Yu Zhao-Xue, Li Shi-Hua, Nguyen Huu-Phuc, Li Xiao-Jiang
Department of Human Genetics, Emory University, School of Medicine, Atlanta, GA 30322, USA.
Hum Mol Genet. 2002 Apr 15;11(8):905-14. doi: 10.1093/hmg/11.8.905.
A pathological hallmark of polyglutamine diseases is the presence of inclusions or aggregates of the expanded polyglutamine protein. Polyglutamine inclusions are present in the neuronal nucleus in a number of inherited neurodegenerative disorders, including Huntington disease (HD). Recent studies suggest that polyglutamine inclusions may sequester polyglutamine-containing transcription factors and deplete their concentration in the nucleus, leading to altered gene expression. To test this hypothesis, we examined the expression and localization of the polyglutamine-containing or glutamine-rich transcription factors TBP, CBP and Sp1 in HD mouse models. All three transcription factors were diffusely distributed in the nucleus, despite the presence of abundant intranuclear inclusions. There were no differences in the nuclear staining of these transcription factors between HD and wild-type mouse brains. Although some CBP staining appeared as dots in the selective brain regions (e.g. hypothalamus and amygdala), double labeling showed that most CBP was not co-localized with huntingtin nuclear inclusions. Electron microscopy confirmed that CBP was diffusely distributed in the nucleus. Western blots showed that these transcription factors were not trapped in huntingtin inclusions. In the striatum of HD mice, which suffers a significant reduction in the expression of a number of genes, mutant huntingtin was present in both an aggregated and a diffuse form. These findings suggest that altered gene expression may result from the interactions of soluble mutant huntingtin with nuclear transcription factors, rather than from the depletion of transcription factors by nuclear inclusions.
多聚谷氨酰胺疾病的一个病理特征是存在扩展的多聚谷氨酰胺蛋白的包涵体或聚集体。多聚谷氨酰胺包涵体存在于多种遗传性神经退行性疾病的神经元细胞核中，包括亨廷顿舞蹈病（HD）。最近的研究表明，多聚谷氨酰胺包涵体可能隔离含多聚谷氨酰胺的转录因子并耗尽其在细胞核中的浓度，从而导致基因表达改变。为了验证这一假设，我们在HD小鼠模型中检测了含多聚谷氨酰胺或富含谷氨酰胺的转录因子TBP、CBP和Sp1的表达及定位。尽管存在大量核内包涵体，但所有这三种转录因子均在细胞核中呈弥散分布。HD小鼠脑与野生型小鼠脑之间这些转录因子的核染色没有差异。虽然在某些脑区（如下丘脑和杏仁核）一些CBP染色呈点状，但双重标记显示大多数CBP并不与亨廷顿蛋白核包涵体共定位。电子显微镜证实CBP在细胞核中呈弥散分布。蛋白质印迹分析表明这些转录因子并未被困在亨廷顿蛋白包涵体中。在许多基因表达显著降低的HD小鼠纹状体中，突变型亨廷顿蛋白以聚集和弥散两种形式存在。这些发现表明，基因表达改变可能是由于可溶性突变型亨廷顿蛋白与核转录因子的相互作用，而非核包涵体导致转录因子耗竭所致。
