Induction of sialyl-Lex expression by herpes simplex virus type 1 is dependent on viral immediate early RNA-activated transcription of host fucosyltransferase genes

Polymorphisms of FUT9 and its relationship with susceptibility towards DHAV-3 in Pekin duck

Duck viral hepatitis severely threatens the development of the duck industry, leading to economic losses every year. Using selected Pekin duck populations exhibiting varying resistance towards Duck Hepatitis A Virus type 3 (DHAV-3), screening for genetic variations, such as single nucleotide polymorphisms (SNP), associated with disease susceptibility will facilitate the breeding of Pekin ducks with enhanced disease resistance. The biological role of fucosyltransferases, which are a type of glycosyltransferase enzymes, is to catalyze the transfer of fucose to molecules such as oligosaccharides, glycoproteins and glycolipids, which is crucial for maintaining immune function by promoting effective pathogen recognition and modulating immune responses through specific fucosylation patterns. Previous studies found that the expression level of the Fucosyltransferase 9 (FUT9) gene in the liver of resistant Pekin ducks was significantly higher than that in susceptible ducks, suggesting its potential association with disease resistance. However, the association between genetic variations in FUT9 and susceptibility to DHAV-3 in ducks remains unclear. This study aims to detect SNPs in the FUT9 gene and explore their relationships with disease mortality and susceptibility, the result will provide a scientific basis for developing effective control strategies in duck breeding. 242 Pekin ducks with varying resistance to DHAV-3 were used in this experiment. 12 SNPs were identified in the coding region of FUT9. And g.76953686 T > C and g.76954451C > T were significantly associated with susceptibility to DHAV-3 in Pekin ducks. The results indicate that variations in the FUT9 gene significantly influence the susceptibility of ducks towards DHAV-3, providing potential genetic markers for enhancing disease resistance breeding in Pekin ducks.

Roles of core fucosylation modification in immune system and diseases

Core fucosylation, catalyzed by α1,6-fucosyltransferase (FUT8), is an important N-glycosylation modification process that attaches a fucose residue via an α1,6-linkage to the core N-acetylglucosamine of N-glycans in mammals. Research over the past three decades has revealed the critical role of FUT8-mediated core fucosylation modification in various physiological and pathological processes, including cell growth, adhesion, receptor activation, antibody-dependent cellular cytotoxicity (ADCC), tumor metastasis and infections. This review discusses the immune system function involving FUT8 and the mechanisms by which core fucosylation regulates immunity and contributes to disease. A deeper understanding of these mechanisms can provide insights into cellular biology and suggest new therapeutic approaches and targets for related diseases.

Identification of Three Novel O-Linked Glycans in the Envelope Protein of Tick-Borne Encephalitis Virus

The tick-borne encephalitis virus is a pathogen endemic to northern Europe and Asia, transmitted through bites from infected ticks. It is a member of the Flaviviridae family and possesses a positive-sense, single-stranded RNA genome encoding a polypeptide that is processed into seven non-structural and three structural proteins, including the envelope (E) protein. The glycosylation of the E protein, involving a single N-linked glycan at position N154, plays a critical role in viral infectivity and pathogenesis. Here, we dissected the entire glycosylation profile of the E protein using liquid chromatography-tandem mass spectrometry and identified three novel O-linked glycans, which were found at relatively low frequency. One of the O-linked glycans was positioned close to the highly conserved N-linked glycan site, and structural analysis suggested that it may be relevant for the function of the E 150-loop. The N154 site was found to be glycosylated with a high frequency, containing oligomannose or complex-type structures, some of which were fucosylated. An unusually high portion of oligomannose N-linked glycan structures exhibited compositions that are normally observed on proteins when they are translocated from the endoplasmic reticulum to the trans-Golgi network, suggesting disruption of the glycan processing pathway in the infected cells from which the E protein was obtained.

EGFR core fucosylation, induced by hepatitis C virus, promotes TRIM40-mediated-RIG-I ubiquitination and suppresses interferon-I antiviral defenses

Aberrant N-glycosylation has been implicated in viral diseases. Alpha-(1,6)-fucosyltransferase (FUT8) is the sole enzyme responsible for core fucosylation of N-glycans during glycoprotein biosynthesis. Here we find that multiple viral envelope proteins, including Hepatitis C Virus (HCV)-E2, Vesicular stomatitis virus (VSV)-G, Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)-Spike and human immunodeficiency virus (HIV)-gp120, enhance FUT8 expression and core fucosylation. HCV-E2 manipulates host transcription factor SNAIL to induce FUT8 expression through EGFR-AKT-SNAIL activation. The aberrant increased-FUT8 expression promotes TRIM40-mediated RIG-I K48-ubiquitination and suppresses the antiviral interferon (IFN)-I response through core fucosylated-EGFR-JAK1-STAT3-RIG-I signaling. FUT8 inhibitor 2FF, N-glycosylation site-specific mutation (Q352AT) of EGFR, and tissue-targeted Fut8 silencing significantly increase antiviral IFN-I responses and suppress RNA viral replication, suggesting that core fucosylation mediated by FUT8 is critical for antiviral innate immunity. These findings reveal an immune evasion mechanism in which virus-induced FUT8 suppresses endogenous RIG-I-mediated antiviral defenses by enhancing core fucosylated EGFR-mediated activation.

Structure and Role of O-Linked Glycans in Viral Envelope Proteins

N- and O-glycans are both important constituents of viral envelope glycoproteins. O-linked glycosylation can be initiated by any of 20 different human polypeptide O-acetylgalactosaminyl transferases, resulting in an important functional O-glycan heterogeneity. O-glycans are organized as solitary glycans or in clusters of multiple glycans forming mucin-like domains. They are functional both in the viral life cycle and in viral colonization of their host. Negatively charged O-glycans are crucial for the interactions between glycosaminoglycan-binding viruses and their host. A novel mechanism, based on controlled electrostatic repulsion, explains how such viruses solve the conflict between optimized viral attachment to target cells and efficient egress of progeny virus. Conserved solitary O-glycans appear important for viral uptake in target cells by contributing to viral envelope fusion. Dual roles of viral O-glycans in the host B cell immune response, either epitope blocking or epitope promoting, may be exploitable for vaccine development. Finally, specific virus-induced O-glycans may be involved in viremic spread.

Single-cell glycomics analysis by CyTOF-Lec reveals glycan features defining cells differentially susceptible to HIV

High-parameter single-cell phenotyping has enabled in-depth classification and interrogation of immune cells, but to date has not allowed for glycan characterization. Here, we develop CyTOF-Lec as an approach to simultaneously characterize many protein and glycan features of human immune cells at the single-cell level. We implemented CyTOF-Lec to compare glycan features between different immune subsets from blood and multiple tissue compartments, and to characterize HIV-infected cell cultures. Using bioinformatics approaches to distinguish preferential infection of cellular subsets from viral-induced remodeling, we demonstrate that HIV upregulates the levels of cell-surface fucose and sialic acid in a cell-intrinsic manner, and that memory CD4+ T cells co-expressing high levels of fucose and sialic acid are highly susceptible to HIV infection. Sialic acid levels were found to distinguish memory CD4+ T cell subsets expressing different amounts of viral entry receptors, pro-survival factors, homing receptors, and activation markers, and to play a direct role in memory CD4+ T cells' susceptibility to HIV infection. The ability of sialic acid to distinguish memory CD4+ T cells with different susceptibilities to HIV infection was experimentally validated through sorting experiments. Together, these results suggest that HIV remodels not only cellular proteins but also glycans, and that glycan expression can differentiate memory CD4+ T cells with vastly different susceptibility to HIV infection.

Dynamic Transcriptome Reveals the Mechanism of Liver Injury Caused by DHAV-3 Infection in Pekin Duck

Duck hepatitis A virus 3 (DHAV-3) is a wild endemic virus, which seriously endangers the duck industry in China. The present study aims to elucidate the mechanism of duck resistance to DHAV-3 infection. Both resistant and susceptible ducks were challenged with DHAV-3 in this experiment. The histopathological features and serum biochemical indices (ALT and AST) were analyzed to estimate liver injury status at 6, 12, 15, and 24 h post-infection (hpi). The dynamic transcriptomes of liver were analyzed to explain the molecular regulation mechanism in ducks against DHAV-3. The result showed that the liver injury in susceptible ducks was more serious than that in the resistant ducks throughout the four time points. A total of 2,127 differentially expressed genes (DEGs) were identified by comparing the transcriptome of the two populations. The expression levels of genes involved in innate immune response increased rapidly in susceptible ducks from 12 hpi. Similarly, the expression of genes involved in cytokine regulation also increased at the same time points, while the expression levels of these genes in resistant ducks remained similar between the various time points. KEGG enrichment analysis of the DEGs revealed that the genes involved in cytokine regulation and apoptosis were highly expressed in susceptible ducks than that in resistant ducks, suggesting that excessive cytokine storm and apoptosis may partially explain the mechanism of liver injury caused by DHAV-3 infection. Besides, we found that the FUT9 gene may contribute to resistance towards DHAV-3 in resistant ducklings. These findings will provide insight into duck resistance and susceptibility to DHAV-3 infection in the early phases, facilitate the development of a strategy for DHAV-3 prevention and treatment, and enhance genetic resistance via genetic selection in animal breeding.

Sialyl-LewisX Glycoantigen Is Enriched on Cells with Persistent HIV Transcription during Therapy

A comprehensive understanding of the phenotype of persistent HIV-infected cells, transcriptionally active and/or transcriptionally inactive, is imperative for developing a cure. The relevance of cell-surface glycosylation to HIV persistence has never been explored. We characterize the relationship between cell-surface glycomic signatures and persistent HIV transcription in vivo. We find that the cell surface of CD4+ T cells actively transcribing HIV, despite suppressive therapy, harbors high levels of fucosylated carbohydrate ligands, including the cell extravasation mediator Sialyl-LewisX (SLeX), compared with HIV-infected transcriptionally inactive cells. These high levels of SLeX are induced by HIV transcription in vitro and are maintained after therapy in vivo. Cells with high-SLeX are enriched with markers associated with HIV susceptibility, signaling pathways that drive HIV transcription, and pathways involved in leukocyte extravasation. We describe a glycomic feature of HIV-infected transcriptionally active cells that not only differentiates them from their transcriptionally inactive counterparts but also may affect their trafficking abilities.

Human adenovirus type 5 increases host cell fucosylation and modifies Ley antigen expression

Certain viral infections are known to modify the glycosylation profile of infected cells through the overexpression of specific host cell fucosyltransferases (FUTs). Infection with CMV (cytomegalovirus), HCV (hepatitis C virus), HSV-1 (herpes simplex virus type-1) and VZV (varicella-zoster virus) increase the expression of fucosylated epitopes, including antigens sLex (Siaα2-3 Galβ1-4(Fucα1-3)GlcNAcβ1-R) and Ley (Fucα1-2 Galβ1-4(Fucα1-3)GlcNAcβ1-R). The reorganization of the glycocalyx induced by viral infection may favor the spread of viral progeny, and alter diverse biological functions mediated by glycans, including recognition by the adaptive immune system. In this work, we aimed to establish whether infection with human adenovirus type 5 (HAd5), a well-known viral vector and infectious agent, causes changes in the glycosylation profile of A549 cells, used as a model of lung epithelium, a natural target of HAd5. We demonstrate for the first time that HAd5 infection causes a significant increase in the cell surface de novo fucosylation, as assessed by metabolic labeling, and that such modification is dependent on the expression of viral genes. The main type of increased fucosylation was determined to be in α1-2 linkage, as assessed by UEA-I lectin binding and supported by the overexpression of FUT1 and FUT2. Also, HAd5-infected cells showed a heterogeneous change in the expression profile of the bi-fucosylated Ley antigen, an antigen associated with enhanced cell proliferation and inhibition of apoptosis.

NFκB-mediated activation of the cellular FUT3, 5 and 6 gene cluster by herpes simplex virus type 1

Herpes simplex virus type 1 has the ability to induce expression of a human gene cluster located on chromosome 19 upon infection. This gene cluster contains three fucosyltransferases (encoded by FUT3, FUT5 and FUT6) with the ability to add a fucose to an N-acetylglucosamine residue. Little is known regarding the transcriptional activation of these three genes in human cells. Intriguingly, herpes simplex virus type 1 activates all three genes simultaneously during infection, a situation not observed in uninfected tissue, pointing towards a virus specific mechanism for transcriptional activation. The aim of this study was to define the underlying mechanism for the herpes simplex virus type 1 activation of FUT3, FUT5 and FUT6 transcription. The transcriptional activation of the FUT-gene cluster on chromosome 19 in fibroblasts was specific, not involving adjacent genes. Moreover, inhibition of NFκB signaling through panepoxydone treatment significantly decreased the induction of FUT3, FUT5 and FUT6 transcriptional activation, as did siRNA targeting of p65, in herpes simplex virus type 1 infected fibroblasts. NFκB and p65 signaling appears to play an important role in the regulation of FUT3, FUT5 and FUT6 transcriptional activation by herpes simplex virus type 1 although additional, unidentified, viral factors might account for part of the mechanism as direct interferon mediated stimulation of NFκB was not sufficient to induce the fucosyltransferase encoding gene cluster in uninfected cells.

Allele-selective RUNX1 binding regulates P1 blood group status by transcriptional control of A4GALT

The intronic A4GALT SNP rs5751348 defines a hematopoietic transcription factor–binding site present in P1 but not P2 blood group alleles. RUNX1 selectively binds to this regulatory site in P1 alleles; small interfering RNA knockdown of RUNX1 downregulates A4GALT transcript levels.

Intact Pneumococci Trigger Transcription of Interferon-Related Genes in Human Monocytes, while Fragmented, Autolyzed Bacteria Subvert This Response

A peculiar trait of pneumococci (Streptococcus pneumoniae) is their propensity to undergo spontaneous lysis during stationary growth due to activation of the enzyme autolysin (LytA), which fragments the peptidoglycan cell wall. The fragments that are generated upon autolysis impair phagocytosis and reduce production of interleukin-12 (IL-12) and gamma interferon (IFN-γ) by human leukocytes in response to intact pneumococci, thereby impeding crucial host defenses. The objective was to identify additional monocyte genes whose transcription is induced by intact pneumococci and subverted by autolyzed bacteria. Monocytes were isolated from healthy blood donors and stimulated for 3 h with UV-inactivated S. pneumoniae (Rx1PLY^- LytA⁺ strain), which is capable of autolyzing, its LytA^- isogenic autolysin-deficient mutant, or a mixture of the two (containing twice the initial bacterial concentration). Gene expression was assessed by Illumina microarray, and selected findings were confirmed by reverse transcription-quantitative real-time PCR (RT-qPCR), enzyme-linked immunosorbent assay (ELISA), and flow cytometry. In all, we identified 121 genes that were upregulated to a significantly higher degree by intact than autolyzed pneumococci. These included IFNB1 and a large set of interferon-induced genes, such as IFIT3, RSAD2, CFCL1, and CXCL10 genes, as well as IL12B and CD40 genes. RT-qPCR revealed that transcription of these genes in response to intact pneumococci diminished when autolyzed pneumococci were admixed and that this pattern was independent of pneumolysin. Thus, transcription of interferon-related genes is triggered by intact pneumococci and subverted by fragments generated by spontaneous bacterial autolysis. We suggest that interferon-related pathways are important for elimination of pneumococci and that autolysis contributes to virulence by extinguishing these pathways.

O-linked glycosylation of the mucin domain of the herpes simplex virus type 1-specific glycoprotein gC-1 is temporally regulated in a seed-and-spread manner

The herpes simplex virus type 1 (HSV-1) glycoprotein gC-1, participating in viral receptor interactions and immunity interference, harbors a mucin-like domain with multiple clustered O-linked glycans. Using HSV-1-infected diploid human fibroblasts, an authentic target for HSV-1 infection, and a protein immunoaffinity procedure, we enriched fully glycosylated gC-1 and a series of its biosynthetic intermediates. This fraction was subjected to trypsin digestion and a LC-MS/MS glycoproteomics approach. In parallel, we characterized the expression patterns of the 20 isoforms of human GalNAc transferases responsible for initiation of O-linked glycosylation. The gC-1 O-glycosylation was regulated in an orderly manner initiated by synchronous addition of one GalNAc unit each to Thr-87 and Thr-91 and one GalNAc unit to either Thr-99 or Thr-101, forming a core glycopeptide for subsequent additions of in all 11 GalNAc residues to selected Ser and Thr residues of the Thr-76-Lys-107 stretch of the mucin domain. The expression patterns of GalNAc transferases in the infected cells suggested that initial additions of GalNAc were carried out by initiating GalNAc transferases, in particular GalNAc-T2, whereas subsequent GalNAc additions were carried out by followup transferases, in particular GalNAc-T10. Essentially all of the susceptible Ser or Thr residues had to acquire their GalNAc units before any elongation to longer O-linked glycans of the gC-1-associated GalNAc units was permitted. Because the GalNAc occupancy pattern is of relevance for receptor binding of gC-1, the data provide a model to delineate biosynthetic steps of O-linked glycosylation of the gC-1 mucin domain in HSV-1-infected target cells.

Involvement of viral glycoprotein gC-1 in expression of the selectin ligand sialyl-Lewis X induced after infection with herpes simplex virus type 1

Several herpesviruses induce expression of the selectin receptor sialyl-Lewis X (sLe(x) ) by activating transcription of one or more of silent host FUT genes, each one encoding a fucosyltransferase that catalyses the rate-limiting step of sLe(x) synthesis. The aim here was to identify the identity of the glycoconjugate associated with sLe(x) glycoepitope in herpes simplex virus type 1 (HSV-1) infected human diploid fibroblasts, using immunofluorescence confocal microscopy. Cells infected with all tested HSV-1 strains analysed demonstrated bright sLe(x) fluorescence, except for two mutant viruses that were unable to induce proper expression of viral glycoprotein gC-1: One gC-1 null mutant and another mutant expressing gC-1 devoid of its major O-glycan-containing region (aa 33-116). The sLe(x) reactivity of HSV-1 infected cells was abolished by mild alkali treatment. Altogether the results indicated that the detectable sLe(x) was associated with O-linked glycans, situated in the mucin region of gC-1. No evidence for sLe(x) (i) in other HSV-1 glycoproteins with mucin domains such as gI-1 or (ii) in host cell glycoproteins/glycolipids was found. Thus, the mucin domain of HSV-1 gC-1 may support expression of selectin ligands such as sLe(x) and other larger O-linked glycans in cell types lacking endogenous mucin domain-containing glycoproteins, optimized for O-glycan expression, provided that the adequate host glycosyltransferase genes are activated.

RNA-sequencing analysis of 5' capped RNAs identifies many new differentially expressed genes in acute hepatitis C virus infection

We describe the first report of RNA sequencing of 5' capped (Pol II) RNAs isolated from acutely hepatitis C virus (HCV) infected Huh 7.5 cells that provides a general approach to identifying differentially expressed annotated and unannotated genes that participate in viral-host interactions. We identified 100, 684, and 1,844 significantly differentially expressed annotated genes in acutely infected proliferative Huh 7.5 cells at 6, 48, and 72 hours, respectively (fold change ≥ 1.5 and Bonferroni adjusted p-values < 0.05). Most of the differentially expressed genes (>80%) and biological pathways (such as adipocytokine, Notch, Hedgehog and NOD-like receptor signaling) were not identified by previous gene array studies. These genes are critical components of host immune, inflammatory and oncogenic pathways and provide new information regarding changes that may benefit the virus or mediate HCV induced pathology. RNAi knockdown studies of newly identified highly upregulated FUT1 and KLHDC7B genes provide evidence that their gene products regulate and facilitate HCV replication in hepatocytes. Our approach also identified novel Pol II unannotated transcripts that were upregulated. Results further identify new pathways that regulate HCV replication in hepatocytes and suggest that our approach will have general applications in studying viral-host interactions in model systems and clinical biospecimens.

Activation of host antiviral RNA-sensing factors necessary for herpes simplex virus type 1-activated transcription of host cell fucosyltransferase genes FUT3, FUT5, and FUT6 and subsequent expression of sLe(x) in virus-infected cells

Herpes simplex virus type 1 (HSV-1) induces expression of a selectin receptor, the carbohydrate epitope sialyl Lewis X (sLe(x)), at the surface of infected cells. The molecular background to this phenomenon is that a viral immediate early RNA interacts with as yet unidentified host factors, eventually resulting in transcription of three dormant host fucosyltransferase genes (FUT3, FUT5, and FUT6), whose gene products are rate-limiting for synthesis of sLe(x). The aim of the present study was to define the immediate targets for the viral RNA in this process. We found that the Protein Kinase R (PKR) inhibitors 2-aminopurine (2-AP) and C16 inhibited FUT3, FUT5, and FUT6 expression as well as HSV-1-induced expression of sLe(x), indicating a primary role of PKR as a viral RNA target. The PKR-dependent activation of the FUT genes seemed neither to involve PKR effects on translation nor to involve NF-kappaB- or JNK-dependent activation. IMD-0354, known as an inhibitor of the NF-kappaB-activating factor IKK-2, induced FUT transcription via a novel IKK-2-independent mechanism, irrespective of whether the cells were virus-infected or not. Altogether, the results suggested that PKR is the primary target for HSV-1 early RNA during induction of FUT3, FUT5, and FUT6, and that the subsequent steps in the transcriptional activation of these host genes involve a hitherto unknown IMD-0354, yet IKK-2-independent, pathway.