Nanduri Priyaanka, Hao Rui, Fitzpatrick Thomas, Yao Tso-Pang
From the Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina 27710.
From the Department of Pharmacology and Cancer Biology, Duke University, Durham, North Carolina 27710
J Biol Chem. 2015 Apr 10;290(15):9455-64. doi: 10.1074/jbc.M114.627950. Epub 2015 Feb 24.
Efficient elimination of misfolded proteins by the proteasome system is critical for proteostasis. Inadequate proteasome capacity can lead to aberrant aggregation of misfolded proteins and inclusion body formation, a hallmark of neurodegenerative disease. The proteasome system cannot degrade aggregated proteins; however, it stimulates autophagy-dependent aggregate clearance by producing unanchored lysine (K)63-linked ubiquitin chains via the proteasomal deubiquitinating enzyme Poh1. The canonical function of Poh1, which removes ubiquitin chains en bloc from proteasomal substrates prior to their degradation, requires intact 26S proteasomes. Here we present evidence that during aggresome clearance, 20S proteasomes dissociate from protein aggregates, while Poh1 and selective subunits of 19S proteasomes are retained. The dissociation of 20S proteasome components requires the molecular chaperone Hsp90. Hsp90 inhibition suppresses 26S proteasome remodeling, unanchored ubiquitin chain production, and aggresome clearance. Our results suggest that 26S proteasomes undergo active remodeling to generate a Poh1-dependent K63-deubiquitinating enzyme to facilitate protein aggregate clearance.
蛋白酶体系统有效清除错误折叠的蛋白质对于蛋白质稳态至关重要。蛋白酶体能力不足会导致错误折叠蛋白质的异常聚集和包涵体形成，这是神经退行性疾病的一个标志。蛋白酶体系统无法降解聚集的蛋白质；然而，它通过蛋白酶体去泛素化酶Poh1产生无锚定的赖氨酸（K）63连接的泛素链，刺激自噬依赖性的聚集体清除。Poh1的经典功能是在蛋白酶体底物降解之前将泛素链从其整体上移除，这需要完整的26S蛋白酶体。在这里，我们提供证据表明，在聚集体清除过程中，20S蛋白酶体与蛋白质聚集体解离，而Poh1和19S蛋白酶体的选择性亚基被保留。20S蛋白酶体组分的解离需要分子伴侣Hsp90。Hsp90抑制会抑制26S蛋白酶体重塑、无锚定泛素链的产生以及聚集体清除。我们的结果表明，26S蛋白酶体经历主动重塑以产生一种依赖Poh1的K63去泛素化酶，以促进蛋白质聚集体的清除。
