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Shim SM, Lee WJ, Kim Y, Chang JW, Song S, Jung YK. Role of S5b/PSMD5 in proteasome inhibition caused by TNF-α/NFκB in higher eukaryotes. Cell Rep 2012; 2:603-15. [PMID: 22921402 DOI: 10.1016/j.celrep.2012.07.013] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2011] [Revised: 05/18/2012] [Accepted: 07/30/2012] [Indexed: 12/13/2022] Open
Abstract
The ubiquitin-proteasome system is essential for maintaining protein homeostasis. However, proteasome dysregulation in chronic diseases is poorly understood. Through genome-wide cell-based screening using 5,500 cDNAs, a signaling pathway leading to NFκB activation was selected as an inhibitor of 26S proteasome. TNF-α increased S5b (HGNC symbol PSMD5; hereafter S5b/PSMD5) expression via NFκB, and the surplus S5b/PSMD5 directly inhibited 26S proteasome assembly and activity. Downregulation of S5b/PSMD5 abolished TNF-α-induced proteasome inhibition. TNF-α enhanced the interaction of S5b/PSMD5 with S7/PSMC2 in nonproteasome complexes, and interference of this interaction rescued TNF-α-induced proteasome inhibition. Transgenic mice expressing S5b/PSMD5 exhibited a reduced life span and premature onset of aging-related phenotypes, including reduced proteasome activity in their tissues. Conversely, S5b/PSMD5 deficiency in Drosophila melanogaster ameliorated the tau rough eye phenotype, enhanced proteasome activity, and extended the life span of tau flies. These results reveal the critical role of S5b/PSMD5 in negative regulation of proteasome by TNF-α/NFκB and provide insights into proteasome inhibition in human disease.
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Affiliation(s)
- Sang Mi Shim
- Global Research Laboratory, School of Biological Science/Bio-MAX Institute, Seoul National University, Gwanak-gu, Seoul, Korea
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52
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Lee KH, Marshall RS, Slivicke LM, Vierstra RD. Genetic analyses of the Arabidopsis 26S proteasome regulatory particle reveal its importance during light stress and a specific role for the N-terminus of RPT2 in development. PLANT SIGNALING & BEHAVIOR 2012; 7:973-978. [PMID: 22836496 PMCID: PMC3474698 DOI: 10.4161/psb.20934] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The 26S proteasome subunit RPT2 is a component of the hexameric ring of AAA-ATPases that forms the base of the 19S regulatory particle (RP). This subunit has specific roles in the yeast and mammalian proteasomes by helping promote assembly of the RP with the 20S core protease (CP) and gate the CP to prevent indiscriminate degradation of cytosolic and nuclear proteins. In plants, this subunit plays an important role in diverse processes that include shoot and root apical meristem maintenance, cell size regulation, trichome branching, and stress responses. Recently, we reported that mutants in RPT2 and several other RP subunits have reduced histone levels, suggesting that at least some of the pleiotropic phenotypes observed in these plants result from aberrant nucleosome assembly. Here, we expand our genetic analysis of RPT2 in Arabidopsis to shed additional light on the roles of the N- and C-terminal ends. We also present data showing that plants bearing mutations in RP subunit genes have their seedling phenotypes exacerbated by prolonged light exposure.
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53
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Heterozygosity for the proteasomal Psmc1 ATPase is insufficient to cause neuropathology in mouse brain, but causes cell cycle defects in mouse embryonic fibroblasts. Neurosci Lett 2012; 521:130-5. [PMID: 22677101 DOI: 10.1016/j.neulet.2012.05.070] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2012] [Revised: 05/14/2012] [Accepted: 05/29/2012] [Indexed: 11/22/2022]
Abstract
The ubiquitin proteasome system (UPS) is a fundamental cellular pathway, degrading most unwanted intracellular soluble proteins. Dysfunction of the UPS has been associated with normal aging as well as various age-related pathological conditions, including chronic human neurodegenerative diseases such as Alzheimer's and Parkinson's diseases, leading to a significant interest in the involvement of this degradative system in neurones. We previously reported that the 26S proteasome was essential for neuronal homeostasis and survival in mouse brains following conditional genetic homozygous knockout of a key subunit of the multi-meric 26S proteasome (19S ATPase Psmc1). Here, we investigated the effects of Psmc1 heterozygosity in the mouse brain and primary mouse embryonic fibroblasts. Neuropathologically and biochemically, Psmc1 heterozygous (Psmc1(+/-)) knockout mice were indistinguishable from wild-type mice. However, we report a novel age-related accumulation of intraneuronal lysine 48-specific polyubiquitin-positive granular staining in both wild-type and heterozygous Psmc1 knockout mouse brain. In Psmc1(+/-) MEFs, we found a significant decrease in PSMC1 levels, altered 26S proteasome assembly and a notable G2/M cell cycle arrest that was not associated with an increase in the cell cycle regulatory protein p21. The disturbance in cell cycle progression may be responsible for the growth inhibitory effects in Psmc1(+/-) MEFs.
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Erales J, Hoyt MA, Troll F, Coffino P. Functional asymmetries of proteasome translocase pore. J Biol Chem 2012; 287:18535-43. [PMID: 22493437 DOI: 10.1074/jbc.m112.357327] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Degradation by proteasomes involves coupled translocation and unfolding of its protein substrates. Six distinct but paralogous proteasome ATPase proteins, Rpt1 to -6, form a heterohexameric ring that acts on substrates. An axially positioned loop (Ar-Φ loop) moves in concert with ATP hydrolysis, engages substrate, and propels it into a proteolytic chamber. The aromatic (Ar) residue of the Ar-Φ loop in all six Rpts of S. cerevisiae is tyrosine; this amino acid is thought to have important functional contacts with substrate. Six yeast strains were constructed and characterized in which Tyr was individually mutated to Ala. The mutant cells were viable and had distinct phenotypes. rpt3, rpt4, and rpt5 Tyr/Ala mutants, which cluster on one side of the ATPase hexamer, were substantially impaired in their capacity to degrade substrates. In contrast, rpt1, rpt2, and rpt6 mutants equaled or exceeded wild type in degradation activity. However, rpt1 and rpt6 mutants had defects that limited cell growth or viability under conditions that stressed the ubiquitin proteasome system. In contrast, the rpt3 mutant grew faster than wild type and to a smaller size, a defect that has previously been associated with misregulation of G1 cyclins. This rpt3 phenotype probably results from altered degradation of cell cycle regulatory proteins. Finally, mutation of five of the Rpt subunits increased proteasome ATPase activity, implying bidirectional coupling between the Ar-Φ loop and the ATP hydrolysis site. The present observations assign specific functions to individual Rpt proteins and provide insights into the diverse roles of the axial loops of individual proteasome ATPases.
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Affiliation(s)
- Jenny Erales
- Department of Microbiology and Immunology, University of California, San Francisco, California 94127, USA
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55
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Lee SH, Moon JH, Yoon SK, Yoon JB. Stable incorporation of ATPase subunits into 19 S regulatory particle of human proteasome requires nucleotide binding and C-terminal tails. J Biol Chem 2012; 287:9269-79. [PMID: 22275368 DOI: 10.1074/jbc.m111.316208] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
The 26 S proteasome is a large multi-subunit protein complex that degrades ubiquitinated proteins in eukaryotic cells. Proteasome assembly is a complex process that involves formation of six- and seven-membered ring structures from homologous subunits. Here we report that the assembly of hexameric Rpt ring of the 19 S regulatory particle (RP) requires nucleotide binding but not ATP hydrolysis. Disruption of nucleotide binding to an Rpt subunit by mutation in the Walker A motif inhibits the assembly of the Rpt ring without affecting heterodimer formation with its partner Rpt subunit. Coexpression of the base assembly chaperones S5b and PAAF1 with mutant Rpt1 and Rpt6, respectively, relieves assembly inhibition of mutant Rpts by facilitating their interaction with adjacent Rpt dimers. The mutation in the Walker B motif which impairs ATP hydrolysis does not affect Rpt ring formation. Incorporation of a Walker B mutant Rpt subunit abrogates the ATPase activity of the 19 S RP, suggesting that failure of the mutant Rpt to undergo the conformational transition from an ATP-bound to an ADP-bound state impairs conformational changes in the other five wild-type Rpts in the Rpt ring. In addition, we demonstrate that the C-terminal tails of Rpt subunits possessing core particle (CP)-binding affinities facilitate the cellular assembly of the 19 S RP, implying that the 20 S CP may function as a template for base assembly in human cells. Taken together, these results suggest that the ATP-bound conformational state of an Rpt subunit with the exposed C-terminal tail is competent for cellular proteasome assembly.
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Affiliation(s)
- Seung-Hoon Lee
- Department of Biochemistry, Yonsei University, Seoul, Korea
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56
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Chamieh H, Marty V, Guetta D, Perollier A, Franzetti B. Stress regulation of the PAN-proteasome system in the extreme halophilic archaeon Halobacterium. Extremophiles 2012; 16:215-25. [PMID: 22215023 DOI: 10.1007/s00792-011-0421-0] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2011] [Accepted: 12/13/2011] [Indexed: 11/24/2022]
Abstract
In Archaea, the importance of the proteasome system for basic biological processes is only poorly understood. Proteasomes were partially purified from Halobacterium by native gradient density ultracentrifugation. The peptidase activity profiles showed that the 20S proteasome accumulation is altered depending on the physiological state of the cells. The amount of active 20S particles increases in Halobacterium cells as a response to thermal and low salt stresses. In the same conditions, Northern experiments showed a positive transcriptional regulation of the alpha and beta proteasome subunits as well as of the two proteasome regulatory ATPases, PANA and PANB. Co-immunoprecipitation experiments demonstrated the existence of a physical interaction between the two Proteasome Activating Nucleotidase (PAN) proteins in cell extracts. Thus, a direct regulation occurs on the PAN-proteasome components to adjust the protein degradation activity to growth and environmental constraints. These results also indicate that, in extreme halophiles, proteasome mediated proteolysis is an important aspect of low salt stress response. The tri-peptide vinyl sulfone inhibitor NLVS was used in cell cultures to study the in vivo function of proteasome in Halobacterium. The chemical inhibition of proteasomes was measured in the cellular extracts. It has no effect on cell growth and mortality under normal growth conditions as well as under heat shock conditions. These results suggest that the PAN activators or other proteases compensate for loss of proteasome activity in stress conditions.
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Affiliation(s)
- H Chamieh
- Extremophiles and Large Molecular Assemblies Group, UMR5075, CNRS, Institut de Biologie Structurale, 41 rue J. Horowitz, 38027, Grenoble Cedex 1, France
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57
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Abstract
Proteasome is a highly organized protease complex comprising a catalytic 20S core particle (CP) and two 19S regulatory particles (RP), which together form the 26S structure. The 26S proteasome is responsible for the degradation of most ubiquitylated proteins through a multistep process involving recognition of the polyubiquitin chain, unfolding of the substrate, and translocation of the substrate into the active site in the cavity of the CP. Recent studies have shed light on various aspects of the complex functions of the 26S proteasome. In addition, the recent identification of various proteasome-dedicated chaperones indicates that the assembly pathways of the RP and CP are multistep processes. In this review, we summarize recent advances in the understanding of the proteasome structure, function, and assembly.
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58
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Abstract
The proteasome is an ATP-dependent molecular machine that degrades proteins through the concerted activity of dozens of subunits. It is the yin to the ribosome's yang, and together these entities mold the protein landscape of the cell. Native gels are generally superior to conventional and affinity purifications for the analytical resolution proteasomal variants, and have thus become a staple of proteasome work. Here, we describe the technique of using native gels to observe proteasomes in complex with ubiquitin conjugates. We discuss the consequences of ubiquitin conjugate length and concentration on the migration of these complexes, the use of this mobility shift to evaluate the relative affinity of mutant proteasomes for ubiquitin conjugates, and the effects of deubiquitinating enzymes and competing ubiquitin-binding proteins on the interactions of ubiquitin conjugates with the proteasome.
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59
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Lee KH, Minami A, Marshall RS, Book AJ, Farmer LM, Walker JM, Vierstra RD. The RPT2 subunit of the 26S proteasome directs complex assembly, histone dynamics, and gametophyte and sporophyte development in Arabidopsis. THE PLANT CELL 2011; 23:4298-317. [PMID: 22158466 PMCID: PMC3269867 DOI: 10.1105/tpc.111.089482] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The regulatory particle (RP) of the 26S proteasome contains a heterohexameric ring of AAA-ATPases (RPT1-6) that unfolds and inserts substrates into the core protease (CP) for degradation. Through genetic analysis of the Arabidopsis thaliana gene pair encoding RPT2, we show that this subunit plays a critical role in 26S proteasome assembly, histone dynamics, and plant development. rpt2a rpt2b double null mutants are blocked in both male and female gamete transmission, demonstrating that the subunit is essential. Whereas rpt2b mutants are phenotypically normal, rpt2a mutants display a range of defects, including impaired leaf, root, trichome, and pollen development, delayed flowering, stem fasciation, hypersensitivity to mitomycin C and amino acid analogs, hyposensitivity to the proteasome inhibitor MG132, and decreased 26S complex stability. The rpt2a phenotype can be rescued by both RPT2a and RPT2b, indicative of functional redundancy, but not by RPT2a mutants altered in ATP binding/hydrolysis or missing the C-terminal hydrophobic sequence that docks the RPT ring onto the CP. Many rpt2a phenotypes are shared with mutants lacking the chromatin assembly factor complex CAF1. Like caf1 mutants, plants missing RPT2a or reduced in other RP subunits contain less histones, thus implicating RPT2 specifically, and the 26S proteasome generally, in plant nucleosome assembly.
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60
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Furth N, Gertman O, Shiber A, Alfassy OS, Cohen I, Rosenberg MM, Doron NK, Friedler A, Ravid T. Exposure of bipartite hydrophobic signal triggers nuclear quality control of Ndc10 at the endoplasmic reticulum/nuclear envelope. Mol Biol Cell 2011; 22:4726-39. [PMID: 21998200 PMCID: PMC3237617 DOI: 10.1091/mbc.e11-05-0463] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Proper functioning of the protein-folding quality control network depends on the network's ability to discern diverse structural perturbations to the native states of its protein substrates. Despite the centrality of the detection of misfolded states to cell home-ostasis, very little is known about the exact sequence and structural features that mark a protein as being misfolded. To investigate these features, we studied the requirements for the degradation of the yeast kinetochore protein Ndc10p. Mutant Ndc10p is a substrate of a protein-folding quality control pathway mediated by the E3 ubiquitin (Ub) ligase Doa10p at the endoplasmic reticulum (ER)/nuclear envelope membrane. Analysis of Ndc10p mutant derivatives, employing a reverse genetics approach, identified an autonomous quality control-associated degradation motif near the C-terminus of the protein. This motif is composed of two indispensable hydrophobic elements: a hydrophobic surface of an amphipathic helix and a loosely structured hydrophobic C-terminal tail. Site-specific point mutations expose these elements, triggering ubiquitin-mediated and HSP70 chaperone-dependent degradation of Ndc10p. These findings substantiate the ability of the ER quality control system to recognize subtle perturbation(s) in the native structure of a nuclear protein.
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Affiliation(s)
- Noa Furth
- Department of Biological Chemistry, A Silberman Institute of Life Sciences, Jerusalem 91904, Israel
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61
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Kruegel U, Robison B, Dange T, Kahlert G, Delaney JR, Kotireddy S, Tsuchiya M, Tsuchiyama S, Murakami CJ, Schleit J, Sutphin G, Carr D, Tar K, Dittmar G, Kaeberlein M, Kennedy BK, Schmidt M. Elevated proteasome capacity extends replicative lifespan in Saccharomyces cerevisiae. PLoS Genet 2011; 7:e1002253. [PMID: 21931558 PMCID: PMC3169524 DOI: 10.1371/journal.pgen.1002253] [Citation(s) in RCA: 173] [Impact Index Per Article: 13.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2011] [Accepted: 07/06/2011] [Indexed: 12/23/2022] Open
Abstract
Aging is characterized by the accumulation of damaged cellular macromolecules caused by declining repair and elimination pathways. An integral component employed by cells to counter toxic protein aggregates is the conserved ubiquitin/proteasome system (UPS). Previous studies have described an age-dependent decline of proteasomal function and increased longevity correlates with sustained proteasome capacity in centenarians and in naked mole rats, a long-lived rodent. Proof for a direct impact of enhanced proteasome function on longevity, however, is still lacking. To determine the importance of proteasome function in yeast aging, we established a method to modulate UPS capacity by manipulating levels of the UPS–related transcription factor Rpn4. While cells lacking RPN4 exhibit a decreased non-adaptable proteasome pool, loss of UBR2, an ubiquitin ligase that regulates Rpn4 turnover, results in elevated Rpn4 levels, which upregulates UPS components. Increased UPS capacity significantly enhances replicative lifespan (RLS) and resistance to proteotoxic stress, while reduced UPS capacity has opposing consequences. Despite tight transcriptional co-regulation of the UPS and oxidative detoxification systems, the impact of proteasome capacity on lifespan is independent of the latter, since elimination of Yap1, a key regulator of the oxidative stress response, does not affect lifespan extension of cells with higher proteasome capacity. Moreover, since elevated proteasome capacity results in improved clearance of toxic huntingtin fragments in a yeast model for neurodegenerative diseases, we speculate that the observed lifespan extension originates from prolonged elimination of damaged proteins in old mother cells. Epistasis analyses indicate that proteasome-mediated modulation of lifespan is at least partially distinct from dietary restriction, Tor1, and Sir2. These findings demonstrate that UPS capacity determines yeast RLS by a mechanism that is distinct from known longevity pathways and raise the possibility that interventions to promote enhanced proteasome function will have beneficial effects on longevity and age-related disease in humans. The ubiquitin/proteasome system (UPS) is an integral part of the machinery that maintains cellular protein homeostasis and represents the major pathway for specific protein degradation in the cytoplasm and nuclei of eukaryotic cells. Its proteolytic capacity declines with age. In parallel, substrate load for the UPS increases in aging cells due to accumulated protein damage. This imbalance is thought to be an origin for the frequently observed accumulation of protein aggregates in aged cells and is thought to contribute to age-related cellular dysfunction. In this study, we investigated the impact of proteasome capacity on replicative lifespan in Saccharomyces cerevisiae using a genetic system that allows manipulation of UPS abundance at the transcriptional level. The results obtained reveal a positive correlation between proteasome capacity and longevity, with reduced lifespan in cells with low proteasome abundance or activity and strong lifespan extension upon up-regulation of the UPS in a mechanism that is at least partially independent of known yeast longevity modulating pathways. The same correlation is observed for oxidative and protein stress tolerance and clearance of toxic huntingtin fragments in a yeast model for neurodegenerative diseases, suggesting that lifespan extension by increased proteasome capacity is caused by improved protein homeostasis.
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Affiliation(s)
- Undine Kruegel
- Department of Biochemistry, Albert Einstein College of Medicine, New York, New York, United States of America
| | - Brett Robison
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
- Buck Institute, Novato, California, United States of America
| | - Thomas Dange
- Department of Biochemistry, Albert Einstein College of Medicine, New York, New York, United States of America
| | - Günther Kahlert
- Max Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Joe R. Delaney
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
- Department of Molecular and Cellular Biology Program, University of Washington, Seattle, Washington, United States of America
| | - Soumya Kotireddy
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
| | | | | | - Christopher J. Murakami
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Jennifer Schleit
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - George Sutphin
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
- Department of Molecular and Cellular Biology Program, University of Washington, Seattle, Washington, United States of America
| | - Daniel Carr
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
| | - Krisztina Tar
- Department of Biochemistry, Albert Einstein College of Medicine, New York, New York, United States of America
| | - Gunnar Dittmar
- Max Delbrueck Center for Molecular Medicine, Berlin, Germany
| | - Matt Kaeberlein
- Department of Pathology, University of Washington, Seattle, Washington, United States of America
- * E-mail: (MS); (BKK); (MK)
| | - Brian K. Kennedy
- Department of Biochemistry, University of Washington, Seattle, Washington, United States of America
- Buck Institute, Novato, California, United States of America
- * E-mail: (MS); (BKK); (MK)
| | - Marion Schmidt
- Department of Biochemistry, Albert Einstein College of Medicine, New York, New York, United States of America
- * E-mail: (MS); (BKK); (MK)
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62
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Ueda M, Matsui K, Ishiguro S, Kato T, Tabata S, Kobayashi M, Seki M, Shinozaki K, Okada K. Arabidopsis RPT2a encoding the 26S proteasome subunit is required for various aspects of root meristem maintenance, and regulates gametogenesis redundantly with its homolog, RPT2b. PLANT & CELL PHYSIOLOGY 2011; 52:1628-40. [PMID: 21784786 DOI: 10.1093/pcp/pcr093] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/21/2023]
Abstract
The 26S proteasome plays fundamental roles in the degradation of short-lived regulatory proteins, thereby controlling diverse cellular processes. In Arabidopsis, the essential RPT2 subunit is encoded by two highly homologous genes: RPT2a and RPT2b. Currently, only RPT2a has been reported to regulate various developmental processes, including the maintenance of the root apical meristem (RAM), although the roles of RPT2a in the RAM are still obscure. Here, we analyzed the cell type-specific requirement for RPT2a. When RPT2a was expressed locally in the rpt2a mutant, pleiotropic defects in the RAM, such as cell death and distorted cellular organization, were rescued differently, suggesting that RPT2a regulates various specific activities, which converge to maintain the RAM. On the other hand, the homologous RPT2b was also expressed in meristems, and the expression of RPT2b protein under the control of the RPT2a promoter complemented the rpt2a RAM defects, although the rpt2b mutant showed no obvious defect in all developmental aspects we examined. These results show that RPT2b might work in the RAM, but is dispensable for RAM maintenance in the presence of RPT2a. In contrast, the rpt2a rpt2b double mutant was lethal in male and female gametophytes, suggesting that RPT2a and RPT2b are redundantly required for gametogenesis. Furthermore, we showed that similar meristematic and gametophytic defects were caused by mutations in other subunit genes, RPT5a and RPT5b, suggesting that proper activity of the proteasome, not an RPT2-specific function, is required. Taken together, our results suggest that RPT2a and RPT2b contribute differently to the proteasome activity required for each developmental context.
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Affiliation(s)
- Minako Ueda
- Department of Botany, Graduate School of Science, Kyoto University, Kyoto, Japan
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63
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Lee SYC, De la Mota-Peynado A, Roelofs J. Loss of Rpt5 protein interactions with the core particle and Nas2 protein causes the formation of faulty proteasomes that are inhibited by Ecm29 protein. J Biol Chem 2011; 286:36641-51. [PMID: 21878651 DOI: 10.1074/jbc.m111.280875] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The proteasome is a large and complex protease formed by 66 polypeptides. The assembly of the proteasome is assisted by at least nine chaperones. One of these chaperones, Nas2/p27, binds to the C-terminal region of the AAA-ATPase Rpt5. We report here that the tail of Rpt5 provides two functions. First, it facilitates the previously reported interaction with the proteasome core particle (CP). Second, it is essential for the interaction with Nas2. Deletion of the C-terminal amino acid of Rpt5 disrupts the CP interaction, but not the binding to Nas2. The latter is surprising considering Nas2 contains a PDZ domain, which is often involved in binding to C termini. Interestingly, deletion of the last three amino acids interferes with both functions. The disruption of the Rpt5-CP interactions gave distinct phenotypes different from disruption of the Nas2-Rpt5 interaction. Additionally, proteasomes purified from a Saccharomyces cerevisiae rpt5-Δ3 strain show a strong enrichment of Ecm29. The function of Ecm29, a proteasome-associated protein, is not well understood. Our data show that Ecm29 can inhibit proteasomes, because our Ecm29-containing proteasomes have reduced suc-LLVY-AMC hydrolytic activity. Consistent with this apparent role as negative regulator, the deletion of ECM29 rescues the phenotypes of rpt5-Δ3 and nas2Δ in an hsm3Δ background. In sum, the interactions facilitated by the tail of Rpt5 act synergistically to minimize the formation of faulty proteasomes, thereby preventing recognition and inhibition by Ecm29.
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Affiliation(s)
- Stella Yu-Chien Lee
- Molecular, Cellular and Developmental Biology Program, Division of Biology, Kansas State University, Manhattan, Kansas 66506, USA
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64
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Bar-Nun S, Glickman MH. Proteasomal AAA-ATPases: structure and function. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2011; 1823:67-82. [PMID: 21820014 DOI: 10.1016/j.bbamcr.2011.07.009] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/05/2011] [Revised: 07/07/2011] [Accepted: 07/18/2011] [Indexed: 01/18/2023]
Abstract
The 26S proteasome is a chambered protease in which the majority of selective cellular protein degradation takes place. Throughout evolution, access of protein substrates to chambered proteases is restricted and depends on AAA-ATPases. Mechanical force generated through cycles of ATP binding and hydrolysis is used to unfold substrates, open the gated proteolytic chamber and translocate the substrate into the active proteases within the cavity. Six distinct AAA-ATPases (Rpt1-6) at the ring base of the 19S regulatory particle of the proteasome are responsible for these three functions while interacting with the 20S catalytic chamber. Although high resolution structures of the eukaryotic 26S proteasome are not yet available, exciting recent studies shed light on the assembly of the hetero-hexameric Rpt ring and its consequent spatial arrangement, on the role of Rpt C-termini in opening the 20S 'gate', and on the contribution of each individual Rpt subunit to various cellular processes. These studies are illuminated by paradigms generated through studying PAN, the simpler homo-hexameric AAA-ATPase of the archaeal proteasome. The similarities between PAN and Rpts highlight the evolutionary conserved role of AAA-ATPase in protein degradation, whereas unique properties of divergent Rpts reflect the increased complexity and tighter regulation attributed to the eukaryotic proteasome.
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Affiliation(s)
- Shoshana Bar-Nun
- Department of Biochemistry and Molecular Biology, George S. Wise Faculty of Life Sciences, Tel Aviv University, Tel Aviv 69978, Israel.
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65
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Kim YC, DeMartino GN. C termini of proteasomal ATPases play nonequivalent roles in cellular assembly of mammalian 26 S proteasome. J Biol Chem 2011; 286:26652-66. [PMID: 21628461 DOI: 10.1074/jbc.m111.246793] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 26 S proteasome comprises two multisubunit subcomplexes as follows: 20 S proteasome and PA700/19 S regulatory particle. The cellular mechanisms by which these subcomplexes assemble into 26 S proteasome and the molecular determinants that govern the assembly process are poorly defined. Here, we demonstrate the nonequivalent roles of the C termini of six AAA subunits (Rpt1-Rpt6) of PA700 in 26 S proteasome assembly in mammalian cells. The C-terminal HbYX motif (where Hb is a hydrophobic residue, Y is tyrosine, and X is any amino acid) of each of two subunits, Rpt3 and Rpt5, but not that of a third subunit Rpt2, was essential for assembly of 26 S proteasome. The C termini of none of the three non-HbYX motif Rpt subunits were essential for cellular 26 S proteasome assembly, although deletion of the last three residues of Rpt6 destabilized the 20 S-PA700 interaction. Rpt subunits defective for assembly into 26 S proteasome due to C-terminal truncations were incorporated into intact PA700. Moreover, intact PA700 accumulated as an isolated subcomplex when cellular 20 S proteasome content was reduced by RNAi. These results indicate that 20 S proteasome is not an obligatory template for assembly of PA700. Collectively, these results identify specific structural elements of two Rpt subunits required for 26 S proteasome assembly, demonstrate that PA700 can be assembled independently of the 20 S proteasome, and suggest that intact PA700 is a direct intermediate in the cellular pathway of 26 S proteasome assembly.
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Affiliation(s)
- Young-Chan Kim
- Department of Physiology, University of Texas Southwestern Medical Center, Dallas, Texas 75390-9040, USA
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66
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Functional macroautophagy induction by influenza A virus without a contribution to major histocompatibility complex class II-restricted presentation. J Virol 2011; 85:6453-63. [PMID: 21525345 DOI: 10.1128/jvi.02122-10] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Major histocompatibility complex (MHC) class II-presented peptides can be derived from both exogenous (extracellular) and endogenous (biosynthesized) sources of antigen. Although several endogenous antigen-processing pathways have been reported, little is known about their relative contributions to global CD4(+) T cell responses against complex antigens. Using influenza virus for this purpose, we assessed the role of macroautophagy, a process in which cytosolic proteins are delivered to the lysosome by de novo vesicle formation and membrane fusion. Influenza infection triggered productive macroautophagy, and autophagy-dependent presentation was readily observed with model antigens that naturally traffic to the autophagosome. Furthermore, treatments that enhance or inhibit macroautophagy modulated the level of presentation from these model antigens. However, validated enzyme-linked immunospot (ELISpot) assays of influenza-specific CD4(+) T cells from infected mice using a variety of antigen-presenting cells, including primary dendritic cells, revealed no detectable macroautophagy-dependent component. In contrast, the contribution of proteasome-dependent endogenous antigen processing to the global influenza CD4(+) response was readily appreciated. The contribution of macroautophagy to the MHC class II-restricted response may vary depending upon the pathogen.
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67
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Hsieh MT, Chen RH. Cdc48 and cofactors Npl4-Ufd1 are important for G1 progression during heat stress by maintaining cell wall integrity in Saccharomyces cerevisiae. PLoS One 2011; 6:e18988. [PMID: 21526151 PMCID: PMC3079750 DOI: 10.1371/journal.pone.0018988] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Accepted: 03/25/2011] [Indexed: 11/30/2022] Open
Abstract
The ubiquitin-selective chaperone Cdc48, a member of the AAA (ATPase Associated with various cellular Activities) ATPase superfamily, is involved in many processes, including endoplasmic reticulum-associated degradation (ERAD), ubiquitin- and proteasome-mediated protein degradation, and mitosis. Although Cdc48 was originally isolated as a cell cycle mutant in the budding yeast Saccharomyces cerevisiae, its cell cycle functions have not been well appreciated. We found that temperature-sensitive cdc48-3 mutant is largely arrested at mitosis at 37°C, whereas the mutant is also delayed in G1 progression at 38.5°C. Reporter assays show that the promoter activity of G1 cyclin CLN1, but not CLN2, is reduced in cdc48-3 at 38.5°C. The cofactor npl4-1 and ufd1-2 mutants also exhibit G1 delay and reduced CLN1 promoter activity at 38.5°C, suggesting that Npl4-Ufd1 complex mediates the function of Cdc48 at G1. The G1 delay of cdc48-3 at 38.5°C is a consequence of cell wall defect that over-activates Mpk1, a MAPK family member important for cell wall integrity in response to stress conditions including heat shock. cdc48-3 is hypersensitive to cell wall perturbing agents and is synthetic-sick with mutations in the cell wall integrity signaling pathway. Our results suggest that the cell wall defect in cdc48-3 is exacerbated by heat shock, which sustains Mpk1 activity to block G1 progression. Thus, Cdc48-Npl4-Ufd1 is important for the maintenance of cell wall integrity in order for normal cell growth and division.
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Affiliation(s)
- Meng-Ti Hsieh
- Molecular Cell Biology, Taiwan International Graduate Program, Institute of Molecular Biology, Academia Sinica, and Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan
| | - Rey-Huei Chen
- Molecular Cell Biology, Taiwan International Graduate Program, Institute of Molecular Biology, Academia Sinica, and Graduate Institute of Life Sciences, National Defense Medical Center, Taipei, Taiwan
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- * E-mail:
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68
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Sipling T, Zhai C, Panaretou B. Emw1p/YNL313cp is essential for maintenance of the cell wall in Saccharomyces cerevisiae. MICROBIOLOGY-SGM 2011; 157:1032-1041. [PMID: 21273246 DOI: 10.1099/mic.0.045971-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
There are six essential genes in the Saccharomyces cerevisiae genome which encode proteins bearing the tetratricopeptide repeat (TPR) domain that mediates protein-protein interaction. Thus far, the function of one of them, YNL313c, remains unknown. Our conditional mutants of YNL313c display osmoremedial temperature sensitivity, hypersensitivity to both Calcofluor White and low concentrations of SDS, and osmoremedial caffeine sensitivity. These are hallmarks of mutants that display cell wall defects. Accordingly we rename the gene as EMW1 (essential for maintenance of the cell wall). Loss of Emw1p function is not associated with abrogation of the cell wall integrity (CWI) MAP kinase cascade. Instead, emw1(ts) mutants activate this cascade even at permissive temperature, indicating that loss of Emw1p function does not cause a defect in sensors and effectors of cell wall signalling, but leads to a cell wall defect directly. Constitutive activation of the CWI cascade is reflected by the overproduction of chitin by emw1(ts) mutants, a compensatory response frequently displayed by cell wall mutants. Growth is restored to emw1(ts) mutants incubated at otherwise non-permissive temperature when GFA1 is overexpressed. GFA1 encodes the hexosephosphate aminotransferase that catalyses the rate-limiting step in the pathway that synthesizes the chitin precursor UDP-GlcNAc. The possibility that Emw1p is required for function of Gfa1p was ruled out, because the emw1(ts) phenotype persists when the requirement for Gfa1p is bypassed. Furthermore, if loss of Emw1p function leads to loss of function of Gfa1p, then chitin synthesis would be diminished. Instead, a stimulation of the synthesis of this polymer is detected. Consequently, the defect associated with emw1(ts) mutants may be associated with compromise in one of the remaining processes that depend on UDP-GlcNAc, namely N-glycosylation or glycosylphosphatidylinositol (GPI)-anchor synthesis.
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Affiliation(s)
- Tatjana Sipling
- Pharmaceutical Science Division, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
| | - Chao Zhai
- Pharmaceutical Science Division, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
| | - Barry Panaretou
- Pharmaceutical Science Division, King's College London, Franklin-Wilkins Building, 150 Stamford Street, London SE1 9NH, UK
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69
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Rotavirus replication requires a functional proteasome for effective assembly of viroplasms. J Virol 2011; 85:2781-92. [PMID: 21228236 DOI: 10.1128/jvi.01631-10] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The ubiquitin-proteasome system has been shown to play an important role in the replication cycle of different viruses. In this study, we describe a strong impairment of rotavirus replication upon inhibition of proteasomal activity. The effect was evidenced at the level of accumulation of viral proteins, viral RNA, and yield of infective particles. Kinetic studies revealed that the early steps of the replicative cycle following attachment, entry, and uncoating were clearly more sensitive to proteasome inhibition. We ruled out a direct inhibition of the viral polymerase activities and stability of viral proteins and found that the crucial step that was impaired by blocking proteasome activity was the assembly of new viroplasms. This was demonstrated by using chemical inhibitors of proteasome and by gene silencing using small interfering RNAs (siRNAs) specific for different proteasomal subunits and for the ubiquitin precursor RPS27A. In addition, we show that the effect of proteasome inhibition on virus infection is not due to increased levels of beta interferon (IFN-β).
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70
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Lopez AD, Tar K, Krügel U, Dange T, Ros IG, Schmidt M. Proteasomal degradation of Sfp1 contributes to the repression of ribosome biogenesis during starvation and is mediated by the proteasome activator Blm10. Mol Biol Cell 2011; 22:528-40. [PMID: 21209318 PMCID: PMC3046052 DOI: 10.1091/mbc.e10-04-0352] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The ribosome transcription activator Sfp1 is degraded by Blm10-proteasomes. Loss of BLM10 results in increased Sfp1 protein levels, increased transcription of ribosomal genes, and increased ribosome levels upon nutrient depletion. Thus Blm10-proteasome-mediated turnover of Sfp1 is a regulatory mechanism for ribosome biosynthesis repression. The regulation of ribosomal protein (RP) gene transcription is tightly linked to the nutrient status of the cell and is under the control of metabolic signaling pathways. In Saccharomyces cerevisiae several transcriptional activators mediate efficient RP gene transcription during logarithmic growth and dissociate from RP gene promoters upon nutrient limitation. Repression of RP gene transcription appears to be regulated predominantly by posttranslational modification and cellular localization of transcriptional activators. We report here that one of these factors, Sfp1, is degraded by the proteasome and that the proteasome activator Blm10 is required for regulated Sfp1 degradation. Loss of Blm10 results in the stabilization and increased nuclear abundance of Sfp1 during nutrient limitation, increased transcription of RP genes, increased levels of RPs, and decreased rapamycin-induced repression of RP genes. Thus we conclude that proteasomal degradation of Sfp1 is mediated by Blm10 and contributes to the repression of ribosome biogenesis under nutrient depletion.
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Affiliation(s)
- Antonio Diaz Lopez
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA
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71
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Peth A, Uchiki T, Goldberg AL. ATP-dependent steps in the binding of ubiquitin conjugates to the 26S proteasome that commit to degradation. Mol Cell 2010; 40:671-81. [PMID: 21095592 DOI: 10.1016/j.molcel.2010.11.002] [Citation(s) in RCA: 131] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2010] [Revised: 07/01/2010] [Accepted: 09/09/2010] [Indexed: 12/12/2022]
Abstract
Eukaryotic cells target proteins for degradation by the 26S proteasome by attaching a ubiquitin chain. Using a rapid assay, we analyzed the initial binding of ubiquitinated proteins to purified 26S particles as an isolated process at 4°C. Subunits Rpn10 and Rpn13 contribute equally to the high-affinity binding of ubiquitin chains, but in their absence, ubiquitin conjugates bind to another site with 4-fold lower affinity. Conjugate binding is stimulated 2- to 4-fold by binding of ATP or the nonhydrolyzable analog, ATPγS (but not ADP), to the 19S ATPases. Following this initial, reversible association, ubiquitin conjugates at 37°C become more tightly bound through a step that requires ATP hydrolysis and a loosely folded domain on the protein, but appears independent of ubiquitin. Unfolded or loosely folded polypeptides can inhibit this tighter binding. This commitment step precedes substrate deubiquitination and allows for selection of ubiquitinated proteins capable of being unfolded and efficiently degraded.
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Affiliation(s)
- Andreas Peth
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA
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72
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Acharya P, Liao M, Engel JC, Correia MA. Liver cytochrome P450 3A endoplasmic reticulum-associated degradation: a major role for the p97 AAA ATPase in cytochrome P450 3A extraction into the cytosol. J Biol Chem 2010; 286:3815-28. [PMID: 21107009 DOI: 10.1074/jbc.m110.186981] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The CYP3A subfamily of hepatic cytochromes P450, being engaged in the metabolism and clearance of >50% of clinically relevant drugs, can significantly influence therapeutics and drug-drug interactions. Our characterization of CYP3A degradation has indicated that CYPs 3A incur ubiquitin-dependent proteasomal degradation (UPD) in an endoplasmic reticulum (ER)-associated degradation (ERAD) process. Cytochromes P450 are monotopic hemoproteins N-terminally anchored to the ER membrane with their protein bulk readily accessible to the cytosolic proteasome. Given this topology, it was unclear whether they would require the AAA-ATPase p97 chaperone complex that retrotranslocates/dislocates ubiquitinated ER-integral and luminal proteins into the cytosol for proteasomal delivery. To assess the in vivo relevance of this p97-CYP3A association, we used lentiviral shRNAs to silence p97 (80% mRNA and 90% protein knockdown relative to controls) in sandwich-cultured rat hepatocytes. This extensive hepatic p97 knockdown remarkably had no effect on cellular morphology, ER stress, and/or apoptosis, despite the well recognized strategic p97 roles in multiple important cellular processes. However, such hepatic p97 knockdown almost completely abrogated CYP3A extraction into the cytosol, resulting in a significant accumulation of parent and ubiquitinated CYP3A species that were firmly ER-tethered. Little detectable CYP3A accumulated in the cytosol, even after concomitant inhibition of proteasomal degradation, thereby documenting a major role of p97 in CYP3A extraction and delivery to the 26 S proteasome during its UPD/ERAD. Intriguingly, the accumulated parent CYP3A was functionally active, indicating that p97 can regulate physiological CYP3A content and thus influence its clinically relevant function.
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Affiliation(s)
- Poulomi Acharya
- Department of Cellular and Molecular Pharmacology, University of California, San Francisco, California 94158-2517, USA
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73
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Chandra A, Chen L, Madura K. Synthetic lethality of rpn11-1 rpn10Δ is linked to altered proteasome assembly and activity. Curr Genet 2010; 56:543-57. [PMID: 20941496 DOI: 10.1007/s00294-010-0321-3] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2010] [Revised: 09/08/2010] [Accepted: 09/08/2010] [Indexed: 11/26/2022]
Abstract
An rpn11-1 temperature-sensitive mutant shows defect in proteolysis, mitochondrial function and proteasome assembly. The Rpn11 protein is a proteasome subunit that deubiquitinates proteolytic substrates. Multiubiquitinated proteins interact with proteasome receptors, such as Rpn10, which intriguingly is also required for promoting proteasome stability. We report here that Rpn10 binds Rpn11, and genetic studies revealed synthetic lethality of an rpn11-1 rpn10Δ double mutant. The carboxy-terminus of Rpn11 is critical for function, as deletion of 7 C-terminal residues prevented suppression of rpn11-1 rpn10Δ. Native gel electrophoresis showed increased levels of the proteasome 20S catalytic particle in rpn11-1 rpn10Δ, and altered assembly. The inviability of rpn11-1 rpn10Δ was suppressed by rpn10(uim), a mutant that can bind the proteasome, but not multiubiquitin chains. rpn10(uim) reduced the levels of free 20S, and increased formation of intact proteasomes. In contrast, rpn10(vwa), which binds multiubiquitin chains but not the proteasome, failed to suppress rpn11-1 rpn10Δ. Moreover, high levels of multiubiquitinated proteins were bound to rpn10(vwa), but were not delivered to the proteasome. Based on these findings, we propose that the lethality of rpn11-1 rpn10Δ results primarily from altered proteasome integrity. It is conceivable that Rpn10/Rpn11 interaction couples proteasome assembly to substrate binding.
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Affiliation(s)
- Abhishek Chandra
- Department of Biochemistry, Robert Wood Johnson Medical School, Piscataway, NJ 08854, USA
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74
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Xie Y. Structure, Assembly and Homeostatic Regulation of the 26S Proteasome. J Mol Cell Biol 2010; 2:308-17. [DOI: 10.1093/jmcb/mjq030] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
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75
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Um JW, Im E, Park J, Oh Y, Min B, Lee HJ, Yoon JB, Chung KC. ASK1 negatively regulates the 26 S proteasome. J Biol Chem 2010; 285:36434-46. [PMID: 20843792 DOI: 10.1074/jbc.m110.133777] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 26 S proteasome, composed of the 20 S core and 19 S regulatory particle, plays a central role in ubiquitin-dependent proteolysis. Disruption of this process contributes to the pathogenesis of the various diseases; however, the mechanisms underlying the regulation of 26 S proteasome activity remain elusive. Here, cell culture experiments and in vitro assays demonstrated that apoptosis signal-regulating kinase 1 (ASK1), a member of the MAPK kinase kinase family, negatively regulated 26 S proteasome activity. Immunoprecipitation/Western blot analyses revealed that ASK1 did not interact with 20 S catalytic core but did interact with ATPases making up the 19 S particle, which is responsible for recognizing polyubiquitinated proteins, unfolding them, and translocating them into the 20 S catalytic core in an ATP-dependent process. Importantly, ASK1 phosphorylated Rpt5, an AAA ATPase of the 19 S proteasome, and inhibited its ATPase activity, an effect that may underlie the ability of ASK1 to inhibit 26 S proteasome activity. The current findings point to a novel role for ASK1 in the regulation of 26 S proteasome and offer new strategies for treating human diseases caused by proteasome malfunction.
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Affiliation(s)
- Ji Won Um
- Department of Biology, College of Life Science and Biotechnology, Yonsei University, Seoul 120-749, Korea
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76
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Structure characterization of the 26S proteasome. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2010; 1809:67-79. [PMID: 20800708 DOI: 10.1016/j.bbagrm.2010.08.008] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2009] [Revised: 08/17/2010] [Accepted: 08/19/2010] [Indexed: 01/27/2023]
Abstract
In all eukaryotic cells, 26S proteasome plays an essential role in the process of ATP-dependent protein degradation. In this review, we focus on structure characterization of the 26S proteasome. Although the progress towards a high-resolution structure of the 26S proteasome has been slow, the recently solved structures of various proteasomal subcomplexes have greatly enhanced our understanding of this large machinery. In addition to having an ATP-dependent proteolytic function, the 26S proteasome is also involved in many non-proteolytic cellular activities, which are often mediated by subunits in its 19S regulatory complex. Thus, we include a detailed discussion of the structures of 19S subunits, including proteasomal ATPases, ubiquitin receptors, deubiquitinating enzymes and subunits that contain PCI domain. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!
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77
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Kwak J, Workman JL, Lee D. The proteasome and its regulatory roles in gene expression. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2010; 1809:88-96. [PMID: 20723625 DOI: 10.1016/j.bbagrm.2010.08.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Revised: 07/30/2010] [Accepted: 08/07/2010] [Indexed: 12/21/2022]
Abstract
Cumulative evidence indicates that the proteasome, which is mainly known as a protein-degrading machine, is very essential for gene expression. Destructive functions of the proteasome, i.e., ubiquitin-dependent proteolytic activity, are significant for activator localization, activator destruction, co-activator/repressor destruction and PIC disassembly. Non-proteolytic functions of the proteasome are important for recruitment of activators and co-activators to promoters, ubiquitin-dependent histone modification, transcription elongation and possibly maturation of mRNA via the facilitation of mRNA export from the nucleus to the cytoplasm. In this review, we discuss how the proteasome regulates transcription at numerous stages during gene expression. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!
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Affiliation(s)
- Jaechan Kwak
- Department of Biological Sciences, KAIST, Yuseong-Gu, Daejeon, 305-701, Korea
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78
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Caron C, Lestrat C, Marsal S, Escoffier E, Curtet S, Virolle V, Barbry P, Debernardi A, Brambilla C, Brambilla E, Rousseaux S, Khochbin S. Functional characterization of ATAD2 as a new cancer/testis factor and a predictor of poor prognosis in breast and lung cancers. Oncogene 2010; 29:5171-81. [PMID: 20581866 DOI: 10.1038/onc.2010.259] [Citation(s) in RCA: 128] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cancer cells frequently express genes normally active in male germ cells. ATAD2 is one of them encoding a conserved factor harbouring an AAA type ATPase domain and a bromodomain. We show here that ATAD2 is highly expressed in testis as well as in many cancers of different origins and that its high expression is a strong predictor of rapid mortality in lung and breast cancers. These observations suggest that ATAD2 acts on upstream and basic cellular processes to enhance oncogenesis in a variety of unrelated cell types. Accordingly, our functional studies show that ATAD2 controls chromatin dynamics, genome transcriptional activities and apoptotic cell response. We could also highlight some of the important intrinsic properties of its two regulatory domains, including a functional cross-talk between the AAA ATPase domain and the bromodomain. Altogether, these data indicate that ATAD2 overexpression in somatic cells, by acting on basic properties of chromatin, may contribute to malignant transformation.
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79
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Gallastegui N, Groll M. The 26S proteasome: assembly and function of a destructive machine. Trends Biochem Sci 2010; 35:634-42. [PMID: 20541423 DOI: 10.1016/j.tibs.2010.05.005] [Citation(s) in RCA: 156] [Impact Index Per Article: 11.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2010] [Revised: 05/06/2010] [Accepted: 05/11/2010] [Indexed: 11/29/2022]
Abstract
The heart of the ubiquitin-mediated degradation pathway, the 26S proteasome, endoproteolytically cleaves most intracellular proteins, thereby maintaining biological homeostasis and regulating many crucial processes in the cell. This hydrolyzing machine comprises more than 30 different subunits, which perform different functions including the recognition, unfolding, translocating and cleavage of protein substrates. Thus, careful assemblage and regulation of the 26S proteasome is essential to ensure correct positioning and function of each subunit, thereby preserving the delicate cellular balance between protein synthesis and degradation. Here, we review the most current research on the 26S proteasome assembly pathway, and describe the mechanism used by the cell to manage the complex structure and functions of the proteasome.
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Affiliation(s)
- Nerea Gallastegui
- Center for Integrated Protein Science at the Department Chemie, Lehrstuhl für Biochemie, Technische Universität München, Lichtenbergstr. 4, 85747 Garching, Germany
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80
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Heterohexameric ring arrangement of the eukaryotic proteasomal ATPases: implications for proteasome structure and assembly. Mol Cell 2010; 38:393-403. [PMID: 20471945 DOI: 10.1016/j.molcel.2010.02.035] [Citation(s) in RCA: 119] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2009] [Revised: 02/01/2010] [Accepted: 02/16/2010] [Indexed: 12/18/2022]
Abstract
The proteasome has a paramount role in eukaryotic cell regulation. It consists of a proteolytic core particle (CP) bound to one or two regulatory particles (RPs). Each RP is believed to include six different AAA+ ATPases in a heterohexameric ring that binds the CP while unfolding and translocating substrates into the core. No atomic-resolution RP structures are available. Guided by crystal structures of related homohexameric prokaryotic ATPases, we use disulfide engineering to show that the eukaryotic ATPases form a ring with the arrangement Rpt1-Rpt2-Rpt6-Rpt3-Rpt4-Rpt5 in fully assembled proteasomes. The arrangement is consistent with known assembly intermediates. This quaternary organization clarifies the functional overlap of specific RP assembly chaperones and led us to identify a potential RP assembly intermediate that includes four ATPases (Rpt6-Rpt3-Rpt4-Rpt5) and their cognate chaperones (Rpn14, Nas6, and Nas2). Finally, the ATPase ring structure casts light on alternative RP structural models and the mechanism of RP action.
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81
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Ordering an engagement ring. Mol Cell 2010; 38:319-20. [PMID: 20471937 DOI: 10.1016/j.molcel.2010.04.021] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
In this issue of Molecular Cell, Tomko et al. (2010) establish that the six distinct ATPase subunits of the eukaryotic proteasome form a heterohexameric ring and resolve how the subunits are arranged within the ring.
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82
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Li S, Spooner RA, Allen SCH, Guise CP, Ladds G, Schnöder T, Schmitt MJ, Lord JM, Roberts LM. Folding-competent and folding-defective forms of ricin A chain have different fates after retrotranslocation from the endoplasmic reticulum. Mol Biol Cell 2010; 21:2543-54. [PMID: 20519439 PMCID: PMC2912342 DOI: 10.1091/mbc.e09-08-0743] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
This study reveals that components of the yeast ERAD-L pathway can discriminate between two subtly different forms of the same toxin substrate. Although precytosolic requirements are similar for both toxin structures, there is a divergence in fate on the cytosolic face of the ER membrane. We report that a toxic polypeptide retaining the potential to refold upon dislocation from the endoplasmic reticulum (ER) to the cytosol (ricin A chain; RTA) and a misfolded version that cannot (termed RTAΔ), follow ER-associated degradation (ERAD) pathways in Saccharomyces cerevisiae that substantially diverge in the cytosol. Both polypeptides are dislocated in a step mediated by the transmembrane Hrd1p ubiquitin ligase complex and subsequently degraded. Canonical polyubiquitylation is not a prerequisite for this interaction because a catalytically inactive Hrd1p E3 ubiquitin ligase retains the ability to retrotranslocate RTA, and variants lacking one or both endogenous lysyl residues also require the Hrd1p complex. In the case of native RTA, we established that dislocation also depends on other components of the classical ERAD-L pathway as well as an ongoing ER–Golgi transport. However, the dislocation pathways deviate strikingly upon entry into the cytosol. Here, the CDC48 complex is required only for RTAΔ, although the involvement of individual ATPases (Rpt proteins) in the 19S regulatory particle (RP) of the proteasome, and the 20S catalytic chamber itself, is very different for the two RTA variants. We conclude that cytosolic ERAD components, particularly the proteasome RP, can discriminate between structural features of the same substrate.
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Affiliation(s)
- Shuyu Li
- Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, United Kingdom
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83
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Sorokin AV, Kim ER, Ovchinnikov LP. Proteasome system of protein degradation and processing. BIOCHEMISTRY (MOSCOW) 2010; 74:1411-42. [PMID: 20210701 DOI: 10.1134/s000629790913001x] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In eukaryotic cells, degradation of most intracellular proteins is realized by proteasomes. The substrates for proteolysis are selected by the fact that the gate to the proteolytic chamber of the proteasome is usually closed, and only proteins carrying a special "label" can get into it. A polyubiquitin chain plays the role of the "label": degradation affects proteins conjugated with a ubiquitin (Ub) chain that consists at minimum of four molecules. Upon entering the proteasome channel, the polypeptide chain of the protein unfolds and stretches along it, being hydrolyzed to short peptides. Ubiquitin per se does not get into the proteasome, but, after destruction of the "labeled" molecule, it is released and labels another molecule. This process has been named "Ub-dependent protein degradation". In this review we systematize current data on the Ub-proteasome system, describe in detail proteasome structure, the ubiquitination system, and the classical ATP/Ub-dependent mechanism of protein degradation, as well as try to focus readers' attention on the existence of alternative mechanisms of proteasomal degradation and processing of proteins. Data on damages of the proteasome system that lead to the development of different diseases are given separately.
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Affiliation(s)
- A V Sorokin
- Institute of Protein Research, Russian Academy of Sciences, Pushchino, Moscow Region, Russia.
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84
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Bhat KP, Truax AD, Brooks JK, Greer SF. Association of the 19S proteasomal ATPases with the ATPase-binding domain of CIITA is essential for CIITA stability and MHC class II expression. Immunol Cell Biol 2010; 88:807-16. [PMID: 20351748 DOI: 10.1038/icb.2010.45] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Major histocompatibility class II (MHC class II) molecules are glycoproteins that present extracellular antigens to CD4(+) T cells and are essential for initiation of adaptive immune responses. MHC class II expression requires recruitment of a master regulator, the class II transactivator (CIITA), to the MHC class II promoter. Others and we have earlier linked CIITA to the ubiquitin-proteasome system by showing that mono-ubiquitination of CIITA increases its transactivity, whereas poly-ubiquitination of CIITA leads to its degradation. We have further shown that the 26S proteasome also has non-proteolytic functions in MHC class II transcription, as 19S ATPase subunits of the 26S proteasome positively regulate MHC class II transcription and are necessary for stable promoter binding of CIITA. Although these basic requirements of the proteasome to initiate MHC class II transcription are known, how CIITA is recruited, stabilized, and degraded remains unclear. Here, we identify a novel N-terminal 19S ATPase-binding domain of CIITA. The ATPase-binding domain lies within the proline/serine/threonine-rich region of CIITA and encompasses a majority of the CIITA degron sequence. Absence of the ATPase-binding domain increases the half-life of CIITA, but blocks MHC class II surface expression, indicating that CIITA requires interaction with the 19S ATPases for both appropriate deployment and destruction.
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Affiliation(s)
- Kavita Purnanda Bhat
- Division of Cellular and Molecular Biology and Physiology, Department of Biology, Georgia State University, Atlanta, GA 30302, USA
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85
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Homoserine toxicity in Saccharomyces cerevisiae and Candida albicans homoserine kinase (thr1Delta) mutants. EUKARYOTIC CELL 2010; 9:717-28. [PMID: 20305002 DOI: 10.1128/ec.00044-10] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
Abstract
In addition to threonine auxotrophy, mutation of the Saccharomyces cerevisiae threonine biosynthetic genes THR1 (encoding homoserine kinase) and THR4 (encoding threonine synthase) results in a plethora of other phenotypes. We investigated the basis for these other phenotypes and found that they are dependent on the toxic biosynthetic intermediate homoserine. Moreover, homoserine is also toxic for Candida albicans thr1Delta mutants. Since increasing levels of threonine, but not other amino acids, overcome the homoserine toxicity of thr1Delta mutants, homoserine may act as a toxic threonine analog. Homoserine-mediated lethality of thr1Delta mutants is blocked by cycloheximide, consistent with a role for protein synthesis in this lethality. We identified various proteasome and ubiquitin pathway components that either when mutated or present in high copy numbers suppressed the thr1Delta mutant homoserine toxicity. Since the doa4Delta and proteasome mutants identified have reduced ubiquitin- and/or proteasome-mediated proteolysis, the degradation of a particular protein or subset of proteins likely contributes to homoserine toxicity.
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86
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Ubiquitinated proteins activate the proteasome by binding to Usp14/Ubp6, which causes 20S gate opening. Mol Cell 2010; 36:794-804. [PMID: 20005843 DOI: 10.1016/j.molcel.2009.11.015] [Citation(s) in RCA: 171] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2008] [Revised: 07/23/2009] [Accepted: 10/27/2009] [Indexed: 12/21/2022]
Abstract
In eukaryotic cells, ubiquitination of proteins leads to their degradation by the 26S proteasome. We tested if the ubiquitin (Ub) chain also regulates the proteasome's capacity for proteolysis. After incubation with polyubiquitinated proteins, 26S proteasomes hydrolyzed peptides and proteins 2- to 7-fold faster. Ub conjugates enhanced peptide hydrolysis by stimulating gate opening in the 20S proteasome. This stimulation was seen when this gate was closed or transiently open, but not maximally open. Gate opening requires conjugate association with Usp14/Ubp6 and also occurs if Ub aldehyde occupies this isopeptidase's active site. No stimulation was observed with 26S from Ubp6Delta mutants, but this effect was restored upon addition of Usp14/Ubp6 (even an inactive Ubp6). The stimulation of gate opening by Ub conjugates through Usp14/Ubp6 requires nucleotide binding to the gate-regulatory ATPases. This activation enhances the selectivity of the 26S proteasome for ubiquitinated proteins and links their deubiquitination to their degradation.
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87
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Malik S, Shukla A, Sen P, Bhaumik SR. The 19 s proteasome subcomplex establishes a specific protein interaction network at the promoter for stimulated transcriptional initiation in vivo. J Biol Chem 2010; 284:35714-24. [PMID: 19843524 DOI: 10.1074/jbc.m109.035709] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The 26 S proteasome complex that comprises the 20 S core and 19 S regulatory (with six ATPases) particles is engaged in an ATP-dependent degradation of a variety of key regulatory proteins and, thus, controls important cellular processes. Interestingly, several recent studies have implicated the 19 S regulatory particle in controlling eukaryotic transcriptional initiation or activation independently of the 20 S core particle. However, the mechanism of action of the 19 S proteasome subcomplex in regulation of eukaryotic transcriptional activation is not clearly understood in vivo. Here, using a chromatin immunoprecipitation assay in conjunction with mutational and transcriptional analyses in Saccharomyces cerevisiae, we show that the 19 S proteasomal subcomplex establishes a specific protein interaction network at the upstream activating sequence of the promoter. Such an interaction network is essential for formation of the preinitiation complex at the core promoter to initiate transcription. Furthermore, we demonstrate that the formation of the transcription complex assembly at the promoter is dependent on 19 S ATPase activity. Intriguingly, 19 S ATPases appear to cross-talk for stimulation of the assembly of transcription factors at the promoter. Together, these results provide significant insights as to how the 19 S proteasome subcomplex regulates the formation of the active transcription complex assembly (and, hence, transcriptional initiation) at the promoter in vivo.
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Affiliation(s)
- Shivani Malik
- Department of Biochemistry and Molecular Biology, Southern Illinois University School of Medicine, Carbondale, Illinois 62901, USA
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88
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Abstract
The 26S proteasome is a large cytoplasmic protease that degrades polyubiquitinated proteins to short peptides in a processive manner. The proteasome 19S regulatory subcomplex tethers the target protein via its polyubiquitin adduct and unfolds the target polypeptide, which is then threaded into the proteolytic site-containing 20S subcomplex. Hul5 is a 19S subcomplex-associated ubiquitin ligase that elongates ubiquitin chains on proteasome-bound substrates. We isolated hul5 Delta as a mutation with which fusions of an unstable cyclin to stable reporter proteins accumulate as partially processed products. These products appear transiently in the wild type but are strongly stabilized in 19S ATPase mutants and in the hul5 Delta mutant, supporting a role for the ATPase subunits in the unfolding of proteasome substrates before insertion into the catalytic cavity and suggesting a role for Hul5 in the processive degradation of proteins that are stalled on the proteasome.
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89
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Stadtmueller BM, Ferrell K, Whitby FG, Heroux A, Robinson H, Myszka DG, Hill CP. Structural models for interactions between the 20S proteasome and its PAN/19S activators. J Biol Chem 2009; 285:13-7. [PMID: 19889631 DOI: 10.1074/jbc.c109.070425] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteasome activity is regulated by sequestration of its proteolytic centers in a barrel-shaped structure that limits substrate access. Substrates enter the proteasome by means of activator complexes that bind to the end rings of proteasome alpha subunits and induce opening of an axial entrance/exit pore. The PA26 activator binds in a pocket on the proteasome surface using main chain contacts of its C-terminal residues and uses an internal activation loop to trigger gate opening by repositioning the proteasome Pro-17 reverse turn. Subunits of the unrelated PAN/19S activators bind with their C termini in the same pockets but can induce proteasome gate opening entirely from interactions of their C-terminal peptides, which are reported to cause gate opening by inducing a rocking motion of proteasome alpha subunits rather than by directly contacting the Pro-17 turn. Here we report crystal structures and binding studies of proteasome complexes with PA26 constructs that display modified C-terminal residues, including those corresponding to PAN. These findings suggest that PA26 and PAN/19S C-terminal residues bind superimposably and that both classes of activator induce gate opening by using direct contacts to residues of the proteasome Pro-17 reverse turn. In the case of the PAN and 19S activators, a penultimate tyrosine/phenylalanine residue contacts the proteasome Gly-19 carbonyl oxygen to stabilize the open conformation.
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Affiliation(s)
- Beth M Stadtmueller
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84112, USA
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90
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The 19S ATPase S6a (S6'/TBP1) regulates the transcription initiation of class II transactivator. J Mol Biol 2009; 395:254-69. [PMID: 19853614 DOI: 10.1016/j.jmb.2009.10.035] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2009] [Revised: 10/13/2009] [Accepted: 10/14/2009] [Indexed: 01/24/2023]
Abstract
Class II transactivator (CIITA) is the master regulator of the major histocompatibility class II transcription complex (MHC-II) and is critical for initiation of adaptive immune responses. We have previously demonstrated that the 19S proteasome ATPase Sug1 plays a significant role in regulating CIITA activity and MHC-II expression. We now show that an additional component of the 19S complex, the 19S ATPase S6a (S6'/Tat-binding protein 1), is crucial for regulating cytokine-inducible transcription of CIITA. Lack of S6a negatively impacts CIITA activity and CIITA expression. Decreased expression of S6a significantly diminishes the recruitment of transcription factors to the CIITA interferon-gamma-inducible promoter [CIITA promoter IV (pIV)] and significantly decreases CIITApIV histone H3 and histone H4 acetylation, with a preferential loss of acetylation at H3 lysine 18 and H4 lysine 8. In addition, we provide evidence for the involvement of the 19S AAA (ATPases associated with diverse cellular activity) ATPase hexamer as the 19S ATPase S6b binds CIITApIV in an S6a-dependent fashion and has effects similar to S6a on CIITApIV histone acetylation. These analyses demonstrate the importance of 19S ATPases in the assembly of CIITApIV transcription machinery and provide additional insight into the regulatory mechanisms of the 19S proteasome in mammalian transcription.
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91
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Sonoda Y, Sako K, Maki Y, Yamazaki N, Yamamoto H, Ikeda A, Yamaguchi J. Regulation of leaf organ size by the Arabidopsis RPT2a 19S proteasome subunit. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2009; 60:68-78. [PMID: 19500299 DOI: 10.1111/j.1365-313x.2009.03932.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/03/2023]
Abstract
The ubiquitin/26S proteasome pathway plays a central role in the degradation of short-lived regulatory proteins, to control many cellular events. To further understand this pathway, we focused on the RPT2 subunit of the 26S proteasome regulatory particle. The Arabidopsis genome contains two genes, AtRPT2a and AtRPT2b, which encode paralog molecules of the RPT2 subunit, with a difference of only three amino acids in the protein sequences. Both genes showed similar mRNA accumulation patterns. However, the rpt2a mutant showed a specific phenotype of enlarged leaves caused by increased cell size, in correlation with increased ploidy. Detailed analyses revealed that cell expansion is increased in the rpt2a mutant by extended endoreduplication early in leaf development. The transcription of genes encoding cell cycle-related components, for DNA replication licensing and the G2/M phase, was also promoted in the rpt2a mutant, suggesting that extended endoreduplication was caused by increased DNA replication, and disrupted regulation of the G2/M checkpoint, at the proliferation stage of leaf development.
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Affiliation(s)
- Yutaka Sonoda
- Faculty of Advanced Life Science, Hokkaido University, Kita-ku N10-W8, Sapporo 060-0810, Japan
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92
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Hofmann L, Saunier R, Cossard R, Esposito M, Rinaldi T, Delahodde A. A nonproteolytic proteasome activity controls organelle fission in yeast. J Cell Sci 2009; 122:3673-83. [PMID: 19773362 DOI: 10.1242/jcs.050229] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
To understand the processes underlying organelle function, dynamics and inheritance, it is necessary to identify and characterize the regulatory components involved. Recently in yeast and mammals, proteins of the membrane fission machinery (Dnm1-Mdv1-Caf4-Fis1 in yeast and DLP1-FIS1 in human) have been shown to have a dual localization on mitochondria and peroxisomes, where they control mitochondrial fission and peroxisome division. Here, we show that whereas vacuole fusion is regulated by the proteasome degradation function, mitochondrial fission and peroxisomal division are not controlled by the proteasome activity but rather depend on a new function of the proteasomal lid subunit Rpn11. Rpn11 was found to regulate the Fis1-dependent fission machinery of both organelles. These findings indicate a unique role of the Rpn11 protein in mitochondrial fission and peroxisomal proliferation that is independent of its role in proteasome-associated deubiquitylation.
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Affiliation(s)
- Line Hofmann
- University of Paris-Sud, CNRS, UMR 8621, Institute of Genetics and Microbiology, Orsay 91405, France
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93
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Abstract
The proteasome is an intricate molecular machine, which serves to degrade proteins following their conjugation to ubiquitin. Substrates dock onto the proteasome at its 19-subunit regulatory particle via a diverse set of ubiquitin receptors and are then translocated into an internal chamber within the 28-subunit proteolytic core particle (CP), where they are hydrolyzed. Substrate is threaded into the CP through a narrow gated channel, and thus translocation requires unfolding of the substrate. Six distinct ATPases in the regulatory particle appear to form a ring complex and to drive unfolding as well as translocation. ATP-dependent, degradation-coupled deubiquitination of the substrate is required both for efficient substrate degradation and for preventing the degradation of the ubiquitin tag. However, the proteasome also contains deubiquitinating enzymes (DUBs) that can remove ubiquitin before substrate degradation initiates, thus allowing some substrates to dissociate from the proteasome and escape degradation. Here we examine the key elements of this molecular machine and how they cooperate in the processing of proteolytic substrates.
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Affiliation(s)
- Daniel Finley
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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94
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Marques AJ, Palanimurugan R, Matias AC, Ramos PC, Dohmen RJ. Catalytic mechanism and assembly of the proteasome. Chem Rev 2009; 109:1509-36. [PMID: 19265443 DOI: 10.1021/cr8004857] [Citation(s) in RCA: 132] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Affiliation(s)
- António J Marques
- Institute for Genetics, University of Cologne, Zulpicher Strasse 47, D-50674 Cologne, Germany
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95
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Kurepa J, Wang S, Li Y, Zaitlin D, Pierce AJ, Smalle JA. Loss of 26S proteasome function leads to increased cell size and decreased cell number in Arabidopsis shoot organs. PLANT PHYSIOLOGY 2009; 150:178-89. [PMID: 19321709 PMCID: PMC2675745 DOI: 10.1104/pp.109.135970] [Citation(s) in RCA: 94] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/20/2009] [Accepted: 03/18/2009] [Indexed: 05/19/2023]
Abstract
Although the final size of plant organs is influenced by environmental cues, it is generally accepted that the primary size determinants are intrinsic factors that regulate and coordinate cell proliferation and cell expansion. Here, we show that optimal proteasome function is required to maintain final shoot organ size in Arabidopsis (Arabidopsis thaliana). Loss of function of the subunit regulatory particle AAA ATPase (RPT2a) causes a weak defect in 26S proteasome activity and leads to an enlargement of leaves, stems, flowers, fruits, seeds, and embryos. These size increases are a result of increased cell expansion that compensates for a reduction in cell number. Increased ploidy levels were found in some but not all enlarged organs, indicating that the cell size increases are not caused by a higher nuclear DNA content. Partial loss of function of the regulatory particle non-ATPase (RPN) subunits RPN10 and RPN12a causes a stronger defect in proteasome function and also results in cell enlargement and decreased cell proliferation. However, the increased cell volumes in rpn10-1 and rpn12a-1 mutants translated into the enlargement of only some, but not all, shoot organs. Collectively, these data show that during Arabidopsis shoot development, the maintenance of optimal proteasome activity levels is important for balancing cell expansion with cell proliferation rates.
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Affiliation(s)
- Jasmina Kurepa
- Plant Physiology, Biochemistry, and Molecular Biology Program, Department of Plant and Soil Sciences, College of Agriculture, University of Kentucky, Lexington, Kentucky 40546, USA
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96
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Le Tallec B, Barrault MB, Guérois R, Carré T, Peyroche A. Hsm3/S5b participates in the assembly pathway of the 19S regulatory particle of the proteasome. Mol Cell 2009; 33:389-99. [PMID: 19217412 DOI: 10.1016/j.molcel.2009.01.010] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/15/2008] [Revised: 10/03/2008] [Accepted: 01/09/2009] [Indexed: 11/19/2022]
Abstract
The 26S proteasome, the central enzyme of the ubiquitin-proteasome system, is comprised of the 20S catalytic core particle (CP) and the 19S regulatory particle (RP), itself composed of two subcomplexes, the base and the lid. 20S proteasome assembly is assisted by several chaperones. Integral subunits of the RP participate in its assembly, but no external factors have been identified so far. Here we characterize the yeast Hsm3 protein, which displays unique features regarding 19S assembly. Hsm3 associates with 19S subcomplexes via a carboxy-terminal domain of the Rpt1 base subunit but is missing in the final 26S proteasome. Moreover, Hsm3 is specifically required for the base subcomplex assembly. Finally, we identify the putative species-specific 19S subunit S5b as a functional homolog of the Hsm3 chaperone in mammals. These findings shed light on chaperone-assisted proteasome assembly in eukaryotes.
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Affiliation(s)
- Benoît Le Tallec
- Laboratoire du Métabolisme de l'ADN et Réponses aux Génotoxiques, SBIGeM, CEA, iBiTecS, Gif-sur-Yvette, F-91191, France
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97
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Gallois JL, Guyon-Debast A, Lécureuil A, Vezon D, Carpentier V, Bonhomme S, Guerche P. The Arabidopsis proteasome RPT5 subunits are essential for gametophyte development and show accession-dependent redundancy. THE PLANT CELL 2009; 21:442-59. [PMID: 19223514 PMCID: PMC2660631 DOI: 10.1105/tpc.108.062372] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/01/2008] [Revised: 01/05/2009] [Accepted: 02/03/2009] [Indexed: 05/19/2023]
Abstract
We investigated the role of the ubiquitin proteasome system (UPS), which allows proteins to be selectively degraded, during gametophyte development in Arabidopsis thaliana. Three mutant alleles altering the UPS were isolated in the Wassilewskija (Ws) accession: they affect the Regulatory Particle 5a (RPT5a) gene, which (along with RPT5b) encodes one of the six AAA-ATPases of the proteasome regulatory particle. In the heterozygous state, all three mutant alleles displayed 50% pollen lethality, suggesting that RPT5a is essential for male gametophyte development. However, a fourth mutant in the Columbia (Col) accession did not display such a phenotype because the RPT5b Col allele complements the rpt5a defect in the male gametophyte, whereas the RPT5b Ws allele does not. Double rpt5a rpt5b mutants showed a complete male and female gametophyte lethal phenotype in a Col background, indicating that RPT5 subunits are essential for both gametophytic phases. Mitotic divisions were affected in double mutant gametophytes correlating with an absence of the proteasome-dependent cyclinA3 degradation. Finally, we show that RPT5b expression is highly increased when proteasome functioning is defective, allowing complementation of the rpt5a mutation. In conclusion, RPT5 subunits are not only essential for both male and female gametophyte development but also display accession-dependent redundancy and are crucial in cell cycle progression.
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Affiliation(s)
- Jean-Luc Gallois
- Institut Jean-Pierre Bourgin, Station de Génétique et d'Amélioration des Plantes UR254, Institut National de la Recherche Agronomique, Centre de Versailles, F-78000 Versailles, France.
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98
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Bech-Otschir D, Helfrich A, Enenkel C, Consiglieri G, Seeger M, Holzhütter HG, Dahlmann B, Kloetzel PM. Polyubiquitin substrates allosterically activate their own degradation by the 26S proteasome. Nat Struct Mol Biol 2009; 16:219-25. [PMID: 19169257 DOI: 10.1038/nsmb.1547] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2008] [Accepted: 12/29/2008] [Indexed: 11/09/2022]
Abstract
The 26S proteasome degrades polyubiquitylated (polyUb) proteins by an ATP-dependent mechanism. Here we show that binding of model polyUb substrates to the 19S regulator of mammalian and yeast 26S proteasomes enhances the peptidase activities of the 20S proteasome about two-fold in a process requiring ATP hydrolysis. Monoubiquitylated proteins or tetraubiquitin alone exert no effect. However, 26S proteasomes from the yeast alpha3DeltaN open-gate mutant and the rpt2YA and rpt5YA mutants with impaired gating can still be activated (approximately 1.3-fold to 1.8-fold) by polyUb-protein binding. Thus, binding of polyUb substrates to the 19S regulator stabilizes gate opening of the 20S proteasome and induces conformational changes of the 20S proteasome that facilitate channeling of substrates and their access to active sites. In consequence, polyUb substrates will allosterically stimulate their own degradation.
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99
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HATTA T, TSUJI N, MIYOSHI T, ALIM MA, ISLAM MK, FUJISAKI K. Leucine Aminopeptidase in the Ixodid Tick Haemaphysalis longicornis: Endogenous Expression Profiles in Midgut. J Vet Med Sci 2009; 71:589-94. [DOI: 10.1292/jvms.71.589] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Affiliation(s)
- Takeshi HATTA
- Laboratory of Parasitic Diseases, National Institute of Animal Health, National Agricultural and Food Research Organization
| | - Naotoshi TSUJI
- Laboratory of Parasitic Diseases, National Institute of Animal Health, National Agricultural and Food Research Organization
| | - Takeharu MIYOSHI
- Laboratory of Parasitic Diseases, National Institute of Animal Health, National Agricultural and Food Research Organization
| | - M. Abdul ALIM
- Laboratory of Parasitic Diseases, National Institute of Animal Health, National Agricultural and Food Research Organization
| | - M. Khyrul ISLAM
- Laboratory of Parasitic Diseases, National Institute of Animal Health, National Agricultural and Food Research Organization
| | - Kozo FUJISAKI
- National Research Center for Protozoan Diseases, Obihiro University of Agriculture and Veterinary Medicine
- Laboratory of Emerging Infectious Diseases, School of Frontier Veterinary Medicine, Kagoshima University
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100
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Rousseau E, Kojima R, Hoffner G, Djian P, Bertolotti A. Misfolding of proteins with a polyglutamine expansion is facilitated by proteasomal chaperones. J Biol Chem 2008; 284:1917-29. [PMID: 18986984 PMCID: PMC2615503 DOI: 10.1074/jbc.m806256200] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Deposition of misfolded proteins with a polyglutamine expansion is a hallmark of Huntington disease and other neurodegenerative disorders. Impairment of the proteolytic function of the proteasome has been reported to be both a cause and a consequence of polyglutamine accumulation. Here we found that the proteasomal chaperones that unfold proteins to be degraded by the proteasome but also have non-proteolytic functions co-localized with huntingtin inclusions both in primary neurons and in Huntington disease patients and formed a complex independently of the proteolytic particle. Overexpression of Rpt4 or Rpt6 facilitated aggregation of mutant huntingtin and ataxin-3 without affecting proteasomal degradation. Conversely, reducing Rpt6 or Rpt4 levels decreased the number of inclusions in primary neurons, indicating that endogenous Rpt4 and Rpt6 facilitate inclusion formation. In vitro reconstitution experiments revealed that purified 19S particles promote mutant huntingtin aggregation. When fused to the ornithine decarboxylase destabilizing sequence, proteins with expanded polyglutamine were efficiently degraded and did not aggregate. We propose that aggregation of proteins with expanded polyglutamine is not a consequence of a proteolytic failure of the 20S proteasome. Rather, aggregation is elicited by chaperone subunits of the 19S particle independently of proteolysis.
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Affiliation(s)
- Erwann Rousseau
- MRC Laboratory of Molecular Biology, Hills Rd., Cambridge CB2 0QH, United Kingdom
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