Aslam Kiran, Tsai Chai-Jui, Hazbun Tony R
a Department of Medicinal Chemistry and Molecular Pharmacology and the Purdue University Center for Cancer Research , Purdue University , West Lafayette , IN , USA.
Prion. 2016 Nov;10(6):444-465. doi: 10.1080/19336896.2016.1234574.
The yeast homolog of DJ-1, Hsp31, is a multifunctional protein that is involved in several cellular pathways including detoxification of the toxic metabolite methylglyoxal and as a protein deglycase. Prior studies ascribed Hsp31 as a molecular chaperone that can inhibit α-Syn aggregation in vitro and alleviate its toxicity in vivo. It was also shown that Hsp31 inhibits Sup35 aggregate formation in yeast, however, it is unknown if Hsp31 can modulate [PSI] phenotype and Sup35 prionogenesis. Other small heat shock proteins, Hsp26 and Hsp42 are known to be a part of a synergistic proteostasis network that inhibits Sup35 prion formation and promotes its disaggregation. Here, we establish that Hsp31 inhibits Sup35 [PSI] prion formation in collaboration with a well-known disaggregase, Hsp104. Hsp31 transiently prevents prion induction but does not suppress induction upon prolonged expression of Sup35 indicating that Hsp31 can be overcome by larger aggregates. In addition, elevated levels of Hsp31 do not cure [PSI] strains indicating that Hsp31 cannot intervene in a pre-existing prion oligomerization cycle. However, Hsp31 can modulate prion status in cooperation with Hsp104 because it inhibits Sup35 aggregate formation and potentiates [PSI] prion curing upon overexpression of Hsp104. The absence of Hsp31 reduces [PSI] prion curing by Hsp104 without influencing its ability to rescue cellular thermotolerance. Hsp31 did not synergize with Hsp42 to modulate the [PSI] phenotype suggesting that both proteins act on similar stages of the prion cycle. We also showed that Hsp31 physically interacts with Hsp104 and together they prevent Sup35 prion toxicity to greater extent than if they were expressed individually. These results elucidate a mechanism for Hsp31 on prion modulation that suggest it acts at a distinct step early in the Sup35 aggregation process that is different from Hsp104. This is the first demonstration of the modulation of [PSI] status by the chaperone action of Hsp31. The delineation of Hsp31's role in the chaperone cycle has implications for understanding the role of the DJ-1 superfamily in controlling misfolded proteins in neurodegenerative disease and cancer.
DJ-1的酵母同源物Hsp31是一种多功能蛋白，参与多种细胞途径，包括有毒代谢物甲基乙二醛的解毒以及作为一种蛋白质去糖基酶。先前的研究将Hsp31归因于一种分子伴侣，它可以在体外抑制α-突触核蛋白聚集，并在体内减轻其毒性。研究还表明，Hsp31可抑制酵母中Sup35聚集体的形成，然而，尚不清楚Hsp31是否能调节[PSI]表型和Sup35朊病毒的形成。已知其他小分子热休克蛋白Hsp26和Hsp42是协同蛋白质稳态网络的一部分，该网络可抑制Sup35朊病毒的形成并促进其解聚。在此，我们证实Hsp31与著名的解聚酶Hsp104协同作用，抑制Sup35 [PSI]朊病毒的形成。Hsp31可短暂阻止朊病毒的诱导，但在Sup35长期表达时不能抑制诱导，这表明较大的聚集体可以克服Hsp31的作用。此外，Hsp31水平的升高并不能治愈[PSI]菌株，这表明Hsp31不能干预预先存在的朊病毒寡聚化循环。然而，Hsp31可以与Hsp104协同调节朊病毒状态，因为它抑制Sup35聚集体的形成，并在Hsp104过表达时增强[PSI]朊病毒的治愈。Hsp31的缺失会降低Hsp104对[PSI]朊病毒的治愈能力，而不影响其挽救细胞耐热性的能力。Hsp31与Hsp42不能协同调节[PSI]表型，这表明这两种蛋白在朊病毒循环的相似阶段发挥作用。我们还表明，Hsp31与Hsp104发生物理相互作用，并且它们共同作用比单独表达时能更大程度地防止Sup35朊病毒的毒性。这些结果阐明了Hsp31对朊病毒调节的机制，表明它在Sup35聚集过程早期的一个独特步骤发挥作用，这与Hsp104不同。这是首次证明Hsp31的伴侣作用对[PSI]状态的调节。阐明Hsp31在伴侣循环中的作用，对于理解DJ-1超家族在神经退行性疾病和癌症中控制错误折叠蛋白的作用具有重要意义。
