1
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Thomas TA, Smith DM. Proteasome activator 28γ (PA28γ) allosterically activates trypsin-like proteolysis by binding to the α-ring of the 20S proteasome. J Biol Chem 2022; 298:102140. [PMID: 35714770 PMCID: PMC9287138 DOI: 10.1016/j.jbc.2022.102140] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2022] [Revised: 06/06/2022] [Accepted: 06/08/2022] [Indexed: 11/21/2022] Open
Abstract
Proteasome activator 28γ (PA28γ/REGγ) is a member of the 11S family of proteasomal regulators that is constitutively expressed in the nucleus and implicated in various diseases, including certain cancers and systemic lupus erythematosus. Despite years of investigation, how PA28γ functions to stimulate proteasomal protein degradation remains unclear. Alternative hypotheses have been proposed for the molecular mechanism of PA28γ, including the following: (1) substrate selection, (2) allosteric upregulation of the trypsin-like (T-L) site, (3) allosteric inhibition of the chymotrypsin-like (CT-L) and caspase-like (C-L) sites, (4) conversion of the CT-L or C-L sites to new T-L sites, and (5) gate opening alone or in combination with a previous hypothesis. Here, by mechanistically decoupling gating effects from active site effects, we unambiguously demonstrate that WT PA28γ allosterically activates the T-L site. We show PA28γ binding increases the Kcat/Km by 13-fold for T-L peptide substrates while having little-to-no effect on hydrolysis kinetics for CT-L or C-L substrates. Furthermore, mutagenesis and domain swaps of PA28γ reveal that it does not select for T-L peptide substrates through either the substrate entry pore or the distal intrinsically disordered region. We also show that a previously reported point mutation can functionally switch PA28γ from a T-L activating to a gate-opening activator in a mutually exclusive fashion. Finally, using cryogenic electron microscopy, we visualized the PA28γ-proteasome complex at 4.3 Å and confirmed its expected quaternary structure. The results of this study provide unambiguous evidence that PA28γ can function by binding the 20S proteasome to allosterically activate the T-L proteolytic site.
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Affiliation(s)
- Taylor A Thomas
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA
| | - David M Smith
- Department of Biochemistry, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA; Department of Neuroscience, Robert C. Byrd Health Sciences Center, West Virginia University, Morgantown, West Virginia, USA; WVU Rockefeller Neuroscience Institute, Morgantown, West Virginia, USA; WVU Cancer Institute, Morgantown, West Virginia, USA.
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2
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Modulation of the 20S Proteasome Activity by Porphyrin Derivatives Is Steered through Their Charge Distribution. Biomolecules 2022; 12:biom12060741. [PMID: 35740865 PMCID: PMC9220251 DOI: 10.3390/biom12060741] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2022] [Revised: 05/15/2022] [Accepted: 05/20/2022] [Indexed: 11/20/2022] Open
Abstract
Cationic porphyrins exhibit an amazing variety of binding modes and inhibition mechanisms of 20S proteasome. Depending on the spatial distribution of their electrostatic charges, they can occupy different sites on α rings of 20S proteasome by exploiting the structural code responsible for the interaction with regulatory proteins. Indeed, they can act as competitive or allosteric inhibitors by binding at the substrate gate or at the grooves between the α subunits, respectively. Moreover, the substitution of a charged moiety in the peripheral arm with a hydrophobic moiety revealed a “new” 20S functional state with higher substrate affinity and catalytic efficiency. In the present study, we expand our structure–activity relationship (SAR) analysis in order to further explore the potential of this versatile class of 20S modulators. Therefore, we have extended the study to additional macrocyclic compounds, displaying different structural features, comparing their interaction behavior on the 20S proteasome with previously investigated compounds. In particular, in order to evaluate how the introduction of a peptidic chain can affect the affinity and the interacting mechanism of porphyrins, we investigate the MTPyApi, a porphyrin derivatized with an Arg–Pro-rich antimicrobial peptide. Moreover, to unveil the role played by the porphyrin core, this was replaced with a corrole scaffold, a “contracted” version of the tetrapyrrolic ring due to the lack of a methine bridge. The analysis has been undertaken by means of integrated kinetic, Nuclear Magnetic Resonance, and computational studies. Finally, in order to assess a potential pharmacological significance of this type of investigation, a preliminary attempt has been performed to evaluate the biological effect of these molecules on MCF7 breast cancer cells in dark conditions, envisaging that porphyrins may indeed represent a powerful tool for the modulation of cellular proteostasis.
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3
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Chen X, Htet ZM, López-Alfonzo E, Martin A, Walters KJ. Proteasome interaction with ubiquitinated substrates: from mechanisms to therapies. FEBS J 2021; 288:5231-5251. [PMID: 33211406 PMCID: PMC8131406 DOI: 10.1111/febs.15638] [Citation(s) in RCA: 30] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2020] [Revised: 11/10/2020] [Accepted: 11/17/2020] [Indexed: 12/11/2022]
Abstract
The 26S proteasome is responsible for regulated proteolysis in eukaryotic cells. Its substrates are diverse in structure, function, sequence length, and amino acid composition, and are targeted to the proteasome by post-translational modification with ubiquitin. Ubiquitination occurs through a complex enzymatic cascade and can also signal for other cellular events, unrelated to proteasome-catalyzed degradation. Like other post-translational protein modifications, ubiquitination is reversible, with ubiquitin chain hydrolysis catalyzed by the action of deubiquitinating enzymes (DUBs), ~ 90 of which exist in humans and allow for temporal events and dynamic ubiquitin-chain remodeling. DUBs have been known for decades to be an integral part of the proteasome, as deubiquitination is coupled to substrate unfolding and translocation into the internal degradation chamber. Moreover, the proteasome also binds several ubiquitinating enzymes and shuttle factors that recruit ubiquitinated substrates. The role of this intricate machinery and how ubiquitinated substrates interact with proteasomes remains an area of active investigation. Here, we review what has been learned about the mechanisms used by the proteasome to bind ubiquitinated substrates, substrate shuttle factors, ubiquitination machinery, and DUBs. We also discuss many open questions that require further study or the development of innovative approaches to be answered. Finally, we address the promise of expanded therapeutic targeting that could benefit from such new discoveries.
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Affiliation(s)
- Xiang Chen
- Protein Processing Section, Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
| | - Zaw Min Htet
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California at Berkeley, CA, USA
| | - Erika López-Alfonzo
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California at Berkeley, CA, USA
| | - Andreas Martin
- Department of Molecular and Cell Biology, California Institute for Quantitative Biosciences, University of California at Berkeley, CA, USA
- Howard Hughes Medical Institute, University of California at Berkeley, CA, USA
| | - Kylie J Walters
- Protein Processing Section, Structural Biophysics Laboratory, Center for Cancer Research, National Cancer Institute, Frederick, MD, USA
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4
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Pecori F, Kondo N, Ogura C, Miura T, Kume M, Minamijima Y, Yamamoto K, Nishihara S. Site-specific O-GlcNAcylation of Psme3 maintains mouse stem cell pluripotency by impairing P-body homeostasis. Cell Rep 2021; 36:109361. [PMID: 34260942 DOI: 10.1016/j.celrep.2021.109361] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 04/09/2021] [Accepted: 06/17/2021] [Indexed: 12/14/2022] Open
Abstract
Mouse embryonic stem cell (ESC) pluripotency is tightly regulated by a complex network composed of extrinsic and intrinsic factors that allow proper organismal development. O-linked β-N-acetylglucosamine (O-GlcNAc) is the sole glycosylation mark found on cytoplasmic and nuclear proteins and plays a pivotal role in regulating fundamental cellular processes; however, its function in ESC pluripotency is still largely unexplored. Here, we identify O-GlcNAcylation of proteasome activator subunit 3 (Psme3) protein as a node of the ESC pluripotency network. Mechanistically, O-GlcNAc modification of serine 111 (S111) of Psme3 promotes degradation of Ddx6, which is essential for processing body (P-body) assembly, resulting in the maintenance of ESC pluripotent state. Conversely, loss of Psme3 S111 O-GlcNAcylation stabilizes Ddx6 and increases P-body levels, culminating in spontaneous exit of ESC from the pluripotent state. Our findings establish O-GlcNAcylation at S111 of Psme3 as a switch that regulates ESC pluripotency via control of P-body homeostasis.
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Affiliation(s)
- Federico Pecori
- Laboratory of Cell Biology, Department of Bioinformatics, Graduate School of Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan
| | - Nanako Kondo
- Laboratory of Cell Biology, Department of Science and Engineering for Sustainable Innovation, Faculty of Science and Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan
| | - Chika Ogura
- Laboratory of Cell Biology, Department of Bioinformatics, Graduate School of Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan
| | - Taichi Miura
- Laboratory of Cell Biology, Department of Bioinformatics, Graduate School of Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan
| | - Masahiko Kume
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
| | - Youhei Minamijima
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
| | - Kazuo Yamamoto
- Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8562, Japan
| | - Shoko Nishihara
- Laboratory of Cell Biology, Department of Bioinformatics, Graduate School of Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan; Laboratory of Cell Biology, Department of Science and Engineering for Sustainable Innovation, Faculty of Science and Engineering, Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan; Glycan & Life System Integration Center (GaLSIC), Soka University, 1-236 Tangi-machi, Hachioji, Tokyo 192-8577, Japan.
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5
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Cascio P. PA28γ: New Insights on an Ancient Proteasome Activator. Biomolecules 2021; 11:228. [PMID: 33562807 PMCID: PMC7915322 DOI: 10.3390/biom11020228] [Citation(s) in RCA: 31] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/02/2021] [Revised: 02/02/2021] [Accepted: 02/03/2021] [Indexed: 02/06/2023] Open
Abstract
PA28 (also known as 11S, REG or PSME) is a family of proteasome regulators whose members are widely present in many of the eukaryotic supergroups. In jawed vertebrates they are represented by three paralogs, PA28α, PA28β, and PA28γ, which assemble as heptameric hetero (PA28αβ) or homo (PA28γ) rings on one or both extremities of the 20S proteasome cylindrical structure. While they share high sequence and structural similarities, the three isoforms significantly differ in terms of their biochemical and biological properties. In fact, PA28α and PA28β seem to have appeared more recently and to have evolved very rapidly to perform new functions that are specifically aimed at optimizing the process of MHC class I antigen presentation. In line with this, PA28αβ favors release of peptide products by proteasomes and is particularly suited to support adaptive immune responses without, however, affecting hydrolysis rates of protein substrates. On the contrary, PA28γ seems to be a slow-evolving gene that is most similar to the common ancestor of the PA28 activators family, and very likely retains its original functions. Notably, PA28γ has a prevalent nuclear localization and is involved in the regulation of several essential cellular processes including cell growth and proliferation, apoptosis, chromatin structure and organization, and response to DNA damage. In striking contrast with the activity of PA28αβ, most of these diverse biological functions of PA28γ seem to depend on its ability to markedly enhance degradation rates of regulatory protein by 20S proteasome. The present review will focus on the molecular mechanisms and biochemical properties of PA28γ, which are likely to account for its various and complex biological functions and highlight the common features with the PA28αβ paralog.
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Affiliation(s)
- Paolo Cascio
- Department of Veterinary Sciences, University of Turin, Largo P. Braccini 2, 10095 Grugliasco, Italy
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6
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Wang Y, Yan K, Lin J, Liu Y, Wang J, Li X, Li X, Hua Z, Zheng Z, Shi J, Sun S, Bi J. CD8+ T Cell Co-Expressed Genes Correlate With Clinical Phenotype and Microenvironments of Urothelial Cancer. Front Oncol 2020; 10:553399. [PMID: 33330025 PMCID: PMC7713665 DOI: 10.3389/fonc.2020.553399] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2020] [Accepted: 10/20/2020] [Indexed: 01/05/2023] Open
Abstract
Purpose To identify immune-related co-expressed genes that promote CD8+ T cell infiltration in bladder cancer, and to explore the interactions among relevant genes in the tumor microenvironment. Method We obtained bladder cancer gene matrix and clinical information data from TCGA, GSE32894 and GSE48075. The “estimate” package was used to calculate tumor purity and immune score. The CIBERSORT algorithm was used to assess CD8+ T cell proportions. Weighted gene co-expression network analysis was used to identify the co-expression modules with CD8+ T cell proportions and bladder tumor purity. Subsequently, we performed correlation analysis among angiogenesis factors, angiogenesis inhibitors, immune inflammatory responses, and CD8+ T cell related genes in tumor microenvironment. Results A CD8+ T cell related co-expression network was identified. Eight co-expressed genes (PSMB8, PSMB9, PSMB10, PSME2, TAP1, IRF1, FBOX6, ETV7) were identified as CD8+ T cell-related genes that promoted infiltration of CD8+ T cells, and were enriched in the MHC class I tumor antigen presentation process. The proteins level encoded by these genes (PSMB10, PSMB9, PSMB8, TAP1, IRF1, and FBXO6) were lower in the high clinical grade patients, which suggested the clinical phenotype correlation both in mRNA and protein levels. These factors negatively correlated with angiogenesis factors and positively correlated with angiogenesis inhibitors. PD-1 and PD-L1 positively correlated with these genes which suggested PD-1 expression level positively correlated with the biological process composed by these co-expression genes. In the high expression group of these genes, inflammation and immune response were more intense, and the tumor purity was lower, suggesting that these genes were immune protective factors that improved the prognosis in patients with bladder cancer. Conclusion These co-expressed genes promote high levels of infiltration of CD8+ T cells in an immunoproteasome process involved in MHC class I molecules. The mechanism might provide new pathways for treatment of patients who are insensitive to PD-1 immunotherapy due to low degrees of CD8+ T cell infiltration.
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Affiliation(s)
- Yutao Wang
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Kexin Yan
- Department of Dermatology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Jiaxing Lin
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Yang Liu
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Jianfeng Wang
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Xuejie Li
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Xinxin Li
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Zhixiong Hua
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Zhenhua Zheng
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Jianxiu Shi
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Siqing Sun
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
| | - Jianbin Bi
- Department of Urology, China Medical University, The First Hospital of China Medical University, Shenyang, China
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7
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Li G, Tang X, Zhang S, Jin M, Wang M, Deng Z, Liu Z, Qian M, Shi W, Wang Z, Xie H, Li J, Liu B. SIRT7 activates quiescent hair follicle stem cells to ensure hair growth in mice. EMBO J 2020; 39:e104365. [PMID: 32696520 PMCID: PMC7507325 DOI: 10.15252/embj.2019104365] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2019] [Revised: 06/11/2020] [Accepted: 06/14/2020] [Indexed: 12/17/2022] Open
Abstract
Hair follicle stem cells (HFSCs) are maintained in a quiescent state until activated to grow, but the mechanisms that reactivate the quiescent HFSC reservoir are unclear. Here, we find that loss of Sirt7 in mice impedes hair follicle life‐cycle transition from telogen to anagen phase, resulting in delay of hair growth. Conversely, Sirt7 overexpression during telogen phase facilitated HSFC anagen entry and accelerated hair growth. Mechanistically, Sirt7 is upregulated in HFSCs during the telogen‐to‐anagen transition, and HFSC‐specific Sirt7 knockout mice (Sirt7f/f;K15‐Cre) exhibit a similar hair growth delay. At the molecular level, Sirt7 interacts with and deacetylates the transcriptional regulator Nfatc1 at K612, causing PA28γ‐dependent proteasomal degradation to terminate Nfatc1‐mediated telogen quiescence and boost anagen entry. Cyclosporin A, a potent calcineurin inhibitor, suppresses nuclear retention of Nfatc1, abrogates hair follicle cycle delay, and promotes hair growth in Sirt7−/− mice. Furthermore, Sirt7 is downregulated in aged HFSCs, and exogenous Sirt7 overexpression promotes hair growth in aged animals. These data reveal that Sirt7 activates HFSCs by destabilizing Nfatc1 to ensure hair follicle cycle initiation.
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Affiliation(s)
- Guo Li
- Department of Dermatology, Xiangya Hospital, Central South University, Changsha, China
| | - Xiaolong Tang
- Shenzhen Key Laboratory for Systemic Aging and Intervention (SAI), National Engineering Research Center for Biotechnology (Shenzhen), International Cancer Center, Shenzhen University, Shenzhen, China.,Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Department of Biochemistry & Molecular Biology, School of Basic Medical Sciences, Shenzhen University, Shenzhen, China
| | - Shuping Zhang
- Department of Dermatology, Xiangya Hospital, Central South University, Changsha, China
| | - Meiling Jin
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences, Shenzhen, China
| | - Ming Wang
- Shenzhen Key Laboratory for Systemic Aging and Intervention (SAI), National Engineering Research Center for Biotechnology (Shenzhen), International Cancer Center, Shenzhen University, Shenzhen, China.,Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Department of Biochemistry & Molecular Biology, School of Basic Medical Sciences, Shenzhen University, Shenzhen, China
| | - Zhili Deng
- Department of Dermatology, Xiangya Hospital, Central South University, Changsha, China
| | - Zuojun Liu
- Shenzhen Key Laboratory for Systemic Aging and Intervention (SAI), National Engineering Research Center for Biotechnology (Shenzhen), International Cancer Center, Shenzhen University, Shenzhen, China.,Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Department of Biochemistry & Molecular Biology, School of Basic Medical Sciences, Shenzhen University, Shenzhen, China
| | - Minxian Qian
- Shenzhen Key Laboratory for Systemic Aging and Intervention (SAI), National Engineering Research Center for Biotechnology (Shenzhen), International Cancer Center, Shenzhen University, Shenzhen, China.,Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Department of Biochemistry & Molecular Biology, School of Basic Medical Sciences, Shenzhen University, Shenzhen, China
| | - Wei Shi
- Department of Dermatology, Xiangya Hospital, Central South University, Changsha, China
| | - Zimei Wang
- Shenzhen Key Laboratory for Systemic Aging and Intervention (SAI), National Engineering Research Center for Biotechnology (Shenzhen), International Cancer Center, Shenzhen University, Shenzhen, China.,Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Department of Biochemistry & Molecular Biology, School of Basic Medical Sciences, Shenzhen University, Shenzhen, China
| | - Hongfu Xie
- Department of Dermatology, Xiangya Hospital, Central South University, Changsha, China
| | - Ji Li
- Department of Dermatology, Xiangya Hospital, Central South University, Changsha, China.,National Clinical Research Center for Geriatric Disorders, Xiangya Hospital, Central South University, Changsha, Hunan, China.,Key Laboratory of Organ Injury, Aging and Regenerative Medicine of Hunan Province, Changsha, Hunan, China.,Department of Dermatology, The Second Affiliated Hospital of Xinjiang Medical University, Urumqi, China
| | - Baohua Liu
- Shenzhen Key Laboratory for Systemic Aging and Intervention (SAI), National Engineering Research Center for Biotechnology (Shenzhen), International Cancer Center, Shenzhen University, Shenzhen, China.,Guangdong Key Laboratory of Genome Stability and Human Disease Prevention, Department of Biochemistry & Molecular Biology, School of Basic Medical Sciences, Shenzhen University, Shenzhen, China.,Guangdong Provincial Key Laboratory of Regional Immunity and Diseases, School of Basic Medical Sciences, Shenzhen University Health Science Center, Shenzhen, China
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8
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Exploring long-range cooperativity in the 20S proteasome core particle from Thermoplasma acidophilum using methyl-TROSY-based NMR. Proc Natl Acad Sci U S A 2020; 117:5298-5309. [PMID: 32094174 DOI: 10.1073/pnas.1920770117] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The 20S core particle (CP) proteasome is a molecular assembly catalyzing the degradation of misfolded proteins or proteins no longer required for function. It is composed of four stacked heptameric rings that form a barrel-like structure, sequestering proteolytic sites inside its lumen. Proteasome function is regulated by gates derived from the termini of α-rings and through binding of regulatory particles (RPs) to one or both ends of the barrel. The CP is dynamic, with an extensive allosteric pathway extending from one end of the molecule to catalytic sites in its center. Here, using methyl-transverse relaxation optimized spectroscopy (TROSY)-based NMR optimized for studies of high-molecular-weight complexes, we evaluate whether the pathway extends over the entire 150-Å length of the molecule. By exploiting a number of different labeling schemes, the two halves of the molecule can be distinguished, so that the effects of 11S RP binding, or the introduction of gate or allosteric pathway mutations at one end of the barrel can be evaluated at the distal end. Our results establish that while 11S binding and the introduction of key mutations affect each half of the CP allosterically, they do not further couple opposite ends of the molecule. This may have implications for the function of so-called "hybrid" proteasomes where each end of the CP is bound with a different regulator, allowing the CP to be responsive to both RPs simultaneously. The methodology presented introduces a general NMR strategy for dissecting pathways of communication in homo-oligomeric molecular machines.
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9
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Zheng Y, Shimamoto S, Maruno T, Kobayashi Y, Matsuura Y, Kawahara K, Yoshida T, Ohkubo T. N-terminal HCV core protein fragment decreases 20S proteasome activity in the presence of PA28γ. Biochem Biophys Res Commun 2018; 509:590-595. [PMID: 30602418 DOI: 10.1016/j.bbrc.2018.12.167] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2018] [Accepted: 12/26/2018] [Indexed: 12/18/2022]
Abstract
The Hepatitis C virus (HCV) core protein plays a crucial role in the development of chronic liver diseases such as chronic hepatitis, cirrhosis, and hepatocellular carcinoma (HCC). Its involvement in these diseases is reportedly abolished by a knockout of the proteasome activator PA28γ gene in transgenic mice, suggesting an interaction between the core protein and the PA28γ-proteasome system. This study found a direct interaction between the N-terminal 1-71 fragment of HCV core protein (Core71) and PA28γ in vitro, and that this interaction was found to enhance PA28γ-20S proteasome complex formation. While 20S proteasome activity was increased by PA28γ, it was significantly reduced by Core71 attachment in a dose-dependent manner. These results suggest that the Core-PA28γ interaction has an important role in regulating 20S proteasome activity and furthers our understanding of the pathogenesis of HCV.
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Affiliation(s)
- Yang Zheng
- Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Shigeru Shimamoto
- Faculty of Science and Engineering, Kindai University, 3-4-1 Kowakae, Higashi-Osaka, Osaka, 577-8502, Japan
| | - Takahiro Maruno
- Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Yuji Kobayashi
- Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Yoshiharu Matsuura
- Research Institute for Microbial Diseases, Osaka University, 3-1 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Kazuki Kawahara
- Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Takuya Yoshida
- Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka, 565-0871, Japan
| | - Tadayasu Ohkubo
- Graduate School of Pharmaceutical Sciences, Osaka University, 1-6 Yamadaoka, Suita, Osaka, 565-0871, Japan.
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10
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Jiang TX, Zhao M, Qiu XB. Substrate receptors of proteasomes. Biol Rev Camb Philos Soc 2018; 93:1765-1777. [DOI: 10.1111/brv.12419] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2017] [Revised: 03/26/2018] [Accepted: 03/28/2018] [Indexed: 01/01/2023]
Affiliation(s)
- Tian-Xia Jiang
- State Key Laboratory of Cognitive Neuroscience & Learning and Ministry of Education Key Laboratory of Cell Proliferation & Regulation Biology, College of Life Sciences; Beijing Normal University, 19 Xinjiekouwai Avenue; Beijing 100875 China
| | - Mei Zhao
- State Key Laboratory of Cognitive Neuroscience & Learning and Ministry of Education Key Laboratory of Cell Proliferation & Regulation Biology, College of Life Sciences; Beijing Normal University, 19 Xinjiekouwai Avenue; Beijing 100875 China
| | - Xiao-Bo Qiu
- State Key Laboratory of Cognitive Neuroscience & Learning and Ministry of Education Key Laboratory of Cell Proliferation & Regulation Biology, College of Life Sciences; Beijing Normal University, 19 Xinjiekouwai Avenue; Beijing 100875 China
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11
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Dato AD, Cunsolo A, Persico M, Santoro AM, D'Urso A, Milardi D, Purrello R, Stefanelli M, Paolesse R, Tundo GR, Sbardella D, Fattorusso C, Coletta M. Electrostatic Map Of Proteasome α-Rings Encodes The Design of Allosteric Porphyrin-Based Inhibitors Able To Affect 20S Conformation By Cooperative Binding. Sci Rep 2017; 7:17098. [PMID: 29213119 PMCID: PMC5719074 DOI: 10.1038/s41598-017-17008-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2017] [Accepted: 11/20/2017] [Indexed: 12/13/2022] Open
Abstract
The importance of allosteric proteasome inhibition in the treatment of cancer is becoming increasingly evident. Motivated by this urgent therapeutic need, we have recently identified cationic porphyrins as a highly versatile class of molecules able to regulate proteasome activity by interfering with gating mechanisms. In the present study, the mapping of electrostatic contacts bridging the regulatory particles with the α-rings of the human 20S proteasome led us to the identification of (meso-tetrakis(4-N-methylphenyl pyridyl)-porphyrin (pTMPyPP4) as a novel non-competitive inhibitor of human 20S proteasome. pTMPyPP4 inhibition mechanism implies a positive cooperative binding to proteasome, which disappears when a permanently open proteasome mutant (α-3ΔN) is used, supporting the hypothesis that the events associated with allosteric proteasome inhibition by pTMPyPP4 interfere with 20S gating and affect its "open-closed" equilibrium. Therefore, we propose that the spatial distribution of the negatively charged residues responsible for the interaction with regulatory particles at the α-ring surface of human 20S may be exploited as a blueprint for the design of allosteric proteasome regulators.
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Affiliation(s)
- Antonio Di Dato
- Dipartimento di Farmacia Università di Napoli "Federico II", Via D. Montesano, 49 I, 80131, Napoli, Italy
| | - Alessandra Cunsolo
- Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A. Doria 6, 95125, Catania, Italy
| | - Marco Persico
- Dipartimento di Farmacia Università di Napoli "Federico II", Via D. Montesano, 49 I, 80131, Napoli, Italy
| | - Anna Maria Santoro
- Istituto di Biostrutture e Bioimmagini-CNR sede secondaria di Catania, Via P. Gaifami, 9- 95126, Catania, Italy
| | - Alessandro D'Urso
- Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A. Doria 6, 95125, Catania, Italy
| | - Danilo Milardi
- Istituto di Biostrutture e Bioimmagini-CNR sede secondaria di Catania, Via P. Gaifami, 9- 95126, Catania, Italy
| | - Roberto Purrello
- Dipartimento di Scienze Chimiche, Università degli Studi di Catania, Viale A. Doria 6, 95125, Catania, Italy.
| | - Manuela Stefanelli
- Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata-Via della Ricerca Scientifica, 00133, Roma, Italy
| | - Roberto Paolesse
- Dipartimento di Scienze e Tecnologie Chimiche, Università di Roma Tor Vergata-Via della Ricerca Scientifica, 00133, Roma, Italy
| | - Grazia R Tundo
- Dipartimento di Scienze Cliniche e Medicina Traslazionale, Università di Roma Tor Vergata, Via Montpellier 1, 00133, Roma, Italy
| | - Diego Sbardella
- Dipartimento di Scienze Cliniche e Medicina Traslazionale, Università di Roma Tor Vergata, Via Montpellier 1, 00133, Roma, Italy
| | - Caterina Fattorusso
- Dipartimento di Farmacia Università di Napoli "Federico II", Via D. Montesano, 49 I, 80131, Napoli, Italy.
| | - Massimo Coletta
- Dipartimento di Scienze Cliniche e Medicina Traslazionale, Università di Roma Tor Vergata, Via Montpellier 1, 00133, Roma, Italy.
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12
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Abstract
In dividing cells, long-lived proteins are continuously diluted by being partitioned into newly formed daughter cells. Conversely, short-lived proteins are cleared from a cell primarily by proteolysis rather than cell division. Thus, when a cell stops dividing, there is a natural tendency for long-lived proteins to accumulate relative to short-lived proteins. This effect is disruptive to cells and leads to the accumulation of aged and damaged proteins over time. Here, we analyzed the degradation of thousands of proteins in dividing and nondividing (quiescent) skin cells. Our results demonstrate that quiescent cells avoid the accumulation of long-lived proteins by enhancing their degradation through pathways involving the lysosome. This mechanism may be important for promotion of protein homeostasis in aged organisms. In dividing cells, cytoplasmic dilution is the dominant route of clearance for long-lived proteins whose inherent degradation is slower than the cellular growth rate. Thus, as cells transition from a dividing to a nondividing state, there is a propensity for long-lived proteins to become stabilized relative to short-lived proteins, leading to alterations in the abundance distribution of the proteome. However, it is not known if cells mount a compensatory response to counter this potentially deleterious proteostatic disruption. We used a proteomic approach to demonstrate that fibroblasts selectively increase degradation rates of long-lived proteins as they transition from a proliferating to a quiescent state. The selective degradation of long-lived proteins occurs by the concurrent activation of lysosomal biogenesis and up-regulation of macroautophagy. Through this mechanism, quiescent cells avoid the accumulation of aged long-lived proteins that would otherwise result from the absence of cytoplasmic dilution by cell division.
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13
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Yersak JM, Montie HL, Chevalier-Larsen ES, Liu Y, Huang L, Rechsteiner M, Merry DE. The 11S Proteasomal Activator REGγ Impacts Polyglutamine-Expanded Androgen Receptor Aggregation and Motor Neuron Viability through Distinct Mechanisms. Front Mol Neurosci 2017; 10:159. [PMID: 28596723 PMCID: PMC5442185 DOI: 10.3389/fnmol.2017.00159] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2017] [Accepted: 05/08/2017] [Indexed: 12/02/2022] Open
Abstract
Spinal and bulbar muscular atrophy (SBMA) is caused by expression of a polyglutamine (polyQ)-expanded androgen receptor (AR). The inefficient nuclear proteasomal degradation of the mutant AR results in the formation of nuclear inclusions containing amino-terminal fragments of the mutant AR. PA28γ (also referred to as REGγ) is a nuclear 11S-proteasomal activator with limited proteasome activation capabilities compared to its cytoplasmic 11S (PA28α, PA28β) counterparts. To clarify the role of REGγ in polyQ-expanded AR metabolism, we carried out genetic and biochemical studies in cell models of SBMA. Overexpression of REGγ in a PC12 cell model of SBMA increased polyQ-expanded AR aggregation and contributed to polyQ-expanded AR toxicity in the presence of dihydrotestosterone (DHT). These effects of REGγ were independent of its association with the proteasome and may be due, in part, to the decreased binding of polyQ-expanded AR by the E3 ubiquitin-ligase MDM2. Unlike its effects in PC12 cells, REGγ overexpression rescued transgenic SBMA motor neurons from DHT-induced toxicity in a proteasome binding-dependent manner, suggesting that the degradation of a specific 11S proteasome substrate or substrates promotes motor neuron viability. One potential substrate that we found to play a role in mutant AR toxicity is the splicing factor SC35. These studies reveal that, depending on the cellular context, two biological roles for REGγ impact cell viability in the face of polyQ-expanded AR; a proteasome binding-independent mechanism directly promotes mutant AR aggregation while a proteasome binding-dependent mechanism promotes cell viability. The balance between these functions likely determines REGγ effects on polyQ-expanded AR-expressing cells.
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Affiliation(s)
- Jill M. Yersak
- Department of Biochemistry and Molecular Biology, Thomas Jefferson UniversityPhiladelphia, PA, United States
| | - Heather L. Montie
- Department of Biochemistry and Molecular Biology, Thomas Jefferson UniversityPhiladelphia, PA, United States
| | - Erica S. Chevalier-Larsen
- Department of Biochemistry and Molecular Biology, Thomas Jefferson UniversityPhiladelphia, PA, United States
| | - Yuhong Liu
- Department of Biochemistry and Molecular Biology, Thomas Jefferson UniversityPhiladelphia, PA, United States
| | - Lan Huang
- Department of Microbiology and Immunology, Thomas Jefferson UniversityPhiladelphia, PA, United States
| | - Martin Rechsteiner
- Department of Biochemistry, University of Utah School of MedicineSalt Lake City, UT, United States
| | - Diane E. Merry
- Department of Biochemistry and Molecular Biology, Thomas Jefferson UniversityPhiladelphia, PA, United States
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14
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Regulation of c-Myc protein stability by proteasome activator REGγ. Cell Death Differ 2014; 22:1000-11. [PMID: 25412630 DOI: 10.1038/cdd.2014.188] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2014] [Revised: 10/09/2014] [Accepted: 10/14/2014] [Indexed: 01/05/2023] Open
Abstract
c-Myc is a key transcriptional factor that has a prominent role in cell growth, differentiation and tumor development. Its protein levels are tightly controlled by ubiquitin-proteasome pathway and frequently deregulated in various cancers. Here, we report that the 11S proteasomal activator REGγ is a novel regulator of c-Myc abundance in cells. We showed that overexpression of wild-type REGγ, but not inactive mutants including N151Y and G250S, significantly promoted the degradation of c-Myc. Depletion of REGγ markedly increased the protein stability of c-Myc. REGγ interacts with the C-terminal region of c-Myc and regulates c-Myc protein turnover. Functionally, REGγ negatively regulates c-Myc-mediated cell proliferation. Interestingly, depletion of the Drosophila Reg homolog (dReg) in developing wings induced the upregulation of Drosophila Myc, which contributes to cell death. Collectively, these results suggest that REGγ proteasome has a conserved role in the regulation of Myc abundance in both mammalian cells and Drosophila.
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15
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Cascio P. PA28αβ: the enigmatic magic ring of the proteasome? Biomolecules 2014; 4:566-84. [PMID: 24970231 PMCID: PMC4101498 DOI: 10.3390/biom4020566] [Citation(s) in RCA: 66] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2014] [Revised: 05/15/2014] [Accepted: 06/08/2014] [Indexed: 11/16/2022] Open
Abstract
PA28αβ is a γ-interferon-induced 11S complex that associates with the ends of the 20S proteasome and stimulates in vitro breakdown of small peptide substrates, but not proteins or ubiquitin-conjugated proteins. In cells, PA28 also exists in larger complexes along with the 19S particle, which allows ATP-dependent degradation of proteins; although in vivo a large fraction of PA28 is present as PA28αβ-20S particles whose exact biological functions are largely unknown. Although several lines of evidence strongly indicate that PA28αβ plays a role in MHC class I antigen presentation, the exact molecular mechanisms of this activity are still poorly understood. Herein, we review current knowledge about the biochemical and biological properties of PA28αβ and discuss recent findings concerning its role in modifying the spectrum of proteasome's peptide products, which are important to better understand the molecular mechanisms and biological consequences of PA28αβ activity.
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Affiliation(s)
- Paolo Cascio
- Department of Veterinary Sciences, University of Turin, Grugliasco 10095, Italy.
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16
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Raule M, Cerruti F, Benaroudj N, Migotti R, Kikuchi J, Bachi A, Navon A, Dittmar G, Cascio P. PA28αβ reduces size and increases hydrophilicity of 20S immunoproteasome peptide products. ACTA ACUST UNITED AC 2014; 21:470-480. [PMID: 24631123 DOI: 10.1016/j.chembiol.2014.02.006] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Revised: 12/20/2013] [Accepted: 02/03/2014] [Indexed: 11/25/2022]
Abstract
The specific roles that immunoproteasome variants play in MHC class I antigen presentation are unknown at present. To investigate the biochemical properties of different immunoproteasome forms and unveil the molecular mechanisms of PA28 activity, we performed in vitro degradation of full-length proteins by 20S, 26S, and PA28αβ-20S immunoproteasomes and analyzed the spectrum of peptides released. Notably, PA28αβ-20S immunoproteasomes hydrolyze proteins at the same low rates as 20S alone, which is in line with PA28, neither stimulating nor preventing entry of unfolded polypeptides into the core particle. Most importantly, binding of PA28αβ to 20S greatly reduces the size of proteasomal products and favors the release of specific, more hydrophilic, longer peptides. Hence, PA28αβ may either allosterically modify proteasome active sites or act as a selective "smart" sieve that controls the efflux of products from the 20S proteolytic chamber.
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Affiliation(s)
- Mary Raule
- Department of Veterinary Sciences, University of Turin, 10095 Grugliasco, Italy
| | - Fulvia Cerruti
- Department of Veterinary Sciences, University of Turin, 10095 Grugliasco, Italy
| | - Nadia Benaroudj
- Unité Biologie des Spirochètes, Institut Pasteur, 75015 Paris, France
| | - Rebekka Migotti
- Mass Spectrometry Core Unit, Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany
| | - Julia Kikuchi
- Mass Spectrometry Core Unit, Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany
| | - Angela Bachi
- IFOM, FIRC Institute of Molecular Oncology, 20139 Milan, Italy
| | - Ami Navon
- Department of Biological Regulation, The Weizmann Institute of Science, 76100 Rehovot, Israel
| | - Gunnar Dittmar
- Mass Spectrometry Core Unit, Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany
| | - Paolo Cascio
- Department of Veterinary Sciences, University of Turin, 10095 Grugliasco, Italy.
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17
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Juenemann K, Schipper-Krom S, Wiemhoefer A, Kloss A, Sanz Sanz A, Reits EAJ. Expanded polyglutamine-containing N-terminal huntingtin fragments are entirely degraded by mammalian proteasomes. J Biol Chem 2013; 288:27068-27084. [PMID: 23908352 DOI: 10.1074/jbc.m113.486076] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Huntington disease is a neurodegenerative disorder caused by an expanded polyglutamine (polyQ) repeat within the protein huntingtin (Htt). N-terminal fragments of the mutant Htt (mHtt) proteins containing the polyQ repeat are aggregation-prone and form intracellular inclusion bodies. Improving the clearance of mHtt fragments by intracellular degradation pathways is relevant to obviate toxic mHtt species and subsequent neurodegeneration. Because the proteasomal degradation pathway has been the subject of controversy regarding the processing of expanded polyQ repeats, we examined whether the proteasome can efficiently degrade Htt-exon1 with an expanded polyQ stretch both in neuronal cells and in vitro. Upon targeting mHtt-exon1 to the proteasome, rapid and complete clearance of mHtt-exon1 was observed. Proteasomal degradation of mHtt-exon1 was devoid of polyQ peptides as partial cleavage products by incomplete proteolysis, indicating that mammalian proteasomes are capable of efficiently degrading expanded polyQ sequences without an inhibitory effect on the proteasomal activity.
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Affiliation(s)
- Katrin Juenemann
- Department of Cellbiology and Histology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
| | - Sabine Schipper-Krom
- Department of Cellbiology and Histology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands
| | - Anne Wiemhoefer
- Department of Cellbiology and Histology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands
| | - Alexander Kloss
- Institut für Biochemie/CCM, Charité-Universitätsmedizin Berlin, Monbijoustrasse 2, Berlin 10117, Germany
| | - Alicia Sanz Sanz
- Department of Cellbiology and Histology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands
| | - Eric A J Reits
- Department of Cellbiology and Histology, Academic Medical Center, University of Amsterdam, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.
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18
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Liu J, Wang Y, Li L, Zhou L, Wei H, Zhou Q, Liu J, Wang W, Ji L, Shan P, Wang Y, Yang Y, Jung SY, Zhang P, Wang C, Long W, Zhang B, Li X. Site-specific acetylation of the proteasome activator REGγ directs its heptameric structure and functions. J Biol Chem 2013; 288:16567-16578. [PMID: 23612972 PMCID: PMC3675592 DOI: 10.1074/jbc.m112.437129] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2012] [Revised: 04/22/2013] [Indexed: 12/22/2022] Open
Abstract
The proteasome activator REGγ has been reported to promote degradation of steroid receptor coactivator-3 and cyclin-dependent kinase inhibitors p21, p16, and p19 in a ubiquitin- and ATP-independent manner. A recent comparative analysis of REGγ expression in mouse and human tissues reveals a unique pattern of REGγ in specific cell types, suggesting undisclosed functions and biological importance of this molecule. Despite the emerging progress made in REGγ-related studies, how REGγ function is regulated remains to be explored. In this study, we report for the first time that REGγ can be acetylated mostly on its lysine 195 (Lys-195) residue by CREB binding protein (CBP), which can be reversed by sirtuin 1 (SIRT1) in mammalian cells. Site-directed mutagenesis abrogated acetylation at Lys-195 and significantly attenuated the capability of REGγ to degrade its target substrates, p21 and hepatitis C virus core protein. Mechanistically, acetylation at Lys-195 is important for the interactions between REGγ monomers and ultimately influences REGγ heptamerization. Biological analysis of cells containing REGγ-WT or REGγ-K195R mutant indicates an impact of acetylation on REGγ-mediated regulation of cell proliferation and cell cycle progression. These findings reveal a previously unknown mechanism in the regulation of REGγ assembly and activity, suggesting a potential venue for the intervention of the ubiquitin-independent REGγ proteasome activity.
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Affiliation(s)
- Jiang Liu
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China; Institute of Aging Research, School of Medicine, Hangzhou Normal University, Hangzhou, Zhejiang 310036, China; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Ying Wang
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China; Institute of Aging Research, School of Medicine, Hangzhou Normal University, Hangzhou, Zhejiang 310036, China; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Lei Li
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Li Zhou
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Haibin Wei
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Qingxia Zhou
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Jian Liu
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Weicang Wang
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Lei Ji
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Peipei Shan
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Yan Wang
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Yuanyuan Yang
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Sung Yun Jung
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Pei Zhang
- Department of Pathology, the Second Chengdu Municipal Hospital, Chengdu, Sichuan 610017, China
| | - Chuangui Wang
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China
| | - Weiwen Long
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030
| | - Bianhong Zhang
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China.
| | - Xiaotao Li
- Shanghai Key Laboratory of Regulatory Biology, Institute of Biomedical Sciences, School of Life Sciences, East China Normal University, Shanghai 200241, China; Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030.
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19
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Proteasome allostery as a population shift between interchanging conformers. Proc Natl Acad Sci U S A 2012; 109:E3454-62. [PMID: 23150576 DOI: 10.1073/pnas.1213640109] [Citation(s) in RCA: 113] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Protein degradation plays a critical role in cellular homeostasis, in regulating the cell cycle, and in the generation of peptides that are used in the immune response. The 20S proteasome core particle (CP), a barrel-like structure consisting of four heptameric protein rings stacked axially on top of each other, is central to this process. CP function is controlled by activator complexes that bind 75 Å away from sites catalyzing proteolysis, and biochemical data are consistent with an allosteric mechanism by which binding is communicated to distal active sites. However, little structural evidence has emerged from the high-resolution images of the CP. Using methyl TROSY NMR spectroscopy, we demonstrate that in solution, the CP interconverts between multiple conformations whose relative populations are shifted on binding of the 11S activator or mutation of residues that contact activators. These conformers differ in contiguous regions of structure that connect activator binding to the CP active sites, and changes in their populations lead to differences in substrate proteolysis patterns. Moreover, various active site modifications result in conformational changes to the activator binding site by modulating the relative populations of these same CP conformers. This distribution is also affected by the binding of a small-molecule allosteric inhibitor of proteolysis, chloroquine, suggesting an important avenue in the development of therapeutics for proteasome inhibition.
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20
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The Ubiquitin-Proteasome System in Huntington's Disease: Are Proteasomes Impaired, Initiators of Disease, or Coming to the Rescue? Biochem Res Int 2012; 2012:837015. [PMID: 23050151 PMCID: PMC3462393 DOI: 10.1155/2012/837015] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2012] [Revised: 08/14/2012] [Accepted: 08/19/2012] [Indexed: 12/11/2022] Open
Abstract
Huntington's disease is a progressive neurodegenerative disease, caused by a polyglutamine expansion in the huntingtin protein. A prominent hallmark of the disease is the presence of intracellular aggregates initiated by N-terminal huntingtin fragments containing the polyglutamine repeat, which recruit components of the ubiquitin-proteasome system. While it is commonly thought that proteasomes are irreversibly sequestered into these aggregates leading to impairment of the ubiquitin-proteasome system, the data on proteasomal impairment in Huntington's disease is contradictory. In addition, it has been suggested that proteasomes are unable to actually cleave polyglutamine sequences in vitro, thereby releasing aggregation-prone polyglutamine peptides in cells. Here, we discuss how the proteasome is involved in the various stages of polyglutamine aggregation in Huntington's disease, and how alterations in activity may improve clearance of mutant huntingtin fragments.
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21
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Stadtmueller BM, Hill CP. Proteasome activators. Mol Cell 2011; 41:8-19. [PMID: 21211719 DOI: 10.1016/j.molcel.2010.12.020] [Citation(s) in RCA: 166] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2010] [Revised: 12/15/2010] [Accepted: 12/15/2010] [Indexed: 01/25/2023]
Abstract
Proteasomes degrade a multitude of protein substrates in the cytosol and nucleus, and thereby are essential for many aspects of cellular function. Because the proteolytic sites are sequestered in a closed barrel-shaped structure, activators are required to facilitate substrate access. Structural and biochemical studies of two activator families, 11S and Blm10, have provided insights to proteasome activation mechanisms, although the biological functions of these factors remain obscure. Recent advances have improved our understanding of the third activator family, including the 19S activator, which targets polyubiquitylated proteins for degradation. Here we present a structural perspective on how proteasomes are activated and how substrates are delivered to the proteolytic sites.
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Affiliation(s)
- Beth M Stadtmueller
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT 84112-5650, USA
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22
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Vettermann C, Castor D, Mekker A, Gerrits B, Karas M, Jäck HM. Proteome profiling suggests a pro-inflammatory role for plasma cells through release of high-mobility group box 1 protein. Proteomics 2011; 11:1228-37. [PMID: 21319304 DOI: 10.1002/pmic.201000491] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2010] [Revised: 11/07/2010] [Accepted: 12/13/2010] [Indexed: 02/06/2023]
Abstract
The final step of B-cell maturation is to differentiate into plasma cells, a process that is accompanied by gross changes in subcellular organization to enable antibody secretion. To better understand this critical step in mounting a humoral immune response, we analyzed proteome dynamics during plasma cell differentiation with combined 2-DE/MS. Thirty-two identified protein spots changed in relative abundance when lipopolysaccharide (LPS)-stimulated primary B cells differentiated into antibody-secreting plasma cells. A correlative analysis of protein and transcript abundance suggested that one third of these proteins are post-transcriptionally regulated. Apart from ER-resident chaperones, lipid metabolic enzymes, and translation initiation factors, we identified several proteins that had not been previously studied in plasma cells. Among them is the transiently upregulated proteasome activator (PA) 28γ, a component of the putative nuclear proteasome. Additionally, we discovered that the non-canonical inflammatory cytokine high-mobility group box 1 (HMG1) was released from plasma cells into the extracellular milieu. This suggests a novel role for plasma cells as pro-inflammatory mediators, which has important implications for various autoimmune diseases and chronic inflammation.
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Affiliation(s)
- Christian Vettermann
- Division of Molecular Immunology, Department of Internal Medicine, Nikolaus-Fiebiger-Center for Molecular Medicine, University of Erlangen-Nürnberg, Erlangen, Germany
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23
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Anupam R, Datta A, Kesic M, Green-Church K, Shkriabai N, Kvaratskhelia M, Lairmore MD. Human T-lymphotropic virus type 1 p30 interacts with REGgamma and modulates ATM (ataxia telangiectasia mutated) to promote cell survival. J Biol Chem 2011; 286:7661-8. [PMID: 21216954 DOI: 10.1074/jbc.m110.176354] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Human T-lymphotropic virus type 1 (HTLV-1) is a causative agent of adult T cell leukemia/lymphoma and a variety of inflammatory disorders. HTLV-1 encodes a nuclear localizing protein, p30, that selectively alters viral and cellular gene expression, activates G(2)-M cell cycle checkpoints, and is essential for viral spread. Here, we used immunoprecipitation and affinity pulldown of ectopically expressed p30 coupled with mass spectrometry to identify cellular binding partners of p30. Our data indicate that p30 specifically binds to cellular ATM (ataxia telangiectasia mutated) and REGγ (a nuclear 20 S proteasome activator). Under conditions of genotoxic stress, p30 expression was associated with reduced levels of ATM and increased cell survival. Knockdown or overexpression of REGγ paralleled p30 expression, suggesting an unexpected enhancement of p30 expression in the presence of REGγ. Finally, size exclusion chromatography revealed the presence of p30 in a high molecular mass complex along with ATM and REGγ. On the basis of our findings, we propose that HTLV-1 p30 interacts with ATM and REGγ to increase viral spread by facilitating cell survival.
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Affiliation(s)
- Rajaneesh Anupam
- Center for Retrovirus Research, Ohio State University, Columbus, Ohio 43210, USA
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24
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Kanai K, Aramata S, Katakami S, Yasuda K, Kataoka K. Proteasome activator PA28{gamma} stimulates degradation of GSK3-phosphorylated insulin transcription activator MAFA. J Mol Endocrinol 2011; 47:119-27. [PMID: 21646385 DOI: 10.1530/jme-11-0044] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
MAFA is a member of the MAF family of basic leucine zipper transcription factors and is a critical regulator of insulin gene expression and islet β-cell function. To be degraded by the proteasome, MAFA must be phosphorylated by GSK3 and MAP kinases at multiple serine and threonine residues (Ser49, Thr53, Thr57, Ser61, and Ser65) within its amino-terminal domain. In this study, we report that MAFA degradation is stimulated by PA28γ (REGγ and PSME3), a member of a family of proteasome activators that bind and activate the 20S proteasome. To date, only a few PA28γ-proteasome pathway substrates have been identified, including steroid receptor coactivator 3 (SRC3) and the cell cycle inhibitor p21 (CIP1). PA28γ binds to MAFA, induces its proteasomal degradation, and thereby attenuates MAFA-driven transcriptional activation of the insulin promoter. Co-expression of GSK3 enhanced the PA28γ-mediated degradation of MAFA, but mutants that contained alanine substitutions at the MAFA phosphorylation sites did not bind PA28γ and were resistant to degradation. We also found that a PA28γ mutant (N151Y) that did not stimulate p21 degradation enhanced MAFA degradation, and another mutant (K188D) that promoted greater p21 degradation did not enhance MAFA degradation. These results suggest that PA28γ stimulates MAFA degradation through a novel molecular mechanism that is distinct from that for the degradation of p21.
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Affiliation(s)
- Kenichi Kanai
- Laboratory of Molecular and Developmental Biology, Graduate School of Biological Science, Nara Institute of Science and Technology, 8916-5 Takayama-cho, Ikoma 630-0192, Japan
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25
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Moriishi K, Shoji I, Mori Y, Suzuki R, Suzuki T, Kataoka C, Matsuura Y. Involvement of PA28gamma in the propagation of hepatitis C virus. Hepatology 2010; 52:411-20. [PMID: 20683941 DOI: 10.1002/hep.23680] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
UNLABELLED We have reported previously that the proteasome activator PA28gamma participates not only in degradation of hepatitis C virus (HCV) core protein in the nucleus but also in the pathogenesis in transgenic mice expressing HCV core protein. However, the biological significance of PA28gamma in the propagation of HCV has not been clarified. PA28gamma is an activator of proteasome responsible for ubiquitin-independent degradation of substrates in the nucleus. In the present study, knockdown of PA28gamma in cells preinfection or postinfection with the JFH-1 strain of HCV impaired viral particle production but exhibited no effect on viral RNA replication. The particle production of HCV in PA28gamma knockdown cells was restored by the expression of an small interfering RNA (siRNA)-resistant PA28gamma. Although viral proteins were detected in the cytoplasm of cells infected with HCV, suppression of PA28gamma expression induced accumulation of HCV core protein in the nucleus. HCV core protein was also degraded in the cytoplasm after ubiquitination by an E3 ubiquitin ligase, E6AP. Knockdown of PA28gamma enhanced ubiquitination of core protein and impaired virus production, whereas that of E6AP reduced ubiquitination of core protein and enhanced virus production. Furthermore, virus production in the PA28gamma knockdown cells was restored through knockdown of E6AP or expression of the siRNA-resistant wild-type but not mutant PA28gamma incapable of activating proteasome activity. CONCLUSION Our results suggest that PA28gamma participates not only in the pathogenesis but also in the propagation of HCV by regulating the degradation of the core protein in both a ubiquitin-dependent and ubiquitin-independent manner.
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Affiliation(s)
- Kohji Moriishi
- Department of Molecular Virology, Research Institute for Microbial Diseases, Osaka University, Osaka, Japan
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26
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Groettrup M, Kirk CJ, Basler M. Proteasomes in immune cells: more than peptide producers? Nat Rev Immunol 2009; 10:73-8. [PMID: 20010787 DOI: 10.1038/nri2687] [Citation(s) in RCA: 247] [Impact Index Per Article: 16.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
When cells are stimulated with pro-inflammatory cytokines, most of their constitutively expressed proteasomes are replaced with immunoproteasomes, which increase the production of peptides for presentation on MHC class I molecules. In addition, cortical thymic epithelial cells selectively express a type of proteasome known as the thymoproteasome that is required for the positive selection of thymocytes. Here, we discuss how these specialized types of proteasome shape the T cell receptor repertoire of cytotoxic T lymphocytes and propose that immunoproteasomes have functions, in addition to antigen processing, that influence cytokine production and T cell differentiation, survival and function. We also discuss how inhibitors of immunoproteasomes can suppress undesired T cell responses in autoimmune diseases.
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Affiliation(s)
- Marcus Groettrup
- Division of Immunology, Department of Biology, University of Constance, Konstanz, Germany.
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Characterization of a REG/PA28 proteasome activator homolog in Dictyostelium discoideum indicates that the ubiquitin- and ATP-independent REGgamma proteasome is an ancient nuclear protease. EUKARYOTIC CELL 2009; 8:844-51. [PMID: 19411624 DOI: 10.1128/ec.00165-08] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The nuclear proteasome activator REGgamma/PA28gamma is an ATP- and ubiquitin-independent activator of the 20S proteasome and has been proposed to degrade and thereby regulate both a key human oncogene, encoding the coactivator SRC-3/AIB1, and the cyclin-dependent kinase inhibitor p21 (Waf/Cip1). We report the identification and characterization of a PA28/REG homolog in Dictyostelium. Association of a recombinant Dictyostelium REG with the purified Dictyostelium 20S proteasome led to the preferential stimulation of the trypsin-like proteasome peptidase activity. Immunolocalization studies demonstrated that the proteasome activator is localized to the nucleus and is present in growing as well as starving Dictyostelium cells. Our results indicate that the Dictyostelium PA28/REG activator can stimulate both the trypsin-like and chymotrypsin-like activities of the 20S proteasome and supports the idea that the REGgamma-20S proteasome represents an early unique nuclear degradation pathway for eukaryotic cells.
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28
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Osna NA, White RL, Krutik VM, Wang T, Weinman SA, Donohue TM. Proteasome activation by hepatitis C core protein is reversed by ethanol-induced oxidative stress. Gastroenterology 2008; 134:2144-52. [PMID: 18549882 PMCID: PMC2517112 DOI: 10.1053/j.gastro.2008.02.063] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Revised: 02/12/2008] [Accepted: 02/21/2008] [Indexed: 02/06/2023]
Abstract
BACKGROUND & AIMS The proteasome is a major cellular proteinase. Its activity is modulated by cellular oxidants. Hepatitis C core protein and ethanol exposure both cause enhanced oxidant generation. The aim was to investigate whether core protein, by its ability to generate oxidants, alters proteasome activity and whether these alterations are further affected by ethanol exposure. METHODS These interactions were examined in Huh-7 cell lines that expressed inducible HCV core protein and/or constitutive cytochrome P450 2E1 (CYP2E1) and as purified components in a cell-free system. Chymotrypsin-like proteasome activity was measured fluorometrically. RESULTS Proteasome activity in core-positive 191-20 cells was 20% higher than that in core-negative cells and was enhanced 3-fold in CYP2E1-expressing L14 cells. Exposure of core-positive cells to glutathione ethyl ester, catalase, or the CYP2E1 inhibitor diallyl sulfide partially reversed the elevation of proteasome activity in core-positive cells, whereas ethanol exposure suppressed proteasome activity. The results indicate that proteasome activity was up-regulated by low levels of core-induced oxidative stress but down-regulated by high levels of ethanol-elicited stress. These findings were partially mimicked in a cell-free system. Addition of core protein enhanced the peptidase activity of purified 20S proteasome containing the proteasome activator PA28 and was further potentiated by addition of liver mitochondrial and/or microsome fractions. However, proteasome activation was significantly attenuated when fractions were obtained from ethanol-fed animals. CONCLUSIONS HCV core protein interacts with PA28, mitochondrial, and endoplasmic reticulum proteins to cause low levels of oxidant stress and proteasome activation, which is dampened during ethanol metabolism when oxidant generation is higher.
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Affiliation(s)
- Natalia A Osna
- Liver Study Unit, Omaha Veterans Affairs Medical Center, Omaha, Nebraska 68105, USA.
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29
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Pratt G, Rechsteiner M. Proteasomes cleave at multiple sites within polyglutamine tracts: activation by PA28gamma(K188E). J Biol Chem 2008; 283:12919-25. [PMID: 18343811 DOI: 10.1074/jbc.m709347200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Eukaryotic proteasomes have been reported to cleave only once within polyglutamine tracts and then only after the N-terminal glutamine (Venkatraman, P., Wetzel, R., Tanaka, M., Nukina, N., and Goldberg, A. L. (2004) Mol. Cell 14, 95-104). We have obtained results that directly conflict with that report. In the presence of the proteasome activator PA28gamma(K188E) human red cell proteasomes progressively degraded fluorescein-GGQ(10)RR or fluorescein-HPHQ(10)RR into small fragments as shown by size exclusion chromatography and mass spectrometry. MALDI-TOF mass spectrometry revealed that proteolytic products arose from cleavage after every glutamine in fluorescein-HPHQ(10)RR, and mass accuracy rules out deamidation of glutamine to glutamic acid as an explanation for peptide degradation. Moreover, degradation cannot be attributed to a contaminating protease because peptide hydrolysis was completely blocked by the proteasome-specific inhibitors, lactacystin and epoxomicin. We conclude that proteasomes cleave repetitively anywhere within a stretch of ten glutamine residues. Thus our results cast doubt on the idea that mammalian proteasomes cannot degrade glutamine-expanded regions within pathogenic polyQ-expanded proteins, such as Huntingtin.
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Affiliation(s)
- Gregory Pratt
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, Utah 84132, USA
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30
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Shibatani T, Carlson EJ, Larabee F, McCormack AL, Früh K, Skach WR. Global organization and function of mammalian cytosolic proteasome pools: Implications for PA28 and 19S regulatory complexes. Mol Biol Cell 2006; 17:4962-71. [PMID: 16987959 PMCID: PMC1679665 DOI: 10.1091/mbc.e06-04-0311] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Proteolytic activity of the 20S proteasome is regulated by activators that govern substrate movement into and out of the catalytic chamber. However, the physiological relationship between activators, and hence the relative role of different proteasome species, remains poorly understood. To address this problem, we characterized the total pool of cytosolic proteasomes in intact and functional form using a single-step method that bypasses the need for antibodies, proteasome modification, or column purification. Two-dimensional Blue Native(BN)/SDS-PAGE and tandem mass spectrometry simultaneously identified six native proteasome populations in untreated cytosol: 20S, singly and doubly PA28-capped, singly 19S-capped, hybrid, and doubly 19S-capped proteasomes. All proteasome species were highly dynamic as evidenced by recruitment and exchange of regulatory caps. In particular, proteasome inhibition with MG132 markedly stimulated PA28 binding to exposed 20S alpha-subunits and generated doubly PA28-capped and hybrid proteasomes. PA28 recruitment virtually eliminated free 20S particles and was blocked by ATP depletion. Moreover, inhibited proteasomes remained stably associated with distinct cohorts of partially degraded fragments derived from cytosolic and ER substrates. These data establish a versatile platform for analyzing substrate-specific proteasome function and indicate that PA28 and 19S activators cooperatively regulate global protein turnover while functioning at different stages of the degradation cycle.
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Affiliation(s)
- Toru Shibatani
- *Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, Portland, OR 97201; and
| | - Eric J. Carlson
- *Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, Portland, OR 97201; and
| | - Fredrick Larabee
- *Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, Portland, OR 97201; and
| | - Ashley L. McCormack
- Vaccine and Gene Therapy Institute, Oregon Health & Sciences University, Beaverton, OR 97006-3448
| | - Klaus Früh
- Vaccine and Gene Therapy Institute, Oregon Health & Sciences University, Beaverton, OR 97006-3448
| | - William R. Skach
- *Department of Biochemistry and Molecular Biology, Oregon Health & Sciences University, Portland, OR 97201; and
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31
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Li X, Lonard DM, Jung SY, Malovannaya A, Feng Q, Qin J, Tsai SY, Tsai MJ, O'Malley BW. The SRC-3/AIB1 coactivator is degraded in a ubiquitin- and ATP-independent manner by the REGgamma proteasome. Cell 2006; 124:381-92. [PMID: 16439211 DOI: 10.1016/j.cell.2005.11.037] [Citation(s) in RCA: 208] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2005] [Revised: 10/25/2005] [Accepted: 11/30/2005] [Indexed: 10/25/2022]
Abstract
Steroid receptor coactivator-3 (SRC-3/AIB1) is an oncogene frequently amplified and overexpressed in breast cancers. Here we report that SRC-3 interacts with REGgamma, a proteasome activator known to stimulate the trypsin-like activity of the 20S proteasome. RNAi knockdown and gain-of-function experiments suggest that REGgamma promotes SRC-3 protein degradation. Cellular levels of REGgamma expression affect estrogen-receptor target-gene expression and cell growth as a result of its ability to promote degradation of the SRC-3 protein. In vitro proteasome proteolysis assays using purified REGgamma, SRC-3, and the 20S proteasome reinforce these conclusions and demonstrate that REGgamma promotes the degradation of SRC-3 in a ubiquitin- and ATP-independent manner. This work demonstrates the first example of a physiologically relevant endogenous cellular target for the REGgamma-proteasome complex. It also highlights the fact that an alternative mode of proteasome-mediated protein degradation, independent of the 19S proteasome regulatory cap, targets the SRC-3 protein for degradation.
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Affiliation(s)
- Xiaotao Li
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA
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32
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Strehl B, Seifert U, Krüger E, Heink S, Kuckelkorn U, Kloetzel PM. Interferon-gamma, the functional plasticity of the ubiquitin-proteasome system, and MHC class I antigen processing. Immunol Rev 2005; 207:19-30. [PMID: 16181324 DOI: 10.1111/j.0105-2896.2005.00308.x] [Citation(s) in RCA: 172] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The proteasome system is a central component of a cascade of proteolytic processing steps required to generate antigenic peptides presented at the cell surface to cytotoxic T lymphocytes by major histocompatibility complex (MHC) class I molecules. The nascent protein pool or DRiPs (defective ribosomal products) appear to represent an important source for MHC class I epitopes. Owing to the destructive activities of aminopeptidases in the cytosol, at most 1% of the peptides generated by the ubiquitin-proteasome system seems to be made available to the immune system. Interferon-gamma (IFN-gamma) helps to override these limitations by the formation of immunoproteasomes, the activator complex PA28, and the induction of several aminopeptidases. Both immunoproteasomes and PA28 use cleavage sites already used by constitutive proteasomes but with altered and in some cases dramatically enhanced frequency. Therefore, two proteolytic cascades appear to have evolved to provide MHC class I epitopes. The 'constitutive proteolytic cascade' is designed to efficiently degrade proteins to single amino acid residues, allowing only a small percentage of peptides to be presented at the cell surface. In contrast, the IFN-gamma-controlled proteolytic cascade generates larger amounts of appropriate antigenic peptides, assuring more peptides to overcome the proteolytic restrictions of the constitutive system, thereby enhancing MHC class I antigen presentation.
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Affiliation(s)
- Britta Strehl
- Institut für Biochemie, Charité, Berlin University Berlin, Germany
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33
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Rechsteiner M, Hill CP. Mobilizing the proteolytic machine: cell biological roles of proteasome activators and inhibitors. Trends Cell Biol 2005; 15:27-33. [PMID: 15653075 DOI: 10.1016/j.tcb.2004.11.003] [Citation(s) in RCA: 261] [Impact Index Per Article: 13.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Proteasomes perform the majority of proteolysis that occurs in the cytosol and nucleus of eukaryotic cells and, thereby, perform crucial roles in cellular regulation and homeostasis. Isolated proteasomes are inactive because substrates cannot access the proteolytic sites. PA28 and PA200 are activators that bind to proteasomes and stimulate the hydrolysis of peptides. Several protein inhibitors of the proteasome have also been identified, and the properties of these activators and inhibitors have been characterized biochemically. By contrast, their physiological roles--which have been reported to include production of antigenic peptides, proteasome assembly and DNA repair--are controversial. In this article, we briefly review the biochemical data and discuss the possible biological roles of PA28, PA200 and proteasome inhibitors.
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Affiliation(s)
- Martin Rechsteiner
- Department of Biochemistry, University of Utah School of Medicine, Salt Lake City, UT 84132, USA.
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34
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Kloetzel PM. The proteasome and MHC class I antigen processing. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2005; 1695:225-33. [PMID: 15571818 DOI: 10.1016/j.bbamcr.2004.10.004] [Citation(s) in RCA: 134] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
By generating peptides from intracellular antigens, which are then presented to T cells, the ubiquitin/26S proteasome system plays a central role in the cellular immune response. Under the control of interferon-gamma the proteolytic properties of the proteasome are adapted to the requirements of the immune system. Interferon-gamma induces the formation of immunoproteasomes and the synthesis of the proteasome activator PA28. Both alter the proteolytic properties of the proteasome complex and enhance proteasomal function in antigen presentation. Thus, a combination of several of regulatory events tunes the proteasome system for maximal efficiency in the generation of MHC class I antigens.
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Affiliation(s)
- Peter-M Kloetzel
- Institut für Biochemie, Charité, Medizinische Fakultät der Humboldt-Universität zu Berlin, Monbijoust.2, 10117 Berlin, Germany.
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35
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Cascio P, Goldberg AL. Preparation of hybrid (19S-20S-PA28) proteasome complexes and analysis of peptides generated during protein degradation. Methods Enzymol 2005; 398:336-52. [PMID: 16275341 DOI: 10.1016/s0076-6879(05)98028-2] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
PA28 (also named REG or 11S) is a ring-shaped (180-kDa) interferon-gamma-induced complex that associates with the 20S proteasome and dramatically stimulates the breakdown of short peptides. Immunoprecipitation studies indicate that in vivo PA28 also exists in larger complexes that also contain the 19S particle, which is required for the ATP-ubiquitin-dependent degradation of proteins. However, because of its lability (e.g., it does not withstand exposure to high ionic strength buffers), this larger complex cannot be purified by standard biochemical protocols. Therefore, we developed a method to reconstitute in vitro such hybrid proteasomes (i.e., PA28-20S-19S) from highly purified components. This chapter describes conditions that allow the association of PA28 with "singly capped" 26S (i.e., 19S-20S) particles. In addition assays are described to measure absolute rates of degradation of several non-ubiquitinated proteins by 26S and 20S proteasomes and methods to analyze the pattern and size distribution of peptides generated during the degradation of these proteins.
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Affiliation(s)
- Paolo Cascio
- Department of Morphophysiology, School of Veterinary Medicine, University of Turin, 10095 Grugliasco, Turin, Italy
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36
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Masters EI, Pratt G, Förster A, Hill CP. Purification and Analysis of Recombinant 11S Activators of the 20S Proteasome: Trypanosoma brucei PA26 and Human PA28α, PA28β, and PA28γ. Methods Enzymol 2005; 398:306-21. [PMID: 16275338 DOI: 10.1016/s0076-6879(05)98025-7] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/23/2023]
Abstract
Proteasomes perform the bulk of nonlysosomal degradation of aberrant, damaged, misfolded, and naturally short-lived regulatory proteins in eukaryotic cells. They are approximately 700-kDa assemblies whose hollow architecture sequesters the proteolytic sites inside a central chamber, thereby ensuring that the activity of isolated proteasomes is repressed. In vivo, proteasomes are activated by protein complexes, including the 11S activators (PA28 and PA26), which bind to one or both ends of the barrel-shaped structure. This chapter describes protocols for the purification of recombinant 11S regulators, characterization of their ability to stimulate proteasome activity, and crystallization of proteasome complexes.
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Affiliation(s)
- Eugene I Masters
- Department of Biology, University of Utah, Salt Lake City, UT 84103, USA
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37
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Kloetzel PM. Generation of major histocompatibility complex class I antigens: functional interplay between proteasomes and TPPII. Nat Immunol 2004; 5:661-9. [PMID: 15224091 DOI: 10.1038/ni1090] [Citation(s) in RCA: 181] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The proteasome is key in the cascade of proteolytic processing required for the generation of peptides presented at the cell surface to cytotoxic T lymphocytes by major histocompatibility complex class I molecules. Proteasome-dependent epitope processing is greatly improved through the interferon-gamma-induced formation of immunoproteasomes and the activator complex PA28. Tripeptidyl aminopeptidase II also has a strong effect on epitope generation. With its endoproteolytic and exoproteolytic activities, TPPII acts 'downstream' of the proteasome and relies on products released by the proteasome. The antigen-processing cascade involving different proteolytic systems raises anew the question of how antigenic peptides are generated. We therefore revisit the interferon-gamma-induced immune adaptation of the proteasome and attempt to redefine its function in connection with the emerging importance of TPPII.
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Affiliation(s)
- Peter M Kloetzel
- Institut für Biochemie, University Medical School-Charité, Humboldt Universität Monbijoustr.2, 10117 Berlin, Germany.
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38
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Gao X, Li J, Pratt G, Wilk S, Rechsteiner M. Purification procedures determine the proteasome activation properties of REGγ (PA28γ). Arch Biochem Biophys 2004; 425:158-64. [PMID: 15111123 DOI: 10.1016/j.abb.2004.03.021] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2003] [Revised: 03/11/2004] [Indexed: 10/26/2022]
Abstract
The proteasome activation properties of recombinant REG gamma molecules depend on purification procedures. Prior to ammonium sulfate precipitation recombinant REG gamma activates the trypsin-like catalytic subunit of the proteasome; afterwards it activates all three catalytic subunits. The expanded activation specificity is accompanied by reduced stability of the REG gamma heptamer providing support for the idea that a "tight" REG gamma heptamer suppresses the proteasome's chymotrypsin-like and postglutamyl-preferring active sites. In an attempt to determine whether REG gamma synthesized in mammalian cells also exhibits restricted activation properties, extracts were prepared from several mammalian organs and cell lines. Surprisingly, endogenous REG gamma was found to be largely monomeric. In an alternate approach, COS7 cells were cotransfected with plasmids expressing FLAG-REG gamma and REG gamma. The expressed FLAG-REG gamma molecules were shown to form oligomers with untagged REG gamma subunits, and the mixed oligomers preferentially activated the proteasome's trypsin-like subunit. Thus, REG gamma molecules synthesized in mammalian cells also exhibit restricted activation properties.
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Affiliation(s)
- Xiaolin Gao
- Department of Biochemistry, University of Utah School of Medicine, 50 N Medical Drive, Salt Lake City, UT 84132, USA
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39
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Barton LF, Runnels HA, Schell TD, Cho Y, Gibbons R, Tevethia SS, Deepe GS, Monaco JJ. Immune Defects in 28-kDa Proteasome Activator γ-Deficient Mice. THE JOURNAL OF IMMUNOLOGY 2004; 172:3948-54. [PMID: 15004203 DOI: 10.4049/jimmunol.172.6.3948] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Protein complexes of the 28-kDa proteasome activator (PA28) family activate the proteasome and may alter proteasome cleavage specificity. Initial investigations have demonstrated a role for the IFN-gamma-inducible PA28alpha/beta complex in Ag processing. Although the noninducible and predominantly nuclear PA28gamma complex has been implicated in affecting proteasome-dependent signaling pathways, such as control of the mitotic cell cycle, there is no previous evidence demonstrating a role for this structure in Ag processing. We therefore generated PA28gamma-deficient mice and investigated their immune function. PA28gamma(-/-) mice display a slight reduction in CD8+ T cell numbers and do not effectively clear a pulmonary fungal infection. However, T cell responses in two viral infection models appear normal in both magnitude and the hierarchy of antigenic epitopes recognized. We conclude that PA28gamma(-/-) mice, like PA28alpha(-/-)/beta(-/-) mice, are deficient in the processing of only specific Ags.
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Affiliation(s)
- Lance F Barton
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati, Cincinnati, OH 45267, USA
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40
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Krüger E, Kuckelkorn U, Sijts A, Kloetzel PM. The components of the proteasome system and their role in MHC class I antigen processing. Rev Physiol Biochem Pharmacol 2004; 148:81-104. [PMID: 12687403 DOI: 10.1007/s10254-003-0010-4] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
By generating peptides from intracellular antigens which are then presented to T cells, the ubiquitin/26S proteasome system plays a central role in the cellular immune response. The proteolytic properties of the proteasome are adapted to the requirements of the immune system by proteasome components whose synthesis is under the control of interferon-gamma. Among these are three subunits with catalytic sites that are incorporated into the enzyme complex during its de novo synthesis. Thus, the proteasome assembly pathway and the formation of immunoproteasomes play a critical regulatory role in the regulation of the proteasome's catalytic properties. In addition, interferon-gamma also induces the synthesis of the proteasome activator PA28 which, as part of the so-called hybrid proteasome, exerts a more selective function in antigen presentation. Consequently, the combination of a number of regulatory events tunes the proteasome system to gain maximal efficiency in the generation of peptides with regard to their quality and quantity.
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Affiliation(s)
- E Krüger
- Institut für Biochemie, Medizinische Fakultät, Humboldt-Universität zu Berlin, Charité, Monbijoust 2, 10117 Berlin, Germany
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41
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Kisselev AF, Garcia-Calvo M, Overkleeft HS, Peterson E, Pennington MW, Ploegh HL, Thornberry NA, Goldberg AL. The caspase-like sites of proteasomes, their substrate specificity, new inhibitors and substrates, and allosteric interactions with the trypsin-like sites. J Biol Chem 2003; 278:35869-77. [PMID: 12815064 DOI: 10.1074/jbc.m303725200] [Citation(s) in RCA: 142] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Proteasomes are the primary sites for protein degradation in mammalian cells. Each proteasome particle contains two chymotrypsin-like, two trypsin-like, and two caspase-like proteolytic sites. Previous studies suggest a complex network of allosteric interactions between these catalytic and multiple regulatory sites. We used positional scanning combinatorial substrate libraries to determine the extended substrate specificity of the caspase-like sites. Based on this analysis, several new substrates were synthesized, the use of which confirmed earlier observations that caspase-like sites (often termed postglutamyl peptide hydrolase) cleave after aspartates better than after glutamates. Highly selective inhibitors of the caspase-like sites were also generated. They stimulated trypsin-like activity of yeast 20 S proteasomes up to 3-fold but not when binding of the inhibitor to the caspase-like sites was prevented in a mutant carrying an uncleaved propeptide. Although substrates of the caspase-like sites allosterically inhibit the chymotrypsin-like activity, inhibitors of the caspase-like sites do not affect the chymotrypsin-like sites. Furthermore, when caspase-like sites were occupied by the uncleaved propeptide or inhibitor, their substrates still inhibited the chymotrypsin-like activity. Thus, occupancy of the caspase-like sites stimulates the trypsin-like activity of proteasomes, but substrates of the caspase-like sites inhibit the chymotrypsin-like activity by binding to a distinct noncatalytic site.
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Affiliation(s)
- Alexei F Kisselev
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA.
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42
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Sijts A, Sun Y, Janek K, Kral S, Paschen A, Schadendorf D, Kloetzel PM. The role of the proteasome activator PA28 in MHC class I antigen processing. Mol Immunol 2002; 39:165-9. [PMID: 12200048 DOI: 10.1016/s0161-5890(02)00099-8] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The proteasome system is the major source for the generation of viral antigens and tumor antigens presented by major histocompatibility complex class I (MHC class I) molecules. A specific feature of the proteasomal antigen processing machinery is that five of its components are inducible by IFN-gamma. Two of these are the alpha and beta subunits of the proteasome activator PA28. Our results show that PA28 selectively up-regulates the presentation of viral MHC class I epitopes and that down regulation PA28 in tumor cells results in impaired presentation of a human TRP2 tumor antigen.
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Affiliation(s)
- Alice Sijts
- Institut für Biochemie, Charité-Medizinische Fakültät der, Humboldt Universität zu Berlin, Monbijoustrasse 2, 10117 Berlin, Germany
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Ustrell V, Hoffman L, Pratt G, Rechsteiner M. PA200, a nuclear proteasome activator involved in DNA repair. EMBO J 2002; 21:3516-25. [PMID: 12093752 PMCID: PMC126083 DOI: 10.1093/emboj/cdf333] [Citation(s) in RCA: 246] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2002] [Revised: 05/17/2002] [Accepted: 05/17/2002] [Indexed: 11/14/2022] Open
Abstract
We have identified a novel 200 kDa nuclear protein that activates the proteasome. The protein, which we call PA200, has been purified to homogeneity from bovine testis and has been shown to activate proteasomal hydrolysis of peptides, but not proteins. Following gamma-irradiation of HeLa cells the uniform nuclear distribution of PA200 changes to a strikingly punctate pattern, a behavior characteristic of many DNA repair proteins. Homologs of PA200 are present in worms, plants and yeast. Others have shown that mutation of yeast PA200 results in hypersensitivity to bleomycin, and exposure of yeast to DNA damaging agents induces the PA200 message. Taken together, these findings implicate PA200 in DNA repair, possibly by recruiting proteasomes to double strand breaks.
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Affiliation(s)
| | - Laura Hoffman
- Department of Biochemistry, University of Utah, 50 N Medical Drive, Salt Lake City, UT 84132 and
Huntsman Cancer Institute, University of Utah, 2000 Circle of Hope Drive, Salt Lake City, UT 84132, USA Corresponding author e-mail:
| | | | - Martin Rechsteiner
- Department of Biochemistry, University of Utah, 50 N Medical Drive, Salt Lake City, UT 84132 and
Huntsman Cancer Institute, University of Utah, 2000 Circle of Hope Drive, Salt Lake City, UT 84132, USA Corresponding author e-mail:
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Kisselev AF, Kaganovich D, Goldberg AL. Binding of hydrophobic peptides to several non-catalytic sites promotes peptide hydrolysis by all active sites of 20 S proteasomes. Evidence for peptide-induced channel opening in the alpha-rings. J Biol Chem 2002; 277:22260-70. [PMID: 11927581 DOI: 10.1074/jbc.m112360200] [Citation(s) in RCA: 141] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The eukaryotic 20 S proteasome contains the following 6 active sites: 2 chymotrypsin-like, 2 trypsin-like, and 2 caspase-like. We previously showed that hydrophobic peptide substrates of the chymotrypsin-like sites allosterically stimulate peptide hydrolysis by the caspase-like sites and their own cleavage. More thorough analysis revealed that these peptides also stimulate peptide hydrolysis by the trypsin-like site. This general activation by hydrophobic peptides occurred even if the chymotrypsin-like sites were occupied by a covalent inhibitor and was highly cooperative, with an average Hill coefficient of 7. Therefore, this stimulation of peptide hydrolysis at all active sites occurs upon binding of hydrophobic peptides to several non-catalytic sites. The stimulation by hydrophobic peptides was not observed in the yeast Delta N alpha 3 mutant 20 S proteasomes, in 20 S-PA26 complexes, or SDS-activated proteasomes and was significantly lower in 26 S proteasomes, all of which appear to have the gated channel in the alpha-rings in an open conformation and hydrolyze peptides at much faster rates than 20 S proteasomes. Also the hydrophobic peptides altered K(m), V(max) of active sites in a similar fashion as PA26 and the Delta N alpha 3 mutation. The activation by hydrophobic peptides was decreased in K(+)-containing buffer, which favors the closed state of the channels. Therefore, hydrophobic peptides stimulate peptide hydrolysis most likely by promoting the opening of the channels in the alpha-rings. During protein breakdown, this peptide-induced channel opening may function to facilitate the release of products from the proteasome.
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Affiliation(s)
- Alexei F Kisselev
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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Abstract
Regulated proteolysis plays important roles in cell physiology as well as in pathological conditions. In most of the cases, regulated proteolysis is carried out by the ubiquitin- and proteasome-dependent proteolytic system, which is also in charge of the bulk of cytoplasmic proteolysis. However, apoptosis or the process of programmed cell death is regulated by a different proteolytic system, i.e. by caspases, a family of specialized cysteine proteases. Nevertheless, there is plenty of evidence of a crosstalk between the apoptotic pathways and the ubiquitin and proteasome system, whose function in apoptosis appears to be very complex. Proteasome inhibitors induce apoptosis in multiple cell types, while in other they are relatively harmless or even prevent apoptosis induced by other stimuli. Proteasomes degrade specific proteins during apoptosis, but on the other hand some components of the proteasome system are degraded by caspases. The knowledge about the involvement of the ubiquitin- and proteasome-dependent system in apoptosis is already clinically exploited, since proteasome inhibitors are being tested as experimental drugs in the treatment of cancer and other pathological conditions, where manipulation of apoptosis is desirable.
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Affiliation(s)
- Cezary Wójcik
- Department of Histology and Embryology, Center of Biostructure Research, Medical University of Warsaw, Warsaw, Poland.
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Harris JL, Alper PB, Li J, Rechsteiner M, Backes BJ. Substrate specificity of the human proteasome. CHEMISTRY & BIOLOGY 2001; 8:1131-41. [PMID: 11755392 DOI: 10.1016/s1074-5521(01)00080-1] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
BACKGROUND Regulated proteolysis by the proteasome is crucial for a broad array of cellular processes, from control of the cell cycle to production of antigens. RESULTS The rules governing the N-terminal primary and extended substrate specificity of the human 20S proteasome in the presence or absence of 11S proteasome activators (REGalpha/beta and REGgamma) have been elaborated using activity-based proteomic library tools. CONCLUSIONS The 11S proteasome activators are shown to be important for both increasing the activity of the 20S proteasome and for altering its cleavage pattern and substrate specificity. These data also establish that the extended substrate specificity is an important factor for proteasomal cleavage. The specificities observed have features in common with major histocompatibility complex (MHC) class I ligands and can be used to improve the prediction of MHC class I restricted cytotoxic T-cell responses.
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Affiliation(s)
- J L Harris
- Genomics Institute of the Novartis Research Foundation, San Diego, CA 92121, USA.
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