Ataxin-2 (Atx2) is a polyglutamine (polyQ) tract-containing RNA-binding protein, while its polyQ expansion may cause protein aggregation that is implicated in the pathogenesis of neurodegenerative diseases such as spinocerebellar ataxia type 2 (SCA2). However, the molecular mechanism underlying how Atx2 aggregation contributes to the proteinopathies remains elusive. Here, we investigated the influence of Atx2 aggregation on the assembly and functionality of cellular processing bodies (P-bodies) by using biochemical and fluorescence imaging approaches. We have revealed that polyQ-expanded (PQE) Atx2 sequesters the DEAD-box RNA helicase (DDX6), an essential component of P-bodies, into aggregates or puncta some RNA sequences. The N-terminal like-Sm (LSm) domain of Atx2 (residues 82–184) and the C-terminal helicase domain of DDX6 are responsible for the interaction and specific sequestration. Moreover, sequestration of DDX6 may aggravate pre-mRNA mis-splicing, and interfere with the assembly of cellular P-bodies, releasing the endoribonuclease MARF1 that promotes mRNA decay and translational repression. Rescuing the DDX6 protein level can recover the assembly and functionality of P-bodies, preventing targeted mRNA from degradation. This study provides a line of evidence for sequestration of the P-body components and impairment of the P-body homeostasis in dysregulating RNA metabolism, which is implicated in the disease pathologies and a potential therapeutic target.

中文翻译：

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PolyQ 扩展的 ataxin-2 聚集通过隔离 RNA 解旋酶 DDX6 损害细胞加工体稳态


Ataxin-2 (Atx2) 是一种含有聚谷氨酰胺 (polyQ) 束的 RNA 结合蛋白，而其 PolyQ 扩展可能会导致蛋白质聚集，从而参与神经退行性疾病，如 2 型脊髓小脑共济失调 (SCA2) 的发病机制。然而，Atx2 聚集如何导致蛋白质病的分子机制仍然难以捉摸。在这里，我们通过使用生化和荧光成像方法研究了 Atx2 聚集对细胞加工体（P 体）的组装和功能的影响。我们发现，polyQ 扩展 (PQE) Atx2 将 P 体的重要组成部分 DEAD-box RNA 解旋酶 (DDX6) 隔离成聚集体或点状某些 RNA 序列。 Atx2 的 N 端类似 Sm (LSm) 结构域（残基 82-184）和 DDX6 的 C 端解旋酶结构域负责相互作用和特异性隔离。此外，DDX6的隔离可能会加剧前mRNA错误剪接，并干扰细胞P体的组装，释放核糖核酸内切酶MARF1，促进mRNA降解和翻译抑制。挽救 DDX6 蛋白水平可以恢复 P 体的组装和功能，从而防止目标 mRNA 降解。这项研究为 RNA 代谢失调中 P 体成分的隔离和 P 体稳态受损提供了一系列证据，这与疾病病理学和潜在的治疗靶点有关。