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Sarango G, Richetta C, Pereira M, Kumari A, Ghosh M, Bertrand L, Pionneau C, Le Gall M, Grégoire S, Jeger‐Madiot R, Rosoy E, Subra F, Delelis O, Faure M, Esclatine A, Graff‐Dubois S, Stevanović S, Manoury B, Ramirez BC, Moris A. The Autophagy Receptor TAX1BP1 (T6BP) improves antigen presentation by MHC-II molecules. EMBO Rep 2022; 23:e55470. [PMID: 36215666 PMCID: PMC9724678 DOI: 10.15252/embr.202255470] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2022] [Revised: 09/16/2022] [Accepted: 09/23/2022] [Indexed: 12/12/2022] Open
Abstract
CD4+ T lymphocytes play a major role in the establishment and maintenance of immunity. They are activated by antigenic peptides derived from extracellular or newly synthesized (endogenous) proteins presented by the MHC-II molecules. The pathways leading to endogenous MHC-II presentation remain poorly characterized. We demonstrate here that the autophagy receptor, T6BP, influences both autophagy-dependent and -independent endogenous presentation of HIV- and HCMV-derived peptides. By studying the immunopeptidome of MHC-II molecules, we show that T6BP affects both the quantity and quality of peptides presented. T6BP silencing induces the mislocalization of the MHC-II-loading compartments and rapid degradation of the invariant chain (CD74) without altering the expression and internalization kinetics of MHC-II molecules. Defining the interactome of T6BP, we identify calnexin as a T6BP partner. We show that the calnexin cytosolic tail is required for this interaction. Remarkably, calnexin silencing replicates the functional consequences of T6BP silencing: decreased CD4+ T cell activation and exacerbated CD74 degradation. Altogether, we unravel T6BP as a key player of the MHC-II-restricted endogenous presentation pathway, and we propose one potential mechanism of action.
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Affiliation(s)
- Gabriela Sarango
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Clémence Richetta
- Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance,LBPA, ENS‐Paris Saclay, CNRS UMR8113Université Paris SaclayGif‐sur‐YvetteFrance
| | - Mathias Pereira
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Anita Kumari
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Michael Ghosh
- Department of Immunology, Institute for Cell BiologyUniversity of TübingenTübingenGermany
| | - Lisa Bertrand
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Cédric Pionneau
- Sorbonne UniversitéINSERM, UMS Production et Analyse de Données en Sciences de la vie et en Santé, PASS, Plateforme Post‐génomique de la Pitié SalpêtrièreParisFrance
| | - Morgane Le Gall
- 3P5 proteom'IC facilityUniversité de Paris, Institut Cochin, INSERM U1016, CNRS‐UMR 8104ParisFrance
| | - Sylvie Grégoire
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Raphaël Jeger‐Madiot
- Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance,Present address:
Sorbonne Université, INSERM U959, Immunology‐Immunopathology‐Immunotherapy (i3)ParisFrance
| | - Elina Rosoy
- Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Frédéric Subra
- LBPA, ENS‐Paris Saclay, CNRS UMR8113Université Paris SaclayGif‐sur‐YvetteFrance
| | - Olivier Delelis
- LBPA, ENS‐Paris Saclay, CNRS UMR8113Université Paris SaclayGif‐sur‐YvetteFrance
| | - Mathias Faure
- CIRI, Centre International de Recherche en Infectiologie, Université de Lyon, Inserm U1111Université Claude Bernard Lyon 1, CNRS, UMR5308, ENS de LyonLyonFrance,Equipe Labellisée par la Fondation pour la Recherche Médicale, FRM
| | - Audrey Esclatine
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance
| | - Stéphanie Graff‐Dubois
- Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance,Present address:
Sorbonne Université, INSERM U959, Immunology‐Immunopathology‐Immunotherapy (i3)ParisFrance
| | - Stefan Stevanović
- Department of Immunology, Institute for Cell BiologyUniversity of TübingenTübingenGermany
| | - Bénédicte Manoury
- Institut Necker Enfants Malades, INSERM U1151‐CNRS UMR 8253, Faculté de médecine NeckerUniversité de ParisParisFrance
| | - Bertha Cecilia Ramirez
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
| | - Arnaud Moris
- Université Paris‐Saclay, CEA, CNRSInstitute for Integrative Biology of the Cell (I2BC)Gif‐sur‐YvetteFrance,Sorbonne UniversitéINSERM, CNRS, Center for Immunology and Microbial Infections (CIMI‐Paris)ParisFrance
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2
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Alam A, Taye N, Patel S, Thube M, Mullick J, Shah VK, Pant R, Roychowdhury T, Banerjee N, Chatterjee S, Bhattacharya R, Roy R, Mukhopadhyay A, Mogare D, Chattopadhyay S. SMAR1 favors immunosurveillance of cancer cells by modulating calnexin and MHC I expression. Neoplasia 2019; 21:945-962. [PMID: 31422285 PMCID: PMC6706529 DOI: 10.1016/j.neo.2019.07.002] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2019] [Accepted: 07/17/2019] [Indexed: 01/17/2023] Open
Abstract
Down-regulation or loss of MHC class I expression is a major mechanism used by cancer cells to evade immunosurveillance and increase their oncogenic potential. MHC I mediated antigen presentation is a complex regulatory process, controlled by antigen processing machinery (APM) dictating immune response. Transcriptional regulation of the APM that can modulate gene expression profile and their correlation to MHC I mediated antigen presentation in cancer cells remain enigmatic. Here, we reveal that Scaffold/Matrix-Associated Region 1- binding protein (SMAR1), positively regulates MHC I surface expression by down-regulating calnexin, an important component of antigen processing machinery (APM) in cancer cells. SMAR1, a bonafide MAR binding protein acts as a transcriptional repressor of several oncogenes. It is down-regulated in higher grades of cancers either through proteasomal degradation or through loss of heterozygosity (LOH) at the Chr.16q24.3 locus where the human homolog of SMAR1 (BANP) has been mapped. It binds to a short MAR region of the calnexin promoter forming a repressor complex in association with GATA2 and HDAC1. A reverse correlation between SMAR1 and calnexin was thus observed in SMAR1-LOH cells and also in tissues from breast cancer patients. To further extrapolate our findings, influenza A (H1N1) virus infection assay was performed. Upon viral infection, the levels of SMAR1 significantly increased resulting in reduced calnexin expression and increased MHC I presentation. Taken together, our observations establish that increased expression of SMAR1 in cancers can positively regulate MHC I surface expression thereby leading to higher chances of tumor regression and elimination of cancer cells.
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Affiliation(s)
- Aftab Alam
- National Centre for Cell Science, Pune, Maharashtra, India
| | - Nandaraj Taye
- National Centre for Cell Science, Pune, Maharashtra, India
| | - Sonal Patel
- National Centre for Cell Science, Pune, Maharashtra, India
| | - Milind Thube
- ICMR-National Institute of Virology, Pune, Maharashtra, India
| | - Jayati Mullick
- ICMR-National Institute of Virology, Pune, Maharashtra, India
| | | | - Richa Pant
- National Centre for Cell Science, Pune, Maharashtra, India
| | | | | | | | | | - Rini Roy
- Netaji Subhas Chandra Bose Cancer Research Institute, Kolkata, India
| | | | - Devraj Mogare
- National Centre for Cell Science, Pune, Maharashtra, India
| | - Samit Chattopadhyay
- National Centre for Cell Science, Pune, Maharashtra, India; Indian Institute of Chemical Biology, Kolkata, India.
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3
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Kotian V, Sarmah D, Kaur H, Kesharwani R, Verma G, Mounica L, Veeresh P, Kalia K, Borah A, Wang X, Dave KR, Yavagal DR, Bhattacharya P. Evolving Evidence of Calreticulin as a Pharmacological Target in Neurological Disorders. ACS Chem Neurosci 2019; 10:2629-2646. [PMID: 31017385 DOI: 10.1021/acschemneuro.9b00158] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Calreticulin (CALR), a lectin-like ER chaperone, was initially known only for its housekeeping function, but today it is recognized for many versatile roles in different compartments of a cell. Apart from canonical roles in protein folding and calcium homeostasis, it performs a variety of noncanonical roles, mostly in CNS development. In the past, studies have linked Calreticulin with various other biological components which are detrimental in deciding the fate of neurons. Many neurological disorders that differ in their etiology are commonly associated with aberrant levels of Calreticulin, that lead to modulation of apoptosis and phagocytosis, and impact on transcriptional pathways, impairment in proteostatis, and calcium imbalances. Such multifaceted properties of Calreticulin are the reason why it has been implicated in vital roles of the nervous system in recent years. Hence, understanding its role in the physiology of neurons would help to unearth its involvement in the spectrum of neurological disorders. This Review aims toward exploring the interplay of Calreticulin in neurological disorders which would aid in targeting Calreticulin for developing novel neurotherapeutics.
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Affiliation(s)
- Vignesh Kotian
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Deepaneeta Sarmah
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Harpreet Kaur
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Radhika Kesharwani
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Geetesh Verma
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Leela Mounica
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Pabbala Veeresh
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Kiran Kalia
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
| | - Anupom Borah
- Cellular and Molecular Neurobiology Laboratory, Department of Life Science and Bioinformatics, Assam University, Silchar, Assam 788011, India
| | - Xin Wang
- Department of Neurosurgery, Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts 02115, United States
| | - Kunjan R. Dave
- Department of Neurology, University of Miami Miller School of Medicine, Miami, Florida 33136, United States
| | - Dileep R. Yavagal
- Department of Neurology and Neurosurgery, University of Miami Miller School of Medicine, Miami, Florida 33136, United States
| | - Pallab Bhattacharya
- Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research (NIPER), Ahmedabad, Gandhinagar, Gujarat 382355, India
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4
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Serrano-Perez MC, Tilley FC, Nevo F, Arrondel C, Sbissa S, Martin G, Tory K, Antignac C, Mollet G. Endoplasmic reticulum-retained podocin mutants are massively degraded by the proteasome. J Biol Chem 2018; 293:4122-4133. [PMID: 29382718 DOI: 10.1074/jbc.ra117.001159] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2017] [Revised: 01/23/2018] [Indexed: 12/13/2022] Open
Abstract
Podocin is a key component of the slit diaphragm in the glomerular filtration barrier, and mutations in the podocin-encoding gene NPHS2 are a common cause of hereditary steroid-resistant nephrotic syndrome. A mutant allele encoding podocin with a p.R138Q amino acid substitution is the most frequent pathogenic variant in European and North American children, and the corresponding mutant protein is poorly expressed and retained in the endoplasmic reticulum both in vitro and in vivo To better understand the defective trafficking and degradation of this mutant, we generated human podocyte cell lines stably expressing podocinwt or podocinR138Q Although it has been proposed that podocin has a hairpin topology, we present evidence for podocinR138QN-glycosylation, suggesting that most of the protein has a transmembrane topology. We find that N-glycosylated podocinR138Q has a longer half-life than non-glycosylated podocinR138Q and that the latter is far more rapidly degraded than podocinwt Consistent with its rapid degradation, podocinR138Q is exclusively degraded by the proteasome, whereas podocinwt is degraded by both the proteasomal and the lysosomal proteolytic machineries. In addition, we demonstrate an enhanced interaction of podocinR138Q with calnexin as the mechanism of endoplasmic reticulum retention. Calnexin knockdown enriches the podocinR138Q non-glycosylated fraction, whereas preventing exit from the calnexin cycle increases the glycosylated fraction. Altogether, we propose a model in which hairpin podocinR138Q is rapidly degraded by the proteasome, whereas transmembrane podocinR138Q degradation is delayed due to entry into the calnexin cycle.
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Affiliation(s)
- Maria-Carmen Serrano-Perez
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
| | - Frances C Tilley
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
| | - Fabien Nevo
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
| | - Christelle Arrondel
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
| | - Selim Sbissa
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
| | - Gaëlle Martin
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
| | - Kalman Tory
- the MTA-SE Lendület Nephrogenetic Laboratory, Hungarian Academy of Sciences and First Department of Pediatrics, Semmelweis University, Budapest 1083, Hungary, and
| | - Corinne Antignac
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France.,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France.,the Département de Génétique, Assistance Publique-Hôpitaux de Paris, Hôpital Necker-Enfants Malades, Paris 75015, France
| | - Géraldine Mollet
- From the Laboratory of Hereditary Kidney Diseases, Inserm UMR 1163, Imagine Institute, Paris 75015, France, .,the Université Paris Descartes-Sorbonne Paris Cité, Imagine Institute, Paris 75015, France
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5
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Lum R, Ahmad S, Hong SJ, Chapman DC, Kozlov G, Williams DB. Contributions of the Lectin and Polypeptide Binding Sites of Calreticulin to Its Chaperone Functions in Vitro and in Cells. J Biol Chem 2016; 291:19631-41. [PMID: 27413183 DOI: 10.1074/jbc.m116.746321] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2016] [Indexed: 11/06/2022] Open
Abstract
Calreticulin is a lectin chaperone of the endoplasmic reticulum that interacts with newly synthesized glycoproteins by binding to Glc1Man9GlcNAc2 oligosaccharides as well as to the polypeptide chain. In vitro, the latter interaction potently suppresses the aggregation of various non-glycosylated proteins. Although the lectin-oligosaccharide association is well understood, the polypeptide-based interaction is more controversial because the binding site on calreticulin has not been identified, and its significance in the biogenesis of glycoproteins in cells remains unknown. In this study, we identified the polypeptide binding site responsible for the in vitro aggregation suppression function by mutating four candidate hydrophobic surface patches. Mutations in only one patch, P19K/I21E and Y22K/F84E, impaired the ability of calreticulin to suppress the thermally induced aggregation of non-glycosylated firefly luciferase. These mutants also failed to bind several hydrophobic peptides that act as substrate mimetics and compete in the luciferase aggregation suppression assay. To assess the relative contributions of the glycan-dependent and -independent interactions in living cells, we expressed lectin-deficient, polypeptide binding-deficient, and doubly deficient calreticulin constructs in calreticulin-negative cells and monitored the effects on the biogenesis of MHC class I molecules, the solubility of mutant forms of α1-antitrypsin, and interactions with newly synthesized glycoproteins. In all cases, we observed a profound impairment in calreticulin function when its lectin site was inactivated. Remarkably, inactivation of the polypeptide binding site had little impact. These findings indicate that the lectin-based mode of client interaction is the predominant contributor to the chaperone functions of calreticulin within the endoplasmic reticulum.
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Affiliation(s)
- Ronnie Lum
- From the Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Samar Ahmad
- From the Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Seo Jung Hong
- From the Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Daniel C Chapman
- From the Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
| | - Guennadi Kozlov
- the Groupe de Recherche Axé sur la Structure des Proteines, Department of Biochemistry, McGill University, Montréal, Québec H3G 0B1, Canada
| | - David B Williams
- From the Departments of Biochemistry and Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada and
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6
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Abstract
The mammalian immune system has evolved to display peptides derived from microbial antigens to immune effector cells. Liberated from the intact antigens through distinct proteolytic mechanisms, these peptides are subsequently transported to the cell surface while bound to chaperone-like receptors known as major histocompatibility complex molecules. These complexes are then scrutinized by T-cells that express receptors with specificity for specific major histocompatibility complex-peptide complexes. In normal uninfected cells, this process of antigen processing and presentation occurs continuously, with the resultant array of self-antigen-derived peptides displayed on the surface of these cells. Changes in this cellular peptide array alert the immune system to changes in the intracellular environment that may be associated with infection, oncogenesis or other abnormal cellular processes, resulting in a cascade of events that result in the elimination of the abnormal cell. Since peptides play such an essential role in informing the immune system of infection with viral or microbial pathogens and the transformation of cells in malignancy, the tools of proteomics, in particular mass spectrometry, are ideally suited to study these immune responses at a molecular level. Recent advances in studies of immune responses that have utilized mass spectrometry and associated technologies are reviewed. The authors gaze into the future and look at current challenges and where proteomics will impact in immunology over the next 5 years.
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Affiliation(s)
- Nicholas A Williamson
- The University of Melbourne, Department of Biochemistry & Molecular Biology, The Bio21 Molecular Science & Biotechnology Institute, 3010, Victoria, Australia.
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7
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Matsuo Y, Masutani H, Son A, Kizaka-Kondoh S, Yodoi J. Physical and functional interaction of transmembrane thioredoxin-related protein with major histocompatibility complex class I heavy chain: redox-based protein quality control and its potential relevance to immune responses. Mol Biol Cell 2009; 20:4552-62. [PMID: 19741092 DOI: 10.1091/mbc.e09-05-0439] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In the endoplasmic reticulum (ER), a variety of oxidoreductases classified in the thioredoxin superfamily have been found to catalyze the formation and rearrangement of disulfide bonds. However, the precise function and specificity of the individual thioredoxin family proteins remain to be elucidated. Here, we characterize a transmembrane thioredoxin-related protein (TMX), a membrane-bound oxidoreductase in the ER. TMX exists in a predominantly reduced form and associates with the molecular chaperon calnexin, which can mediate substrate binding. To determine the target molecules for TMX, we apply a substrate-trapping approach based on the reaction mechanism of thiol-disulfide exchange, identifying major histocompatibility complex (MHC) class I heavy chain (HC) as a candidate substrate. Unlike the classical ER oxidoreductases such as protein disulfide isomerase and ERp57, TMX seems not to be essential for normal assembly of MHC class I molecules. However, we show that TMX-class I HC interaction is enhanced during tunicamycin-induced ER stress, and TMX prevents the ER-to-cytosol retrotranslocation of misfolded class I HC targeted for proteasomal degradation. These results suggest a specific role for TMX and its mechanism of action in redox-based ER quality control.
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Affiliation(s)
- Yoshiyuki Matsuo
- Department of Biological Responses, Institute for Virus Research, Graduate School of Medicine, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
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8
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Guérin R, Beauregard PB, Leroux A, Rokeach LA. Calnexin regulates apoptosis induced by inositol starvation in fission yeast. PLoS One 2009; 4:e6244. [PMID: 19606215 PMCID: PMC2705804 DOI: 10.1371/journal.pone.0006244] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Accepted: 06/08/2009] [Indexed: 12/21/2022] Open
Abstract
Inositol is a precursor of numerous phospholipids and signalling molecules essential for the cell. Schizosaccharomyces pombe is naturally auxotroph for inositol as its genome does not have a homologue of the INO1 gene encoding inositol-1-phosphate synthase, the enzyme responsible for inositol biosynthesis. In this work, we demonstrate that inositol starvation in S. pombe causes cell death with apoptotic features. This apoptotic death is dependent on the metacaspase Pca1p and is affected by the UPR transducer Ire1p. Previously, we demonstrated that calnexin is involved in apoptosis induced by ER stress. Here, we show that cells expressing a lumenal version of calnexin exhibit a 2-fold increase in the levels of apoptosis provoked by inositol starvation. This increase is reversed by co-expression of a calnexin mutant spanning the transmembrane domain and C-terminal cytosolic tail. Coherently, calnexin is physiologically cleaved at the end of its lumenal domain, under normal growth conditions when cells approach stationary phase. This cleavage suggests that the two naturally produced calnexin fragments are needed to continue growth into stationary phase and to prevent cell death. Collectively, our observations indicate that calnexin takes part in at least two apoptotic pathways in S. pombe, and suggest that the cleavage of calnexin has regulatory roles in apoptotic processes involving calnexin.
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Affiliation(s)
- Renée Guérin
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada
| | | | - Alexandre Leroux
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada
| | - Luis A. Rokeach
- Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada
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9
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Guérin R, Arseneault G, Dumont S, Rokeach LA. Calnexin is involved in apoptosis induced by endoplasmic reticulum stress in the fission yeast. Mol Biol Cell 2008; 19:4404-20. [PMID: 18701708 DOI: 10.1091/mbc.e08-02-0188] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Stress conditions affecting the functions of the endoplasmic reticulum (ER) cause the accumulation of unfolded proteins. ER stress is counteracted by the unfolded-protein response (UPR). However, under prolonged stress the UPR initiates a proapoptotic response. Mounting evidence indicate that the ER chaperone calnexin is involved in apoptosis caused by ER stress. Here, we report that overexpression of calnexin in Schizosaccharomyces pombe induces cell death with apoptosis markers. Cell death was partially dependent on the Ire1p ER-stress transducer. Apoptotic death caused by calnexin overexpression required its transmembrane domain (TM), and involved sequences on either side of the ER membrane. Apoptotic death caused by tunicamycin was dramatically reduced in a strain expressing endogenous levels of calnexin lacking its TM and cytosolic tail. This demonstrates the involvement of calnexin in apoptosis triggered by ER stress. A genetic screen identified the S. pombe homologue of the human antiapoptotic protein HMGB1 as a suppressor of apoptotic death due to calnexin overexpression. Remarkably, overexpression of human calnexin in S. pombe also provoked apoptotic death. Our results argue for the conservation of the role of calnexin in apoptosis triggered by ER stress, and validate S. pombe as a model to elucidate the mechanisms of calnexin-mediated cell death.
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Affiliation(s)
- Renée Guérin
- Department of Biochemistry, Université de Montréal, Montréal, QC H3C 3J7, Canada
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10
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Hebert DN, Molinari M. In and out of the ER: protein folding, quality control, degradation, and related human diseases. Physiol Rev 2007; 87:1377-408. [PMID: 17928587 DOI: 10.1152/physrev.00050.2006] [Citation(s) in RCA: 484] [Impact Index Per Article: 28.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A substantial fraction of eukaryotic gene products are synthesized by ribosomes attached at the cytosolic face of the endoplasmic reticulum (ER) membrane. These polypeptides enter cotranslationally in the ER lumen, which contains resident molecular chaperones and folding factors that assist their maturation. Native proteins are released from the ER lumen and are transported through the secretory pathway to their final intra- or extracellular destination. Folding-defective polypeptides are exported across the ER membrane into the cytosol and destroyed. Cellular and organismal homeostasis relies on a balanced activity of the ER folding, quality control, and degradation machineries as shown by the dozens of human diseases related to defective maturation or disposal of individual polypeptides generated in the ER.
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Affiliation(s)
- Daniel N Hebert
- Department of Biochemistry and Molecular Biology, Program in Molecular and Cellular Biology, University of Massachusetts, Amherst, Massachusetts 01003, USA.
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11
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van Lith M, Benham AM. The DMalpha and DMbeta chain cooperate in the oxidation and folding of HLA-DM. THE JOURNAL OF IMMUNOLOGY 2007; 177:5430-9. [PMID: 17015729 DOI: 10.4049/jimmunol.177.8.5430] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
HLA-DM (DM) is a heterodimeric MHC molecule that catalyzes the peptide loading of classical MHC class II molecules in the endosomal/lysosomal compartments of APCs. Although the function of DM is well-established, little is known about how DMalpha and beta-chains fold, oxidize, and form a complex in the endoplasmic reticulum (ER). In this study, we show that glycosylation promotes, but is not essential for, DMalphabeta ER exit. However, glycosylation of DMalpha N15 is required for oxidation of the alpha-chain. The DMalpha and beta-chains direct each others fate: single DMalpha chains cannot fully oxidize without DMbeta, while DMbeta forms disulfide-linked homodimers without DMalpha. Correct oxidation and subsequent ER egress depend on the unique DMbeta C25 and C35 residues. This suggests that the C25-C35 disulfide bond in the peptide-binding domain overcomes the need for stabilizing peptides required by other MHC molecules.
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Affiliation(s)
- Marcel van Lith
- Department of Biological Sciences, University of Durham, Durham, United Kingdom
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12
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Williams DB. Beyond lectins: the calnexin/calreticulin chaperone system of the endoplasmic reticulum. J Cell Sci 2006; 119:615-23. [PMID: 16467570 DOI: 10.1242/jcs.02856] [Citation(s) in RCA: 341] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Calnexin and calreticulin are related proteins that comprise an ER chaperone system that ensures the proper folding and quality control of newly synthesized glycoproteins. The specificity for glycoproteins is conferred by a lectin site that recognizes an early oligosaccharide processing intermediate on the folding glycoprotein, Glc1Man9GlcNAc2. In addition, calnexin and calreticulin possess binding sites for ATP, Ca2+, non-native polypeptides and ERp57, an enzyme that catalyzes disulfide bond formation, reduction and isomerization. Recent studies have revealed the locations of some of these ligand-binding sites and have provided insights into how they contribute to overall chaperone function. In particular, the once controversial non-native-polypeptide-binding site has now been shown to function both in vitro and in cells. Furthermore, there is clear evidence that ERp57 participates in glycoprotein biogenesis either alone or in tandem with calnexin and calreticulin.
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Affiliation(s)
- David B Williams
- Department of Biochemistry and Immunology, University of Toronto, Toronto, Ontario, Canada, M5S 1A8.
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13
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Wanamaker CP, Green WN. N-linked glycosylation is required for nicotinic receptor assembly but not for subunit associations with calnexin. J Biol Chem 2005; 280:33800-10. [PMID: 16091366 PMCID: PMC2373277 DOI: 10.1074/jbc.m501813200] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
We investigated how asparagine (N)-linked glycosylation affects assembly of acetylcholine receptors (AChRs) in the endoplasmic reticulum (ER). Block of N-linked glycosylation inhibited AChR assembly whereas block of glucose trimming partially blocked assembly at the late stages. Removal of each of seven glycans had a distinct effect on AChR assembly, ranging from no effect to total loss of assembly. Because the chaperone calnexin (CN) associates with N-linked glycans, we examined CN interactions with AChR subunits. CN rapidly associates with 50% or more of newly synthesized AChR subunits, but not with subunits after maturation. Block of N-linked glycosylation or trimming did not alter CN-AChR subunit associations nor did subunit mutations prevent N-linked glycosylation. Additionally, CN associations with subunits lacking N-linked glycans occurred without subunit aggregation or misfolding. Our data indicate that CN associates with AChR subunits without N-linked glycan interactions. Furthermore, CN-subunit associations only occur early in AChR assembly and have no role in events later that require N-linked glycosylation.
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Affiliation(s)
- Christian P. Wanamaker
- From the Committee on Neurobiology and Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637
| | - William N. Green
- From the Committee on Neurobiology and Department of Neurobiology, Pharmacology, and Physiology, University of Chicago, Chicago, Illinois 60637
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14
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Zhu X, Peng J, Chen D, Liu X, Ye L, Iijima H, Kadavil K, Lencer WI, Blumberg RS. Calnexin and ERp57 facilitate the assembly of the neonatal Fc receptor for IgG with beta 2-microglobulin in the endoplasmic reticulum. THE JOURNAL OF IMMUNOLOGY 2005; 175:967-76. [PMID: 16002696 DOI: 10.4049/jimmunol.175.2.967] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
The neonatal FcR (FcRn) consists of an MHC class I-like H chain in noncovalent association with beta(2)-microglobulin (beta(2)m). The proper folding of FcRn in the endoplasmic reticulum is essential for FcRn function. Using a low stringency immunoprecipitation of human FcRn, we observed the coprecipitation of an 88-kDa band. Mass spectrometry analysis revealed that this band was identical with calnexin (CNX). This association was verified by Western blotting the CNX or FcRn immunoprecipitates with either an anti-FcRn or anti-CNX Ab. In the beta(2)m-null FO-1 cell transfected with FcRn H chain alone or both FcRn H chain and beta(2)m, CNX bound to the FcRn H chain before the FcRn H chain association with beta(2)m. However, calreticulin only bound to the FcRn H chain-beta(2)m complex. Furthermore, the thiol oxidoreductase ERp57 was detected in FcRn-CNX complexes, suggesting its role in disulfide bond formation of the FcRn H chain. Removal of the N-linked glycosylation site from the FcRn H chain resulted in a decreased association of the FcRn H chain for beta(2)m. However, the absence of CNX did not significantly affect FcRn assembly as defined by the ability of FcRn to bind IgG and exit to the cell surface. This suggests that other chaperones compensate for the function of CNX in FcRn assembly. In addition, we found that tapasin and TAP were not involved in FcRn assembly, as shown by coimmunoprecipitation in THP-1 cells and IgG-binding assays in 721.220 (tapasin-deficient) and 721.174 (TAP-deficient) cells transfected with FcRn. These findings show the importance of chaperones in FcRn assembly.
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Affiliation(s)
- Xiaoping Zhu
- Laboratory of Immunology, Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, 8075 Greenmead Drive, College Park, MD 20742, USA.
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15
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Thammavongsa V, Mancino L, Raghavan M. Polypeptide Substrate Recognition by Calnexin Requires Specific Conformations of the Calnexin Protein. J Biol Chem 2005; 280:33497-505. [PMID: 16061483 DOI: 10.1074/jbc.m503648200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calnexin is an endoplasmic reticulum chaperone that binds to substrates containing monoglucosylated oligosaccharides. Whether calnexin can also directly recognize polypeptide components of substrates is controversial. We found that calnexin displayed significant conformational lability for a chaperone and that heat treatment and calcium depletion induced the formation of calnexin dimers and higher order oligomers. These conditions enhanced the chaperone activity of calnexin toward glycosylated and non-glycosylated major histocompatibility complex (MHC) class I heavy chains, and enhanced calnexin binding to MHC class I heavy chains. In contrast to these observations, calnexin binding to oligosaccharide substrates has been reported to be impaired under calcium-depleting conditions. Calnexin dimers were induced in HeLa cells upon heat shock and under calcium-depleting conditions, and heat shock enhanced calnexin binding to MHC class I heavy chains in HeLa cells. Virus-induced endoplasmic reticulum stress also resulted in the appearance of calnexin dimers. Tunicamycin treatment of HeLa cells induced a slow accumulation of calnexin dimers, the appearance of which correlated with enhanced calnexin binding to deglycosylated MHC class I heavy chains. In vitro, the presence of calnexin-specific oligosaccharides inhibited the formation of calnexin dimers and higher order structures. Together, these data indicate that polypeptide binding is favored by conditions that induce partial unfolding of calnexin monomers, whereas oligosaccharide binding is favored by conditions that enhance the structural stability (folding) of calnexin monomers. Conditions that induce the calnexin "polypeptide-binding" conformation also induce self-association of calnexin if the concentration is sufficiently high; however, calnexin dimerization/oligomerization per se is not essential for polypeptide substrate binding.
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Affiliation(s)
- Vilasack Thammavongsa
- Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-0620, USA
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16
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Bedard K, Szabo E, Michalak M, Opas M. Cellular Functions of Endoplasmic Reticulum Chaperones Calreticulin, Calnexin, and ERp57. INTERNATIONAL REVIEW OF CYTOLOGY 2005; 245:91-121. [PMID: 16125546 DOI: 10.1016/s0074-7696(05)45004-4] [Citation(s) in RCA: 114] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Glycosylated proteins destined for the cell surface or to be secreted from the cell are trafficked through the endoplasmic reticulum during synthesis and folding. Correct folding is determined in large part by the sequence of the protein, but it is also assisted by interaction with enzymes and chaperones of the endoplasmic reticulum. Calreticulin, calnexin, and ERp57 are among the endoplasmic chaperones that interact with partially folded glycoproteins and determine if the proteins are to be released from the endoplasmic reticulum to be expressed, or alternatively, if they are to be sent to the proteosome for degradation. Studies on the effect of alterations in the expression and function of these proteins are providing information about the importance of this quality control system, as well as uncovering other important functions these proteins play outside of the endoplasmic reticulum.
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Affiliation(s)
- Karen Bedard
- Membrane Protein Research Group and Department of Biochemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2H7
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17
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Wearsch PA, Jakob CA, Vallin A, Dwek RA, Rudd PM, Cresswell P. Major Histocompatibility Complex Class I Molecules Expressed with Monoglucosylated N-Linked Glycans Bind Calreticulin Independently of Their Assembly Status. J Biol Chem 2004; 279:25112-21. [PMID: 15056662 DOI: 10.1074/jbc.m401721200] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The assembly of major histocompatibility complex (MHC) class I molecules with peptides in the endoplasmic reticulum (ER) is a critical step in the presentation of viral antigens to CD8+ T cells. This process is subject to quality control restrictions that prevent free class I heavy chains (HCs) and peptide-free HC-beta(2)-microglobulin (beta(2)m) dimers from exiting the ER. The lectin-like chaperone calreticulin associates with HC-beta(2)m heterodimers prior to peptide binding, but its precise role in regulating the subsequent events of peptide association and ER to Golgi transport remains undefined. In vitro analysis of the assembly process has been limited by the specificity of calreticulin for monoglucosylated N-linked glycans, which are transient biosynthetic intermediates. To address this problem, we developed a novel expression system using Saccharomyces cerevisiae glycosylation mutants to produce class I HC bearing N-linked oligosaccharides with the specific structure Glc(1)Man(9)GlcNAc(2). The monoglucosylated glycan proved to be both necessary and sufficient for in vitro binding of calreticulin to MHC class I molecules. Calreticulin bound as efficiently to peptide-loaded MHC class I complexes as it did to folding intermediates created in vitro, namely free class I HC and empty HC-beta(2)m heterodimers. Thus, calreticulin is unable to discriminate between native and non-native MHC class I conformations and therefore unlikely to play a role in the recognition and release of peptide-loaded complexes from the ER. Furthermore, the recombinant expression system developed in this study can be used to produce a broad range of calreticulin substrates to elucidate its general mechanism of activity in vitro.
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Affiliation(s)
- Pamela A Wearsch
- Section of Immunobiology, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06520-8011, USA
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18
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Leach MR, Williams DB. Lectin-deficient Calnexin Is Capable of Binding Class I Histocompatibility Molecules in Vivo and Preventing Their Degradation. J Biol Chem 2004; 279:9072-9. [PMID: 14699098 DOI: 10.1074/jbc.m310788200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calnexin is a membrane-bound lectin of the endoplasmic reticulum (ER) that binds transiently to newly synthesized glycoproteins. By interacting with oligosaccharides of the form Glc(1)Man(9)GlcNAc(2), calnexin enhances the folding of glycoprotein substrates, retains misfolded variants in the ER, and in some cases participates in their degradation. Calnexin has also been shown to bind polypeptides in vivo that do not possess a glycan of this form and to function in vitro as a molecular chaperone for nonglycosylated proteins. To test the relative importance of the lectin site compared with the polypeptide-binding site, we have generated six calnexin mutants defective in oligosaccharide binding using site-directed mutagenesis. Expressed as glutathione S-transferase fusions, these mutants were still capable of binding ERp57, a thiol oxidoreductase, and preventing the aggregation of a nonglycosylated substrate, citrate synthase. They were, however, unable to bind Glc(1) Man(9)GlcNAc(2) oligosaccharide and were compromised in preventing the aggregation of the monoglucosylated substrate jack bean alpha-mannosidase. Two of these mutants were then engineered into full-length calnexin for heterologous expression in Drosophila cells along with the murine class I histocompatibility molecules K(b) and D(b) as model glycoproteins. In this system, lectin site-defective calnexin was able to replace wild type calnexin in forming a complex with K(b) and D(b) heavy chains and preventing their degradation. Thus, at least for class I molecules, the lectin site of calnexin is dispensable for some of its chaperone functions.
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Affiliation(s)
- Michael R Leach
- Department of Biochemistry, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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19
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Purcell AW, Gorman JJ. Immunoproteomics: Mass spectrometry-based methods to study the targets of the immune response. Mol Cell Proteomics 2004; 3:193-208. [PMID: 14718575 DOI: 10.1074/mcp.r300013-mcp200] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mammalian immune system has evolved to display fragments of protein antigens derived from microbial pathogens to immune effector cells. These fragments are typically peptides liberated from the intact antigens through distinct proteolytic mechanisms that are subsequently transported to the cell surface bound to chaperone-like receptors known as major histocompatibility complex (MHC) molecules. These complexes are then scrutinized by effector T cells that express clonally distributed T cell receptors with specificity for specific MHC-peptide complexes. In normal uninfected cells, this process of antigen processing and presentation occurs continuously, with the resultant array of self-antigen-derived peptides displayed on the surface of these cells. Changes in this peptide landscape of cells act to alert immune effector cells to changes in the intracellular environment that may be associated with infection, malignant transformation, or other abnormal cellular processes, resulting in a cascade of events that result in their elimination. Because peptides play such a crucial role in informing the immune system of infection with viral or microbial pathogens and the transformation of cells in malignancy, the tools of proteomics, in particular mass spectrometry, are ideally suited to study these immune responses at a molecular level. Here we review recent advances in the studies of immune responses that have utilized mass spectrometry and associated technologies, with specific examples from collaboration between our laboratories.
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Affiliation(s)
- A W Purcell
- Department of Microbiology and Immunology and ImmunoID, The University of Melbourne, Victoria 3010, Australia.
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20
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Purcell AW, Zeng W, Mifsud NA, Ely LK, Macdonald WA, Jackson DC. Dissecting the role of peptides in the immune response: theory, practice and the application to vaccine design. J Pept Sci 2003; 9:255-81. [PMID: 12803494 DOI: 10.1002/psc.456] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Analytical biochemistry and synthetic peptide based chemistry have helped to reveal the pivotal role that peptides play in determining the specificity, magnitude and quality of both humoral (antibody) and cellular (cytotoxic and helper T cell) immune responses. In addition, peptide based technologies are now at the forefront of vaccine design and medical diagnostics. The chemical technologies used to assemble peptides into immunogenic structures have made great strides over the past decade and assembly of highly pure peptides which can be incorporated into high molecular weight species, multimeric and even branched structures together with non-peptidic material is now routine. These structures have a wide range of applications in designer vaccines and diagnostic reagents. Thus the tools of the peptide chemist are exquisitely placed to answer questions about immune recognition and along the way to provide us with new and improved vaccines and diagnostics.
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Affiliation(s)
- Anthony W Purcell
- Department of Microbiology and Immunology, The University of Melbourne, Parkville, Victoria 3010, Australia.
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21
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Calnexin and Calreticulin, Molecular Chaperones of the Endoplasmic Reticulum. ACTA ACUST UNITED AC 2003. [DOI: 10.1007/978-1-4419-9258-1_6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/27/2023]
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22
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23
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Trombetta ES, Parodi AJ. N-glycan processing and glycoprotein folding. ADVANCES IN PROTEIN CHEMISTRY 2002; 59:303-44. [PMID: 11868276 DOI: 10.1016/s0065-3233(01)59010-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Affiliation(s)
- E S Trombetta
- Instituto de Investigaciones Biotecnológicas, Universidad de San Martín, (1650) San Martin, Pcia. de Buenos Aires, Argentina
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24
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Stumptner-Cuvelette P, Benaroch P. Multiple roles of the invariant chain in MHC class II function. BIOCHIMICA ET BIOPHYSICA ACTA 2002; 1542:1-13. [PMID: 11853874 DOI: 10.1016/s0167-4889(01)00166-5] [Citation(s) in RCA: 123] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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25
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Abstract
Retention of misfolded proteins in the endoplasmic reticulum (ER) is a primary mechanism of quality control. To discover whether quality control can monitor assembly inside the hydrophobic ER membrane, we characterized the folding and transport of the tetraspanin glycoprotein CD82. Truncated forms of CD82 that are missing one or more transmembrane segments remain in the ER. A construct (TM 2-4) that is missing the first transmembrane segment remains in the ER, even though its extracellular domain, which is facing the ER lumen, has folded to the native structure. Transport to the cell surface is restored by co-expressing the missing segment (TM 1) as a separate polypeptide. Prior to leaving the ER, CD82 transiently associates with the membrane-bound chaperone calnexin but not with its soluble homolog calreticulin. TM 2-4, in contrast, remains in a prolonged interaction with calnexin that is partially reversed by co-expressing TM 1. These findings establish a simple system to study transmembrane domain assembly, show that ER quality control can directly monitor assembly inside the lipid bilayer and suggest that calnexin may play a role in this process.
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Affiliation(s)
| | - Peter Cresswell
- Section of Immunobiology, Yale University School of Medicine and Howard Hughes Medical Institute, 310 Cedar Street, New Haven, CT 06510, USA
Corresponding author e-mail:
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26
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Danilczyk UG, Williams DB. The lectin chaperone calnexin utilizes polypeptide-based interactions to associate with many of its substrates in vivo. J Biol Chem 2001; 276:25532-40. [PMID: 11337494 DOI: 10.1074/jbc.m100270200] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calnexin and calreticulin are molecular chaperones of the endoplasmic reticulum that bind to newly synthesized glycoproteins in part through a lectin site specific for monoglucosylated (Glc(1)Man(7-9)GlcNAc(2)) oligosaccharides. In addition to this lectin-oligosaccharide interaction, in vitro studies have demonstrated that calnexin and calreticulin can bind to polypeptide segments of both glycosylated and nonglycosylated proteins. However, the in vivo relevance of this latter interaction has been questioned. We examined whether polypeptide-based interactions occur between calnexin and its substrates in vivo using the glucosidase inhibitor castanospermine or glucosidase-deficient cells to prevent the formation of monoglucosylated oligosaccharides. We show that if care is taken to preserve weak interactions, the block in lectin-oligosaccharide binding leads to the loss of some calnexin-substrate complexes, but many others remain readily detectable. Furthermore, we demonstrate that calnexin is capable of associating in vivo with a substrate that completely lacks Asn-linked oligosaccharides. The binding of calnexin to proteins that lack monoglucosylated oligosaccharides could not be attributed to nonspecific adsorption nor to its inclusion in protein aggregates. We conclude that both lectin-oligosaccharide and polypeptide-based interactions occur between calnexin and diverse proteins in vivo and that the strength of the latter interaction varies substantially between protein substrates.
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Affiliation(s)
- U G Danilczyk
- Department of Immunology, University of Toronto, Toronto, Ontario M5S 1A8, Canada
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27
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Jakob CA, Chevet E, Thomas DY, Bergeron JJ. Lectins of the ER quality control machinery. Results Probl Cell Differ 2001; 33:1-17. [PMID: 11190669 DOI: 10.1007/978-3-540-46410-5_1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/12/2023]
Affiliation(s)
- C A Jakob
- Department of Anatomy and Cell Biology, McGill University, Montreal, QC, H3A 2B2, Canada
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28
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Affiliation(s)
- J Pieters
- Basel Institute for Immunology, Switzerland
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29
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Abstract
An unconventional mechanism for retaining improperly folded glycoproteins and facilitating acquisition of their native tertiary and quaternary structures operates in the endoplasmic reticulum. Recognition of folding glycoproteins by two resident lectins, membrane-bound calnexin and its soluble homolog, calreticulin, is mediated by protein-linked monoglucosylated oligosaccharides. These oligosaccharides contain glucose (Glc), mannose (Man), and N-acetylglucosamine (GlcNAc) in the general form Glc1Man7-9GlcNAc2. They are formed by glucosidase I- and II-catalyzed partial deglucosylation of the oligosaccharide transferred from dolichol diphosphate derivatives to Asn residues in nascent polypeptide chains (Glc3Man9GlcNAc2). Further deglucosylation of the oligosaccharides by glucosidase II liberates glycoproteins from their calnexin/calreticulin anchors. Monoglucosylated glycans are then recreated by the UDP-Glc:glycoprotein glucosyltransferase (GT), and thus recognized again by the lectins, only when linked to improperly folded protein moieties, as GT behaves as a sensor of glycoprotein conformations. The deglucosylation-reglucosylation cycle continues until proper folding is achieved. The lectin-monoglucosylated oligosaccharide interaction is one of the alternative ways by which cells retain improperly folded glycoproteins in the endoplasmic reticulum. Although it decreases the folding rate, it increases folding efficiency, prevents premature glycoprotein oligomerization and degradation, and suppresses formation of non-native disulfide bonds by hindering aggregation and thus allowing interaction of protein moieties of folding glycoproteins with classical chaperones and other proteins that assist in folding.
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Affiliation(s)
- A J Parodi
- Instituto de Investigaciones Bioquímicas Fundación Campomar, Antonio Machado 151, 1405 Buenos Aires, Argentina.
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30
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Ho SC, Chaudhuri S, Bachhawat A, McDonald K, Pillai S. Accelerated proteasomal degradation of membrane Ig heavy chains. JOURNAL OF IMMUNOLOGY (BALTIMORE, MD. : 1950) 2000; 164:4713-9. [PMID: 10779777 DOI: 10.4049/jimmunol.164.9.4713] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Membrane IgG H chains turn over considerably more rapidly than secretory Ig H chains in the 18-81 A2 pre-B cell line. This rapid degradation occurs in proteasomes. N-Glycosylated membrane Ig H chains accumulate in the endoplasmic reticulum in the presence of proteasomal inhibitors, suggesting that retrotranslocation and proteasomal degradation of membrane Ig H chains may be closely coupled processes. Accelerated proteasomal degradation of membrane Ig H chains was also observed in transfected nonlymphoid cells. At steady state, the membrane form of the H chain associates more readily with Bip and calnexin than its secretory counterpart. The preferential recognition of membrane, as opposed to secretory, Ig H chains by some endoplasmic reticulum chaperones, may provide an explanation for the accelerated proteasomal degradation of the former.
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Affiliation(s)
- S C Ho
- Massachusetts General Hospital Cancer Center and Harvard Medical School, Boston, MA 02129, USA
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31
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Danilczyk UG, Cohen-Doyle MF, Williams DB. Functional relationship between calreticulin, calnexin, and the endoplasmic reticulum luminal domain of calnexin. J Biol Chem 2000; 275:13089-97. [PMID: 10777614 DOI: 10.1074/jbc.275.17.13089] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Calnexin is a membrane protein of the endoplasmic reticulum (ER) that functions as a molecular chaperone and as a component of the ER quality control machinery. Calreticulin, a soluble analog of calnexin, is thought to possess similar functions, but these have not been directly demonstrated in vivo. Both proteins contain a lectin site that directs their association with newly synthesized glycoproteins. Although many glycoproteins bind to both calnexin and calreticulin, there are differences in the spectrum of glycoproteins that each binds. Using a Drosophila expression system and the mouse class I histocompatibility molecule as a model glycoprotein, we found that calreticulin does possess apparent chaperone and quality control functions, enhancing class I folding and subunit assembly, stabilizing subunits, and impeding export of assembly intermediates from the ER. Indeed, the functions of calnexin and calreticulin were largely interchangeable. We also determined that a soluble form of calnexin (residues 1-387) can functionally replace its membrane-bound counterpart. However, when calnexin was expressed as a soluble protein in L cells, the pattern of associated glycoproteins changed to resemble that of calreticulin. Conversely, membrane-anchored calreticulin bound to a similar set of glycoproteins as calnexin. Therefore, the different topological environments of calnexin and calreticulin are important in determining their distinct substrate specificities.
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Affiliation(s)
- U G Danilczyk
- Department of Immunology, University of Toronto, Toronto, Ontario, Canada M5S 1A8
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32
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Ehtesham NZ, Phan TN, Gaikwad A, Sopory SK, Tuteja N. Calnexin from Pisum sativum: cloning of the cDNA and characterization of the encoded protein. DNA Cell Biol 1999; 18:853-62. [PMID: 10595399 DOI: 10.1089/104454999314854] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
A full-length cDNA of 1951 bp encoding a calnexin (CNX) protein was cloned from a Pisum sativum expression library. The open reading frame (ORF) within this cDNA encodes a 551-amino acid protein with a calculated molecular mass of 62.47 kDa that exhibits extensive homology with the CNX proteins from soybean (80%), Arabidopsis thaliana (70%), maize (70%), and dog (39%). The characteristic CNX signature motifs, KPEDWDE and GXW, generally found in molecular chaperones, are present in pea CNX (PsCNX), along with putative sites for Ca2+ binding and phosphorylation. In PsCNX, a signal sequence and a single transmembrane domain are also present at the N- and C-terminal ends, respectively. The PsCNX protein is expressed constitutively at the RNA level in vegetative and flowering tissues, as was evident from Northern analysis. Expression of PsCNX was light independent. In vitro translation of PsCNX cDNA yielded a 75-kDa precursor, which, in the presence of canine microsomal membranes, was cotranslationally processed into a 72.5-kDa product and was imported and localized to the endoplasmic reticulum. Trypsin treatment of the in vitro translated PsCNX in the presence of canine microsomes generated a further processed 67-kDa intraluminal form. The results with PsCNX also showed that the plant protein is a phosphoprotein containing phosphoserine residues, as evidenced by immunoprecipitation of PsCNX with anti-phosphoserine antibody. The PsCNX protein was also phosphorylated by endogenous kinases of pea microsomes.
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Affiliation(s)
- N Z Ehtesham
- Plant Molecular Biology, International Center for Genetic Engineering and Biotechnology, New Delhi, India
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33
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Ihara Y, Cohen-Doyle MF, Saito Y, Williams DB. Calnexin discriminates between protein conformational states and functions as a molecular chaperone in vitro. Mol Cell 1999; 4:331-41. [PMID: 10518214 DOI: 10.1016/s1097-2765(00)80335-4] [Citation(s) in RCA: 132] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
Although calnexin is thought to function as a molecular chaperone for glycoproteins, a prevalent view is that it cannot distinguish between protein conformational states, binding solely through its lectin site to monoglucosylated oligosaccharides. Using purified components in vitro, calnexin effectively prevented the aggregation not only of glycoproteins bearing monoglucosylated oligosaccharides but also proteins lacking N-glycans, an effect enhanced by ATP. It also suppressed the thermal denaturation of nonglycosylated proteins and enhanced their refolding in conjunction with other cellular components. Calnexin formed stable complexes with unfolded conformers of these proteins but not with the native molecules. Therefore, in addition to being a lectin, calnexin functions as a bona fide molecular chaperone capable of interacting with polypeptide segments of folding glycoproteins.
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Affiliation(s)
- Y Ihara
- Department of Biochemistry, University of Toronto, Ontario, Canada
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34
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Ashman JB, Miller J. A Role for the Transmembrane Domain in the Trimerization of the MHC Class II-Associated Invariant Chain. THE JOURNAL OF IMMUNOLOGY 1999. [DOI: 10.4049/jimmunol.163.5.2704] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Abstract
MHC class II and invariant chain (Ii) associate early in biosynthesis to form a nonameric complex. Ii first assembles into a trimer and then associates with three class II αβ heterodimers. Although the membrane-proximal region of the Ii luminal domain is structurally disordered, the C-terminal segment of the luminal domain is largely α-helical and contains a major interaction site for the Ii trimer. In this study, we show that the Ii transmembrane domain plays an important role in the formation of Ii trimers. The Ii transmembrane domain contains an unusual patch of hydrophilic residues near the luminal interface. Substitution of these polar residues with nonpolar amino acids resulted in a decrease in the efficiency of Ii trimerization and subsequent class II association. Moreover, N-terminal fragments of Ii were found to trimerize independently of the luminal α-helical domain. Progressive C-terminal truncations mapped a homotypic association site to the first 80 aa of Ii. Together, these results implicate the Ii transmembrane domain as a site of trimer interaction that can play an important role in the initiation of trimer formation.
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Affiliation(s)
| | - Jim Miller
- *Committee on Immunology and
- †Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637
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35
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Zapun A, Jakob CA, Thomas DY, Bergeron JJ. Protein folding in a specialized compartment: the endoplasmic reticulum. Structure 1999; 7:R173-82. [PMID: 10467145 DOI: 10.1016/s0969-2126(99)80112-9] [Citation(s) in RCA: 66] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
The endoplasmic reticulum ensures proper folding of secretory proteins. In this review, we summarize and discuss the functions of different classes of folding mediators in the secretory pathway and propose updated models of the quality control system.
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Affiliation(s)
- A Zapun
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
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36
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Oliver JD, Roderick HL, Llewellyn DH, High S. ERp57 functions as a subunit of specific complexes formed with the ER lectins calreticulin and calnexin. Mol Biol Cell 1999; 10:2573-82. [PMID: 10436013 PMCID: PMC25489 DOI: 10.1091/mbc.10.8.2573] [Citation(s) in RCA: 243] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
ERp57 is a lumenal protein of the endoplasmic reticulum (ER) and a member of the protein disulfide isomerase (PDI) family. In contrast to archetypal PDI, ERp57 interacts specifically with newly synthesized glycoproteins. In this study we demonstrate that ERp57 forms discrete complexes with the ER lectins, calnexin and calreticulin. Specific ERp57/calreticulin complexes exist in canine pancreatic microsomes, as demonstrated by SDS-PAGE after cross-linking, and by native electrophoresis in the absence of cross-linking. After in vitro translation and import into microsomes, radiolabeled ERp57 can be cross-linked to endogenous calreticulin and calnexin while radiolabeled PDI cannot. Likewise, radiolabeled calreticulin is cross-linked to endogenous ERp57 but not PDI. Similar results were obtained in Lec23 cells, which lack the glucosidase I necessary to produce glycoprotein substrates capable of binding to calnexin and calreticulin. This observation indicates that ERp57 interacts with both of the ER lectins in the absence of their glycoprotein substrate. This result was confirmed by a specific interaction between in vitro synthesized calreticulin and ERp57 prepared in solution in the absence of other ER components. We conclude that ERp57 forms complexes with both calnexin and calreticulin and propose that it is these complexes that can specifically modulate glycoprotein folding within the ER lumen.
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Affiliation(s)
- J D Oliver
- School of Biological Sciences, University of Manchester, Manchester, M13 9PT, United Kingdom
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37
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Popov M, Reithmeier RA. Calnexin interaction with N-glycosylation mutants of a polytopic membrane glycoprotein, the human erythrocyte anion exchanger 1 (band 3). J Biol Chem 1999; 274:17635-42. [PMID: 10364201 DOI: 10.1074/jbc.274.25.17635] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The interaction of the endoplasmic reticulum chaperone calnexin with N-glycosylation mutants of a polytopic membrane glycoprotein, the human erythrocyte anion exchanger (AE1), was characterized by cell-free translation and in transfected HEK293 cells, followed by co-immunoprecipitation using anti-calnexin antibody. AE1 contains 12-14 transmembrane segments and has a single site of N-glycosylation at Asn-642 in the fourth extracytosolic loop. This site was mutated (N642D) to create a nonglycosylated protein. Calnexin showed a preferential interaction with N-glycosylated AE1 relative to nonglycosylated AE1 both in vitro and in vivo. This interaction could be blocked by inhibition of glucosidases I and II with castanospermine. Calnexin had access to novel N-glycosylated sites created in other extracytosolic loops in AE1 by site-directed or insertional mutagenesis. The interaction with AE1 was enhanced when multiple sites were introduced into the same loop or into two different loops. An association of calnexin with truncated versions of N-glycosylated AE1 was detected after release of the nascent chains from ribosomes with puromycin. The results show that the interaction of calnexin with the polytopic membrane glycoprotein AE1 was dependent on the presence but not the location of the oligosaccharide. Furthermore, calnexin was associated with AE1 after release of AE1 from the translocation machinery.
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Affiliation(s)
- M Popov
- Medical Research Council Group in Membrane Biology, Departments of Medicine and Biochemistry, University of Toronto, Ontario M5S 1A8, Canada
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38
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Labriola C, Cazzulo JJ, Parodi AJ. Trypanosoma cruzi calreticulin is a lectin that binds monoglucosylated oligosaccharides but not protein moieties of glycoproteins. Mol Biol Cell 1999; 10:1381-94. [PMID: 10233151 PMCID: PMC25283 DOI: 10.1091/mbc.10.5.1381] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Trypanosoma cruzi is a protozoan parasite that belongs to an early branch in evolution. Although it lacks several features of the pathway of protein N-glycosylation and oligosaccharide processing present in the endoplasmic reticulum of higher eukaryotes, it displays UDP-Glc:glycoprotein glucosyltransferase and glucosidase II activities. It is herewith reported that this protozoan also expresses a calreticulin-like molecule, the third component of the quality control of glycoprotein folding. No calnexin-encoding gene was detected. Recombinant T. cruzi calreticulin specifically recognized free monoglucosylated high-mannose-type oligosaccharides. Addition of anti-calreticulin serum to extracts obtained from cells pulse-chased with [35S]Met plus [35S]Cys immunoprecipitated two proteins that were identified as calreticulin and the lysosomal proteinase cruzipain (a major soluble glycoprotein). The latter but not the former protein disappeared from immunoprecipitates upon chasing cells. Contrary to what happens in mammalian cells, addition of the glucosidase II inhibitor 1-deoxynojirimycin promoted calreticulin-cruzipain interaction. This result is consistent with the known pathway of protein N-glycosylation and oligosaccharide processing occurring in T. cruzi. A treatment of the calreticulin-cruzipain complexes with endo-beta-N-acetylglucosaminidase H either before or after addition of anti-calreticulin serum completely disrupted calreticulin-cruzipain interaction. In addition, mature monoglucosylated but not unglucosylated cruzipain isolated from lysosomes was found to interact with recombinant calreticulin. It was concluded that the quality control of glycoprotein folding appeared early in evolution, and that T. cruzi calreticulin binds monoglucosylated oligosaccharides but not the protein moiety of cruzipain. Furthermore, evidence is presented indicating that glucosyltransferase glucosylated cruzipain at its last folding stages.
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Affiliation(s)
- C Labriola
- Instituto de Investigaciones Bioquímicas Fundación Campomar, 1405 Buenos Aires, Argentina
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39
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Jannatipour M, Callejo M, Parodi AJ, Armstrong J, Rokeach LA. Calnexin and BiP interact with acid phosphatase independently of glucose trimming and reglucosylation in Schizosaccharomyces pombe. Biochemistry 1998; 37:17253-61. [PMID: 9860839 DOI: 10.1021/bi981785c] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The association of newly synthesized glycoproteins with the ER molecular chaperones calnexin and immunoglobulin binding protein (BiP) has been well documented in a variety of higher eukaryotes. Here we report that Cnx1p, the calnexin homologue in Schizosaccharomyces pombe, associates with newly synthesized molecules of the secreted glycoprotein acid phosphatase. Unlike ligand binding to mammalian calnexin, glucose trimming and reglucosylation of acid phosphatase by UDP-Glc:glycoprotein glucosyltransferase were shown to be dispensable for its binding to Cnx1p. Thus, despite the essentiality of Cnx1p for S. pombe viability, the glucose trimming and reglucosylation cycle does not appear to be required for protein folding in the fission yeast. The association of core-glycosylated acid phosphatase with Cnx1p after exposure of cells to heat shock or to DTT was shown to be reversible. However, Cnx1p stably associated with unglycosylated acid phosphatase after treatment with the core-glycosylation inhibitor tunicamycin. BiP was found to coprecipitate with Cnx1p, under normal and stress conditions, and following inhibition of protein synthesis by cycloheximide. We postulate that Cnx1p and BiP are part of a complex that is involved in the folding of both core-glycosylated trimmed ligands and unglycosylated proteins.
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Affiliation(s)
- M Jannatipour
- Département de biochimie, Université de Montréal, Québec, Canada
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40
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Ohsako S, Janulis L, Hayashi Y, Bunick D. Characterization of domains in mice of calnexin-t, a putative molecular chaperone required in sperm fertility, with use of glutathione S-transferase-fusion proteins. Biol Reprod 1998; 59:1214-23. [PMID: 9780330 DOI: 10.1095/biolreprod59.5.1214] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
Calnexin-t (calmegin) is a male germ cell-specific variant of calnexin, a membrane bound-molecular chaperone in the endoplasmic reticulum (ER). Although it is temporally expressed during spermatogenesis, it has recently been shown to be highly involved in sperm fertility. To investigate the biochemical states of calnexin-t during spermatogenesis, we produced a series of glutathione S-transferase-fusion proteins with several specific coding domains of calnexin-t. Immunostaining and 45Ca2+ overlay assays clearly showed that the internal proline-rich repeat region has Ca2+-binding ability and contains an epitope recognized by monoclonal antibody 1C9. Western blot analysis of protein extracts from the testes of 10-, 18-, 26-, and 60-day-old mice revealed only a single 101-kDa protein during testicular development by 1C9. Anti-C, a cytoplasmic domain-specific antibody generated by immunization with recombinant protein, produced the same results, indicating that the 101-kDa form of calnexin-t is prevalent at all stages of spermatogenesis expressing calnexin-t. In paraffin sections of mouse testis, Anti-C stained spermatocytes and spermatids intensely, whereas 1C9 stained spermatocytes only slightly but spermatids intensely, suggesting that the affinity of 1C9 for its epitope is lower in pachytene spermatocytes than in spermatids. Acid phosphatase treatment of the 101-kDa form generated a 93-kDa band that in turn could be recovered to the 101-kDa form by incubation with HeLa cell S100 fraction, indicating that the 101-kDa form is a phosphorylated type of calnexin-t. The sites of phosphorylation were shown to be restricted to the cytoplasmic domain. Our results suggest that the structure of the ER luminal domain of calnexin-t is likely to differ in middle pachytene versus haploid germ cell phases. In addition, the cytoplasmic domain of calnexin-t was shown to be highly phosphorylated immediately after protein synthesis and constitutively phosphorylated during spermatogenesis.
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Affiliation(s)
- S Ohsako
- Department of Veterinary Biosciences, University of Illinois, Urbana, Illinois 61802, USA
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41
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Arunachalam B, Pan M, Cresswell P. Intracellular Formation and Cell Surface Expression of a Complex of an Intact Lysosomal Protein and MHC Class II Molecules. THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.160.12.5797] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
The generation of invariant chain-free MHC class II molecules and their association with endocytically generated peptides are thought to occur in specialized lysosome-like compartments called MIICs (MHC class II compartments). A number of in vitro studies have shown that large denatured proteins can bind to class II molecules, and that class II association can protect the bound segment of protein from proteolytic degradation. In this work, we present what we believe is the first example of an intact endogenous protein (IP30) binding in an allele-dependent fashion to class II molecules in vivo. IP30 is an IFN-γ-inducible 35-kDa glycoprotein that localizes in MIICs. In this study, we show that intact IP30 binds to certain HLA-DR alleles via an N-terminal prosequence. The association takes place in the endocytic pathway following removal of invariant chain from class II molecules and before their cell surface expression. We also show that DR-IP30 complexes are SDS stable. The potential precursor-product relationship between DR-IP30 complexes and the DR-peptide complex is discussed.
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Affiliation(s)
| | - Mary Pan
- †Howard Hughes Medical Institute, Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06510
| | - Peter Cresswell
- †Howard Hughes Medical Institute, Section of Immunobiology, Yale University School of Medicine, New Haven, CT 06510
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42
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Guerra CB, Busch R, Doebele RC, Liu W, Sawada T, Kwok WW, Chang MDY, Mellins ED. Novel Glycosylation of HLA-DRα Disrupts Antigen Presentation Without Altering Endosomal Localization. THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.160.9.4289] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
The HLA-DR hemizygous B lymphoblastoid cell line, 10.24.6, has a DRA mutation (Pro96→Ser) that creates a novel glycosylation site at Asn94. The mutant DR molecules are primarily associated with nested fragments of invariant chain (class II-associated invariant chain peptides), and their interaction with HLA-DM is impaired. Here we further analyzed the defect in 10.24.6 cells. Expressing Ser96 mutant DRA cDNA in DRA-null cells recapitulated the 10.24.6 phenotype, indicating that the mutation causes the Ag presentation defect. A mutation to Ala96α, which does not introduce an extra glycan, generated a normal phenotype; the critical role of the glycan was further supported by experiments in which N-glycosylation was blocked by tunicamycin. We also evaluated whether the 10.24.6 mutation affected DR3 maturation or trafficking. Metabolic labeling and subcellular fractionation showed that assembly, endosomal transport, and invariant chain proteolysis of mutant DR3 molecules were similar to wild-type. A slight delay in export from the endoplasmic reticulum to the Golgi apparatus in 10.24.6 cells probably did not contribute significantly to the Ag presentation defect, because the abundance of DM and mutant DR in peptide-loading compartments was normal at steady state. Our results indicate that proper localization of these molecules does not depend on their interaction.
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Affiliation(s)
- Carolyn B. Guerra
- *School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
| | - Robert Busch
- †Department of Pediatrics, Stanford University Medical Center, Stanford, CA 94305
| | - Robert C. Doebele
- *School of Medicine, University of Pennsylvania, Philadelphia, PA 19104
- †Department of Pediatrics, Stanford University Medical Center, Stanford, CA 94305
| | - Wendy Liu
- †Department of Pediatrics, Stanford University Medical Center, Stanford, CA 94305
| | - Tetsuji Sawada
- ‡Department of Medicine, North Shore University Hospital-New York University School of Medicine, Manhasset, NY 11030; and
| | | | - Ming-der Y. Chang
- ‡Department of Medicine, North Shore University Hospital-New York University School of Medicine, Manhasset, NY 11030; and
| | - Elizabeth D. Mellins
- †Department of Pediatrics, Stanford University Medical Center, Stanford, CA 94305
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43
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Nordeng TW, Gorvel JP, Bakke O. Intracellular transport of molecules engaged in the presentation of exogenous antigens. Curr Top Microbiol Immunol 1998; 232:179-215. [PMID: 9557399 DOI: 10.1007/978-3-642-72045-1_9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- T W Nordeng
- Department of Biology, University of Oslo, Norway
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44
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Pipe SW, Morris JA, Shah J, Kaufman RJ. Differential interaction of coagulation factor VIII and factor V with protein chaperones calnexin and calreticulin. J Biol Chem 1998; 273:8537-44. [PMID: 9525969 DOI: 10.1074/jbc.273.14.8537] [Citation(s) in RCA: 114] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Factor VIII (FVIII) and factor V (FV) are homologous coagulation cofactors sharing a similar domain organization (A1-A2-B-A3-C1-C2) and are both extensively glycosylated within their B-domains. In mammalian cell expression systems, compared with FV, the FVIII primary translation product is inefficiently transported out of the endoplasmic reticulum. Here we show that FVIII is degraded within the cell by a lactacystin-inhibitable pathway, implicating the cytosolic 20 S proteasome machinery. Protein chaperones calnexin (CNX) and calreticulin (CRT) preferentially interact with glycoproteins containing monoglucosylated N-linked oligosaccharides and are proposed to traffic proteins through degradative and/or secretory pathways. Utilizing co-immunoprecipitation assays, intracellular FVIII was detected in association with CNX maximally within 30 min to 1 h following synthesis, whereas FV could not be detected in association with CNX. In contrast, both FVIII and FV displayed interaction with CRT during transit through the secretory pathway. B-domain deleted FVIII significantly reduced the CNX and CRT interaction, indicating the B-domain may represent a primary CNX and CRT interaction site. In the presence of inhibitors of glucose trimming, the interactions of FVIII with CNX, and of FVIII and FV with CRT, were significantly reduced whereas the secretion of FVIII, and not FV, was inhibited. In addition, transfection in a glucosidase I-deficient Chinese hamster ovary cell line (Lec23) demonstrated that both degradation and secretion of FVIII were inhibited, with little effect on the secretion of FV. These results support that CNX and CRT binding, mediated at least in part by the B-domain of FVIII, is required for efficient FVIII degradation and secretion. In contrast, FV does not require CNX interaction for efficient secretion. The results suggest a unique requirement for carbohydrate processing and molecular chaperone interactions that may limit the productive secretion of FVIII.
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Affiliation(s)
- S W Pipe
- Department of Pediatrics, The University of Michigan Medical Center, Ann Arbor, Michigan 48109, USA
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45
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Bikoff EK, Kenty G, Van Kaer L. Distinct Peptide Loading Pathways for MHC Class II Molecules Associated with Alternative Ii Chain Isoforms. THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.160.7.3101] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
Mutant mouse strains expressing either p31 or p41 Ii chain appear equally competent with respect to their class II functional activities including Ag presentation and CD4+ T cell development. To further explore possibly divergent roles provided by alternative Ii chain isoforms, we compare class II structure and function in double mutants also carrying a null allele at the H2-DM locus. As for DM mutants expressing wild-type Ii chain, AαbAβb dimers present in DM-deficient mice expressing either Ii chain isoform appear equally occupied by class II-associated Ii chain-derived peptides (CLIP). Surprisingly, in functional assays, these novel mouse strains exhibit strikingly different phenotypes. Thus, DM-deficient mice expressing wild-type Ii chain or p31 alone are both severely compromised in their abilities to present peptides. In contrast, double mutants expressing the p41 isoform display markedly enhanced peptide-loading capabilities, approaching those observed for wild-type mice. The present data strengthen evidence for divergent class II presentation pathways and demonstrate for the first time that functionally distinct roles are mediated by alternatively spliced forms of the MHC class II-associated Ii chain in a physiologic setting.
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Affiliation(s)
- Elizabeth K. Bikoff
- *Department of Molecular and Cellular Biology, The Biological Laboratories, Harvard University, Cambridge, MA 02138; and
| | - George Kenty
- *Department of Molecular and Cellular Biology, The Biological Laboratories, Harvard University, Cambridge, MA 02138; and
| | - Luc Van Kaer
- †Howard Hughes Medical Institute, Department of Microbiology and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232
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46
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Vassilakos A, Michalak M, Lehrman MA, Williams DB. Oligosaccharide binding characteristics of the molecular chaperones calnexin and calreticulin. Biochemistry 1998; 37:3480-90. [PMID: 9521669 DOI: 10.1021/bi972465g] [Citation(s) in RCA: 202] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Calnexin and calreticulin are homologous molecular chaperones of the endoplasmic reticulum. Their binding to newly synthesized glycoproteins is mediated, at least in part, by a lectin site that recognizes the early N-linked oligosaccharide processing intermediate, Glc1Man9GlcNAc2. We compared the oligosaccharide binding specificities of calnexin and calreticulin in an effort to determine the basis for reported differences in their association with various glycoproteins. Using mono-, di-, and oligosaccharides to inhibit the binding of Glc1Man9GlcNAc2 to calreticulin and to a truncated, soluble form of calnexin, we show that the entire Glc alpha 1-3Man alpha 1-2Man alpha 1-2Man structure, extending from the alpha 1-3 branch point of the oligosaccharide core, is recognized by both proteins. Furthermore, analysis of the binding of monoglucosylated oligosaccharides containing progressively fewer mannose residues suggests that for both proteins the alpha 1-6 mannose branch point of the oligosaccharide core is also essential for recognition. Consistent with their essentially identical substrate specificities, calnexin and calreticulin exhibited the same relative affinities when competing for binding to the Glc1Man9GlcNAc2 oligosaccharide. Thus, differential glycoprotein binding cannot be attributed to differences in the lectin specificities or binding affinities of calnexin and calreticulin. We also examined the effects of ATP, calcium, and disulfide reduction on the lectin properties of calnexin and calreticulin. Whereas oligosaccharide binding was only slightly enhanced for both proteins in the presence of high concentrations of a number of adenosine nucleotides, removal of bound calcium abrogated oligosaccharide binding, an effect that was largely reversible upon readdition of calcium. Disulfide reduction had no effect on oligosaccharide binding by calnexin, but binding by calreticulin was inhibited by 70%. Finally, deletion mutagenesis of calnexin and calreticulin identified a central proline-rich region characterized by two tandem repeat motifs as a segment capable of binding oligosaccharide. This segment bears no sequence homology to the carbohydrate recognition domains of other lectins.
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Affiliation(s)
- A Vassilakos
- Department of Biochemistry, University of Toronto, Ontario, Canada
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47
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McGinnes LW, Morrison TG. Role of carbohydrate processing and calnexin binding in the folding and activity of the HN protein of Newcastle disease virus. Virus Res 1998; 53:175-85. [PMID: 9620209 DOI: 10.1016/s0168-1702(97)00144-5] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The role of carbohydrate processing and calnexin binding in the folding pathway and activity of the hemagglutinin-neuraminidase (HN) protein of Newcastle disease virus (NDV) was explored in infected cells using the inhibitor castanospermine (CST). Calnexin-HN protein complexes were demonstrated by coimmunoprecipitation using antibody specific for calnexin or HN protein. As in other systems, this complex was not detected in CST treated cells. In cells incubated in CST, the synthesis and stability of the HN protein was unaffected. However, as monitored by the appearance of conformationally sensitive antigenic sites, the folding of the HN protein in CST treated cells was approximately twice as slow than in untreated cells. This folding was ultimately efficient since there was no evidence for significant amounts of irreversibly aggregated forms which never acquired a mature conformation. Most significantly, the folding sequence as measured by the order of appearance of conformationally sensitive antigenic sites (McGinnes and Morrison, Virology 199, 255) was unaffected by CST. Thus while calnexin functions to speed the folding of the HN protein, it is not required for the folding of this protein. In addition, the protein synthesized in the presence of CST had significant levels of neuraminidase and hemagglutination activity suggesting that processing of the carbohydrate has a minimal role in the activity of the protein.
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Affiliation(s)
- L W McGinnes
- Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester 01655, USA
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Zhang Q, Salter RD. Distinct Patterns of Folding and Interactions with Calnexin and Calreticulin in Human Class I MHC Proteins with Altered N-Glycosylation. THE JOURNAL OF IMMUNOLOGY 1998. [DOI: 10.4049/jimmunol.160.2.831] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Abstract
Calnexin is a lectin-like chaperone that binds to class I MHC molecules soon after their synthesis, retaining unassembled heavy chains and also assisting their folding. Following association with β2-microglobulin (β2m) in the endoplasmic reticulum, a large proportion of human class I molecules release from calnexin, whereas mouse class I molecules do not. We asked whether addition of a second N-glycan to the human class I molecule A*0201 at position 176, a site present in mouse, would affect its binding to calnexin. The 176dg mutant with N-glycans at positions 86 and 176, when transfected into CIR cells, demonstrated increased binding to calnexin, detectable both before and after association with β2m, and reduced interaction with calreticulin and TAP relative to wild-type protein bearing a single N-glycan at position 86. Cell surface levels of the mutant were decreased only slightly relative to the wild type, suggesting that the protein is not misfolded or grossly altered structurally. A subpopulation of mutant molecules was retained in the endoplasmic reticulum, and surprisingly, these molecules reacted with w6/32, which recognizes an epitope present on transport-competent class I HLA complexes. Transfection into Daudi cells demonstrated that 176dg reacts with w6/32 in the absence of β2m, suggesting that the Ab epitope can be induced by binding of calnexin. These data may explain previously noted differences between mouse and human class I MHC proteins and demonstrate that the location of N-oligosaccharides within proteins can influence their folding and interactions with chaperones such as calnexin and calreticulin.
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Affiliation(s)
- Qing Zhang
- Department of Pathology and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
| | - Russell D. Salter
- Department of Pathology and University of Pittsburgh Cancer Institute, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213
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Hebert DN, Zhang JX, Chen W, Foellmer B, Helenius A. The number and location of glycans on influenza hemagglutinin determine folding and association with calnexin and calreticulin. J Cell Biol 1997; 139:613-23. [PMID: 9348279 PMCID: PMC2141715 DOI: 10.1083/jcb.139.3.613] [Citation(s) in RCA: 202] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Calnexin and calreticulin are homologous molecular chaperones that promote proper folding, oligomeric assembly, and quality control of newly synthesized glycoproteins in the endoplasmic reticulum (ER). Both are lectins that bind to substrate glycoproteins that have monoglucosylated N-linked oligosaccharides. Their binding to newly translated influenza virus hemagglutinin (HA), and various mutants thereof, was analyzed in microsomes after in vitro translation and expression in live CHO cells. A large fraction of the HA molecules was found to occur in ternary HA- calnexin-calreticulin complexes. In contrast to calnexin, calreticulin was found to bind primarily to early folding intermediates. Analysis of HA mutants with different numbers and locations of N-linked glycans showed that although the two chaperones share the same carbohydrate specificity, they display distinct binding properties; calreticulin binding depends on the oligosaccharides in the more rapidly folding top/hinge domain of HA whereas calnexin is less discriminating. Calnexin's binding was reduced if the HA was expressed as a soluble anchor-free protein rather than membrane bound. When the co- and posttranslational folding and trimerization of glycosylation mutants was analyzed, it was observed that removal of stem domain glycans caused accelerated folding whereas removal of the top domain glycans (especially the oligosaccharide attached to Asn81) inhibited folding. In summary, the data established that individual N-linked glycans in HA have distinct roles in calnexin/calreticulin binding and in co- and posttranslational folding.
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Affiliation(s)
- D N Hebert
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut 06520-8002, USA
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Wada I, Kai M, Imai S, Sakane F, Kanoh H. Promotion of transferrin folding by cyclic interactions with calnexin and calreticulin. EMBO J 1997; 16:5420-32. [PMID: 9312001 PMCID: PMC1170173 DOI: 10.1093/emboj/16.17.5420] [Citation(s) in RCA: 69] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Calnexin, an abundant membrane protein, and its lumenal homolog calreticulin interact with nascent proteins in the endoplasmic reticulum. Because they have an affinity for monoglucosylated N-linked oligosaccharides which can be regenerated from the aglucosylated sugar, it has been speculated that this repeated oligosaccharide binding may play a role in nascent chain folding. To investigate the process, we have developed a novel assay system using microsomes freshly prepared from pulse labeled HepG2 cells. Unlike the previously described oxidative folding systems which required rabbit reticulocyte lysates, the oxidative folding of transferrin in isolated microsomes could be carried out in a defined solution. In this system, addition of a glucose donor, UDP-glucose, to the microsomes triggered glucosylation of transferrin and resulted in its cyclic interaction with calnexin and calreticulin. When the folding of transferrin in microsomes was analyzed, UDP-glucose enhanced the amount of folded transferrin and reduced the disulfide-linked aggregates. Analysis of transferrin folding in briefly heat-treated microsomes revealed that UDP-glucose was also effective in elimination of heat-induced misfolding. Incubation of the microsomes with an alpha-glucosidase inhibitor, castanospermine, prolonged the association of transferrin with the chaperones and prevented completion of folding and, importantly, aggregate formation, particularly in the calnexin complex. Accordingly, we demonstrate that repeated binding of the chaperones to the glucose of the transferrin sugar moiety prevents and corrects misfolding of the protein.
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Affiliation(s)
- I Wada
- Department of Biochemistry, Sapporo Medical University School of Medicine, South-1, West-17, Sapporo 060, Japan
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