PAC1 Gene Knockout Reveals an Essential Role of Chaperone-Mediated 20S Proteasome Biogenesis and Latent 20S Proteasomes in Cellular Homeostasis
PAC1 Gene Knockout Reveals an Essential Role of Chaperone-Mediated 20S Proteasome Biogenesis and Latent 20S Proteasomes in Cellular Homeostasis
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DOI：
10.1128/mcb.00216-10
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发表时间：
2010-08-01
影响因子：
5.3
通讯作者：
Murata, Shigeo
中科院分区：
文献类型：
--
作者：
Sasaki, Katsuhiro;Hamazaki, Jun;Murata, Shigeo
26S蛋白酶体是泛素依赖性蛋白水解的中心酶，是一种高度复杂的结构，包括33个不同的亚基。最近的研究表明，酵母和哺乳动物中有多种专用分子伴侣参与蛋白酶体组装。然而，这些分子伴侣中没有一个是酵母活力所必需的。PAC1是一种哺乳动物蛋白酶体组装分子伴侣，在20 S蛋白酶体（26 S蛋白酶体的催化核心）的初始组装中发挥作用，但在敲除时不会导致20 S蛋白酶体的完全丧失。因此，分子伴侣依赖性和非依赖性组装途径都存在于细胞中，但分子伴侣依赖性途径的贡献仍不清楚。为了阐明其在哺乳动物中的生物学意义，我们产生了PAC1条件性敲除小鼠。PAC1基因敲除小鼠表现出早期胚胎致死性，表明PAC1对哺乳动物的发育，特别是爆炸性细胞增殖至关重要。在静止的成年肝细胞中，PAC 1负责产生大部分20 S蛋白酶体。PAC1缺陷肝细胞含有正常量的26 S蛋白酶体，但它们完全失去了游离的潜伏20 S蛋白酶体。它们还积累了泛素化蛋白，并表现出过早衰老。我们的研究结果表明PAC1依赖的装配途径和潜在的20 S蛋白酶体的重要性，以维持细胞的完整性。
The 26S proteasome, a central enzyme for ubiquitin-dependent proteolysis, is a highly complex structure comprising 33 distinct subunits. Recent studies have revealed multiple dedicated chaperones involved in proteasome assembly both in yeast and in mammals. However, none of these chaperones is essential for yeast viability. PAC1 is a mammalian proteasome assembly chaperone that plays a role in the initial assembly of the 20S proteasome, the catalytic core of the 26S proteasome, but does not cause a complete loss of the 20S proteasome when knocked down. Thus, both chaperone-dependent and -independent assembly pathways exist in cells, but the contribution of the chaperone-dependent pathway remains unclear. To elucidate its biological significance in mammals, we generated PAC1 conditional knockout mice. PAC1-null mice exhibited early embryonic lethality, demonstrating that PAC1 is essential for mammalian development, especially for explosive cell proliferation. In quiescent adult hepatocytes, PAC1 is responsible for producing the majority of the 20S proteasome. PAC1-deficient hepatocytes contained normal amounts of the 26S proteasome, but they completely lost the free latent 20S proteasome. They also accumulated ubiquitinated proteins and exhibited premature senescence. Our results demonstrate the importance of the PAC1-dependent assembly pathway and of the latent 20S proteasomes for maintaining cellular integrity.