1
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Peterson BG, Hwang J, Russ JE, Schroeder JW, Freddolino PL, Baldridge RD. Deep mutational scanning highlights a role for cytosolic regions in Hrd1 function. Cell Rep 2023; 42:113451. [PMID: 37980570 PMCID: PMC10751623 DOI: 10.1016/j.celrep.2023.113451] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 10/10/2023] [Accepted: 11/01/2023] [Indexed: 11/21/2023] Open
Abstract
Misfolded endoplasmic reticulum (ER) proteins are degraded through a process called ER-associated degradation (ERAD). Soluble, lumenal ERAD targets are recognized, retrotranslocated across the ER membrane, ubiquitinated, extracted from the membrane, and degraded by the proteasome using an ERAD pathway containing a ubiquitin ligase called Hrd1. To determine how Hrd1 mediates these processes, we developed a deep mutational scanning approach to identify residues involved in Hrd1 function, including those exclusively required for lumenal degradation. We identify several regions required for different Hrd1 functions. Most surprisingly, we find two cytosolic regions of Hrd1 required for lumenal ERAD substrate degradation. Using in vivo and in vitro approaches, we define roles for disordered regions between structural elements that are required for Hrd1 autoubiquitination and substrate interaction. Our results demonstrate that disordered cytosolic regions promote substrate retrotranslocation by controlling Hrd1 activation and establishing directionality of retrotranslocation for lumenal substrate across the ER membrane.
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Affiliation(s)
- Brian G Peterson
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jiwon Hwang
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jennifer E Russ
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jeremy W Schroeder
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - P Lydia Freddolino
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA; Cellular and Molecular Biology Program, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA; Department of Computational Medicine and Bioinformatics, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Ryan D Baldridge
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA; Cellular and Molecular Biology Program, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA.
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2
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Rudinskiy M, Molinari M. ER-to-lysosome-associated degradation in a nutshell: mammalian, yeast, and plant ER-phagy as induced by misfolded proteins. FEBS Lett 2023; 597:1928-1945. [PMID: 37259628 DOI: 10.1002/1873-3468.14674] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/01/2023] [Revised: 05/10/2023] [Accepted: 05/22/2023] [Indexed: 06/02/2023]
Abstract
Conserved catabolic pathways operate to remove aberrant polypeptides from the endoplasmic reticulum (ER), the major biosynthetic organelle of eukaryotic cells. The best known are the ER-associated degradation (ERAD) pathways that control the retrotranslocation of terminally misfolded proteins across the ER membrane for clearance by the cytoplasmic ubiquitin/proteasome system. In this review, we catalog folding-defective mammalian, yeast, and plant proteins that fail to engage ERAD machineries. We describe that they rather segregate in ER subdomains that eventually vesiculate. These ER-derived vesicles are captured by double membrane autophagosomes, engulfed by endolysosomes/vacuoles, or fused with degradative organelles to clear cells from their toxic cargo. These client-specific, mechanistically diverse ER-phagy pathways are grouped under the umbrella term of ER-to-lysosome-associated degradation for description in this essay.
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Affiliation(s)
- Mikhail Rudinskiy
- Università della Svizzera italiana, Lugano, Switzerland
- Institute for Research in Biomedicine, Bellinzona, Switzerland
- Department of Biology, Swiss Federal Institute of Technology, Zurich, Switzerland
| | - Maurizio Molinari
- Università della Svizzera italiana, Lugano, Switzerland
- Institute for Research in Biomedicine, Bellinzona, Switzerland
- School of Life Sciences, École Polytechnique Fédérale de Lausanne, Switzerland
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3
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Peterson BG, Hwang J, Russ JE, Schroeder J, Freddolino PL, Baldridge RD. Deep mutational scanning highlights a new role for cytosolic regions in Hrd1 function. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.04.03.535444. [PMID: 37066402 PMCID: PMC10103981 DOI: 10.1101/2023.04.03.535444] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Misfolded endoplasmic reticulum proteins are degraded through a process called endoplasmic reticulum associated degradation (ERAD). Soluble, lumenal ERAD targets are recognized, retrotranslocated across the ER membrane, ubiquitinated, extracted from the membrane, and degraded by the proteasome using an ERAD pathway containing a ubiquitin ligase called Hrd1. To determine how Hrd1 mediates these processes, we developed a deep mutational scanning approach to identify residues involved in Hrd1 function, including those exclusively required for lumenal degradation. We identified several regions required for different Hrd1 functions. Most surprisingly, we found two cytosolic regions of Hrd1 required for lumenal ERAD substrate degradation. Using in vivo and in vitro approaches, we defined roles for disordered regions between structural elements that were required for Hrd1's ability to autoubiquitinate and interact with substrate. Our results demonstrate that disordered cytosolic regions promote substrate retrotranslocation by controlling Hrd1 activation and establishing directionality of retrotranslocation for lumenal substrate across the endoplasmic reticulum membrane.
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Affiliation(s)
- Brian G. Peterson
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jiwon Hwang
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jennifer E. Russ
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jeremy Schroeder
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Peter L. Freddolino
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
- Cellular and Molecular Biology Program, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
- Department of Computational Medicine and Bioinformatics, University of Michigan Medical School
| | - Ryan D. Baldridge
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
- Cellular and Molecular Biology Program, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
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4
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Hwang J, Peterson BG, Knupp J, Baldridge RD. The ERAD system is restricted by elevated ceramides. SCIENCE ADVANCES 2023; 9:eadd8579. [PMID: 36638172 PMCID: PMC9839339 DOI: 10.1126/sciadv.add8579] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/08/2022] [Accepted: 12/15/2022] [Indexed: 06/17/2023]
Abstract
Misfolded proteins in the endoplasmic reticulum (ER) are removed through a process known as ER-associated degradation (ERAD). ERAD occurs through an integral membrane protein quality control system that recognizes substrates, retrotranslocates the substrates across the membrane, and ubiquitinates and extracts the substrates from the membrane for degradation at the cytosolic proteasome. While ERAD systems are known to regulate lipid biosynthetic enzymes, the regulation of ERAD systems by the lipid composition of cellular membranes remains unexplored. Here, we report that the ER membrane composition influences ERAD function by incapacitating substrate extraction. Unbiased lipidomic profiling revealed that elevation of specific very-long-chain ceramides leads to a marked increase in the level of ubiquitinated substrates in the ER membrane and concomitantly reduces extracted substrates in the cytoplasm. This work reveals a previously unrecognized mechanism in which ER membrane lipid remodeling changes the activity of ERAD.
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Affiliation(s)
- Jiwon Hwang
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Brian G. Peterson
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
| | - Jeffrey Knupp
- Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI 48109, USA
| | - Ryan D. Baldridge
- Department of Biological Chemistry, University of Michigan Medical School, 1150 W Medical Center Drive, Ann Arbor, MI 48109, USA
- Cellular and Molecular Biology Program, University of Michigan Medical School, Ann Arbor, MI 48109, USA
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5
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Karamali N, Ebrahimnezhad S, Khaleghi Moghadam R, Daneshfar N, Rezaiemanesh A. HRD1 in human malignant neoplasms: Molecular mechanisms and novel therapeutic strategy for cancer. Life Sci 2022; 301:120620. [PMID: 35533759 DOI: 10.1016/j.lfs.2022.120620] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Revised: 05/01/2022] [Accepted: 05/04/2022] [Indexed: 10/18/2022]
Abstract
In tumor cells, the endoplasmic reticulum (ER) plays an essential role in maintaining cellular proteostasis by stimulating unfolded protein response (UPR) underlying stress conditions. ER-associated degradation (ERAD) is a critical pathway of the UPR to protect cells from ER stress-induced apoptosis and the elimination of unfolded or misfolded proteins by the ubiquitin-proteasome system (UPS). 3-Hydroxy-3-methylglutaryl reductase degradation (HRD1) as an E3 ubiquitin ligase plays an essential role in the ubiquitination and dislocation of misfolded protein in ERAD. In addition, HRD1 can target other normal folded proteins. In various types of cancer, the expression of HRD1 is dysregulated, and it targets different molecules to develop cancer hallmarks or suppress the progression of the disease. Recent investigations have defined the role of HRD1 in drug resistance in types of cancer. This review focuses on the molecular mechanisms of HRD1 and its roles in cancer pathogenesis and discusses the worthiness of targeting HRD1 as a novel therapeutic strategy in cancer.
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Affiliation(s)
- Negin Karamali
- Student Research Committee, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran; Department of Immunology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran.
| | - Samaneh Ebrahimnezhad
- Student Research Committee, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran; Department of Immunology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran.
| | - Reihaneh Khaleghi Moghadam
- Student Research Committee, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran; Department of Immunology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran.
| | - Niloofar Daneshfar
- Student Research Committee, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran; Department of Immunology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran.
| | - Alireza Rezaiemanesh
- Department of Immunology, School of Medicine, Kermanshah University of Medical Sciences, Kermanshah, Iran.
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6
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Freije BJ, Freije WM, Do TU, Adkins GE, Bruch A, Hurtig JE, Morano KA, Schaffrath R, West JD. Identifying Interaction Partners of Yeast Protein Disulfide Isomerases Using a Small Thiol-Reactive Cross-Linker: Implications for Secretory Pathway Proteostasis. Chem Res Toxicol 2022; 35:326-336. [PMID: 35084835 PMCID: PMC8860869 DOI: 10.1021/acs.chemrestox.1c00376] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Protein disulfide isomerases (PDIs) function in forming the correct disulfide bonds in client proteins, thereby aiding the folding of proteins that enter the secretory pathway. Recently, several PDIs have been identified as targets of organic electrophiles, yet the client proteins of specific PDIs remain largely undefined. Here, we report that PDIs expressed in Saccharomyces cerevisiae are targets of divinyl sulfone (DVSF) and other thiol-reactive protein cross-linkers. Using DVSF, we identified the interaction partners that were cross-linked to Pdi1 and Eug1, finding that both proteins form cross-linked complexes with other PDIs, as well as vacuolar hydrolases, proteins involved in cell wall biosynthesis and maintenance, and many ER proteostasis factors involved ER stress signaling and ER-associated protein degradation (ERAD). The latter discovery prompted us to examine the effects of DVSF on ER quality control, where we found that DVSF inhibits the degradation of the ERAD substrate CPY*, in addition to covalently modifying Ire1 and blocking the activation of the unfolded protein response. Our results reveal that DVSF targets many proteins within the ER proteostasis network and suggest that these proteins may be suitable targets for covalent therapeutic development in the future.
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Affiliation(s)
- Benjamin J. Freije
- Biochemistry & Molecular Biology Program; Departments of Biology and Chemistry; The College of Wooster; Wooster, OH USA
| | - Wilson M. Freije
- Biochemistry & Molecular Biology Program; Departments of Biology and Chemistry; The College of Wooster; Wooster, OH USA
| | - To Uyen Do
- Biochemistry & Molecular Biology Program; Departments of Biology and Chemistry; The College of Wooster; Wooster, OH USA
| | - Grace E. Adkins
- Biochemistry & Molecular Biology Program; Departments of Biology and Chemistry; The College of Wooster; Wooster, OH USA
| | - Alexander Bruch
- Fachgebiet Mikrobiologie; Institut für Biologie; Universität Kassel; Kassel, Germany
| | - Jennifer E. Hurtig
- Biochemistry & Molecular Biology Program; Departments of Biology and Chemistry; The College of Wooster; Wooster, OH USA,Department of Microbiology & Molecular Genetics; McGovern Medical School; University of Texas at Houston; Houston, TX USA
| | - Kevin A. Morano
- Department of Microbiology & Molecular Genetics; McGovern Medical School; University of Texas at Houston; Houston, TX USA
| | - Raffael Schaffrath
- Fachgebiet Mikrobiologie; Institut für Biologie; Universität Kassel; Kassel, Germany
| | - James D. West
- Biochemistry & Molecular Biology Program; Departments of Biology and Chemistry; The College of Wooster; Wooster, OH USA,Corresponding author , phone: 330-263-2368
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7
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Davidson S, Yu CH, Steiner A, Ebstein F, Baker PJ, Jarur-Chamy V, Hrovat Schaale K, Laohamonthonkul P, Kong K, Calleja DJ, Harapas CR, Balka KR, Mitchell J, Jackson JT, Geoghegan ND, Moghaddas F, Rogers KL, Mayer-Barber KD, De Jesus AA, De Nardo D, Kile BT, Sadler AJ, Poli MC, Krüger E, Goldbach Mansky R, Masters SL. Protein kinase R is an innate immune sensor of proteotoxic stress via accumulation of cytoplasmic IL-24. Sci Immunol 2022; 7:eabi6763. [PMID: 35148201 PMCID: PMC11036408 DOI: 10.1126/sciimmunol.abi6763] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Proteasome dysfunction can lead to autoinflammatory disease associated with elevated type I interferon (IFN-αβ) and NF-κB signaling; however, the innate immune pathway driving this is currently unknown. Here, we identified protein kinase R (PKR) as an innate immune sensor for proteotoxic stress. PKR activation was observed in cellular models of decreased proteasome function and in multiple cell types from patients with proteasome-associated autoinflammatory disease (PRAAS). Furthermore, genetic deletion or small-molecule inhibition of PKR in vitro ameliorated inflammation driven by proteasome deficiency. In vivo, proteasome inhibitor-induced inflammatory gene transcription was blunted in PKR-deficient mice compared with littermate controls. PKR also acted as a rheostat for proteotoxic stress by triggering phosphorylation of eIF2α, which can prevent the translation of new proteins to restore homeostasis. Although traditionally known as a sensor of RNA, under conditions of proteasome dysfunction, PKR sensed the cytoplasmic accumulation of a known interactor, interleukin-24 (IL-24). When misfolded IL-24 egress into the cytosol was blocked by inhibition of the endoplasmic reticulum-associated degradation pathway, PKR activation and subsequent inflammatory signaling were blunted. Cytokines such as IL-24 are normally secreted from cells; therefore, cytoplasmic accumulation of IL-24 represents an internal danger-associated molecular pattern. Thus, we have identified a mechanism by which proteotoxic stress is detected, causing inflammation observed in the disease PRAAS.
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Affiliation(s)
- Sophia Davidson
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Chien-Hsiung Yu
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Annemarie Steiner
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
- Institute of Structural Biology, University Hospital Bonn, Bonn 53127, Germany
| | - Frédéric Ebstein
- University Medicine Greifswald, Institute of Medical Biochemistry and Molecular Biology, Greifswald 17475, Germany
| | - Paul J. Baker
- Inflammation and Innate Immunity Unit, Laboratory of Clinical Immunology and Microbiology, NIAID, NIH, Bethesda, MD 20892, USA
| | - Valentina Jarur-Chamy
- Immunogenetics and Translational Immunology Program. Facultad de Medicina, Universidad del Desarrollo Clínica Alemana, Santiago, Chile
| | - Katja Hrovat Schaale
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Pawat Laohamonthonkul
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Klara Kong
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Dale J. Calleja
- Ubiquitin Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Cassandra R. Harapas
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Katherine R. Balka
- Department of Anatomy and Developmental Biology, Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
| | - Jacob Mitchell
- Translational Autoinflammatory Disease Studies (TADS), Laboratory of Clinical Immunology and Microbiology, NIAID, NIH, Bethesda, MD 20892, USA
| | - Jacob T. Jackson
- Immunology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Niall D. Geoghegan
- Centre for Dynamic Imaging, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Fiona Moghaddas
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
| | - Kelly L. Rogers
- Centre for Dynamic Imaging, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
| | - Katrin D. Mayer-Barber
- Inflammation and Innate Immunity Unit, Laboratory of Clinical Immunology and Microbiology, NIAID, NIH, Bethesda, MD 20892, USA
| | - Adriana A. De Jesus
- Translational Autoinflammatory Disease Studies (TADS), Laboratory of Clinical Immunology and Microbiology, NIAID, NIH, Bethesda, MD 20892, USA
| | - Dominic De Nardo
- Department of Anatomy and Developmental Biology, Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
| | - Benjamin T. Kile
- Department of Anatomy and Developmental Biology, Monash Biomedicine Discovery Institute, Monash University, Clayton, Victoria, Australia
- Faculty of Health and Medical Sciences, University of Adelaide, Adelaide, South Australia 5000, Australia
| | - Anthony J. Sadler
- Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Clayton, Victoria, Australia
- Department of Molecular and Translational Sciences, Monash University, Clayton, Victoria, Australia
| | - M. Cecilia Poli
- Immunogenetics and Translational Immunology Program. Facultad de Medicina, Universidad del Desarrollo Clínica Alemana, Santiago, Chile
- Division of Pediatric Immunology, Allergy, and Rheumatology, Department of Pediatrics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Elke Krüger
- University Medicine Greifswald, Institute of Medical Biochemistry and Molecular Biology, Greifswald 17475, Germany
| | - Raphaela Goldbach Mansky
- Translational Autoinflammatory Disease Studies (TADS), Laboratory of Clinical Immunology and Microbiology, NIAID, NIH, Bethesda, MD 20892, USA
| | - Seth L. Masters
- Inflammation Division, Walter and Eliza Hall Institute of Medical Research, Parkville, Victoria 3052, Australia
- Department of Medical Biology, University of Melbourne, Parkville, Victoria 3010, Australia
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8
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Nakatsukasa K, Wigge S, Takano Y, Kawarasaki T, Kamura T, Brodsky JL. A positive genetic selection for transmembrane domain mutations in HRD1 underscores the importance of Hrd1 complex integrity during ERAD. Curr Genet 2022; 68:227-242. [PMID: 35041076 PMCID: PMC9036396 DOI: 10.1007/s00294-022-01227-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2021] [Revised: 12/29/2021] [Accepted: 12/30/2021] [Indexed: 11/26/2022]
Abstract
Misfolded proteins in the endoplasmic reticulum (ER) are retrotranslocated to the cytosol for ubiquitination and degradation by the proteasome. During this process, known as ER-associated degradation (ERAD), the ER-embedded Hrd1 ubiquitin ligase plays a central role in recognizing, ubiquitinating, and retrotranslocating scores of lumenal and integral membrane proteins. To better define the mechanisms underlying Hrd1 function in Saccharomyces cerevisiae, several model substrates have been developed. One substrate is Sec61-2, a temperature sensitive allele of the Sec61 translocation channel. Cells expressing Sec61-2 grow at 25 °C because the protein is stable, but sec61-2 yeast are inviable at 38 °C because the mutated protein is degraded in a Hrd1-dependent manner. Therefore, deleting HRD1 stabilizes Sec61-2 and hence sec61-2hrd1∆ double mutants are viable at 38 °C. This unique phenotype allowed us to perform a non-biased screen for loss-of-function alleles in HRD1. Based on its importance in mediating substrate retrotranslocation, the screen was also developed to focus on mutations in sequences encoding Hrd1's transmembrane-rich domain. Ultimately, a group of recessive mutations was identified in HRD1, including an ensemble of destabilizing mutations that resulted in the delivery of Hrd1 to the ERAD pathway. A more stable mutant resided in a buried transmembrane domain, yet the Hrd1 complex was disrupted in yeast expressing this mutant. Together, these data confirm the importance of Hrd1 complex integrity during ERAD, suggest that allosteric interactions between transmembrane domains regulate Hrd1 complex formation, and provide the field with new tools to define the dynamic interactions between ERAD components during substrate retrotranslocation.
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Affiliation(s)
- Kunio Nakatsukasa
- Graduate School of Science, Nagoya City University, Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8501, Japan.
| | - Sylvia Wigge
- Department of Biological Sciences, University of Pittsburgh, A320 Langley Hall, Pittsburgh, PA, 15260, USA
| | - Yuki Takano
- Graduate School of Science, Nagoya City University, Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8501, Japan
| | - Tomoyuki Kawarasaki
- Graduate School of Science, Nagoya City University, Yamanohata 1, Mizuho-cho, Mizuho-ku, Nagoya, Aichi, 467-8501, Japan
| | - Takumi Kamura
- Division of Biological Sciences, Graduate School of Science, Nagoya University, Nagoya, Aichi, 464-8602, Japan
| | - Jeffrey L Brodsky
- Department of Biological Sciences, University of Pittsburgh, A320 Langley Hall, Pittsburgh, PA, 15260, USA.
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9
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Peng K, Kroukamp H, Pretorius IS, Paulsen IT. Yeast Synthetic Minimal Biosensors for Evaluating Protein Production. ACS Synth Biol 2021; 10:1640-1650. [PMID: 34126009 DOI: 10.1021/acssynbio.0c00633] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
The unfolded protein response (UPR) is a highly conserved cellular response in eukaryotic cells to counteract endoplasmic reticulum (ER) stress, typically triggered by unfolded protein accumulation. In addition to its relevance to human diseases like cancer, the induction of the UPR has a significant impact on the recombinant protein production in eukaryotic cell factories, including the industrial workhorseSaccharomyces cerevisiae. Being able to accurately detect and measure this ER stress response in single cells, enables the rapid optimization of protein production conditions and high-throughput strain selection strategies. Current methodologies to monitor the UPR in S. cerevisiae are often temporally and spatially removed from the cultivation stage or lack updated systematic evaluation. To this end, we constructed and systematically evaluated a series of high-throughput UPR sensors by different designs, incorporating either yeast native UPR promoters or novel synthetic minimal UPR promoters. The native promoters of DER1 and ERO1 were identified to have suitable UPR biosensor properties and served as an expression level guide for orthogonal sensor benchmarking. Our best synthetic minimal sensor is only 98 bp in length, has minimal homology to other native yeast sequences and displayed superior sensor characteristics. The synthetic minimal UPR sensor was able to accurately distinguish between cells expressing different heterologous proteins and between the different secretion levels of the same protein. This work demonstrated the potential of synthetic UPR biosensors as high-throughput tools to predict the protein production capacity of strains, interrogate protein properties hampering their secretion, and guide rational engineering strategies for optimal heterologous protein production.
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Affiliation(s)
- Kai Peng
- ARC Centre of Excellence in Synthetic Biology, Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
| | - Heinrich Kroukamp
- ARC Centre of Excellence in Synthetic Biology, Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
- Biomolecular Discovery and Design Research Centre, Macquarie University, Sydney, NSW 2109, Australia
| | | | - Ian T. Paulsen
- ARC Centre of Excellence in Synthetic Biology, Department of Molecular Sciences, Macquarie University, Sydney, NSW 2109, Australia
- Biomolecular Discovery and Design Research Centre, Macquarie University, Sydney, NSW 2109, Australia
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10
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Piirainen MA, Frey AD. Investigating the role of ERAD on antibody processing in glycoengineered Saccharomyces cerevisiae. FEMS Yeast Res 2021; 20:5700285. [PMID: 31922547 DOI: 10.1093/femsyr/foaa002] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2019] [Accepted: 01/09/2020] [Indexed: 01/01/2023] Open
Abstract
N-glycosylation plays an important role in the endoplasmic reticulum quality control (ERQC). N-glycan biosynthesis pathways have been engineered in yeasts and fungi to enable the production of therapeutic glycoproteins with human-compatible N-glycosylation, and some glycoengineering approaches alter the synthesis of the lipid-linked oligosaccharide (LLO). Because the effects of LLO engineering on ERQC are currently unknown, we characterized intracellular processing of IgG in glycoengineered Δalg3 Δalg11 Saccharomyces cerevisiae strain and analyzed how altered LLO structures affect endoplasmic reticulum-associated degradation (ERAD). Intracellular IgG light and heavy chain molecules expressed in Δalg3 Δalg11 strain are ERAD substrates and targeted to ERAD independently of Yos9p and Htm1p, whereas in the presence of ALG3 ERAD targeting is dependent on Yos9p but does not require Htm1p. Blocking of ERAD accumulated ER and post-Golgi forms of IgG and increased glycosylation of matα secretion signal but did not improve IgG secretion. Our results show ERAD targeting of a heterologous glycoprotein in yeast, and suggest that proteins in the ER can be targeted to ERAD via other mechanisms than the Htm1p-Yos9p-dependent route when the LLO biosynthesis is altered.
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Affiliation(s)
- Mari A Piirainen
- Department of Bioproducts and Biosystems, Aalto University, Finland, Kemistintie 1, 02150 Espoo, Finland
| | - Alexander D Frey
- Department of Bioproducts and Biosystems, Aalto University, Finland, Kemistintie 1, 02150 Espoo, Finland
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11
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Ninagawa S, George G, Mori K. Mechanisms of productive folding and endoplasmic reticulum-associated degradation of glycoproteins and non-glycoproteins. Biochim Biophys Acta Gen Subj 2020; 1865:129812. [PMID: 33316349 DOI: 10.1016/j.bbagen.2020.129812] [Citation(s) in RCA: 33] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2020] [Revised: 12/09/2020] [Accepted: 12/09/2020] [Indexed: 12/22/2022]
Abstract
BACKGROUND The quality of proteins destined for the secretory pathway is ensured by two distinct mechanisms in the endoplasmic reticulum (ER): productive folding of newly synthesized proteins, which is assisted by ER-localized molecular chaperones and in most cases also by disulfide bond formation and transfer of an oligosaccharide unit; and ER-associated degradation (ERAD), in which proteins unfolded or misfolded in the ER are recognized and processed for delivery to the ER membrane complex, retrotranslocated through the complex with simultaneous ubiquitination, extracted by AAA-ATPase to the cytosol, and finally degraded by the proteasome. SCOPE OF REVIEW We describe the mechanisms of productive folding and ERAD, with particular attention to glycoproteins versus non-glycoproteins, and to yeast versus mammalian systems. MAJOR CONCLUSION Molecular mechanisms of the productive folding of glycoproteins and non-glycoproteins mediated by molecular chaperones and protein disulfide isomerases are well conserved from yeast to mammals. Additionally, mammals have gained an oligosaccharide structure-dependent folding cycle for glycoproteins. The molecular mechanisms of ERAD are also well conserved from yeast to mammals, but redundant expression of yeast orthologues in mammals has been encountered, particularly for components involved in recognition and processing of glycoproteins and components of the ER membrane complex involved in retrotranslocation and simultaneous ubiquitination of glycoproteins and non-glycoproteins. This may reflect an evolutionary consequence of increasing quantity or quality needs toward mammals. GENERAL SIGNIFICANCE The introduction of innovative genome editing technology into analysis of the mechanisms of mammalian ERAD, as exemplified here, will provide new insights into the pathogenesis of various diseases.
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Affiliation(s)
- Satoshi Ninagawa
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
| | - Ginto George
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
| | - Kazutoshi Mori
- Department of Biophysics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan.
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12
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Murakami-Sekimata A, Sekimata M, Sato N, Hayasaka Y, Nakano A. Deletion of PIN4 Suppresses the Protein Transport Defects Caused by sec12-4 Mutation in Saccharomyces cerevisiae. Microb Physiol 2020; 30:25-35. [PMID: 32958726 DOI: 10.1159/000509633] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2020] [Accepted: 06/24/2020] [Indexed: 11/19/2022]
Abstract
Newly synthesized secretory proteins are released into the lumen of the endoplasmic reticulum (ER). The secretory proteins are surrounded by coat protein complex II (COPII) vesicles, and transported from the ER and reach their destinations through the Golgi apparatus. Sec12p is a guanine nucleotide exchange factor for Sar1p, which initiates COPII vesicle budding from the ER. The activation of Sar1p by Sec12p and the subsequent COPII coat assembly have been well characterized, but the events that take place upstream of Sec12p remain unclear. In this study, we isolated the novel extragenic suppressor of sec12-4, PIN4/MDT1, a cell cycle checkpoint target. A yeast two-hybrid screening was used to identify Pin4/Mdt1p as a binding partner of the casein kinase I isoform Hrr25p, which we have previously identified as a modulator of Sec12p function. Deletion of PIN4 suppressed both defects of temperature-sensitive growth and the partial protein transport observed in sec12-4 mutants. The results of this study suggest that Pin4p provides novel aspects of Sec12p modulations.
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Affiliation(s)
- Akiko Murakami-Sekimata
- Division of Theoretical Nursing and Genetics, Graduate School of Medical Science, Yamagata University Faculty of Medicine, Yamagata, Japan,
| | - Masayuki Sekimata
- Radioisotope Research Center, School of Medicine, Fukushima Medical University, Fukushima, Japan
| | - Natsumi Sato
- Division of Theoretical Nursing and Genetics, Graduate School of Medical Science, Yamagata University Faculty of Medicine, Yamagata, Japan
| | - Yuto Hayasaka
- Division of Theoretical Nursing and Genetics, Graduate School of Medical Science, Yamagata University Faculty of Medicine, Yamagata, Japan
| | - Akihiko Nakano
- Live Cell Super-Resolution Imaging Research Team, Extreme Photonics Research Group, RIKEN Center for Advanced Photonics, Wako, Japan
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13
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Hosomi A, Iida K, Cho T, Iida H, Kaneko M, Suzuki T. The ER-associated protease Ste24 prevents N-terminal signal peptide-independent translocation into the endoplasmic reticulum in Saccharomyces cerevisiae. J Biol Chem 2020; 295:10406-10419. [PMID: 32513868 DOI: 10.1074/jbc.ra120.012575] [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] [Received: 01/08/2020] [Revised: 06/03/2020] [Indexed: 12/14/2022] Open
Abstract
Soluble proteins destined for the secretory pathway contain an N-terminal signal peptide that induces their translocation into the endoplasmic reticulum (ER). The importance of N-terminal signal peptides for ER translocation has been extensively examined over the past few decades. However, in the budding yeast Saccharomyces cerevisiae, a few proteins devoid of a signal peptide are still translocated into the ER and then N-glycosyl-ated. Using signal peptide-truncated reporter proteins, here we report the detection of significant translocation of N-terminal signal peptide-truncated proteins in a yeast mutant strain (ste24Δ) that lacks the endopeptidase Ste24 at the ER membrane. Furthermore, several ER/cytosolic proteins, including Sec61, Sec66, and Sec72, were identified as being involved in the translocation process. On the basis of screening for 20 soluble proteins that may be N-glycosylated in the ER in the ste24Δ strain, we identified the transcription factor Rme1 as a protein that is partially N-glycosylated despite the lack of a signal peptide. These results clearly indicate that some proteins lacking a signal peptide can be translocated into the ER and that Ste24 typically suppresses this process.
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Affiliation(s)
- Akira Hosomi
- Department of Agriculture, Graduate School of Science and Technology, Shinshu University, Kamiina, Nagano, Japan
| | - Kazuko Iida
- Laboratory of Biomembrane, Tokyo Metropolitan Institute of Medical Science, Setagaya, Tokyo, Japan
| | - Toshihiko Cho
- Department of Biology, Tokyo Gakugei University, Koganei, Tokyo, Japan
| | - Hidetoshi Iida
- Department of Biology, Tokyo Gakugei University, Koganei, Tokyo, Japan
| | - Masashi Kaneko
- Department of Agriculture, Graduate School of Science and Technology, Shinshu University, Kamiina, Nagano, Japan
| | - Tadashi Suzuki
- Glycometabolic Biochemistry Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama, Japan
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14
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Wu X, Siggel M, Ovchinnikov S, Mi W, Svetlov V, Nudler E, Liao M, Hummer G, Rapoport TA. Structural basis of ER-associated protein degradation mediated by the Hrd1 ubiquitin ligase complex. Science 2020; 368:368/6489/eaaz2449. [PMID: 32327568 DOI: 10.1126/science.aaz2449] [Citation(s) in RCA: 119] [Impact Index Per Article: 29.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2019] [Revised: 01/18/2020] [Accepted: 03/11/2020] [Indexed: 12/13/2022]
Abstract
Misfolded luminal endoplasmic reticulum (ER) proteins undergo ER-associated degradation (ERAD-L): They are retrotranslocated into the cytosol, polyubiquitinated, and degraded by the proteasome. ERAD-L is mediated by the Hrd1 complex (composed of Hrd1, Hrd3, Der1, Usa1, and Yos9), but the mechanism of retrotranslocation remains mysterious. Here, we report a structure of the active Hrd1 complex, as determined by cryo-electron microscopy analysis of two subcomplexes. Hrd3 and Yos9 jointly create a luminal binding site that recognizes glycosylated substrates. Hrd1 and the rhomboid-like Der1 protein form two "half-channels" with cytosolic and luminal cavities, respectively, and lateral gates facing one another in a thinned membrane region. These structures, along with crosslinking and molecular dynamics simulation results, suggest how a polypeptide loop of an ERAD-L substrate moves through the ER membrane.
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Affiliation(s)
- Xudong Wu
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Marc Siggel
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany
| | - Sergey Ovchinnikov
- Faculty of Arts and Sciences, Center for Systems Biology, Harvard University, Cambridge, MA 02138, USA
| | - Wei Mi
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.,Present address: Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Vladimir Svetlov
- Howard Hughes Medical Institute and Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
| | - Evgeny Nudler
- Howard Hughes Medical Institute and Department of Biochemistry and Molecular Pharmacology, New York University School of Medicine, New York, NY 10016, USA
| | - Maofu Liao
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
| | - Gerhard Hummer
- Department of Theoretical Biophysics, Max Planck Institute of Biophysics, 60438 Frankfurt am Main, Germany.,Institute of Biophysics, Goethe University Frankfurt, 60438 Frankfurt am Main, Germany
| | - Tom A Rapoport
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA.
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15
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The degradation-promoting roles of deubiquitinases Ubp6 and Ubp3 in cytosolic and ER protein quality control. PLoS One 2020; 15:e0232755. [PMID: 32401766 PMCID: PMC7219781 DOI: 10.1371/journal.pone.0232755] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2020] [Accepted: 04/21/2020] [Indexed: 11/19/2022] Open
Abstract
The quality control of intracellular proteins is achieved by degrading misfolded proteins which cannot be refolded by molecular chaperones. In eukaryotes, such degradation is handled primarily by the ubiquitin-proteasome system. However, it remained unclear whether and how protein quality control deploys various deubiquitinases. To address this question, we screened deletions or mutation of the 20 deubiquitinase genes in Saccharomyces cerevisiae and discovered that almost half of the mutations slowed the removal of misfolded proteins whereas none of the remaining mutations accelerated this process significantly. Further characterization revealed that Ubp6 maintains the level of free ubiquitin to promote the elimination of misfolded cytosolic proteins, while Ubp3 supports the degradation of misfolded cytosolic and ER luminal proteins by different mechanisms.
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16
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Hrd1 forms the retrotranslocation pore regulated by auto-ubiquitination and binding of misfolded proteins. Nat Cell Biol 2020; 22:274-281. [DOI: 10.1038/s41556-020-0473-4] [Citation(s) in RCA: 34] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Accepted: 01/20/2020] [Indexed: 01/01/2023]
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17
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Zhang J, Wu J, Liu L, Li J. The Crucial Role of Demannosylating Asparagine-Linked Glycans in ERADicating Misfolded Glycoproteins in the Endoplasmic Reticulum. FRONTIERS IN PLANT SCIENCE 2020; 11:625033. [PMID: 33510762 PMCID: PMC7835635 DOI: 10.3389/fpls.2020.625033] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/02/2020] [Accepted: 12/08/2020] [Indexed: 05/04/2023]
Abstract
Most membrane and secreted proteins are glycosylated on certain asparagine (N) residues in the endoplasmic reticulum (ER), which is crucial for their correct folding and function. Protein folding is a fundamentally inefficient and error-prone process that can be easily interfered by genetic mutations, stochastic cellular events, and environmental stresses. Because misfolded proteins not only lead to functional deficiency but also produce gain-of-function cellular toxicity, eukaryotic organisms have evolved highly conserved ER-mediated protein quality control (ERQC) mechanisms to monitor protein folding, retain and repair incompletely folded or misfolded proteins, or remove terminally misfolded proteins via a unique ER-associated degradation (ERAD) mechanism. A crucial event that terminates futile refolding attempts of a misfolded glycoprotein and diverts it into the ERAD pathway is executed by removal of certain terminal α1,2-mannose (Man) residues of their N-glycans. Earlier studies were centered around an ER-type α1,2-mannosidase that specifically cleaves the terminal α1,2Man residue from the B-branch of the three-branched N-linked Man9GlcNAc2 (GlcNAc for N-acetylglucosamine) glycan, but recent investigations revealed that the signal that marks a terminally misfolded glycoprotein for ERAD is an N-glycan with an exposed α1,6Man residue generated by members of a unique folding-sensitive α1,2-mannosidase family known as ER-degradation enhancing α-mannosidase-like proteins (EDEMs). This review provides a historical recount of major discoveries that led to our current understanding on the role of demannosylating N-glycans in sentencing irreparable misfolded glycoproteins into ERAD. It also discusses conserved and distinct features of the demannosylation processes of the ERAD systems of yeast, mammals, and plants.
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Affiliation(s)
- Jianjun Zhang
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
- Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
| | - Jiarui Wu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
- Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
| | - Linchuan Liu
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
- Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
| | - Jianming Li
- State Key Laboratory for Conservation and Utilization of Subtropical Agro-Bioresources, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
- Guangdong Key Laboratory for Innovative Development and Utilization of Forest Plant Germplasm, College of Forestry and Landscape Architecture, South China Agricultural University, Guangzhou, China
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI, United States
- *Correspondence: Jianming Li, ;
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18
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Peterson BG, Glaser ML, Rapoport TA, Baldridge RD. Cycles of autoubiquitination and deubiquitination regulate the ERAD ubiquitin ligase Hrd1. eLife 2019; 8:50903. [PMID: 31713515 PMCID: PMC6914336 DOI: 10.7554/elife.50903] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2019] [Accepted: 11/11/2019] [Indexed: 12/28/2022] Open
Abstract
Misfolded proteins in the lumen of the endoplasmic reticulum (ER) are retrotranslocated into the cytosol and polyubiquitinated before being degraded by the proteasome. The multi-spanning ubiquitin ligase Hrd1 forms the retrotranslocation channel and associates with three other membrane proteins (Hrd3, Usa1, Der1) of poorly defined function. The Hrd1 channel is gated by autoubiquitination, but how Hrd1 escapes degradation by the proteasome and returns to its inactive ground state is unknown. Here, we show that autoubiquitination of Hrd1 is counteracted by Ubp1, a deubiquitinating enzyme that requires its N-terminal transmembrane segment for activity towards Hrd1. The Hrd1 partner Hrd3 serves as a brake for autoubiquitination, while Usa1 attenuates Ubp1’s deubiquitination activity through an inhibitory effect of its UBL domain. These results lead to a model in which the Hrd1 channel is regulated by cycles of autoubiquitination and deubiquitination, reactions that are modulated by the other components of the Hrd1 complex. Just like factories make mistakes when producing products, cells make mistakes when producing proteins. In cells, a compartment called the endoplasmic reticulum is where about one third of all proteins are produced, and where new proteins undergo quality control. Damaged or misfolded proteins are removed by a process called endoplasmic reticulum-associated degradation (ERAD for short), because if damaged proteins accumulate, cells become stressed. One type of ERAD is driven by a protein called Hrd1. Together with other components, Hrd1 labels damaged proteins with a ubiquitin tag that acts as a flag for degradation. Hrd1 has a paradoxical feature, however. To be active, Hrd1 tags itself with ubiquitin but this also makes it more prone to becoming degraded. How does Hrd1 remain active while avoiding its own degradation? To address this question, Peterson et al. forced budding yeast cells to produce high levels of 23 different enzymes that remove ubiquitin tags. One of these enzymes, called Ubp1, was able remove the ubiquitin tag from Hrd1, though it had not been seen in the ERAD pathway before. Further experiments also showed that Ubp1 was able to regulate Hrd1 activity, making Ubp1 a regulator of Hrd1 dependent protein quality control. Without protein quality control, damaged proteins can contribute to various diseases. ERAD is a common quality control system for proteins, present in many different species, ranging from yeast to animals. Therefore, understanding how ERAD works in budding yeast may also increase understanding of how human cells deal with damaged proteins.
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Affiliation(s)
- Brian G Peterson
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, United States
| | - Morgan L Glaser
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, United States
| | - Tom A Rapoport
- Department of Cell Biology, Harvard Medical School, Howard Hughes Medical Institute, Boston, United States
| | - Ryan D Baldridge
- Department of Biological Chemistry, University of Michigan Medical School, Ann Arbor, United States
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19
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Kong KYE, Hung TNF, Man PHM, Wong TN, Cheng T, Jin DY. Post-transcriptional negative feedback regulation of proteostasis through the Dis3 ribonuclease and its disruption by polyQ-expanded Huntingtin. Nucleic Acids Res 2019; 47:10040-10058. [PMID: 31428776 PMCID: PMC6821268 DOI: 10.1093/nar/gkz722] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 08/05/2019] [Accepted: 08/08/2019] [Indexed: 11/17/2022] Open
Abstract
When proteostasis is disrupted by stresses such as heat shock, the heat stress response will be stimulated, leading to up-regulation of molecular chaperones by transcriptional activation and mRNA stabilization for restoring proteostasis. Although the mechanisms for their transcriptional activation have been clearly defined, how chaperone mRNAs are stabilized remains largely unknown. Starting by exploring the coupling between the apparently unrelated RNA degradation and protein quality control (PQC) systems, we show that the Dis3 ribonuclease, catalytic subunit of the RNA exosome required for RNA degradation, suppresses PQC activity in unstressed cells by degrading mRNAs encoding the Hsp70 cofactors Sis1, Ydj1 and Fes1, as well as some other chaperones or PQC factors, thereby limiting their protein expression. Dis3 is stabilized through its binding to Sis1 and the Hsp70s Ssa1/2. Upon heat stress, loss of Sis1 and Ssa1/2 availability triggers Dis3 ubiquitination and degradation, leading to stabilization of those chaperone mRNAs originally targeted by Dis3. We further demonstrate that polyQ-expanded huntingtin delays Dis3 degradation during heat stress and thus hinders chaperone mRNA stabilization. Our findings not only reveal a post-transcriptional negative feedback loop for maintaining proteostasis, but also uncover a mechanism that contributes to the impaired heat stress response in Huntington's disease.
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Affiliation(s)
- Ka-Yiu Edwin Kong
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong
| | | | | | - Tin-Ning Wong
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong
| | - Tao Cheng
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong
| | - Dong-Yan Jin
- School of Biomedical Sciences, The University of Hong Kong, Hong Kong
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20
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Makino M, Sahara T, Morita N, Ueno H. Carboxypeptidase Y activity and maintenance is modulated by a large helical structure. FEBS Open Bio 2019; 9:1337-1343. [PMID: 31173671 PMCID: PMC6609556 DOI: 10.1002/2211-5463.12686] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2019] [Revised: 05/20/2019] [Accepted: 06/06/2019] [Indexed: 11/29/2022] Open
Abstract
Yeast carboxypeptidase Y (CPY) is a serine protease with broad substrate specificity. Structurally, CPY belongs to the α/β hydrolase fold family and contains characteristic large helices, termed the V‐shape helix, above the active site cavity. Four intramolecular disulfide bonds are located in and around the V‐shape helix. In this study, mutant CPYs were constructed in which one of these disulfide bonds was disrupted. Mutants lacking the C193–C207 bond located at the beginning of the V‐shape helix aggregated easily, while mutants lacking the C262–C268 bond located at the end of the V‐shape helix displayed decreased hydrolytic activity. The results indicate that the V‐shape helix is involved in CPY catalysis and in maintenance of its conformation.
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Affiliation(s)
- Mai Makino
- Department of Biochemistry, Nara Medical University, Kashihara, Japan
| | - Takehiko Sahara
- Bio-Design Research Group, Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Naoki Morita
- Molecular and Biological Technology Research Group, Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Sapporo, Japan
| | - Hiroshi Ueno
- Laboratory of Biochemistry and Applied Microbiology, School of Agriculture, Ryukoku University, Otsu, Japan
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21
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Schmidt RM, Schessner JP, Borner GH, Schuck S. The proteasome biogenesis regulator Rpn4 cooperates with the unfolded protein response to promote ER stress resistance. eLife 2019; 8:43244. [PMID: 30865586 PMCID: PMC6415940 DOI: 10.7554/elife.43244] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2018] [Accepted: 02/27/2019] [Indexed: 12/27/2022] Open
Abstract
Misfolded proteins in the endoplasmic reticulum (ER) activate the unfolded protein response (UPR), which enhances protein folding to restore homeostasis. Additional pathways respond to ER stress, but how they help counteract protein misfolding is incompletely understood. Here, we develop a titratable system for the induction of ER stress in yeast to enable a genetic screen for factors that augment stress resistance independently of the UPR. We identify the proteasome biogenesis regulator Rpn4 and show that it cooperates with the UPR. Rpn4 abundance increases during ER stress, first by a post-transcriptional, then by a transcriptional mechanism. Induction of RPN4 transcription is triggered by cytosolic mislocalization of secretory proteins, is mediated by multiple signaling pathways and accelerates clearance of misfolded proteins from the cytosol. Thus, Rpn4 and the UPR are complementary elements of a modular cross-compartment response to ER stress.
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Affiliation(s)
- Rolf M Schmidt
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance and CellNetworks Cluster of Excellence, Heidelberg, Germany
| | - Julia P Schessner
- Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Georg Hh Borner
- Department of Proteomics and Signal Transduction, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Sebastian Schuck
- Center for Molecular Biology of Heidelberg University (ZMBH), DKFZ-ZMBH Alliance and CellNetworks Cluster of Excellence, Heidelberg, Germany
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22
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Mehrtash AB, Hochstrasser M. Ubiquitin-dependent protein degradation at the endoplasmic reticulum and nuclear envelope. Semin Cell Dev Biol 2018; 93:111-124. [PMID: 30278225 DOI: 10.1016/j.semcdb.2018.09.013] [Citation(s) in RCA: 78] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2018] [Revised: 09/26/2018] [Accepted: 09/27/2018] [Indexed: 01/01/2023]
Abstract
Numerous nascent proteins undergo folding and maturation within the luminal and membrane compartments of the endoplasmic reticulum (ER). Despite the presence of various factors in the ER that promote protein folding, many proteins fail to properly fold and assemble and are subsequently degraded. Regulatory proteins in the ER also undergo degradation in a way that is responsive to stimuli or the changing needs of the cell. As in most cellular compartments, the ubiquitin-proteasome system (UPS) is responsible for the majority of the degradation at the ER-in a process termed ER-associated degradation (ERAD). Autophagic processes utilizing ubiquitin-like protein-conjugating systems also play roles in protein degradation at the ER. The ER is continuous with the nuclear envelope (NE), which consists of the outer nuclear membrane (ONM) and inner nuclear membrane (INM). While ERAD is known also to occur at the NE, only some of the ERAD ubiquitin-ligation pathways function at the INM. Protein degradation machineries in the ER/NE target a wide variety of substrates in multiple cellular compartments, including the cytoplasm, nucleoplasm, ER lumen, ER membrane, and the NE. Here, we review the protein degradation machineries of the ER and NE and the underlying mechanisms dictating recognition and processing of substrates by these machineries.
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Affiliation(s)
- Adrian B Mehrtash
- Department of Molecular, Cellular, & Developmental Biology, Yale University, New Haven, 06520, CT, USA.
| | - Mark Hochstrasser
- Department of Molecular Biophysics & Biochemistry, Yale University, New Haven, CT, 06520, USA; Department of Molecular, Cellular, & Developmental Biology, Yale University, New Haven, 06520, CT, USA.
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23
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Hwang J, Qi L. Quality Control in the Endoplasmic Reticulum: Crosstalk between ERAD and UPR pathways. Trends Biochem Sci 2018; 43:593-605. [PMID: 30056836 PMCID: PMC6327314 DOI: 10.1016/j.tibs.2018.06.005] [Citation(s) in RCA: 325] [Impact Index Per Article: 54.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2018] [Revised: 05/30/2018] [Accepted: 06/11/2018] [Indexed: 01/14/2023]
Abstract
Endoplasmic reticulum (ER)-associated degradation (ERAD) and the unfolded protein response (UPR) are two key quality-control machineries in the cell. ERAD is responsible for the clearance of misfolded proteins in the ER for cytosolic proteasomal degradation, while UPR is activated in response to the accumulation of misfolded proteins. It has long been thought that ERAD is an integral part of UPR because expression of many ERAD genes is controlled by UPR; however, recent studies have suggested that ERAD has a direct role in controlling the protein turnover and abundance of IRE1α, the most conserved UPR sensor. Here, we review recent advances in our understanding of IRE1α activation and propose that UPR and ERAD engage in an intimate crosstalk to define folding capacity and maintain homeostasis in the ER.
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Affiliation(s)
- Jiwon Hwang
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105, USA.
| | - Ling Qi
- Department of Molecular & Integrative Physiology, University of Michigan Medical School, Ann Arbor, MI 48105, USA; Division of Metabolism, Endocrinology & Diabetes, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, MI 48105, USA.
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24
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Schneider KL, Nyström T, Widlund PO. Studying Spatial Protein Quality Control, Proteopathies, and Aging Using Different Model Misfolding Proteins in S. cerevisiae. Front Mol Neurosci 2018; 11:249. [PMID: 30083092 PMCID: PMC6064742 DOI: 10.3389/fnmol.2018.00249] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2018] [Accepted: 07/02/2018] [Indexed: 12/14/2022] Open
Abstract
Protein quality control (PQC) is critical to maintain a functioning proteome. Misfolded or toxic proteins are either refolded or degraded by a system of temporal quality control and can also be sequestered into aggregates or inclusions by a system of spatial quality control. Breakdown of this concerted PQC network with age leads to an increased risk for the onset of disease, particularly neurological disease. Saccharomyces cerevisiae has been used extensively to elucidate PQC pathways and general evolutionary conservation of the PQC machinery has led to the development of several useful S. cerevisiae models of human neurological diseases. Key to both of these types of studies has been the development of several different model misfolding proteins, which are used to challenge and monitor the PQC machinery. In this review, we summarize and compare the model misfolding proteins that have been used to specifically study spatial PQC in S. cerevisiae, as well as the misfolding proteins that have been shown to be subject to spatial quality control in S. cerevisiae models of human neurological diseases.
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Affiliation(s)
- Kara L Schneider
- Department of Microbiology and Immunology, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Thomas Nyström
- Department of Microbiology and Immunology, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
| | - Per O Widlund
- Department of Microbiology and Immunology, Institute of Biomedicine, Sahlgrenska Academy, University of Gothenburg, Gothenburg, Sweden
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25
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Berner N, Reutter KR, Wolf DH. Protein Quality Control of the Endoplasmic Reticulum and Ubiquitin-Proteasome-Triggered Degradation of Aberrant Proteins: Yeast Pioneers the Path. Annu Rev Biochem 2018; 87:751-782. [PMID: 29394096 DOI: 10.1146/annurev-biochem-062917-012749] [Citation(s) in RCA: 91] [Impact Index Per Article: 15.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Cells must constantly monitor the integrity of their macromolecular constituents. Proteins are the most versatile class of macromolecules but are sensitive to structural alterations. Misfolded or otherwise aberrant protein structures lead to dysfunction and finally aggregation. Their presence is linked to aging and a plethora of severe human diseases. Thus, misfolded proteins have to be rapidly eliminated. Secretory proteins constitute more than one-third of the eukaryotic proteome. They are imported into the endoplasmic reticulum (ER), where they are folded and modified. A highly elaborated machinery controls their folding, recognizes aberrant folding states, and retrotranslocates permanently misfolded proteins from the ER back to the cytosol. In the cytosol, they are degraded by the highly selective ubiquitin-proteasome system. This process of protein quality control followed by proteasomal elimination of the misfolded protein is termed ER-associated degradation (ERAD), and it depends on an intricate interplay between the ER and the cytosol.
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Affiliation(s)
- Nicole Berner
- Institute of Biochemistry and Technical Biochemistry, University of Stuttgart, 70569 Stuttgart, Germany; , ,
| | - Karl-Richard Reutter
- Institute of Biochemistry and Technical Biochemistry, University of Stuttgart, 70569 Stuttgart, Germany; , ,
| | - Dieter H Wolf
- Institute of Biochemistry and Technical Biochemistry, University of Stuttgart, 70569 Stuttgart, Germany; , ,
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26
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Vincenz-Donnelly L, Holthusen H, Körner R, Hansen EC, Presto J, Johansson J, Sawarkar R, Hartl FU, Hipp MS. High capacity of the endoplasmic reticulum to prevent secretion and aggregation of amyloidogenic proteins. EMBO J 2018; 37:337-350. [PMID: 29247078 PMCID: PMC5793802 DOI: 10.15252/embj.201695841] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2016] [Revised: 10/19/2017] [Accepted: 10/25/2017] [Indexed: 01/09/2023] Open
Abstract
Protein aggregation is associated with neurodegeneration and various other pathologies. How specific cellular environments modulate the aggregation of disease proteins is not well understood. Here, we investigated how the endoplasmic reticulum (ER) quality control system handles β-sheet proteins that were designed de novo to form amyloid-like fibrils. While these proteins undergo toxic aggregation in the cytosol, we find that targeting them to the ER (ER-β) strongly reduces their toxicity. ER-β is retained within the ER in a soluble, polymeric state, despite reaching very high concentrations exceeding those of ER-resident molecular chaperones. ER-β is not removed by ER-associated degradation (ERAD) but interferes with ERAD of other proteins. These findings demonstrate a remarkable capacity of the ER to prevent the formation of insoluble β-aggregates and the secretion of potentially toxic protein species. Our results also suggest a generic mechanism by which proteins with exposed β-sheet structure in the ER interfere with proteostasis.
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Affiliation(s)
- Lisa Vincenz-Donnelly
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
- Munich Cluster for Systems Neurology (SyNergy), Munich, Germany
| | - Hauke Holthusen
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
| | - Roman Körner
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
- Munich Cluster for Systems Neurology (SyNergy), Munich, Germany
| | - Erik C Hansen
- Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany
| | - Jenny Presto
- Division of Neurogeriatrics, Department of Neurobiology, Care Sciences and Society (NVS), Centre for Alzheimer Research, Karolinska Institutet, Huddinge, Sweden
| | - Jan Johansson
- Division of Neurogeriatrics, Department of Neurobiology, Care Sciences and Society (NVS), Centre for Alzheimer Research, Karolinska Institutet, Huddinge, Sweden
| | - Ritwick Sawarkar
- Max Planck Institute of Immunobiology and Epigenetics, Freiburg, Germany
| | - F Ulrich Hartl
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
- Munich Cluster for Systems Neurology (SyNergy), Munich, Germany
| | - Mark S Hipp
- Department of Cellular Biochemistry, Max Planck Institute of Biochemistry, Martinsried, Germany
- Munich Cluster for Systems Neurology (SyNergy), Munich, Germany
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27
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Slp1-Emp65: A Guardian Factor that Protects Folding Polypeptides from Promiscuous Degradation. Cell 2017; 171:346-357.e12. [DOI: 10.1016/j.cell.2017.08.036] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2017] [Revised: 07/06/2017] [Accepted: 08/21/2017] [Indexed: 02/05/2023]
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28
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Defenouillère Q, Fromont-Racine M. The ribosome-bound quality control complex: from aberrant peptide clearance to proteostasis maintenance. Curr Genet 2017; 63:997-1005. [PMID: 28528489 DOI: 10.1007/s00294-017-0708-5] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2017] [Revised: 05/16/2017] [Accepted: 05/17/2017] [Indexed: 01/01/2023]
Abstract
Proteostasis in eukaryotes is maintained by compartment-specific quality control pathways, which enable the refolding or the degradation of defective polypeptides to prevent the toxicity that may arise from their aggregation. Among these processes, translational protein quality control is performed by the Ribosome-bound Quality Control complex (RQC), which recognizes nascent peptides translated from aberrant mRNAs, polyubiquitylates these aberrant peptides, extracts them from the stalled 60S subunit and finally escorts them to the proteasome for degradation. In this review, we focus on the mechanism of action of the RQC complex from stalled 60S binding to aberrant peptide delivery to the proteasome and describe the cellular consequences of a deficiency in the RQC pathway, such as aberrant protein aggregation. In addition, this review covers the recent discoveries concerning the role of cytosolic chaperones, as well as Tom1, to prevent the accumulation of aberrant protein aggregates in case of a deficiency in the RQC pathway.
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Affiliation(s)
- Quentin Defenouillère
- Institut Pasteur, Génétique des Interactions Macromoléculaires, Centre National de la Recherche Scientifique, UMR 3525, 75724, Paris Cedex 15, France. .,Membrane Trafficking, Ubiquitin and Signaling, Institut Jacques Monod, UMR7592 CNRS/Université Paris-Diderot, 15 Rue Hélène Brion, Bât. Buffon, 75205, Paris Cedex 13, France.
| | - Micheline Fromont-Racine
- Institut Pasteur, Génétique des Interactions Macromoléculaires, Centre National de la Recherche Scientifique, UMR 3525, 75724, Paris Cedex 15, France
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29
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Takahashi S, Sato N, Kikuchi J, Kakinuma H, Okawa J, Masuyama Y, Iwasa S, Irokawa H, Hwang GW, Naganuma A, Kohara M, Kuge S. Immature Core protein of hepatitis C virus induces an unfolded protein response through inhibition of ERAD-L in a yeast model system. Genes Cells 2017; 22:160-173. [PMID: 28097745 DOI: 10.1111/gtc.12464] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2016] [Accepted: 11/29/2016] [Indexed: 01/18/2023]
Abstract
The structural protein Core of hepatitis C virus (HCV), a cytosolic protein, induces endoplasmic reticulum (ER) stress and unfolded protein response (UPR) in hepatocytes, and is responsible for the pathogenesis of persistent HCV infection. Using yeast as a model system, we evaluated mechanisms underlying Core-induced interference of ER homeostasis and UPR, and found that UPR is induced by the immature Core (aa 1-191, Core191) but not by the mature Core (aa 1-177, Core177). Interestingly, Core191 inhibits both ERAD-L, a degradation system responsible for misfolded/unfolded proteins in the ER lumen, and ERAD-M, a degradation system responsible for proteins carrying a misfolded/unfolded region in the ER membrane. In contrast, Core177 inhibits ERAD-M but not ERAD-L. In addition, requirement of an unfolded protein sensor in the ER lumen suggested that inhibition of ERAD-L is probably responsible for Core191-dependent UPR activation. These results implicate inadequate maturation of Core as a trigger for induction of ER stress and UPR.
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Affiliation(s)
- Shota Takahashi
- Department of Microbiology, Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi, 981-8558, Japan
| | - Naoko Sato
- Department of Microbiology, Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi, 981-8558, Japan.,Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Junichi Kikuchi
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Hideaki Kakinuma
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Jun Okawa
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Yukiko Masuyama
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Singo Iwasa
- Department of Microbiology, Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi, 981-8558, Japan
| | - Hayato Irokawa
- Department of Microbiology, Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi, 981-8558, Japan
| | - Gi-Wook Hwang
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Akira Naganuma
- Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
| | - Michinori Kohara
- Department of Microbiology and Cell Biology, Tokyo Metropolitan Institute of Medical Science, Kamikitazawa, Setagaya-ku, Tokyo, 156-8506, Japan
| | - Shusuke Kuge
- Department of Microbiology, Faculty of Pharmaceutical Sciences, Tohoku Medical and Pharmaceutical University, 4-4-1 Komatsushima, Aoba-ku, Sendai, Miyagi, 981-8558, Japan.,Laboratory of Molecular and Biochemical Toxicology, Graduate School of Pharmaceutical Sciences, Tohoku University, Aoba-ku, Sendai, Miyagi, 980-8578, Japan
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30
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Bao Y, Howell SH. The Unfolded Protein Response Supports Plant Development and Defense as well as Responses to Abiotic Stress. FRONTIERS IN PLANT SCIENCE 2017; 8:344. [PMID: 28360918 PMCID: PMC5350557 DOI: 10.3389/fpls.2017.00344] [Citation(s) in RCA: 62] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/08/2016] [Accepted: 02/27/2017] [Indexed: 05/19/2023]
Abstract
The unfolded protein response (UPR) is a stress response conserved in eukaryotic organisms and activated by the accumulation of misfolded proteins in the endoplasmic reticulum (ER). Adverse environmental conditions disrupt protein folding in the ER and trigger the UPR. Recently, it was found that the UPR can be elicited in the course of plant development and defense. During vegetative plant development, the UPR is involved in normal root growth and development, the effect of which can be largely attributed to the influence of the UPR on plant hormone biology. The UPR also functions in plant reproductive development by protecting male gametophyte development from heat stress. In terms of defense, the UPR has been implicated in virus and microbial defense. Viral defense represents a double edge sword in that various virus infections activate the UPR, however, in a number of cases, the UPR actually supports viral infections. The UPR also plays a role in plant immunity to bacterial infections, again through the action of plant hormones in regulating basal immunity responses.
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31
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Silmon de Monerri NC, Yakubu RR, Chen AL, Bradley PJ, Nieves E, Weiss LM, Kim K. The Ubiquitin Proteome of Toxoplasma gondii Reveals Roles for Protein Ubiquitination in Cell-Cycle Transitions. Cell Host Microbe 2016; 18:621-33. [PMID: 26567513 DOI: 10.1016/j.chom.2015.10.014] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Revised: 09/15/2015] [Accepted: 10/22/2015] [Indexed: 12/28/2022]
Abstract
Protein ubiquitination plays key roles in protein turnover, cellular signaling, and intracellular transport. The genome of Toxoplasma gondii encodes ubiquitination machinery, but the roles of this posttranslational modification (PTM) are unknown. To examine the prevalence and function of ubiquitination in T. gondii, we mapped the ubiquitin proteome of tachyzoites. Over 500 ubiquitin-modified proteins, with almost 1,000 sites, were identified on proteins with diverse localizations and functions. Enrichment analysis demonstrated that 35% of ubiquitinated proteins are cell-cycle regulated. Unexpectedly, most classic cell-cycle regulators conserved in T. gondii were not detected in the ubiquitinome. Furthermore, many ubiquitinated proteins localize to the cytoskeleton and inner membrane complex, a structure beneath the plasma membrane facilitating division and host invasion. Comparing the ubiquitinome with other PTM proteomes reveals waves of PTM enrichment during the cell cycle. Thus, T. gondii PTMs are implicated as critical regulators of cell division and cell-cycle transitions.
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Affiliation(s)
| | - Rama R Yakubu
- Department of Pathology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Allan L Chen
- Department of Microbiology, Immunology and Molecular Genetics, University of California Los Angeles, Los Angeles, CA 90095-1489, USA
| | - Peter J Bradley
- Department of Microbiology, Immunology and Molecular Genetics, University of California Los Angeles, Los Angeles, CA 90095-1489, USA
| | - Edward Nieves
- Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Developmental & Molecular Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Louis M Weiss
- Department of Pathology, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA
| | - Kami Kim
- Department of Pathology, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Medicine, Albert Einstein College of Medicine, Bronx, NY 10461, USA; Department of Microbiology and Immunology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
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32
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Baldridge RD, Rapoport TA. Autoubiquitination of the Hrd1 Ligase Triggers Protein Retrotranslocation in ERAD. Cell 2016; 166:394-407. [PMID: 27321670 DOI: 10.1016/j.cell.2016.05.048] [Citation(s) in RCA: 144] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Revised: 04/19/2016] [Accepted: 05/13/2016] [Indexed: 12/16/2022]
Abstract
Misfolded proteins of the ER are retrotranslocated to the cytosol, where they are polyubiquitinated, extracted from the membrane, and degraded by the proteasome. To investigate how the ER-associated Degradation (ERAD) machinery can accomplish retrotranslocation of a misfolded luminal protein domain across a lipid bilayer, we have reconstituted retrotranslocation with purified S. cerevisiae proteins, using proteoliposomes containing the multi-spanning ubiquitin ligase Hrd1. Retrotranslocation of the luminal domain of a membrane-spanning substrate is triggered by autoubiquitination of Hrd1. Substrate ubiquitination is a subsequent event, and the Cdc48 ATPase that completes substrate extraction from the membrane is not required for retrotranslocation. Ubiquitination of lysines in Hrd1's RING-finger domain is required for substrate retrotranslocation in vitro and for ERAD in vivo. Our results suggest that Hrd1 forms a ubiquitin-gated protein-conducting channel.
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Affiliation(s)
- Ryan D Baldridge
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
| | - Tom A Rapoport
- Howard Hughes Medical Institute and Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115, USA.
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33
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Smith N, Adle DJ, Zhao M, Qin X, Kim H, Lee J. Endoplasmic Reticulum-associated Degradation of Pca1p, a Polytopic Protein, via Interaction with the Proteasome at the Membrane. J Biol Chem 2016; 291:15082-92. [PMID: 27226596 DOI: 10.1074/jbc.m116.726265] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/07/2016] [Indexed: 11/06/2022] Open
Abstract
Endoplasmic reticulum-associated degradation (ERAD) plays a critical role in the destruction of terminally misfolded proteins at the secretory pathway. The system also regulates expression levels of several proteins such as Pca1p, a cadmium exporter in yeast. To gain better insight into the mechanisms underlying ERAD of Pca1p and other polytopic proteins by the proteasome in the cytosol, our study determined the roles for the molecular factors of ERAD in dislodging Pca1p from the endoplasmic reticulum (ER). Inactivation of the 20S proteasome leads to accumulation of ubiquitinated Pca1p in the ER membrane, suggesting a role for the proteasome in extraction of Pca1p from the ER. Pca1p formed a complex with the proteasome at the membrane in a Doa10p E3 ligase-dependent manner. Cdc48p is required for recruiting the proteasome to Pca1p. Although the Ufd2p E4 ubiquitin chain extension enzyme is involved in efficient degradation of Pca1p, Ufd2p-deficient cells did not affect the formation of a complex between Pca1p and the proteasome. Two other polytopic membrane proteins undergoing ERAD, Ste6*p and Hmg2p, also displayed the same outcomes observed for Pca1p. However, poly-ubiquitinated Cpy1*p, a luminal ERAD substrate, was detected in the cytosol independent of proteolytic activities of the proteasome. These results indicate that extraction and degradation of polytopic membrane proteins at the ER is a coupled event. This mechanism would relieve the cost of exposed hydrophobic domains in the cytosol during ERAD.
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Affiliation(s)
- Nathan Smith
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, Nebraska, 68588-0664 and
| | - David J Adle
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, Nebraska, 68588-0664 and
| | - Miaoyun Zhao
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, Nebraska, 68588-0664 and
| | - Xiaojuan Qin
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, Nebraska, 68588-0664 and the College of Life and Environmental Sciences, Shanghai Normal University, Shanghai, China 200234
| | - Heejeong Kim
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, Nebraska, 68588-0664 and
| | - Jaekwon Lee
- From the Department of Biochemistry and Redox Biology Center, University of Nebraska, Lincoln, Nebraska, 68588-0664 and
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34
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Margulis NG, Wilson JD, Bentivoglio CM, Dhungel N, Gitler AD, Barlowe C. Analysis of COPII Vesicles Indicates a Role for the Emp47-Ssp120 Complex in Transport of Cell Surface Glycoproteins. Traffic 2016; 17:191-210. [PMID: 26650540 DOI: 10.1111/tra.12356] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2015] [Revised: 11/30/2015] [Accepted: 11/30/2015] [Indexed: 10/22/2022]
Abstract
Coat protein complex II (COPII) vesicle formation at the endoplasmic reticulum (ER) transports nascent secretory proteins forward to the Golgi complex. To further define the machinery that packages secretory cargo and targets vesicles to Golgi membranes, we performed a comprehensive proteomic analysis of purified COPII vesicles. In addition to previously known proteins, we identified new vesicle proteins including Coy1, Sly41 and Ssp120, which were efficiently packaged into COPII vesicles for trafficking between the ER and Golgi compartments. Further characterization of the putative calcium-binding Ssp120 protein revealed a tight association with Emp47 and in emp47Δ cells Ssp120 was mislocalized and secreted. Genetic analyses demonstrated that EMP47 and SSP120 display identical synthetic positive interactions with IRE1 and synthetic negative interactions with genes involved in cell wall assembly. Our findings support a model in which the Emp47-Ssp120 complex functions in transport of plasma membrane glycoproteins through the early secretory pathway.
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Affiliation(s)
- Neil G Margulis
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH, 03755, USA
| | - Joshua D Wilson
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH, 03755, USA
| | | | - Nripesh Dhungel
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, 94305, USA.,Present address: Singer Instruments, Roadwater, Watchet, Somerset, TA23 0RE, UK
| | - Aaron D Gitler
- Department of Genetics, Stanford University School of Medicine, Stanford, CA, 94305, USA
| | - Charles Barlowe
- Department of Biochemistry, Geisel School of Medicine at Dartmouth, Hanover, NH, 03755, USA
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35
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Yang X, Srivastava R, Howell SH, Bassham DC. Activation of autophagy by unfolded proteins during endoplasmic reticulum stress. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2016; 85:83-95. [PMID: 26616142 DOI: 10.1111/tpj.13091] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/20/2015] [Revised: 11/18/2015] [Accepted: 11/20/2015] [Indexed: 05/20/2023]
Abstract
Endoplasmic reticulum stress is defined as the accumulation of unfolded proteins in the endoplasmic reticulum, and is caused by conditions such as heat or agents that cause endoplasmic reticulum stress, including tunicamycin and dithiothreitol. Autophagy, a major pathway for degradation of macromolecules in the vacuole, is activated by these stress agents in a manner dependent on inositol-requiring enzyme 1b (IRE1b), and delivers endoplasmic reticulum fragments to the vacuole for degradation. In this study, we examined the mechanism for activation of autophagy during endoplasmic reticulum stress in Arabidopsis thaliana. The chemical chaperones sodium 4-phenylbutyrate and tauroursodeoxycholic acid were found to reduce tunicamycin- or dithiothreitol-induced autophagy, but not autophagy caused by unrelated stresses. Similarly, over-expression of BINDING IMMUNOGLOBULIN PROTEIN (BIP), encoding a heat shock protein 70 (HSP70) molecular chaperone, reduced autophagy. Autophagy activated by heat stress was also found to be partially dependent on IRE1b and to be inhibited by sodium 4-phenylbutyrate, suggesting that heat-induced autophagy is due to accumulation of unfolded proteins in the endoplasmic reticulum. Expression in Arabidopsis of the misfolded protein mimics zeolin or a mutated form of carboxypeptidase Y (CPY*) also induced autophagy in an IRE1b-dependent manner. Moreover, zeolin and CPY* partially co-localized with the autophagic body marker GFP-ATG8e, indicating delivery to the vacuole by autophagy. We conclude that accumulation of unfolded proteins in the endoplasmic reticulum is a trigger for autophagy under conditions that cause endoplasmic reticulum stress.
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Affiliation(s)
- Xiaochen Yang
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA, 50011, USA
- Interdepartmental Plant Biology Program, Iowa State University, Ames, IA, 50011, USA
| | - Renu Srivastava
- Plant Sciences Institute, Iowa State University, Ames, IA, 50011, USA
| | - Stephen H Howell
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA, 50011, USA
- Interdepartmental Plant Biology Program, Iowa State University, Ames, IA, 50011, USA
- Plant Sciences Institute, Iowa State University, Ames, IA, 50011, USA
| | - Diane C Bassham
- Department of Genetics, Development and Cell Biology, Iowa State University, Ames, IA, 50011, USA
- Interdepartmental Plant Biology Program, Iowa State University, Ames, IA, 50011, USA
- Plant Sciences Institute, Iowa State University, Ames, IA, 50011, USA
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36
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Xu C, Ng DTW. Glycosylation-directed quality control of protein folding. Nat Rev Mol Cell Biol 2015; 16:742-52. [PMID: 26465718 DOI: 10.1038/nrm4073] [Citation(s) in RCA: 255] [Impact Index Per Article: 28.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Membrane-bound and soluble proteins of the secretory pathway are commonly glycosylated in the endoplasmic reticulum. These adducts have many biological functions, including, notably, their contribution to the maturation of glycoproteins. N-linked glycans are of oligomeric structure, forming configurations that provide blueprints to precisely instruct the folding of protein substrates and the quality control systems that scrutinize it. O-linked mannoses are simpler in structure and were recently found to have distinct functions in protein quality control that do not require the complex structure of N-linked glycans. Together, recent studies reveal the breadth and sophistication of the roles of these glycan-directed modifications in protein biogenesis.
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Affiliation(s)
- Chengchao Xu
- Temasek Life Sciences Laboratory, National University of Singapore, 1 Research Link, Singapore 117604.,Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543
| | - Davis T W Ng
- Temasek Life Sciences Laboratory, National University of Singapore, 1 Research Link, Singapore 117604.,Department of Biological Sciences, National University of Singapore, 14 Science Drive 4, Singapore 117543.,Duke University-National University of Singapore Graduate Medical School, 8 College Road, Singapore 169857
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37
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Amm I, Norell D, Wolf DH. Absence of the Yeast Hsp31 Chaperones of the DJ-1 Superfamily Perturbs Cytoplasmic Protein Quality Control in Late Growth Phase. PLoS One 2015; 10:e0140363. [PMID: 26466368 PMCID: PMC4605529 DOI: 10.1371/journal.pone.0140363] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2015] [Accepted: 09/24/2015] [Indexed: 01/26/2023] Open
Abstract
The Saccharomyces cerevisiae heat shock proteins Hsp31, Hsp32, Hsp33 and Hsp34 belong to the DJ-1/ThiJ/PfpI superfamily which includes the human protein DJ-1 (PARK7) as the most prominent member. Mutations in the DJ-1 gene are directly linked to autosomal recessive, early-onset Parkinson's disease. DJ-1 acts as an oxidative stress-induced chaperone preventing aggregation and fibrillation of α-synuclein, a critical factor in the development of the disease. In vivo assays in Saccharomyces cerevisiae using the model substrate ΔssCPY*Leu2myc (ΔssCL*myc) as an aggregation-prone misfolded cytoplasmic protein revealed an influence of the Hsp31 chaperone family on the steady state level of this substrate. In contrast to the ubiquitin ligase of the N-end rule pathway Ubr1, which is known to be prominently involved in the degradation process of misfolded cytoplasmic proteins, the absence of the Hsp31 chaperone family does not impair the degradation of newly synthesized misfolded substrate. Also degradation of substrates with strong affinity to Ubr1 like those containing the type 1 N-degron arginine is not affected by the absence of the Hsp31 chaperone family. Epistasis analysis indicates that one function of the Hsp31 chaperone family resides in a pathway overlapping with the Ubr1-dependent degradation of misfolded cytoplasmic proteins. This pathway gains relevance in late growth phase under conditions of nutrient limitation. Additionally, the Hsp31 chaperones seem to be important for maintaining the cellular Ssa Hsp70 activity which is important for Ubr1-dependent degradation.
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Affiliation(s)
- Ingo Amm
- Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, Stuttgart, Germany
| | - Derrick Norell
- Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, Stuttgart, Germany
| | - Dieter H. Wolf
- Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, Stuttgart, Germany
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Nakatsukasa K, Okumura F, Kamura T. Proteolytic regulation of metabolic enzymes by E3 ubiquitin ligase complexes: lessons from yeast. Crit Rev Biochem Mol Biol 2015; 50:489-502. [PMID: 26362128 DOI: 10.3109/10409238.2015.1081869] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Eukaryotic organisms use diverse mechanisms to control metabolic rates in response to changes in the internal and/or external environment. Fine metabolic control is a highly responsive, energy-saving process that is mediated by allosteric inhibition/activation and/or reversible modification of preexisting metabolic enzymes. In contrast, coarse metabolic control is a relatively long-term and expensive process that involves modulating the level of metabolic enzymes. Coarse metabolic control can be achieved through the degradation of metabolic enzymes by the ubiquitin-proteasome system (UPS), in which substrates are specifically ubiquitinated by an E3 ubiquitin ligase and targeted for proteasomal degradation. Here, we review select multi-protein E3 ligase complexes that directly regulate metabolic enzymes in Saccharomyces cerevisiae. The first part of the review focuses on the endoplasmic reticulum (ER) membrane-associated Hrd1 and Doa10 E3 ligase complexes. In addition to their primary roles in the ER-associated degradation pathway that eliminates misfolded proteins, recent quantitative proteomic analyses identified native substrates of Hrd1 and Doa10 in the sterol synthesis pathway. The second part focuses on the SCF (Skp1-Cul1-F-box protein) complex, an abundant prototypical multi-protein E3 ligase complex. While the best-known roles of the SCF complex are in the regulation of the cell cycle and transcription, accumulating evidence indicates that the SCF complex also modulates carbon metabolism pathways. The increasing number of metabolic enzymes whose stability is directly regulated by the UPS underscores the importance of the proteolytic regulation of metabolic processes for the acclimation of cells to environmental changes.
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Affiliation(s)
- Kunio Nakatsukasa
- a Division of Biological Sciences , Graduate School of Science, Nagoya University , Nagoya , Aichi , Japan
| | - Fumihiko Okumura
- a Division of Biological Sciences , Graduate School of Science, Nagoya University , Nagoya , Aichi , Japan
| | - Takumi Kamura
- a Division of Biological Sciences , Graduate School of Science, Nagoya University , Nagoya , Aichi , Japan
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Piña FJ, Niwa M. The ER Stress Surveillance (ERSU) pathway regulates daughter cell ER protein aggregate inheritance. eLife 2015; 4. [PMID: 26327697 PMCID: PMC4555637 DOI: 10.7554/elife.06970] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2015] [Accepted: 08/04/2015] [Indexed: 12/11/2022] Open
Abstract
Stress induced by cytoplasmic protein aggregates can have deleterious consequences for the cell, contributing to neurodegeneration and other diseases. Protein aggregates are also formed within the endoplasmic reticulum (ER), although the fate of ER protein aggregates, specifically during cell division, is not well understood. By simultaneous visualization of both the ER itself and ER protein aggregates, we found that ER protein aggregates that induce ER stress are retained in the mother cell by activation of the ER Stress Surveillance (ERSU) pathway, which prevents inheritance of stressed ER. In contrast, under conditions of normal ER inheritance, ER protein aggregates can enter the daughter cell. Thus, whereas cytoplasmic protein aggregates are retained in the mother cell to protect the functional capacity of daughter cells, the fate of ER protein aggregates is determined by whether or not they activate the ERSU pathway to impede transmission of the cortical ER during the cell cycle.
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Affiliation(s)
- Francisco J Piña
- Division of Biological Sciences, Section of Molecular Biology, Univeristy of California, San Diego, San Diego, United States
| | - Maho Niwa
- Division of Biological Sciences, Section of Molecular Biology, Univeristy of California, San Diego, San Diego, United States
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40
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Harada Y, Hirayama H, Suzuki T. Generation and degradation of free asparagine-linked glycans. Cell Mol Life Sci 2015; 72:2509-33. [PMID: 25772500 PMCID: PMC11113800 DOI: 10.1007/s00018-015-1881-7] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2014] [Revised: 02/19/2015] [Accepted: 03/05/2015] [Indexed: 10/23/2022]
Abstract
Asparagine (N)-linked protein glycosylation, which takes place in the eukaryotic endoplasmic reticulum (ER), is important for protein folding, quality control and the intracellular trafficking of secretory and membrane proteins. It is known that, during N-glycosylation, considerable amounts of lipid-linked oligosaccharides (LLOs), the glycan donor substrates for N-glycosylation, are hydrolyzed to form free N-glycans (FNGs) by unidentified mechanisms. FNGs are also generated in the cytosol by the enzymatic deglycosylation of misfolded glycoproteins during ER-associated degradation. FNGs derived from LLOs and misfolded glycoproteins are eventually merged into one pool in the cytosol and the various glycan structures are processed to a near homogenous glycoform. This article summarizes the current state of our knowledge concerning the formation and catabolism of FNGs.
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Affiliation(s)
- Yoichiro Harada
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center, Global Research Cluster, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
| | - Hiroto Hirayama
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center, Global Research Cluster, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
| | - Tadashi Suzuki
- Glycometabolome Team, Systems Glycobiology Research Group, RIKEN-Max Planck Joint Research Center, Global Research Cluster, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198 Japan
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41
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Mueller S, Wahlander A, Selevsek N, Otto C, Ngwa EM, Poljak K, Frey AD, Aebi M, Gauss R. Protein degradation corrects for imbalanced subunit stoichiometry in OST complex assembly. Mol Biol Cell 2015; 26:2596-608. [PMID: 25995378 PMCID: PMC4501358 DOI: 10.1091/mbc.e15-03-0168] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Accepted: 05/11/2015] [Indexed: 01/06/2023] Open
Abstract
A combination of SILAC and targeted mass spectrometry provides a sensitive method to measure protein half-lives in yeast. Degradation rates are generally low in wild-type cells; however, ERAD is important to correct for imbalanced subunit stoichiometry. This approach is used to establish an assembly model for the OST complex. Protein degradation is essential for cellular homeostasis. We developed a sensitive approach to examining protein degradation rates in Saccharomyces cerevisiae by coupling a SILAC approach to selected reaction monitoring (SRM) mass spectrometry. Combined with genetic tools, this analysis made it possible to study the assembly of the oligosaccharyl transferase complex. The ER-associated degradation machinery compensated for disturbed homeostasis of complex components by degradation of subunits in excess. On a larger scale, protein degradation in the ER was found to be a minor factor in the regulation of protein homeostasis in exponentially growing cells, but ERAD became relevant when the gene dosage was affected, as demonstrated in heterozygous diploid cells. Hence the alleviation of fitness defects due to abnormal gene copy numbers might be an important function of protein degradation.
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Affiliation(s)
- Susanne Mueller
- Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Asa Wahlander
- Functional Genomics Center Zurich, UZH/ETH Zurich, CH-8057 Zurich, Switzerland
| | - Nathalie Selevsek
- Functional Genomics Center Zurich, UZH/ETH Zurich, CH-8057 Zurich, Switzerland
| | - Claudia Otto
- Department of Health Sciences and Technology, Institute of Food, Nutrition and Health, ETH Zürich, CH-8092 Zurich, Switzerland
| | - Elsy Mankah Ngwa
- Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Kristina Poljak
- Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Alexander D Frey
- Department of Biotechnology and Chemical Technology, Aalto University, FI-00076 Aalto, Finland
| | - Markus Aebi
- Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zurich, CH-8093 Zurich, Switzerland
| | - Robert Gauss
- Institute of Microbiology, Department of Biology, Swiss Federal Institute of Technology, ETH Zurich, CH-8093 Zurich, Switzerland
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Scazzari M, Amm I, Wolf DH. Quality control of a cytoplasmic protein complex: chaperone motors and the ubiquitin-proteasome system govern the fate of orphan fatty acid synthase subunit Fas2 of yeast. J Biol Chem 2015; 290:4677-4687. [PMID: 25564609 PMCID: PMC4335207 DOI: 10.1074/jbc.m114.596064] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 12/10/2014] [Indexed: 11/06/2022] Open
Abstract
For the assembly of protein complexes in the cell, the presence of stoichiometric amounts of the respective protein subunits is of utmost importance. A surplus of any of the subunits may trigger unspecific and harmful protein interactions and has to be avoided. A stoichiometric amount of subunits must finally be reached via transcriptional, translational, and/or post-translational regulation. Synthesis of saturated 16 and 18 carbon fatty acids is carried out by fatty acid synthase: in yeast Saccharomyces cerevisiae, a 2.6-MDa molecular mass assembly containing six protomers each of two different subunits, Fas1 (β) and Fas2 (α). The (α)6(β)6 complex carries six copies of all eight enzymatic activities required for fatty acid synthesis. The FAS1 and FAS2 genes in yeast are unlinked and map on two different chromosomes. Here we study the fate of the α-subunit of the complex, Fas2, when its partner, the β-subunit Fas1, is absent. Individual subunits of fatty acid synthase are proteolytically degraded when the respective partner is missing. Elimination of Fas2 is achieved by the proteasome. Here we show that a ubiquitin transfer machinery is required for Fas2 elimination. The major ubiquitin ligase targeting the superfluous Fas2 subunit to the proteasome is Ubr1. The ubiquitin-conjugating enzymes Ubc2 and Ubc4 assist the degradation process. The AAA-ATPase Cdc48 and the Hsp70 chaperone Ssa1 are crucially involved in the elimination of Fas2.
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Affiliation(s)
- Mario Scazzari
- From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Ingo Amm
- From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany
| | - Dieter H Wolf
- From the Institut für Biochemie, Universität Stuttgart, Pfaffenwaldring 55, 70569 Stuttgart, Germany.
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43
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Key steps in ERAD of luminal ER proteins reconstituted with purified components. Cell 2014; 158:1375-1388. [PMID: 25215493 PMCID: PMC4163015 DOI: 10.1016/j.cell.2014.07.050] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2014] [Revised: 06/06/2014] [Accepted: 07/02/2014] [Indexed: 11/20/2022]
Abstract
Misfolded proteins of the endoplasmic reticulum (ER) are retrotranslocated into the cytosol, polyubiquitinated, and degraded by the proteasome, a process called ER-associated protein degradation (ERAD). Here, we use purified components from Saccharomyces cerevisiae to analyze the mechanism of retrotranslocation of luminal substrates (ERAD-L), recapitulating key steps in a basic process in which the ubiquitin ligase Hrd1p is the only required membrane protein. We show that Hrd1p interacts with substrate through its membrane-spanning domain and discriminates misfolded from folded polypeptides. Both Hrd1p and substrate are polyubiquitinated, resulting in the binding of Cdc48p ATPase complex. Subsequently, ATP hydrolysis by Cdc48p releases substrate from Hrd1p. Finally, ubiquitin chains are trimmed by the deubiquitinating enzyme Otu1p, which is recruited and activated by the Cdc48p complex. Cdc48p-dependent membrane extraction of polyubiquitinated proteins can be reproduced with reconstituted proteoliposomes. Our results suggest a model for retrotranslocation in which Hrd1p forms a membrane conduit for misfolded proteins.
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44
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Zattas D, Hochstrasser M. Ubiquitin-dependent protein degradation at the yeast endoplasmic reticulum and nuclear envelope. Crit Rev Biochem Mol Biol 2014; 50:1-17. [PMID: 25231236 DOI: 10.3109/10409238.2014.959889] [Citation(s) in RCA: 63] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The endoplasmic reticulum (ER) is the primary organelle in eukaryotic cells where membrane and secreted proteins are inserted into or across cell membranes. Its membrane bilayer and luminal compartments provide a favorable environment for the folding and assembly of thousands of newly synthesized proteins. However, protein folding is intrinsically error-prone, and various stress conditions can further increase levels of protein misfolding and damage, particularly in the ER, which can lead to cellular dysfunction and disease. The ubiquitin-proteasome system (UPS) is responsible for the selective destruction of a vast array of protein substrates, either for protein quality control or to allow rapid changes in the levels of specific regulatory proteins. In this review, we will focus on the components and mechanisms of ER-associated protein degradation (ERAD), an important branch of the UPS. ER membranes extend from subcortical regions of the cell to the nuclear envelope, with its continuous outer and inner membranes; the nuclear envelope is a specialized subdomain of the ER. ERAD presents additional challenges to the UPS beyond those faced with soluble substrates of the cytoplasm and nucleus. These include recognition of sugar modifications that occur in the ER, retrotranslocation of proteins across the membrane bilayer, and transfer of substrates from the ER extraction machinery to the proteasome. Here, we review characteristics of ERAD substrate degradation signals (degrons), mechanisms underlying substrate recognition and processing by the ERAD machinery, and ideas on the still unresolved problem of how substrate proteins are moved across and extracted from the ER membrane.
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Affiliation(s)
- Dimitrios Zattas
- Department of Molecular Biophysics & Biochemistry, Yale University , New Haven, CT , USA
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45
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Smith MH, Rodriguez EH, Weissman JS. Misfolded proteins induce aggregation of the lectin Yos9. J Biol Chem 2014; 289:25670-7. [PMID: 25086047 DOI: 10.1074/jbc.m114.583344] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
A substantial fraction of nascent proteins delivered into the endoplasmic reticulum (ER) never reach their native conformations. Eukaryotes use a series of complementary pathways to efficiently recognize and dispose of these terminally misfolded proteins. In this process, collectively termed ER-associated degradation (ERAD), misfolded proteins are retrotranslocated to the cytosol, polyubiquitinated, and degraded by the proteasome. Although there has been great progress in identifying ERAD components, how these factors accurately identify substrates remains poorly understood. The targeting of misfolded glycoproteins in the ER lumen for ERAD requires the lectin Yos9, which recognizes the glycan species found on terminally misfolded proteins. In a role that remains poorly characterized, Yos9 also binds the protein component of ERAD substrates. Here, we identified a 45-kDa domain of Yos9, consisting of residues 22-421, that is proteolytically stable, highly structured, and able to fully support ERAD in vivo. In vitro binding studies show that Yos9(22-421) exhibits sequence-specific recognition of linear peptides from the ERAD substrate, carboxypeptidase Y G255R (CPY*), and binds a model unfolded peptide ΔEspP and protein Δ131Δ in solution. Binding of Yos9 to these substrates results in their cooperative aggregation. Although the physiological consequences of this substrate-induced aggregation remain to be seen, it has the potential to play a role in the regulation of ERAD.
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Affiliation(s)
- Melanie H Smith
- From the Department of Cellular and Molecular Pharmacology, Graduate Group in Biophysics, California Institute for Quantitative Biosciences, Center for RNA Systems Biology, and Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, California 94158
| | - Edwin H Rodriguez
- From the Department of Cellular and Molecular Pharmacology, Graduate Group in Biophysics, California Institute for Quantitative Biosciences, Center for RNA Systems Biology, and Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, California 94158
| | - Jonathan S Weissman
- From the Department of Cellular and Molecular Pharmacology, Graduate Group in Biophysics, California Institute for Quantitative Biosciences, Center for RNA Systems Biology, and Howard Hughes Medical Institute, University of California at San Francisco, San Francisco, California 94158
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46
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Zacchi LF, Wu HC, Bell SL, Millen L, Paton AW, Paton JC, Thomas PJ, Zolkiewski M, Brodsky JL. The BiP molecular chaperone plays multiple roles during the biogenesis of torsinA, an AAA+ ATPase associated with the neurological disease early-onset torsion dystonia. J Biol Chem 2014; 289:12727-47. [PMID: 24627482 PMCID: PMC4007462 DOI: 10.1074/jbc.m113.529123] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/21/2013] [Revised: 03/09/2014] [Indexed: 01/02/2023] Open
Abstract
Early-onset torsion dystonia (EOTD) is a neurological disorder characterized by involuntary and sustained muscle contractions that can lead to paralysis and abnormal posture. EOTD is associated with the deletion of a glutamate (ΔE) in torsinA, an endoplasmic reticulum (ER) resident AAA(+) ATPase. To date, the effect of ΔE on torsinA and the reason that this mutation results in EOTD are unclear. Moreover, there are no specific therapeutic options to treat EOTD. To define the underlying biochemical defects associated with torsinAΔE and to uncover factors that might be targeted to offset defects associated with torsinAΔE, we developed a yeast torsinA expression system and tested the roles of ER chaperones in mediating the folding and stability of torsinA and torsinAΔE. We discovered that the ER lumenal Hsp70, BiP, an associated Hsp40, Scj1, and a nucleotide exchange factor, Lhs1, stabilize torsinA and torsinAΔE. BiP also maintained torsinA and torsinAΔE solubility. Mutations predicted to compromise specific torsinA functional motifs showed a synthetic interaction with the ΔE mutation and destabilized torsinAΔE, suggesting that the ΔE mutation predisposes torsinA to defects in the presence of secondary insults. In this case, BiP was required for torsinAΔE degradation, consistent with data that specific chaperones exhibit either pro-degradative or pro-folding activities. Finally, using two independent approaches, we established that BiP stabilizes torsinA and torsinAΔE in mammalian cells. Together, these data define BiP as the first identified torsinA chaperone, and treatments that modulate BiP might improve symptoms associated with EOTD.
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Affiliation(s)
- Lucía F. Zacchi
- From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Hui-Chuan Wu
- the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Samantha L. Bell
- From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
| | - Linda Millen
- the Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, and
| | - Adrienne W. Paton
- the Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - James C. Paton
- the Research Centre for Infectious Diseases, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, South Australia 5005, Australia
| | - Philip J. Thomas
- the Department of Physiology, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390, and
| | - Michal Zolkiewski
- the Department of Biochemistry and Molecular Biophysics, Kansas State University, Manhattan, Kansas 66506
| | - Jeffrey L. Brodsky
- From the Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
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47
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Jiang H, Xiong S, Xia X. Retinitis pigmentosa‑associated rhodopsin mutant T17M induces endoplasmic reticulum (ER) stress and sensitizes cells to ER stress-induced cell death. Mol Med Rep 2014; 9:1737-42. [PMID: 24573320 DOI: 10.3892/mmr.2014.1987] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/15/2013] [Accepted: 02/14/2014] [Indexed: 11/06/2022] Open
Abstract
Retinitis pigmentosa (RP) is a group of inherited diseases that primarily affect light‑sensitive rods and cones in the retina. Rhodopsin mutations, including the T17M mutation, are associated with the autosomal dominant form of retinitis pigmentosa (ADRP) and have been linked to abnormal protein folding. However, the molecular mechanisms underlying T17M rhodopsin‑induced retinal degeneration are yet to be elucidated. In the present study, Human embryonic kidney (HEK) 293 and ARPE‑19 cells were transfected with myc‑tagged wild‑type (WT) and T17M rhodopsin constructs. Cells were fixed and stained with anti‑myc antibodies and the localization of WT and T17M rhodopsin was visualized using immunofluorescence microscopy. Turnover rates of WT and T17M rhodopsin were measured using western blot analysis. In addition, endoplasmic reticulum (ER) stress‑induced cell death was analyzed in WT and T17M rhodopsin‑transfected cells using nuclear staining. Misfolded T17M rhodopsin was observed to be abnormally localized in the ER, while WT rhodopsin was predominantly found at the plasma membrane. Protein turnover analysis revealed that T17M rhodopsin was more rapidly degraded by proteasomes than WT rhodopsin. Furthermore, overexpression of T17M rhodopsin was observed to induce cell death and increase cytotoxicity; predisposing cells to ER stress‑induced cell death. These findings show novel insight into the properties of T17M rhodopsin and highlight the role of ER stress in T17M‑associated RP.
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Affiliation(s)
- Haibo Jiang
- Department of Ophthalmology, Xiangya Hospital, Central South University, Changsha, Hunan 410078, P.R. China
| | - Siqi Xiong
- Department of Ophthalmology, Xiangya Hospital, Central South University, Changsha, Hunan 410078, P.R. China
| | - Xiaobo Xia
- Department of Ophthalmology, Xiangya Hospital, Central South University, Changsha, Hunan 410078, P.R. China
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48
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Mark KG, Simonetta M, Maiolica A, Seller CA, Toczyski DP. Ubiquitin ligase trapping identifies an SCF(Saf1) pathway targeting unprocessed vacuolar/lysosomal proteins. Mol Cell 2014; 53:148-61. [PMID: 24389104 DOI: 10.1016/j.molcel.2013.12.003] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2013] [Revised: 11/15/2013] [Accepted: 11/26/2013] [Indexed: 12/31/2022]
Abstract
We have developed a technique, called Ubiquitin Ligase Substrate Trapping, for the isolation of ubiquitinated substrates in complex with their ubiquitin ligase (E3). By fusing a ubiquitin-associated (UBA) domain to an E3 ligase, we were able to selectively purify the polyubiquitinated forms of E3 substrates. Using ligase traps of eight different F box proteins (SCF specificity factors) coupled with mass spectrometry, we identified known, as well as previously unreported, substrates. Polyubiquitinated forms of candidate substrates associated with their cognate F box partner, but not other ligase traps. Interestingly, the four most abundant candidate substrates identified for the F box protein Saf1 were all vacuolar/lysosomal proteins. Analysis of one of these substrates, Prb1, showed that Saf1 selectively promotes ubiquitination of the unprocessed form of the zymogen. This suggests that Saf1 is part of a pathway that targets protein precursors for proteasomal degradation.
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Affiliation(s)
- Kevin G Mark
- Department of Biochemistry and Biophysics, Helen Diller Family Comprehensive Cancer Center, San Francisco, CA 94158, USA
| | - Marco Simonetta
- Department of Biochemistry and Biophysics, Helen Diller Family Comprehensive Cancer Center, San Francisco, CA 94158, USA
| | - Alessio Maiolica
- Department of Biology, Institute of Molecular Systems Biology, ETH Zürich, Zürich CH-8093, Switzerland
| | - Charles A Seller
- Department of Biochemistry and Biophysics, Helen Diller Family Comprehensive Cancer Center, San Francisco, CA 94158, USA
| | - David P Toczyski
- Department of Biochemistry and Biophysics, Helen Diller Family Comprehensive Cancer Center, San Francisco, CA 94158, USA.
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49
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Protein quality control and elimination of protein waste: The role of the ubiquitin–proteasome system. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2014; 1843:182-96. [DOI: 10.1016/j.bbamcr.2013.06.031] [Citation(s) in RCA: 292] [Impact Index Per Article: 29.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/03/2013] [Revised: 06/28/2013] [Accepted: 06/29/2013] [Indexed: 01/26/2023]
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50
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Servas C, Römisch K. The Sec63p J-domain is required for ERAD of soluble proteins in yeast. PLoS One 2013; 8:e82058. [PMID: 24324744 PMCID: PMC3852996 DOI: 10.1371/journal.pone.0082058] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2013] [Accepted: 10/28/2013] [Indexed: 12/02/2022] Open
Abstract
How misfolded proteins are exported from the ER to the cytosol for degradation (ER-associated Degradation, ERAD) and which proteins are participating in this process is not understood. Several studies using a single, leaky mutant indicated that Sec63p might be involved in ERAD. More recently, Sec63p was also found strongly associated with proteasomes attached to the protein-conducting channel in the ER membrane which presumably form part of the export machinery. These observations prompted us to reinvestigate the role of Sec63p in ERAD by generating new mutants which were selected in a screen monitoring the intracellular accumulation of the ERAD substrate CPY*. We show that a mutation in the DnaJ-domain of Sec63p causes a defect in ERAD, whereas mutations in the Brl, acidic, and transmembrane domains only affect protein import into the ER. Unexpectedly, mutations in the acidic domain which mediates interaction of Sec63p with Sec62p also caused defects in cotranslational import. In contrast to mammalian cells where SEC63 expression levels affect steady-state levels of multi-spanning transmembrane proteins, the sec63 J-domain mutant was only defective in ERAD of soluble substrates.
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Affiliation(s)
- Christina Servas
- Department of Microbiology, Faculty of Natural Sciences and Technology VIII, Saarland University, Saarbrücken, Germany
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