-binding site are indistinguishable from flies that do not express any SCA3 protein. Also, reducing levels of VCP through RNA-interference has a similar, protective effect to mutating the VCP-binding site of pathogenic ataxin-3. Based on in vivo pulse-chases, aggregated species of ataxin-3 are highly stable, in a manner independent of VCP-binding. Collectively, our results highlight an important role for the ataxin-3-VCP interaction in SCA3, based on a model that posits a seeding effect from VCP on pathogenic ataxin-3 aggregation and subsequent toxicity.
在由异常扩展的多聚谷氨酰胺（polyQ）重复引起的 9 种主要遗传性、年龄依赖性神经退行性疾病中，有一种是脊髓小脑性共济失调 3 型（SCA3）。SCA3 是由去泛素化酶（DUB）、ataxin-3 中的 polyQ 扩展引起的。与 SCA3 相关的分子后果仍不清楚。在这里，我们通过关注这种 DUB 与包含 Valosin 的蛋白（VCP）之间的相互作用，试图了解 SCA3 中蛋白质结构域的作用。VCP 通过位于 polyQ 重复之前的富含精氨酸的区域直接与 ataxin-3 结合。我们在黑腹果蝇中研究了该相互作用在 ataxin-3 依赖性变性中的重要性。我们使用新的同基因蝇系进行的实验，这些蝇系表达具有完整或突变的 VCP 结合位点的致病性 ataxin-3，结果表明，破坏 ataxin-3-VCP 相互作用会延迟体内毒性蛋白的聚集。重要的是，表达具有突变的 VCP 结合位点的致病性 ataxin-3 的早期苍蝇与不表达任何 SCA3 蛋白的苍蝇无法区分。此外，通过 RNA 干扰降低 VCP 水平与突变致病性 ataxin-3 的 VCP 结合位点具有相似的保护作用。基于体内脉冲追踪实验，聚集的 ataxin-3 物种非常稳定，与 VCP 结合无关。总的来说，我们的结果基于一个假设，即 VCP 对致病性 ataxin-3 聚集和随后的毒性具有“种子”效应，突出了 ataxin-3-VCP 相互作用在 SCA3 中的重要作用。
