School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Shatin, NT, Hong Kong.
Biochem J. 2012 May 1;443(3):681-9. doi: 10.1042/BJ20112175.
An unstable expansion of the polyglutamine repeat within exon 1 of the protein Htt (huntingtin) causes HD (Huntington's disease). Mounting evidence shows that accumulation of N-terminal mutant Htt fragments is the source of disruption of normal cellular processes which ultimately leads to neuronal cell death. Understanding the degradation mechanism of mutant Htt and improving its clearance has emerged as a new direction in developing therapeutic approaches to treat HD. In the present study we show that the brain-enriched adaptor protein FE65 is a novel interacting partner of Htt. The binding is mediated through WW-polyproline interaction and is dependent on the length of the polyglutamine tract. Interestingly, a reduction in mutant Htt protein level was observed in FE65-knockdown cells, and the process requires the UPS (ubiquitin/proteasome system). Moreover, the ubiquitination level of mutant Htt was found to be enhanced when FE65 is knocked down. Immunofluroescence staining revealed that FE65 associates with mutant Htt aggregates. Additionally, we demonstrated that overexpression of FE65 increases mutant Htt-induced cell death both in vitro and in vivo. These results suggest that FE65 facilitates the accumulation of mutant Htt in cells by preventing its degradation via the UPS, and thereby enhances the toxicity of mutant Htt.
亨廷顿病（HD）是由蛋白 Htt（亨廷顿蛋白）第 1 外显子中多聚谷氨酰胺重复不稳定扩张引起的。越来越多的证据表明，N 端突变 Htt 片段的积累是破坏正常细胞过程的根源，最终导致神经元细胞死亡。了解突变 Htt 的降解机制并提高其清除率已成为开发治疗 HD 方法的新方向。在本研究中，我们表明富含脑的衔接蛋白 FE65 是 Htt 的一个新的相互作用伙伴。这种结合是通过 WW-多脯氨酸相互作用介导的，并且依赖于多谷氨酰胺片段的长度。有趣的是，在 FE65 敲低细胞中观察到突变 Htt 蛋白水平降低，该过程需要 UPS（泛素/蛋白酶体系统）。此外，当 FE65 被敲低时，突变 Htt 的泛素化水平被发现增强。免疫荧光染色显示 FE65 与突变 Htt 聚集体相关。此外，我们证明了 FE65 的过表达增加了体外和体内突变 Htt 诱导的细胞死亡。这些结果表明，FE65 通过 UPS 防止其降解，从而促进突变 Htt 的积累，从而增强突变 Htt 的毒性。
