The Erns Carboxyterminus: Much More Than a Membrane Anchor

Pestiviruses express the unique essential envelope protein Erns, which exhibits RNase activity, is attached to membranes by a long amphipathic helix, and is partially secreted from infected cells. The RNase activity of Erns is directly connected with pestivirus virulence. Formation of homodimers and secretion of the protein are hypothesized to be important for its role as a virulence factor, which impairs the host’s innate immune response to pestivirus infection. The unusual membrane anchor of Erns raises questions with regard to proteolytic processing of the viral polyprotein at the Erns carboxy-terminus. Moreover, the membrane anchor is crucial for establishing the critical equilibrium between retention and secretion and ensures intracellular accumulation of the protein at the site of virus budding so that it is available to serve both as structural component of the virion and factor controlling host immune reactions. In the present manuscript, we summarize published as well as new data on the molecular features of Erns including aspects of its interplay with the other two envelope proteins with a special focus on the biochemistry of the Erns membrane anchor.

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Nonameric Peptide Orchestrates Signal Transduction in the Activating HLA-E/NKG2C/CD94 Immune Complex as Revealed by All-Atom Simulations

International Journal of Molecular Sciences ◽

10.3390/ijms22136670 ◽

2021 ◽

Vol 22 (13) ◽

pp. 6670

Author(s):

Eva Prašnikar ◽

Andrej Perdih ◽

Jure Borišek

Keyword(s):

Signal Transduction ◽

Cell Activation ◽

Nk Cell ◽

Innate Immune ◽

Target Cells ◽

Molecular Events ◽

Activating Receptors ◽

Molecular Machinery ◽

Infected Cells ◽

Bond Network

The innate immune system’s natural killer (NK) cells exert their cytolytic function against a variety of pathological challenges, including tumors and virally infected cells. Their activation depends on net signaling mediated via inhibitory and activating receptors that interact with specific ligands displayed on the surfaces of target cells. The CD94/NKG2C heterodimer is one of the NK activating receptors and performs its function by interacting with the trimeric ligand comprised of the HLA-E/β2m/nonameric peptide complex. Here, simulations of the all-atom multi-microsecond molecular dynamics in five immune complexes provide atomistic insights into the receptor–ligand molecular recognition, as well as the molecular events that facilitate the NK cell activation. We identify NKG2C, the HLA-Eα2 domain, and the nonameric peptide as the key elements involved in the molecular machinery of signal transduction via an intertwined hydrogen bond network. Overall, the study addresses the complex intricacies that are necessary to understand the mechanisms of the innate immune system.

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Natural Cytotoxicity Receptors: Pattern Recognition and Involvement of Carbohydrates

The Scientific World JOURNAL ◽

10.1100/tsw.2005.22 ◽

2005 ◽

Vol 5 ◽

pp. 151-154 ◽

Cited By ~ 10

Author(s):

Angel Porgador

Keyword(s):

Pattern Recognition ◽

Cell Membrane ◽

Cell Surface ◽

Innate Immune ◽

Target Cells ◽

Natural Cytotoxicity ◽

Tumor Cell Membrane ◽

Infected Cells ◽

Natural Cytotoxicity Receptors ◽

New Evidence

Natural cytotoxicity receptors (NCRs), expressed by natural killer (NK) cells, trigger NK lysis of tumor and virus-infected cells on interaction with cell-surface ligands of these target cells. We have determined that viral hemagglutinins expressed on the surface of virus-infected cells are involved in the recognition by the NCRs, NKp44 and NKp46. Recognition of tumor cells by the NCRs NKp30 and NKp46 involves heparan sulfate epitopes expressed on the tumor cell membrane. Our studies provide new evidence for the identity of the ligands for NCRs and indicate that a broader definition should be applied to pathological patterns recognized by innate immune receptors. Since nonmicrobial endogenous carbohydrate structures contribute significantly to this recognition, there is an imperative need to develop appropriate tools for the facile sequencing of carbohydrate moieties.

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Immunopharmacological Activity of Betulin in Inflammation-associated Carcinogenesis

Anti-Cancer Agents in Medicinal Chemistry ◽

10.2174/1871520617666171012124820 ◽

2018 ◽

Vol 18 (5) ◽

pp. 645-651 ◽

Cited By ~ 5

Author(s):

Anja Schwiebs ◽

Heinfried H. Radeke

Keyword(s):

Immune Cell ◽

Inflammatory Diseases ◽

Innate Immune ◽

Interleukin 12 ◽

Dual Function ◽

Special Focus ◽

Birch Bark ◽

Pentacyclic Triterpene ◽

Cancer And Inflammation ◽

Potential Use

This review highlights the multiple properties of the birch bark-derived pentacyclic triterpene betulin with special focus on its pharmacological activity in cancer and inflammation. While less well characterized compared to its hydrophilic derivative, betulinic acid, it exhibits potent anticancer activity described in many publications. Indeed, underinvestigated are its immunomodulatory functions in inflammatory diseases that appeared to enhance innate immune cell activities in an adjuvant-like fashion towards an interleukin-12 driven antitumor immunity. Herein, we like to emphasize the simultaneous and dual function of betulin on the basis of recent investigations of the tumor microenvironment and enlighten the potential use of betulin in the control of inflammation-associated carcinogenesis.

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New perspectives on IL-33 and IL-1 family cytokines as innate environmental sensors

Biochemical Society Transactions ◽

10.1042/bst20170567 ◽

2018 ◽

Vol 46 (5) ◽

pp. 1345-1353 ◽

Cited By ~ 3

Author(s):

Ian C. Scott ◽

D. Gareth Rees ◽

E. Suzanne Cohen

Keyword(s):

Immune Responses ◽

Allergic Inflammation ◽

Proteolytic Processing ◽

Innate Immune ◽

Environmental Sensors ◽

Biological Functions ◽

Soluble Receptors ◽

Direct Sensing ◽

Proteolytic Activities

Interleukin (IL)-1 family cytokines are important initiators of innate immunity and host defence; however, their uncontrolled activities can cause tissue-damaging inflammation. Consequently, IL-1 family cytokines have sophisticated regulatory mechanisms to control their activities including proteolytic processing for their activation and the deployment of soluble receptors and receptor antagonists to limit their activities. IL-33 is a promoter of type 2 immunity and allergic inflammation through its alarmin activity that can rapidly initiate local immune responses by stimulating innate immune cells following exposure to environmental insults, pathogens, or sterile injury. Recent publications have provided new insights into how the range and duration of IL-33 activity is regulated by direct sensing of host-derived and exogenous proteolytic activities as well as oxidative changes during tissue damage. Here, we discuss how this impacts our understanding of the roles of IL-33 in initiating immune responses and the evidence that these sensing mechanisms might regulate the activities of other IL-1 family cytokines and their biological functions. Finally, we discuss translational challenges these discoveries pose for the accurate detection of different forms of these cytokines.

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Adaptive and Innate Immune Cells in Fetal Human Cytomegalovirus-Infected Brains

Microorganisms ◽

10.3390/microorganisms8020176 ◽

2020 ◽

Vol 8 (2) ◽

pp. 176 ◽

Cited By ~ 1

Author(s):

Yann Sellier ◽

Florence Marliot ◽

Bettina Bessières ◽

Julien Stirnemann ◽

Ferechte Encha-Razavi ◽

...

Keyword(s):

T Cells ◽

Nk Cells ◽

Immune Cells ◽

Plasma Cells ◽

Ex Vivo ◽

Fetal Brain ◽

Brain Lesions ◽

Innate Immune ◽

Innate Immune Cells ◽

Infected Cells

Background: The understanding of the pathogenesis of cytomegalovirus (CMV)-induced fetal brain lesions is limited. We aimed to quantify adaptive and innate immune cells and CMV-infected cells in fetal brains with various degrees of brain damage. Methods: In total, 26 archived embedded fetal brains were studied, of which 21 were CMV-infected and classified in severely affected (n = 13) and moderately affected (n = 8), and 5 were uninfected controls. The respective magnitude of infected cells, immune cells (CD8+, B cells, plasma cells, NK cells, and macrophages), and expression of immune checkpoint receptors (PD-1/PD-L1 and LAG-3) were measured by immunochemistry and quantified by quantitative imaging analysis. Results: Quantities of CD8+, plasma cells, NK cells, macrophages, and HCMV+ cells and expression of PD-1/PD-L1 and LAG-3 were significantly higher in severely affected than in moderately affected brains (all p values < 0.05). A strong link between higher number of stained cells for HCMV/CD8 and PD-1 and severity of brain lesions was found by component analysis. Conclusions: The higher expression of CD8, PD-1, and LAG-3 in severely affected brains could reflect immune exhaustion of cerebral T cells. These exhausted T cells could be ineffective in controlling viral multiplication itself, leading to more severe brain lesions. The study of the functionality of brain leucocytes ex vivo is needed to confirm this hypothesis.

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Virus-Mediated Cell-Cell Fusion

International Journal of Molecular Sciences ◽

10.3390/ijms21249644 ◽

2020 ◽

Vol 21 (24) ◽

pp. 9644

Author(s):

Héloïse Leroy ◽

Mingyu Han ◽

Marie Woottum ◽

Lucie Bracq ◽

Jérôme Bouchet ◽

...

Keyword(s):

Cell Fusion ◽

Fusion Proteins ◽

Target Cells ◽

Special Focus ◽

Human Pathogens ◽

General Process ◽

Tissue Organization ◽

Donor Cells ◽

Infected Cells ◽

Cell Cell

Cell-cell fusion between eukaryotic cells is a general process involved in many physiological and pathological conditions, including infections by bacteria, parasites, and viruses. As obligate intracellular pathogens, viruses use intracellular machineries and pathways for efficient replication in their host target cells. Interestingly, certain viruses, and, more especially, enveloped viruses belonging to different viral families and including human pathogens, can mediate cell-cell fusion between infected cells and neighboring non-infected cells. Depending of the cellular environment and tissue organization, this virus-mediated cell-cell fusion leads to the merge of membrane and cytoplasm contents and formation of multinucleated cells, also called syncytia, that can express high amount of viral antigens in tissues and organs of infected hosts. This ability of some viruses to trigger cell-cell fusion between infected cells as virus-donor cells and surrounding non-infected target cells is mainly related to virus-encoded fusion proteins, known as viral fusogens displaying high fusogenic properties, and expressed at the cell surface of the virus-donor cells. Virus-induced cell-cell fusion is then mediated by interactions of these viral fusion proteins with surface molecules or receptors involved in virus entry and expressed on neighboring non-infected cells. Thus, the goal of this review is to give an overview of the different animal virus families, with a more special focus on human pathogens, that can trigger cell-cell fusion.

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System-Based Approaches to Delineate the Antiviral Innate Immune Landscape

Viruses ◽

10.3390/v12101196 ◽

2020 ◽

Vol 12 (10) ◽

pp. 1196

Author(s):

Karsten Krey ◽

Aleksandra W. Babnis ◽

Andreas Pichlmair

Keyword(s):

Large Scale ◽

Innate Immune ◽

Host Interactions ◽

Interferon Stimulated Genes ◽

Cellular Processes ◽

Virus Inhibition ◽

Cellular Factors ◽

Functional Factors ◽

Infected Cells ◽

Screening Approaches

Viruses pose substantial challenges for society, economy, healthcare systems, and research. Their distinctive pathologies are based on specific interactions with cellular factors. In order to develop new antiviral treatments, it is of central importance to understand how viruses interact with their host and how infected cells react to the virus on a molecular level. Invading viruses are commonly sensed by components of the innate immune system, which is composed of a highly effective yet complex network of proteins that, in most cases, mediate efficient virus inhibition. Central to this process is the activity of interferons and other cytokines that coordinate the antiviral response. So far, numerous methods have been used to identify how viruses interact with cellular processes and revealed that the innate immune response is highly complex and involves interferon-stimulated genes and their binding partners as functional factors. Novel approaches and careful experimental design, combined with large-scale, high-throughput methods and cutting-edge analysis pipelines, have to be utilized to delineate the antiviral innate immune landscape at a global level. In this review, we describe different currently used screening approaches, how they contributed to our knowledge on virus–host interactions, and essential considerations that have to be taken into account when planning such experiments.

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Mutations in a Highly Conserved Motif of nsp1β Protein Attenuate the Innate Immune Suppression Function of Porcine Reproductive and Respiratory Syndrome Virus

Journal of Virology ◽

10.1128/jvi.03069-15 ◽

2016 ◽

Vol 90 (7) ◽

pp. 3584-3599 ◽

Cited By ~ 23

Author(s):

Yanhua Li ◽

Duan-Liang Shyu ◽

Pengcheng Shang ◽

Jianfa Bai ◽

Kang Ouyang ◽

...

Keyword(s):

Immune Response ◽

Immune Responses ◽

Innate Immune ◽

Respiratory Syndrome Virus ◽

Adaptive Immune Responses ◽

Virus Growth ◽

Conserved Motif ◽

Adaptive Immune ◽

Infected Cells ◽

Growth Ability

ABSTRACTPorcine reproductive and respiratory syndrome virus (PRRSV) nonstructural protein 1β (nsp1β) is a multifunctional viral protein, which is involved in suppressing the host innate immune response and activating a unique −2/−1 programmed ribosomal frameshifting (PRF) signal for the expression of frameshifting products. In this study, site-directed mutagenesis analysis showed that the R128A or R129A mutation introduced into a highly conserved motif (123GKYLQRRLQ131) reduced the ability of nsp1β to suppress interferon beta (IFN-β) activation and also impaired nsp1β's function as a PRF transactivator. Three recombinant viruses, vR128A, vR129A, and vRR129AA, carrying single or double mutations in the GKYLQRRLQ motif were characterized. In comparison to the wild-type (WT) virus, vR128A and vR129A showed slightly reduced growth abilities, while the vRR129AA mutant had a significantly reduced growth ability in infected cells. Consistent with the attenuated growth phenotypein vitro, pigs infected with nsp1β mutants had lower levels of viremia than did WT virus-infected pigs. Compared to the WT virus in infected cells, all three mutated viruses stimulated high levels of IFN-α expression and exhibited a reduced ability to suppress the mRNA expression of selected interferon-stimulated genes (ISGs). In pigs infected with nsp1β mutants, IFN-α production was increased in the lungs at early time points postinfection, which was correlated with increased innate NK cell function. Furthermore, the augmented innate response was consistent with the increased production of IFN-γ in pigs infected with mutated viruses. These data demonstrate that residues R128 and R129 are critical for nsp1β function and that modifying these key residues in the GKYLQRRLQ motif attenuates virus growth ability and improves the innate and adaptive immune responses in infected animals.IMPORTANCEPRRSV infection induces poor antiviral innate IFN and cytokine responses, which results in weak adaptive immunity. One of the strategies in next-generation vaccine construction is to manipulate viral proteins/genetic elements involved in antagonizing the host immune response. PRRSV nsp1β was identified to be a strong innate immune antagonist. In this study, two basic amino acids, R128 and R129, in a highly conserved GKYLQRRLQ motif were determined to be critical for nsp1β function. Mutations introduced into these two residues attenuated virus growth and improved the innate and adaptive immune responses of infected animals. Technologies developed in this study could be broadly applied to current commercial PRRSV modified live-virus (MLV) vaccines and other candidate vaccines.

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Viable Polioviruses That Encode 2A Proteins with Fluorescent Protein Tags

Journal of Virology ◽

10.1128/jvi.01578-09 ◽

2009 ◽

Vol 84 (3) ◽

pp. 1477-1488 ◽

Cited By ~ 29

Author(s):

Natalya L. Teterina ◽

Eric A. Levenson ◽

Ellie Ehrenfeld

Keyword(s):

Fusion Protein ◽

Fluorescent Protein ◽

Viral Rna ◽

Progeny Virus ◽

C Terminus ◽

Membrane Reorganization ◽

Infected Cells ◽

Viral Polyprotein ◽

Fluorescent Protein Tags

ABSTRACT The 2A proteins of the Picornaviridae enterovirus genus are small cysteine proteinases that catalyze essential cleavages in the viral polyprotein in cis and in several cellular proteins in trans. In addition, 2A has been implicated in the process of viral RNA replication, independent of its protease functions. We have generated viable polioviruses that encode 2A proteins containing fluorescent protein tag insertions at either of two sites in the 2A protein structure. Viruses containing an insertion of Discosoma sp. red fluorescent protein (DsRed) after residue 144 of 2A, near the C terminus, produced plaques only slightly smaller than wild-type (wt) virus. The polyprotein harboring the 2A-DsRed fusion protein was efficiently and accurately cleaved; fluorescent 2A proteinase retained protease activity in trans and supported translation and replication of viral RNA, both in vitro and in infected cells. Intracellular membrane reorganization to support viral RNA synthesis was indistinguishable from that induced by wt virus. Infected cells exhibited strong red fluorescence from expression of the 2A-DsRed fusion protein, and the progeny virus was stable for three to four passages, after which deletions within the DsRed coding sequence began to accumulate. Confocal microscopic imaging and analysis revealed a portion of 2A-DsRed in punctate foci concentrated in the perinuclear region that colocalized with replication protein 2C. The majority of 2A, however, was associated with an extensive structural matrix throughout the cytoplasm and was not released from infected cells permeabilized with digitonin.

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Old World hantaviruses do not produce detectable amounts of dsRNA in infected cells and the 5′ termini of their genomic RNAs are monophosphorylated

Journal of General Virology ◽

10.1099/vir.0.029405-0 ◽

2011 ◽

Vol 92 (5) ◽

pp. 1199-1204 ◽

Cited By ~ 21

Author(s):

Hao Wang ◽

Antti Vaheri ◽

Friedemann Weber ◽

Alexander Plyusnin

Keyword(s):

Rna Virus ◽

Innate Immune ◽

Hantaan Virus ◽

Signalling Pathways ◽

Genomic Rna ◽

Genomic Rnas ◽

Old World ◽

Interferon Induction ◽

Infected Cells ◽

Negative Sense

dsRNA and 5′-triphosphate RNA are considered critical activators of the innate immune response because of their interaction with pattern recognition receptors. It has been reported that no dsRNA is detected in negative-sense RNA virus-infected cells and that Hantaan virus (HTNV) genomic RNA bears a 5′ monophosphate group. In this paper we examine the 5′ termini of genomic RNAs of and dsRNA production by two major groups of Old World hantaviruses. No detectable amounts of dsRNA were found in infected cells. Also, the genomic RNAs of these hantaviruses bear a 5′ monophosphate group and therefore are unable to trigger interferon induction. Taken together with the earlier data on HTNV, these results suggest that in addition to the dsRNA and genomic RNA, which may be only minimally involved in the induction of innate immunity, other cellular signalling pathways may also be involved and that these await further investigation.

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