Tumor necrosis factor receptor-associated factor 6 (TRAF6) associates with huntingtin protein and promotes its atypical ubiquitination to enhance aggregate formation.
Tumor necrosis factor receptor-associated factor 6 (TRAF6) associates with huntingtin protein and promotes its atypical ubiquitination to enhance aggregate formation.
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DOI：
10.1074/jbc.m110.187591
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发表时间：
2011-07-15
期刊：
影响因子：
--
通讯作者：
Persichetti F
中科院分区：
文献类型：
--
作者：
Zucchelli S;Marcuzzi F;Codrich M;Agostoni E;Vilotti S;Biagioli M;Pinto M;Carnemolla A;Santoro C;Gustincich S;Persichetti F
亨廷顿病(HD)是一种神经退行性疾病，由亨廷顿蛋白(HTT)第一外显子上的多谷氨酸(HTT)扩张引起，该蛋白的氨基末端片段(N-HTT)具有促进聚集的特性。突变的N-HTT聚集体富含泛素，并含有泛素E3连接酶，这表明泛素化在聚集体形成中发挥了作用。在这里，我们报道了肿瘤坏死因子受体相关因子6(TRAF6)在体外与WT和多聚Q扩展的N-HTT结合，以及在体内与小鼠和人脑的内源性全长蛋白结合。内源性TRAF6被募集到突变型N-HTT形成的细胞包涵体中。TRAF6的瞬时过表达促进WT和突变体N-HTT与Lys6、Lys27和Lys29的非典型泛素化形成连锁。相互作用和泛素化似乎都与多Q长度无关。在培养细胞中，TRAF6促进了突变型N-HTT聚集体的形成，但对WT N-HTT蛋白的定位没有影响。只有当TRAF6和Lys6、Lys27和Lys29泛素突变体表达时，突变的N-HTT包涵体才会对泛素染色产生浓集。最后，我们发现TRAF6在HD患者死后大脑中的表达上调，因为它存在于不溶性部分。这些结果表明，TRAF6非典型泛素化在HD发病机制中值得研究。
Huntington disease (HD) is a neurodegenerative disorder caused by an expansion of polyglutamines in the first exon of huntingtin (HTT), which confers aggregation-promoting properties to amino-terminal fragments of the protein (N-HTT). Mutant N-HTT aggregates are enriched for ubiquitin and contain ubiquitin E3 ligases, thus suggesting a role for ubiquitination in aggregate formation. Here, we report that tumor necrosis factor receptor-associated factor 6 (TRAF6) binds to WT and polyQ-expanded N-HTT in vitro as well as to endogenous full-length proteins in mouse and human brain in vivo. Endogenous TRAF6 is recruited to cellular inclusions formed by mutant N-HTT. Transient overexpression of TRAF6 promotes WT and mutant N-HTT atypical ubiquitination with Lys6, Lys27, and Lys29 linkage formation. Both interaction and ubiquitination seem to be independent from polyQ length. In cultured cells, TRAF6 enhances mutant N-HTT aggregate formation, whereas it has no effect on WT N-HTT protein localization. Mutant N-HTT inclusions are enriched for ubiquitin staining only when TRAF6 and Lys6, Lys27, and Lys29 ubiquitin mutants are expressed. Finally, we show that TRAF6 is up-regulated in post-mortem brains from HD patients where it is found in the insoluble fraction. These results suggest that TRAF6 atypical ubiquitination warrants investigation in HD pathogenesis.