51
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Zhang J, Lan Y, Sanyal S. Modulation of Lipid Droplet Metabolism-A Potential Target for Therapeutic Intervention in Flaviviridae Infections. Front Microbiol 2017; 8:2286. [PMID: 29234310 PMCID: PMC5712332 DOI: 10.3389/fmicb.2017.02286] [Citation(s) in RCA: 53] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2017] [Accepted: 11/06/2017] [Indexed: 12/21/2022] Open
Abstract
Lipid droplets (LDs) are endoplasmic reticulum (ER)-related dynamic organelles that store and regulate fatty acids and neutral lipids. They play a central role in cellular energy storage, lipid metabolism and cellular homeostasis. It has become evident that viruses have co-evolved in order to exploit host lipid metabolic pathways. This is especially characteristic of the Flaviviridae family, including hepatitis C virus (HCV) and several flaviviruses. Devoid of an appropriate lipid biosynthetic machinery of their own, these single-strand positive-sense RNA viruses can induce dramatic changes in host metabolic pathways to establish a favorable environment for viral multiplication and acquire essential components to facilitate their assembly and traffic. Here we have reviewed the current knowledge on the intracellular life cycle of those from the Flaviviridae family, with particular emphasis on HCV and dengue virus (DENV), and their association with the biosynthesis and metabolism of LDs, with the aim to identify potential antiviral targets for development of novel therapeutic interventions.
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Affiliation(s)
- Jingshu Zhang
- HKU-Pasteur Research Pole, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Yun Lan
- HKU-Pasteur Research Pole, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
| | - Sumana Sanyal
- HKU-Pasteur Research Pole, School of Public Health, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China.,School of Biomedical Sciences, Li Ka Shing Faculty of Medicine, University of Hong Kong, Hong Kong, China
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52
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Abstract
Microtubules (MTs) form a rapidly adaptable network of filaments that radiate throughout the cell. These dynamic arrays facilitate a wide range of cellular processes, including the capture, transport, and spatial organization of cargos and organelles, as well as changes in cell shape, polarity, and motility. Nucleating from MT-organizing centers, including but by no means limited to the centrosome, MTs undergo rapid transitions through phases of growth, pause, and catastrophe, continuously exploring and adapting to the intracellular environment. Subsets of MTs can become stabilized in response to environmental cues, acquiring distinguishing posttranslational modifications and performing discrete functions as specialized tracks for cargo trafficking. The dynamic behavior and organization of the MT array is regulated by MT-associated proteins (MAPs), which include a subset of highly specialized plus-end-tracking proteins (+TIPs) that respond to signaling cues to alter MT behavior. As pathogenic cargos, viruses require MTs to transport to and from their intracellular sites of replication. While interactions with and functions for MT motor proteins are well characterized and extensively reviewed for many viruses, this review focuses on MT filaments themselves. Changes in the spatial organization and dynamics of the MT array, mediated by virus- or host-induced changes to MT regulatory proteins, not only play a central role in the intracellular transport of virus particles but also regulate a wider range of processes critical to the outcome of infection.
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53
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Welte MA, Gould AP. Lipid droplet functions beyond energy storage. Biochim Biophys Acta Mol Cell Biol Lipids 2017; 1862:1260-1272. [PMID: 28735096 PMCID: PMC5595650 DOI: 10.1016/j.bbalip.2017.07.006] [Citation(s) in RCA: 331] [Impact Index Per Article: 47.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Revised: 07/17/2017] [Accepted: 07/17/2017] [Indexed: 02/07/2023]
Abstract
Lipid droplets are cytoplasmic organelles that store neutral lipids and are critically important for energy metabolism. Their function in energy storage is firmly established and increasingly well characterized. However, emerging evidence indicates that lipid droplets also play important and diverse roles in the cellular handling of lipids and proteins that may not be directly related to energy homeostasis. Lipid handling roles of droplets include the storage of hydrophobic vitamin and signaling precursors, and the management of endoplasmic reticulum and oxidative stress. Roles of lipid droplets in protein handling encompass functions in the maturation, storage, and turnover of cellular and viral polypeptides. Other potential roles of lipid droplets may be connected with their intracellular motility and, in some cases, their nuclear localization. This diversity highlights that lipid droplets are very adaptable organelles, performing different functions in different biological contexts. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
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Affiliation(s)
- Michael A Welte
- Department of Biology, University of Rochester, Rochester, NY, United States.
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54
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Karamichali E, Serti E, Gianneli A, Papaefthymiou A, Kakkanas A, Foka P, Seremetakis A, Katsarou K, Trougakos IP, Georgopoulou U. The unexpected function of a highly conserved YXXΦ motif in HCV core protein. INFECTION GENETICS AND EVOLUTION 2017; 54:251-262. [PMID: 28687362 DOI: 10.1016/j.meegid.2017.07.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/19/2017] [Revised: 06/27/2017] [Accepted: 07/02/2017] [Indexed: 01/09/2023]
Abstract
Hepatitis C virus (HCV) is an RNA positive strand virus, member of the Flaviviridae family. The HCV viral particle is composed of a capsid containing the genome, surrounded by an endoplasmic reticulum (ER)-derived lipid bilayer where E1 and E2 are assembled as heterodimers. However, different forms of viral particles have been identified in the serum of HCV-infected patients, including non-enveloped particles. Previous reports have demonstrated that HCV non-enveloped capsid-like particles (HCVne) can be generated by HCV core protein sequence. This sequence possesses a highly conserved ΥΧΧΦ motif and distal di-leucine motifs that confer primary endocytosis signals, enabling HCVne to enter hepatic cells via clathrin-mediated endocytosis. Although HCV core's primary function is to encapsidate the viral genome, it also interacts with a variety of cellular proteins in order to regulate host cell functions such as gene transcription, lipid metabolism, apoptosis and several signaling pathways. In this report, we demonstrate that the YXXΦ motif of HCV core protein is crucial for the architectural integrity of the particulate form of HCVne. Moreover, we show that the YXXΦ motif in the HCV core sequence plays a pivotal role in the signaling events following HCVne clathrin-mediated endocytosis by inducing the AP-2 clathrin adaptor protein, which in turn redirect HCVne trafficking to the lipid droplets (LDs) via the endosomal-lysosomal pathway. HCVne and LDs co-localization affects the HCV life cycle by enhancing viral replication.
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Affiliation(s)
| | - Elisavet Serti
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Greece
| | | | | | | | - Pelagia Foka
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Greece
| | | | | | - Ioannis P Trougakos
- Department of Cell Biology and Biophysics, Faculty of Biology, University of Athens, Panepistimiopolis, Athens 15784, Greece
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55
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Schuldiner M, Bohnert M. A different kind of love - lipid droplet contact sites. Biochim Biophys Acta Mol Cell Biol Lipids 2017. [PMID: 28627434 DOI: 10.1016/j.bbalip.2017.06.005] [Citation(s) in RCA: 127] [Impact Index Per Article: 18.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
Lipid droplets (LDs) store lipids and hence serve as energy reservoir and as a source for building-blocks for the organelle membrane systems. LD biology therefore depends on tight communication with other organelles. The unique architecture of LDs, consisting of a neutral lipid core shielded by a phospholipid-monolayer, is however an obstacle to bulk-exchange of bilayer-bounded vesicles with other organelles. In recent years, it is emerging that contact sites, places where two organelles are positioned in close proximity allowing vesicle-independent communication, are an important way to integrate LDs into the organellar landscape. However, few LD contact sites have been studied in depth and our understanding of their structure, extent and function is only starting to emerge. Here, we highlight recent findings on the functions of LD contact sites and on the proteins involved in their formation and hypothesize about the unique characteristics of the contact sites formed by these intriguing organelles. This article is part of a Special Issue entitled: Recent Advances in Lipid Droplet Biology edited by Rosalind Coleman and Matthijs Hesselink.
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Affiliation(s)
- Maya Schuldiner
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel
| | - Maria Bohnert
- Department of Molecular Genetics, Weizmann Institute of Science, Rehovot 7610001, Israel.
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56
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Barisch C, Soldati T. Breaking fat! How mycobacteria and other intracellular pathogens manipulate host lipid droplets. Biochimie 2017; 141:54-61. [PMID: 28587792 DOI: 10.1016/j.biochi.2017.06.001] [Citation(s) in RCA: 45] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2017] [Accepted: 06/01/2017] [Indexed: 01/15/2023]
Abstract
Tuberculosis (Tb) is a lung infection caused by Mycobacterium tuberculosis (Mtb). With one third of the world population latently infected, it represents the most prevalent bacterial infectious diseases worldwide. Typically, persistence is linked to so-called "dormant" slow-growing bacteria, which have a low metabolic rate and a reduced response to antibiotic treatments. However, dormant bacteria regain growth and virulence when the immune system is weakened, leading again to the active form of the disease. Fatty acids (FAs) released from host triacylglycerols (TAGs) and sterols are proposed to serve as sole carbon sources during infection. The metabolism of FAs requires beta-oxidation as well as gluconeogenesis and the glyoxylate shunt. Interestingly, the Mtb genome encodes more than hundred proteins involved in the five reactions of beta-oxidation, clearly demonstrating the importance of lipids as energy source. FAs have also been proposed to play a role during resuscitation, the resumption of replicative activities from dormancy. Lipid droplets (LDs) are energy and carbon reservoirs and have been described in all domains. TAGs and sterol esters (SEs) are stored in their hydrophobic core, surrounded by a phospholipid monolayer. Importantly, host LDs have been described as crucial for several intracellular bacterial pathogens and viruses and specifically translocate to the pathogen-containing vacuole (PVC) during mycobacteria infection. FAs released from host LDs are used by the pathogen as energy source and as building blocks for membrane synthesis. Despite their essential role, the mechanisms by which pathogenic mycobacteria induce the cellular redistribution of LDs and gain access to the stored lipids are still poorly understood. This review describes recent evidence about the dual interaction of mycobacteria with host LDs and membrane phospholipids and integrates them in a broader view of the underlying cellular processes manipulated by various intracellular pathogens to gain access to host lipids.
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Affiliation(s)
- Caroline Barisch
- Department of Biochemistry, Faculty of Sciences, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211, Geneva-4, Switzerland.
| | - Thierry Soldati
- Department of Biochemistry, Faculty of Sciences, University of Geneva, 30 quai Ernest-Ansermet, Science II, 1211, Geneva-4, Switzerland
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57
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Pène V, Lemasson M, Harper F, Pierron G, Rosenberg AR. Role of cleavage at the core-E1 junction of hepatitis C virus polyprotein in viral morphogenesis. PLoS One 2017; 12:e0175810. [PMID: 28437468 PMCID: PMC5402940 DOI: 10.1371/journal.pone.0175810] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2016] [Accepted: 03/31/2017] [Indexed: 12/17/2022] Open
Abstract
In hepatitis C virus (HCV) polyprotein sequence, core protein terminates with E1 envelope signal peptide. Cleavage by signal peptidase (SP) separates E1 from the complete form of core protein, anchored in the endoplasmic reticulum (ER) membrane by the signal peptide. Subsequent cleavage of the signal peptide by signal-peptide peptidase (SPP) releases the mature form of core protein, which preferentially relocates to lipid droplets. Both of these cleavages are required for the HCV infectious cycle, supporting the idea that HCV assembly begins at the surface of lipid droplets, yet SPP-catalyzed cleavage is dispensable for initiation of budding in the ER. Here we have addressed at what step(s) of the HCV infectious cycle SP-catalyzed cleavage at the core-E1 junction is required. Taking advantage of the sole system that has allowed visualization of HCV budding events in the ER lumen of mammalian cells, we showed that, unexpectedly, mutations abolishing this cleavage did not prevent but instead tended to promote the initiation of viral budding. Moreover, even though no viral particles were released from Huh-7 cells transfected with a full-length HCV genome bearing these mutations, intracellular viral particles containing core protein protected by a membrane envelope were formed. These were visualized by electron microscopy as capsid-containing particles with a diameter of about 70 nm and 40 nm before and after delipidation, respectively, comparable to intracellular wild-type particle precursors except that they were non-infectious. Thus, our results show that SP-catalyzed cleavage is dispensable for HCV budding per se, but is required for the viral particles to acquire their infectivity and secretion. These data support the idea that HCV assembly occurs in concert with budding at the ER membrane. Furthermore, capsid-containing particles did not accumulate in the absence of SP-catalyzed cleavage, suggesting the quality of newly formed viral particles is controlled before secretion.
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Affiliation(s)
- Véronique Pène
- Université Paris Descartes, EA 4474 “Virologie de l’Hépatite C”, Paris, France
| | - Matthieu Lemasson
- Université Paris Descartes, EA 4474 “Virologie de l’Hépatite C”, Paris, France
| | - Francis Harper
- CNRS UMR 9196, Institut Gustave Roussy, Villejuif, France
| | - Gérard Pierron
- CNRS UMR 9196, Institut Gustave Roussy, Villejuif, France
| | - Arielle R. Rosenberg
- Université Paris Descartes, EA 4474 “Virologie de l’Hépatite C”, Paris, France
- AP-HP, Hôpital Cochin, Service de Virologie, Paris, France
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58
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El-Ekiaby NM, Mekky RY, Riad SE, Elhelw DS, El-Sayed M, Esmat G, Abdelaziz AI. miR-148a and miR-30a limit HCV-dependent suppression of the lipid droplet protein, ADRP, in HCV infected cell models. J Med Virol 2017; 89:653-659. [PMID: 27591428 DOI: 10.1002/jmv.24677] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/31/2016] [Indexed: 02/05/2023]
Abstract
Hepatitis C Virus (HCV) promotes lipid droplet (LD) formation and perturbs the expression of the LD associated PAT proteins ADRP and TIP47, to promote its own lifecycle. HCV enhances TIP47 and suppresses ADRP by displacing it from LD surface in infected cell models. We have previously shown that suppression of TIP47 by miR-148a and miR-30a decreased intracellular LDs and HCV RNA. Thus, this study aimed at examining whether this microRNA-mediated suppression of HCV would limit HCV-dependent displacement of ADRP from LDs. ADRP expression was examined in 21 HCV-infected liver biopsies and 9 healthy donor liver tissues as well as in HCV-infected Huh7 cells using qRT-PCR. miR-148a and miR-30a expression was manipulated using specific oligos in JFH-1 infected, oleic acid treated cells, to study their impact on ADRP expression using qRT-PCR, and immunofluorescence microscopy. Intracellular HCV RNA was assessed using qRT-PCR. ADRP is down regulated in patients as well as HCVcc-JFH-I infected cell models. Forcing the expression of both miRNAs induced ADRP on the mRNA and protein levels. This study shows that HCV suppresses hepatic ADRP expression in infected patients and cell lines. Forcing the expression of miR-148a and miR-30a limits the suppressive effect of HCV on ADRP. J. Med. Virol. 89:653-659, 2017. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Nada M El-Ekiaby
- Department of Pharmacology and Toxicology, Molecular Pathology Research Group, German University in Cairo, New Cairo City-Main Entrance Al Tagamoa Al Khames, Cairo, Egypt
- Scientific Affairs Unit, Egyptian Company for Biological Sciences, Giza, Egypt
| | - Radwa Y Mekky
- Department of Pharmacology and Toxicology, Molecular Pathology Research Group, German University in Cairo, New Cairo City-Main Entrance Al Tagamoa Al Khames, Cairo, Egypt
- Faculty of Biotechnology, October University of Modern Sciences and Arts, Giza, Egypt
| | - Sarah E Riad
- Department of Pharmacology and Toxicology, Molecular Pathology Research Group, German University in Cairo, New Cairo City-Main Entrance Al Tagamoa Al Khames, Cairo, Egypt
| | - Dalia S Elhelw
- Department of Pharmacology and Toxicology, Molecular Pathology Research Group, German University in Cairo, New Cairo City-Main Entrance Al Tagamoa Al Khames, Cairo, Egypt
| | | | - Gamal Esmat
- Endemic Medicine and Hepatology, Cairo University, Cairo, Egypt
| | - Ahmed I Abdelaziz
- Department of Pharmacology and Toxicology, Molecular Pathology Research Group, German University in Cairo, New Cairo City-Main Entrance Al Tagamoa Al Khames, Cairo, Egypt
- Biotechnology Graduate Program, American University in Cairo, AUC Avenue, New Cairo, Cairo, Egypt
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59
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Meyers A, Chourey K, Weiskittel TM, Pfiffner S, Dunlap JR, Hettich RL, Dalhaimer P. The protein and neutral lipid composition of lipid droplets isolated from the fission yeast, Schizosaccharomyces pombe. J Microbiol 2017; 55:112-122. [PMID: 28120187 DOI: 10.1007/s12275-017-6205-1] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2016] [Revised: 10/04/2016] [Accepted: 10/20/2016] [Indexed: 12/17/2022]
Abstract
Lipid droplets consist of a core of neutral lipids surrounded by a phospholipid monolayer with bound proteins. Much of the information on lipid droplet function comes from proteomic and lipodomic studies that identify the components of droplets isolated from organisms throughout the phylogenetic tree. Here, we add to that important inventory by reporting lipid droplet factors from the fission yeast, Schizosaccharomyces pombe. Unique to this study was the fact that cells were cultured in three different environments: 1) late log growth phase in glucose-based media, 2) stationary phase in glucosebased media, and 3) late log growth phase in media containing oleic acid. We confirmed colocalization of major factors with lipid droplets using live-cell fluorescent microscopy. We also analyzed droplets from each of the three conditions for sterol ester (SE) and triacylglycerol (TAG) content, along with their respective fatty acid compositions. We identified a previously undiscovered lipid droplet protein, Vip1p, which affects droplet size distribution. The results provide further insight into the workings of these ubiquitous organelles.
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Affiliation(s)
- Alex Meyers
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA
| | - Karuna Chourey
- Oak Ridge National Laboratory, Oak Ridge, TN, 37831, USA
| | - Taylor M Weiskittel
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA
| | - Susan Pfiffner
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA
| | - John R Dunlap
- Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA.,Advanced Microscopy and Imaging Center, University of Tennessee, Knoxville, TN, 37996, USA
| | | | - Paul Dalhaimer
- Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996-2200, USA. .,Department of Biochemistry, Cellular and Molecular Biology, University of Tennessee, Knoxville, TN, 37996, USA. .,Institute of Biomedical Engineering, University of Tennessee, Knoxville, TN, 37996, USA.
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60
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Ferguson D, Zhang J, Davis MA, Helsley RN, Vedin LL, Lee RG, Crooke RM, Graham MJ, Allende DS, Parini P, Brown JM. The lipid droplet-associated protein perilipin 3 facilitates hepatitis C virus-driven hepatic steatosis. J Lipid Res 2016; 58:420-432. [PMID: 27941027 DOI: 10.1194/jlr.m073734] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2016] [Indexed: 12/18/2022] Open
Abstract
Hepatitis C virus (HCV) is an enveloped RNA virus responsible for 170 million cases of viral hepatitis worldwide. Over 50% of chronically infected HCV patients develop hepatic steatosis, and steatosis can be induced by expression of HCV core protein (core) alone. Additionally, core must associate with cytoplasmic lipid droplets (LDs) for steatosis development and viral particle assembly. Due to the importance of the LD as a key component of hepatic lipid storage and as a platform for HCV particle assembly, it seems this dynamic subcellular organelle is a gatekeeper in the pathogenesis of viral hepatitis. Here, we hypothesized that core requires the host LD scaffold protein, perilipin (PLIN)3, to induce hepatic steatosis. To test our hypothesis in vivo, we have studied core-induced hepatic steatosis in the absence or presence of antisense oligonucleotide-mediated knockdown of PLIN3. PLIN3 knockdown blunted HCV core-induced steatosis in transgenic mice fed either chow or a moderate fat diet. Collectively, our studies demonstrate that the LD scaffold protein, PLIN3, is essential for HCV core-induced hepatic steatosis and provide new insights into the pathogenesis of HCV.
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Affiliation(s)
- Daniel Ferguson
- Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, Cleveland, OH.,Department of Pathology, Wake Forest School of Medicine, Winston-Salem, NC
| | - Jun Zhang
- Department of Pathology, Wake Forest School of Medicine, Winston-Salem, NC
| | - Matthew A Davis
- Department of Pathology, Wake Forest School of Medicine, Winston-Salem, NC
| | - Robert N Helsley
- Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, Cleveland, OH
| | - Lise-Lotte Vedin
- Clinical Chemistry, Department of Laboratory Medicine, Karolinska Institute, Stockholm, Sweden
| | - Richard G Lee
- Clinical Chemistry, Department of Laboratory Medicine, Karolinska Institute, Stockholm, Sweden
| | - Rosanne M Crooke
- Clinical Chemistry, Department of Laboratory Medicine, Karolinska Institute, Stockholm, Sweden
| | - Mark J Graham
- Clinical Chemistry, Department of Laboratory Medicine, Karolinska Institute, Stockholm, Sweden
| | | | - Paolo Parini
- Clinical Chemistry, Department of Laboratory Medicine, Karolinska Institute, Stockholm, Sweden
| | - J Mark Brown
- Department of Cellular and Molecular Medicine, Cleveland Clinic Lerner Research Institute, Cleveland, OH
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61
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Genomics of human fatty liver disease reveal mechanistically linked lipid droplet-associated gene regulations in bland steatosis and nonalcoholic steatohepatitis. Transl Res 2016; 177:41-69. [PMID: 27376874 DOI: 10.1016/j.trsl.2016.06.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/26/2016] [Revised: 05/13/2016] [Accepted: 06/08/2016] [Indexed: 12/11/2022]
Abstract
Nonalcoholic fatty liver disease (NAFLD) is a common disorder hallmarked by excessive lipid deposits. Based on our recent research on lipid droplet (LD) formation in hepatocytes, we investigated LD-associated gene regulations in NAFLD of different grades, that is, steatosis vs steatohepatitis by comparing liver biopsies from healthy controls (N = 13) and NAFLD patients (N = 102). On average, more than 700 differentially expressed genes (DEGs) were identified of which 146 are mechanistically linked to LD formation. We identified 51 LD-associated DEGs frequently regulated in patient samples (range ≥5 to ≤102) with the liver-receptor homolog-1(NR5A2), that is, a key regulator of cholesterol metabolism being commonly repressed among 100 patients examined. With bland steatosis, notable regulations involved hypoxia-inducible lipid droplet-associated-protein and diacylglycerol-O-acyltransferase-2 renowned for their role in LD-growth. Conversely, nonalcoholic steatohepatitis-associated DEGs coded for epidermal growth factor receptor and TLR4 signaling with decreased expression of the GTPase Rab5 and the lipid phosphohydrolase PPAP2B thus highlighting adaptive responses to inflammation, LDL-mediated endocytosis and lipogenesis, respectively. Studies with steatotic primary human hepatocyte cultures demonstrated induction of LD-associated PLIN2, CIDEC, DNAAF1, whereas repressed expression of CPT1A, ANGPTL4, and PKLR informed on burdened mitochondrial metabolism. Equally, repressed expression of the B-lymphocyte chemoattractant CXCL13 and STAT4 as well as induced FGF21 evidenced amelioration of steatosis-related inflammation. In-vitro/in-vivo patient sample comparisons confirmed C-reactive protein, SOCS3, NR5A2, and SOD2 as commonly regulated. Lastly, STRING network analysis highlighted potential "druggable" targets with PLIN2, CIDEC, and hypoxia-inducible lipid droplet-associated-protein being confirmed by immunofluorescence microscopy. In conclusion, steatosis and steatohepatitis specific gene regulations informed on the pathogenesis of NAFLD to broaden the perspective of targeted therapies.
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62
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Rojas Á, Del Campo JA, Clement S, Lemasson M, García-Valdecasas M, Gil-Gómez A, Ranchal I, Bartosch B, Bautista JD, Rosenberg AR, Negro F, Romero-Gómez M. Effect of Quercetin on Hepatitis C Virus Life Cycle: From Viral to Host Targets. Sci Rep 2016; 6:31777. [PMID: 27546480 PMCID: PMC4992894 DOI: 10.1038/srep31777] [Citation(s) in RCA: 66] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 07/26/2016] [Indexed: 12/13/2022] Open
Abstract
Quercetin is a natural flavonoid, which has been shown to have anti hepatitis C virus (HCV) properties. However, the exact mechanisms whereby quercetin impacts the HCV life cycle are not fully understood. We assessed the effect of quercetin on different steps of the HCV life cycle in Huh-7.5 cells and primary human hepatocytes (PHH) infected with HCVcc. In both cell types, quercetin significantly decreased i) the viral genome replication; ii) the production of infectious HCV particles and iii) the specific infectivity of the newly produced viral particles (by 85% and 92%, Huh7.5 and PHH respectively). In addition, when applied directly on HCV particles, quercetin reduced their infectivity by 65%, suggesting that it affects the virion integrity. Interestingly, the HCV-induced up-regulation of diacylglycerol acyltransferase (DGAT) and the typical localization of the HCV core protein to the surface of lipid droplets, known to be mediated by DGAT, were both prevented by quercetin. In conclusion, quercetin appears to have direct and host-mediated antiviral effects against HCV.
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Affiliation(s)
- Ángela Rojas
- UCM Digestive Diseases, Virgen Macarena-Virgen del Rocío University Hospitals and CIBERehd, Institute of Biomedicine, University of Sevilla, Sevilla, Spain.,Unit for the Clinical Management of Digestive Diseases, Hospital Universitario Valme de Sevilla, Sevilla, Spain
| | - Jose A Del Campo
- Unit for the Clinical Management of Digestive Diseases, Hospital Universitario Valme de Sevilla, Sevilla, Spain
| | - Sophie Clement
- Division of Clinical Pathology, University Hospital, Geneva, Switzerland
| | | | - Marta García-Valdecasas
- UCM Digestive Diseases, Virgen Macarena-Virgen del Rocío University Hospitals and CIBERehd, Institute of Biomedicine, University of Sevilla, Sevilla, Spain.,Unit for the Clinical Management of Digestive Diseases, Hospital Universitario Valme de Sevilla, Sevilla, Spain
| | - Antonio Gil-Gómez
- UCM Digestive Diseases, Virgen Macarena-Virgen del Rocío University Hospitals and CIBERehd, Institute of Biomedicine, University of Sevilla, Sevilla, Spain.,Unit for the Clinical Management of Digestive Diseases, Hospital Universitario Valme de Sevilla, Sevilla, Spain
| | - Isidora Ranchal
- Unit for the Clinical Management of Digestive Diseases, Hospital Universitario Valme de Sevilla, Sevilla, Spain
| | - Birke Bartosch
- Inserm U1052, Cancer Research Centre, University of Lyon, France DevWeCan Laboratories of Excellence Network (Labex), Lyon, France
| | - Juan D Bautista
- Biochemistry and Molecular Biology, Faculty of Pharmacy, University of Sevilla, Spain
| | | | - Francesco Negro
- Division of Clinical Pathology, University Hospital, Geneva, Switzerland.,Division of Gastroenterology and Hepatology, University Hospital, Geneva, Switzerland
| | - Manuel Romero-Gómez
- UCM Digestive Diseases, Virgen Macarena-Virgen del Rocío University Hospitals and CIBERehd, Institute of Biomedicine, University of Sevilla, Sevilla, Spain
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63
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Abstract
Dengue virus affects hundreds of millions of people each year around the world, causing a tremendous social and economic impact on affected countries. The aim of this review is to summarize our current knowledge of the functions, structure, and interactions of the viral capsid protein. The primary role of capsid is to package the viral genome. There are two processes linked to this function: the recruitment of the viral RNA during assembly and the release of the genome during infection. Although particle assembly takes place on endoplasmic reticulum membranes, capsid localizes in nucleoli and lipid droplets. Why capsid accumulates in these locations during infection remains unknown. In this review, we describe available data and discuss new ideas on dengue virus capsid functions and interactions. We believe that a deeper understanding of how the capsid protein works during infection will create opportunities for novel antiviral strategies, which are urgently needed to control dengue virus infections.
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Affiliation(s)
- Laura A Byk
- Fundación Instituto Leloir-National Research Council for Science and Technology (CONICET), Buenos Aires 1405, Argentina;
| | - Andrea V Gamarnik
- Fundación Instituto Leloir-National Research Council for Science and Technology (CONICET), Buenos Aires 1405, Argentina;
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Meyers NL, Fontaine KA, Kumar GR, Ott M. Entangled in a membranous web: ER and lipid droplet reorganization during hepatitis C virus infection. Curr Opin Cell Biol 2016; 41:117-24. [PMID: 27240021 DOI: 10.1016/j.ceb.2016.05.003] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Revised: 05/04/2016] [Accepted: 05/05/2016] [Indexed: 12/19/2022]
Abstract
Hepatitis C virus (HCV) is a major cause of liver disease worldwide. To establish and maintain chronic infection, HCV extensively rearranges cellular organelles to generate distinct compartments for viral RNA replication and virion assembly. Here, we review our current knowledge of how HCV proliferates and remodels ER-derived membranes while preserving and expanding associated lipid droplets during viral infection. Unraveling the molecular mechanisms responsible for HCV-induced membrane reorganization will enhance our understanding of the HCV life-cycle, the associated liver pathology, and the biology of the ER:lipid droplet interface in general.
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Affiliation(s)
- Nathan L Meyers
- Gladstone Institutes, University of California San Francisco, 1650 Owens Street, San Francisco, CA 94941, United States
| | - Krystal A Fontaine
- Gladstone Institutes, University of California San Francisco, 1650 Owens Street, San Francisco, CA 94941, United States
| | - G Renuka Kumar
- Gladstone Institutes, University of California San Francisco, 1650 Owens Street, San Francisco, CA 94941, United States
| | - Melanie Ott
- Gladstone Institutes, University of California San Francisco, 1650 Owens Street, San Francisco, CA 94941, United States.
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65
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Awan Z, Tay ESE, Eyre NS, Wu LE, Beard MR, Boo I, Drummer HE, George J, Douglas MW. Calsyntenin-1 mediates hepatitis C virus replication. J Gen Virol 2016; 97:1877-1887. [PMID: 27221318 DOI: 10.1099/jgv.0.000511] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The hepatitis C virus (HCV) RNA genome of 9.6 kb encodes only 10 proteins, and so is highly dependent on host hepatocyte factors to facilitate replication. We aimed to identify host factors involved in the egress of viral particles. By screening the supernatant of HCV-infected Huh7 cells using SILAC-based proteomics, we identified the transmembrane protein calsyntenin-1 as a factor specifically secreted by infected cells. Calsyntenin-1 has previously been shown to mediate transport of endosomes along microtubules in neurons, through interactions with kinesin light chain-1. Here we demonstrate for the first time, we believe, a similar role for calsyntenin-1 in Huh7 cells, mediating intracellular transport of endosomes. In HCV-infected cells we show that calsyntenin-1 contributes to the early stages of the viral replication cycle and the formation of the replication complex. Importantly, we demonstrate in our model that silencing calsyntenin-1 disrupts the viral replication cycle, confirming the reliance of HCV on this protein as a host factor. Characterizing the function of calsyntenin-1 will increase our understanding of the HCV replication cycle and pathogenesis, with potential application to other viruses sharing common pathways.
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Affiliation(s)
- Zunaira Awan
- Storr Liver Centre, The Westmead Millennium Institute for Medical Research, The University of Sydney at Westmead Hospital, 176 Hawkesbury Rd, Westmead NSW 2145, Australia
| | - Enoch S E Tay
- Storr Liver Centre, The Westmead Millennium Institute for Medical Research, The University of Sydney at Westmead Hospital, 176 Hawkesbury Rd, Westmead NSW 2145, Australia
| | - Nicholas S Eyre
- Hepatitis C Virus Research Laboratory, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, Australia
| | - Lindsay E Wu
- University of New South Wales, Sydney NSW 2052, Australia
| | - Michael R Beard
- Hepatitis C Virus Research Laboratory, School of Molecular and Biomedical Science, University of Adelaide, Adelaide, Australia
| | - Irene Boo
- Centre for Biomedical Research, Burnet Institute, 85 Commercial Rd, Melbourne VIC 3004, Australia
| | - Heidi E Drummer
- Centre for Biomedical Research, Burnet Institute, 85 Commercial Rd, Melbourne VIC 3004, Australia.,Department of Microbiology, 19 Innovation Walk, Monash University, Victoria, Australia.,Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia
| | - Jacob George
- Storr Liver Centre, The Westmead Millennium Institute for Medical Research, The University of Sydney at Westmead Hospital, 176 Hawkesbury Rd, Westmead NSW 2145, Australia
| | - Mark W Douglas
- Storr Liver Centre, The Westmead Millennium Institute for Medical Research, The University of Sydney at Westmead Hospital, 176 Hawkesbury Rd, Westmead NSW 2145, Australia.,Centre for Infectious Diseases and Microbiology, Marie Bashir Institute for Infectious Diseases and Biosecurity, University of Sydney at Westmead Hospital, Westmead NSW 2145, Australia
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66
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Vieyres G, Welsch K, Gerold G, Gentzsch J, Kahl S, Vondran FWR, Kaderali L, Pietschmann T. ABHD5/CGI-58, the Chanarin-Dorfman Syndrome Protein, Mobilises Lipid Stores for Hepatitis C Virus Production. PLoS Pathog 2016; 12:e1005568. [PMID: 27124600 PMCID: PMC4849665 DOI: 10.1371/journal.ppat.1005568] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 03/22/2016] [Indexed: 02/06/2023] Open
Abstract
Hepatitis C virus (HCV) particles closely mimic human very-low-density lipoproteins (VLDL) to evade humoral immunity and to facilitate cell entry. However, the principles that govern HCV association with VLDL components are poorly defined. Using an siRNA screen, we identified ABHD5 (α/β hydrolase domain containing protein 5, also known as CGI-58) as a new host factor promoting both virus assembly and release. ABHD5 associated with lipid droplets and triggered their hydrolysis. Importantly, ABHD5 Chanarin-Dorfman syndrome mutants responsible for a rare lipid storage disorder in humans were mislocalised, and unable to consume lipid droplets or support HCV production. Additional ABHD5 mutagenesis revealed a novel tribasic motif that does not influence subcellular localization but determines both ABHD5 lipolytic and proviral properties. These results indicate that HCV taps into the lipid droplet triglyceride reservoir usurping ABHD5 lipase cofactor function. They also suggest that the resulting lipid flux, normally devoted to VLDL synthesis, also participates in the assembly and release of the HCV lipo-viro-particle. Altogether, our study provides the first association between the Chanarin-Dorfman syndrome protein and an infectious disease and sheds light on the hepatic manifestations of this rare genetic disorder as well as on HCV morphogenesis. HCV replication is linked to the host lipid metabolism, and virions are secreted as lipo-viro-particles whose density, size and biochemical content resemble VLDL. HCV assembles close to lipid droplets and is released via the secretory pathway, but it remains unclear how it accesses the VLDL assembly pathway. In this study, we identified ABHD5 as a new host factor supporting HCV assembly and release. ABHD5 is a lipid droplet-associated lipase cofactor. In hepatocytes, ABHD5 was proposed to promote the recruitment of triglycerides from cytosolic towards luminal lipid droplets by mediating a cycle of phospholipid hydrolysis/re-esterification. Our data suggest that this ABHD5-dependent lipid transfer is not only required for VLDL maturation, but also for HCV assembly and virion release, indicating that lipid remodelling impacts on both assembly and virus transport. Finally, ABHD5 is associated with the Chanarin-Dorfman syndrome, a rare human genetic lipid metabolism disorder. We found that the Chanarin-Dorfman syndrome mutants were unable to support HCV assembly, pointing at a new host polymorphism that could determine susceptibility to HCV infection. Altogether, our results establish a new link between HCV, VLDL assembly and lipid remodeling pathways and open new possibilities to study the etiology of the liver manifestations of the Chanarin-Dorfman syndrome.
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Affiliation(s)
- Gabrielle Vieyres
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Kathrin Welsch
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Gisa Gerold
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Juliane Gentzsch
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Sina Kahl
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
| | - Florian W. R. Vondran
- German Centre for Infection Research (DZIF), partner site Hannover-Braunschweig, Braunschweig, Germany
- ReMediES, Department of General, Visceral and Transplant Surgery, Hannover Medical School, Hannover, Germany
| | - Lars Kaderali
- Institute for Bioinformatics, University Medicine Greifswald, Greifswald, Germany
| | - Thomas Pietschmann
- Institute of Experimental Virology, TWINCORE, Centre for Experimental and Clinical Infection Research; a joint venture between the Medical School Hannover (MHH) and the Helmholtz Centre for Infection Research (HZI), Hannover, Germany
- German Centre for Infection Research (DZIF), partner site Hannover-Braunschweig, Braunschweig, Germany
- * E-mail:
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67
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Tschapalda K, Zhang YQ, Liu L, Golovnina K, Schlemper T, Eichmann TO, Lal-Nag M, Sreenivasan U, McLenithan J, Ziegler S, Sztalryd C, Lass A, Auld D, Oliver B, Waldmann H, Li Z, Shen M, Boxer MB, Beller M. A Class of Diacylglycerol Acyltransferase 1 Inhibitors Identified by a Combination of Phenotypic High-throughput Screening, Genomics, and Genetics. EBioMedicine 2016; 8:49-59. [PMID: 27428418 PMCID: PMC4919474 DOI: 10.1016/j.ebiom.2016.04.014] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2015] [Revised: 04/02/2016] [Accepted: 04/12/2016] [Indexed: 12/13/2022] Open
Abstract
Excess lipid storage is an epidemic problem in human populations. Thus, the identification of small molecules to treat or prevent lipid storage-related metabolic complications is of great interest. Here we screened > 320.000 compounds for their ability to prevent a cellular lipid accumulation phenotype. We used fly cells because the multifarious tools available for this organism should facilitate unraveling the mechanism-of-action of active small molecules. Of the several hundred lipid storage inhibitors identified in the primary screen we concentrated on three structurally diverse and potent compound classes active in cells of multiple species (including human) and negligible cytotoxicity. Together with Drosophila in vivo epistasis experiments, RNA-Seq expression profiles suggested that the target of one of the small molecules was diacylglycerol acyltransferase 1 (DGAT1), a key enzyme in the production of triacylglycerols and prominent human drug target. We confirmed this prediction by biochemical and enzymatic activity tests. We identified > 600 potent small molecule inhibitors of cellular lipid storage deposition. RNA-Seq expression profiling discriminated the activity of three lead scaffolds and guided subsequent functional studies. We discovered a class of DGAT1 inhibitors, which is active in fly and mammalian cell lines as well as whole flies.
Obesity and other lipid storage associated diseases are a growing health threat of human populations. In an undirected phenotypic screen, we identified pharmacologically active small molecules that reduce or enhance lipid storage. Our work focuses on three lead structures that prevent lipid storage in diverse cellular systems including cells from a diabetes patient. In order to elucidate the compound mechanisms-of-action and cellular targets, we used a combination of RNA-Seq transcriptional profiling and diverse functional assays. Our results strongly suggest that one of our lead structures represents a class of inhibitors targeting the key lipogenic enzyme diacylglycerol acyltransferase 1.
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Affiliation(s)
- Kirsten Tschapalda
- Systems Biology of Lipid Metabolism, Heinrich Heine University Düsseldorf, Germany; Institute for Mathematical Modeling of Biological Systems, Heinrich Heine University Düsseldorf, Germany; Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany; Department of Molecular Developmental Biology, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Ya-Qin Zhang
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Li Liu
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Kseniya Golovnina
- National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, USA
| | - Thomas Schlemper
- Systems Biology of Lipid Metabolism, Heinrich Heine University Düsseldorf, Germany; Institute for Mathematical Modeling of Biological Systems, Heinrich Heine University Düsseldorf, Germany
| | | | - Madhu Lal-Nag
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Urmila Sreenivasan
- Department of Medicine, Division of Endocrinology University of Maryland School of Medicine, USA
| | - John McLenithan
- Department of Medicine, Division of Endocrinology University of Maryland School of Medicine, USA
| | - Slava Ziegler
- Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Carole Sztalryd
- Department of Medicine, Division of Endocrinology University of Maryland School of Medicine, USA; Baltimore VA Medical Center, VA Research Service, Geriatric Research, Education and Clinical Center (GRECC) and VA Maryland Health Care System, Department of Medicine, Division of Endocrinology University of Maryland School of Medicine, USA
| | - Achim Lass
- Institute of Molecular Biosciences, University of Graz, Austria
| | - Douglas Auld
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Brian Oliver
- National Institute of Diabetes, Digestive and Kidney Diseases, National Institutes of Health, Bethesda, USA
| | - Herbert Waldmann
- Department of Chemical Biology, Max Planck Institute of Molecular Physiology, Dortmund, Germany
| | - Zhuyin Li
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Min Shen
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Matthew B Boxer
- National Center for Advancing Translational Sciences, National Institutes of Health, Rockville, USA
| | - Mathias Beller
- Systems Biology of Lipid Metabolism, Heinrich Heine University Düsseldorf, Germany; Institute for Mathematical Modeling of Biological Systems, Heinrich Heine University Düsseldorf, Germany.
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68
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Hepatitis C Virus-Induced Degradation of Cell Death-Inducing DFFA-Like Effector B Leads to Hepatic Lipid Dysregulation. J Virol 2016; 90:4174-85. [PMID: 26865724 DOI: 10.1128/jvi.02891-15] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2015] [Accepted: 02/03/2016] [Indexed: 12/25/2022] Open
Abstract
UNLABELLED Individuals chronically infected with hepatitis C virus (HCV) commonly exhibit hepatic intracellular lipid accumulation, termed steatosis. HCV infection perturbs host lipid metabolism through both cellular and virus-induced mechanisms, with the viral core protein playing an important role in steatosis development. We have recently identified a liver protein, the cell death-inducing DFFA-like effector B (CIDEB), as an HCV entry host dependence factor that is downregulated by HCV infection in a cell culture model. In this study, we investigated the biological significance and molecular mechanism of this downregulation. HCV infection in a mouse model downregulated CIDEB in the liver tissue, and knockout of the CIDEB gene in a hepatoma cell line results in multiple aspects of lipid dysregulation that can contribute to hepatic steatosis, including reduced triglyceride secretion, lower lipidation of very-low-density lipoproteins, and increased lipid droplet (LD) stability. The potential link between CIDEB downregulation and steatosis is further supported by the requirement of the HCV core and its LD localization for CIDEB downregulation, which utilize a proteolytic cleavage event that is independent of the cellular proteasomal degradation of CIDEB. IMPORTANCE Our data demonstrate that HCV infection of human hepatocytesin vitroandin vivoresults in CIDEB downregulation via a proteolytic cleavage event. Reduction of CIDEB protein levels by HCV or gene editing, in turn, leads to multiple aspects of lipid dysregulation, including LD stabilization. Consequently, CIDEB downregulation may contribute to HCV-induced hepatic steatosis.
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69
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Abstract
Lipid droplets are the intracellular sites for neutral lipid storage. They are critical for lipid metabolism and energy homeostasis, and their dysfunction has been linked to many diseases. Accumulating evidence suggests that the roles lipid droplets play in biology are significantly broader than previously anticipated. Lipid droplets are the source of molecules important in the nucleus: they can sequester transcription factors and chromatin components and generate the lipid ligands for certain nuclear receptors. Lipid droplets have also emerged as important nodes for fatty acid trafficking, both inside the cell and between cells. In immunity, new roles for droplets, not directly linked to lipid metabolism, have been uncovered, with evidence that they act as assembly platforms for specific viruses and as reservoirs for proteins that fight intracellular pathogens. Until recently, knowledge about droplets in the nervous system has been minimal, but now there are multiple links between lipid droplets and neurodegeneration: many candidate genes for hereditary spastic paraplegia also have central roles in lipid-droplet formation and maintenance, and mitochondrial dysfunction in neurons can lead to transient accumulation of lipid droplets in neighboring glial cells, an event that may, in turn, contribute to neuronal damage. As the cell biology and biochemistry of lipid droplets become increasingly well understood, the next few years should yield many new mechanistic insights into these novel functions of lipid droplets.
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70
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Branche E, Conzelmann S, Parisot C, Bedert L, Lévy PL, Bartosch B, Clément S, Negro F. Hepatitis C Virus Increases Occludin Expression via the Upregulation of Adipose Differentiation-Related Protein. PLoS One 2016; 11:e0146000. [PMID: 26731658 PMCID: PMC4701191 DOI: 10.1371/journal.pone.0146000] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2015] [Accepted: 12/11/2015] [Indexed: 12/12/2022] Open
Abstract
The hepatitis C virus (HCV) life cycle is closely associated with lipid metabolism. In particular, HCV assembly initiates at the surface of lipid droplets. To further understand the role of lipid droplets in HCV life cycle, we assessed the relationship between HCV and the adipose differentiation-related protein (ADRP), a lipid droplet-associated protein. Different steps of HCV life cycle were assessed in HCV-infected human Huh-7 hepatoma cells overexpressing ADRP upon transduction with a lentiviral vector. HCV infection increased ADRP mRNA and protein expression levels by 2- and 1.5-fold, respectively. The overexpression of ADRP led to an increase of (i) the surface of lipid droplets, (ii) the total cellular neutral lipid content (2.5- and 5-fold increase of triglycerides and cholesterol esters, respectively), (iii) the cellular free cholesterol level (5-fold) and (iv) the HCV particle production and infectivity (by 2- and 3.5-fold, respectively). The investigation of different steps of the HCV life cycle indicated that the ADRP overexpression, while not affecting the viral replication, promoted both virion egress and entry (~12-fold), the latter possibly via an increase of its receptor occludin. Moreover, HCV infection induces an increase of both ADRP and occludin expression. In HCV infected cells, the occludin upregulation was fully prevented by the ADRP silencing, suggesting a specific, ADRP-dependent mechanism. Finally, in HCV-infected human livers, occludin and ADRP mRNA expression levels correlated with each other. Alltogether, these findings show that HCV induces ADRP, which in turns appears to confer a favorable environment to viral spread.
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Affiliation(s)
- Emilie Branche
- Department of Immunology and Pathology, Faculty of Medicine, Geneva, Switzerland
| | - Stéphanie Conzelmann
- Department of Immunology and Pathology, Faculty of Medicine, Geneva, Switzerland
| | - Clotilde Parisot
- Department of Immunology and Pathology, Faculty of Medicine, Geneva, Switzerland
| | - Ludmila Bedert
- Department of Immunology and Pathology, Faculty of Medicine, Geneva, Switzerland
| | - Pierre L. Lévy
- Department of Immunology and Pathology, Faculty of Medicine, Geneva, Switzerland
| | - Birke Bartosch
- CRCL, INSERM U1052, CNRS 5286, University of Lyon, Lyon, France
| | - Sophie Clément
- Divisions of Clinical Pathology, University Hospital, Geneva, Switzerland
- * E-mail: (FN); (SC)
| | - Francesco Negro
- Divisions of Clinical Pathology, University Hospital, Geneva, Switzerland
- Gastroenterology and Hepatology, University Hospital, Geneva, Switzerland
- * E-mail: (FN); (SC)
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71
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Lipid droplets, lipophagy, and beyond. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1861:793-805. [PMID: 26713677 DOI: 10.1016/j.bbalip.2015.12.010] [Citation(s) in RCA: 112] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2015] [Revised: 12/06/2015] [Accepted: 12/17/2015] [Indexed: 02/06/2023]
Abstract
Lipids are essential components for life. Their various structural and physical properties influence diverse cellular processes and, thereby, human health. Lipids are not genetically encoded but are synthesized and modified by complex metabolic pathways, supplying energy, membranes, signaling molecules, and hormones to affect growth, physiology, and response to environmental insults. Lipid homeostasis is crucial, such that excess fatty acids (FAs) can be harmful to cells. To prevent such lipotoxicity, cells convert excess FAs into neutral lipids for storage in organelles called lipid droplets (LDs). These organelles do not simply manage lipid storage and metabolism but also are involved in protein quality management, pathogenesis, immune responses, and, potentially, neurodegeneration. In recent years, a major trend in LD biology has centered around the physiology of lipid mobilization via lipophagy of fat stored within LDs. This review summarizes key findings in LD biology and lipophagy, offering novel insights into this rapidly growing field. This article is part of a Special Issue entitled: The cellular lipid landscape edited by Tim P. Levine and Anant K. Menon.
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72
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Mashek DG, Khan SA, Sathyanarayan A, Ploeger JM, Franklin MP. Hepatic lipid droplet biology: Getting to the root of fatty liver. Hepatology 2015; 62:964-7. [PMID: 25854913 PMCID: PMC4549163 DOI: 10.1002/hep.27839] [Citation(s) in RCA: 85] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2015] [Accepted: 04/04/2015] [Indexed: 12/22/2022]
Abstract
Hepatic steatosis is defined by the accumulation of lipid droplets (LDs). Once thought to be only inert energy storage depots, LDs are increasingly recognized as organelles that have important functions in hepatocytes beyond lipid storage. The lipid and protein composition of LDs is highly dynamic and influences their intrinsic metabolism and signaling properties, which ultimately links them to the changes in hepatic function. This concise review highlights recent discoveries in LD biology and unique aspects of hepatic LDs and their role in liver disease.
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Affiliation(s)
- Douglas G Mashek
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN
| | - Salmaan A Khan
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN
| | | | - Jonathan M Ploeger
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN
| | - Mallory P Franklin
- Department of Food Science and Nutrition, University of Minnesota, St. Paul, MN
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Ploen D, Hildt E. Hepatitis C virus comes for dinner: How the hepatitis C virus interferes with autophagy. World J Gastroenterol 2015; 21:8492-8507. [PMID: 26229393 PMCID: PMC4515832 DOI: 10.3748/wjg.v21.i28.8492] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/03/2015] [Revised: 05/10/2015] [Accepted: 06/16/2015] [Indexed: 02/06/2023] Open
Abstract
Autophagy is a highly-regulated, conserved cellular process for the degradation of intracellular components in lysosomes to maintain the energetic balance of the cell. It is a pro-survival mechanism that plays an important role during development, differentiation, apoptosis, ageing and innate and adaptive immune response. Besides, autophagy has been described to be involved in the development of various human diseases, e.g., chronic liver diseases and the development of hepatocellular carcinoma. The hepatitis C virus (HCV) is a major cause of chronic liver diseases. It has recently been described that HCV, like other RNA viruses, hijacks the autophagic machinery to improve its replication. However, the mechanisms underlying its activation are conflicting. HCV replication and assembly occurs at the so-called membranous web that consists of lipid droplets and rearranged endoplasmic reticulum-derived membranes including single-, double- and multi-membrane vesicles. The double-membrane vesicles have been identified to contain NS3, NS5A, viral RNA and the autophagosomal marker microtubule-associated protein 1 light chain 3, corroborating the involvement of the autophagic pathway in the HCV life-cycle. In this review, we will highlight the crosstalk of the autophagosomal compartment with different steps of the HCV life-cycle and address its implications on favoring the survival of infected hepatocytes.
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74
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Iglesias NG, Mondotte JA, Byk LA, De Maio FA, Samsa MM, Alvarez C, Gamarnik AV. Dengue Virus Uses a Non-Canonical Function of the Host GBF1-Arf-COPI System for Capsid Protein Accumulation on Lipid Droplets. Traffic 2015; 16:962-77. [PMID: 26031340 DOI: 10.1111/tra.12305] [Citation(s) in RCA: 55] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2015] [Revised: 05/22/2015] [Accepted: 05/24/2015] [Indexed: 12/14/2022]
Abstract
Dengue viruses cause the most important human viral disease transmitted by mosquitoes. In recent years, a great deal has been learned about molecular details of dengue virus genome replication; however, little is known about genome encapsidation and the functions of the viral capsid protein. During infection, dengue virus capsid progressively accumulates around lipid droplets (LDs) by an unknown mechanism. Here, we examined the process by which the viral capsid is transported from the endoplasmic reticulum (ER) membrane, where the protein is synthesized, to LDs. Using different methods of intervention, we found that the GBF1-Arf1/Arf4-COPI pathway is necessary for capsid transport to LDs, while the process is independent of both COPII components and Golgi integrity. The transport was sensitive to Brefeldin A, while a drug resistant form of GBF1 was sufficient to restore capsid subcellular distribution in infected cells. The mechanism by which LDs gain or lose proteins is still an open question. Our results support a model in which the virus uses a non-canonical function of the COPI system for capsid accumulation on LDs, providing new ideas for antiviral strategies.
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Affiliation(s)
- Nestor G Iglesias
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires, 1405, Argentina
| | - Juan A Mondotte
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires, 1405, Argentina
| | - Laura A Byk
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires, 1405, Argentina
| | - Federico A De Maio
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires, 1405, Argentina
| | - Marcelo M Samsa
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires, 1405, Argentina
| | - Cecilia Alvarez
- Centro de Investigaciones en Bioquímica Clínica e Inmunología-CONICET, Departamento de Bioquímica Clínica, Facultad de Ciencias Químicas, UNC, 5000, Córdoba, Argentina
| | - Andrea V Gamarnik
- Fundación Instituto Leloir-CONICET, Avenida Patricias Argentinas 435, Buenos Aires, 1405, Argentina
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75
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Barbosa AD, Savage DB, Siniossoglou S. Lipid droplet-organelle interactions: emerging roles in lipid metabolism. Curr Opin Cell Biol 2015; 35:91-7. [PMID: 25988547 DOI: 10.1016/j.ceb.2015.04.017] [Citation(s) in RCA: 107] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2015] [Revised: 04/27/2015] [Accepted: 04/28/2015] [Indexed: 01/02/2023]
Abstract
Cellular homeostasis depends on the precisely coordinated use of lipids as fuels for energy production, building blocks for membrane biogenesis or chemical signals for intra-cellular and inter-cellular communication. Lipid droplets (LDs) are universally conserved dynamic organelles that can store and mobilize fatty acids and other lipid species for their multiple cellular roles. Increasing evidence suggests that contact zones between LDs and other organelles play important roles in the trafficking of lipids and in the regulation of lipid metabolism. Here we review recent advances regarding the nature and functional relevance of interactions between LDs and other organelles-particularly the endoplasmic reticulum (ER), LDs, mitochondria and vacuoles-that highlight their importance for lipid metabolism.
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Affiliation(s)
- Antonio Daniel Barbosa
- Cambridge Institute for Medical Research, University of Cambridge, CB2 0XY Cambridge, United Kingdom
| | - David B Savage
- University of Cambridge Metabolic Research Laboratories, Wellcome Trust-Medical Research Council Institute of Metabolic Science, Cambridge CB2 0QQ, United Kingdom
| | - Symeon Siniossoglou
- Cambridge Institute for Medical Research, University of Cambridge, CB2 0XY Cambridge, United Kingdom.
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Welte MA. As the fat flies: The dynamic lipid droplets of Drosophila embryos. Biochim Biophys Acta Mol Cell Biol Lipids 2015; 1851:1156-85. [PMID: 25882628 DOI: 10.1016/j.bbalip.2015.04.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 03/31/2015] [Accepted: 04/06/2015] [Indexed: 01/09/2023]
Abstract
Research into lipid droplets is rapidly expanding, and new cellular and organismal roles for these lipid-storage organelles are continually being discovered. The early Drosophila embryo is particularly well suited for addressing certain questions in lipid-droplet biology and combines technical advantages with unique biological phenomena. This review summarizes key features of this experimental system and the techniques available to study it, in order to make it accessible to researchers outside this field. It then describes the two topics most heavily studied in this system, lipid-droplet motility and protein sequestration on droplets, discusses what is known about the molecular players involved, points to open questions, and compares the results from Drosophila embryo studies to what it is known about lipid droplets in other systems.
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Affiliation(s)
- Michael A Welte
- Department of Biology University of Rochester, RC Box 270211, 317 Hutchison Hall, Rochester, NY 14627, USA.
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77
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Jiang XH, Xie YT, Jiang B, Tang MY, Ma T, Peng H. Inhibition of expression of hepatitis C virus 1b genotype core and NS4B genes in HepG2 cells using artificial microRNAs. Mol Med Rep 2015; 12:1905-13. [PMID: 25847260 DOI: 10.3892/mmr.2015.3571] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2014] [Accepted: 02/05/2015] [Indexed: 11/06/2022] Open
Abstract
The present study aimed to evaluate the silencing effect of artificial microRNAs (amiRNAs) against the hepatitis C virus (HCV) 1b (HCV1b) genotype core (C) and non-structural protein 4B (NS4B) genes. pDsRed-monomer-Core and pDsRed-monomer-NS4B plasmids, containing the target genes were constructed. A total of eight artificial micro RNA (amiRNA)-expressing plasmids, namely, pmiRE-C-mi1 to -mi4 and pmiRE-NS4B-mi1 to -mi4, were designed and constructed to interfere with various sites of the core and NS4B genes, and the amiRNA interfering plasmid and the corresponding target gene-expressing plasmid were co-transfected into HepG2 cells. At 48 h after transfection, HCV core and NS4B gene expression levels were detected using fluorescence microscopy, flow cytometry, reverse transcription quantitative polymerase chain reaction and western blot analysis. Fluorescence microscopy revealed that the target gene-transfected cells expressed red fluorescent protein, whereas the interfering plasmid-transfected cells exhibited expression of green fluorescent protein. The percentage of red fluorescent proteins and mean fluorescence intensity, as well as protein expression levels of the core and NS4B genes within the cells, which were co-transfected by the amiRNA interfering plasmid and the target gene, were significantly decreased. The results of the present study confirmed that amiRNAs may effectively and specifically inhibit the expression of HCV1b core and NS4B genes in HepG2 cells, potentially providing a novel therapeutic strategy for the treatment of HCV.
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Affiliation(s)
- Xiao-Hua Jiang
- Department of Infectious Diseases, Xiangya Hospital of Central South University, Changsha, Hunan 410087, P.R. China
| | - Yu-Tao Xie
- Department of Infectious Diseases, Xiangya Hospital of Central South University, Changsha, Hunan 410087, P.R. China
| | - Bo Jiang
- Department of Infectious Diseases, The First Affiliated Hospital of The University of South China, Hengyang, Hunan 421001, P.R. China
| | - Meng-Ying Tang
- Department of Infectious Diseases, The First Affiliated Hospital of The University of South China, Hengyang, Hunan 421001, P.R. China
| | - Tao Ma
- Department of Infectious Diseases, The First Affiliated Hospital of The University of South China, Hengyang, Hunan 421001, P.R. China
| | - Hua Peng
- Department of Infectious Diseases, The First Affiliated Hospital of The University of South China, Hengyang, Hunan 421001, P.R. China
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78
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Dynamic Interaction of Stress Granules, DDX3X, and IKK-α Mediates Multiple Functions in Hepatitis C Virus Infection. J Virol 2015; 89:5462-77. [PMID: 25740981 DOI: 10.1128/jvi.03197-14] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Accepted: 02/25/2015] [Indexed: 12/27/2022] Open
Abstract
The ubiquitous ATP-dependent RNA helicase DDX3X is involved in many cellular functions, including innate immunity, and is a pivotal host factor for hepatitis C virus (HCV) infection. Recently, we showed that DDX3X specifically recognizes the HCV 3' untranslated region (UTR), leading to the activation of IKK-α and a cascade of lipogenic signaling to facilitate lipid droplet biogenesis and viral assembly (Q. Li, V. Pene, S. Krishnamurthy, H. Cha, and T. J. Liang, Nat Med 19:722-729, 2013, http://dx.doi.org/10.1038/nm.3190). The interaction of DDX3X with HCV core protein seems to be dispensable for its proviral role. In this study, through systematic imaging and biochemical and virologic approaches, we identified a dynamic association between DDX3X and various cellular compartments and viral elements mediating multiple functions of DDX3X in productive HCV infection. Upon HCV infection, the HCV 3'UTR interacts with DDX3X and IKK-α, which redistribute to speckle-like cytoplasmic structures shown to be stress granules (SGs). As viral proteins accumulate in infected cells, DDX3X granules together with SG-associated proteins redistribute and colocalize with HCV core protein around lipid droplets (LDs). IKK-α, however, does not relocate to the LD but translocates to the nucleus. In HCV-infected cells, various HCV nonstructural proteins also interact or colocalize with DDX3X in close proximity to SGs and LDs, consistent with the tight juxtaposition of the replication complex and the assembly site at the surface of LDs. Short interfering RNA (siRNA)-mediated silencing of DDX3X and multiple SG components markedly inhibits HCV infection. Our data suggest that DDX3X initiates a multifaceted cellular program involving dynamic associations with HCV RNA and proteins, IKK-α, SG, and LD surfaces for its crucial role in the HCV life cycle. IMPORTANCE DDX3X is a proviral host factor for HCV infection. Recently, we showed that DDX3X binds to the HCV 3'UTR, activating IKK-α and cellular lipogenesis to facilitate viral assembly (Q. Li et al., Nat Med 19:722-729, 2013, http://dx.doi.org/10.1038/nm.3190). Here, we report associations of DDX3X with various cellular compartments and viral elements that mediate its multiple functions in the HCV life cycle. Upon infection, the HCV 3'UTR redistributes DDX3X and IKK-α to speckle-like cytoplasmic structures shown to be SGs. Subsequently, interactions between DDX3X, SG, and HCV proteins facilitate the translocation of DDX3X-SG complexes to the LD surface. HCV nonstructural proteins are shown to colocalize with DDX3X in close proximity to SGs and LDs, consistent with the tight juxtaposition of the HCV replication complex and assembly site at the LD surface. Our data demonstrate that DDX3X initiates a multifaceted cellular program involving dynamic associations with HCV elements, IKK-α, SGs, and LDs for its critical role in HCV infection.
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79
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Gross DA, Silver DL. Cytosolic lipid droplets: from mechanisms of fat storage to disease. Crit Rev Biochem Mol Biol 2015; 49:304-26. [PMID: 25039762 DOI: 10.3109/10409238.2014.931337] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The lipid droplet (LD) is a phylogenetically conserved organelle. In eukaryotes, it is born from the endoplasmic reticulum, but unlike its parent organelle, LDs are the only known cytosolic organelles that are micellar in structure. LDs are implicated in numerous physiological and pathophysiological functions. Many aspects of the LD has captured the attention of diverse scientists alike and has recently led to an explosion in information on the LD biogenesis, expansion and fusion, identification of LD proteomes and diseases associated with LD biology. This review will provide a brief history of this fascinating organelle and provide some contemporary views of unanswered questions in LD biogenesis.
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Affiliation(s)
- David A Gross
- Program in Cardiovascular & Metabolic Disorders, Duke-NUS Graduate Medical School Singapore , Singapore , and
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80
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Dolan PT, Roth AP, Xue B, Sun R, Dunker AK, Uversky VN, LaCount DJ. Intrinsic disorder mediates hepatitis C virus core-host cell protein interactions. Protein Sci 2014; 24:221-35. [PMID: 25424537 DOI: 10.1002/pro.2608] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2014] [Accepted: 11/19/2014] [Indexed: 12/18/2022]
Abstract
Viral proteins bind to numerous cellular and viral proteins throughout the infection cycle. However, the mechanisms by which viral proteins interact with such large numbers of factors remain unknown. Cellular proteins that interact with multiple, distinct partners often do so through short sequences known as molecular recognition features (MoRFs) embedded within intrinsically disordered regions (IDRs). In this study, we report the first evidence that MoRFs in viral proteins play a similar role in targeting the host cell. Using a combination of evolutionary modeling, protein-protein interaction analyses and forward genetic screening, we systematically investigated two computationally predicted MoRFs within the N-terminal IDR of the hepatitis C virus (HCV) Core protein. Sequence analysis of the MoRFs showed their conservation across all HCV genotypes and the canine and equine Hepaciviruses. Phylogenetic modeling indicated that the Core MoRFs are under stronger purifying selection than the surrounding sequence, suggesting that these modules have a biological function. Using the yeast two-hybrid assay, we identified three cellular binding partners for each HCV Core MoRF, including two previously characterized cellular targets of HCV Core (DDX3X and NPM1). Random and site-directed mutagenesis demonstrated that the predicted MoRF regions were required for binding to the cellular proteins, but that different residues within each MoRF were critical for binding to different partners. This study demonstrated that viruses may use intrinsic disorder to target multiple cellular proteins with the same amino acid sequence and provides a framework for characterizing the binding partners of other disordered regions in viral and cellular proteomes.
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Affiliation(s)
- Patrick T Dolan
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, West Lafayette, Indiana, 47907
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81
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Hepatitis C virus life cycle and lipid metabolism. BIOLOGY 2014; 3:892-921. [PMID: 25517881 PMCID: PMC4280516 DOI: 10.3390/biology3040892] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/07/2014] [Revised: 12/04/2014] [Accepted: 12/08/2014] [Indexed: 12/12/2022]
Abstract
Hepatitis C Virus (HCV) infects over 150 million people worldwide. In most cases HCV infection becomes chronic, causing liver disease ranging from fibrosis to cirrhosis and hepatocellular carcinoma. HCV affects the cholesterol homeostasis and at the molecular level, every step of the virus life cycle is intimately connected to lipid metabolism. In this review, we present an update on the lipids and apolipoproteins that are involved in the HCV infectious cycle steps: entry, replication and assembly. Moreover, the result of the assembly process is a lipoviroparticle, which represents a peculiarity of hepatitis C virion. This review illustrates an example of an intricate virus-host interaction governed by lipid metabolism.
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82
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Camus G, Schweiger M, Herker E, Harris C, Kondratowicz AS, Tsou CL, Farese RV, Herath K, Previs SF, Roddy TP, Pinto S, Zechner R, Ott M. The hepatitis C virus core protein inhibits adipose triglyceride lipase (ATGL)-mediated lipid mobilization and enhances the ATGL interaction with comparative gene identification 58 (CGI-58) and lipid droplets. J Biol Chem 2014; 289:35770-80. [PMID: 25381252 DOI: 10.1074/jbc.m114.587816] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Liver steatosis is a common health problem associated with hepatitis C virus (HCV) and an important risk factor for the development of liver fibrosis and cancer. Steatosis is caused by triglycerides (TG) accumulating in lipid droplets (LDs), cellular organelles composed of neutral lipids surrounded by a monolayer of phospholipids. The HCV nucleocapsid core localizes to the surface of LDs and induces steatosis in cultured cells and mouse livers by decreasing intracellular TG degradation (lipolysis). Here we report that core at the surface of LDs interferes with the activity of adipose triglyceride lipase (ATGL), the key lipolytic enzyme in the first step of TG breakdown. Expressing core in livers or mouse embryonic fibroblasts of ATGL(-/-) mice no longer decreases TG degradation as observed in LDs from wild-type mice, supporting the model that core reduces lipolysis by engaging ATGL. Core must localize at LDs to inhibit lipolysis, as ex vivo TG hydrolysis is impaired in purified LDs coated with core but not when free core is added to LDs. Coimmunoprecipitation experiments revealed that core does not directly interact with the ATGL complex but, unexpectedly, increased the interaction between ATGL and its activator CGI-58 as well as the recruitment of both proteins to LDs. These data link the anti-lipolytic activity of the HCV core protein with altered ATGL binding to CGI-58 and the enhanced association of both proteins with LDs.
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Affiliation(s)
- Gregory Camus
- From the Gladstone Institute of Virology and Immunology, San Francisco, California 94158
| | - Martina Schweiger
- From the Gladstone Institute of Virology and Immunology, San Francisco, California 94158, Institute of Molecular Biosciences, University of Graz, 8010 Graz, Austria
| | - Eva Herker
- From the Gladstone Institute of Virology and Immunology, San Francisco, California 94158, UCSF Liver Center, University of California, San Francisco, California 94158, Heinrich-Pette-Institute, Leibniz Institute for Experimental Virology, 20251 Hamburg, Germany
| | - Charles Harris
- UCSF Liver Center, University of California, San Francisco, California 94158, Gladstone Institute of Cardiovascular Disease, San Francisco, California 94158, Department of Medicine, University of California, San Francisco, California 94158, Division of Endocrinology Metabolism and Lipid Research, Washington University School of Medicine, St. Louis, Missouri 63110
| | - Andrew S Kondratowicz
- From the Gladstone Institute of Virology and Immunology, San Francisco, California 94158
| | - Chia-Lin Tsou
- From the Gladstone Institute of Virology and Immunology, San Francisco, California 94158
| | - Robert V Farese
- UCSF Liver Center, University of California, San Francisco, California 94158, Gladstone Institute of Cardiovascular Disease, San Francisco, California 94158, Department of Medicine, University of California, San Francisco, California 94158, Department of Biochemistry and Biophysics, University of California, San Francisco, California 94158, and
| | - Kithsiri Herath
- Merck Research Laboratories, Merck and Co., Inc., Kenilworth, New Jersey 07065
| | - Stephen F Previs
- Merck Research Laboratories, Merck and Co., Inc., Kenilworth, New Jersey 07065
| | - Thomas P Roddy
- Merck Research Laboratories, Merck and Co., Inc., Kenilworth, New Jersey 07065
| | - Shirly Pinto
- Merck Research Laboratories, Merck and Co., Inc., Kenilworth, New Jersey 07065
| | - Rudolf Zechner
- Institute of Molecular Biosciences, University of Graz, 8010 Graz, Austria
| | - Melanie Ott
- From the Gladstone Institute of Virology and Immunology, San Francisco, California 94158, UCSF Liver Center, University of California, San Francisco, California 94158, Department of Medicine, University of California, San Francisco, California 94158,
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83
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Eyre NS, Helbig KJ, Beard MR. Current and future targets of antiviral therapy in the hepatitis C virus life cycle. Future Virol 2014. [DOI: 10.2217/fvl.14.83] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
ABSTRACT Advances in our understanding of the hepatitis C virus (HCV) life cycle have enabled the development of numerous clinically advanced direct-acting antivirals. Indeed, the recent approval of first-generation direct-acting antivirals that target the viral NS3–4A protease and NS5B RNA-dependent RNA polymerase brings closer the possibility of universally efficacious and well-tolerated antiviral therapies for this insidious infection. However, the complexities of comorbidities, unforeseen side effects or drug–drug interactions, viral diversity, the high mutation rate of HCV RNA replication and the elegant and constantly evolving mechanisms employed by HCV to evade host and therapeutically implemented antiviral strategies remain as significant obstacles to this goal. Here, we review advances in our understanding of the HCV life cycle and associated opportunities for antiviral therapy.
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Affiliation(s)
- Nicholas S Eyre
- School of Molecular & Biomedical Science, The University of Adelaide & Centre for Cancer Biology, SA Pathology, Adelaide, South Australia, Australia
| | - Karla J Helbig
- School of Molecular & Biomedical Science, The University of Adelaide & Centre for Cancer Biology, SA Pathology, Adelaide, South Australia, Australia
| | - Michael R Beard
- School of Molecular & Biomedical Science, The University of Adelaide & Centre for Cancer Biology, SA Pathology, Adelaide, South Australia, Australia
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84
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Dubuisson J, Cosset FL. Virology and cell biology of the hepatitis C virus life cycle: an update. J Hepatol 2014; 61:S3-S13. [PMID: 25443344 DOI: 10.1016/j.jhep.2014.06.031] [Citation(s) in RCA: 126] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/19/2014] [Revised: 06/25/2014] [Accepted: 06/26/2014] [Indexed: 02/07/2023]
Abstract
Hepatitis C virus (HCV) is an important human pathogen that causes hepatitis, liver cirrhosis and hepatocellular carcinoma. It imposes a serious problem to public health in the world as the population of chronically infected HCV patients who are at risk of progressive liver disease is projected to increase significantly in the next decades. However, the arrival of new antiviral molecules is progressively changing the landscape of hepatitis C treatment. The search for new anti-HCV therapies has also been a driving force to better understand how HCV interacts with its host, and major progresses have been made on the various steps of the HCV life cycle. Here, we review the most recent advances in the fast growing knowledge on HCV life cycle and interaction with host factors and pathways.
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Affiliation(s)
- Jean Dubuisson
- Institut Pasteur de Lille, Center for Infection & Immunity of Lille (CIIL), F-59019 Lille, France; CNRS UMR8204, F-59021 Lille, France; Inserm U1019, F-59019 Lille, France; Université Lille Nord de France, F-59000 Lille, France.
| | - François-Loïc Cosset
- CIRI - International Center for Infectiology Research, Team EVIR, Université de Lyon, Lyon, France; Inserm, U1111, Lyon, France; Ecole Normale Supérieure de Lyon, Lyon, France; CNRS, UMR5308, Lyon, France; Université Lyon 1, Centre International de Recherche en Infectiologie, Lyon, France; LabEx Ecofect, Université de Lyon, Lyon, France.
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85
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Afzal MS, Zaidi NUSS, Dubuisson J, Rouille Y. Hepatitis C virus capsid protein and intracellular lipids interplay and its association with hepatic steatosis. HEPATITIS MONTHLY 2014; 14:e17812. [PMID: 25237371 PMCID: PMC4165984 DOI: 10.5812/hepatmon.17812] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/24/2014] [Revised: 03/09/2014] [Accepted: 05/08/2014] [Indexed: 12/11/2022]
Abstract
BACKGROUND Hepatitis C Virus (HCV) is a major causative agent for chronic liver disease worldwide. Hepatic steatosis is a frequent histological feature in patients with chronic HCV. Both host and viral factors are involved in steatosis development. It results from uncontrolled growth of cytoplasmic lipid droplets (LDs) in hepatocytes. LDs are intracellular organelles playing key role in the HCV life cycle. HCV core protein localizes at the LD surface and this localization is crucial for virion production. OBJECTIVES We explored in vitro interplay of core and LDs to investigate the role of core in steatosis. MATERIALS AND METHODS Core expression vectors were transfected in Huh-7 cells. The effect of core protein on LDs content and distribution in the cells was monitored by confocal microscopy. Cells were treated with oleic acid to analyze the effect of increased intracellular LDs on core expression. Core protein expression was monitored by western blot analysis. RESULTS Core expression altered the intracellular lipid metabolism, which resulted in a change in LDs morphology. Core LDs interaction was required for this effect since the mutation of two prolines (P138A, P143A), which impair LDs localization, had no impact on LDs morphology. Conversely, oleic acid induced intracellular LD content resulted in increased core expression. CONCLUSIONS Core-LDs interaction may be an underlying molecular mechanism to induce liver steatosis in patients with HCV infection. This interaction is also crucial for efficient viral replication and persistence in infected cells. Steatosis can also interfere with efficient standard interferon therapy treatment. Management of steatosis should be considered along with standard care for achieving higher sustained virological response (SVR) in patients receiving interferon regimen.
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Affiliation(s)
- Muhammad Sohail Afzal
- Center for Infection and Immunity of Lille (CIIL), Institut Pasteur de Lille, Univ Lille Nord de France, Lille, France
- Atta ur Rahman School of Applied Biosciences, National University of Sciences and Technology, H-12 Islamabad, Pakistan
- Corresponding Author: Muhammad Sohail Afzal, Atta ur Rahman School of Applied Biosciences (ASAB), National University of Sciences and Technology (NUST), H-12, Islamabad, Pakistan. Tel: +92-3215244808, Fax: +92-5190856102, E-mail:
| | - Najam Us Sahar Sadaf Zaidi
- Atta ur Rahman School of Applied Biosciences, National University of Sciences and Technology, H-12 Islamabad, Pakistan
| | - Jean Dubuisson
- Center for Infection and Immunity of Lille (CIIL), Institut Pasteur de Lille, Univ Lille Nord de France, Lille, France
| | - Yves Rouille
- Center for Infection and Immunity of Lille (CIIL), Institut Pasteur de Lille, Univ Lille Nord de France, Lille, France
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86
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Dansako H, Hiramoto H, Ikeda M, Wakita T, Kato N. Rab18 is required for viral assembly of hepatitis C virus through trafficking of the core protein to lipid droplets. Virology 2014; 462-463:166-74. [PMID: 24997429 DOI: 10.1016/j.virol.2014.05.017] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2014] [Revised: 03/11/2014] [Accepted: 05/14/2014] [Indexed: 11/28/2022]
Abstract
During persistent infection of HCV, the HCV core protein (HCV-JFH-1 strain of genotype 2a) is recruited to lipid droplets (LDs) for viral assembly, but the mechanism of recruitment of the HCV core protein is uncertain. Here, we demonstrated that one of the Ras-related small GTPases, Rab18, was required for trafficking of the core protein around LDs. The knockdown of Rab18 reduced intracellular and extracellular viral infectivity, but not intracellular viral replication in HCV-JFH-1-infected RSc cells (an HuH-7-derived cell line). Exogenous expression of Rab18 increased extracellular viral infectivity almost two-fold. Furthermore, Rab18 was co-localized with the core protein in HCV-JFH-1-infected RSc cells, and the knockdown of Rab18 blocked recruitment of the HCV-JFH-1 core protein to LDs. These results suggest that Rab18 has an important role in viral assembly through the trafficking of the core protein to LDs.
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Affiliation(s)
- Hiromichi Dansako
- Department of Tumor Virology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
| | - Hiroki Hiramoto
- Department of Tumor Virology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
| | - Masanori Ikeda
- Department of Tumor Virology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan
| | - Takaji Wakita
- Department of Virology II, National Institute of Infectious Disease, 1-23-1 Toyama, Shinjuku-ku, Tokyo 162-8640, Japan
| | - Nobuyuki Kato
- Department of Tumor Virology, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, 2-5-1 Shikata-cho, Kita-ku, Okayama 700-8558, Japan.
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87
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Liefhebber JMP, Hague CV, Zhang Q, Wakelam MJO, McLauchlan J. Modulation of triglyceride and cholesterol ester synthesis impairs assembly of infectious hepatitis C virus. J Biol Chem 2014; 289:21276-88. [PMID: 24917668 PMCID: PMC4118089 DOI: 10.1074/jbc.m114.582999] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
In hepatitis C virus infection, replication of the viral genome and virion assembly are linked to cellular metabolic processes. In particular, lipid droplets, which store principally triacylglycerides (TAGs) and cholesterol esters (CEs), have been implicated in production of infectious virus. Here, we examine the effect on productive infection of triacsin C and YIC-C8-434, which inhibit synthesis of TAGs and CEs by targeting long-chain acyl-CoA synthetase and acyl-CoA:cholesterol acyltransferase, respectively. Our results present high resolution data on the acylglycerol and cholesterol ester species that were affected by the compounds. Moreover, triacsin C, which blocks both triglyceride and cholesterol ester synthesis, cleared most of the lipid droplets in cells. By contrast, YIC-C8-434, which only abrogates production of cholesterol esters, induced an increase in size of droplets. Although both compounds slightly reduced viral RNA synthesis, they significantly impaired assembly of infectious virions in infected cells. In the case of triacsin C, reduced stability of the viral core protein, which forms the virion nucleocapsid and is targeted to the surface of lipid droplets, correlated with lower virion assembly. In addition, the virus particles that were released from cells had reduced specific infectivity. YIC-C8-434 did not alter the association of core with lipid droplets but appeared to decrease production of infectious virus particles, suggesting a block in virion assembly. Thus, the compounds have antiviral properties, indicating that targeting synthesis of lipids stored in lipid droplets might be an option for therapeutic intervention in treating chronic hepatitis C virus infection.
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Affiliation(s)
- Jolanda M P Liefhebber
- From the Medical Research Council-University of Glasgow Centre for Virus Research, 8 Church Street, Glasgow G11 5JR, Scotland, United Kingdom and
| | - Charlotte V Hague
- From the Medical Research Council-University of Glasgow Centre for Virus Research, 8 Church Street, Glasgow G11 5JR, Scotland, United Kingdom and
| | - Qifeng Zhang
- The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, United Kingdom
| | - Michael J O Wakelam
- The Babraham Institute, Babraham Research Campus, Cambridge CB22 3AT, United Kingdom
| | - John McLauchlan
- From the Medical Research Council-University of Glasgow Centre for Virus Research, 8 Church Street, Glasgow G11 5JR, Scotland, United Kingdom and
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88
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Lai CK, Saxena V, Tseng CH, Jeng KS, Kohara M, Lai MMC. Nonstructural protein 5A is incorporated into hepatitis C virus low-density particle through interaction with core protein and microtubules during intracellular transport. PLoS One 2014; 9:e99022. [PMID: 24905011 PMCID: PMC4048239 DOI: 10.1371/journal.pone.0099022] [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: 02/11/2014] [Accepted: 05/09/2014] [Indexed: 01/16/2023] Open
Abstract
Nonstructural protein 5A (NS5A) of hepatitis C virus (HCV) serves dual functions in viral RNA replication and virus assembly. Here, we demonstrate that HCV replication complex along with NS5A and Core protein was transported to the lipid droplet (LD) through microtubules, and NS5A-Core complexes were then transported from LD through early-to-late endosomes to the plasma membrane via microtubules. Further studies by cofractionation analysis and immunoelectron microscopy of the released particles showed that NS5A-Core complexes, but not NS4B, were present in the low-density fractions, but not in the high-density fractions, of the HCV RNA-containing virions and associated with the internal virion core. Furthermore, exosomal markers CD63 and CD81 were also detected in the low-density fractions, but not in the high-density fractions. Overall, our results suggest that HCV NS5A is associated with the core of the low-density virus particles which exit the cell through a preexisting endosome/exosome pathway and may contribute to HCV natural infection.
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Affiliation(s)
- Chao-Kuen Lai
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- Graduate Institute of Toxicology, National Taiwan University, Taipei, Taiwan
| | - Vikas Saxena
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Chung-Hsin Tseng
- Department of Microbiology and Immunology, and Center of Infectious Disease and Signaling Research, National Cheng Kung University, Tainan, Taiwan
| | - King-Song Jeng
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
| | - Michinori Kohara
- Department of Microbiology and Cell Biology, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Michael M. C. Lai
- Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan
- Department of Molecular Microbiology and Immunology, University of Southern California, Los Angeles, California, United States of America
- Department of Microbiology and Immunology, and Center of Infectious Disease and Signaling Research, National Cheng Kung University, Tainan, Taiwan
- * E-mail:
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89
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Arrese EL, Saudale FZ, Soulages JL. Lipid Droplets as Signaling Platforms Linking Metabolic and Cellular Functions. Lipid Insights 2014; 7:7-16. [PMID: 25221429 PMCID: PMC4161058 DOI: 10.4137/lpi.s11128] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
The main cells of the adipose tissue of animals, adipocytes, are characterized by the presence of large cytosolic lipid droplets (LDs) that store triglyceride (TG) and cholesterol. However, most cells have LDs and the ability to store lipids. LDs have a well-known central role in storage and provision of fatty acids and cholesterol. However, the complexity of the regulation of lipid metabolism on the surface of the LDs is still a matter of intense study. Beyond this role, a number of recent studies have suggested that LDs have major functions in other cellular processes, such as protein storage and degradation, infection, and immunity. Thus, our perception of LDs has been radically transformed from simple globules of fat to highly dynamic organelles of unexpected complexity. Here, we compiled some recent evidence supporting the emerging view that LDs act as platforms connecting a number of relevant metabolic and cellular functions.
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Affiliation(s)
- Estela L Arrese
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| | - Fredy Z Saudale
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
| | - Jose L Soulages
- Department of Biochemistry and Molecular Biology; Oklahoma State University; Stillwater, OK, 74078, USA
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90
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Role of intracellular events in the pathogenesis of dengue; an overview. Microb Pathog 2014; 69-70:45-52. [PMID: 24685697 DOI: 10.1016/j.micpath.2014.03.004] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2013] [Revised: 03/17/2014] [Accepted: 03/20/2014] [Indexed: 01/01/2023]
Abstract
Dengue is one of the most important mosquito-borne viral diseases that are relentlessly spreading in newer areas in the tropical and subtropical regions of the World. In last fifty years, in spite of intensive and extensive investigations, pathogenesis of dengue is still not clearly understood. Recently, the research focus is on studying the role of intracellular events in pathogenesis of viral infections. Entry of virion in the host cell is followed by quick succession of events, unfolded protein response, lipid bodies and lipophagy, endoplasmic reticulum stress and recent demonstration of autophagy. The turbulence caused by these events may result in clearance of the virus/enhanced replication and survival of the host cell/apoptosis. Both, increased virus load and apoptosis of host cell may have pathological effects on the host. In the present review, we have summed up the role of various intracellular events in viral infections with special emphasis on Dengue virus infection.
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91
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Incorporation of hepatitis C virus E1 and E2 glycoproteins: the keystones on a peculiar virion. Viruses 2014; 6:1149-87. [PMID: 24618856 PMCID: PMC3970144 DOI: 10.3390/v6031149] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2013] [Revised: 02/21/2014] [Accepted: 02/27/2014] [Indexed: 12/13/2022] Open
Abstract
Hepatitis C virus (HCV) encodes two envelope glycoproteins, E1 and E2. Their structure and mode of fusion remain unknown, and so does the virion architecture. The organization of the HCV envelope shell in particular is subject to discussion as it incorporates or associates with host-derived lipoproteins, to an extent that the biophysical properties of the virion resemble more very-low-density lipoproteins than of any virus known so far. The recent development of novel cell culture systems for HCV has provided new insights on the assembly of this atypical viral particle. Hence, the extensive E1E2 characterization accomplished for the last two decades in heterologous expression systems can now be brought into the context of a productive HCV infection. This review describes the biogenesis and maturation of HCV envelope glycoproteins, as well as the interplay between viral and host factors required for their incorporation in the viral envelope, in a way that allows efficient entry into target cells and evasion of the host immune response.
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92
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Dynamic imaging of the hepatitis C virus NS5A protein during a productive infection. J Virol 2014; 88:3636-52. [PMID: 24429364 DOI: 10.1128/jvi.02490-13] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
UNLABELLED Hepatitis C virus (HCV) NS5A is essential for viral genome replication within cytoplasmic replication complexes and virus assembly at the lipid droplet (LD) surface, although its definitive functions are poorly understood. We developed approaches to investigate NS5A dynamics during a productive infection. We report here that NS5A motility and efficient HCV RNA replication require the microtubule network and the cytoplasmic motor dynein and demonstrate that both motile and relatively static NS5A-positive foci are enriched with host factors VAP-A and Rab5A. Pulse-chase imaging revealed that newly synthesized NS5A foci are small and distinct from aged foci, while further studies using a unique dual fluorescently tagged infectious HCV chimera showed a relatively stable association of NS5A foci with core-capped LDs. These results reveal new details about the dynamics and maturation of NS5A and the nature of potential sites of convergence of HCV replication and assembly pathways. IMPORTANCE Hepatitis C virus (HCV) is a major cause of serious liver disease worldwide. An improved understanding of the HCV replication cycle will enable development of novel and improved antiviral strategies. Here we have developed complementary fluorescent labeling and imaging approaches to investigate the localization, traffic and interactions of the HCV NS5A protein in living, virus-producing cells. These studies reveal new details as to the traffic, composition and biogenesis of NS5A foci and the nature of their association with putative sites of virus assembly.
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93
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Hepatitis C virus stimulates low-density lipoprotein receptor expression to facilitate viral propagation. J Virol 2013; 88:2519-29. [PMID: 24352472 DOI: 10.1128/jvi.02727-13] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
UNLABELLED Lipids play a crucial role in multiple aspects of hepatitis C virus (HCV) life cycle. HCV modulates host lipid metabolism to enrich the intracellular milieu with lipids to facilitate its proliferation. However, very little is known about the influence of HCV on lipid uptake from bloodstream. Low-density lipoprotein receptor (LDLR) is involved in uptake of cholesterol rich low-density lipoprotein (LDL) particles from the bloodstream. The association of HCV particles with lipoproteins implicates their role in HCV entry; however, the precise role of LDLR in HCV entry still remains controversial. Here, we investigate the effect of HCV infection on LDLR expression and the underlying mechanism(s) involved. We demonstrate that HCV stimulates LDLR expression in both HCV-infected Huh7 cells and in liver tissue from chronic hepatitis C patients. Fluorescence activated cell sorting and immunofluorescence analysis revealed enhanced cell surface and total expression of LDLR in HCV-infected cells. Increased LDLR expression resulted in the enhanced uptake of lipoprotein particles by HCV-infected cells. Analysis of LDLR gene promoter identified a pivotal role of sterol-regulatory element binding proteins (SREBPs), in the HCV-mediated stimulation of LDLR transcription. In addition, HCV negatively modulated the expression of proprotein convertase subtilisin/kexin type 9 (PCSK9), a protein that facilitates LDLR degradation. Ectopic expression of wild-type PCSK9 or gain-of-function PCSK9 mutant negatively affected HCV replication. Overall, our results demonstrate that HCV regulates LDLR expression at transcriptional and posttranslational level via SREBPs and PCSK9 to promote lipid uptake and facilitate viral proliferation. IMPORTANCE HCV modulates host lipid metabolism to promote enrichment of lipids in intracellular environment, which are essential in multiple aspects of HCV life cycle. However, very little is known about the influence of HCV on lipid uptake from the bloodstream. LDLR is involved in uptake of cholesterol rich lipid particles from bloodstream. In this study, we investigated the effect of HCV on LDLR expression and the underlying mechanism triggered by the virus to modulate LDLR expression. Our observations suggest that HCV upregulates LDLR expression at both the protein and the transcript levels and that this upregulation likely contributes toward the uptake of serum lipids by infected hepatocytes. Abrogation of HCV-mediated upregulation of LDLR inhibits serum lipid uptake and thereby perturbs HCV replication. Overall, our findings highlight the importance of serum lipid uptake by infected hepatocytes in HCV life cycle.
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94
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Lyn RK, Hope G, Sherratt AR, McLauchlan J, Pezacki JP. Bidirectional lipid droplet velocities are controlled by differential binding strengths of HCV core DII protein. PLoS One 2013; 8:e78065. [PMID: 24223760 PMCID: PMC3815211 DOI: 10.1371/journal.pone.0078065] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2013] [Accepted: 09/09/2013] [Indexed: 12/16/2022] Open
Abstract
Host cell lipid droplets (LD) are essential in the hepatitis C virus (HCV) life cycle and are targeted by the viral capsid core protein. Core-coated LDs accumulate in the perinuclear region and facilitate viral particle assembly, but it is unclear how mobility of these LDs is directed by core. Herein we used two-photon fluorescence, differential interference contrast imaging, and coherent anti-Stokes Raman scattering microscopies, to reveal novel core-mediated changes to LD dynamics. Expression of core protein’s lipid binding domain II (DII-core) induced slower LD speeds, but did not affect directionality of movement on microtubules. Modulating the LD binding strength of DII-core further impacted LD mobility, revealing the temporal effects of LD-bound DII-core. These results for DII-core coated LDs support a model for core-mediated LD localization that involves core slowing down the rate of movement of LDs until localization at the perinuclear region is accomplished where LD movement ceases. The guided localization of LDs by HCV core protein not only is essential to the viral life cycle but also poses an interesting target for the development of antiviral strategies against HCV.
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Affiliation(s)
- Rodney K. Lyn
- National Research Council of Canada, Ottawa, Ontario, Canada
- Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada
| | - Graham Hope
- Medical Research Council-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom
| | | | - John McLauchlan
- Medical Research Council-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom
- * E-mail: (JPP); (JM)
| | - John Paul Pezacki
- National Research Council of Canada, Ottawa, Ontario, Canada
- Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada
- * E-mail: (JPP); (JM)
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95
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Dolan PT, Zhang C, Khadka S, Arumugaswami V, Vangeloff AD, Heaton NS, Sahasrabudhe S, Randall G, Sun R, LaCount DJ. Identification and comparative analysis of hepatitis C virus-host cell protein interactions. MOLECULAR BIOSYSTEMS 2013; 9:3199-209. [PMID: 24136289 DOI: 10.1039/c3mb70343f] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Hepatitis C virus (HCV) alters the global behavior of the host cell to create an environment conducive to its own replication, but much remains unknown about how HCV proteins elicit these changes. Thus, a better understanding of the interface between the virus and host cell is required. Here we report the results of a large-scale yeast two-hybrid screen to identify protein-protein interactions between HCV genotype 2a (strain JFH1) and cellular factors. Our study identified 112 unique interactions between 7 HCV and 94 human proteins, over 40% of which have been linked to HCV infection by other studies. These interactions develop a more complete picture of HCV infection, providing insight into HCV manipulation of pathways, such as lipid and cholesterol metabolism, that were previously linked to HCV infection and implicating novel targets within microtubule-organizing centers, the complement system and cell cycle regulatory machinery. In an effort to understand the relationship between HCV and related viruses, we compared the HCV 2a interactome to those of other HCV genotypes and to the related dengue virus. Greater overlap was observed between HCV and dengue virus targets than between HCV genotypes, demonstrating the value of parallel screening approaches when comparing virus-host cell interactomes. Using siRNAs to inhibit expression of cellular proteins, we found that five of the ten shared targets tested (CUL7, PCM1, RILPL2, RNASET2, and TCF7L2) were required for replication of both HCV and dengue virus. These shared interactions provide insight into common features of the viral life cycles of the family Flaviviridae.
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Affiliation(s)
- Patrick T Dolan
- Department of Medicinal Chemistry and Molecular Pharmacology, Purdue University, RHPH 514, 575 Stadium Mall Drive, West Lafayette, IN 47907, USA.
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96
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Monoubiquitination of ancient ubiquitous protein 1 promotes lipid droplet clustering. PLoS One 2013; 8:e72453. [PMID: 24039768 PMCID: PMC3764060 DOI: 10.1371/journal.pone.0072453] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2013] [Accepted: 07/17/2013] [Indexed: 01/08/2023] Open
Abstract
Lipid droplets, the intracellular storage organelles for neutral lipids, exist in a wide range of sizes and of morphologically distinct organization, from loosely dispersed lipid droplets to tightly packed lipid droplet clusters. We show that the lipid droplet protein AUP1 induces cluster formation. A fraction of AUP1 is monoubiquitinated at various lysine residues. This process depends on its internal CUE domain, which is a known ubiquitin-binding domain. AUP1 with a deleted or point mutagenized CUE domain, as well as a lysine-free mutant, are not ubiquitinated and do not induce lipid droplet clustering. When such ubiquitination deficient mutants are fused to ubiquitin, clustering is restored. AUP1 mutants with defective droplet targeting fail to induce clustering. Also, another lipid droplet protein, NSDHL, with a fused ubiquitin does not induce clustering. The data indicate that monoubiquitinated AUP1 on the lipid droplet surface specifically induces clustering, and suggest a homophilic interaction with a second AUP1 molecule or a heterophilic interaction with another ubiquitin-binding protein.
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97
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Krahmer N, Farese RV, Walther TC. Balancing the fat: lipid droplets and human disease. EMBO Mol Med 2013; 5:973-83. [PMID: 23740690 PMCID: PMC3721468 DOI: 10.1002/emmm.201100671] [Citation(s) in RCA: 309] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/21/2013] [Revised: 04/30/2013] [Accepted: 05/02/2013] [Indexed: 01/04/2023] Open
Abstract
Lipid droplets (LDs) are dynamic, cytosolic lipid-storage organelles found in nearly all cell types. Too many or too few LDs during excess or deficient fat storage lead to many different human diseases. Recent insights into LD biology and LD protein functions shed new light on mechanisms underlying those metabolic pathologies. These findings will likely provide opportunities for treatment of diseases associated with too much or too little fat.
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Affiliation(s)
- Natalie Krahmer
- Department of Cell Biology, Yale School of MedicineNew Haven, CT, USA
| | - Robert V Farese
- Gladstone Institutes, Departments of Medicine and Biochemistry & Biophysics, University of CaliforniaSan Francisco, CA, USA
| | - Tobias C Walther
- Department of Cell Biology, Yale School of MedicineNew Haven, CT, USA
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98
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Orlicky DJ, Monks J, Stefanski AL, McManaman JL. Dynamics and molecular determinants of cytoplasmic lipid droplet clustering and dispersion. PLoS One 2013; 8:e66837. [PMID: 23825572 PMCID: PMC3692517 DOI: 10.1371/journal.pone.0066837] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2013] [Accepted: 05/12/2013] [Indexed: 11/18/2022] Open
Abstract
Perilipin-1 (Plin1), a prominent cytoplasmic lipid droplet (CLD) binding phosphoprotein and key physiological regulator of triglyceride storage and lipolysis in adipocytes, is thought to regulate the fragmentation and dispersion of CLD that occurs in response to β-adrenergic activation of adenylate cyclase. Here we investigate the dynamics and molecular determinants of these processes using cell lines stably expressing recombinant forms of Plin1 and/or other members of the perilipin family. Plin1 and a C-terminal CLD-binding fragment of Plin1 (Plin1CT) induced formation of single dense CLD clusters near the microtubule organizing center, whereas neither an N-terminal CLD-binding fragment of Plin1, nor Plin2 or Plin3 induced clustering. Clustered CLD coated by Plin1, or Plin1CT, dispersed in response to isoproterenol, or other agents that activate adenylate cyclase, in a process inhibited by the protein kinase A inhibitor, H89, and blocked by microtubule disruption. Isoproterenol-stimulated phosphorylation of CLD-associated Plin1 on serine 492 preceded their dispersion, and live cell imaging showed that cluster dispersion involved initial fragmentation of tight clusters into multiple smaller clusters, which then fragmented into well-dispersed individual CLD. siRNA knockdown of the cortical actin binding protein, moesin, induced disaggregation of tight clusters into multiple smaller clusters, and inhibited the reaggregation of dispersed CLD into tight clusters. Together these data suggest that the clustering and dispersion processes involve a complex orchestration of phosphorylation-dependent, microtubule-dependent and independent, and microfilament dependent steps.
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Affiliation(s)
- David J. Orlicky
- Department of Pathology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Jenifer Monks
- Division of Basic Reproductive Sciences, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - Adrianne L. Stefanski
- Division of Basic Reproductive Sciences, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- Graduate Program in Reproductive Sciences, University of Colorado School of Medicine, Aurora, Colorado, United States of America
| | - James L. McManaman
- Division of Basic Reproductive Sciences, Department of Obstetrics and Gynecology, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- Graduate Program in Reproductive Sciences, University of Colorado School of Medicine, Aurora, Colorado, United States of America
- * E-mail:
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99
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Mazumder N, Lyn RK, Singaravelu R, Ridsdale A, Moffatt DJ, Hu CW, Tsai HR, McLauchlan J, Stolow A, Kao FJ, Pezacki JP. Fluorescence lifetime imaging of alterations to cellular metabolism by domain 2 of the hepatitis C virus core protein. PLoS One 2013; 8:e66738. [PMID: 23826122 PMCID: PMC3691201 DOI: 10.1371/journal.pone.0066738] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2013] [Accepted: 05/09/2013] [Indexed: 12/15/2022] Open
Abstract
Hepatitis C virus (HCV) co-opts hepatic lipid pathways to facilitate its pathogenesis. The virus alters cellular lipid biosynthesis and trafficking, and causes an accumulation of lipid droplets (LDs) that gives rise to hepatic steatosis. Little is known about how these changes are controlled at the molecular level, and how they are related to the underlying metabolic states of the infected cell. The HCV core protein has previously been shown to independently induce alterations in hepatic lipid homeostasis. Herein, we demonstrate, using coherent anti-Stokes Raman scattering (CARS) microscopy, that expression of domain 2 of the HCV core protein (D2) fused to GFP is sufficient to induce an accumulation of larger lipid droplets (LDs) in the perinuclear region. Additionally, we performed fluorescence lifetime imaging of endogenous reduced nicotinamide adenine dinucleotides [NAD(P)H], a key coenzyme in cellular metabolic processes, to monitor changes in the cofactor’s abundance and conformational state in D2-GFP transfected cells. When expressed in Huh-7 human hepatoma cells, we observed that the D2-GFP induced accumulation of LDs correlated with an increase in total NAD(P)H fluorescence and an increase in the ratio of free to bound NAD(P)H. This is consistent with an approximate 10 fold increase in cellular NAD(P)H levels. Furthermore, the lifetimes of bound and free NAD(P)H were both significantly reduced – indicating viral protein-induced alterations in the cofactors’ binding and microenvironment. Interestingly, the D2-expressing cells showed a more diffuse localization of NAD(P)H fluorescence signal, consistent with an accumulation of the co-factor outside the mitochondria. These observations suggest that HCV causes a shift of metabolic control away from the use of the coenzyme in mitochondrial electron transport and towards glycolysis, lipid biosynthesis, and building of new biomass. Overall, our findings demonstrate that HCV induced alterations in hepatic metabolism is tightly linked to alterations in NAD(P)H functional states.
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Affiliation(s)
- Nirmal Mazumder
- Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan
| | - Rodney K. Lyn
- National Research Council of Canada, Ottawa, Ontario, Canada
- Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada
| | - Ragunath Singaravelu
- National Research Council of Canada, Ottawa, Ontario, Canada
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
| | - Andrew Ridsdale
- National Research Council of Canada, Ottawa, Ontario, Canada
| | | | - Chih-Wei Hu
- Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan
| | - Han-Ruei Tsai
- Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan
| | - John McLauchlan
- Medical Research Council - University of Glasgow Center for Virus Research, Glasgow, United Kingdom
| | - Albert Stolow
- National Research Council of Canada, Ottawa, Ontario, Canada
- Department of Physics, Queen’s University, Kingston, Ontario, Canada
| | - Fu-Jen Kao
- Institute of Biophotonics, National Yang-Ming University, Taipei, Taiwan
- * E-mail: (JPP); (FK)
| | - John Paul Pezacki
- National Research Council of Canada, Ottawa, Ontario, Canada
- Department of Chemistry, University of Ottawa, Ottawa, Ontario, Canada
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ottawa, Ontario, Canada
- * E-mail: (JPP); (FK)
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100
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Hepatitis C virus, cholesterol and lipoproteins--impact for the viral life cycle and pathogenesis of liver disease. Viruses 2013; 5:1292-324. [PMID: 23698400 PMCID: PMC3712309 DOI: 10.3390/v5051292] [Citation(s) in RCA: 106] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Revised: 04/10/2013] [Accepted: 04/27/2013] [Indexed: 02/07/2023] Open
Abstract
Hepatitis C virus (HCV) is a leading cause of chronic liver disease, including chronic hepatitis, fibrosis, cirrhosis, and hepatocellular carcinoma. Hepatitis C infection associates with lipid and lipoprotein metabolism disorders such as hepatic steatosis, hypobetalipoproteinemia, and hypocholesterolemia. Furthermore, virus production is dependent on hepatic very-low-density lipoprotein (VLDL) assembly, and circulating virions are physically associated with lipoproteins in complexes termed lipoviral particles. Evidence has indicated several functional roles for the formation of these complexes, including co-opting of lipoprotein receptors for attachment and entry, concealing epitopes to facilitate immune escape, and hijacking host factors for HCV maturation and secretion. Here, we review the evidence surrounding pathogenesis of the hepatitis C infection regarding lipoprotein engagement, cholesterol and triglyceride regulation, and the molecular mechanisms underlying these effects.
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