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Cabana VC, Bouchard AY, Sénécal AM, Ghilarducci K, Kourrich S, Cappadocia L, Lussier MP. RNF13 Dileucine Motif Variants L311S and L312P Interfere with Endosomal Localization and AP-3 Complex Association. Cells 2021; 10:cells10113063. [PMID: 34831286 PMCID: PMC8620429 DOI: 10.3390/cells10113063] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2021] [Revised: 11/03/2021] [Accepted: 11/04/2021] [Indexed: 12/24/2022] Open
Abstract
Developmental and epileptic encephalopathies (DEE) are rare and serious neurological disorders characterized by severe epilepsy with refractory seizures and a significant developmental delay. Recently, DEE73 was linked to genetic alterations of the RNF13 gene, which convert positions 311 or 312 in the RNF13 protein from leucine to serine or proline, respectively (L311S and L312P). Using a fluorescence microscopy approach to investigate the molecular and cellular mechanisms affected by RNF13 protein variants, the current study shows that wild-type RNF13 localizes extensively with endosomes and lysosomes, while L311S and L312P do not extensively colocalize with the lysosomal marker Lamp1. Our results show that RNF13 L311S and L312P proteins affect the size of endosomal vesicles along with the temporal and spatial progression of fluorescently labeled epidermal growth factor, but not transferrin, in the endolysosomal system. Furthermore, GST-pulldown and co-immunoprecipitation show that RNF13 variants disrupt association with AP-3 complex. Knockdown of AP-3 complex subunit AP3D1 alters the lysosomal localization of wild-type RNF13 and similarly affects the size of endosomal vesicles. Importantly, our study provides a first step toward understanding the cellular and molecular mechanism altered by DEE73-associated genetic variations of RNF13.
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Affiliation(s)
- Valérie C. Cabana
- Département de Chimie, Université du Québec à Montréal, Montréal, QC H2X 2J6, Canada; (V.C.C.); (A.Y.B.); (A.M.S.); (K.G.); (L.C.)
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
| | - Antoine Y. Bouchard
- Département de Chimie, Université du Québec à Montréal, Montréal, QC H2X 2J6, Canada; (V.C.C.); (A.Y.B.); (A.M.S.); (K.G.); (L.C.)
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
| | - Audrey M. Sénécal
- Département de Chimie, Université du Québec à Montréal, Montréal, QC H2X 2J6, Canada; (V.C.C.); (A.Y.B.); (A.M.S.); (K.G.); (L.C.)
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
| | - Kim Ghilarducci
- Département de Chimie, Université du Québec à Montréal, Montréal, QC H2X 2J6, Canada; (V.C.C.); (A.Y.B.); (A.M.S.); (K.G.); (L.C.)
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
| | - Saïd Kourrich
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
- Département des Sciences Biologiques, Université du Québec à Montréal, Montréal, QC H2X 1Y4, Canada
- Department of Psychiatry, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA
| | - Laurent Cappadocia
- Département de Chimie, Université du Québec à Montréal, Montréal, QC H2X 2J6, Canada; (V.C.C.); (A.Y.B.); (A.M.S.); (K.G.); (L.C.)
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
| | - Marc P. Lussier
- Département de Chimie, Université du Québec à Montréal, Montréal, QC H2X 2J6, Canada; (V.C.C.); (A.Y.B.); (A.M.S.); (K.G.); (L.C.)
- Centre d’Excellence en Recherche sur les Maladies Orphelines—Fondation Courtois (CERMO-FC), Université du Québec à Montréal, Montréal, QC H2X 3Y7, Canada;
- Correspondence: ; Tel.: +1-(514)-987-3000 (ext. 5591); Fax: +1-(514)-987-4054
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Margiotta A, Frei DM, Sendstad IH, Janssen L, Neefjes J, Bakke O. Invariant chain regulates endosomal fusion and maturation through an interaction with the SNARE Vti1b. J Cell Sci 2020; 133:jcs244624. [PMID: 32907852 DOI: 10.1242/jcs.244624] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2020] [Accepted: 08/25/2020] [Indexed: 01/01/2023] Open
Abstract
The invariant chain (Ii, also known as CD74) is a multifunctional regulator of adaptive immune responses and is responsible for sorting major histocompatibility complex class I and class II (MHCI and MHCII, respectively) molecules, as well as other Ii-associated molecules, to a specific endosomal pathway. When Ii is expressed, endosomal maturation and proteolytic degradation of proteins are delayed and, in non-antigen presenting cells, the endosomal size increases, but the molecular mechanisms underlying this are not known. We identified that a SNARE, Vti1b, is essential for regulating these Ii-induced effects. Vti1b binds to Ii and is localized at the contact sites of fusing Ii-positive endosomes. Furthermore, truncated Ii lacking the cytoplasmic tail, which is not internalized from the plasma membrane, relocates Vti1b to the plasma membrane. Knockout of Ii in an antigen-presenting cell line was found to speed up endosomal maturation, whereas silencing of Vti1b inhibits the Ii-induced maturation delay. Our results suggest that Ii, by interacting with the SNARE Vti1b in antigen-presenting cells, directs specific Ii-associated SNARE-mediated fusion in the early part of the endosomal pathway that leads to a slower endosomal maturation for efficient antigen processing and MHC antigen loading.
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Affiliation(s)
- Azzurra Margiotta
- Department of Molecular Biosciences, University of Oslo, PB 1066, 0316 Oslo, Norway
| | - Dominik M Frei
- Department of Molecular Biosciences, University of Oslo, PB 1066, 0316 Oslo, Norway
| | | | - Lennert Janssen
- Department of Cell and Chemical Biology, Oncode Institute, Leiden University Medical Center LUMC, Leiden, The Netherlands
| | - Jacques Neefjes
- Department of Cell and Chemical Biology, Oncode Institute, Leiden University Medical Center LUMC, Leiden, The Netherlands
| | - Oddmund Bakke
- Department of Molecular Biosciences, University of Oslo, PB 1066, 0316 Oslo, Norway
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3
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Tohme M, Maisonneuve L, Achour K, Dussiot M, Maschalidi S, Manoury B. TLR7 trafficking and signaling in B cells is regulated by the MHCII-associated invariant chain. J Cell Sci 2020; 133:jcs.236711. [PMID: 32079661 DOI: 10.1242/jcs.236711] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2019] [Accepted: 02/04/2020] [Indexed: 11/20/2022] Open
Abstract
Toll-like receptor 7 (TLR7) is an endosomal receptor that recognizes single-stranded RNA from viruses. Its trafficking and activation is regulated by the endoplasmic reticulum (ER) chaperone UNC93B1 and lysosomal proteases. UNC93B1 also modulates major histocompatibility complex class II (MHCII) antigen presentation, and deficiency in MHCII protein diminishes TLR9 signaling. These results indicate a link between proteins that regulate both innate and adaptive responses. Here, we report that TLR7 resides in lysosomes and interacts with the MHCII-chaperone molecule, the invariant chain (Ii) or CD74, in B cells. In the absence of CD74, TLR7 displays both ER and lysosomal localization, leading to an increase in pro-inflammatory cytokine production. Furthermore, stimulation with TLR7 but not TLR9, is inefficient in boosting antigen presentation in Ii-deficient cells. In contrast, in B cells lacking TLR7 or mutated for UNC93B1, which are able to trigger TLR7 activation, antigen presentation is enhanced. This suggests that TLR7 signaling in B cells is controlled by the Ii chain.
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Affiliation(s)
- Mira Tohme
- Nkarta Therapeutics, South San Fransisco, CA 94080, USA
| | - Lucie Maisonneuve
- Institut Necker Enfant Malade, INSERM U1151-CNRS UMR 8253, 75015 Paris, France.,Université de Paris, Faculté de médecine, 75015 Paris, France
| | - Karim Achour
- Institut de recherche Servier, 3 rue de la république, 92150 Suresnes, France
| | - Michaël Dussiot
- Institut Imagine, INSERM U1163, CNRS ERL 8254, Université Paris Descartes, Sorbonne Paris-Cité, Laboratoire d'Excellence GR-Ex, 75015 Paris, France
| | - Sophia Maschalidi
- VIB-UGent Center for Inflammation Research, UGent-VIB Research Building FSVM, Technologiepark 71, 9052 Ghent, Belgium
| | - Bénédicte Manoury
- Institut Necker Enfant Malade, INSERM U1151-CNRS UMR 8253, 75015 Paris, France .,Université de Paris, Faculté de médecine, 75015 Paris, France
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Cargo Sorting at the trans-Golgi Network for Shunting into Specific Transport Routes: Role of Arf Small G Proteins and Adaptor Complexes. Cells 2019; 8:cells8060531. [PMID: 31163688 PMCID: PMC6627992 DOI: 10.3390/cells8060531] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2019] [Revised: 05/29/2019] [Accepted: 05/30/2019] [Indexed: 01/27/2023] Open
Abstract
The trans-Golgi network (TGN) is responsible for selectively recruiting newly synthesized cargo into transport carriers for delivery to their appropriate destination. In addition, the TGN is responsible for receiving and recycling cargo from endosomes. The membrane organization of the TGN facilitates the sorting of cargoes into distinct populations of transport vesicles. There have been significant advances in defining the molecular mechanism involved in the recognition of membrane cargoes for recruitment into different populations of transport carriers. This machinery includes cargo adaptors of the adaptor protein (AP) complex family, and monomeric Golgi-localized γ ear-containing Arf-binding protein (GGA) family, small G proteins, coat proteins, as well as accessory factors to promote budding and fission of transport vesicles. Here, we review this literature with a particular focus on the transport pathway(s) mediated by the individual cargo adaptors and the cargo motifs recognized by these adaptors. Defects in these cargo adaptors lead to a wide variety of diseases.
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5
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Fougeroux C, Turner L, Bojesen AM, Lavstsen T, Holst PJ. Modified MHC Class II-Associated Invariant Chain Induces Increased Antibody Responses against Plasmodium falciparum Antigens after Adenoviral Vaccination. THE JOURNAL OF IMMUNOLOGY 2019; 202:2320-2331. [PMID: 30833346 DOI: 10.4049/jimmunol.1801210] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Accepted: 02/01/2019] [Indexed: 01/04/2023]
Abstract
Adenoviral vectors can induce T and B cell immune responses to Ags encoded in the recombinant vector. The MHC class II invariant chain (Ii) has been used as an adjuvant to enhance T cell responses to tethered Ag encoded in adenoviral vectors. In this study, we modified the Ii adjuvant by insertion of a furin recognition site (Ii-fur) to obtain a secreted version of the Ii. To test the capacity of this adjuvant to enhance immune responses, we recombined vectors to encode Plasmodium falciparum virulence factors: two cysteine-rich interdomain regions (CIDR) α1 (IT4var19 and PFCLINvar30 var genes), expressed as a dimeric Ag. These domains are members of a highly polymorphic protein family involved in the vascular sequestration and immune evasion of parasites in malaria. The Ii-fur molecule directed secretion of both Ags in African green monkey cells and functioned as an adjuvant for MHC class I and II presentation in T cell hybridomas. In mice, the Ii-fur adjuvant induced a similar T cell response, as previously demonstrated with Ii, accelerated and enhanced the specific Ab response against both CIDR Ags, with an increased binding capacity to the cognate endothelial protein C receptor, and enhanced the breadth of the response toward different CIDRs. We also demonstrate that the endosomal sorting signal, secretion, and the C-terminal part of Ii were needed for the full adjuvant effect for Ab responses. We conclude that engineered secretion of Ii adjuvant-tethered Ags establishes a single adjuvant and delivery vehicle platform for potent T and B cell-dependent immunity.
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Affiliation(s)
- Cyrielle Fougeroux
- Center for Medical Parasitology, Department of International Health, Immunology and Microbiology, University of Copenhagen, 2200 Copenhagen, Denmark; and
| | - Louise Turner
- Center for Medical Parasitology, Department of International Health, Immunology and Microbiology, University of Copenhagen, 2200 Copenhagen, Denmark; and
| | - Anders Miki Bojesen
- Department of Veterinary and Animal Sciences, University of Copenhagen, 1870 Frederiksberg, Denmark
| | - Thomas Lavstsen
- Center for Medical Parasitology, Department of International Health, Immunology and Microbiology, University of Copenhagen, 2200 Copenhagen, Denmark; and
| | - Peter Johannes Holst
- Center for Medical Parasitology, Department of International Health, Immunology and Microbiology, University of Copenhagen, 2200 Copenhagen, Denmark; and
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Javitt A, Barnea E, Kramer MP, Wolf-Levy H, Levin Y, Admon A, Merbl Y. Pro-inflammatory Cytokines Alter the Immunopeptidome Landscape by Modulation of HLA-B Expression. Front Immunol 2019; 10:141. [PMID: 30833945 PMCID: PMC6387973 DOI: 10.3389/fimmu.2019.00141] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2018] [Accepted: 01/17/2019] [Indexed: 12/18/2022] Open
Abstract
Antigen presentation on HLA molecules is a major mechanism by which the immune system monitors self and non-self-recognition. Importantly, HLA-I presentation has gained much attention through its role in eliciting anti-tumor immunity. Several determinants controlling the peptides presented on HLA have been uncovered, mainly through the study of model substrates and large-scale immunopeptidome analyses. These determinants include the relative abundances of proteins in the cell, the stability or turnover rate of these proteins and the binding affinities of a given peptide to the HLA haplotypes found in a cell. However, the regulatory principles involved in selection and regulation of specific antigens in response to tumor pro-inflammatory signals remain largely unknown. Here, we chose to examine the effect that TNFα and IFNγ stimulation may exert on the immunopeptidome landscape of lung cancer cells. We show that the expression of many of the proteins involved in the class I antigen presentation pathway are changed by pro-inflammatory cytokines. Further, we could show that increased expression of the HLA-B allomorph drives a significant change in HLA-bound antigens, independently of the significant changes observed in the cellular proteome. Finally, we observed increased HLA-B levels in correlation with tumor infiltration across the TCGA lung cancer cohorts. Taken together, our results suggest that the immunopeptidome landscape should be examined in the context of anti-tumor immunity whereby signals in the microenvironment may be critical in shaping and modulating this important aspect of host-tumor interactions.
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Affiliation(s)
- Aaron Javitt
- Department of Immunology, Weizmann Institute of ScienceRehovot, Israel
| | - Eilon Barnea
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa, Israel
| | | | - Hila Wolf-Levy
- Department of Immunology, Weizmann Institute of ScienceRehovot, Israel
| | - Yishai Levin
- The Nancy and Stephen Grand Israel National Center for Personalized Medicine, de Botton Institute for Protein Profiling, Weizmann Institute of Science, Rehovot, Israel
| | - Arie Admon
- Faculty of Biology, Technion-Israel Institute of Technology, Haifa, Israel
| | - Yifat Merbl
- Department of Immunology, Weizmann Institute of ScienceRehovot, Israel
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7
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Zapata L, Pich O, Serrano L, Kondrashov FA, Ossowski S, Schaefer MH. Negative selection in tumor genome evolution acts on essential cellular functions and the immunopeptidome. Genome Biol 2018; 19:67. [PMID: 29855388 PMCID: PMC5984361 DOI: 10.1186/s13059-018-1434-0] [Citation(s) in RCA: 55] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2017] [Accepted: 04/20/2018] [Indexed: 01/08/2023] Open
Abstract
Background Natural selection shapes cancer genomes. Previous studies used signatures of positive selection to identify genes driving malignant transformation. However, the contribution of negative selection against somatic mutations that affect essential tumor functions or specific domains remains a controversial topic. Results Here, we analyze 7546 individual exomes from 26 tumor types from TCGA data to explore the portion of the cancer exome under negative selection. Although we find most of the genes neutrally evolving in a pan-cancer framework, we identify essential cancer genes and immune-exposed protein regions under significant negative selection. Moreover, our simulations suggest that the amount of negative selection is underestimated. We therefore choose an empirical approach to identify genes, functions, and protein regions under negative selection. We find that expression and mutation status of negatively selected genes is indicative of patient survival. Processes that are most strongly conserved are those that play fundamental cellular roles such as protein synthesis, glucose metabolism, and molecular transport. Intriguingly, we observe strong signals of selection in the immunopeptidome and proteins controlling peptide exposition, highlighting the importance of immune surveillance evasion. Additionally, tumor type-specific immune activity correlates with the strength of negative selection on human epitopes. Conclusions In summary, our results show that negative selection is a hallmark of cell essentiality and immune response in cancer. The functional domains identified could be exploited therapeutically, ultimately allowing for the development of novel cancer treatments. Electronic supplementary material The online version of this article (10.1186/s13059-018-1434-0) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Luis Zapata
- Genomic and Epigenomic Variation in Disease Group, Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain.,Centre for Evolution and Cancer, The Institute of Cancer Research, London, UK
| | - Oriol Pich
- Evolutionary Genomics Group, Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain.,Institute for Research in Biomedicine (IRB Barcelona), The Barcelona Institute of Science and Technology, Baldiri Reixac, 10, 08028, Barcelona, Spain
| | - Luis Serrano
- Design of Biological Systems Group, Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain.,Universitat Pompeu Fabra (UPF), Barcelona, Spain.,Institució Catalana de Recerca i Estudis Avançats (ICREA), Pg. Lluis Companys 23, 08010, Barcelona, Spain
| | - Fyodor A Kondrashov
- IST Austria (Institute of Science and Technology Austria), Am Campus 1, 3400, Klosterneuburg, Austria
| | - Stephan Ossowski
- Genomic and Epigenomic Variation in Disease Group, Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain. .,Universitat Pompeu Fabra (UPF), Barcelona, Spain. .,Institute of Medical Genetics and Applied Genomics, University of Tübingen, Tübingen, Germany.
| | - Martin H Schaefer
- Design of Biological Systems Group, Centre for Genomic Regulation (CRG), The Barcelona Institute of Science and Technology, Dr. Aiguader 88, 08003, Barcelona, Spain.
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Interactions between the Hepatitis C Virus Nonstructural 2 Protein and Host Adaptor Proteins 1 and 4 Orchestrate Virus Release. mBio 2018. [PMID: 29535204 PMCID: PMC5850324 DOI: 10.1128/mbio.02233-17] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Hepatitis C virus (HCV) spreads via secreted cell-free particles or direct cell-to-cell transmission. Yet, virus-host determinants governing differential intracellular trafficking of cell-free- and cell-to-cell-transmitted virus remain unknown. The host adaptor proteins (APs) AP-1A, AP-1B, and AP-4 traffic in post-Golgi compartments, and the latter two are implicated in basolateral sorting. We reported that AP-1A mediates HCV trafficking during release, whereas the endocytic adaptor AP-2 mediates entry and assembly. We demonstrated that the host kinases AAK1 and GAK regulate HCV infection by controlling these clathrin-associated APs. Here, we sought to define the roles of AP-4, a clathrin-independent adaptor; AP-1A; and AP-1B in HCV infection. We screened for interactions between HCV proteins and the μ subunits of AP-1A, AP-1B, and AP-4 by mammalian cell-based protein fragment complementation assays. The nonstructural 2 (NS2) protein emerged as an interactor of these adaptors in this screening and by coimmunoprecipitations in HCV-infected cells. Two previously unrecognized dileucine-based motifs in the NS2 C terminus mediated AP binding and HCV release. Infectivity and coculture assays demonstrated that while all three adaptors mediate HCV release and cell-free spread, AP-1B and AP-4, but not AP-1A, mediate cell-to-cell spread. Live-cell imaging revealed HCV cotrafficking with AP-1A, AP-1B, and AP-4 and that AP-4 mediates HCV trafficking in a post-Golgi compartment. Lastly, HCV cell-to-cell spread was regulated by AAK1 and GAK and thus susceptible to treatment with AAK1 and GAK inhibitors. These data provide a mechanistic understanding of HCV trafficking in distinct release pathways and reveal a requirement for APs in cell-to-cell viral spread. HCV spreads via cell-free infection or cell-to-cell contact that shields it from antibody neutralization, thereby facilitating viral persistence. Yet, factors governing this differential sorting remain unknown. By integrating proteomic, RNA interference, genetic, live-cell imaging, and pharmacological approaches, we uncover differential coopting of host adaptor proteins (APs) to mediate HCV traffic at distinct late steps of the viral life cycle. We reported that AP-1A and AP-2 mediate HCV trafficking during release and assembly, respectively. Here, we demonstrate that dileucine motifs in the NS2 protein mediate AP-1A, AP-1B, and AP-4 binding and cell-free virus release. Moreover, we reveal that AP-4, an adaptor not previously implicated in viral infections, mediates cell-to-cell spread and HCV trafficking. Lastly, we demonstrate cell-to-cell spread regulation by AAK1 and GAK, host kinases controlling APs, and susceptibility to their inhibitors. This study provides mechanistic insights into virus-host determinants that facilitate HCV trafficking, with potential implications for pathogenesis and antiviral agent design.
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Vien TN, Moss SJ, Davies PA. Regulating the Efficacy of Inhibition Through Trafficking of γ-Aminobutyric Acid Type A Receptors. Anesth Analg 2017; 123:1220-1227. [PMID: 27285004 DOI: 10.1213/ane.0000000000001349] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Trafficking of anesthetic-sensitive receptors within the plasma membrane, or from one cellular component to another, occurs continuously. Changes in receptor trafficking have implications in altering anesthetic sensitivity. γ-Aminobutyric acid type A receptors (GABAARs) are anion-permeable ion channels and are the major class of receptor in the adult mammalian central nervous system that mediates inhibition. GABAergic signaling allows for precise synchronized firing of action potentials within brain circuits that is critical for cognition, behavior, and consciousness. This precision depends upon tightly controlled trafficking of GABAARs into the membrane. General anesthetics bind to and allosterically enhance GABAARs by prolonging the open state of the receptor and thereby altering neuronal and brain circuit activity. Subunit composition and GABAAR localization strongly influence anesthetic end points; therefore, changes in GABAAR trafficking could have significant consequences to anesthetic sensitivity. GABAARs are not static membrane structures but are in a constant state of flux between extrasynaptic and synaptic locations and are continually endocytosed and recycled from and to the membrane. Neuronal activity, posttranslational modifications, and some naturally occurring and synthetic compounds can influence the expression and trafficking of GABAARs. In this article, we review GABAARs, their trafficking, and how phosphorylation of GABAAR subunits can influence the surface expression and function of the receptor. Ultimately, alterations of GABAAR trafficking could modify anesthetic end points, both unintentionally through pathologic processes but potentially as a therapeutic target to adjust anesthetic-sensitive GABAARs.
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Affiliation(s)
- Thuy N Vien
- From the *Department of Neuroscience, Tufts University School of Medicine, Sackler School of Graduate Biomedical Sciences, Boston, Massachusetts; and †Department of Neuroscience, Tufts University School of Medicine, Boston, Massachusetts
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Johnson A, Vert G. Single Event Resolution of Plant Plasma Membrane Protein Endocytosis by TIRF Microscopy. FRONTIERS IN PLANT SCIENCE 2017; 8:612. [PMID: 28484480 PMCID: PMC5401915 DOI: 10.3389/fpls.2017.00612] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/16/2016] [Accepted: 04/04/2017] [Indexed: 05/02/2023]
Abstract
Endocytosis is a key process in the internalization of extracellular materials and plasma membrane proteins, such as receptors and transporters, thereby controlling many aspects of cell signaling and cellular homeostasis. Endocytosis in plants has an essential role not only for basic cellular functions but also for growth and development, nutrient delivery, toxin avoidance, and pathogen defense. The precise mechanisms of endocytosis in plants remain quite elusive. The lack of direct visualization and examination of single events of endocytosis has greatly hampered our ability to precisely monitor the cell surface lifetime and the recruitment profile of proteins driving endocytosis or endocytosed cargos in plants. Here, we discuss the necessity to systematically implement total internal reflection fluorescence microcopy (TIRF) in the Plant Cell Biology community and present reliable protocols for high spatial and temporal imaging of endocytosis in plants using clathrin-mediated endocytosis as a test case, since it represents the major route for internalization of cell-surface proteins in plants. We developed a robust method to directly visualize cell surface proteins using TIRF microscopy combined to a high throughput, automated and unbiased analysis pipeline to determine the temporal recruitment profile of proteins to single sites of endocytosis, using the departure of clathrin as a physiological reference for scission. Using this 'departure assay', we assessed the recruitment of two different AP-2 subunits, alpha and mu, to the sites of endocytosis and found that AP2A1 was recruited in concert with clathrin, while AP2M was not. This validated approach therefore offers a powerful solution to better characterize the plant endocytic machinery and the dynamics of one's favorite cargo protein.
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11
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Zumthor JP, Cernikova L, Rout S, Kaech A, Faso C, Hehl AB. Static Clathrin Assemblies at the Peripheral Vacuole-Plasma Membrane Interface of the Parasitic Protozoan Giardia lamblia. PLoS Pathog 2016; 12:e1005756. [PMID: 27438602 PMCID: PMC4954726 DOI: 10.1371/journal.ppat.1005756] [Citation(s) in RCA: 35] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Accepted: 06/18/2016] [Indexed: 11/19/2022] Open
Abstract
Giardia lamblia is a parasitic protozoan that infects a wide range of vertebrate hosts including humans. Trophozoites are non-invasive but associate tightly with the enterocyte surface of the small intestine. This narrow ecological specialization entailed extensive morphological and functional adaptations during host-parasite co-evolution, including a distinctly polarized array of endocytic organelles termed peripheral vacuoles (PVs), which are confined to the dorsal cortical region exposed to the gut lumen and are in close proximity to the plasma membrane (PM). Here, we investigated the molecular consequences of these adaptations on the Giardia endocytic machinery and membrane coat complexes. Despite the absence of canonical clathrin coated vesicles in electron microscopy, Giardia possesses conserved PV-associated clathrin heavy chain (GlCHC), dynamin-related protein (GlDRP), and assembly polypeptide complex 2 (AP2) subunits, suggesting a novel function for GlCHC and its adaptors. We found that, in contrast to GFP-tagged AP2 subunits and DRP, CHC::GFP reporters have no detectable turnover in living cells, indicating fundamental differences in recruitment to the membrane and disassembly compared to previously characterized clathrin coats. Histochemical localization in electron tomography showed that these long-lived GlCHC assemblies localized at distinctive approximations between the plasma and PV membrane. A detailed protein interactome of GlCHC revealed all of the conserved factors in addition to novel or highly diverged proteins, including a putative clathrin light chain and lipid-binding proteins. Taken together, our data provide strong evidence for giardial CHC as a component of highly stable assemblies at PV-PM junctions that likely have a central role in organizing continuities between the PM and PV membranes for controlled sampling of the fluid environment. This suggests a novel function for CHC in Giardia and the extent of molecular remodeling of endocytosis in this species. In canonical clathrin mediated endocytosis (CME) models, the concerted action of ca. 50 proteins mediates the uptake of extracellular components. The key player in this process is clathrin which coats transport intermediates called clathrin coated vesicles (CCV). The intestinal parasite Giardia lamblia has undergone extensive remodeling during colonization of the mammalian duodenum. Here, we report on unique features of this parasite’s endocytic system, consisting of fixed peripheral vacuoles (PV) in close proximity to the exposed plasma membrane (PM), with no discernible CCVs. Using state-of-the-art imaging strategies, we show that the surface of Giardia trophozoites is pock-marked with PM invaginations reaching to the underlying PV membrane. Co-immunoprecipitation and analysis of protein dynamics reveal that, in line with the absence of CCVs, giardial clathrin assemblies have no dynamic behavior. CHC still remains associated to AP2 and dynamin, both conserved dynamic CME components, and to a newly identified putative clathrin light chain. The emerging model calls for giardial clathrin organized into static cores surrounded by dynamic interaction partners, and most likely involved in the regulation of fusion between the PM and the PVs in a “kiss-and-flush”-like mechanism. This suggests that Giardia harbors a conceptually novel function for clathrin in endocytosis, which might be a consequence of host-parasite co-evolution.
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Affiliation(s)
| | - Lenka Cernikova
- Institute of Parasitology, University of Zurich, Zurich, Switzerland
| | - Samuel Rout
- Institute of Parasitology, University of Zurich, Zurich, Switzerland
| | - Andres Kaech
- Center for Microscopy and Image Analysis, University of Zurich, Zurich, Switzerland
| | - Carmen Faso
- Institute of Parasitology, University of Zurich, Zurich, Switzerland
- * E-mail: (CF); (ABH)
| | - Adrian B. Hehl
- Institute of Parasitology, University of Zurich, Zurich, Switzerland
- * E-mail: (CF); (ABH)
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Kibria KMK, Hossain MU, Oany AR, Ahmad SAI. Novel insights on ENTH domain-containing proteins in apicomplexan parasites. Parasitol Res 2016; 115:2191-202. [PMID: 26922178 DOI: 10.1007/s00436-016-4961-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2015] [Accepted: 02/17/2016] [Indexed: 11/27/2022]
Abstract
The phylum Apicomplexa includes a large group of early branching eukaryotes having significant medical and economical importance. The molecular machinery responsible for protein trafficking is poorly understood in these apicomplexans. One of the most important proteins involved in clathrin-mediated protein trafficking is Epsin, which contains ENTH domain, a conserved domain crucial for membrane bending leading to vesicle formation. We undertook homology searching and phylogenetic analyses to produce a rigorously annotated set of Epsin homologs retrieved from diverse apicomplexan genomes. Genomic and phylogenetic comparisons revealed that apicomplexans contain unusual Epsin homologs that are distinct from those observed in mammals and yeast. Although there are four Epsin genes in mammalian system and five in the yeast genome, apicomplexan parasites consist only a single Epsin gene. The apicomplexan Epsin contains the conserved ENTH domain consisting of phosphoinositide (PtdIns)-binding sites which indicate about their functional significance in the formation of vesicles; however, the absence of ubiquitin-interacting motif (UIM) suggests a possible different mechanism for protein trafficking. The existence of dileucine motif in Plasmodium, Cryptosporidum parvum and Eimeria tenella Epsins might solve their functionality while lacking a lot of conserved motifs as this motif is known to interact with different adaptor protein complexes (AP1, AP2 and AP3). Other Epsin homologs are also shown to have different peptide motifs reported for possible interaction with α-ear appendage, γ-ear appendage and EH domain present in different adaptors. Bioinformatic and phylogenetic analyses suggest that the apicomplexan Epsins have unusual functionality from that of the mammalian Epsins. This detailed study may greatly facilitate future molecular cell biological investigation for the role of Epsins in these parasites.
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Affiliation(s)
- K M Kaderi Kibria
- Department of Biotechnology and Genetic Engineering, Mawlana Bhashani Science and Technology University, Santosh, Tangail, 1902, Bangladesh.
| | - Mohammad Uzzal Hossain
- Department of Biotechnology and Genetic Engineering, Mawlana Bhashani Science and Technology University, Santosh, Tangail, 1902, Bangladesh
| | - Arafat Rahman Oany
- Department of Biotechnology and Genetic Engineering, Mawlana Bhashani Science and Technology University, Santosh, Tangail, 1902, Bangladesh
| | - Shah Adil Ishtiyaq Ahmad
- Department of Biotechnology and Genetic Engineering, Mawlana Bhashani Science and Technology University, Santosh, Tangail, 1902, Bangladesh
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Alternative Splicing in Ca(V)2.2 Regulates Neuronal Trafficking via Adaptor Protein Complex-1 Adaptor Protein Motifs. J Neurosci 2016; 35:14636-52. [PMID: 26511252 DOI: 10.1523/jneurosci.3034-15.2015] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
N-type voltage-gated calcium (Ca(V)2.2) channels are expressed in neurons and targeted to the plasma membrane of presynaptic terminals, facilitating neurotransmitter release. Here, we find that the adaptor protein complex-1 (AP-1) mediates trafficking of Ca(V)2.2 from the trans-Golgi network to the cell surface. Examination of splice variants of Ca(V)2.2, containing either exon 37a (selectively expressed in nociceptors) or 37b in the proximal C terminus, reveal that canonical AP-1 binding motifs, YxxΦ and [DE]xxxL[LI], present only in exon 37a, enhance intracellular trafficking of exon 37a-containing Ca(V)2.2 to the axons and plasma membrane of rat DRG neurons. Finally, we identify differential effects of dopamine-2 receptor (D2R) and its agonist-induced activation on trafficking of Ca(V)2.2 isoforms. D2R slowed the endocytosis of Ca(V)2.2 containing exon 37b, but not exon 37a, and activation by the agonist quinpirole reversed the effect of the D2R. Our work thus reveals key mechanisms involved in the trafficking of N-type calcium channels.
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Abstract
The innate immune system provides the first barrier against pathogens. Intracellular Toll-like receptors (TLR3, 7 and 9) localise in endosomes and sense nucleotides from viruses and bacteria. This recognition induces their conformational changes resulting in the production of proinflammatory cytokines and MHC class II (MHCII) antigenic presentation. In the absence of stimulation, TLRs are retained in the endoplasmic reticulum. Upon stimulation, they relocate to the endo-lysosomal compartment, allowing the recruitment of the adaptor molecules, MyD88 or TRIF. Increasing evidences describe a cross talk between proteins that regulate both innate and adaptive immune responses. For example, proteolytic enzymes which are required for breaking down exogenous antigen to generate suitable peptides for MHCII molecules are also essential to activate endosomal TLRs and MHCII molecules were recently described to regulate TLR signalling. But other proteins are possibly involved and regulated differentially between cell types. We have observed that intracellular TLR trafficking and signalling in B cells are different from dendritic cells and macrophages and involved the MHCII chaperone molecule, the invariant chain (Ii).
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Endocytosis and Trafficking of Natriuretic Peptide Receptor-A: Potential Role of Short Sequence Motifs. MEMBRANES 2015; 5:253-87. [PMID: 26151885 PMCID: PMC4584282 DOI: 10.3390/membranes5030253] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/18/2015] [Revised: 06/25/2015] [Accepted: 06/25/2015] [Indexed: 12/19/2022]
Abstract
The targeted endocytosis and redistribution of transmembrane receptors among membrane-bound subcellular organelles are vital for their correct signaling and physiological functions. Membrane receptors committed for internalization and trafficking pathways are sorted into coated vesicles. Cardiac hormones, atrial and brain natriuretic peptides (ANP and BNP) bind to guanylyl cyclase/natriuretic peptide receptor-A (GC-A/NPRA) and elicit the generation of intracellular second messenger cyclic guanosine 3',5'-monophosphate (cGMP), which lowers blood pressure and incidence of heart failure. After ligand binding, the receptor is rapidly internalized, sequestrated, and redistributed into intracellular locations. Thus, NPRA is considered a dynamic cellular macromolecule that traverses different subcellular locations through its lifetime. The utilization of pharmacologic and molecular perturbants has helped in delineating the pathways of endocytosis, trafficking, down-regulation, and degradation of membrane receptors in intact cells. This review describes the investigation of the mechanisms of internalization, trafficking, and redistribution of NPRA compared with other cell surface receptors from the plasma membrane into the cell interior. The roles of different short-signal peptide sequence motifs in the internalization and trafficking of other membrane receptors have been briefly reviewed and their potential significance in the internalization and trafficking of NPRA is discussed.
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Adiko AC, Babdor J, Gutiérrez-Martínez E, Guermonprez P, Saveanu L. Intracellular Transport Routes for MHC I and Their Relevance for Antigen Cross-Presentation. Front Immunol 2015; 6:335. [PMID: 26191062 PMCID: PMC4489332 DOI: 10.3389/fimmu.2015.00335] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2015] [Accepted: 06/15/2015] [Indexed: 01/22/2023] Open
Abstract
Cross-presentation, in which exogenous antigens are presented via MHC I complexes, is involved both in the generation of anti-infectious and anti-tumoral cytotoxic CD8+ T cells and in the maintenance of immune tolerance. While cross-presentation was described almost four decades ago and while it is now established that some dendritic cell (DC) subsets are better than others in processing and cross-presenting internalized antigens, the involved molecular mechanisms remain only partially understood. Some of the least explored molecular mechanisms in cross-presentation concern the origin of cross-presenting MHC I molecules and the cellular compartments where antigenic peptide loading occurs. This review focuses on MHC I molecules and their intracellular trafficking. We discuss the source of cross-presenting MHC I in DCs as well as the role of the endocytic pathway in their recycling from the cell surface. Next, we describe the importance of the TAP peptide transporter for delivering peptides to MHC I during cross-presentation. Finally, we highlight the impact of innate immunity mechanisms on specific antigen cross-presentation mechanisms in which TLR activation modulates MHC I trafficking and TAP localization.
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Affiliation(s)
- Aimé Cézaire Adiko
- INSERM U1149, Faculté Bichat Medical School, ELR8252 CNRS, Center for Research on Inflammation , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité , Paris , France
| | - Joel Babdor
- INSERM UMR 1163, Laboratory of Cellular and Molecular Mechanisms of Hematological Disorders and Therapeutic Implications , Paris , France ; Université Paris Descartes, Sorbonne Paris Cité , Paris , France ; Imagine Institute , Paris , France
| | - Enric Gutiérrez-Martínez
- Laboratory of Phagocyte Immunobiology, Peter Gorer Department of Immunobiology, King's College London , London , UK
| | - Pierre Guermonprez
- Laboratory of Phagocyte Immunobiology, Peter Gorer Department of Immunobiology, King's College London , London , UK
| | - Loredana Saveanu
- INSERM U1149, Faculté Bichat Medical School, ELR8252 CNRS, Center for Research on Inflammation , Paris , France ; Université Paris Diderot, Sorbonne Paris Cité , Paris , France
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Michelet X, Garg S, Wolf BJ, Tuli A, Ricciardi-Castagnoli P, Brenner MB. MHC Class II Presentation Is Controlled by the Lysosomal Small GTPase, Arl8b. THE JOURNAL OF IMMUNOLOGY 2015; 194:2079-88. [DOI: 10.4049/jimmunol.1401072] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
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18
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Liu YH, Lin JY. Recent advances of cluster of differentiation 74 in cancer. World J Immunol 2014; 4:174-184. [DOI: 10.5411/wji.v4.i3.174] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/08/2014] [Revised: 06/03/2014] [Accepted: 07/29/2014] [Indexed: 02/05/2023] Open
Abstract
Cluster of differentiation 74 (CD74) performs multiple roles in B cells, T cells, and antigen-presenting cells within the immune system; it also participates in major histocompatibility complex class II-restricted antigen presentation and inflammation. Recently, a role for CD74 in carcinogenesis has been described. CD74 promotes cell proliferation and motility and prevents cell death in a macrophage migration inhibitory factor-dependent manner. Its roles as an accessory signal receptor on the cell surface and the ability to interact with other signaling molecules make CD74 an attractive therapeutic target for the treatment of cancer. This review focuses on the original role of CD74 in the immune system and its emerging tumor-related functions. First, the structure of CD74 will be summarized. Second, the current understandings about the expression, cellular localization, molecular mechanisms and signaling pathways of CD74 in immunity and cancer will be reviewed. Third, the examples that suggest CD74 is a promising molecular therapeutic target are reviewed and discussed. Although the safety and efficacy of CD74-targeted strategies are under development, deeply understanding of the regulation of CD74 will hold promise for the use of CD74 as a therapeutic target and may develop the CD74-targeted therapeutic agents such as neutralized antibody and compounds.
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Gleeson PA. The role of endosomes in innate and adaptive immunity. Semin Cell Dev Biol 2014; 31:64-72. [PMID: 24631355 DOI: 10.1016/j.semcdb.2014.03.002] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 02/28/2014] [Accepted: 03/01/2014] [Indexed: 12/16/2022]
Abstract
The regulation of the immune system is critical for the generation of effective immune responses to a range of pathogens, as well as for protection against unwanted responses. The regulation of many immune response pathways are directly dependent on the organisation and activities of intracellular endosomal compartments associated with cargo sorting, membrane trafficking and signalling. Over the last 5-10 years, the appreciation of the important contribution of the endosomal system has expanded dramatically to include antigen presentation of MHC class I, MHC class II and CD1 molecules, as well as the regulation of antigen receptor signalling and pattern recognition receptor signalling of the innate immune system. This review summarises some of the very diverse and key roles played by endosomes in generating effective innate and adaptive immune responses.
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Affiliation(s)
- Paul A Gleeson
- The Department of Biochemistry and Molecular Biology and Bio21 Molecular Science and Biotechnology Institute, The University of Melbourne, Victoria 3010, Australia.
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20
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Gadeyne A, Sánchez-Rodríguez C, Vanneste S, Di Rubbo S, Zauber H, Vanneste K, Van Leene J, De Winne N, Eeckhout D, Persiau G, Van De Slijke E, Cannoot B, Vercruysse L, Mayers J, Adamowski M, Kania U, Ehrlich M, Schweighofer A, Ketelaar T, Maere S, Bednarek S, Friml J, Gevaert K, Witters E, Russinova E, Persson S, De Jaeger G, Van Damme D. The TPLATE Adaptor Complex Drives Clathrin-Mediated Endocytosis in Plants. Cell 2014; 156:691-704. [DOI: 10.1016/j.cell.2014.01.039] [Citation(s) in RCA: 149] [Impact Index Per Article: 14.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2013] [Revised: 10/28/2013] [Accepted: 01/16/2014] [Indexed: 10/25/2022]
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ten Broeke T, Wubbolts R, Stoorvogel W. MHC class II antigen presentation by dendritic cells regulated through endosomal sorting. Cold Spring Harb Perspect Biol 2013; 5:a016873. [PMID: 24296169 DOI: 10.1101/cshperspect.a016873] [Citation(s) in RCA: 117] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
For the initiation of adaptive immune responses, dendritic cells present antigenic peptides in association with major histocompatibility complex class II (MHCII) to naïve CD4(+) T lymphocytes. In this review, we discuss how antigen presentation is regulated through intracellular processing and trafficking of MHCII. Newly synthesized MHCII is chaperoned by the invariant chain to endosomes, where peptides from endocytosed pathogens can bind. In nonactivated dendritic cells, peptide-loaded MHCII is ubiquitinated and consequently sorted by the ESCRT machinery to intraluminal vesicles of multivesicular bodies, ultimately leading to lysosomal degradation. Ubiquitination of newly synthesized MHCII is blocked when dendritic cells are activated, now allowing its transfer to the cell surface. This mode of regulation for MHCII is a prime example of how molecular processing and sorting at multivesicular bodies can determine the expression of signaling receptors at the plasma membrane.
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Affiliation(s)
- Toine ten Broeke
- Utrecht University, Faculty of Veterinary Medicine, Department of Biochemistry and Cell Biology, Yalelaan 2, 3584 CM, Utrecht, The Netherlands
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Internalizing MHC class II-peptide complexes are ubiquitinated in early endosomes and targeted for lysosomal degradation. Proc Natl Acad Sci U S A 2013; 110:20188-93. [PMID: 24277838 DOI: 10.1073/pnas.1312994110] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
As sentinels of the immune system, dendritic cells (DCs) continuously generate and turnover antigenic peptide-MHC class II complexes (pMHC-II). pMHC-II generation is a complex process that involves many well-characterized MHC-II biosynthetic intermediates; however, the mechanisms leading to MHC-II turnover/degradation are poorly understood. We now show that pMHC-II complexes undergoing clathrin-independent endocytosis from the DC surface are efficiently ubiquitinated by the E3 ubiquitin ligase March-I in early endosomes, whereas biosynthetically immature MHC-II-Invariant chain (Ii) complexes are not. The inability of MHC-II-Ii to serve as a March-I substrate is a consequence of Ii sorting motifs that divert the MHC-II-Ii complex away from March-I(+) early endosomes. When these sorting motifs are mutated, or when clathrin-mediated endocytosis is inhibited, MHC-II-Ii complexes internalize by using a clathrin-independent endocytosis pathway and are now ubiquitinated as efficiently as pMHC-II complexes. These data show that the selective ubiquitination of internalizing surface pMHC-II in March-I(+) early endosomes promotes degradation of "old" pMHC-II and spares forms of MHC-II that have not yet loaded antigenic peptides or have not yet reached the DC surface.
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23
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Rosnoblet C, Legrand D, Demaegd D, Hacine-Gherbi H, de Bettignies G, Bammens R, Borrego C, Duvet S, Morsomme P, Matthijs G, Foulquier F. Impact of disease-causing mutations on TMEM165 subcellular localization, a recently identified protein involved in CDG-II. Hum Mol Genet 2013; 22:2914-28. [PMID: 23575229 DOI: 10.1093/hmg/ddt146] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
TMEM165 has recently been identified as a novel protein involved in CDG-II. TMEM165 has no biological function described so far. Different mutations were recently found in patients with Golgi glycosylation defects and harboring a peculiar skeletal phenotype. In this study, we examined the effect of naturally occurring mutations on the intracellular localization of TMEM165 and their abilities to complement the TMEM165-deficient yeast, gdt1▵. Wild-type TMEM165 was present within Golgi compartment, plasma membrane and late endosomes/lysosomes, whereas mutated TMEM165 were found differentially localized according to the mutations. We demonstrated that, in the yeast functional assay with TMEM165 ortholog Gdt1, the homozygous point mutation correlating with a mild phenotype restores the yeast functional assay, whereas the truncated mutation, associated with severe disease, failed to restore Gdt1 function. These studies highly suggest that these clinically relevant point mutations do not affect the protein function but critically changes the subcellular protein localization. Moreover, the data point to a critical role of the YNRL motif in TMEM165 subcellular localization.
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Affiliation(s)
- Claire Rosnoblet
- CNRS-UMR 8576, Structural and Functional Glycobiology Unit, IFR 147, University of Lille 1, 59655 Villeneuve d’Ascq, France
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Streeter J, Thiel W, Brieger K, Miller Jr. FJ. Opportunity Nox: The Future of NADPH Oxidases as Therapeutic Targets in Cardiovascular Disease. Cardiovasc Ther 2012; 31:125-37. [DOI: 10.1111/j.1755-5922.2011.00310.x] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
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Towards a systems understanding of MHC class I and MHC class II antigen presentation. Nat Rev Immunol 2011; 11:823-36. [PMID: 22076556 DOI: 10.1038/nri3084] [Citation(s) in RCA: 1191] [Impact Index Per Article: 91.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The molecular details of antigen processing and presentation by MHC class I and class II molecules have been studied extensively for almost three decades. Although the basic principles of these processes were laid out approximately 10 years ago, the recent years have revealed many details and provided new insights into their control and specificity. MHC molecules use various biochemical reactions to achieve successful presentation of antigenic fragments to the immune system. Here we present a timely evaluation of the biology of antigen presentation and a survey of issues that are considered unresolved. The continuing flow of new details into our understanding of the biology of MHC class I and class II antigen presentation builds a system involving several cell biological processes, which is discussed in this Review.
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Towards a systems understanding of MHC class I and MHC class II antigen presentation. Nat Rev Immunol 2011. [PMID: 22076556 DOI: 10.1038/nri3084.] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The molecular details of antigen processing and presentation by MHC class I and class II molecules have been studied extensively for almost three decades. Although the basic principles of these processes were laid out approximately 10 years ago, the recent years have revealed many details and provided new insights into their control and specificity. MHC molecules use various biochemical reactions to achieve successful presentation of antigenic fragments to the immune system. Here we present a timely evaluation of the biology of antigen presentation and a survey of issues that are considered unresolved. The continuing flow of new details into our understanding of the biology of MHC class I and class II antigen presentation builds a system involving several cell biological processes, which is discussed in this Review.
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27
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Schwartz V, Krüttgen A, Weis J, Weber C, Ostendorf T, Lue H, Bernhagen J. Role for CD74 and CXCR4 in clathrin-dependent endocytosis of the cytokine MIF. Eur J Cell Biol 2011; 91:435-49. [PMID: 22014447 DOI: 10.1016/j.ejcb.2011.08.006] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2011] [Revised: 08/02/2011] [Accepted: 08/28/2011] [Indexed: 11/18/2022] Open
Abstract
Macrophage migration inhibitory factor (MIF) is a pleiotropic cytokine that plays a role in innate and adaptive immunity. Depending on the cellular context and disease state, MIF signaling is mediated by its receptors CXCR2, CXCR4 and/or CD74. Although it is known that MIF is endocytosed, the exact mechanism has remained unknown. In exploring the mechanism of MIF endocytosis with biologically active Alexa(546)MIF, pathway-specific inhibitors (monodansylcadaverine, MDC; chlorpromazine, CPZ; dynasore; dominant-negative dynamin, bafilomycin, nocodazole) and receptor overexpression and blockade approaches, we identified a clathrin/dynamin-dependent endocytosis pathway as the main track for MIF internalization. MIF endocytosis was rapid and colocalization with both early and late endosomal vesicles in a microtubule- and acidification-dependent manner was observed. LDL endocytosis (which is clathrin-mediated) served as a control and was similarly inhibited by MDC or dynasore. When MIF endocytosis was compared to that of transferrin, acetylated LDL, and choleratoxin B (the latter internalized by a clathrin-independent pathway) by colocalization studies, the MIF internalization pathway clearly resembled that of LDL but also shared early trafficking with transferrin, whereas no colocalization with choleratoxin was noted. To identify the receptors involved in MIF endocytosis, we focused on CD74 and CXCR4 which form a heteromeric complex. Ectopic overexpression of CD74 in HEK293 and HeLa cells, which do not endogenously express CD74, led to a marked acceleration of MIF endocytosis while pharmacological blockade of CXCR4, which is endogenously expressed on these cells, with AMD3100 led to a 20% reduction of MIF endocytosis in HEK293-CD74 transfectants, whereas in untransfected cells, a blockade of 40% was observed. Of note, both CD74 and CXCR4 strongly colocalize with Alexa(546)MIF both on the plasma membrane and in endosomal compartments. Moreover, MIF-stimulated AKT signaling, which was previously shown to involve both CD74 and CXCR4, was reduced by endocytosis inhibitors, indicating that MIF signaling is at least in part due to endosomal signaling mechanisms. Thus, MIF uptake follows a rapid LDL-like, clathrin- and dynamin-dependent endocytosis pathway, which is dependent on the receptors CD74 and CXCR4 and leads to the initiation of endosomal signaling responses.
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Affiliation(s)
- Verena Schwartz
- Institute of Biochemistry and Molecular Cell Biology, RWTH Aachen University, Pauwelsstraße 30, D-52074 Aachen, Germany
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Koch N, Zacharias M, König A, Temme S, Neumann J, Springer S. Stoichiometry of HLA class II-invariant chain oligomers. PLoS One 2011; 6:e17257. [PMID: 21364959 PMCID: PMC3043101 DOI: 10.1371/journal.pone.0017257] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 01/27/2011] [Indexed: 01/25/2023] Open
Abstract
BACKGROUND The HLA gene complex encodes three class II isotypes, DR, DQ, and DP. HLA class II molecules are peptide receptors that present antigens for recognition by T lymphocytes. In antigen presenting cells, the assembly of matched α and β subunits to heterodimers is chaperoned by invariant chain (Ii). Ii forms a homotrimer with three binding sites for class II heterodimers. The current model of class II and Ii structure states that three αβ heterodimers bind to an Ii trimer. METHODOLOGY/PRINCIPAL FINDINGS [corrected] We have now analyzed the composition and size of the complexes of class II and Ii using epitope tagged class II subunits and density gradient experiments. We show here that class II-Ii oligomers consist of one class II heterodimer associated with one Ii trimer, such that the DR, DQ and DP isotypes are contained within separate complexes with Ii. CONCLUSION/SIGNIFICANCE We propose a structural model of the class II-Ii oligomer and speculate that the pentameric class II-Ii complex is bent towards the cell membrane, inhibiting the binding of additional class II heterodimers to Ii.
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Affiliation(s)
- Norbert Koch
- Division of Immunobiology, Institute of Genetics, University of Bonn, Bonn, Germany.
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Pandey KN. Small peptide recognition sequence for intracellular sorting. Curr Opin Biotechnol 2011; 21:611-20. [PMID: 20817434 DOI: 10.1016/j.copbio.2010.08.007] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2010] [Revised: 08/10/2010] [Accepted: 08/11/2010] [Indexed: 02/05/2023]
Abstract
Increasing evidence indicate that complex arrays of short signals and recognition peptide sequence ensure accurate trafficking and distribution of transmembrane receptors and/or proteins and their ligands into intracellular compartments. Internalization and subsequent trafficking of cell-surface receptors into the cell interior is mediated by specific short-sequence peptide signals within the cytoplasmic domains of these receptor proteins. The short signals usually consist of small linear amino acid sequences, which are recognized by adaptor coat proteins along the endocytic and sorting pathways. In recent years, much has been learned about the function and mechanisms of endocytic pathways responsible for the trafficking and molecular sorting of membrane receptors and their ligands into intracellular compartments, however, the significance and scope of the short-sequence motifs in these cellular events is not well understood. Here a particular emphasis has been given to the functions of short-sequence signal motifs responsible for the itinerary and destination of membrane receptors and proteins moving into subcellular compartments.
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Affiliation(s)
- Kailash N Pandey
- Department of Physiology, Tulane University Health Sciences Center, School of Medicine, New Orleans, LA 70112, USA.
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Borghese F, Clanchy FIL. CD74: an emerging opportunity as a therapeutic target in cancer and autoimmune disease. Expert Opin Ther Targets 2011; 15:237-51. [PMID: 21208136 DOI: 10.1517/14728222.2011.550879] [Citation(s) in RCA: 109] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
INTRODUCTION CD74, also known as the invariant chain, participates in several key processes of the immune system, including antigen presentation, B-cell differentiation and inflammatory signaling. Despite being described more than 3 decades ago, new functions and novel interactions for this evolutionarily conserved molecule are still being unraveled. As a participant in several immunological processes and an indicator of disease in some conditions, it has potential as a therapeutic target. AREAS COVERED The relationship between the structure of CD74 variants and their physiological functions is detailed in this review. The function of CD74 in several cell lineages is examined with a focus on the interactions with cathepsins and, in an inflammatory milieu, the pro-inflammatory cytokine macrophage migratory inhibitory factor. The role of CD74 signaling in inflammatory and carcinogenic processes is outlined as is the use of CD74 as a therapeutic target (in cancer) and tool (as a vaccine). EXPERT OPINION CD74 has several roles within the cell and throughout the immune system. Most prominent amongst these are the complex relationships with MIF and cathepsins. Modulation of CD74 function shows promise for the effective amelioration of disease.
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Affiliation(s)
- Federica Borghese
- Sapienza University of Rome, Department of Clinical Medicine, Clinical Immunology Unit, Umberto I Policlinico di Roma, 155 Viale del Policlinico, Rome, IT 00161
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Landsverk OJB, Bakke O, Gregers TF. MHC II and the endocytic pathway: regulation by invariant chain. Scand J Immunol 2009; 70:184-93. [PMID: 19703008 DOI: 10.1111/j.1365-3083.2009.02301.x] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The major histocompatibility complex (MHC) class I and II molecules perform vital functions in innate and adaptive immune responses towards invading pathogens. MHC class I molecules load peptides in the endoplasmatic reticulum (ER) and display them to the T cell receptors (TcR) on CD8(+) T lymphocytes. MHC class II molecules (MHC II) acquire their peptides in endosomes and present these to the TcR on CD4+ T lymphocytes. They are vital for the generation of humoral immune responses. MHC II assembly in the ER and trafficking to endosomes is guided by a specialized MHC II chaperone termed the invariant chain (Ii). Ii self-associates into a trimer in the ER, this provides a scaffold for the assembly of three MHC II heterodimers and blocks their peptide binding grooves, thereby avoiding premature peptide binding. Ii then transports the nascent MHC II to more or less specialized compartment where they can load peptides derived from internalized pathogens.
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Affiliation(s)
- O J B Landsverk
- Centre for Immune Regulation, Department of Molecular Biosciences, University of Oslo, 0316 Oslo, Norway
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32
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Boonen M, Rezende de Castro R, Cuvelier G, Hamer I, Jadot M. A dileucine signal situated in the C-terminal tail of the lysosomal membrane protein p40 is responsible for its targeting to lysosomes. Biochem J 2008; 414:431-40. [PMID: 18479248 DOI: 10.1042/bj20071626] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2023]
Abstract
Transport of newly synthesized lysosomal membrane proteins from the TGN (trans-Golgi network) to the lysosomes is due to the presence of specific signals in their cytoplasmic domains that are recognized by cytosolic adaptors. p40, a hypothetical transporter of 372 amino acids localized in the lysosomal membrane, contains four putative lysosomal sorting motifs in its sequence: three of the YXXphi-type (Y(6)QLF, Y(106)VAL, Y(333)NGL) and one of the [D/E]XXXL[L/I]-type (EQERL(360)L(361)). To test the role of these motifs in the biosynthetic transport of p40, we replaced the most critical residues of these consensus sequences, the tyrosine residue or the leucine-leucine pair, by alanine or alanine-valine respectively. We analysed the subcellular localization of the mutated p40 proteins in transfected HeLa cells by confocal microscopy and by biochemical approaches (subcellular fractionation on self-forming Percoll density gradients and cell surface biotinylation). The results of the present study show that p40 is mistargeted to the plasma membrane when its dileucine motif is disrupted. No role of the tyrosine motifs could be put forward. Taken together, our results provide evidence that the sorting of p40 from the TGN to the lysosomes is directed by the dileucine EQERL(360)L(361) motif situated in its C-terminal tail.
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Affiliation(s)
- Marielle Boonen
- URPhiM, Laboratoire de Chimie Physiologique, FUNDP, B-5000 Namur, Belgium
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33
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Blot V, McGraw TE. Molecular mechanisms controlling GLUT4 intracellular retention. Mol Biol Cell 2008; 19:3477-87. [PMID: 18550797 PMCID: PMC2488284 DOI: 10.1091/mbc.e08-03-0236] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In basal adipocytes, glucose transporter 4 (GLUT4) is sequestered intracellularly by an insulin-reversible retention mechanism. Here, we analyze the roles of three GLUT4 trafficking motifs (FQQI, TELEY, and LL), providing molecular links between insulin signaling, cellular trafficking machinery, and the motifs in the specialized trafficking of GLUT4. Our results support a GLUT4 retention model that involves two linked intracellular cycles: one between endosomes and a retention compartment, and the other between endosomes and specialized GLUT4 transport vesicles. Targeting of GLUT4 to the former is dependent on the FQQI motif and its targeting to the latter is dependent on the TELEY motif. These two motifs act independently in retention, with the TELEY-dependent step being under the control of signaling downstream of the AS160 rab GTPase activating protein. Segregation of GLUT4 from endosomes, although positively correlated with the degree of basal retention, does not completely account for GLUT4 retention or insulin-responsiveness. Mutation of the LL motif slows return to basal intracellular retention after insulin withdrawal. Knockdown of clathrin adaptin protein complex-1 (AP-1) causes a delay in the return to intracellular retention after insulin withdrawal. The effects of mutating the LL motif and knockdown of AP-1 were not additive, establishing that AP-1 regulation of GLUT4 trafficking requires the LL motif.
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Affiliation(s)
- Vincent Blot
- Department of Biochemistry, Weill Cornell Medical College, New York, NY 10065, USA
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Competition model for upregulation of the major histocompatibility complex class II-associated invariant chain by human immunodeficiency virus type 1 Nef. J Virol 2008; 82:7758-67. [PMID: 18524831 DOI: 10.1128/jvi.02668-07] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) Nef protein upregulates the expression of the invariant chain (Ii)/major histocompatibility complex class II (MHC-II) complex at the cell surface. This complex appears to reach the antigen-loading endosomal compartment at least in part via an indirect pathway in which it is internalized from the cell surface via the adaptor protein 2 (AP-2) complex. Here we provide evidence for a competition model to explain how Nef upregulates the expression of Ii at the cell surface. In this model, Nef and Ii compete for binding to AP-2. In support of this model, Nef decreased the rate of internalization of Ii from the cell surface. The AP-binding dileucine motif in Nef, ENTSLL(165), was necessary and sufficient for the upregulation of Ii. In addition, two leucine-based AP-binding motifs in the Ii cytoplasmic tail, DDQRDLI(8) and EQLPML(17), were critical for the efficient upregulation of Ii by Nef. Experiments using Nef variants in which the native dileucine-based sorting motif was replaced with similar motifs from cellular transmembrane proteins allowed modulation of AP-binding specificity. Analysis of these variants suggested that the binding of Nef to AP-2 is sufficient to upregulate Ii at the plasma membrane. Finally, interference with the expression of AP-2 caused an upregulation of Ii at the plasma membrane, and this decreased the effect of Nef. These data indicate that Nef usurps AP-2 complexes to dysregulate Ii trafficking and potentially interfere with antigen presentation in the context of MHC-II.
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Walseng E, Bakke O, Roche PA. Major histocompatibility complex class II-peptide complexes internalize using a clathrin- and dynamin-independent endocytosis pathway. J Biol Chem 2008; 283:14717-27. [PMID: 18378669 DOI: 10.1074/jbc.m801070200] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Major histocompatibility complex (MHC) class II molecules (MHC-II) function by binding antigenic peptides and displaying these peptides on the surface of antigen presenting cells (APCs) for recognition by peptide-MHC-II (pMHC-II)-specific CD4 T cells. It is known that cell surface MHC-II can internalize, exchange antigenic peptides in endosomes, and rapidly recycle back to the plasma membrane; however, the molecular machinery and trafficking pathways utilized by internalizing/recycling MHC-II have not been identified. We now demonstrate that unlike newly synthesized invariant chain-associated MHC-II, mature cell surface pMHC-II complexes internalize following clathrin-, AP-2-, and dynamin-independent endocytosis pathways. Immunofluorescence microscopy of MHC-II expressing HeLa-CIITA cells, human B cells, and human DCs revealed that pMHC enters Arf6(+)Rab35(+)EHD1(+) tubular endosomes following endocytosis. These data contrast the internalization pathways followed by newly synthesized and peptide-loaded MHC-II molecules and demonstrates that cell surface pMHC-II internalize and rapidly recycle from early endocytic compartments in tubular endosomes.
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Affiliation(s)
- Even Walseng
- Experimental Immunology Branch, NCI, NIH, Bethesda, MD 20892, USA
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36
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Mason AK, Jacobs BE, Welling PA. AP-2-dependent internalization of potassium channel Kir2.3 is driven by a novel di-hydrophobic signal. J Biol Chem 2008; 283:5973-84. [PMID: 18180291 DOI: 10.1074/jbc.m709756200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023] Open
Abstract
The localization and density of Kir2.3 channels are influenced by the balance between PDZ protein interaction at the cell surface and routing into the endocytic pathway. Here, we explore mechanisms by which the Kir2.3 channel is directed into the endocytic pathway. We found that Kir2.3 channels are constitutively internalized from the cell surface in a dynamin-dependent manner, indicative of vesicle-mediated endocytosis. The rate of Kir2.3 endocytosis was dramatically attenuated following RNA interference-mediated knockdown of either alpha adaptin (AP-2 clathrin adaptor) or clathrin heavy chain, revealing that Kir2.3 is internalized by an AP-2 clathrin-dependent mechanism. Structure-rationalized mutagenesis studies of a number of different potential AP-2 interaction motifs indicate that internalization of Kir2.3 is largely dependent on a non-canonical di-isoleucine motif (II413) embedded within the C terminus. Internalization assays using CD4-Kir2.3 chimeras demonstrate that the di-isoleucine signal acts in an autonomous and transplantable manner. Kir2.3 co-immunoprecipitates with alpha adaptin, and disruption of the di-isoleucine motif decreased interaction of the channel with AP-2. Replacement of the di-isoleucine motif with a canonical di-leucine internalization signal actually blocked Kir2.3 endocytosis. Moreover, in yeast three-hybrid studies, the Kir2.3 di-isoleucine motif does not bind the AP-2 alphaC-sigma2 hemicomplex in the way that has been recently observed for canonical di-leucine signals. Altogether, the results indicate that Kir2.3 channels are marked for clathrin-dependent internalization from the plasma membrane by a novel AP-2-dependent signal.
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Affiliation(s)
- Amanda K Mason
- Department of Physiology, University of Maryland School of Medicine, Baltimore, MD 21201, USA
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Duffield A, Caplan MJ, Muth TR. Chapter 4 Protein Trafficking in Polarized Cells. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 270:145-79. [DOI: 10.1016/s1937-6448(08)01404-4] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
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38
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Berger AC, Salazar G, Styers ML, Newell-Litwa KA, Werner E, Maue RA, Corbett AH, Faundez V. The subcellular localization of the Niemann-Pick Type C proteins depends on the adaptor complex AP-3. J Cell Sci 2007; 120:3640-52. [PMID: 17895371 DOI: 10.1242/jcs.03487] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Niemann-Pick Type C (NP-C) disease, caused by mutations in either human NPC1 (hNPC1) or human NPC2 (hNPC2), is characterized by the accumulation of unesterified cholesterol in late endosomes. Although it is known that the NP-C proteins are targeted to late endosomal/lysosomal compartments, their delivery mechanisms have not been fully elucidated. To identify mechanisms regulating NP-C protein localization, we used Saccharomyces cerevisiae, which expresses functional homologs of both NP-C proteins - scNcr1p and scNpc2p. Targeting of scNcr1p to the vacuole was perturbed in AP-3-deficient yeast cells, whereas the delivery of scNpc2p was affected by deficiencies in either AP-3 or GGA. We focused on the role of the AP-3 pathway in the targeting of the mammalian NP-C proteins. We found that, although mouse NPC1 (mNPC1) and hNPC2 co-localize with AP-3 to a similar extent in fibroblasts, hNPC2 preferentially co-localizes with AP-1. Importantly, the targeting of both mammalian NPC1 and NPC2 is dependent on AP-3. Moreover, and consistent with the NP-C proteins playing a role in cholesterol metabolism, AP-3-deficient cells have reduced levels of cholesterol. These results provide information about how the NP-C proteins are targeted to their sites of action and illustrate the possibility that defective sorting of the NP-C proteins along the endocytic route can alter cellular cholesterol.
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Affiliation(s)
- Adam C Berger
- Department of Cell Biology, Emory University School of Medicine, Atlanta, GA 30322, USA
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39
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Arneson LS, Miller J. The chondroitin sulfate form of invariant chain trimerizes with conventional invariant chain and these complexes are rapidly transported from the trans-Golgi network to the cell surface. Biochem J 2007; 406:97-103. [PMID: 17492940 PMCID: PMC1948987 DOI: 10.1042/bj20070446] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Targeting of MHCII-invariant chain complexes from the trans-Golgi network to endosomes is mediated by two di-leucine-based signals present in the cytosolic domain of invariant chain. Generation of this endosomal targeting signal is also dependent on multimerization of the invariant chain cytosolic domain sequences, mediated through assembly of invariant chain into homotrimers. A small subset of invariant chain is modified by the addition of chondroitin sulfate and is expressed on the cell surface in association with MHCII. In the present study, we have followed the biosynthetic pathway and route of intracellular transport of this proteoglycan form of invariant chain. We found that the efficiency of chondroitin sulfate modification can be increased by altering the invariant chain amino acid sequence around Ser-201 to the xylosylation consensus sequence. Our results also indicate that, following sulfation, the proteoglycan form is transported rapidly from the trans-Golgi network to the cell surface and is degraded following internalization into an endocytic compartment. Invariant chain-chondroitin sulfate is present in invariant chain trimers that also include conventional non-proteoglycan forms of invariant chain. These data indicate that invariant chain-chondroitin sulfate-containing complexes are transported rapidly from the trans-Golgi network to the cell surface in spite of the presence of an intact endosomal localization signal. Furthermore, these results suggest that invariant chain-chondroitin sulfate may play an important role in the generation of cell-surface pools of invariant chain that can serve as receptors for CD44 and macrophage migration inhibitory factor.
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Affiliation(s)
- Lynne S Arneson
- Department of Biology, American University, Hurst Hall 101, 4400 Massachusetts Ave NW, Washington, DC 20016, USA.
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40
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Doray B, Lee I, Knisely J, Bu G, Kornfeld S. The gamma/sigma1 and alpha/sigma2 hemicomplexes of clathrin adaptors AP-1 and AP-2 harbor the dileucine recognition site. Mol Biol Cell 2007; 18:1887-96. [PMID: 17360967 PMCID: PMC1855031 DOI: 10.1091/mbc.e07-01-0012] [Citation(s) in RCA: 139] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The clathrin adaptors AP-1 and AP-2 bind cargo proteins via two types of motifs: tyrosine-based Yxx phi and dileucine-based [DE]XXXL[LI]. Although it is well established that Yxx phi motifs bind to the mu subunits of AP-1 or AP-2, dileucine motifs have been reported to bind to either the mu or beta subunits of these adaptors as well as the gamma/sigma1 hemicomplex of AP-1. To clarify this controversy, the various subunits of AP-1 and AP-2 were expressed individually and in hemicomplex form in insect cells, and they were used in glutathione S-transferase pull-down assays to determine their binding properties. We report that the gamma/sigma1 or alpha/sigma2 hemicomplexes bound the dileucine-based motifs of several proteins quite strongly, whereas binding by the beta1/mu1 and beta2/mu2 hemicomplexes, and the individual beta or mu subunits, was extremely weak or undetectable. The gamma/sigma1 and alpha/sigma2 hemicomplexes displayed substantial differences in their preference for particular dileucine-based motifs. Most strikingly, an aspartate at position -4 compromised binding to the gamma/sigma1 hemicomplex, whereas minimally affecting binding to alpha/sigma2. There was an excellent correlation between binding to the alpha/sigma2 hemicomplex and in vivo internalization mediated by the dileucine-based sorting signals. These findings provide new insights into the trafficking mechanisms of D/EXXXL[LI]-mediated sorting signals.
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Affiliation(s)
| | | | - Jane Knisely
- Pediatrics, Washington University School of Medicine, St. Louis, MO 63110
| | - Guojun Bu
- Pediatrics, Washington University School of Medicine, St. Louis, MO 63110
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41
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Schmidt U, Briese S, Leicht K, Schürmann A, Joost HG, Al-Hasani H. Endocytosis of the glucose transporter GLUT8 is mediated by interaction of a dileucine motif with the β2-adaptin subunit of the AP-2 adaptor complex. J Cell Sci 2006; 119:2321-31. [PMID: 16723738 DOI: 10.1242/jcs.02943] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The glucose transporter GLUT8 cycles between intracellular vesicles and the plasma membrane. Like the insulin-responsive glucose transporter GLUT4, GLUT8 is primarily located in intracellular compartments under basal conditions. Whereas translocation of GLUT4 to the plasma membrane is stimulated by insulin, the distribution of GLUT8 is not affected by insulin treatment in adipose cells. However, blocking endocytosis by co-expression of a dominant-negative dynamin GTPase (K44A) or mutation of the N-terminal dileucine (LL12/13) motif in GLUT8 leads to accumulation of the glucose transporter at the cell surface in a variety of different cell types. Yeast two-hybrid analyses and GST pulldown assays reveal that the LL signal constitutes a binding site for the β2-adaptin subunit of the heterotetrameric AP-2 adaptor complex, implicating this motif in targeting of GLUT8 to clathrin-coated vesicles. Moreover, yeast two-hybrid assays provide evidence that the binding site for the LL motif maps to the appendage domain of β2-adaptin. To analyze the biological significance of the LL/β2 interaction, we utilized RNA interference to specifically knockdown AP-2. Our results show that RNAi-mediated targeting of the μ2 subunit leads to cellular depletion of AP-2, but not AP-1 adaptor complexes in HeLa cells. As a consequence, GLUT8 accumulates at the plasma membrane at comparable levels to those observed in K44A-transfected cells. Conversely, the intracellular localization of mutant GLUT8-LL/AA is restored by replacing the LL motif in GLUT8 with the transferrin receptor-derived μ2-adaptin binding motif YTRF, indicating that for endocytosis both AP-2 binding motifs can substitute for each other. Thus, our data demonstrate that recruitment of GLUT8 to the endocytic machinery occurs via direct interaction of the dileucine motif with β2-adaptin, and that endocytosis might be the main site at which GLUT8 is likely to be regulated.
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Affiliation(s)
- Ulrike Schmidt
- German Institute of Human Nutrition, Potsdam, Nuthetal, Germany
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42
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Gupta SN, Kloster MM, Rodionov DG, Bakke O. Re-routing of the invariant chain to the direct sorting pathway by introduction of an AP3-binding motif from LIMP II. Eur J Cell Biol 2006; 85:457-67. [PMID: 16542748 DOI: 10.1016/j.ejcb.2006.02.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2005] [Revised: 02/01/2006] [Accepted: 02/02/2006] [Indexed: 11/16/2022] Open
Abstract
AP3 is a heteromeric adaptor protein complex involved in the biogenesis of late endosomal/lysosomal structures. It recognizes tyrosine- and leucine-based sorting signals present in the cytoplasmic tails or loops of a number of proteins and is thought to be responsible for the direct transport of these proteins from the Golgi network to late endosomal/lysosomal structures. We have previously reported (Rodionov, Höning, Silye, Kongsvik, von Figura, Bakke, 2002. Structural requirements for interactions between leucine-sorting signals and clathrin-associated adaptor protein complex AP3. J. Biol. Chem. 277, 47436-47443) that in vitro binding of AP3 to the leucine signals is dependent on the nature of three residues immediately upstream of the leucine signal and suggested that these three amino acids define whether the protein is sorted to endosomes via the plasma membrane (PM) or traffics directly to the late endosomes/lysosomes. In this paper, we show in vivo evidence that residues favoring AP3 binding introduced into a protein that is transported via the PM such as the invariant chain can re-route such protein into direct sorting to late endosomal/lysosomal structures.
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Affiliation(s)
- Shailly N Gupta
- Department of Molecular Biosciences, University of Oslo, N-0316 Oslo, Norway
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Torii S, Saito N, Kawano A, Zhao S, Izumi T, Takeuchi T. Cytoplasmic Transport Signal is Involved in Phogrin Targeting and Localization to Secretory Granules. Traffic 2005; 6:1213-24. [PMID: 16262730 DOI: 10.1111/j.1600-0854.2005.00353.x] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Phogrin is an integral glycoprotein primarily expressed in neuroendocrine cells. The predominant localization of phogrin is on dense-core secretory granules, and the lumenal domain has been shown to be involved in its efficient sorting to the regulated secretory pathway. Here, we present data showing that a leucine-based sorting signal [EExxxIL] within the cytoplasmic tail contributes its steady-state localization to secretory granules. Deletion mutants in the tail region failed to represent granular distribution in pancreatic beta-cell line, MIN6, and anterior pituitary cell line, AtT-20. A sorting signal mutant with two glutamic acids substituted into alanines (EE/AA) is primarily accumulated in the Golgi area instead of secretory granules, and another mutant (IL/AA) is trapped at the plasma membrane due to a defect in endocytosis. We further demonstrate that the leucine-based sorting signal of phogrin specifically interacts with both adaptor protein (AP)-1 and AP-2 clathrin adaptor complexes in vitro. These observations, along with previous studies, suggest that distinct domains of phogrin mediate proper localization of this transmembrane protein on secretory granules.
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Affiliation(s)
- Seiji Torii
- Laboratory of Secretion Biology, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan
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Santambrogio L, Potolicchio I, Fessler SP, Wong SH, Raposo G, Strominger JL. Involvement of caspase-cleaved and intact adaptor protein 1 complex in endosomal remodeling in maturing dendritic cells. Nat Immunol 2005; 6:1020-8. [PMID: 16170319 DOI: 10.1038/ni1250] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2004] [Accepted: 08/09/2005] [Indexed: 01/01/2023]
Abstract
The involvement of the tetrameric adaptor protein 1 (AP-1) complex in protein sorting in intracellular compartments is not yet completely defined. Here we report that in immature dendritic cells, the beta1- and gamma-subunits of AP-1 underwent caspase 3-catalyzed cleavage in their hinge regions, resulting in removal of the C-terminal 'ear' domains. Cleavage was inhibited by lipopolysaccharide or caspase inhibitors, each of which led to maturation of the dendritic cells, demonstrated by endosomal remodeling and an increase in surface expression of peptide-loaded major histocompatibility complex class II. Overexpression of similarly truncated AP-1 together with 'silencing' of the endogenous genes in immature dendritic cells did not compromise delivery of major histocompatibility complex class II invariant chain to endosomal compartments. However, after lipopolysaccharide-induced maturation, overexpression of truncated AP-1 and 'silencing' of endogenous genes did result in the anomalous surface accumulation of invariant chain and the peptide-editing molecule H2-DM. Thus, at least one function for intact AP-1 is to retain some proteins in endosomes during the dendritic cell maturation process in which others are allowed to egress to the cell surface.
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Affiliation(s)
- Laura Santambrogio
- Department of Cancer Immunology and AIDS, Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA.
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Weise F, Thilo L, Engstler M, Wiese M, Benzel I, Kühn C, Bühring HJ, Overath P. Binding affinity and capacity of putative adaptor-mediated sorting of a Type I membrane protein in Leishmania mexicana. Mol Biochem Parasitol 2005; 142:203-11. [PMID: 15890416 DOI: 10.1016/j.molbiopara.2005.04.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Revised: 03/28/2005] [Accepted: 04/11/2005] [Indexed: 10/25/2022]
Abstract
The membrane-bound acid phosphatase (MBAP), a Type I membrane protein predominantly associated with endosomal/lysosomal structures of Leishmania mexicana promastigotes, contains motifs in its cytosolic COOH-terminal tail (-MEVWRRYMKFKNKQSEAIIV-COOH) akin to tyrosine- and di-leucine-based sorting signals in multicellular organisms. Here, we first show that the COOH-terminal residues IIV of MBAP, but not the Y-residue, are required for endosomal targeting, suggesting specific binding to an adaptor complex at the cell surface. We then determine whether specific binding can be saturated by analysing the efficiency of endosomal targeting for increasing numbers of MBAP molecules per cell. The ratio of the steady-state abundance of wild-type MBAP on the cell surface to MBAP on endosomes increases until the distribution is no longer different from that observed for a mutant MBAP which lacks the IIV-motif or for a glycosylphosphatidylinositol-anchored form, both of which are distributed according to bulk membrane flow. A quantitative analysis of these in vivo results indicates specific binding to a putative adaptor complex with an affinity of about 10-4M to 50,000 sorting sites on the cell surface.
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Affiliation(s)
- Frank Weise
- Max-Planck-Institut für Biologie, Abteilung Membranbiochemie, D-72076 Tübingen, Germany
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46
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Coleman SH, Van Damme N, Day JR, Noviello CM, Hitchin D, Madrid R, Benichou S, Guatelli JC. Leucine-specific, functional interactions between human immunodeficiency virus type 1 Nef and adaptor protein complexes. J Virol 2005; 79:2066-78. [PMID: 15681409 PMCID: PMC546596 DOI: 10.1128/jvi.79.4.2066-2078.2005] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The human immunodeficiency virus type 1 virulence protein Nef interacts with the endosomal sorting machinery via a leucine-based motif. Similar sequences within the cytoplasmic domains of cellular transmembrane proteins bind to the adaptor protein (AP) complexes of coated vesicles to modulate protein traffic, but the molecular basis of the interactions between these motifs and the heterotetrameric complexes is controversial. To identify the target of the Nef leucine motif, the native sequence was replaced with either leucine- or tyrosine-based AP-binding sequences from cellular proteins, and the interactions with AP subunits were correlated with function. Tyrosine motifs predictably modulated the interactions between Nef and the mu subunits of AP-1, AP-2, and AP-3; heterologous leucine motifs caused little change in these interactions. Conversely, leucine motifs mediated a ternary interaction between Nef and hemicomplexes containing the sigma1 plus gamma subunits of AP-1 or the sigma3 plus delta subunits of AP-3, whereas tyrosine motifs did not. Similarly, only leucine motifs supported the Nef-mediated association of AP-1 and AP-3 with endosomal membranes in cells treated with brefeldin A. Functionally, Nef proteins containing leucine motifs down-regulated CD4 from the cell surface and enhanced viral replication, whereas those containing tyrosine motifs were inactive. Apparently, the interaction of Nef with the mu subunits of AP complexes is insufficient for function. A leucine-specific mode of interaction that likely involves AP hemicomplexes is further required for Nef activity. The mu and hemicomplex interactions may cooperate to yield high avidity binding of AP complexes to Nef. This binding likely underlies the unusual ability of Nef to induce the stabilization of these complexes on endosomal membranes, an activity that correlates with enhancement of viral replication.
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Affiliation(s)
- Scott H Coleman
- Department of Medicine, University of California, San Diego, La Jolla, CA 92093-0679, USA
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47
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McCormick PJ, Martina JA, Bonifacino JS. Involvement of clathrin and AP-2 in the trafficking of MHC class II molecules to antigen-processing compartments. Proc Natl Acad Sci U S A 2005; 102:7910-5. [PMID: 15911768 PMCID: PMC1138261 DOI: 10.1073/pnas.0502206102] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2005] [Indexed: 11/18/2022] Open
Abstract
Major histocompatibility complex class II (MHC-II) molecules are composed of two polymorphic chains, alpha and beta, which assemble with an invariant chain, Ii, in the endoplasmic reticulum. The assembled MHC-II complexes are transported to the Golgi complex and then to late endosomes/lysosomes, where Ii is degraded and alphabeta dimers bind peptides derived from exogenous antigens. Targeting of MHC-II molecules to these compartments is mediated by two dileucine-based signals in the cytoplasmic domain of Ii. These signals bind in vitro to two adaptor protein (AP) complexes, AP-1 and AP-2, which are components of clathrin coats involved in vesicle formation and cargo sorting. The physiological roles of these proteins in MHC-II molecule trafficking, however, remain to be addressed. Here, we report the use of RNA interference to examine the involvement of clathrin and four AP complexes (AP-1, AP-2, AP-3, and AP-4) in MHC-II molecule trafficking in vivo. We found that depletion of clathrin or AP-2 caused >10-fold increases in Ii expression on the cell surface and a concomitant decrease in Ii localization to endosomal/lysosomal vesicles. In addition, depletion of clathrin or AP-2 delayed the degradation of Ii and reduced the surface expression of peptide-loaded alphabeta dimers. In contrast, depletion of AP-1, AP-3, or AP-4 had little or no effect. These findings demonstrate that clathrin and AP-2 participate in MHC-II molecule trafficking in vivo. Because AP-2 is only associated with the plasma membrane, these results also indicate that a significant pool of MHC-II molecules traffic to the endosomal-lysosomal system by means of the cell surface.
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Affiliation(s)
- Peter J McCormick
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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48
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Dugast M, Toussaint H, Dousset C, Benaroch P. AP2 clathrin adaptor complex, but not AP1, controls the access of the major histocompatibility complex (MHC) class II to endosomes. J Biol Chem 2005; 280:19656-64. [PMID: 15749704 DOI: 10.1074/jbc.m501357200] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Newly synthesized MHC II alpha- and beta-chains associated with the invariant chain chaperone (Ii) enter the endocytic pathway for Ii degradation and loading with peptides before transport to the cell surface. It is unclear how alphabetaIi complexes are sorted from the Golgi apparatus and directed to endosomes. However, indirect evidence tends to support direct transport involving the AP1 clathrin adaptor complex. Surprisingly, we show here that knocking down the production of AP1 by RNA interference did not affect the trafficking of alphabetaIi complexes. In contrast, AP2 depletion led to a large increase in surface levels of alphabetaIi complexes, inhibited their rapid internalization, and strongly delayed the appearance of mature MHC II in intracellular compartments. Thus, in the cell systems studied here, rapid internalization of alphabetaIi complexes via an AP2-dependent pathway represents a key step for MHC II delivery to endosomes and lysosomes.
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Affiliation(s)
- Marc Dugast
- INSERM U520 Institut Curie, Section de Recherche, Paris, France
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Lizée G, Basha G, Jefferies WA. Tails of wonder: endocytic-sorting motifs key for exogenous antigen presentation. Trends Immunol 2005; 26:141-9. [PMID: 15745856 DOI: 10.1016/j.it.2005.01.005] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Antigen-presenting molecules, including MHC I, II and CD1, have central roles in the induction of T cell-mediated immunity against pathogens and tumors and also in the maintenance of tolerance towards self-antigens. The presentation of exogenously derived peptide and lipid antigens to specific T cells by professional antigen-presenting cells (pAPCs) is an essential part of both processes. Exogenous antigen loading takes place mostly within specialized endocytic and phagocytic compartments of pAPCs and targeting of antigen-presenting molecules to these intracellular compartments is mediated by highly conserved cytoplasmic sorting motifs. Recent data have revealed that the cytoplasmic tails of antigen-presenting molecules, by controlling the access of these molecules to exogenously derived antigens, have a crucially important and largely underappreciated role in the generation of tolerance and T-cell mediated immunity.
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Affiliation(s)
- Gregory Lizée
- Biomedical Research Centre, The Michael Smith Laboratories, Department of Microbiology and Immunology, University of British Columbia, 2222 Health Sciences Mall, Vancouver, BC, Canada, V6T 1Z3
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Barois N, Bakke O. The adaptor protein AP-4 as a component of the clathrin coat machinery: a morphological study. Biochem J 2005; 385:503-10. [PMID: 15377281 PMCID: PMC1134722 DOI: 10.1042/bj20041010] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2004] [Revised: 09/01/2004] [Accepted: 09/17/2004] [Indexed: 11/17/2022]
Abstract
The four members of the AP (adaptor protein) family are heterotetrameric cytosolic complexes that are involved in the intracellular trafficking of cargo proteins between different organelles. They interact with motifs present in the cytoplasmic tails of their specific cargo proteins at different intracellular locations. While AP-1, AP-2 and AP-3 have been investigated extensively, very few studies have focused on the fourth member, AP-4. In the present study, we report on the intracellular localization of AP-4 in the MDCK (Madin-Darby canine kidney) and MelJuSo cell lines after immunogold labelling of ultrathin cryosections. We find that AP-4 is localized mainly in the Golgi complex, as well as on endosomes and transport vesicles. Interestingly, we show for the first time that AP-4 is localized with the clathrin coat machinery in the Golgi complex and in the endocytic pathway. Furthermore, we find that AP-4 is localized with the CI-MPR (cation-independent mannose 6-phosphate receptor), but not with the transferrin receptor, LAMP-2 (lysosomal-associated membrane protein-2) or invariant chain. The difference in morphology between CI-MPR/AP-4-positive vesicles and CI-MPR/AP-1-positive vesicles raises the possibility that AP-4 acts at a location different from that of AP-1 in the intracellular trafficking pathway of CI-MPR.
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Key Words
- adaptor protein-4 (ap-4)
- cation-independent mannose 6-phosphate receptor
- clathrin coat
- immuno-electron microscopy
- intracellular trafficking
- ap, adaptor protein
- cd-mpr, cation-dependent mannose 6-phosphate receptor
- ci-mpr, cation-independent mannose 6-phosphate receptor
- hrp, horseradish peroxidase
- ii, invariant chain
- lamp, lysosomal-associated membrane protein
- ldlr, low-density lipoprotein receptor
- mdck, madin–darby canine kidney
- mpr, mannose 6-phosphate receptor
- pag, protein a-coated colloidal gold particles
- tfr, transferrin receptor
- tgn, trans-golgi network
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Affiliation(s)
- Nicolas Barois
- *Department of Molecular Cell Biology, University of Oslo, PB 1041 Blindern, N-0316 Oslo, Norway
| | - Oddmund Bakke
- *Department of Molecular Cell Biology, University of Oslo, PB 1041 Blindern, N-0316 Oslo, Norway
- †Department of Biomedicine, Jonas Lies vei 91, N-5000 Bergen, Norway
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