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Kremlitzka M, Colineau L, Nowacka AA, Mohlin FC, Wozniak K, Blom AM, King BC. Alternative translation and retrotranslocation of cytosolic C3 that detects cytoinvasive bacteria. Cell Mol Life Sci 2022; 79:291. [PMID: 35546365 PMCID: PMC9095555 DOI: 10.1007/s00018-022-04308-z] [Citation(s) in RCA: 13] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2022] [Revised: 03/29/2022] [Accepted: 04/12/2022] [Indexed: 01/05/2023]
Abstract
Complement C3 was originally regarded as a serum effector protein, although recent data has emerged suggesting that intracellular C3 can also regulate basic cellular processes. Despite the growing interest in intracellular C3 functions, the mechanism behind its generation has not been demonstrated. In this study we show that C3 can be expressed from an alternative translational start site, resulting in C3 lacking the signal peptide, which is therefore translated in the cytosol. In contrast to the secreted form, alternatively translated cytosolic C3 is not glycosylated, is present mainly in a reduced state, and is turned over by the ubiquitin–proteasome system. C3 can also be retrotranslocated from the endoplasmic reticulum into the cytosol, structurally resembling secreted C3. Finally, we demonstrate that intracellular cytosolic C3 can opsonize invasive Staphylococcus aureus within epithelial cell, slowing vacuolar escape as well as impacting bacterial survival on subsequent exposure to phagocytes. Our work therefore reveals the existence and origin of intracellular, cytosolic C3, and demonstrates functions for cytosolic C3 in intracellular detection of cytoinvasive pathogens.
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Affiliation(s)
- Mariann Kremlitzka
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden.,Department of Immunology, Eötvös Loránd University, Budapest, Hungary
| | - Lucie Colineau
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Alicja A Nowacka
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Frida C Mohlin
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Katarzyna Wozniak
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
| | - Anna M Blom
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden.
| | - Ben C King
- Division of Medical Protein Chemistry, Department of Translational Medicine, Lund University, Malmö, Sweden
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2
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Das P, Xu WK, Gautam AKS, Lozano MM, Dudley JP. A Retrotranslocation Assay That Predicts Defective VCP/p97-Mediated Trafficking of a Retroviral Signal Peptide. mBio 2022; 13:e0295321. [PMID: 35089078 PMCID: PMC8725593 DOI: 10.1128/mbio.02953-21] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2021] [Accepted: 11/18/2021] [Indexed: 12/12/2022] Open
Abstract
Studies of viral replication have provided critical insights into host processes, including protein trafficking and turnover. Mouse mammary tumor virus (MMTV) is a betaretrovirus that encodes a functional 98-amino-acid signal peptide (SP). MMTV SP is generated from both Rem and envelope precursor proteins by signal peptidase cleavage in the endoplasmic reticulum (ER) membrane. We previously showed that SP functions as a human immunodeficiency virus type 1 (HIV-1) Rev-like protein that is dependent on the AAA ATPase valosin-containing protein (VCP)/p97 to subvert ER-associated degradation (ERAD). SP contains a nuclear localization sequence (NLS)/nucleolar localization sequence (NoLS) within the N-terminal 45 amino acids. To directly determine the SP regions needed for membrane extraction and trafficking, we developed a quantitative retrotranslocation assay with biotin acceptor peptide (BAP)-tagged SP proteins. Use of alanine substitution mutants of BAP-tagged MMTV SP in retrotranslocation assays revealed that mutation of amino acids 57 and 58 (M57-58) interfered with ER membrane extraction, whereas adjacent mutations did not. The M57-58 mutant also showed reduced interaction with VCP/p97 in coimmunoprecipitation experiments. Using transfection and reporter assays to measure activity of BAP-tagged proteins, both M57-58 and an adjacent mutant (M59-61) were functionally defective compared to wild-type SP. Confocal microscopy revealed defects in SP nuclear trafficking and abnormal localization of both M57-58 and M59-61. Furthermore, purified glutathione S-transferase (GST)-tagged M57-58 and M59-61 demonstrated reduced ability to oligomerize compared to tagged wild-type SP. These experiments suggest that SP amino acids 57 and 58 are critical for VCP/p97 interaction and retrotranslocation, whereas residues 57 to 61 are critical for oligomerization and nuclear trafficking independent of the NLS/NoLS. Our results emphasize the complex host interactions with long signal peptides. IMPORTANCE Endoplasmic reticulum-associated degradation (ERAD) is a form of cellular protein quality control that is manipulated by viruses, including the betaretrovirus, mouse mammary tumor virus (MMTV). MMTV-encoded signal peptide (SP) has been shown to interact with an essential ERAD factor, VCP/p97 ATPase, to mediate its extraction from the ER membrane, also known as retrotranslocation, for RNA binding and nuclear function. In this paper, we developed a quantitative retrotranslocation assay that identified an SP substitution mutant, which is defective for VCP interaction as well as nuclear trafficking, oligomer formation, and function. An adjacent SP mutant was competent for retrotranslocation and VCP interaction but shared the other defects. Our results revealed the requirement for VCP during SP trafficking and the complex cellular pathways used by long signal peptides.
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Affiliation(s)
- Poulami Das
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
- LaMontagne Center for Infectious Disease, The University of Texas at Austin, Austin, Texas, USA
| | - Wendy Kaichun Xu
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
- LaMontagne Center for Infectious Disease, The University of Texas at Austin, Austin, Texas, USA
| | - Amit Kumar Singh Gautam
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
- LaMontagne Center for Infectious Disease, The University of Texas at Austin, Austin, Texas, USA
| | - Mary M. Lozano
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
- LaMontagne Center for Infectious Disease, The University of Texas at Austin, Austin, Texas, USA
| | - Jaquelin P. Dudley
- Department of Molecular Biosciences, The University of Texas at Austin, Austin, Texas, USA
- LaMontagne Center for Infectious Disease, The University of Texas at Austin, Austin, Texas, USA
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3
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Schmidt CC, Vasic V, Stein A. Doa10 is a membrane protein retrotranslocase in ER-associated protein degradation. eLife 2020; 9:56945. [PMID: 32588820 PMCID: PMC7319771 DOI: 10.7554/elife.56945] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2020] [Accepted: 05/28/2020] [Indexed: 12/17/2022] Open
Abstract
In endoplasmic reticulum-associated protein degradation (ERAD), membrane proteins are ubiquitinated, extracted from the membrane, and degraded by the proteasome. The cytosolic ATPase Cdc48 drives extraction by pulling on polyubiquitinated substrates. How hydrophobic transmembrane (TM) segments are moved from the phospholipid bilayer into cytosol, often together with hydrophilic and folded ER luminal protein parts, is not known. Using a reconstituted system with purified proteins from Saccharomyces cerevisiae, we show that the ubiquitin ligase Doa10 (Teb-4/MARCH6 in animals) is a retrotranslocase that facilitates membrane protein extraction. A substrate’s TM segment interacts with the membrane-embedded domain of Doa10 and then passively moves into the aqueous phase. Luminal substrate segments cross the membrane in an unfolded state. Their unfolding occurs on the luminal side of the membrane by cytoplasmic Cdc48 action. Our results reveal how a membrane-bound retrotranslocase cooperates with the Cdc48 ATPase in membrane protein extraction. The inside of a cell contains many different compartments called organelles, which are separated by membranes. Each organelle is composed of a unique set of proteins and performs specific roles in the cell. The endoplasmic reticulum, or ER for short, is an organelle where many proteins are produced. Most of these proteins are then released from the cell or sorted to other organelles. The ER has a strict quality control system that ensures any faulty proteins are quickly marked for the cell to destroy. However, the destruction process itself does not happen in the ER, so faulty proteins first need to leave this organelle. This is achieved by a group of proteins known as endoplasmic reticulum-associated protein degradation machinery (or ERAD for short). To extract a faulty protein from the ER, proteins of the ER and outside the ER cooperate. First, an ERAD protein called Doa10 attaches a small protein tag called ubiquitin to the faulty proteins to mark them for destruction. Then, outside of the ER, a protein called Cdc48 ‘grabs’ the ubiquitin tag and pulls. But that is only part of the story. Many of the proteins made by the ER have tethers that anchor them firmly to the membrane, making them much harder to remove. To get a better idea of how the extraction works, Schmidt et al. rebuilt the ERAD machinery in a test tube. This involved purifying proteins from yeast and inserting them into artificial membranes, allowing closer study of each part of the process. This revealed that attaching ubiquitin tags to faulty proteins is only one part of Doa10's role; it also participates in the extraction itself. Part of Doa10 resides within the membrane, and this ‘membrane-spanning domain’ can interact with faulty proteins, loosening their membrane anchors. At the same time, Cdc48 pulls from the outside. This pulling force causes the faulty proteins to unfold, allowing them to pass through the membrane. Given these findings, the next step is to find out exactly how Doa10 works by looking at its three-dimensional structure. This could have implications not only for the study of ERAD, but of similar quality control processes in other organelles too. A build-up of faulty proteins can cause diseases like neurodegeneration, so understanding how cells remove faulty proteins could help future medical research.
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Affiliation(s)
- Claudia C Schmidt
- Research Group Membrane Protein Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Vedran Vasic
- Research Group Membrane Protein Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Alexander Stein
- Research Group Membrane Protein Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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4
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Shi J, Hu X, Guo Y, Wang L, Ji J, Li J, Zhang ZR. A technique for delineating the unfolding requirements for substrate entry into retrotranslocons during endoplasmic reticulum-associated degradation. J Biol Chem 2019; 294:20084-20096. [PMID: 31748412 DOI: 10.1074/jbc.ra119.010019] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2019] [Revised: 11/13/2019] [Indexed: 11/06/2022] Open
Abstract
The endoplasmic reticulum-associated degradation (ERAD) pathway mediates the endoplasmic reticulum-to-cytosol retrotranslocation of defective proteins through protein complexes called retrotranslocons. Defective proteins usually have complex conformations and topologies, and it is unclear how ERAD can thread these conformationally diverse protein substrates through the retrotranslocons. Here, we investigated the substrate conformation flexibility necessary for transport via retrotranslocons on the ERAD-L, ERAD-M, and HIV-encoded protein Vpu-hijacked ERAD branches. To this end, we appended various ERAD substrates with specific domains whose conformations were tunable in flexibility or tightness by binding to appropriate ligands. With this technique, we could define the capacity of specific retrotranslocons in disentangling very tight, less tight but well-folded, and unstructured conformations. The Hrd1 complex, the retrotranslocon on the ERAD-L branch, permitted the passage of substrates with a proteinase K-resistant tight conformation, whereas the E3 ligase gp78-mediated ERAD-M allowed passage only of nearly completely disordered but not well-folded substrates and thus may have the least unfoldase activity. Vpu-mediated ERAD, containing a potential retrotranslocon, could unfold well-folded substrates for successful retrotranslocation. However, substrate retrotranslocation in Vpu-mediated ERAD was blocked by enhanced conformational tightness of the substrate. On the basis of these findings, we propose a mechanism underlying polypeptide movement through the endoplasmic reticulum membrane. We anticipate that our biochemical system paves the way for identifying the factors necessary for the retrotranslocation of membrane proteins.
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Affiliation(s)
- Junfen Shi
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Xianyan Hu
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Yuan Guo
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Linhan Wang
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Jia Ji
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Jiqiang Li
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China.,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
| | - Zai-Rong Zhang
- Interdisciplinary Research Center on Biology and Chemistry, Shanghai Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 201210, China .,University of Chinese Academy of Sciences, Shijingshan District, Beijing 100049, China
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5
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The NAE Pathway: Autobahn to the Nucleus for Cell Surface Receptors. Cells 2019; 8:cells8080915. [PMID: 31426451 PMCID: PMC6721735 DOI: 10.3390/cells8080915] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Revised: 08/13/2019] [Accepted: 08/13/2019] [Indexed: 12/19/2022] Open
Abstract
Various growth factors and full-length cell surface receptors such as EGFR are translocated from the cell surface to the nucleoplasm, baffling cell biologists to the mechanisms and functions of this process. Elevated levels of nuclear EGFR correlate with poor prognosis in various cancers. In recent years, nuclear EGFR has been implicated in regulating gene transcription, cell proliferation and DNA damage repair. Different models have been proposed to explain how the receptors are transported into the nucleus. However, a clear consensus has yet to be reached. Recently, we described the nuclear envelope associated endosomes (NAE) pathway, which delivers EGFR from the cell surface to the nucleus. This pathway involves transport, docking and fusion of NAEs with the outer membrane of the nuclear envelope. EGFR is then presumed to be transported through the nuclear pore complex, extracted from membranes and solubilised. The SUN1/2 nuclear envelope proteins, Importin-beta, nuclear pore complex proteins and the Sec61 translocon have been implicated in the process. While this framework can explain the cell surface to nucleus traffic of EGFR and other cell surface receptors, it raises several questions that we consider in this review, together with implications for health and disease.
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6
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Lata S, Mishra R, Banerjea AC. Proteasomal Degradation Machinery: Favorite Target of HIV-1 Proteins. Front Microbiol 2018; 9:2738. [PMID: 30524389 PMCID: PMC6262318 DOI: 10.3389/fmicb.2018.02738] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2018] [Accepted: 10/26/2018] [Indexed: 12/17/2022] Open
Abstract
Proteasomal degradation pathways play a central role in regulating a variety of protein functions by controlling not only their turnover but also the physiological behavior of the cell. This makes it an attractive target for the pathogens, especially viruses which rely on the host cellular machinery for their propagation and pathogenesis. Viruses have evolutionarily developed various strategies to manipulate the host proteasomal machinery thereby creating a cellular environment favorable for their own survival and replication. Human immunodeficiency virus-1 (HIV-1) is one of the most dreadful viruses which has rapidly spread throughout the world and caused high mortality due to its high evolution rate. Here, we review the various mechanisms adopted by HIV-1 to exploit the cellular proteasomal machinery in order to escape the host restriction factors and components of host immune system for supporting its own multiplication, and successfully created an infection.
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Affiliation(s)
- Sneh Lata
- Virology Lab II, National Institute of Immunology, New Delhi, India
| | - Ritu Mishra
- Virology Lab II, National Institute of Immunology, New Delhi, India
| | - Akhil C Banerjea
- Virology Lab II, National Institute of Immunology, New Delhi, India
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7
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Cesaratto F, Sasset L, Myers MP, Re A, Petris G, Burrone OR. BiP/GRP78 Mediates ERAD Targeting of Proteins Produced by Membrane-Bound Ribosomes Stalled at the STOP-Codon. J Mol Biol 2018; 431:123-141. [PMID: 30367842 PMCID: PMC7094721 DOI: 10.1016/j.jmb.2018.10.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2018] [Revised: 10/15/2018] [Accepted: 10/16/2018] [Indexed: 11/29/2022]
Abstract
Translational stalling of ribosome bound to endoplasmic reticulum (ER) membrane requires an accurate clearance of the associated polypeptides, which is not completely understood in mammals. We characterized in mammalian cells the model of ribosomal stalling at the STOP-codon based on proteins tagged at the C-terminus with the picornavirus 2A peptide followed by a termination codon instead of the Proline (2A*). We exploited the 2A* stalling model to characterize the pathway of degradation of ER-targeted polypeptides. We report that the ER chaperone BiP/GRP78 is a new main factor involved. Moreover, degradation of the ER-stalled polypeptides required the activities of the AAA-ATPase VCP/p97, its associated deubiquitinylase YOD1, the ribosome-associated ubiquitin ligase Listerin and the proteasome. In human proteome, we found two human C-terminal amino acid sequences that cause similar stalling at the STOP-codon. Our data suggest that translational stalling at the ER membrane activates protein degradation at the interface of ribosomal- and ER-associated quality control systems. Ribosomal stalling at the STOP-codon causes degradation of the translated protein. Picornavirus 2A peptide and related sequences cause ribosome stalling at STOP-codon. BiP/GRP78 recognizes polypeptides produced by membrane-bound stalled ribosomes. ER-stalled polypeptides are disposed of through the ERAD pathway. BIP/GRP78 is a novel key player for ERAD targeting of stalled ribosomal peptides.
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Affiliation(s)
- Francesca Cesaratto
- Laboratory of Molecular Immunology, International Centre for Genetic Engineering and Biotechnology, ICGEB, Padriciano 99, 34149 Trieste, Italy
| | - Linda Sasset
- Laboratory of Molecular Immunology, International Centre for Genetic Engineering and Biotechnology, ICGEB, Padriciano 99, 34149 Trieste, Italy
| | - Michael P Myers
- Laboratory of Protein Networks, International Centre for Genetic Engineering and Biotechnology, ICGEB, Padriciano 99, 34149 Trieste, Italy
| | - Angela Re
- Centre for Integrative Biology (CIBIO), University of Trento, Via Sommarive 9, 38123 Trento, Italy; Center for Sustainable Future Technologies, Fondazione Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy; Center for Sustainable Future Technologies, Fondazione Istituto Italiano di Tecnologia, C.so Trento 21, 10129 Torino, Italy
| | - Gianluca Petris
- Centre for Integrative Biology (CIBIO), University of Trento, Via Sommarive 9, 38123 Trento, Italy.
| | - Oscar R Burrone
- Laboratory of Molecular Immunology, International Centre for Genetic Engineering and Biotechnology, ICGEB, Padriciano 99, 34149 Trieste, Italy.
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8
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Ellgaard L, Sevier CS, Bulleid NJ. How Are Proteins Reduced in the Endoplasmic Reticulum? Trends Biochem Sci 2018; 43:32-43. [PMID: 29153511 PMCID: PMC5751730 DOI: 10.1016/j.tibs.2017.10.006] [Citation(s) in RCA: 71] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Revised: 10/23/2017] [Accepted: 10/24/2017] [Indexed: 12/16/2022]
Abstract
The reversal of thiol oxidation in proteins within the endoplasmic reticulum (ER) is crucial for protein folding, degradation, chaperone function, and the ER stress response. Our understanding of this process is generally poor but progress has been made. Enzymes performing the initial reduction of client proteins, as well as the ultimate electron donor in the pathway, have been identified. Most recently, a role for the cytosol in ER protein reduction has been revealed. Nevertheless, how reducing equivalents are transferred from the cytosol to the ER lumen remains an open question. We review here why proteins are reduced in the ER, discuss recent data on catalysis of steps in the pathway, and consider the implications for redox homeostasis within the early secretory pathway.
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Affiliation(s)
- Lars Ellgaard
- Department of Biology, University of Copenhagen, 2200 Copenhagen, Denmark.
| | - Carolyn S Sevier
- Department of Molecular Medicine, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853-2703, USA.
| | - Neil J Bulleid
- Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow G12 8QQ, UK.
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9
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Hijacking of the Ubiquitin/Proteasome Pathway by the HIV Auxiliary Proteins. Viruses 2017; 9:v9110322. [PMID: 29088112 PMCID: PMC5707529 DOI: 10.3390/v9110322] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2017] [Revised: 10/26/2017] [Accepted: 10/30/2017] [Indexed: 02/08/2023] Open
Abstract
The ubiquitin-proteasome system (UPS) ensures regulation of the protein pool in the cell by ubiquitination of proteins followed by their degradation by the proteasome. It plays a central role in the cell under normal physiological conditions as well as during viral infections. On the one hand, the UPS can be used by the cell to degrade viral proteins, thereby restricting the viral infection. On the other hand, it can also be subverted by the virus to its own advantage, notably to induce degradation of cellular restriction factors. This makes the UPS a central player in viral restriction and counter-restriction. In this respect, the human immunodeficiency viruses (HIV-1 and 2) represent excellent examples. Indeed, many steps of the HIV life cycle are restricted by cellular proteins, some of which are themselves components of the UPS. However, HIV itself hijacks the UPS to mediate defense against several cellular restriction factors. For example, the HIV auxiliary proteins Vif, Vpx and Vpu counteract specific restriction factors by the recruitment of cellular UPS components. In this review, we describe the interplay between HIV and the UPS to illustrate its role in the restriction of viral infections and its hijacking by viral proteins for counter-restriction.
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10
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Sikorska N, Lemus L, Aguilera-Romero A, Manzano-Lopez J, Riezman H, Muñiz M, Goder V. Limited ER quality control for GPI-anchored proteins. J Cell Biol 2017; 213:693-704. [PMID: 27325793 PMCID: PMC4915193 DOI: 10.1083/jcb.201602010] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2016] [Accepted: 05/26/2016] [Indexed: 02/06/2023] Open
Abstract
Sikorska et al. find that remodeling of a GPI anchor after its attachment to proteins inside the ER strongly promotes ER export but occurs independently of protein folding, thereby effectively limiting ER quality control, potentially including ER-associated degradation of all GPI-anchored proteins. Endoplasmic reticulum (ER) quality control mechanisms target terminally misfolded proteins for ER-associated degradation (ERAD). Misfolded glycophosphatidylinositol-anchored proteins (GPI-APs) are, however, generally poor ERAD substrates and are targeted mainly to the vacuole/lysosome for degradation, leading to predictions that a GPI anchor sterically obstructs ERAD. Here we analyzed the degradation of the misfolded GPI-AP Gas1* in yeast. We could efficiently route Gas1* to Hrd1-dependent ERAD and provide evidence that it contains a GPI anchor, ruling out that a GPI anchor obstructs ERAD. Instead, we show that the normally decreased susceptibility of Gas1* to ERAD is caused by canonical remodeling of its GPI anchor, which occurs in all GPI-APs and provides a protein-independent ER export signal. Thus, GPI anchor remodeling is independent of protein folding and leads to efficient ER export of even misfolded species. Our data imply that ER quality control is limited for the entire class of GPI-APs, many of them being clinically relevant.
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Affiliation(s)
- Natalia Sikorska
- Department of Genetics, University of Seville, 41012 Seville, Spain
| | - Leticia Lemus
- Department of Genetics, University of Seville, 41012 Seville, Spain
| | - Auxiliadora Aguilera-Romero
- National Centre of Competence in Research, Chemical Biology, Sciences II, University of Geneva, 1211 Geneva 4, Switzerland Department of Biochemistry, Sciences II, University of Geneva, 1211 Geneva 4, Switzerland
| | - Javier Manzano-Lopez
- Department of Cell Biology, University of Seville, 41012 Seville, Spain Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío, Consejo Superior de Investigaciones Científicas, University of Seville, 41013 Seville, Spain
| | - Howard Riezman
- National Centre of Competence in Research, Chemical Biology, Sciences II, University of Geneva, 1211 Geneva 4, Switzerland Department of Biochemistry, Sciences II, University of Geneva, 1211 Geneva 4, Switzerland
| | - Manuel Muñiz
- Department of Cell Biology, University of Seville, 41012 Seville, Spain Instituto de Biomedicina de Sevilla, Hospital Universitario Virgen del Rocío, Consejo Superior de Investigaciones Científicas, University of Seville, 41013 Seville, Spain
| | - Veit Goder
- Department of Genetics, University of Seville, 41012 Seville, Spain
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11
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Mouse Mammary Tumor Virus Signal Peptide Uses a Novel p97-Dependent and Derlin-Independent Retrotranslocation Mechanism To Escape Proteasomal Degradation. mBio 2017; 8:mBio.00328-17. [PMID: 28351922 PMCID: PMC5371415 DOI: 10.1128/mbio.00328-17] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Multiple pathogens, including viruses and bacteria, manipulate endoplasmic reticulum-associated degradation (ERAD) to avoid the host immune response and promote their replication. The betaretrovirus mouse mammary tumor virus (MMTV) encodes Rem, which is a precursor protein that is cleaved into a 98-amino-acid signal peptide (SP) and a C-terminal protein (Rem-CT). SP uses retrotranslocation for ER membrane extraction and yet avoids ERAD by an unknown mechanism to enter the nucleus and function as a Rev-like protein. To determine how SP escapes ERAD, we used a ubiquitin-activated interaction trap (UBAIT) screen to trap and identify transient protein interactions with SP, including the ERAD-associated p97 ATPase, but not E3 ligases or Derlin proteins linked to retrotranslocation, polyubiquitylation, and proteasomal degradation of extracted proteins. A dominant negative p97 ATPase inhibited both Rem and SP function. Immunoprecipitation experiments indicated that Rem, but not SP, is polyubiquitylated. Using both yeast and mammalian expression systems, linkage of a ubiquitin-like domain (UbL) to SP or Rem induced degradation by the proteasome, whereas SP was stable in the absence of the UbL. ERAD-associated Derlin proteins were not required for SP activity. Together, these results suggested that Rem uses a novel p97-dependent, Derlin-independent retrotranslocation mechanism distinct from other pathogens to avoid SP ubiquitylation and proteasomal degradation. Bacterial and viral infections produce pathogen-specific proteins that interfere with host functions, including the immune response. Mouse mammary tumor virus (MMTV) is a model system for studies of human complex retroviruses, such as HIV-1, as well as cancer induction. We have shown that MMTV encodes a regulatory protein, Rem, which is cleaved into an N-terminal signal peptide (SP) and a C-terminal protein (Rem-CT) within the endoplasmic reticulum (ER) membrane. SP function requires ER membrane extraction by retrotranslocation, which is part of a protein quality control system known as ER-associated degradation (ERAD) that is essential to cellular health. Through poorly understood mechanisms, certain pathogen-derived proteins are retrotranslocated but not degraded. We demonstrate here that MMTV SP retrotranslocation from the ER membrane avoids degradation through a unique process involving interaction with cellular p97 ATPase and failure to acquire cellular proteasome-targeting sequences.
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12
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Abstract
The endoplasmic reticulum is the port of entry for proteins into the secretory pathway and the site of synthesis for several important lipids, including cholesterol, triacylglycerol, and phospholipids. Protein production within the endoplasmic reticulum is tightly regulated by a cohort of resident machinery that coordinates the folding, modification, and deployment of secreted and integral membrane proteins. Proteins failing to attain their native conformation are degraded through the endoplasmic reticulum-associated degradation (ERAD) pathway via a series of tightly coupled steps: substrate recognition, dislocation, and ubiquitin-dependent proteasomal destruction. The same ERAD machinery also controls the flux through various metabolic pathways by coupling the turnover of metabolic enzymes to the levels of key metabolites. We review the current understanding and biological significance of ERAD-mediated regulation of lipid metabolism in mammalian cells.
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Affiliation(s)
- Julian Stevenson
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
| | - Edmond Y Huang
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
| | - James A Olzmann
- Program in Metabolic Biology, Department of Nutritional Sciences and Toxicology, University of California, Berkeley, California 94720;
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Abstract
ER-associated degradation (ERAD) is a protein clearance mechanism by which misfolded, misassembled, or metabolically regulated proteins are specifically dislocated from the ER into the cytosol and degraded by the ubiquitin proteasome system. ERAD very likely evolved to maintain proteostasis and sterol homeostasis in the ER. However, the ironic truth is that membrane-penetrating transportation and protein degradation machineries in ERAD are preferably hijacked by exogenous pathogens such as viruses and toxins for their invasion and evasion from immunological surveillance. In this Review, we provide an overview of our current understanding of the pathogenic hijacking of the host cell ERAD, in which pathogens exploit the complex ERAD machinery in a variety of manners for their own use, suggesting flexibility and plasticity of the molecular machinery of ERAD.
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Sasset L, Petris G, Cesaratto F, Burrone OR. The VCP/p97 and YOD1 Proteins Have Different Substrate-dependent Activities in Endoplasmic Reticulum-associated Degradation (ERAD). J Biol Chem 2015; 290:28175-28188. [PMID: 26463207 DOI: 10.1074/jbc.m115.656660] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2015] [Indexed: 11/06/2022] Open
Abstract
Endoplasmic reticulum-associated degradation (ERAD) is an essential quality control mechanism of the folding state of proteins in the secretory pathway that targets unfolded/misfolded polypeptides for proteasomal degradation. The cytosolic p97/valosin-containing protein is an essential ATPase for degradation of ERAD substrates. It has been considered necessary during retro-translocation to extract proteins from the endoplasmic reticulum that are otherwise supposed to accumulate in the endoplasmic reticulum lumen. The activity of the p97-associated deubiquitinylase YOD1 is also required for substrate disposal. We used the in vivo biotinylation retro-translocation assay in mammalian cells under conditions of impaired p97 or YOD1 activity to directly discriminate their requirements and diverse functions in ERAD. Using different ERAD substrates, we found that both proteins participate in two distinct retro-translocation steps. For CD4 and MHC-Iα, which are induced to degradation by the HIV-1 protein Vpu and by the CMV immunoevasins US2 and US11, respectively, p97 and YOD1 have a retro-translocation-triggering role. In contrast, for three other spontaneous ERAD model substrates (NS1, NHK-α1AT, and BST-2/Tetherin), p97 and YOD1 are required in the downstream events of substrate deglycosylation and proteasomal degradation.
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Affiliation(s)
- Linda Sasset
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Gianluca Petris
- CIBIO, University of Trento, Via delle Regole 101, 38123 Mattarello, Italy.
| | - Francesca Cesaratto
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Oscar R Burrone
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
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Cesaratto F, López-Requena A, Burrone OR, Petris G. Engineered tobacco etch virus (TEV) protease active in the secretory pathway of mammalian cells. J Biotechnol 2015; 212:159-66. [PMID: 26327323 DOI: 10.1016/j.jbiotec.2015.08.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2015] [Revised: 08/25/2015] [Accepted: 08/27/2015] [Indexed: 01/05/2023]
Abstract
Tobacco etch virus protease (TEVp) is a unique endopeptidase with stringent substrate specificity. TEVp has been widely used as a purified protein for in vitro applications, but also as a biological tool directly expressing it in living cells. To adapt the protease to diverse applications, several TEVp mutants with different stability and enzymatic properties have been reported. Herein we describe the development of a novel engineered TEVp mutant designed to be active in the secretory pathway. While wild type TEVp targeted to the secretory pathway of mammalian cells is synthetized as an N-glycosylated and catalytically inactive enzyme, a TEVp mutant with selected mutations at two verified N-glycosylation sites and at an exposed cysteine was highly efficient. This mutant was very active in the endoplasmic reticulum (ER) of living cells and can be used as a biotechnological tool to cleave proteins within the secretory pathway. As an immediate practical application we report the expression of a complete functional monoclonal antibody expressed from a single polypeptide, which was cleaved by our TEVp mutant into the two antibody chains and secreted as an assembled and functional molecule. In addition, we show active TEVp mutants lacking auto-cleavage activity.
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Affiliation(s)
- Francesca Cesaratto
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Alejandro López-Requena
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy; Immunobiology Division, Center of Molecular Immunology, P.O. Box 16040, Havana 11600, Cuba
| | - Oscar R Burrone
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy
| | - Gianluca Petris
- International Centre for Genetic Engineering and Biotechnology, Padriciano 99, 34149 Trieste, Italy.
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Vpu Protein: The Viroporin Encoded by HIV-1. Viruses 2015; 7:4352-68. [PMID: 26247957 PMCID: PMC4576185 DOI: 10.3390/v7082824] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/29/2015] [Revised: 06/29/2015] [Accepted: 07/28/2015] [Indexed: 02/06/2023] Open
Abstract
Viral protein U (Vpu) is a lentiviral viroporin encoded by human immunodeficiency virus type 1 (HIV-1) and some simian immunodeficiency virus (SIV) strains. This small protein of 81 amino acids contains a single transmembrane domain that allows for supramolecular organization via homoligomerization or interaction with other proteins. The topology and trafficking of Vpu through subcellular compartments result in pleiotropic effects in host cells. Notwithstanding the high variability of its amino acid sequence, the functionality of Vpu is well conserved in pandemic virus isolates. This review outlines our current knowledge on the interactions of Vpu with the host cell. The regulation of cellular physiology by Vpu and the validity of this viroporin as a therapeutic target are also discussed.
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Byun H, Gou Y, Zook A, Lozano MM, Dudley JP. ERAD and how viruses exploit it. Front Microbiol 2014; 5:330. [PMID: 25071743 PMCID: PMC4080680 DOI: 10.3389/fmicb.2014.00330] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2014] [Accepted: 06/16/2014] [Indexed: 01/09/2023] Open
Abstract
Endoplasmic reticulum (ER)-associated degradation (ERAD) is a universally important process among eukaryotic cells. ERAD is necessary to preserve cell integrity since the accumulation of defective proteins results in diseases associated with neurological dysfunction, cancer, and infections. This process involves recognition of misfolded or misassembled proteins that have been translated in association with ER membranes. Recognition of ERAD substrates leads to their extraction through the ER membrane (retrotranslocation or dislocation), ubiquitination, and destruction by cytosolic proteasomes. This review focuses on ERAD and its components as well as how viruses use this process to promote their replication and to avoid the immune response.
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Affiliation(s)
- Hyewon Byun
- Department of Molecular Biosciences, Center for Infectious Diseases and Institute for Cellular and Molecular Biology, The University of Texas at Austin Austin, TX, USA
| | - Yongqiang Gou
- Department of Molecular Biosciences, Center for Infectious Diseases and Institute for Cellular and Molecular Biology, The University of Texas at Austin Austin, TX, USA
| | - Adam Zook
- Department of Molecular Biosciences, Center for Infectious Diseases and Institute for Cellular and Molecular Biology, The University of Texas at Austin Austin, TX, USA
| | - Mary M Lozano
- Department of Molecular Biosciences, Center for Infectious Diseases and Institute for Cellular and Molecular Biology, The University of Texas at Austin Austin, TX, USA
| | - Jaquelin P Dudley
- Department of Molecular Biosciences, Center for Infectious Diseases and Institute for Cellular and Molecular Biology, The University of Texas at Austin Austin, TX, USA
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18
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Petris G, Bestagno M, Arnoldi F, Burrone OR. New tags for recombinant protein detection and O-glycosylation reporters. PLoS One 2014; 9:e96700. [PMID: 24802141 PMCID: PMC4011882 DOI: 10.1371/journal.pone.0096700] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2013] [Accepted: 04/10/2014] [Indexed: 01/24/2023] Open
Abstract
Monoclonal antibodies (mAbs), because of their unique specificity, are irreplaceable tools for scientific research. Precise mapping of the antigenic determinants allows the development of epitope tagging approaches to be used with recombinant proteins for several purposes. Here we describe a new family of tags derived from the epitope recognized by a single highly specific mAb (anti-roTag mAb), which was obtained from a pool of mAbs reacting with the rotavirus nonstructural protein 5 (NSP5). The variable regions of the anti-roTag mAb were identified and their binding capacity verified upon expression as a single-chain/miniAb. The minimal epitope, termed roTag, was identified as a 10 amino acid sequence (SISSSIFKNE). The affinity of the anti-roTag/roTag interaction was found to be comparable to that of the anti-SV5/SV5 tag interaction. roTag was successfully used for detection of several recombinant cytosolic, secretory and membrane proteins. Two additional variants of roTag of 10 and 13 amino acids containing O-glycosylation susceptible sites (termed OG-tag and roTagO) were constructed and characterised. These tags were useful to detect proteins passing through the Golgi apparatus, the site of O-glycosylation.
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Affiliation(s)
- Gianluca Petris
- International Centre for Genetic Engineering and Biotechnology (ICGEB), Trieste, Italy
| | - Marco Bestagno
- International Centre for Genetic Engineering and Biotechnology (ICGEB), Trieste, Italy
| | - Francesca Arnoldi
- International Centre for Genetic Engineering and Biotechnology (ICGEB), Trieste, Italy
- Department of Medicine, Surgery and Health Sciences, University of Trieste, Trieste, Italy
| | - Oscar R. Burrone
- International Centre for Genetic Engineering and Biotechnology (ICGEB), Trieste, Italy
- * E-mail:
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Sauter D. Counteraction of the multifunctional restriction factor tetherin. Front Microbiol 2014; 5:163. [PMID: 24782851 PMCID: PMC3989765 DOI: 10.3389/fmicb.2014.00163] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Accepted: 03/26/2014] [Indexed: 01/28/2023] Open
Abstract
The interferon-inducible restriction factor tetherin (also known as CD317, BST-2 or HM1.24) has emerged as a key component of the antiviral immune response. Initially, tetherin was shown to restrict replication of various enveloped viruses by inhibiting the release of budding virions from infected cells. More recently, it has become clear that tetherin also acts as a pattern recognition receptor inducing NF-κB-dependent proinflammatory gene expression in virus infected cells. Whereas the ability to restrict virion release is highly conserved among mammalian tetherin orthologs and thus probably an ancient function of this protein, innate sensing seems to be an evolutionarily recent activity. The potent and broad antiviral activity of tetherin is reflected by the fact that many viruses evolved means to counteract this restriction factor. A continuous arms race with viruses has apparently driven the evolution of different isoforms of tetherin with different functional properties. Interestingly, tetherin has also been implicated in cellular processes that are unrelated to immunity, such as the organization of the apical actin network and membrane microdomains or stabilization of the Golgi apparatus. In this review, I summarize our current knowledge of the different functions of tetherin and describe the molecular strategies that viruses have evolved to antagonize or evade this multifunctional host restriction factor.
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Affiliation(s)
- Daniel Sauter
- Institute of Molecular Virology, Ulm University Medical Center Ulm, Germany
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Fisher E, Lake E, McLeod RS. Apolipoprotein B100 quality control and the regulation of hepatic very low density lipoprotein secretion. J Biomed Res 2014; 28:178-93. [PMID: 25013401 PMCID: PMC4085555 DOI: 10.7555/jbr.28.20140019] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2014] [Accepted: 02/15/2014] [Indexed: 12/19/2022] Open
Abstract
Apolipoprotein B (apoB) is the main protein component of very low density lipoprotein (VLDL) and is necessary for the assembly and secretion of these triglyceride (TG)-rich particles. Following release from the liver, VLDL is converted to low density lipoprotein (LDL) in the plasma and increased production of VLDL can therefore play a detrimental role in cardiovascular disease. Increasing evidence has helped to establish VLDL assembly as a target for the treatment of dyslipidemias. Multiple factors are involved in the folding of the apoB protein and the formation of a secretion-competent VLDL particle. Failed VLDL assembly can initiate quality control mechanisms in the hepatocyte that target apoB for degradation. ApoB is a substrate for endoplasmic reticulum associated degradation (ERAD) by the ubiquitin proteasome system and for autophagy. Efficient targeting and disposal of apoB is a regulated process that modulates VLDL secretion and partitioning of TG. Emerging evidence suggests that significant overlap exists between these degradative pathways. For example, the insulin-mediated targeting of apoB to autophagy and postprandial activation of the unfolded protein response (UPR) may employ the same cellular machinery and regulatory cues. Changes in the quality control mechanisms for apoB impact hepatic physiology and pathology states, including insulin resistance and fatty liver. Insulin signaling, lipid metabolism and the hepatic UPR may impact VLDL production, particularly during the postprandial state. In this review we summarize our current understanding of VLDL assembly, apoB degradation, quality control mechanisms and the role of these processes in liver physiology and in pathologic states.
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Affiliation(s)
- Eric Fisher
- Biochemistry & Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Elizabeth Lake
- Biochemistry & Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
| | - Roger S McLeod
- Biochemistry & Molecular Biology, Faculty of Medicine, Dalhousie University, Halifax, NS B3H 4R2, Canada
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