Subcellular localization of proteasomes and their regulatory complexes in mammalian cells. Biochem J 346(Pt 1):155-161

Department of Biochemistry, University of Bristol, School of Medical Sciences, Bristol BS8 1TD, U.K.
Biochemical Journal (Impact Factor: 4.4). 03/2000; 346 Pt 1(1):155-61. DOI: 10.1042/0264-6021:3460155
Source: PubMed


Proteasomes can exist in several different molecular forms in mammalian cells. The core 20S proteasome, containing the proteolytic sites, binds regulatory complexes at the ends of its cylindrical structure. Together with two 19S ATPase regulatory complexes it forms the 26S proteasome, which is involved in ubiquitin-dependent proteolysis. The 20S proteasome can also bind 11S regulatory complexes (REG, PA28) which play a role in antigen processing, as do the three variable gamma-interferon-inducible catalytic beta-subunits (e.g. LMP7). In the present study, we have investigated the subcellular distribution of the different forms of proteasomes using subunit specific antibodies. Both 20S proteasomes and their 19S regulatory complexes are found in nuclear, cytosolic and microsomal preparations isolated from rat liver. LMP7 was enriched approximately two-fold compared with core alpha-type proteasome subunits in the microsomal preparations. 20S proteasomes were more abundant than 26S proteasomes, both in liver and cultured cell lines. Interestingly, some significant differences were observed in the distribution of different subunits of the 19S regulatory complexes. S12, and to a lesser extent p45, were found to be relatively enriched in nuclear fractions from rat liver, and immunofluorescent labelling of cultured cells with anti-p45 antibodies showed stronger labelling in the nucleus than in the cytoplasm. The REG was found to be localized predominantly in the cytoplasm. Three- to six-fold increases in the level of REG were observed following gamma-interferon treatment of cultured cells but gamma-interferon had no obvious effect on its subcellular distribution. These results demonstrate that different regulatory complexes and subpopulations of proteasomes have different distributions within mammalian cells and, therefore, that the distribution is more complex than has been reported for yeast proteasomes.

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Available from: Rachael Zoe Murray, Jul 03, 2014
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    • "PSA activity of proteasome is the main responsible for the degradation of polyQ, which are highly toxic and associated with neurodegenerative diseases when accumulated (Bhutani et al., 2007; Menzies et al., 2010). Increased PSA activity found in low density microsomal fraction (proteasome-containing fraction) (Brooks et al., 2000) should affect the immune system in obese. Finally, MetAP is a metalloproteinase best known to be responsible for the removal of the amino acid Met from the N-terminus of newly synthesized proteins, facilitating their translocation from the ribosomes (Kishor et al., 2013; Mauriz et al., 2010). "
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    ABSTRACT: This study checked the existence of a diverse array of aminopeptidase (AP) enzymes in high (HDM) and low (LDM) density microsomal and plasma membrane (MF) fractions from adipocytes of control, monosodium glutamate obese and food deprived rats. Gene expression was detected for ArgAP, AspAP, MetAP, and two AlaAP (APM and PSA). APM and PSA had the highest catalytic efficiency, whereas AspAP the highest affinity. Subcellular distribution of AP activities depended on metabolic status. Comparing catalytic levels, AspAP in HDM, LDM and MF was absent in obese and control under food deprivation; PSA in LDM was 3.5-times higher in obese than in normally fed control and control and obese under food deprivation; MetAP in MF was 4.5-times higher in obese than in food deprived obese. Data show new AP enzymes genetically expressed in subcellular compartments of adipocytes, three of them with altered catalytic levels that respond to whole-body energetic demands. Copyright © 2015. Published by Elsevier Ireland Ltd.
    Full-text · Article · Aug 2015 · Molecular and Cellular Endocrinology
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    • "It is also noteworthy that the cylinder-shaped 20S catalytic core of the 26S proteasome can dissociate from the larger complex and is itself catalytically active, degrading proteins in the absence of ATP and ubiquitin. In fact, the 20S proteasome is the predominant enzyme form in most mammalian cells [64] and rather selectively degrades oxidized, misfolded and covalently modified proteins [65] [66]. Such degradation is critical as a means of cellular detoxification, as damaged proteins are potentially harmful because they can become entangled into protein aggregates. "
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    ABSTRACT: In this review, we describe research findings on the effects of alcohol exposure on two major catabolic systems in liver cells: the ubiquitin–proteasome system (UPS) and autophagy. These hydrolytic systems are not unique to liver cells; they exist in all eukaryotic tissues and cells. However, because the liver is the principal site of ethanol metabolism, it sustains the greatest damage from heavy drinking. Thus, the focus of this review is to specifically describe how ethanol oxidation modulates the activities of the UPS and autophagy and the mechanisms by which these changes contribute to the pathogenesis of alcohol-induced liver injury. Here, we describe the history and the importance of cellular hydrolytic systems, followed by a description of each catabolic pathway and the differential modulation of each by ethanol exposure. Overall, the evidence for an involvement of these catabolic systems in the pathogenesis of alcoholic liver disease is quite strong. It underscores their importance, not only as effective means of cellular recycling and eventual energy generation, but also as essential components of cellular defense.
    Full-text · Article · Dec 2014
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    • "More recently, Ubx4 was shown to regulate proteasome localization along with Cdc48 [37]. In mammalian cells, proteasomes are distributed throughout the cytosol and nucleus [42], while in budding yeast, proteasomes are enriched in the nucleus [43]. We found that proteasomes, as visualized by Pre6-GFP, concentrated to a discrete spot when UBX4 expression was repressed through GAL promoter in the cdc48-3 strain (Figure 5d). "
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    ABSTRACT: Background In mammalian cells, ASPL is involved in insulin-stimulated redistribution of the glucose transporter GLUT4 and assembly of the Golgi apparatus. Its putative yeast orthologue, Ubx4, is important for proteasome localization, endoplasmic reticulum-associated protein degradation (ERAD), and UV-induced degradation of RNA polymerase. Results Here, we show that ASPL is a cofactor of the hexameric ATPase complex, known as p97 or VCP in mammals and Cdc48 in yeast. In addition, ASPL interacts in vitro with NSF, another hexameric ATPase complex. ASPL localizes to the ER membrane. The central area in ASPL, containing both a SHP box and a UBX domain, is required for binding to the p97 N-domain. Knock-down of ASPL does not impair degradation of misfolded secretory proteins via the ERAD pathway. Deletion of UBX4 in yeast causes cycloheximide sensitivity, while ubx4 cdc48-3 double mutations cause proteasome mislocalization. ASPL alleviates these defects, but not the impaired ERAD. Conclusions In conclusion, ASPL and Ubx4 are homologous proteins with only partially overlapping functions. Both interact with p97/Cdc48, but while Ubx4 is important for ERAD, ASPL appears not to share this function.
    Full-text · Article · Jul 2014 · BMC Cell Biology
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