Webb Julie L, Ravikumar Brinda, Rubinsztein David C
Department of Medical Genetics, Cambridge Institute for Medical Research, Wellcome/MRC Building, Addenbrooke's Hospital, Hills Road, Cambridge CB2 2XY, UK.
Int J Biochem Cell Biol. 2004 Dec;36(12):2541-50. doi: 10.1016/j.biocel.2004.02.003.
Large cytoplasmic inclusions called aggresomes are seen in many protein conformational diseases including Huntington's disease and Parkinson's disease. The roles of inclusions and aggresomes in these diseases are unresolved critical issues that have been vigorously debated. Two recent studies used microtubule disruption with nocodazole to inhibit aggresome formation and observed increased toxicity of expanded polyglutamines in the context of huntingtin exon 1 and a truncated androgen receptor. Increased toxicity of expanded polyglutamines in the presence of nocodazole was correlated with decreased protein turnover, leading the authors to conclude that aggresomes were cytoprotective and that they directly enhanced clearance of the toxic proteins. Here we show that nocodazole has additional effects, which provide a simple alternative explanation for these previous observations. We confirmed aggresome formation in cells expressing proteins with polyalanine and polyglutamine expansions. As expected, we found a reduction in aggresome formation when microtubule function was disrupted using nocodazole. However, in addition to this effect, nocodazole treatment increased the proportions of cells with nuclear inclusions in PC12 cells expressing huntingtin exon 1 with 74 glutamines. This can be explained as nocodazole inhibits autophagosome-lysosome fusion, a key step in mutant huntingtin exon 1 clearance. This effect alone can explain the previous observations with this compound in polyglutamine diseases and raises doubts about the interpretation of some of the data that have been used to argue that aggresomes protect against polyglutamine mutations.
在包括亨廷顿舞蹈症和帕金森病在内的许多蛋白质构象疾病中，都能观察到名为聚集体的大型细胞质内含物。内含物和聚集体在这些疾病中的作用是尚未解决的关键问题，一直存在激烈的争论。最近的两项研究使用诺考达唑破坏微管来抑制聚集体形成，并观察到在亨廷顿蛋白外显子1和截短的雄激素受体的背景下，扩展的聚谷氨酰胺毒性增加。在诺考达唑存在的情况下，扩展的聚谷氨酰胺毒性增加与蛋白质周转率降低相关，这使得作者得出结论，聚集体具有细胞保护作用，并且它们直接增强了有毒蛋白质的清除。在这里，我们表明诺考达唑还有其他作用，这为这些先前的观察结果提供了一个简单的替代解释。我们证实了在表达具有聚丙氨酸和聚谷氨酰胺扩展的蛋白质的细胞中形成了聚集体。正如预期的那样，当使用诺考达唑破坏微管功能时，我们发现聚集体形成减少。然而，除了这种作用外，诺考达唑处理增加了在表达含有74个谷氨酰胺的亨廷顿蛋白外显子1的PC12细胞中具有核内含物的细胞比例。这可以解释为诺考达唑抑制自噬体 - 溶酶体融合，这是突变的亨廷顿蛋白外显子1清除的关键步骤。仅这一作用就可以解释先前使用该化合物在聚谷氨酰胺疾病中的观察结果，并对一些用于论证聚集体可防止聚谷氨酰胺突变的数据解释提出质疑。
