Ubiquilin/Dsk2 promotes inclusion body formation and vacuole (lysosome)-mediated disposal of mutated huntingtin.
Ubiquilin/Dsk2 promotes inclusion body formation and vacuole (lysosome)-mediated disposal of mutated huntingtin.
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DOI：
10.1091/mbc.e16-01-0026
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发表时间：
2016-07-01
影响因子：
3.3
通讯作者：
Wang Y
中科院分区：
文献类型：
--
作者：
Chuang KH;Liang F;Higgins R;Wang Y
以前的工作建立了泛素蛋白与几种神经退行性疾病的联系。芽殖酵母的结果表明，泛素蛋白通过促进包涵体的形成，促进错误折叠蛋白的溶酶体依赖性清除。泛素蛋白含有一个泛素样结构域（UBL）和一个泛素相关结构域，分别与蛋白酶体和泛素化底物相互作用。以前的工作建立了泛素突变和神经退行性疾病之间的联系，但泛素蛋白的功能仍然难以捉摸。在这里，我们使用了一个错误折叠的亨廷顿蛋白外显子I含有103-聚谷氨酰胺扩展（Htt 103 QP）作为模型底物的泛素蛋白的功能研究。我们发现酵母ubiquilin突变体（dsk 2 Δ）对Htt 103 QP的过表达敏感，并且在Htt 103 QP包涵体的形成方面存在缺陷。我们的证据进一步表明Dsk 2的UBL结构域对于包涵体的形成是至关重要的。感兴趣的是，当在明显的包涵体形成之前短时间诱导Htt 103 QP时，Dsk 2被检测为Htt 103 QP降解。然而，当包涵体在长的Htt 103 QP诱导后形成时，Dsk 2是有效的Htt 103 QP清除所需的，以及用于将Htt 103 QP自噬依赖性递送到空泡（溶酶体）中。因此，我们的数据表明，Dsk 2通过促进包涵体的形成，促进空泡介导的错误折叠蛋白的清除。重要的是，dsk 2突变体中包涵体形成的缺陷可以被人ubiquilin 1或2拯救，这表明ubiquilin蛋白的功能保守性。
Previous work established the link of ubiquilin proteins to several neurodegenerative diseases. The results from budding yeast indicate that ubiquilin proteins facilitate lysosome-dependent clearance of misfolded proteins by promoting inclusion body formation. Ubiquilin proteins contain a ubiquitin-like domain (UBL) and ubiquitin-associated domain(s) that interact with the proteasome and ubiquitinated substrates, respectively. Previous work established the link between ubiquilin mutations and neurodegenerative diseases, but the function of ubiquilin proteins remains elusive. Here we used a misfolded huntingtin exon I containing a 103-polyglutamine expansion (Htt103QP) as a model substrate for the functional study of ubiquilin proteins. We found that yeast ubiquilin mutant (dsk2Δ) is sensitive to Htt103QP overexpression and has a defect in the formation of Htt103QP inclusion bodies. Our evidence further suggests that the UBL domain of Dsk2 is critical for inclusion body formation. Of interest, Dsk2 is dispensable for Htt103QP degradation when Htt103QP is induced for a short time before noticeable inclusion body formation. However, when the inclusion body forms after a long Htt103QP induction, Dsk2 is required for efficient Htt103QP clearance, as well as for autophagy-dependent delivery of Htt103QP into vacuoles (lysosomes). Therefore our data indicate that Dsk2 facilitates vacuole-mediated clearance of misfolded proteins by promoting inclusion body formation. Of importance, the defect of inclusion body formation in dsk2 mutants can be rescued by human ubiquilin 1 or 2, suggesting functional conservation of ubiquilin proteins.