Caspase-mediated proteolysis of the polyglutamine disease protein ataxin-3
Caspase-mediated proteolysis of the polyglutamine disease protein ataxin-3
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DOI：
10.1111/j.1471-4159.2004.02369.x
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发表时间：
2004-05-01
影响因子：
4.7
通讯作者：
Paulson, HL
中科院分区：
文献类型：
--
作者：
Berke, SJS;Schmied, FAF;Paulson, HL
脊髓小脑性共济失调3型，也称为Machado-Joseph病，是许多遗传性神经退行性疾病之一，由编码多聚谷氨酰胺的CAG重复序列在其他不相关的疾病基因中扩增引起。多聚谷氨酰胺疾病的特征在于疾病蛋白质错误折叠和聚集;通常在受影响的神经元的核内。虽然多聚谷氨酰胺介导的细胞死亡的确切机制仍然难以捉摸，但有证据表明，多聚谷氨酰胺疾病蛋白通过半胱天冬酶的蛋白水解有助于发病机制。使用细胞模型，我们现在表明，内源性脊髓小脑共济失调3型疾病蛋白，共济失调蛋白-3，在凋亡的范例蛋白水解，导致全长共济失调蛋白-3的损失和相应的外观约28 kDa的片段含有谷氨酰胺重复。广谱半胱天冬酶抑制剂阻断共济失调蛋白-3的蛋白水解，研究表明半胱天冬酶-1是裂解的主要介质。定点诱变实验消除蛋白质中的三个，六个或九个潜在的半胱天冬酶切割位点表明，在该位点（S）的冗余切割可以发生，如前所述的其他疾病蛋白，但也映射一个主要的切割事件的一个集群的天冬氨酸残基内的泛素结合结构域的共济失调蛋白-3附近的多聚谷氨酰胺道。最后，半胱天冬酶介导的扩展共济失调蛋白-3切割导致共济失调蛋白-3聚集增加，表明半胱天冬酶介导的蛋白水解在脊髓小脑共济失调3型发病机制中的潜在作用。
Spinocerebellar ataxia type-3, also known as Machado-Joseph Disease, is one of many inherited neurodegenerative disorders caused by polyglutamine-encoding CAG repeat expansions in otherwise unrelated disease genes. Polyglutamine disorders are characterized by disease protein misfolding and aggregation; often within the nuclei of affected neurons. Although the precise mechanism of polyglutamine-mediated cell death remains elusive, evidence suggests that proteolysis of polyglutamine disease proteins by caspases contributes to pathogenesis. Using cellular models we now show that the endogenous spinocerebellar ataxia type-3 disease protein, ataxin-3, is proteolyzed in apoptotic paradigms, resulting in the loss of full-length ataxin-3 and the corresponding appearance of an approximately 28-kDa fragment containing the glutamine repeat. Broad-spectrum caspase inhibitors block ataxin-3 proteolysis and studies suggest that caspase-1 is a primary mediator of cleavage. Site-directed mutagenesis experiments eliminating three, six or nine potential caspase cleavage sites in the protein suggest redundancy in the site(s) at which cleavage can occur, as previously described for other disease proteins; but also map a major cleavage event to a cluster of aspartate residues within the ubiquitin-binding domain of ataxin-3 near the polyglutamine tract. Finally, caspase-mediated cleavage of expanded ataxin-3 resulted in increased ataxin-3 aggregation, suggesting a potential role for caspase-mediated proteolysis in spinocerebellar ataxia type-3 pathogenesis.