Interference of Crx-dependent transcription by ataxin-7 involves interaction between the glutamine regions and requires the ataxin-7 carboxy-terminal region for nuclear localization
Interference of Crx-dependent transcription by ataxin-7 involves interaction between the glutamine regions and requires the ataxin-7 carboxy-terminal region for nuclear localization
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DOI：
10.1093/hmg/ddh005
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发表时间：
2004-01-01
影响因子：
3.5
通讯作者：
La Spada, AR
中科院分区：
文献类型：
--
作者：
Chen, SM;Peng, GH;La Spada, AR
脊髓小脑型共济失调7型(SCA7)是一种遗传性神经退行性疾病，由ataxin-7蛋白中的多聚谷氨酰胺束扩张引起。SCA7的一个独特特征是视网膜中的光感受器细胞退化，导致视锥-杆状营养不良。在我们建立的SCA7转基因小鼠模型中，发现视锥-杆状营养不良涉及由于干扰CRX而导致光感受器基因表达的变化。CRX是一种同源结构域转录因子，含有富含谷氨酰胺的区域。为了确定CRX-ataxin-7相互作用的基础，我们产生了CRX和ataxin-7截断和点突变，并测试了其中一种蛋白的突变版本与另一种蛋白的正常版本进行免疫共沉淀的能力。因此，CRX的ataxin-7相互作用域被定位于其谷氨酰胺富集区，而ataxin-7‘S CRX结合域被定位于其谷氨酰胺束。通过在HEK293细胞中进行CRX反式激活分析，并将CRX转录干扰的程度与每个蛋白质的谷氨酰胺区域的完整性相关联，证实了每种蛋白质各自的谷氨酰胺区域对于生产性相互作用的重要性。另外，还证实了ataxin-7必须定位于细胞核以抑制CRx的反式激活，并且可能的核定位信号被映射到ataxin-7‘S羧基末端。最后，利用染色质免疫沉淀，证明了CRX和ataxin-7在体内通过共同占据CRX调节的视网膜基因的启动子和增强子区域而参与了功能上显著的相互作用。结果提示，SCA7病的发病机制之一是转录失调，CRX转录干扰是SCA7视锥视杆细胞营养不良视网膜变性的主导因素。
Spinocerebellar ataxia type 7 (SCA7) is an inherited neurodegenerative disorder caused by expansion of a polyglutamine tract in the ataxin-7 protein. A unique feature of SCA7 is degeneration of photoreceptor cells in the retina, resulting in cone-rod dystrophy. In an SCA7 transgenic mouse model that we developed, it was found that the cone-rod dystrophy involves altered photoreceptor gene expression due to interference with Crx, a homeodomain transcription factor containing a glutamine-rich region. To determine the basis of the Crx-ataxin-7 interaction, Crx and ataxin-7 truncation and point mutants were generated, and the ability of mutant versions of either protein to co-immunoprecipitate the normal version of the other protein was tested. Thus Crx's ataxin-7 interaction domain was localized to its glutamine-rich region and ataxin-7's Crx binding domain was mapped to its glutamine tract. The importance of each protein's respective glutamine region for a productive interaction was confirmed by performing Crx transactivation assays in HEK293 cells and correlating the extent of Crx transcription interference with the intactness of each protein's glutamine region. It was also established that ataxin-7 must localize to the nucleus to repress Crx transactivation, and the likely nuclear localization signals were mapped to ataxin-7's carboxy-terminal region. Finally, using chromatin immunoprecipitation, it was demonstrated that Crx and ataxin-7 engage in a functionally significant interaction by co-occupying the promoter and enhancer regions of Crx-regulated retinal genes in vivo. The results suggest that one mechanism of SCA7 disease pathogenesis is transcription dysregulation, and that Crx transcription interference is a predominant factor in SCA7 cone-rod dystrophy retinal degeneration.