Schilling G, Sharp A H, Loev S J, Wagster M V, Li S H, Stine O C, Ross C A
Department of Psychiatry, Johns Hopkins University, School of Medicine, Baltimore, MD 21205-2196, USA.
Hum Mol Genet. 1995 Aug;4(8):1365-71. doi: 10.1093/hmg/4.8.1365.
Huntington's disease (HD) is an inherited, neurodegenerative disorder caused by expansion of a CAG repeat in the IT15 gene, leading to an expanded glutamine repeat in the HD protein. The mechanism by which the expanded repeat causes expression of the disease is not known, though there do not appear to be changes in the mRNA levels. We have conducted quantitative Western blot analyses of HD patients and controls. Expression of the IT15 protein is essentially equal in control and HD frontal cortex. In caudate from HD patients, IT15 protein is decreased in parallel with the decrease in a neuronal marker, suggesting that loss of IT15 protein is secondary to neuronal loss. In order to determine expression of the two alleles of the IT15 protein we used Western blots of 4% polyacrylamide gels. Both alleles of the IT15 protein were expressed at similar levels in HD lymphoblastoid cell lines and HD post-mortem hippocampus and cerebellum (regions relatively spared in HD), indicating that even very long CAG repeats can be translated into polyglutamine. In contrast, in cerebral cortex and caudate (regions severely affected in HD), in the longer expanded repeat cases the expanded allele of the IT15 protein was present at a significantly lower level (compared with the normal length allele), often with a smear of more slowly migrating reactivity above it. These data suggest the possibility of altered structure, abnormal processing or abnormality of protein-protein interactions involving the IT15 protein with the expanded glutamine repeat.
亨廷顿舞蹈症（HD）是一种遗传性神经退行性疾病，由IT15基因中CAG重复序列的扩增引起，导致HD蛋白中谷氨酰胺重复序列的扩增。尽管mRNA水平似乎没有变化，但扩增的重复序列导致疾病表达的机制尚不清楚。我们对HD患者和对照进行了定量蛋白质免疫印迹分析。IT15蛋白在对照和HD额叶皮质中的表达基本相等。在HD患者的尾状核中，IT15蛋白随着神经元标志物的减少而平行下降，这表明IT15蛋白的丢失继发于神经元的丢失。为了确定IT15蛋白两个等位基因的表达，我们使用了4%聚丙烯酰胺凝胶的蛋白质免疫印迹。IT15蛋白的两个等位基因在HD淋巴母细胞系以及HD死后海马体和小脑（HD中相对未受影响的区域）中以相似水平表达，这表明即使是非常长的CAG重复序列也可以翻译成多聚谷氨酰胺。相比之下，在大脑皮质和尾状核（HD中严重受影响的区域）中，在较长的扩增重复序列病例中，IT15蛋白的扩增等位基因水平明显较低（与正常长度等位基因相比），其上方常常有一条迁移较慢的反应性条带拖尾。这些数据表明，涉及具有扩增谷氨酰胺重复序列的IT15蛋白的结构改变、异常加工或蛋白质 - 蛋白质相互作用异常是有可能的。
