Indirect inhibition of 26S proteasome activity in a cellular model of Huntington's disease.
Indirect inhibition of 26S proteasome activity in a cellular model of Huntington's disease.
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DOI：
10.1083/jcb.201110093
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发表时间：
2012-03-05
期刊：
影响因子：
--
通讯作者：
Kopito RR
中科院分区：
文献类型：
--
作者：
Hipp MS;Patel CN;Bersuker K;Riley BE;Kaiser SE;Shaler TA;Brandeis M;Kopito RR
错误折叠的亨廷顿蛋白可能会破坏细胞的蛋白质稳态，并导致对有限的26 S蛋白酶体能力的竞争，而不是直接损害26 S蛋白酶体。在人类神经退行性疾病，如亨廷顿病中，泛素（Ub）结合物的特异性积累表明，高度聚集的蛋白质干扰26 S蛋白酶体活性。在本文中，我们研究了可能的机制，其中的N-末端片段的突变亨廷顿蛋白（htt; N-htt）抑制26 S功能。我们发现，泛素化的N-htt-无论是否聚集-没有窒息或堵塞蛋白酶体。当突变体N-htt的浓度超过溶解度阈值时，Ub依赖性和Ub非依赖性蛋白酶体报告物都积累，这表明26 S底物的稳定性与Ub缀合受损无关。在此溶解度阈值以上，突变体N-htt被迅速募集到最初缺乏Ub的细胞质内含物中。虽然合成多泛素化的N-htt与其他Ub缀合物竞争进入蛋白酶体，但细胞中绝大多数突变N-htt不是Ub缀合的。我们的数据证实，蛋白酶体不直接受损的聚集的N-末端片段的htt，相反，我们的数据表明，Ub的积累与受损的功能的细胞蛋白稳态网络。
Rather than directly impairing 26S proteasomes, misfolded huntingtin may disrupt cellular proteostasis and lead to competition for limited 26S proteasome capacity. Pathognomonic accumulation of ubiquitin (Ub) conjugates in human neurodegenerative diseases, such as Huntington’s disease, suggests that highly aggregated proteins interfere with 26S proteasome activity. In this paper, we examine possible mechanisms by which an N-terminal fragment of mutant huntingtin (htt; N-htt) inhibits 26S function. We show that ubiquitinated N-htt—whether aggregated or not—did not choke or clog the proteasome. Both Ub-dependent and Ub-independent proteasome reporters accumulated when the concentration of mutant N-htt exceeded a solubility threshold, indicating that stabilization of 26S substrates is not linked to impaired Ub conjugation. Above this solubility threshold, mutant N-htt was rapidly recruited to cytoplasmic inclusions that were initially devoid of Ub. Although synthetically polyubiquitinated N-htt competed with other Ub conjugates for access to the proteasome, the vast majority of mutant N-htt in cells was not Ub conjugated. Our data confirm that proteasomes are not directly impaired by aggregated N-terminal fragments of htt; instead, our data suggest that Ub accumulation is linked to impaired function of the cellular proteostasis network.
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