Proteasome subunit α1 overexpression preferentially drives canonical proteasome biogenesis and enhances stress tolerance in yeast

Abstract

The 26S proteasome conducts the majority of regulated protein catabolism in eukaryotes. At the heart of the proteasome is the barrel-shaped 20S core particle (CP), which contains two β-rings sandwiched between two α-rings. Whereas canonical CPs contain α-rings with seven subunits arranged α1-α7, a non-canonical CP in which a second copy of the α4 subunit replaces the α3 subunit occurs in both yeast and humans. The mechanisms that control canonical versus non-canonical CP biogenesis remain poorly understood. Here, we have repurposed a split-protein reporter to identify genes that can enhance canonical proteasome assembly in mutant yeast producing non-canonical α4-α4 CPs. We identified the proteasome subunit α1 as an enhancer of α3 incorporation, and find that elevating α1 protein levels preferentially drives canonical CP assembly under conditions that normally favor α4-α4 CP formation. Further, we demonstrate that α1 is stoichiometrically limiting for α-ring assembly, and that enhancing α1 levels is sufficient to increase proteasome abundance and enhance stress tolerance in yeast. Together, our data indicate that the abundance of α1 exerts multiple impacts on proteasome assembly and composition, and we propose that the limited α1 levels observed in yeast may prime cells for alternative proteasome assembly following environmental stimuli.

An evolutionarily distinct chaperone promotes 20S proteasome α-ring assembly in plants

“…How the α 1 , α 2 , α 3 and α 4 subunits then integrate is unclear, but the hetero-dimeric Pba3-Pba4 chaperone in yeast (also known as Irc25-Poc4) and the PAC3-PAC4 chaperone in mammals (also termed PSMG3-PSMG4) appear critical for correct stoichiometry of the α 3 and α 4 subunits (Kusmierczyk et al, 2008;Padmanabhan et al, 2016;Takagi et al, 2014), and integration of the α 1 subunit appears rate limiting (Howell et al, 2019). The Pba1-Pba2 and Pba3-Pba4 pairs also prevent premature association of CP assembly intermediates with the RP or other activating factors, in some cases by outcompeting HbYX-containing RP subunits such as Rpt5 for CP binding until the CP rings mature (Kock et al, 2015;Stadtmueller et al, 2012;Wani et al, 2015).…”

miR-1 sustains muscle physiology by controlling V-ATPase complex assembly

“…We further asked how deregulation of individual subunits affects mitochondrial structure and proteostasis in muscle. We reasoned that gain of function of the V-ATPase complex could occur if there was one or a subset of limiting subunits and their up-regulation enabled formation of more complexes, similar to what has been observed for proteasome assembly in yeast (46). In this scenario, only the upregulation of the one or of all the limiting subunits simultaneously would lead to formation of more V-ATPase, but up-regulation of any other individual subunit would not.…”

Research progress on proteasome subunits in regulating occurrence and development of hepatocellular carcinoma

“…其功能知之甚少，一般认为在协同β亚基的催化活 动中发挥作用 [45] 。β亚基由PSMB1~7基因编码， 其中的β1、β2、β5具有不同的蛋白酶催化特性，分 别表现为类胱天蛋白酶样活性、酪氨酸蛋白酶活 性、胰凝乳蛋白酶样活性 [46] 。在靶蛋白进入蛋白 酶体内部的过程中，蛋白酶体的调节颗粒负责靶 蛋白的选择，而核心颗粒则执行对靶蛋白的降解， 进入核心颗粒的蛋白质最终都被水解成2~24个氨 基酸大小的肽段 [47] 。 目前核心颗粒亚基与HCC直接相关的研究相 对较少。在小鼠的HCC中，核心颗粒亚基PSMA6 与PSMB4表达均上调，提示核心颗粒亚基参与 HCC的调控过程 [35] 。Qin等 [48] 研究发现，HCC肿 瘤组织间液中的PSMA1的水平显著降低，认为 PSMA1具有作为HCC的诊断标志的潜力。PSMB7…”