Targeting STT3A-oligosaccharyltransferase with NGI-1 causes herpes simplex virus 1 dysfunction

Glycosylation Triggers Cathepsin D Maturation and Secretion to Promote Gastric Cancer Development

Cathepsin D (CTSD) is a lysosomal aspartic protease with high expression in cancers. CTSD localized in different subcellular regions performs distinct roles. However, the precise regulation of its intracellular trafficking and extracellular secretion remains incompletely understood. This study showed that glycosylation modifications of CTSD determined its maturation and secretion in gastric cancer (GC) cells. Specifically, glycosylation at asparagine 134 (N134) dictated the intracellular trafficking and maturation of CTSD within lysosomes, through facilitating its sorting into COPII vesicles. Glycosylation at asparagine 263 (N263) was essential for the secretion of the proenzyme form of CTSD (pro-CTSD) via a novel pathway dependent on the small GTPase Rab3D. Notably, the extracellular release of pro-CTSD occurred more rapidly than its intracellular trafficking from the endoplasmic reticulum to lysosomes. This enhanced secretion speed may rapidly elevate the levels of pro-CTSD in the tumor microenvironment in response to extracellular stimuli. Ultimately, glycosylation at N134 and N263 regulated the autophagy and cell proliferation, respectively. These findings show the role of glycosylation in triggering the maturation and secretion of CTSD in GC cells. Through modulating its cellular trafficking, differential glycosylation modifications of CTSD defined the malignant behavior of GC cells.

Shared host genetic landscape of respiratory viral infection

Respiratory viruses represent a major global health burden. Although these viruses have different life cycles, they may depend on common host genetic factors, which could be targeted by broad-spectrum host-directed therapies. We used genome-wide CRISPR screens and advanced data analytics to map a network of host genes that support infection by nine human respiratory viruses [influenza A virus, parainfluenza virus, human rhinovirus, respiratory syncytial virus, human coronavirus (HCoV)-229E, HCoV-NL63, HCoV-OC43, Middle East respiratory syndrome-related coronavirus, and severe acute respiratory syndrome-related coronavirus 2]. We explored shared pathways using knowledge graphs to inform on pharmacological targets. We selected and validated STT3A/B proteins of the N-oligosaccharyltransferase complex as host targets of broad-spectrum antiviral small molecules. Our work highlights the commonalities of viral host genetic dependencies and the feasibility of using this information to develop broad-spectrum antiviral agents.

Magnesium-Impregnated Membrane Promotes Bone Regeneration in Rat Skull Defect by N-Linked Glycosylation of SPARC via MagT1

Autograft has long been the gold standard for various bone surgeries. Nevertheless, the increasing usage of synthetic implants is taking over the operation rooms due to biosafety and standardized protocols. To fulfill such tremendous needs, a magnesium-impregnated membrane is devised that steadily releases magnesium ions to stimulate osteogenesis. The compatibility of Magnesium oxide (MgO) particles is enhanced through hydration and grafting, characterized by scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). With detailed degradation profiles, an in-depth investigation of Magnesium transporter 1 (MagT1) for magnesium intake is carried out and engaging in the N-linked glycosylation by using RNAi and inhibitors. The glycosylation of secreted protein acidic and rich in cysteine (SPARC) affected extracellular secretion and mineral deposition, demonstrated by immunostaining and density-dependent color-SEM (DDC-SEM). Skull defects are treated by implanting magnesium-impregnated membranes in rats and evaluated them by micro-CT and histological exams. This study revealed the compatible integration of grafted magnesium hydroxide (g-MH) particles is the key to functional performance and critical to applicability in vivo; meanwhile, it opens the door to a biological rationale for designing biomimetic materials.

Preparing for the next viral threat with broad-spectrum antivirals

There is a large global unmet need for the development of countermeasures to combat hundreds of viruses known to cause human disease and for the establishment of a therapeutic portfolio for future pandemic preparedness. Most approved antiviral therapeutics target proteins encoded by a single virus, providing a narrow spectrum of coverage. This, combined with the slow pace and high cost of drug development, limits the scalability of this direct-acting antiviral (DAA) approach. Here, we summarize progress and challenges in the development of broad-spectrum antivirals that target either viral elements (proteins, genome structures, and lipid envelopes) or cellular proviral factors co-opted by multiple viruses via newly discovered compounds or repurposing of approved drugs. These strategies offer new means for developing therapeutics against both existing and emerging viral threats that complement DAAs.

A comprehensive SARS-CoV-2-human protein-protein interactome reveals COVID-19 pathobiology and potential host therapeutic targets

Studying viral-host protein-protein interactions can facilitate the discovery of therapies for viral infection. We use high-throughput yeast two-hybrid experiments and mass spectrometry to generate a comprehensive SARS-CoV-2-human protein-protein interactome network consisting of 739 high-confidence binary and co-complex interactions, validating 218 known SARS-CoV-2 host factors and revealing 361 novel ones. Our results show the highest overlap of interaction partners between published datasets and of genes differentially expressed in samples from COVID-19 patients. We identify an interaction between the viral protein ORF3a and the human transcription factor ZNF579, illustrating a direct viral impact on host transcription. We perform network-based screens of >2,900 FDA-approved or investigational drugs and identify 23 with significant network proximity to SARS-CoV-2 host factors. One of these drugs, carvedilol, shows clinical benefits for COVID-19 patients in an electronic health records analysis and antiviral properties in a human lung cell line infected with SARS-CoV-2. Our study demonstrates the value of network systems biology to understand human-virus interactions and provides hits for further research on COVID-19 therapeutics.

B7 family protein glycosylation: Promising novel targets in tumor treatment

Cancer immunotherapy, including the inhibition of immune checkpoints, improves the tumor immune microenvironment and is an effective tool for cancer therapy. More effective and alternative inhibitory targets are critical for successful immune checkpoint blockade therapy. The interaction of the immunomodulatory ligand B7 family with corresponding receptors induces or inhibits T cell responses by sending co-stimulatory and co-inhibitory signals respectively. Blocking the glycosylation of the B7 family members PD-L1, PD-L2, B7-H3, and B7-H4 inhibited the self-stability and receptor binding of these immune checkpoint proteins, leading to immunosuppression and rapid tumor progression. Therefore, regulation of glycosylation may be the "golden key" to relieve tumor immunosuppression. The exploration of a more precise glycosylation regulation mechanism and glycan structure of B7 family proteins is conducive to the discovery and clinical application of antibodies and small molecule inhibitors.

A comprehensive SARS-CoV-2-human protein-protein interactome network identifies pathobiology and host-targeting therapies for COVID-19

Physical interactions between viral and host proteins are responsible for almost all aspects of the viral life cycle and the host's immune response. Studying viral-host protein-protein interactions is thus crucial for identifying strategies for treatment and prevention of viral infection. Here, we use high-throughput yeast two-hybrid and affinity purification followed by mass spectrometry to generate a comprehensive SARS-CoV-2-human protein-protein interactome network consisting of both binary and co-complex interactions. We report a total of 739 high-confidence interactions, showing the highest overlap of interaction partners among published datasets as well as the highest overlap with genes differentially expressed in samples (such as upper airway and bronchial epithelial cells) from patients with SARS-CoV-2 infection. Showcasing the utility of our network, we describe a novel interaction between the viral accessory protein ORF3a and the host zinc finger transcription factor ZNF579 to illustrate a SARS-CoV-2 factor mediating a direct impact on host transcription. Leveraging our interactome, we performed network-based drug screens for over 2,900 FDA-approved/investigational drugs and obtained a curated list of 23 drugs that had significant network proximities to SARS-CoV-2 host factors, one of which, carvedilol, showed promising antiviral properties. We performed electronic health record-based validation using two independent large-scale, longitudinal COVID-19 patient databases and found that carvedilol usage was associated with a significantly lowered probability (17%-20%, P < 0.001) of obtaining a SARS-CoV-2 positive test after adjusting various confounding factors. Carvedilol additionally showed anti-viral activity against SARS-CoV-2 in a human lung epithelial cell line [half maximal effective concentration (EC 50 ) value of 4.1 µM], suggesting a mechanism for its beneficial effect in COVID-19. Our study demonstrates the value of large-scale network systems biology approaches for extracting biological insight from complex biological processes.

Nascent Glycoproteome Reveals That N-Linked Glycosylation Inhibitor-1 Suppresses Expression of Glycosylated Lysosome-Associated Membrane Protein-2

Glycosylation inhibition has great potential in cancer treatment. However, the corresponding cellular response, protein expression and glycosylation changes remain unclear. As a cell-permeable small-molecule inhibitor with reduced cellular toxicity, N-linked glycosylation inhibitor-1 (NGI-1) has become a great approach to regulate glycosylation in mammalian cells. Here for the first time, we applied a nascent proteomic method to investigate the effect of NGI-1 in hepatocellular carcinoma (HCC) cell line. Besides, hydrophilic interaction liquid chromatography (HILIC) was adopted for the enrichment of glycosylated peptides. Glycoproteomic analysis revealed the abundance of glycopeptides from LAMP2, NICA, and CEIP2 was significantly changed during NGI-1 treatment. Moreover, the alterations of LAMP2 site-specific intact N-glycopeptides were comprehensively assessed. NGI-1 treatment also led to the inhibition of Cathepsin D maturation and the induction of autophagy. In summary, we provided evidence that NGI-1 repressed the expression of glycosylated LAMP2 accompanied with the occurrence of lysosomal defects and autophagy.

Glycosylation of viral proteins: Implication in virus-host interaction and virulence

Glycans are among the most important cell molecular components. However, given their structural diversity, their functions have not been fully explored. Glycosylation is a vital post-translational modification for various proteins. Many bacteria and viruses rely on N-linked and O-linked glycosylation to perform critical biological functions. The diverse functions of glycosylation on viral proteins during viral infections, including Dengue, Zika, influenza, and human immunodeficiency viruses as well as coronaviruses have been reported. N-linked glycosylation is the most common form of protein modification, and it modulates folding, transportation and receptor binding. Compared to N-linked glycosylation, the functions of O-linked viral protein glycosylation have not been comprehensively evaluated. In this review, we summarize findings on viral protein glycosylation, with particular attention to studies on N-linked glycosylation in viral life cycles. This review informs the development of virus-specific vaccines or inhibitors.

Aberrant Cellular Glycosylation May Increase the Ability of Influenza Viruses to Escape Host Immune Responses through Modification of the Viral Glycome

Individuals with metabolic dysregulation of cellular glycosylation often experience severe influenza disease, with a poor immune response to the virus and low vaccine efficacy. Here, we investigate the consequences of aberrant cellular glycosylation for the glycome and the biology of influenza virus. We transiently induced aberrant N-linked glycosylation in cultured cells with an oligosaccharyltransferase inhibitor, NGI-1. Cells treated with NGI-1 produced morphologically unaltered viable influenza virus with sequence-neutral glycosylation changes (primarily reduced site occupancy) in the hemagglutinin and neuraminidase proteins. Hemagglutinin with reduced glycan occupancy required a higher concentration of surfactant protein D (an important innate immunity respiratory tract collectin) for inhibition compared to that with normal glycan occupancy. Immunization of mice with NGI-1-treated virus significantly reduced antihemagglutinin and antineuraminidase titers of total serum antibody and reduced hemagglutinin protective antibody responses. Our data suggest that aberrant cellular glycosylation may increase the risk of severe influenza as a result of the increased ability of glycome-modified influenza viruses to evade the immune response.

Targeting conserved N-glycosylation blocks SARS-CoV-2 variant infection in vitro

Background

Despite clinical success with anti-spike vaccines, the effectiveness of neutralizing antibodies and vaccines has been compromised by rapidly spreading SARS-CoV-2 variants. Viruses can hijack the glycosylation machinery of host cells to shield themselves from the host's immune response and attenuate antibody efficiency. However, it remains unclear if targeting glycosylation on viral spike protein can impair infectivity of SARS-CoV-2 and its variants.

Methods

We adopted flow cytometry, ELISA, and BioLayer interferometry approaches to assess binding of glycosylated or deglycosylated spike with ACE2. Viral entry was determined by luciferase, immunoblotting, and immunofluorescence assays. Genome-wide association study (GWAS) revealed a significant relationship between STT3A and COVID-19 severity. NF-κB/STT3A-regulated N-glycosylation was investigated by gene knockdown, chromatin immunoprecipitation, and promoter assay. We developed an antibody-drug conjugate (ADC) that couples non-neutralization anti-spike antibody with NGI-1 (4G10-ADC) to specifically target SARS-CoV-2-infected cells.

Findings

The receptor binding domain and three distinct SARS-CoV-2 surface N-glycosylation sites among 57,311 spike proteins retrieved from the NCBI-Virus-database are highly evolutionarily conserved (99.67%) and are involved in ACE2 interaction. STT3A is a key glycosyltransferase catalyzing spike glycosylation and is positively correlated with COVID-19 severity. We found that inhibiting STT3A using N-linked glycosylation inhibitor-1 (NGI-1) impaired SARS-CoV-2 infectivity and that of its variants [Alpha (B.1.1.7) and Beta (B.1.351)]. Most importantly, 4G10-ADC enters SARS-CoV-2-infected cells and NGI-1 is subsequently released to deglycosylate spike protein, thereby reinforcing the neutralizing abilities of antibodies, vaccines, or convalescent sera and reducing SARS-CoV-2 variant infectivity.

Interpretation

Our results indicate that targeting evolutionarily-conserved STT3A-mediated glycosylation via an ADC can exert profound impacts on SARS-CoV-2 variant infectivity. Thus, we have identified a novel deglycosylation method suitable for eradicating SARS-CoV-2 variant infection in vitro.

Funding

A full list of funding bodies that contributed to this study can be found in the Acknowledgements section

Antiviral Classification

Over the past 60 years, more than 100 antiviral drugs or their combinations have been approved for clinical use. Antiviral drugs can be classified according to their chemical nature (e.g., small-molecules, peptides, biologics) or mechanisms of drug actions against specific viral proteins (e.g., polymerase inhibitors, protease inhibitors, glycoprotein inhibitors). This article provides an overview of antiviral classifications in 10 important human viruses: hepatitis B virus (HBV), hepatitis C virus (HCV), human immunodeficiency virus (HIV), human cytomegalovirus (HCMV), herpes simplex virus (HSV), variola virus (human smallpox), varicella zoster virus (VZV), influenza virus, respiratory syncytial virus (RSV), and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2).

The AT1 receptor autoantibody causes hypoglycemia in fetal rats via promoting the STT3A-GLUT1-glucose uptake axis in liver

Blood glucose is of great importance to development and metabolic homeostasis in fetuses. Stimulation of harmful factors during gestation induces pathoglycemia. Angiotensin II type 1 receptor autoantibody (AT1-AA), a newly discovered gestational harmful factor, has been shown to induce intrauterine growth restriction in fetuses and glucose disorders in adults. However, whether and how AT1-AA influences the blood glucose level of fetuses during gestation is not yet clear. The purpose of the current study was to observe the fetal blood glucose level of AT1-AA-positive pregnant rats during late pregnancy and to determine the roles that hepatic glucose transporters play in this process. We established AT1-AA-positive pregnant rats by injecting AT1-AA into the caudal veins of rats in the 2nd trimester of gestation. Although the fetal blood glucose level in the 3rd trimester of gestation decreased, hepatic glucose uptake increased detected. Through separating membrane and cytosolic proteins, we demonstrated that both the expression and membrane transport ratio of glucose transporter 1 (GLUT1), which is responsible for glucose transport in fetal hepatocytes, were upregulated, accompanied by increased expression of N-glycosyltransferase STT3A, which contributes to the N-glycosylation of GLUT1. In vitro, we identified that AT1-AA increased glucose uptake, the expression and membrane transport ratio of GLUT1 and the expression of STT3A in HepG2 cell lines via separating membrane and cytosolic proteins and immunofluorescence, resulting in the decreased glucose content in the medium. The GLUT1 inhibitor WZB117 reversed the decreases in glucose content in the medium, the increases in glucose uptake, the increases in the expression and membrane transport ratio of GLUT1 caused by AT1-AA. The N-glycosyltransferase inhibitor NGI as well as si-STT3A reversed the AT1-AA-induced upregulation of the STT3A-GLUT1-glucose uptake effect. This study demonstrates that AT1-AA lowers the blood glucose level of fetuses via the STT3A-GLUT1-glucose uptake axis in liver.