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Halcrow PW, Quansah DN, Kumar N, Steiner JP, Nath A, Geiger JD. HERV-K (HML-2) Envelope Protein Induces Mitochondrial Depolarization and Neurotoxicity via Endolysosome Iron Dyshomeostasis. J Neurosci 2024; 44:e0826232024. [PMID: 38383499 PMCID: PMC10993035 DOI: 10.1523/jneurosci.0826-23.2024] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2023] [Revised: 01/08/2024] [Accepted: 02/10/2024] [Indexed: 02/23/2024] Open
Abstract
Human endogenous retroviruses (HERVs) are associated with the pathogenesis of amyotrophic lateral sclerosis (ALS); a disease characterized by motor neuron degeneration and cell death. The HERV-K subtype HML-2 envelope protein (HERV-K Env) is expressed in the brain, spinal cord, and cerebrospinal fluid of people living with ALS and through CD98 receptor-linked interactions causes neurodegeneration. HERV-K Env-induced increases in oxidative stress are implicated in the pathogenesis of ALS, and ferrous iron (Fe2+) generates reactive oxygen species (ROS). Endolysosome stores of Fe2+ are central to iron trafficking and endolysosome deacidification releases Fe2+ into the cytoplasm. Because HERV-K Env is an arginine-rich protein that is likely endocytosed and arginine is a pH-elevating amino acid, it is important to determine HERV-K Env effects on endolysosome pH and whether HERV-K Env-induced neurotoxicity is downstream of Fe2+ released from endolysosomes. Here, we showed using SH-SY5Y human neuroblastoma cells and primary cultures of human cortical neurons (HCNs, information on age and sex was not available) that HERV-K Env (1) is endocytosed via CD98 receptors, (2) concentration dependently deacidified endolysosomes, (3) decreased endolysosome Fe2+ concentrations, (4) increased cytosolic and mitochondrial Fe2+ and ROS levels, (5) depolarized mitochondrial membrane potential, and (6) induced cell death, effects blocked by an antibody against the CD98 receptor and by the endolysosome iron chelator deferoxamine. Thus, HERV-K Env-induced increases in cytosolic and mitochondrial Fe2+ and ROS as well as cell death appear to be mechanistically caused by HERV-K Env endocytosis, endolysosome deacidification, and endolysosome Fe2+ efflux into the cytoplasm.
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Affiliation(s)
- Peter W. Halcrow
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202
| | - Darius N.K. Quansah
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202
| | - Nirmal Kumar
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202
| | - Joseph P. Steiner
- Section for Infections of the Nervous System, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Avindra Nath
- Section for Infections of the Nervous System, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, Maryland 20892
| | - Jonathan D. Geiger
- Department of Biomedical Sciences, University of North Dakota School of Medicine and Health Sciences, Grand Forks, North Dakota 58202
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Liu S, Heumüller SE, Hossinger A, Müller SA, Buravlova O, Lichtenthaler SF, Denner P, Vorberg IM. Reactivated endogenous retroviruses promote protein aggregate spreading. Nat Commun 2023; 14:5034. [PMID: 37596282 PMCID: PMC10439213 DOI: 10.1038/s41467-023-40632-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2022] [Accepted: 08/02/2023] [Indexed: 08/20/2023] Open
Abstract
Prion-like spreading of protein misfolding is a characteristic of neurodegenerative diseases, but the exact mechanisms of intercellular protein aggregate dissemination remain unresolved. Evidence accumulates that endogenous retroviruses, remnants of viral germline infections that are normally epigenetically silenced, become upregulated in neurodegenerative diseases such as amyotrophic lateral sclerosis and tauopathies. Here we uncover that activation of endogenous retroviruses affects prion-like spreading of proteopathic seeds. We show that upregulation of endogenous retroviruses drastically increases the dissemination of protein aggregates between cells in culture, a process that can be inhibited by targeting the viral envelope protein or viral protein processing. Human endogenous retrovirus envelopes of four different clades also elevate intercellular spreading of proteopathic seeds, including pathological Tau. Our data support a role of endogenous retroviruses in protein misfolding diseases and suggest that antiviral drugs could represent promising candidates for inhibiting protein aggregate spreading.
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Affiliation(s)
- Shu Liu
- German Center for Neurodegenerative Diseases Bonn (DZNE), Venusberg Campus 1/ 99, 53127, Bonn, Germany
- German Federal Institute for Risk Assessment (BfR), German Centre for the Protection of Laboratory Animals (Bf3R), Max-Dohrn-Straße 8-10, 10589, Berlin, Germany
| | | | - André Hossinger
- German Center for Neurodegenerative Diseases Bonn (DZNE), Venusberg Campus 1/ 99, 53127, Bonn, Germany
| | - Stephan A Müller
- German Center for Neurodegenerative Diseases (DZNE), Munich, Germany
| | - Oleksandra Buravlova
- German Center for Neurodegenerative Diseases Bonn (DZNE), Venusberg Campus 1/ 99, 53127, Bonn, Germany
| | - Stefan F Lichtenthaler
- German Center for Neurodegenerative Diseases (DZNE), Munich, Germany
- Neuroproteomics, School of Medicine, Klinikum rechts der Isar, Technical University of Munich, 81675, Munich, Germany
- Munich Cluster for Systems Neurology (SyNergy), Munich, Germany
| | - Philip Denner
- German Center for Neurodegenerative Diseases Bonn (DZNE), Venusberg Campus 1/ 99, 53127, Bonn, Germany
| | - Ina M Vorberg
- German Center for Neurodegenerative Diseases Bonn (DZNE), Venusberg Campus 1/ 99, 53127, Bonn, Germany.
- Department of Neurology, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany, Venusberg-Campus 1, 53127, Bonn, Germany.
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A Comprehensive Analysis of Human Endogenous Retroviruses HERV-K (HML.2) from Teratocarcinoma Cell Lines and Detection of Viral Cargo in Microvesicles. Int J Mol Sci 2021; 22:ijms222212398. [PMID: 34830279 PMCID: PMC8619701 DOI: 10.3390/ijms222212398] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Revised: 11/14/2021] [Accepted: 11/15/2021] [Indexed: 12/12/2022] Open
Abstract
About 8% of our genome is composed of sequences from Human Endogenous Retroviruses (HERVs). The HERV-K (HML.2) family, here abbreviated HML.2, is able to produce virus particles that were detected in cell lines, malignant tumors and in autoimmune diseases. Parameters and properties of HML.2 released from teratocarcinoma cell lines GH and Tera-1 were investigated in detail. In most experiments, analyzed viruses were purified by density gradient centrifugation. HML.2 structural proteins, reverse transcriptase (RT) activity, viral RNA (vRNA) and particle morphology were analyzed. The HML.2 markers were predominantly detected in fractions with a buoyant density of 1.16 g/cm3. Deglycosylation of TM revealed truncated forms of transmembrane (TM) protein. Free virions and extracellular vesicles (presumably microvesicles—MVs) with HML.2 elements, including budding intermediates, were detected by electron microscopy. Viral elements and assembled virions captured and exported by MVs can boost specific immune responses and trigger immunomodulation in recipient cells. Sequencing of cDNA clones demonstrated exclusive presence of HERV-K108 env in HML.2 from Tera-1 cells. Not counting two recombinant variants, four known env sequences were found in HML.2 from GH cells. Obtained results shed light on parameters and morphology of HML.2. A possible mechanism of HML.2-induced diseases is discussed.
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Garcia-Montojo M, Doucet-O'Hare T, Henderson L, Nath A. Human endogenous retrovirus-K (HML-2): a comprehensive review. Crit Rev Microbiol 2018; 44:715-738. [PMID: 30318978 DOI: 10.1080/1040841x.2018.1501345] [Citation(s) in RCA: 110] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The human genome contains a large number of retroviral elements acquired over the process of evolution, some of which are specific to primates. However, as many of these are defective or silenced through epigenetic changes, they were historically considered "junk DNA" and their potential role in human physiology or pathological circumstances have been poorly studied. The most recently acquired, human endogenous retrovirus-K (HERV-K), has multiple copies in the human genome and some of them have complete open reading frames that are transcribed and translated, especially in early embryogenesis. Phylogenetically, HERV-K is considered a supergroup of viruses. One of the subtypes, termed HML-2, seems to be the most active and hence, it is the best studied. Aberrant expression of HML-2 in adult tissues has been associated with certain types of cancer and with neurodegenerative diseases. This review discusses the discovery of these viruses, their classification, structure, regulation and potential for replication, physiological roles, and their involvement in disease pathogenesis. Finally, it presents different therapeutic approaches being considered to target these viruses.
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Affiliation(s)
- Marta Garcia-Montojo
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
| | - Tara Doucet-O'Hare
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
| | - Lisa Henderson
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
| | - Avindra Nath
- a Section of Infections of the Nervous System , National Institute of Neurological Disorders and Stroke, National Institutes of Health , Bethesda , MD , USA
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Robinson-McCarthy LR, McCarthy KR, Raaben M, Piccinotti S, Nieuwenhuis J, Stubbs SH, Bakkers MJG, Whelan SPJ. Reconstruction of the cell entry pathway of an extinct virus. PLoS Pathog 2018; 14:e1007123. [PMID: 30080900 PMCID: PMC6095630 DOI: 10.1371/journal.ppat.1007123] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 08/16/2018] [Accepted: 07/16/2018] [Indexed: 12/16/2022] Open
Abstract
Endogenous retroviruses (ERVs), remnants of ancient germline infections, comprise 8% of the human genome. The most recently integrated includes human ERV-K (HERV-K) where several envelope (env) sequences remain intact. Viral pseudotypes decorated with one of those Envs are infectious. Using a recombinant vesicular stomatitis virus encoding HERV-K Env as its sole attachment and fusion protein (VSV-HERVK) we conducted a genome-wide haploid genetic screen to interrogate the host requirements for infection. This screen identified 11 genes involved in heparan sulfate biosynthesis. Genetic inhibition or chemical removal of heparan sulfate and addition of excess soluble heparan sulfate inhibit infection. Direct binding of heparin to soluble HERV-K Env and purified VSV-HERVK defines it as critical for viral attachment. Cell surface bound VSV-HERVK particles are triggered to infect on exposure to acidic pH, whereas acid pH pretreatment of virions blocks infection. Testing of additional endogenous HERV-K env sequences reveals they bind heparin and mediate acid pH triggered fusion. This work reconstructs and defines key steps in the infectious entry pathway of an extinct virus.
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Affiliation(s)
- Lindsey R. Robinson-McCarthy
- Program in Virology, Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Kevin R. McCarthy
- Laboratory of Molecular Medicine, Children’s Hospital, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Matthijs Raaben
- Division of Biochemistry, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Silvia Piccinotti
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Joppe Nieuwenhuis
- Division of Biochemistry, Netherlands Cancer Institute, Amsterdam, The Netherlands
| | - Sarah H. Stubbs
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Mark J. G. Bakkers
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Sean P. J. Whelan
- Program in Virology, Harvard Medical School, Boston, Massachusetts, United States of America
- Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts, United States of America
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Grant R, Keele B, Kuller L, Watanabe R, Perret A, Smedley J. Identification of novel simian endogenous retroviruses that are indistinguishable from simian retrovirus (SRV) on current SRV diagnostic assays. J Med Primatol 2018; 46:158-161. [PMID: 28748668 DOI: 10.1111/jmp.12297] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/26/2017] [Indexed: 01/05/2023]
Abstract
Simian betaretroviruses include the well-known exogenous simian retroviruses (SRV-1 through SRV-8), and some closely related simian endogenous retroviruses (SERV). Here, we characterized two new viral genomes, which appear to represent novel SERVs but have characteristics of both SRV and SERV highlighting the need to develop new assays providing molecular and serologic differentiation of SERV and SRV to avoid false positives.
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Affiliation(s)
- Richard Grant
- Washington National Primate Research Center, University of Washington, Seattle, WA, USA
| | - Brandon Keele
- AIDS and Cancer Virus Program, Leidos Biomedical Research Inc., Frederick National Laboratory for Cancer Research, Frederick, MD, USA
| | - LaRene Kuller
- Washington National Primate Research Center, University of Washington, Seattle, WA, USA
| | - Robin Watanabe
- Washington National Primate Research Center, University of Washington, Seattle, WA, USA
| | - Alex Perret
- Washington National Primate Research Center, University of Washington, Seattle, WA, USA
| | - Jeremy Smedley
- Washington National Primate Research Center, University of Washington, Seattle, WA, USA
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Kassiotis G, Stoye JP. Making a virtue of necessity: the pleiotropic role of human endogenous retroviruses in cancer. Philos Trans R Soc Lond B Biol Sci 2018; 372:rstb.2016.0277. [PMID: 28893944 PMCID: PMC5597744 DOI: 10.1098/rstb.2016.0277] [Citation(s) in RCA: 51] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/09/2017] [Indexed: 12/18/2022] Open
Abstract
Like all other mammals, humans harbour an astonishing number of endogenous retroviruses (ERVs), as well as other retroelements, embedded in their genome. These remnants of ancestral germline infection with distinct exogenous retroviruses display various degrees of open reading frame integrity and replication capability. Modern day exogenous retroviruses, as well as the infectious predecessors of ERVs, are demonstrably oncogenic. Further, replication-competent ERVs continue to cause cancers in many other species of mammal. Moreover, human cancers are characterized by transcriptional activation of human endogenous retroviruses (HERVs). These observations conspire to incriminate HERVs as causative agents of human cancer. However, exhaustive investigation of cancer genomes suggests that HERVs have entirely lost the ability for re-infection and thus the potential for insertional mutagenic activity. Although there may be non-insertional mechanisms by which HERVs contribute to cancer development, recent evidence also uncovers potent anti-tumour activities exerted by HERV replication intermediates or protein products. On balance, it appears that HERVs, despite their oncogenic past, now represent potential targets for immune-mediated anti-tumour mechanisms. This article is part of the themed issue ‘Human oncogenic viruses’.
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Affiliation(s)
- George Kassiotis
- Retroviral Immunology, The Francis Crick Institute, London, UK .,Department of Medicine, Faculty of Medicine, Imperial College London, London, UK
| | - Jonathan P Stoye
- Retrovirus-Host Interactions, The Francis Crick Institute, London, UK .,Department of Medicine, Faculty of Medicine, Imperial College London, London, UK
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Hohn O, Mostafa S, Norley S, Bannert N. Development of an antigen-capture ELISA for the detection of the p27-CA protein of HERV-K(HML-2). J Virol Methods 2016; 234:186-92. [PMID: 27142113 DOI: 10.1016/j.jviromet.2016.04.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Revised: 04/26/2016] [Accepted: 04/27/2016] [Indexed: 10/21/2022]
Abstract
The detection or quantification of retroviruses is often achieved using an antigen-capture ELISA (AC-ELISA) that targets the Gag capsid (CA) protein. We report here the development of an AC-ELISA specific for the p27-CA protein of HERV-K(HML-2). A monoclonal p27-specific antibody is used for capture and a polyclonal anti-p27-CA immune serum generated in rabbits serves for detection. The assay was shown to be specific for HERV-K(HML-2), showing no evidence of cross reactivity with the human retroviruses HIV-1, HIV-2 and HTLV-1 or with XMRV (as a model non-human gammaretrovirus). Using purified recombinant antigen, the limit of detection was shown to be 130pg/ml. The AC-ELISA can be used to quantify HERV-K(HML-2) expression in teratocarcinoma cell lines and to normalize HERV particles generated by transfecting HEK 293T cells with full-length molecular clones. This novel AC-ELISA also proved useful in studies of virus regulation, for example in demonstrating that HERV-K(HML-2) expression is dramatically enhanced by overexpression of Staufen-1, a binding partner of the HERV-K(HML-2) Rec protein. This specific and sensitive HERV-K(HML-2) AC-ELISA will be a useful tool for investigating many aspects of endogenous retroviruses, from basic research to the role they may play in human diseases or as a surrogate marker for particular diseases.
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Affiliation(s)
- Oliver Hohn
- Robert Koch Institute, Division for HIV and Other Retroviruses, Nordufer 20, 13353 Berlin, Germany
| | - Saeed Mostafa
- Robert Koch Institute, Division for HIV and Other Retroviruses, Nordufer 20, 13353 Berlin, Germany
| | - Stephen Norley
- Robert Koch Institute, Division for HIV and Other Retroviruses, Nordufer 20, 13353 Berlin, Germany
| | - Norbert Bannert
- Robert Koch Institute, Division for HIV and Other Retroviruses, Nordufer 20, 13353 Berlin, Germany.
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Infectious Entry Pathway Mediated by the Human Endogenous Retrovirus K Envelope Protein. J Virol 2016; 90:3640-9. [PMID: 26792739 DOI: 10.1128/jvi.03136-15] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2015] [Accepted: 01/12/2016] [Indexed: 12/22/2022] Open
Abstract
UNLABELLED Endogenous retroviruses (ERVs), the majority of which exist as degraded remnants of ancient viruses, comprise approximately 8% of the human genome. The youngest human ERVs (HERVs) belong to the HERV-K(HML-2) subgroup and were endogenized within the past 1 million years. The viral envelope protein (ENV) facilitates the earliest events of endogenization (cellular attachment and entry), and here, we characterize the requirements for HERV-K ENV to mediate infectious cell entry. Cell-cell fusion assays indicate that a minimum of two events are required for fusion, proteolytic processing by furin-like proteases and exposure to acidic pH. We generated an infectious autonomously replicating recombinant vesicular stomatitis virus (VSV) in which the glycoprotein was replaced by HERV-K ENV. HERV-K ENV imparts an endocytic entry pathway that requires dynamin-mediated membrane scission and endosomal acidification but is distinct from clathrin-dependent or macropinocytic uptake pathways. The lack of impediments to the replication of the VSV core in eukaryotic cells allowed us to broadly survey the HERV-K ENV-dictated tropism. Unlike extant betaretroviral envelopes, which impart a narrow species tropism, we found that HERV-K ENV mediates broad tropism encompassing cells from multiple mammalian and nonmammalian species. We conclude that HERV-K ENV dictates an evolutionarily conserved entry pathway and that the restriction of HERV-K to primate genomes reflects downstream stages of the viral replication cycle. IMPORTANCE Approximately 8% of the human genome is of retroviral origin. While many of those viral genomes have become inactivated, some copies of the most recently endogenized human retrovirus, HERV-K, can encode individual functional proteins. Here, we characterize the envelope protein (ENV) of the virus to define how it mediates infection of cells. We demonstrate that HERV-K ENV undergoes a proteolytic processing step and triggers membrane fusion in response to acidic pH--a strategy common to many viral fusogens. Our data suggest that the infectious entry pathway mediated by this ENV requires endosomal acidification and the GTPase dynamin but does not require clathrin-dependent uptake. In marked contrast to other betaretroviruses, HERV-K ENV imparts broad species tropism in cultured cells. This work provides new insights into the entry pathway of an extinct human virus and provides a powerful tool to further probe the endocytic route by which HERV-K infects cells.
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