BST-2/tetherin: a new component of the innate immune response to enveloped viruses

Explore the shared molecular mechanism between dermatomyositis and nasopharyngeal cancer by bioinformatic analysis

BACKGROUND

Dermatomyositis (DM) is prone to nasopharyngeal carcinoma (NPC), but the mechanism is unclear. This study aimed to explore the potential pathogenesis of DM and NPC.

METHODS

The datasets GSE46239, GSE142807, GSE12452, and GSE53819 were downloaded from the GEO dataset. The disease co-expression module was obtained by R-package WGCNA. We built PPI networks for the key modules. ClueGO was used to analyze functional enrichment for the key modules. DEG analysis was performed with the R-package "limma". R-package "pROC" was applied to assess the diagnostic performance of hub genes. MiRNA-mRNA networks were constructed using MiRTarBase and miRWalk databases.

RESULTS

The key modules that positively correlated with NPC and DM were found. Its intersecting genes were enriched in the negative regulation of viral gene replication pathway. Similarly, overlapping down-regulated DEGs in DM and NPC were also enriched in negatively regulated viral gene replication. Finally, we identified 10 hub genes that primarily regulate viral biological processes and type I interferon responses. Four key genes (GBP1, IFIH1, IFIT3, BST2) showed strong diagnostic performance, with AUC>0.8. In both DM and NPC, the expression of key genes was correlated with macrophage infiltration level. Based on hub genes' miRNA-mRNA network, hsa-miR-146a plays a vital role in DM-associated NPC.

CONCLUSIONS

Our research discovered pivot genes between DM and NPC. Viral gene replication and response to type I interferon may be the crucial bridge between DM and NPC. By regulating hub genes, MiR-146a will provide new strategies for diagnosis and treatment in DM complicated by NPC patients. For individuals with persistent viral replication in DM, screening for nasopharyngeal cancer is necessary.

A tale of endurance: bats, viruses and immune dynamics

The emergence of highly zoonotic viral infections has propelled bat research forward. The viral outbreaks including Hendra virus, Nipah virus, Marburg virus, Ebola virus, Rabies virus, Middle East respiratory syndrome coronavirus, SARS-CoV and the latest SARS-CoV-2 have been epidemiologically linked to various bat species. Bats possess unique immunological characteristics that allow them to serve as a potential viral reservoir. Bats are also known to protect themselves against viruses and maintain their immunity. Therefore, there is a need for in-depth understanding into bat-virus biology to unravel the major factors contributing to the coexistence and spread of viruses.

Chimeric antigen receptor T cell-based targeting of CD317 as a novel immunotherapeutic strategy against glioblastoma

BACKGROUND

Chimeric antigen receptor (CAR) T cell therapy has proven to be successful against hematological malignancies. However, exploiting CAR T cells to treat solid tumors is more challenging for various reasons including the lack of suitable target antigens. Here, we identify the transmembrane protein CD317 as a novel target antigen for CAR T cell therapy against glioblastoma, one of the most aggressive solid tumors.

METHODS

CD317-targeting CAR T cells were generated by lentivirally transducing human T cells from healthy donors. The anti-glioma activity of CD317-CAR T cells toward various glioma cells was assessed in vitro in cell lysis assays. Subsequently, we determined the efficacy of CD317-CAR T cells to control tumor growth in vivo in clinically relevant mouse glioma models.

RESULTS

We generated CD317-specific CAR T cells and demonstrate strong anti-tumor activity against several glioma cell lines as well as primary patient-derived cells with varying CD317 expression levels in vitro. A CRISPR/Cas9-mediated knockout of CD317 protected glioma cells from CAR T cell lysis, demonstrating the target specificity of the approach. Silencing of CD317 expression in T cells by RNA interference reduced fratricide of engineered T cells and further improved their effector function. Using orthotopic glioma mouse models, we demonstrate the antigen-specific anti-tumor activity of CD317-CAR T cells, which resulted in prolonged survival and cure of a fraction of CAR T cell-treated animals.

CONCLUSIONS

These data reveal a promising role of CD317-CAR T cell therapy against glioblastoma, which warrants further evaluation to translate this immunotherapeutic strategy into clinical neuro-oncology.

Identification of BST2 as a conjunctival epithelial stem/progenitor cell marker

The conjunctival epithelium consists of conjunctival epithelial cells and goblet cells derived from conjunctival epithelial stem/progenitor cells. However, the source of these cells is not well known because no specific markers for conjunctival epithelial stem/progenitor cells have been discovered. Therefore, to identify conjunctival epithelial stem/progenitor cell markers, we performed single-cell RNA sequencing of a conjunctival epithelial cell population derived from human-induced pluripotent stem cells (hiPSCs). The following conjunctival epithelial markers were identified: BST2, SLC2A3, AGR2, TMEM54, OLR1, and TRIM29. Notably, BST2 was strongly positive in the basal conjunctival epithelium, which is thought to be rich in stem/progenitor cells. Moreover, BST2 was able to sort conjunctival epithelial stem/progenitor cells from hiPSC-derived ocular surface epithelial cell populations. BST2-positive cells were highly proliferative and capable of successfully generating conjunctival epithelial sheets containing goblet cells. In conclusion, BST2 has been identified as a specific marker of conjunctival epithelial stem/progenitor cells.

Astragaloside IV promotes pharmacological effect of Descurainia sophia seeds on isoproterenol-induced cardiomyopathy in rats by synergistically modulating the myosin motor

Descurainia sophia seeds (DS), Astragalus mongholicus (AM), and their formulas are widely used to treat heart failure caused by various cardiac diseases in traditional Chinese medicine practice. However, the molecular mechanism of action of DS and AM has not been completely understood. Herein, we first used mass spectrometry coupled to UPLC to characterize the chemical components of DS and AM decoctions, then applied MS-based quantitative proteomic analysis to profile protein expression in the heart of rats with isoproterenol-induced cardiomyopathy (ISO-iCM) before and after treated with DS alone or combined with AM, astragaloside IV (AS4), calycosin-7-glucoside (C7G), and Astragalus polysaccharides (APS) from AM. We demonstrated for the first time that DS decoction alone could reverse the most of differentially expressed proteins in the heart of the rats with ISO-iCM, including the commonly recognized biomarkers natriuretic peptides (NPPA) of cardiomyopathy and sarcomeric myosin light chain 4 (MYL4), relieving ISO-iCM in rats, but AM did not pronouncedly improve the pharmacological efficiency of DS. Significantly, we revealed that AS4 remarkably promoted the pharmacological potency of DS by complementarily reversing myosin motor MYH6/7, and further downregulating NPPA and MYL4. In contrast, APS reduced the efficiency of DS due to upregulating NPPA and MYL4. These findings not only provide novel insights to better understanding in the combination principle of traditional Chinese medicine but also highlight the power of mass spectrometric proteomics strategy combined with conventional pathological approaches for the traditional medicine research.

Substitutions in Nef That Uncouple Tetherin and SERINC5 Antagonism Impair Simian Immunodeficiency Virus Replication in Primary Rhesus Macaque Lymphocytes

Most simian immunodeficiency viruses (SIVs) use Nef to counteract restriction by the tetherin proteins of their nonhuman primate hosts. In addition to counteracting tetherin, SIV Nef has a number of other functions, including the downmodulation of CD3, CD4, and major histocompatibility complex class I (MHC I) molecules from the surface of SIV-infected cells and the enhancement of viral infectivity by preventing the incorporation of SERINC5 into virions. Although these activities require different surfaces of Nef, they can be difficult to separate because of their dependence on similar interactions with AP-1 or AP-2 for clathrin-mediated endocytosis. We previously observed extensive overlap of the SIV Nef residues required for counteracting tetherin and SERINC5. Here, we define substitutions in Nef that separate anti-tetherin activity from SERINC5 antagonism and other activities of Nef. This information was used to engineer an infectious molecular clone of SIV (SIV_mac239nef_SA) that is sensitive to tetherin but retains CD3, CD4, MHC I, and SERINC5 downmodulation. In primary rhesus macaque CD4⁺ T cells, SIV_mac239nef_SA exhibits impaired replication compared to wild-type SIV_mac239 under conditions of interferon-induced upregulation of tetherin. These results demonstrate that tetherin antagonism can be separated from other Nef functions and that resistance to tetherin is essential for optimal replication in primary CD4⁺ T cells. IMPORTANCE Tetherin is an interferon-inducible transmembrane protein that prevents the detachment of enveloped viruses from infected cells by physically tethering nascent virions to cellular membranes. SIV Nef downmodulates simian tetherin to overcome this restriction in nonhuman primate hosts. Nef also enhances virus infectivity by preventing the incorporation of SERINC5 into virions and contributes to immune evasion by downmodulating other proteins from the cell surface. To assess the contribution of tetherin antagonism to virus replication, we engineered an infectious molecular clone of SIV with substitutions in Nef that uncouple tetherin antagonism from other Nef functions. These substitutions impaired virus replication in interferon-treated macaque CD4⁺ T cells, revealing the impact of tetherin on SIV replication under physiological conditions in primary CD4⁺ lymphocytes.

HIV-1 restriction by SERINC5

Serine incorporator 5 (SERINC5 or SER5) is a multipass transmembrane protein with ill-defined cellular activities. SER5 was recently described as a human immunodeficiency virus 1 (HIV-1) restriction factor capable of inhibiting HIV-1 that does not express its accessory protein Nef (Δ Nef). SER5 incorporated into the viral membrane impairs the entry of HIV-1 by disrupting the fusion between the viral and the plasma membrane after envelope receptor interaction induced the first steps of the fusion process. The mechanisms of how SER5 prevents membrane fusion are not fully understood and viral envelope proteins were identified that escape the SER5-mediated restriction. Primate lentiviruses, such as HIV-1 and simian immunodeficiency viruses (SIVs), use their accessory protein Nef to downregulate SER5 from the plasma membrane by inducing an endocytic pathway. In addition to being directly antiviral, recent data suggest that SER5 is an important adapter protein in innate signaling pathways leading to the induction of inflammatory cytokines. This review discusses the current knowledge about HIV-1 restriction by SER5.

TMEM106A inhibits enveloped virus release from cell surface

Enveloped viruses pose constant threat to hosts from ocean to land. Virion particle release from cell surface is a critical step in the viral life cycle for most enveloped viruses, making it a common antiviral target for the host defense system. Here we report that host factor TMEM106A inhibits the release of enveloped viruses from the cell surface. TMEM106A is a type II transmembrane protein localized on the plasma membrane and can be incorporated into HIV-1 virion particles. Through intermolecular interactions of its C-terminal domains on virion particle and plasma membrane, TMEM106A traps virion particles to the cell surface. HIV-1 Env interacts with TMEM106A to interfere with the intermolecular interactions and partially suppresses its antiviral activity. TMEM106A orthologs from various species displayed potent antiviral activity against multiple enveloped viruses. These results suggest that TMEM106A is an evolutionarily conserved antiviral factor that inhibits the release of enveloped viruses from the cell surface.

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Type II transmembrane protein TMEM106A can be incorporated into virion particles

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TMEM106A inhibits enveloped virion release through C-terminal molecular interactions

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HIV-1 envelope protein interacts with TMEM106A and suppresses its antiviral activity

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TMEM106A is an evolutionarily conserved antiviral factor against multiple viruses

Bone marrow stromal antigen 2 (BST-2) genetic variants influence expression levels and disease outcome in HIV-1 chronically infected patients

Background

Bone marrow stromal antigen 2 (BST-2) also known as Tetherin (CD317/HM1.24), is a host restriction factor that blocks the release of HIV-1 virions from infected cells. Previous studies reported that BST-2 genetic variants or single nucleotide polymorphims (SNPs) have a preventative role during HIV-1 infection. However, the influence of BST-2 SNPs on expression levels remains unknown. In this study, we investigated the influence of BST-2 SNPs on expression levels and disease outcome in HIV-1 subtype C chronically infected antiretroviral therapy naïve individuals.

Results

We quantified BST-2 mRNA levels in peripheral blood mononuclear cells (PBMCs), determined BST-2 protein expression on the surface of CD4⁺ T cells using flow cytometry and genotyped two intronic single nucleotide polymorphisms (SNPs) rs919267 and rs919266 together with one SNP rs9576 located in the 3’ untranslated region (UTR) of bst-2 gene using TaqMan assays from HIV-1 uninfected and infected participants. Subsequently, we determined the ability of plasma antibody levels to mediate antibody-dependent cellular phagocytosis (ADCP) using gp120 consensus C and p24 subtype B/C protein. Fc receptor-mediated NK cell degranulation was evaluated as a surrogate for ADCC activity using plasma from HIV-1 positive participants. BST-2 mRNA expression levels in PBMCs and protein levels on CD4⁺ T cells were lower in HIV-1 infected compared to uninfected participants (p = 0.075 and p < 0.001, respectively). rs919267CT (p = 0.042) and rs919267TT (p = 0.045) were associated with lower BST-2 mRNA expression levels compared to rs919267CC in HIV-1 uninfected participants. In HIV-1 infected participants, rs919267CT associated with lower CD4 counts, (p = 0.003), gp120-IgG1 (p = 0.040), gp120-IgG3 (p = 0.016) levels but higher viral loads (p = 0.001) while rs919267TT was associated with lower BST-2 mRNA levels (p = 0.046), CD4 counts (p = 0.001), gp120-IgG1 levels (p = 0.033) but higher plasma viral loads (p = 0.007). Conversely, rs9576CA was associated with higher BST-2 mRNA expression levels (p = 0.027), CD4 counts (p = 0.079), gp120-IgG1 (p = 0.009), gp120-IgG3 (p = 0.039) levels but with lower viral loads (p = 0.037).

Conclusion

Our findings show that bst-2 SNPs mediate BST-2 expression and disease outcome, correlate with gp120-IgG1, gp120-IgG3 levels but not p24-IgG levels, ADCC and ADCP activity.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12977-022-00588-2.

BST2 suppresses LINE-1 retrotransposition by reducing the promoter activity of LINE-1 5'-UTR

Endogenous retrotransposons are considered the “molecular fossils” of ancient retroviral insertions. Several studies have indicated that host factors restrict both retroviruses and retrotransposons through different mechanisms. Type 1 long interspersed elements (LINE-1 or L1) are the only active retroelements that can replicate autonomously in the human genome. A recent study reported that LINE-1 retrotransposition is potently suppressed by BST2, a host restriction factor that prevents viral release mainly by physically tethering enveloped virions (such as HIV) to the surface of producer cells. However, no endoplasmic membrane structure has been associated with LINE-1 replication, suggesting that BST2 may utilize a distinct mechanism to suppress LINE-1. In this study, we showed that BST2 is a potent LINE-1 suppressor. Further investigations suggested that BST2 reduces the promoter activity of LINE-1 5′ untranslated region (UTR) and lowers the levels of LINE-1 RNA, proteins, and events during LINE-1 retrotransposition. Surprisingly, although BST2 apparently uses different mechanisms against HIV and LINE-1, two membrane-associated domains that are essential for BST2-mediated HIV tethering also proved important for BST2-induced inhibition of LINE-1 5′ UTR. Additionally, by suppressing LINE-1, BST2 prevented LINE-1-induced genomic DNA damage and innate immune activation. Taken together, our data uncovered the mechanism of BST2-mediated LINE-1 suppression and revealed new roles of BST2 as a promoter regulator, genome stabilizer, and innate immune suppressor.

IMPORTANCE BST2 is a potent antiviral protein that suppresses the release of several enveloped viruses, mainly by tethering the envelope of newly synthesized virions and restraining them on the surface of producer cells. In mammalian cells, there are numerous DNA elements replicating through reverse transcription, among which LINE-1 is the only retroelement that can replicate autonomously. Although LINE-1 retrotransposition does not involve the participation of a membrane structure, BST2 has been reported as an efficient LINE-1 suppressor, suggesting a different mechanism for BST2-mediated LINE-1 inhibition and a new function for BST2 itself. We found that BST2 specifically represses the promoter activity of LINE-1 5′ UTR, resulting in decreased levels of LINE-1 transcription, translation, and subsequent retrotransposition. Additionally, by suppressing LINE-1 activity, BST2 maintains genome stability and regulates innate immune activation. These findings expand our understanding of BST2 and its biological significance.

Zn-Induced Interactions Between SARS-CoV-2 orf7a and BST2/Tetherin

We present in this work a first X-ray Absorption Spectroscopy study of the interactions of Zn with human BST2/tetherin and SARS-CoV-2 orf7a proteins as well as with some of their complexes. The analysis of the XANES region of the measured spectra shows that Zn binds to BST2, as well as to orf7a, thus resulting in the formation of BST2-orf7a complexes. This structural information confirms the the conjecture, recently put forward by some of the present Authors, according to which the accessory orf7a (and possibly also orf8) viral protein are capable of interfering with the BST2 antiviral activity. Our explanation for this behavior is that, when BST2 gets in contact with Zn bound to the orf7a Cys15 ligand, it has the ability of displacing the metal owing to the creation of a new disulfide bridge across the two proteins. The formation of this BST2-orf7a complex destabilizes BST2 dimerization, thus impairing the antiviral activity of the latter.

Transcriptomic Characterization Reveals Attributes of High Influenza Virus Productivity in MDCK Cells

The Madin–Darby Canine Kidney (MDCK) cell line is among the most commonly used cell lines for the production of influenza virus vaccines. As cell culture-based manufacturing is poised to replace egg-based processes, increasing virus production is of paramount importance. To shed light on factors affecting virus productivity, we isolated a subline, H1, which had twice the influenza virus A (IAV) productivity of the parent (P) through cell cloning, and characterized H1 and P in detail on both physical and molecular levels. Transcriptome analysis revealed that within a few hours after IAV infection, viral mRNAs constituted over one fifth of total mRNA, with several viral genes more highly expressed in H1 than P. Functional analysis of the transcriptome dynamics showed that H1 and P responded similarly to IAV infection, and were both subjected to host shutoff and inflammatory responses. Importantly, H1 was more active in translation and RNA processing intrinsically and after infection. Furthermore, H1 had more subdued inflammatory and antiviral responses. Taken together, we postulate that the high productivity of IAV hinges on the balance between suppression of host functions to divert cellular resources and the sustaining of sufficient activities for virus replication. Mechanistic insights into virus productivity can facilitate the process optimization and cell line engineering for advancing influenza vaccine manufacturing.

Updating on Roles of HIV Intrinsic Factors: A Review of Their Antiviral Mechanisms and Emerging Functions

BACKGROUND

Host restriction factors are cellular proteins that inhibit specific steps of the viral life cycle. Since the 1970s, several new factors have been identified, including human immunodeficiency virus-1 (HIV-1) replication restriction. Evidence accumulated in the last decade has substantially broadened our understanding of the molecular mechanisms utilized to abrogate the HIV-1 life cycle.

SUMMARY

In this review, we focus on the interaction between host restriction factors participating in the early phase of HIV-1 infection, particularly CA-targeting proteins. Host factors involved in the late phase of the replication cycle, such as viral assembly and egress factors, are also described. Additionally, current reports on well-known antiviral intrinsic factors, as well as other viral restriction factors with their emerging roles, are included.

CONCLUSION

A comprehensive understanding of the interactions between viruses and hosts is expected to provide insight into the design of novel HIV-1 therapeutic interventions.

Murine BST2/tetherin promotes measles virus infection of neurons

BST2/tetherin is a transmembrane protein with antiviral activity; it is synthesized following exposure to interferons, and restricts the release of budding virus particles by tethering them to the host cell membrane. We previously showed that BST2 is induced in primary neurons following measles virus (MV) infection or type I interferon; however, BST2 was dispensable for protection against challenge with neuron-restricted MV. Here, we define the contribution of BST-2 in neuronal MV infection. Surprisingly, and in contrast to its antiviral role in non-neuronal cells, murine BST2 promotes MV infection in brains of permissive mice and in primary neuron cultures. Moreover, BST2 expression was predominantly observed in the non-synaptic fraction of purified neurons. These studies highlight a cell-type dependent role of a well-characterized antiviral protein in enhancing neuronal infection.

Innate Immune Responses to Herpesvirus Infection

Infection of a host cell by an invading viral pathogen triggers a multifaceted antiviral response. One of the most potent defense mechanisms host cells possess is the interferon (IFN) system, which initiates a targeted, coordinated attack against various stages of viral infection. This immediate innate immune response provides the most proximal defense and includes the accumulation of antiviral proteins, such as IFN-stimulated genes (ISGs), as well as a variety of protective cytokines. However, viruses have co-evolved with their hosts, and as such, have devised distinct mechanisms to undermine host innate responses. As large, double-stranded DNA viruses, herpesviruses rely on a multitude of means by which to counter the antiviral attack. Herein, we review the various approaches the human herpesviruses employ as countermeasures to the host innate immune response.

Dendritic Cell-Mediated Regulation of Liver Ischemia-Reperfusion Injury and Liver Transplant Rejection

Liver allograft recipients are more likely to develop transplantation tolerance than those that receive other types of organ graft. Experimental studies suggest that immune cells and other non-parenchymal cells in the unique liver microenvironment play critical roles in promoting liver tolerogenicity. Of these, liver interstitial dendritic cells (DCs) are heterogeneous, innate immune cells that appear to play pivotal roles in the instigation, integration and regulation of inflammatory responses after liver transplantation. Interstitial liver DCs (recruited in situ or derived from circulating precursors) have been implicated in regulation of both ischemia/reperfusion injury (IRI) and anti-donor immunity. Thus, livers transplanted from mice constitutively lacking DCs into syngeneic, wild-type recipients, display increased tissue injury, indicating a protective role of liver-resident donor DCs against transplant IRI. Also, donor DC depletion before transplant prevents mouse spontaneous liver allograft tolerance across major histocompatibility complex (MHC) barriers. On the other hand, mouse liver graft-infiltrating host DCs that acquire donor MHC antigen via “cross-dressing”, regulate anti-donor T cell reactivity in association with exhaustion of graft-infiltrating T cells and promote allograft tolerance. In an early phase clinical trial, infusion of donor-derived regulatory DCs (DCreg) before living donor liver transplantation can induce alterations in host T cell populations that may be conducive to attenuation of anti-donor immune reactivity. We discuss the role of DCs in regulation of warm and liver transplant IRI and the induction of liver allograft tolerance. We also address design of cell therapies using DCreg to reduce the immunosuppressive drug burden and promote clinical liver allograft tolerance.

Gene variants of coagulation related proteins that interact with SARS-CoV-2

Thrombosis is a recognized complication of Coronavirus disease of 2019 (COVID-19) and is often associated with poor prognosis. There is a well-recognized link between coagulation and inflammation, however, the extent of thrombotic events associated with COVID-19 warrants further investigation. Poly(A) Binding Protein Cytoplasmic 4 (PABPC4), Serine/Cysteine Proteinase Inhibitor Clade G Member 1 (SERPING1) and Vitamin K epOxide Reductase Complex subunit 1 (VKORC1), which are all proteins linked to coagulation, have been shown to interact with SARS proteins. We computationally examined the interaction of these with SARS-CoV-2 proteins and, in the case of VKORC1, we describe its binding to ORF7a in detail. We examined the occurrence of variants of each of these proteins across populations and interrogated their potential contribution to COVID-19 severity. Potential mechanisms, by which some of these variants may contribute to disease, are proposed. Some of these variants are prevalent in minority groups that are disproportionally affected by severe COVID-19. Therefore, we are proposing that further investigation around these variants may lead to better understanding of disease pathogenesis in minority groups and more informed therapeutic approaches.

IFITM3-specific antibody reveals IFN preferences and slow IFN induction of the antiviral factor IFITM3 in humans

Using a specific antibody, we found that expression of the viral restriction factor IFITM3 differs across cell types within the immune compartment with higher expression in myeloid rather than lymphoid cells. IFITM3 expression was increased following IFN stimulation, mostly type I, in immune cells, with the exception of T cells.

BST-2/Tetherin is involved in BAFF-enhanced proliferation and survival via canonical NF-κB signaling in neoplastic B-lymphoid cells

The development of Sjögren's syndrome (SS) is accompanied by B cell hyperproliferation and mutation. Our previous study identified aberrant expression of BST-2 (also known as Tetherin/CD317) in B cells from either the peripheral blood or infiltrated salivary glands. However, the roles of BST-2 in the regulation of B cell activation remain unknown. In this study, we identified that BST-2 can respond to BAFF simulation but not to other B cell simulators in neoplastic B cell lines. A CCK-8 assay, an EdU assay and Annexin V/PI staining indicated that BST-2 inhibition attenuated BAFF-enhanced proliferation and survival in both Raji cells and Daudi cells. Screening of BAFF-related signaling in neoplastic B-lymphoid cells indicated that BST-2 was involved in the regulation of NF-κB signaling upon BAFF simulation. However, inhibition of NF-κB by JSH-23 significantly reduced the proliferation and survival of Raji and Daudi cells under both normal and BAFF-simulated conditions. Collectively, our results indicate that BST-2/Tetherin is a BAFF-responsive membrane factor involved in the regulation of NF-κB signaling, thereby assisting in the proliferation and survival of neoplastic B-lymphoid cells. Our study provides a potential molecular mechanism underlying aberrant overactivation of B cells upon SS development.

CD317 mediates immunocytolysis resistance by RICH2/cytoskeleton-dependent membrane protection

Immune evasion is a common hallmark of cancers. Immunotherapies that aim at restoring or increasing the immune response against cancers have revolutionized outcomes for patients, but the mechanisms of resistance remain poorly defined. Here, we report that CD317, a surface molecule with a unique topology that is double anchored into the membrane, protects tumor cells from immunocytolysis. CD317 knockdown in tumor cells renders more severe death in response to NK or chimeric antigen receptor-modified NK cells challenge. Such effects of CD317 silencing might be the results of increasing sensitivity of tumor cells to immune killing rather than strengthening immune response, since neither effector-target cell contact nor the activation of effector cells was affected, and the enhanced cytolysis was also not counteracted by the addition of recombinant CD317 proteins. Mechanistically, CD317 might endow tumor cells with more flexibility to modulate cytoskeleton through its association with RICH2, thereby protects membrane integrity against perforin and consequently promotes survival in response to immunocytolysis. These results reveal a new mechanism of immunocytolysis resistance and suggest CD317 as an attractive target which can be exploited for improving the efficacy of cancer immunotherapies.

Site-Specific Evolutionary Rate Shifts in HIV-1 and SIV

Site-specific evolutionary rate shifts are defined as protein sites, where the rate of substitution has changed dramatically across the phylogeny. With respect to a given clade, sites may either undergo a rate acceleration or a rate deceleration, reflecting a site that was conserved and became variable, or vice-versa, respectively. Sites displaying such a dramatic evolutionary change may point to a loss or gain of function at the protein site, reflecting adaptation, or they may indicate epistatic interactions among sites. Here, we analyzed full genomes of HIV and SIV-1 and identified 271 rate-shifting sites along the HIV-1/SIV phylogeny. The majority of rate shifts occurred at long branches, often corresponding to cross-species transmission branches. We noted that in most proteins, the number of rate accelerations and decelerations was equal, and we suggest that this reflects epistatic interactions among sites. However, several accessory proteins were enriched for either accelerations or decelerations, and we suggest that this may be a signature of adaptation to new hosts. Interestingly, the non-pandemic HIV-1 group O clade exhibited a substantially higher number of rate-shift events than the pandemic group M clade. We propose that this may be a reflection of the height of the species barrier between gorillas and humans versus chimpanzees and humans. Our results provide a genome-wide view of the constraints operating on proteins of HIV-1 and SIV.

Microbial Biofilms: Human T-cell Leukemia Virus Type 1 First in Line for Viral Biofilm but Far Behind Bacterial Biofilms

Human T-cell leukemia virus type 1 (HTLV-1) is a retrovirus associated with adult T-cell leukemia (ATL) and HTLV-1-associated myelopathy/tropical spastic paraparesis (HAM/TSP). To date, it is the unique published example of a virus able to form a biofilm at the surface of infected cells. Deeply studied in bacteria, bacterial biofilms represent multicellular assemblies of bacteria in contact with a surface and shielded by the extracellular matrix (ECM). Microbial lifestyle in biofilms, either viral or bacterial, is opposed structurally and physiologically to an isolated lifestyle, in which viruses or bacteria freely float in their environment. HTLV-1 biofilm formation is believed to be promoted by viral proteins, mainly Tax, through remodeling of the ECM of the infected cells. HTLV-1 biofilm has been linked to cell-to-cell transmission of the virus. However, in comparison to bacterial biofilms, very little is known on kinetics of viral biofilm formation or dissemination, but also on its pathophysiological roles, such as escape from immune detection or therapeutic strategies, as well as promotion of leukemogenesis. The switch between production of cell-free isolated virions and cell-associated viral biofilm, although not fully apprehended yet, remains a key step to understand HTLV-1 infection and pathogenesis.

Transcriptome analysis reveals immune-related gene expression changes with age in giant panda (Ailuropoda melanoleuca) blood

The giant panda (Ailuropoda melanoleuca), an endangered species endemic to western China, has long been threatened with extinction that is exacerbated by highly contagious and fatal diseases. Aging is the most well-defined risk factor for diseases and is associated with a decline in immune function leading to increased susceptibility to infection and reduced response to vaccination. Therefore, this study aimed to determine which genes and pathways show differential expression with age in blood tissues. We obtained 210 differentially expressed genes by RNA-seq, including 146 up-regulated and 64 down-regulated genes in old pandas (18-21yrs) compared to young pandas (2-6yrs). We identified ISG15, STAT1, IRF7 and DDX58 as the hub genes in the protein-protein interaction network. All of these genes were up-regulated with age and played important roles in response to pathogen invasion. Functional enrichment analysis indicated that up-regulated genes were mainly involved in innate immune response, while the down-regulated genes were mainly related to B cell activation. These may suggest that the innate immunity is relatively well preserved to compensate for the decline in the adaptive immune function. In conclusion, our findings will provide a foundation for future studies on the molecular mechanisms underlying immune changes associated with ageing.

The N-glycosylation of Equine Tetherin Affects Antiviral Activity by Regulating Its Subcellular Localization

Tetherin is an interferon-inducible type II transmembrane glycoprotein which inhibits the release of viruses, including retroviruses, through a “physical tethering” model. However, the role that the glycosylation of tetherin plays in its antiviral activity remains controversial. In this study, we found that mutation of N-glycosylation sites resulted in an attenuation of the antiviral activity of equine tetherin (eqTHN), as well as a reduction in the expression of eqTHN at the plasma membrane (PM). In addition, eqTHN N-glycosylation mutants colocalize obviously with ER, CD63, LAMP1 and endosomes, while WT eqTHN do not. Furthermore, we also found that N-glycosylation impacts the transport of eqTHN in the cell not by affecting the endocytosis, but rather by influencing the anterograde trafficking of the protein. These results suggest that the N-glycosylation of eqTHN is important for the antiviral activity of the protein through regulating its normal subcellular localization. This finding will enhance our understanding of the function of this important restriction factor.

The Role of Atypical Ubiquitin Chains in the Regulation of the Antiviral Innate Immune Response

It is well established that polyubiquitin chains, in particular those linked through K48 and K63, play a key role in the regulation of the antiviral innate immune response. However, the role of the atypical chains linked via any of the other lysine residues (K6, K11, K27, K29, and K33) and the M1-linked linear chains have not been investigated very well yet in this context. This is partially due to a lack of tools to study these linkages in their biological context. Interestingly though, recent findings underscore the importance of the atypical chains in the regulation of the antiviral immune response. This review will highlight the most important advances in the study of the role of atypical ubiquitin chains, particularly in the regulation of intracellular antiviral innate immune signaling pathways. We will also discuss the development of new tools and how these can increase our knowledge of the role of atypical ubiquitin chains.

Viral Manipulations of the Cullin-RING Ubiquitin Ligases

Cullin-RING ubiquitin ligases (CRLs) are efficient and diverse toolsets of the cells to regulate almost every biological process. However, these characteristics have also been usurped by many viruses to optimize for their replication. CRLs are often at the forefront of the arms races in the coevolution of viruses and hosts. Here we review the modes of actions and functional consequences of viral manipulations of host cell CRLs. We also discuss the therapeutic applications to target these viral manipulations for treating viral infections.

Web of interferon stimulated antiviral factors to control the influenza A viruses replication

Influenza viruses cause mild to severe infections in animals and humans worldwide with significant morbidity and mortality. Infection of eukaryotic cells with influenza A viruses triggers the induction of innate immune system through the interaction between pattern recognition receptors (PRRs) and pathogen associated molecular patterns (PAMPs), which culminate in the induction of interferons (IFNs). Consequently, IFNs bind to their cognate receptors on the cellular membrane and activate the signaling pathway for transcriptional regulation of interferon-stimulated genes (ISGs) through Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. Cumulative actions of these ISGs establish an antiviral state of the host. Several ISGs have been described, which play critical roles to inhibit the infection and replication of influenza A viruses at multiple steps of virus life cycle. In this review, the dynamics and redundancy of these ISGs against influenza A viruses are discussed. Additionally, current understanding and molecular mechanisms that are underlying the roles of ISGs in pathogenesis of influenza virus are critically reviewed.

How HIV Nef Proteins Hijack Membrane Traffic To Promote Infection

The accessory protein Nef of human immunodeficiency virus (HIV) is a primary determinant of viral pathogenesis. Nef is abundantly expressed during infection and reroutes a variety of cell surface proteins to disrupt host immunity and promote the viral replication cycle. Nef counteracts host defenses by sequestering and/or degrading its targets via the endocytic and secretory pathways. Nef does this by physically engaging a number of host trafficking proteins. Substantial progress has been achieved in identifying the targets of Nef, and a structural and mechanistic understanding of Nef's ability to command the protein trafficking machinery has recently started to coalesce. Comparative analysis of HIV and simian immunodeficiency virus (SIV) Nef proteins in the context of recent structural advances sheds further light on both viral evolution and the mechanisms whereby trafficking is hijacked. This review describes how advances in cell and structural biology are uncovering in growing detail how Nef subverts the host immune system, facilitates virus release, and enhances viral infectivity.

Host-HIV-1 Interactome: A Quest for Novel Therapeutic Intervention

The complex nature and structure of the human immunodeficiency virus has rendered the cure for HIV infections elusive. The advances in antiretroviral treatment regimes and the development of highly advanced anti-retroviral therapy, which primarily targets the HIV enzymes, have dramatically changed the face of the HIV epidemic worldwide. Despite this remarkable progress, patients treated with these drugs often witness inadequate efficacy, compound toxicity and non-HIV complications. Considering the limited inventory of druggable HIV proteins and their susceptibility to develop drug resistance, recent attempts are focussed on targeting HIV-host interactomes that are essential for viral reproduction. Noticeably, unlike other viruses, HIV subverts the host nuclear pore complex to enter into and exit through the nucleus. Emerging evidence suggests a crucial role of interactions between HIV-1 proteins and host nucleoporins that underlie the import of the pre-integration complex into the nucleus and export of viral RNAs into the cytoplasm during viral replication. Nevertheless, the interaction of HIV-1 with nucleoporins has been poorly described and the role of nucleoporins during nucleocytoplasmic transport of HIV-1 still remains unclear. In this review, we highlight the advances and challenges in developing a more effective antiviral arsenal by exploring critical host-HIV interactions with a special focus on nuclear pore complex (NPC) and nucleoporins.

Complex Problems Require Ternary Solutions: Another Lesson from SIV Nef

In this issue of Cell Host & Microbe, Buffalo et al. describe a cryo-EM structure of SIV Nef complexed with AP-2 and tetherin. The structure helps explain why human tetherin is Nef-resistant and why lentiviruses that successfully emerged in humans (HIV-1 and HIV-2) had to evolve novel anti-tetherin strategies.

Beyond Tethering the Viral Particles: Immunomodulatory Functions of Tetherin (BST-2)

Host response to viral infection is a highly regulated process involving engagement of various host factors, cytokines, chemokines, and stimulatory signals that pave the way for an antiviral immune response. The response is manifested in terms of viral sequestration, phagocytosis, and inhibition of genome replication, and, finally, if required, lymphocyte-mediated clearance of virally infected cells. During this process, cross-talk between viral and host factors can shape disease outcomes and immunopathology. Bone marrow stromal antigen 2 (BST-2), also know as tetherin, is induced by type I interferon produced in response to viral infections, as well as in certain cancers. BST-2 has been shown to be a host restriction factor of virus multiplication through its ability to physically tether budding virions and restrict viral spread. However, BST-2 has other roles in the host antiviral response. This review focuses on the diverse functions of BST-2 and its downstream signaling pathways in regulating host immune responses.

Ubiquitination and SUMOylation in HIV Infection: Friends and Foes

As intracellular parasites, viruses hijack the cellular machinery to facilitate their replication and spread. This includes favouring the expression of their viral genes over host genes, appropriation of cellular molecules, and manipulation of signalling pathways, including the post-translational machinery. HIV, the causative agent of AIDS, is notorious for using post-translational modifications to generate infectious particles. Here, we discuss the mechanisms by which HIV usurps the ubiquitin and SUMO pathways to modify both viral and host factors to achieve a productive infection, and also how the host innate sensing system uses these post-translational modifications to hinder HIV replication.

Single-cell analysis reveals T cell infiltration in old neurogenic niches

The mammalian brain contains neurogenic niches comprising neural stem cells (NSCs) and other cell types. Neurogenic niches become less functional with age, but how they change during aging remains unclear. Here we perform single cell RNA-sequencing of young and old neurogenic niches in mice. Analysis of 14,685 single cell transcriptomes reveals a decrease in activated NSCs, changes in endothelial cells and microglia, and infiltration of T cells in old neurogenic niches. Surprisingly, T cells in old brains are clonally expanded and generally distinct from those in old blood, suggesting they may experience specific antigens. T cells from old brains express interferon γ, and the subset of NSCs with a high interferon response shows decreased proliferation in vivo. Interestingly, T cells can inhibit NSC proliferation in co-cultures and in vivo, in part by secreting interferon. Our study reveals an interaction between T cells and NSCs in old brains, opening potential avenues to counter age-related decline in brain function.

In Silico Insights into HIV-1 Vpu-Tetherin Interactions and Its Mutational Counterparts

Tetherin, an interferon-induced host protein encoded by the bone marrow stromal antigen 2 (BST2/CD317/HM1.24) gene, is involved in obstructing the release of many retroviruses and other enveloped viruses by cross-linking the budding virus particles to the cell surface. This activity is antagonized in the case of human immunodeficiency virus (HIV)-1 wherein its accessory protein Viral Protein U (Vpu) interacts with tetherin, causing its downregulation from the cell surface. Vpu and tetherin connect through their transmembrane (TM) domains, culminating into events leading to tetherin degradation by recruitment of β-TrCP2. However, mutations in the TM domains of both proteins are reported to act as a resistance mechanism to Vpu countermeasure impacting tetherin's sensitivity towards Vpu but retaining its antiviral activity. Our study illustrates the binding aspects of blood-derived, brain-derived, and consensus HIV-1 Vpu with tetherin through protein-protein docking. The analysis of the bound complexes confirms the blood-derived Vpu-tetherin complex to have the best binding affinity as compared to other two. The mutations in tetherin and Vpu are devised computationally and are subjected to protein-protein interactions. The complexes are tested for their binding affinities, residue connections, hydrophobic forces, and, finally, the effect of mutation on their interactions. The single point mutations in tetherin at positions L23Y, L24T, and P40T, and triple mutations at {L22S, F44Y, L37I} and {L23T, L37T, T45I}, while single point mutations in Vpu at positions A19H and W23Y and triplet of mutations at {V10K, A11L, A19T}, {V14T, I18T, I26S}, and {A11T, V14L, A15T} have revealed no polar contacts with minimal hydrophobic interactions between Vpu and tetherin, resulting in reduced binding affinity. Additionally, we have explored the aggregation potential of tetherin and its association with the brain-derived Vpu protein. This work is a possible step toward an understanding of Vpu-tetherin interactions.

Modulation of Innate Immune Signaling Pathways by Herpesviruses

Herpesviruses can be detected by pattern recognition receptors (PRRs), which then activate downstream adaptors, kinases and transcription factors (TFs) to induce the expression of interferons (IFNs) and inflammatory cytokines. IFNs further activate the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway, inducing the expression of interferon-stimulated genes (ISGs). These signaling events constitute host innate immunity to defeat herpesvirus infection and replication. A hallmark of all herpesviruses is their ability to establish persistent infection in the presence of active immune response. To achieve this, herpesviruses have evolved multiple strategies to suppress or exploit host innate immune signaling pathways to facilitate their infection. This review summarizes the key host innate immune components and their regulation by herpesviruses during infection. Also we highlight unanswered questions and research gaps for future perspectives.

Accumulation of Cytoplasmic DNA Due to ATM Deficiency Activates the Microglial Viral Response System with Neurotoxic Consequences

ATM (ataxia-telangiectasia mutated) is a PI3K-like kinase best known for its role in the DNA damage response (DDR), especially after double-strand breaks. Mutations in the ATM gene result in a condition known as ataxia-telangiectasia (A-T) that is characterized by cancer predisposition, radiosensitivity, neurodegeneration, sterility, and acquired immune deficiency. We show here that the innate immune system is not spared in A-T. ATM-deficient microglia adopt an active phenotype that includes the overproduction of proinflammatory cytokines that are toxic to cultured neurons and likely contribute to A-T neurodegeneration. Causatively, ATM dysfunction results in the accumulation of DNA in the cytoplasm of microglia as well as a variety of other cell types. In microglia, cytoplasmic DNA primes an antiviral response via the DNA sensor, STING (stimulator of interferon genes). The importance of this response pathway is supported by our finding that inhibition of STING blocks the overproduction of neurotoxic cytokines. Cytosolic DNA also activates the AIM2 (absent in melanoma 2) containing inflammasome and induces proteolytic processing of cytokine precursors such as pro-IL-1β. Our study furthers our understanding of neurodegeneration in A-T and highlights the role of cytosolic DNA in the innate immune response.SIGNIFICANCE STATEMENT Conventionally, the immune deficiencies found in ataxia-telangiectasia (A-T) patients are viewed as defects of the B and T cells of the acquired immune system. In this study, we demonstrate the microglia of the innate immune system are also affected and uncover the mechanism by which this occurs. Loss of ATM (ataxia-telangiectasia mutated) activity leads to a slowing of DNA repair and an accumulation of cytoplasmic fragments of genomic DNA. This ectopic DNA induces the antivirus response, which triggers the production of neurotoxic cytokines. This expands our understanding of the neurodegeneration found in A-T and offers potentially new therapeutic options.

IRF1 Maintains Optimal Constitutive Expression of Antiviral Genes and Regulates the Early Antiviral Response

Viral defense at mucosal sites depends on interferons (IFN) and IFN stimulated genes (ISGs), either of which may be constitutively expressed to maintain an “antiviral state” (AVS). However, the mechanisms that govern the AVS are poorly defined. Using a BEAS-2B respiratory epithelial cell line deficient in IRF1, we demonstrate higher susceptibility to infection with vesicular stomatitis virus (VSV) and influenza virus. IRF1-mediated restriction of VSV is IFN-independent, as blockade of types I and III IFNs and JAK-STAT signaling before infection did not affect VSV infection of either parent or IRF1 KO cells. Transcriptome analysis revealed that IRF1 regulates constitutive expression of ~300 genes, including antiviral ISGs: OAS2, BST2, and RNASEL and knockdown of any of these IRF1-dependent genes increased VSV infection. Additionally, IRF1 enhances rapid expression of IFNβ and IFNλ after stimulation with poly I:C and also regulates ISG expression. Mechanistically, IRF1 enhances recruitment of BRD4 to promotor-enhancer regions of ISGs for rapid expression and maintains levels of histone H3K4me1 for optimal constitutive expression. Finally, IRF1 also regulates constitutive expression of TLR2 and TLR3 and promotes signaling through these pattern recognition receptors (PRR). These data reveal multiple roles for IRF1 toward effective anti-viral responses by maintaining IFN-independent constitutive expression of anti-viral ISGs and supporting early IFN-dependent responses to PRR stimulation.

CD317 Activates EGFR by Regulating Its Association with Lipid Rafts

EGFR regulates various fundamental cellular processes, and its constitutive activation is a common driver for cancer. Anti-EGFR therapies have shown benefit in cancer patients, yet drug resistance almost inevitably develops, emphasizing the need for a better understanding of the mechanisms that govern EGFR activation. Here we report that CD317, a surface molecule with a unique topology, activated EGFR in hepatocellular carcinoma (HCC) cells by regulating its localization on the plasma membrane. CD317 was upregulated in HCC cells, promoting cell-cycle progression and enhancing tumorigenic potential in a manner dependent on EGFR. Mechanistically, CD317 associated with lipid rafts and released EGFR from these ordered membrane domains, facilitating the activation of EGFR and the initiation of downstream signaling pathways, including the Ras-Raf-MEK-ERK and JAK-STAT pathways. Moreover, in HCC mouse models and patient samples, upregulation of CD317 correlated with EGFR activation. These results reveal a previously unrecognized mode of regulation for EGFR and suggest CD317 as an alternative target for treating EGFR-driven malignancies. SIGNIFICANCE: Activation of EGFR by CD317 in hepatocellular carcinoma cells suggests CD317 as an alternative target for treating EGFR-dependent tumors.

Membrane partitioning of peptide aggregates: coarse-grained molecular dynamics simulations

Coarse-grained molecular dynamics (CGMD) simulation technique (MARTINI force field) is applied to monitor the aggregation of helical peptides representing the transmembrane sequence and its extension of bone marrow stromal cell antigen 2 (BST-2). One of the peptides is coupled with a protein transducing domain (PTD) of nine arginine residues (R9) at its N-terminal side as well as a peptide, pep11**, which has been shown to bind to human papilloma virus 16 (HPV16) E6 oncoprotein. A short hydrophobic stretch of the transmembrane domain (TMD) of BST-2 aggregates the fastest and inserts into a lipid membrane. An aggregate of R9-pep11** attaches to the membrane via simultaneous contact of many arginine residues. Monomers from the aggregates of the shortest of the hydrophobic TMDs dissolve into the opposing leaflet when the aggregate spans the bilayer. A 'flipping' of the individual monomeric peptides is not observed.Communicated by Ramaswamy H. Sarma.

Polymorphisms in Rhesus Macaque Tetherin Are Associated with Differences in Acute Viremia in Simian Immunodeficiency Virus Δnef-Infected Animals

Tetherin (BST-2 or CD317) is an interferon-inducible transmembrane protein that inhibits virus release from infected cells. To determine the extent of sequence variation and the impact of polymorphisms in rhesus macaque tetherin on simian immunodeficiency virus (SIV) infection, tetherin alleles were sequenced from 146 rhesus macaques, including 68 animals infected with wild-type SIVmac239 and 47 animals infected with SIVmac239Δnef Since Nef is the viral gene product of SIV that counteracts restriction by tetherin, these groups afford a comparison of the effects of tetherin polymorphisms on SIV strains that are, and are not, resistant to tetherin. We identified 15 alleles of rhesus macaque tetherin with dimorphic residues at 9 positions. The relationship between these alleles and plasma viral loads was compared during acute infection, prior to the onset of adaptive immunity. Acute viremia did not differ significantly among the wild-type SIV-infected animals; however, differences in acute viral loads were associated with polymorphisms in tetherin among the animals infected with SIVΔnef In particular, polymorphisms at positions 43 and 111 (P43 and H111) were associated with lower acute-phase viral loads for SIVΔnef infection. These observations reveal extensive polymorphism in rhesus macaque tetherin, maintained perhaps as a consequence of variability in the selective pressure of diverse viral pathogens, and identify tetherin alleles that may have an inherently greater capacity to restrict SIV replication in the absence of Nef.IMPORTANCE As a consequence of ongoing evolutionary conflict with viral pathogens, tetherin has accumulated numerous species-specific differences that represent important barriers to the transmission of viruses between species. This study reveals extensive polymorphism in rhesus macaque tetherin and identifies specific alleles that are associated with lower viral loads during the first few weeks after infection with nef-deleted SIV. These observations suggest that the variable selective pressure of viral pathogens, in addition to driving the diversification of tetherin among species, also operates within certain species to maintain sequence variation in tetherin.

Circulating healing (CH) cells expressing BST2 are functionally activated by the injury-regulated systemic factor HGFA

Background

Restoration of damaged tissues through the activation of endogenous progenitors is an attractive therapeutic option. A deep evaluation of the intrinsic stem/progenitor cell properties as well as the reciprocal interactions with injured environments is of critical importance.

Methods

Here, we show that bone marrow stromal cell antigen 2 (BST2) allows the isolation of a population of circulating progenitors, the circulating healing (CH) cells, characterized by a distinctive core signature. The bone marrow (BM) origin of BST2^pos CH cells has been strengthened by the co-expression of leptin receptor, the hallmark of a subpopulation of BM-skeletal stem cells.

Results

BST2^pos CH cells retained the capacity to (i) respond to injury signals generated by a bone fracture, (ii) modify the expression of cell motility genes following damage, and (iii) react to hepatocyte growth factor-activator (HGFA), an injury-related stimulus sufficient to induce their transition into G_ALERT, a state in which cells are functionally activated and participate in tissue repair.

Conclusions

Taken together, these results could pave the way for the identification of new strategies to enhance and potentiate endogenous regenerative mechanisms for future therapies.

Electronic supplementary material

The online version of this article (10.1186/s13287-018-1056-1) contains supplementary material, which is available to authorized users.

The avian influenza virus PA segment mediates strain-specific antagonism of BST-2/tetherin

BST-2 is an antiviral protein described as a powerful cross-species transmission barrier for simian immunodeficiency viruses. Influenza viruses appear to interact with BST-2, raising the possibility that BST-2 may be a barrier for cross-species transmission. An MDCK-based cell line expressing human BST-2 was generated to study human-derived A/Puerto Rico/8/36 (H1N1; PR8) as well as two low pathogenic avian influenza viruses (subtypes H4N6 and H6N1). The H4N6 and H6N1 viruses were less affected by BST-2 expression than PR8, due to their ability to decrease BST-2 levels, a function localized to the PA segment of both avian viruses. Experiments with PA-mutant and -chimeric viruses confirmed that the avian PA segment conferred BST-2 downregulation and antagonism. These results indicate a species-specific ability of PA from low pathogenic avian viruses to mitigate human BST-2 antiviral activity, suggesting that BST-2 is unlikely to be a general cross-species barrier to transmission of such viruses to humans.

Limiting Respiratory Viral Infection by Targeting Antiviral and Immunological Functions of BST-2/Tetherin: Knowledge and Gaps

Recent findings regarding the cellular biology and immunology of BST-2 (also known as tetherin) indicate that its function could be exploited as a universal replication inhibitor of enveloped respiratory viruses (e.g., influenza, respiratory syncytial virus, etc.). BST-2 inhibits viral replication by preventing virus budding from the plasma membrane and by inducing an antiviral state in cells adjacent to infection via unique inflammatory signaling mechanisms. This review presents the first comprehensive summary of what is currently known about BST-2 anti-viral function against respiratory viruses, how these viruses construct countermeasures to antagonize BST-2, and how BST-2 function might be targeted to develop therapies to treat respiratory virus infections. The authors address the current gaps in knowledge, including the need for mechanistic understanding of BST-2 antagonism by respiratory viruses, that should be bridged to achieve that goal.

Strain-Specific Antagonism of the Human H1N1 Influenza A Virus against Equine Tetherin

Tetherin/BST-2/CD317 is an interferon-induced host restriction factor that can block the budding of enveloped viruses by tethering them to the cell surface. Many viruses use certain proteins to counteract restriction by tetherin from their natural hosts, but not from other species. The influenza A virus (FLUAV) has a wide range of subtypes with different host tropisms. Human tetherin (huTHN) has been reported to restrict only specific FLUAV strains and the viral hemagglutinin (HA) and neuraminidase (NA) genes determine the sensitivity to huTHN. Whether tetherins from other hosts can block human FLUAV is still unknown. Here, we evaluate the impact of equine tetherin (eqTHN) and huTHN on the replication of A/Sichuan/1/2009 (H1N1) and A/equine/Xinjiang/1/2007 (H3N8) strains. Our results show that eqTHN had higher restriction activity towards both viruses, and its shorter cytoplasmic tail contributed to that activity. We further demonstrated that HA and NA of A/Hamburg/4/2009 (H1N1) could counteract eqTHN. Notably, our results indicate that four amino acids, 13T and 49L of HA and 32T and 80V of NA, were involved in blocking the restriction activity of eqTHN. These findings reveal interspecies restriction by eqTHN towards FLUAV, and the role of the HA and NA proteins in overcoming this restriction.

Host Immune Response to Influenza A Virus Infection

Influenza A viruses (IAVs) are contagious pathogens responsible for severe respiratory infection in humans and animals worldwide. Upon detection of IAV infection, host immune system aims to defend against and clear the viral infection. Innate immune system is comprised of physical barriers (mucus and collectins), various phagocytic cells, group of cytokines, interferons (IFNs), and IFN-stimulated genes, which provide first line of defense against IAV infection. The adaptive immunity is mediated by B cells and T cells, characterized with antigen-specific memory cells, capturing and neutralizing the pathogen. The humoral immune response functions through hemagglutinin-specific circulating antibodies to neutralize IAV. In addition, antibodies can bind to the surface of infected cells and induce antibody-dependent cell-mediated cytotoxicity or complement activation. Although there are neutralizing antibodies against the virus, cellular immunity also plays a crucial role in the fight against IAVs. On the other hand, IAVs have developed multiple strategies to escape from host immune surveillance for successful replication. In this review, we discuss how immune system, especially innate immune system and critical molecules are involved in the antiviral defense against IAVs. In addition, we highlight how IAVs antagonize different immune responses to achieve a successful infection.

Experimental Adaptive Evolution of Simian Immunodeficiency Virus SIVcpz to Pandemic Human Immunodeficiency Virus Type 1 by Using a Humanized Mouse Model

Human immunodeficiency virus type 1 (HIV-1), the causative agent of AIDS, originated from simian immunodeficiency virus from chimpanzees (SIVcpz), the precursor of the human virus, approximately 100 years ago. This indicates that HIV-1 has emerged through the cross-species transmission of SIVcpz from chimpanzees to humans. However, it remains unclear how SIVcpz has evolved into pandemic HIV-1 in humans. To address this question, we inoculated three SIVcpz strains (MB897, EK505, and MT145), four pandemic HIV-1 strains (NL4-3, NLCSFV3, JRCSF, and AD8), and two nonpandemic HIV-1 strains (YBF30 and DJO0131). Humanized mice infected with SIVcpz strain MB897, a virus phylogenetically similar to pandemic HIV-1, exhibited a peak viral load comparable to that of mice infected with pandemic HIV-1, while peak viral loads of mice infected with SIVcpz strain EK505 or MT145 as well as nonpandemic HIV-1 strains were significantly lower. These results suggest that SIVcpz strain MB897 is preadapted to humans, unlike the other SIVcpz strains. Moreover, viral RNA sequencing of MB897-infected humanized mice identified a nonsynonymous mutation in env, a G413R substitution in gp120. The infectivity of the gp120 G413R mutant of MB897 was significantly higher than that of parental MB897. Furthermore, we demonstrated that the gp120 G413R mutant of MB897 augments the capacity for viral replication in both in vitro cell cultures and humanized mice. Taken together, this is the first experimental investigation to use an animal model to demonstrate a gain-of-function evolution of SIVcpz into pandemic HIV-1.IMPORTANCE From the mid-20th century, humans have been exposed to the menace of infectious viral diseases, such as severe acute respiratory syndrome coronavirus, Ebola virus, and Zika virus. These outbreaks of emerging/reemerging viruses can be triggered by cross-species viral transmission from wild animals to humans, or zoonoses. HIV-1, the causative agent of AIDS, emerged by the cross-species transmission of SIVcpz, the HIV-1 precursor in chimpanzees, around 100 years ago. However, the process by which SIVcpz evolved to become HIV-1 in humans remains unclear. Here, by using a hematopoietic stem cell-transplanted humanized-mouse model, we experimentally recapitulate the evolutionary process of SIVcpz to become HIV-1. We provide evidence suggesting that a strain of SIVcpz, MB897, preadapted to infect humans over other SIVcpz strains. We further demonstrate a gain-of-function evolution of SIVcpz in infected humanized mice. Our study reveals that pandemic HIV-1 has emerged through at least two steps: preadaptation and subsequent gain-of-function mutations.

Analysis of cross-population differentiation between Thoroughbred and Jeju horses

Objective

This study was intended to identify genes positively selected in Thoroughbred horses (THBs) that potentially contribute to their running performances.

Methods

The genomes of THB and Jeju horses (JH, Korean native horse) were compared to identify genes positively selected in THB. We performed cross-population extended haplotype homozygosity (XP-EHH) and cross-population composite likelihood ratio test (XP-CLR) statistical methods for our analysis using whole genome resequencing data of 14 THB and 6 JH.

Results

We identified 98 (XP-EHH) and 200 (XP-CLR) genes that are under positive selection in THB. Gene enrichment analysis identified 72 gene ontology biological process (GO BP) terms. The genes and GO BP terms explained some of THB’s characteristics such as immunity, energy metabolism and eye size and function related to running performances. GO BP terms that play key roles in several cell signaling mechanisms, which affected ocular size and visual functions were identified. GO BP term Eye photoreceptor cell differentiation is among the terms annotated presumed to affect eye size.

Conclusion

Our analysis revealed some positively selected candidate genes in THB related to their racing performances. The genes detected are related to the immunity, ocular size and function, and energy metabolism.

Viperin Targets Flavivirus Virulence by Inducing Assembly of Noninfectious Capsid Particles

Efficient antiviral immunity requires interference with virus replication at multiple layers targeting diverse steps in the viral life cycle. We describe here a novel flavivirus inhibition mechanism that results in interferon-mediated obstruction of tick-borne encephalitis virus particle assembly and involves release of malfunctioning membrane-associated capsid (C) particles. This mechanism is controlled by the activity of the interferon-induced protein viperin, a broad-spectrum antiviral interferon-stimulated gene. Through analysis of the viperin-interactome, we identified the Golgi brefeldin A-resistant guanine nucleotide exchange factor 1 (GBF1) as the cellular protein targeted by viperin. Viperin-induced antiviral activity, as well as C-particle release, was stimulated by GBF1 inhibition and knockdown and reduced by elevated levels of GBF1. Our results suggest that viperin targets flavivirus virulence by inducing the secretion of unproductive noninfectious virus particles via a GBF1-dependent mechanism. This as-yet-undescribed antiviral mechanism allows potential therapeutic intervention.

IMPORTANCE The interferon response can target viral infection on almost every level; however, very little is known about the interference of flavivirus assembly. We show here that interferon, through the action of viperin, can disturb the assembly of tick-borne encephalitis virus. The viperin protein is highly induced after viral infection and exhibit broad-spectrum antiviral activity. However, the mechanism of action is still elusive and appears to vary between the different viruses, indicating that cellular targets utilized by several viruses might be involved. In this study, we show that viperin induces capsid particle release by interacting and inhibiting the function of the cellular protein Golgi brefeldin A-resistant guanine nucleotide exchange factor 1 (GBF1). GBF1 is a key protein in the cellular secretory pathway and is essential in the life cycle of many viruses, also targeted by viperin, implicating GBF1 as a novel putative drug target.