The essential role of clathrin-mediated endocytosis in the infectious entry of human enterovirus 71

Peptide nanocarriers co-delivering an antisense oligonucleotide and photosensitizer elicit synergistic cytotoxicity

Combination therapies demand co-delivery platforms with efficient entrapment of distinct payloads and specific delivery to cells and possibly organelles. Herein, we introduce the combination of two therapeutic modalities, gene and photodynamic therapy, in a purely peptidic platform. The simultaneous formation and cargo loading of the multi-micellar platform is governed by self-assembly at the nanoscale. The multi-micellar architecture of the nanocarrier and the positive charge of its constituent micelles offer controlled dual loading capacity with distinct locations for a hydrophobic photosensitizer (PS) and negatively charged antisense oligonucleotides (ASOs). Moreover, the nuclear localization signal (NLS) sequence built-in the peptide targets PS + ASO-loaded nanocarriers to the nucleus. Breast cancer cells treated with nanocarriers demonstrated photo-triggered enhancement of radical oxygen species (ROS) associated with increased cell death. Besides, delivery of ASO payloads resulted in up to 90 % knockdown of Bcl-2, an inhibitor of apoptosis that is overexpressed in more than half of all human cancers. Simultaneous delivery of PS and ASO elicited synergistic apoptosis to an extent that could not be reached by singly loaded nanocarriers or the free form of the drugs. Both, the distinct location of loaded compounds that prevents them from interfering with each other, and the highly efficient cellular delivery support the great potential of this versatile peptide platform in combination therapy.

Recent Progress in Innate Immune Responses to Enterovirus A71 and Viral Evasion Strategies

Enterovirus A71 (EV-A71) is a major pathogen causing hand, foot, and mouth disease (HFMD) in children worldwide. It can lead to severe gastrointestinal, pulmonary, and neurological complications. The innate immune system, which rapidly detects pathogens via pathogen-associated molecular patterns or pathogen-encoded effectors, serves as the first defensive line against EV-A71 infection. Concurrently, the virus has developed various sophisticated strategies to evade host antiviral responses and establish productive infection. Thus, the virus-host interactions and conflicts, as well as the ability to govern biological events at this first line of defense, contribute significantly to the pathogenesis and outcomes of EV-A71 infection. In this review, we update recent progress on host innate immune responses to EV-A71 infection. In addition, we discuss the underlying strategies employed by EV-A71 to escape host innate immune responses. A better understanding of the interplay between EV-A71 and host innate immunity may unravel potential antiviral targets, as well as strategies that can improve patient outcomes.

N-terminal acetyltransferase 6 facilitates enterovirus 71 replication by regulating PI4KB expression and replication organelle biogenesis

Enterovirus 71 (EV71) is one of the major pathogens causing hand, foot, and mouth disease in children under 5 years old, which can result in severe neurological complications and even death. Due to limited treatments for EV71 infection, the identification of novel host factors and elucidation of mechanisms involved will help to counter this viral infection. N-terminal acetyltransferase 6 (NAT6) was identified as an essential host factor for EV71 infection with genome-wide CRISPR/Cas9 screening. NAT6 facilitates EV71 viral replication depending on its acetyltransferase activity but has little effect on viral release. In addition, NAT6 is also required for Echovirus 7 and coxsackievirus B5 infection, suggesting it might be a pan-enterovirus host factor. We further demonstrated that NAT6 is required for Golgi integrity and viral replication organelle (RO) biogenesis. NAT6 knockout significantly inhibited phosphatidylinositol 4-kinase IIIβ (PI4KB) expression and PI4P production, both of which are key host factors for enterovirus infection and RO biogenesis. Further mechanism studies confirmed that NAT6 formed a complex with its substrate actin and one of the PI4KB recruiters-acyl-coenzyme A binding domain containing 3 (ACBD3). Through modulating actin dynamics, NAT6 maintained the integrity of the Golgi and the stability of ACBD3, thereby enhancing EV71 infection. Collectively, these results uncovered a novel mechanism of N-acetyltransferase supporting EV71 infection.IMPORTANCEEnterovirus 71 (EV71) is an important pathogen for children under the age of five, and currently, no effective treatment is available. Elucidating the mechanism of novel host factors supporting viral infection will reveal potential antiviral targets and aid antiviral development. Here, we demonstrated that a novel N-acetyltransferase, NAT6, is an essential host factor for EV71 replication. NAT6 could promote viral replication organelle (RO) formation to enhance viral replication. The formation of enterovirus ROs requires numerous host factors, including acyl-coenzyme A binding domain containing 3 (ACBD3) and phosphatidylinositol 4-kinase IIIβ (PI4KB). NAT6 could stabilize the PI4KB recruiter, ACBD3, by inhibiting the autophagy degradation pathway. This study provides a fresh insight into the relationship between N-acetyltransferase and viral infection.

Enterovirus A71 does not meet the uncoating receptor SCARB2 at the cell surface

Enterovirus A71 (EV-A71) infection involves a variety of receptors. Among them, two transmembrane protein receptors have been investigated in detail and shown to be critical for infection: P-selectin glycoprotein ligand-1 (PSGL-1) in lymphocytes (Jurkat cells), and scavenger receptor class B member 2 (SCARB2) in rhabdomyosarcoma (RD) cells. PSGL-1 and SCARB2 have been reported to be expressed on the surface of Jurkat and RD cells, respectively. In the work reported here, we investigated the roles of PSGL-1 and SCARB2 in the process of EV-A71 entry. We first examined the expression of SCARB2 in Jurkat cells, and detected it within the cytoplasm, but not on the cell surface. Further, using PSGL-1 and SCARB2 knockout cells, we found that although both PSGL-1 and SCARB2 are essential for virus infection of Jurkat cells, virus attachment to these cells requires only PSGL-1. These results led us to evaluate the cell surface expression and the roles of SCARB2 in other EV-A71-susceptible cell lines. Surprisingly, in contrast to the results of previous studies, we found that SCARB2 is absent from the surface of RD cells and other susceptible cell lines we examined, and that although SCARB2 is essential for infection of these cells, it is dispensable for virus attachment. These results indicate that a receptor other than SCARB2 is responsible for virus attachment to the cell and probably for internalization of virions, not only in Jurkat cells but also in RD cells and other EV-A71-susceptible cells. SCARB2 is highly concentrated in lysosomes and late endosomes, where it is likely to trigger acid-dependent uncoating of virions, the critical final step of the entry process. Our results suggest that the essential interactions between EV-A71 and SCARB2 occur, not at the cell surface, but within the cell.

Advances in anti-EV-A71 drug development research

BACKGROUND

Enterovirus A71 (EV-A71) is capable of causing hand, foot and mouth disease (HFMD), which may lead to neurological sequelae and even death. As EV-A71 is resistant to environmental changes and mutates easily, there is still a lack of effective treatments or globally available vaccines.

AIM OF REVIEW

For more than 50 years since the HFMD epidemic, related drug research has been conducted. Progress in this area can promote the further application of existing potential drugs and develop more efficient and safe antiviral drugs, and provide useful reference for protecting the younger generation and maintaining public health security.

KEY SCIENTIFIC CONCEPTS OF REVIEW

At present, researchers have identified hundreds of EV-A71 inhibitors based on screening repurposed drugs, targeted structural design, and rational modification of previously effective drugs as the main development strategies. This review systematically introduces the current potential drugs to inhibit EV-A71 infection, including viral inhibitors targeting key sites such as the viral capsid, RNA-dependent RNA polymerase (RdRp), 2C protein, internal ribosome entry site (IRES), 3C proteinase (3Cpro), and 2A proteinase (2Apro), starting from each stage of the viral life cycle. Meanwhile, the progress of host-targeting antiviral drugs and their development are summarized in terms of regulating host immunity, inhibiting autophagy or apoptosis, and regulating the cellular redox environment. In addition, the current clinical methods for the prevention and treatment of HFMD are summarized and discussed with the aim of providing support and recommendations for the treatment of enterovirus infections including EV-A71.

Targeting pyroptosis with nanoparticles to alleviate neuroinflammatory for preventing secondary damage following traumatic brain injury

Posttraumatic neuroinflammation is a key driver of secondary injury after traumatic brain injury (TBI). Pyroptosis, a proinflammatory form of programmed cell death, considerably activates strong neuroinflammation and amplifies the inflammatory response by releasing inflammatory contents. Therefore, treatments targeting pyroptosis may have beneficial effects on the treatment of secondary brain damage after TBI. Here, a cysteine-alanine-glutamine-lysine peptide-modified β-lactoglobulin (β-LG) nanoparticle was constructed to deliver disulfiram (DSF), C-β-LG/DSF, to inhibit pyroptosis and decrease neuroinflammation, thereby preventing TBI-induced secondary injury. In the post-TBI mice model, C-β-LG/DSF selectively targets the injured brain, increases DSF accumulation, and extends the time of the systemic circulation of DSF. C-β-LG/DSF can alleviate brain edema and inflammatory response, inhibit secondary brain injury, promote learning, and improve memory recovery in mice after trauma. Therefore, this study likely provided a potential approach for reducing the secondary spread of TBI.

A tradeoff between enterovirus A71 particle stability and cell entry

A central role of viral capsids is to protect the viral genome from the harsh extracellular environment while facilitating initiation of infection when the virus encounters a target cell. Viruses are thought to have evolved an optimal equilibrium between particle stability and efficiency of cell entry. In this study, we genetically perturb this equilibrium in a non-enveloped virus, enterovirus A71 to determine its structural basis. We isolate a single-point mutation variant with increased particle thermotolerance and decreased efficiency of cell entry. Using cryo-electron microscopy and molecular dynamics simulations, we determine that the thermostable native particles have acquired an expanded conformation that results in a significant increase in protein dynamics. Examining the intermediate states of the thermostable variant reveals a potential pathway for uncoating. We propose a sequential release of the lipid pocket factor, followed by internal VP4 and ultimately the viral RNA.

Engineered vitamin E-tethered non-immunogenic facial lipopeptide for developing improved siRNA based combination therapy against metastatic breast cancer

RNA interference based therapeutic gene silencing is an emerging platform for managing highly metastatic breast cancer. Cytosolic delivery of functional siRNA remains the key obstacle for efficient RNAi therapy. To overcome the challenges of siRNA delivery, we have engineered a vitamin E-tethered, short, optimum protease stabilized facial lipopeptide based non-immunogenic, biocompatible siRNA transporter to facilitate the clinical translation in future. Our designed lipopeptide has an Arginine-Sarcosine-Arginine segment for providing optimum protease-stability, minimizing adjacent arginine-arginine repulsion and reducing intermolecular aggregation and α-tocopherol as the lipidic moiety for facilitating cellular permeabilization. Interestingly, our designed non-immunogenic siRNA transporter has exhibited significantly better long term transfection efficiency than HiPerFect and can transfect hard to transfect primary cell line, HUVEC. Our engineered siRNA therapeutics demonstrated high efficacy in managing metastasis against triple negative breast cancer by disrupting the crosstalk of endothelial cells and MDA-MB-231 and reduced stemness and metastatic markers, as evidenced by downregulating critical oncogenic pathways. Our study aimed at silencing Notch1 signalling to achieve "multi-targeted" therapy with a single putative molecular medicine. We have further developed mechanistically rational combination therapy combining Notch1 silencing with a repurposed drug m-TOR inhibitor, metformin, which demonstrated synergistic interaction and enhanced antitumor efficacy against cancer metastasis.

Enterovirus 71 enters human brain microvascular endothelial cells through an ARF6-mediated endocytic pathway

Infection of the central nervous system caused by enterovirus 71 (EV71) remains the main cause of death in hand-foot-and-mouth disease. However, the mechanism responsible for how EV71 breaks through the blood-brain barrier to infect brain cells has yet to be elucidated. By performing a high-throughput small interfering RNA (siRNA) screening and validation, we found that the infection of human brain microvascular endothelial cells (HBMECs) by EV71 was independent of the endocytosis pathways mediated by caveolin, clathrin, and macropinocytosis but dependent on ADP-ribosylation factor 6 (ARF6), a small guanosinetriphosphate (GTP)-binding protein of the Ras superfamily. The specific siRNA targeting ARF6 markedly inhibited HBMECs susceptibility to EV71. EV71 infectivity was inhibited by NAV-2729, a specific inhibitor of ARF6, in a dose-dependent manner. The subcellular analysis demonstrated the co-localization of the endocytosed EV71 and ARF6, while knockdown of ARF6 with siRNA remarkably influenced EV71 endocytosis. By immunoprecipitation assays, we found a direct interaction of ARF6 with EV71 viral protein. Furthermore, ARF1, another small GTP-binding protein, was also found to participate in ARF6-mediated EV71 endocytosis. Murine experiments demonstrated that NAV-2729 significantly alleviated mortality caused by EV71 infection. Our study revealed a new pathway by which EV71 enters the HBMECs and provides new targets for drug development.

Identification of a novel acylthiourea-based potent broad-spectrum inhibitor for enterovirus 3D polymerase in vitro and in vivo

Enterovirus infections have become a serious public health threat to young children, leading to hand-foot-and-mouth disease and more severe nervous system diseases. Due to the lack of licensed anti enterovirus drugs, we reported herein that a Tenovin-1 analog, acylthiourea-based 4-(tert-butyl)-N-((4-(4-(tert-butyl)benzamido)phenyl)carbamothioyl) benzamide (AcTU), displayed low nanomolar anti-EV-A71 activity with an EC₅₀ of 1.0 nM in RD cells. Moreover, AcTU exhibited nanomolar to picomolar inhibitory activity against a series of enteroviruses including EV-D68, CV-A21, CV-A16 and CV-B1 (EC₅₀ = 0.75-17.15 nM). Mechanistic studies indicated that AcTU inhibited enterovirus proliferation by targeting 3D polymerase. In addition, AcTU displayed moderate pharmacokinetic properties in rats (F = 7.4%, T_1/2 = 3.26 h), and in vivo protection studies demonstrated that AcTU orally administered at 0.6 mg/kg/d was highly protective against lethal EV-A71 challenge in mice, potentially reducing mortality from 100% to 20% as well as alleviating symptoms. These results suggested that AcTU could be a potent clinical candidate for the treatment of enterovirus infections.

EV-A71 Mechanism of Entry: Receptors/Co-Receptors, Related Pathways and Inhibitors

Enterovirus A71, a non-enveloped single-stranded (+) RNA virus, enters host cells through three stages: attachment, endocytosis and uncoating. In recent years, receptors/co-receptors anchored on the host cell membrane and involved in this process have been continuously identified. Among these, hSCARB-2 was the first receptor revealed to specifically bind to a definite site of the EV-A71 viral capsid and plays an indispensable role during viral entry. It actually acts as the main receptor due to its ability to recognize all EV-A71 strains. In addition, PSGL-1 is the second EV-A71 receptor discovered. Unlike hSCARB-2, PSGL-1 binding is strain-specific; only 20% of EV-A71 strains isolated to date are able to recognize and bind it. Some other receptors, such as sialylated glycan, Anx 2, HS, HSP90, vimentin, nucleolin and fibronectin, were discovered successively and considered as "co-receptors" because, without hSCARB-2 or PSGL-1, they are not able to mediate entry. For cypA, prohibitin and hWARS, whether they belong to the category of receptors or of co-receptors still needs further investigation. In fact, they have shown to exhibit an hSCARB-2-independent entry. All this information has gradually enriched our knowledge of EV-A71's early stages of infection. In addition to the availability of receptors/co-receptors for EV-A71 on host cells, the complex interaction between the virus and host proteins and various intracellular signaling pathways that are intricately connected to each other is critical for a successful EV-A71 invasion and for escaping the attack of the immune system. However, a lot remains unknown about the EV-A71 entry process. Nevertheless, researchers have been continuously interested in developing EV-A71 entry inhibitors, as this study area offers a large number of targets. To date, important progress has been made toward the development of several inhibitors targeting: receptors/co-receptors, including their soluble forms and chemically designed compounds; virus capsids, such as capsid inhibitors designed on the VP1 capsid; compounds potentially interfering with related signaling pathways, such as MAPK-, IFN- and ATR-inhibitors; and other strategies, such as siRNA and monoclonal antibodies targeting entry. The present review summarizes these latest studies, which are undoubtedly of great significance in developing a novel therapeutic approach against EV-A71.

Viral modulation of lipid rafts and their potential as putative antiviral targets

Lipid rafts are ubiquitous in cells. They are identified as cholesterol and glycosphingolipid enriched microdomains on cellular membranes. They serve as platforms for cellular communications by functioning in signal transduction and membrane trafficking. Such structural organisation fulfils cellular needs for normal function, but at the same time increases vulnerability of cells to pathogen invasion. Viruses rely heavily on lipid rafts in basically every stage of the viral life cycle for successful infection. Various mechanisms of lipid rafts modification exploited by diverse viruses for attachment, internalisation, membrane fusion, genome replication, assembly and release have been brought to light. This review focuses on virus-raft interactions and how a wide range of viruses manipulate lipid rafts at distinct stages of infection. The importance of virus-raft interactions in viral infections has inspired researchers to discover and develop antivirals that target this interaction, such as statins, methyl-β-cyclodextrin, viperin, 25-hydroxycholesterol and even anti-malarial drugs. The therapeutic modulations of lipid rafts as potential antiviral intervention from in vitro and in vivo evidence are discussed herein.

Seneca Valley virus enters cells through multiple pathways and traffics intracellularly via the endolysosomal pathway

Seneca Valley virus (SVV, also known as Senecavirus A), an oncolytic virus, is a nonenveloped, positive-strand RNA virus and the sole member of the genus Senecavirus within the family Picornaviridae. The mechanisms of SVV entry into cells are currently almost unknown. In the present study, we found that SVV entry into HEK293T cells is acidic pH-dependent by using ammonium chloride (NH₄Cl) and chloroquine, both of which could inhibit SVV infection. We confirmed that dynamin II is required for SVV entry by using dynasore, silencing the dynamin II protein, or expressing the dominant-negative (DN) K44A mutant of dynamin II. Then, we discovered that chlorpromazine (CPZ) treatment or knockdown of the clathrin heavy chain (CLTC) protein significantly inhibited SVV infection. In addition, overexpression of CLTC promoted SVV infection. Caveolin-1 and membrane cholesterol were also required for SVV endocytosis. Notably, utilizing genistein, EIPA or nocodazole, we observed that macropinocytosis and microtubules are not involved in SVV entry. Furthermore, overexpression of the Rab7 and Rab9 proteins but not the Rab5 or Rab11 proteins promoted SVV infection. The findings were further validated by the knockdown of four Rabs and Lamp1 proteins, indicating that after internalization, SVV is transported from late endosomes to the trans-Golgi network (TGN) or lysosomes, respectively, eventually releasing its RNA into the cytosol from the lysosomes. Our findings concretely revealed SVV endocytosis mechanisms in HEK293T cells and provided an insightful theoretical foundation for further research into SVV oncolytic mechanisms.

Combating coxsackievirus B infections

Coxsackieviruses B (CVB) are small, non-enveloped, single-stranded RNA viruses belonging to the Enterovirus genus of the Picornaviridae family. They are common worldwide and cause a wide variety of human diseases ranging from those having relatively mild symptoms to severe acute and chronic pathologies such as cardiomyopathy and type 1 diabetes. The development of safe and effective strategies to combat these viruses remains a challenge. The present review outlines current approaches to control CVB infections and associated diseases. Various drugs targeting viral or host proteins involved in viral replication as well as vaccines have been developed and shown potential to prevent or combat CVB infections in vitro and in vivo in animal models. Repurposed drugs and alternative strategies targeting miRNAs or based on plant extracts and probiotics and their derivatives have also shown antiviral effects against CVB. In addition, clinical trials with vaccines and drugs are underway and offer hope for the prevention or treatment of CVB-induced diseases.

Exosomes released from cisplatin-resistant ovarian cancer cells modulate the reprogramming of cells in tumor microenvironments toward the cancerous cells

Exosomes released from cancer cells are involved in the reorganization of the tumor microenvironment which is the essential aspect of cancer pathogenesis. The intercommunications between cancer cells and diverse cell types in the microenvironment are accomplished by exosomes in ovarian cancer. Internalization pathway, intracellular fate, and biological functions in recipient cells mediated by exosomes released from cisplatin-resistant A2780cis have been studied. Also, histopathological evaluation of tumor, ovary, liver tissues and lymph nodes in vivo studies have been performed. The recipient cells internalized the exosomes via active uptake mechanisms, as shown by confocal microscopy. However, inhibitor studies and flow cytometry analysis showed that each recipient cell line used different uptake pathways. Also, confocal microscopy imaging indicated that the internalized exosomes trapped in the endosomes or phagosomes were distributed to the different cellular compartments including ER, Golgi, and lysosome. The transfer of exosomal oncogenic cargo into the cells modified the intracellular signaling of recipient cells including invasion and metastasis by Boyden-Chamber assay, proliferation by ATP analysis, epithelial-mesenchymal transition (EMT) markers at protein and mRNA levels by western blotting and real-time PCR, and protein kinases in the phospho-kinase array. This remodeling contributed to the initiation of carcinogenesis in ovarian epithelial and peritoneal mesothelial cells, and the progression of carcinogenesis in ovarian cancer cells. In addition, intraperitoneal tumor model studies show that exosomes released from cisplatin-resistant A2780cis cells may play role in the enlargement of lymph nodes, and tumor formations integrated with the liver, attached to the stomach and in the ovarian tissues.

Proteomic and metabonomic analysis uncovering Enterovirus A71 reprogramming host cell metabolic pathway

Enterovirus A71 (EV71) infection can cause hand, foot, and mouth disease (HFMD) and severe neurological complications in children. However, the biological processes regulated by EV71 remain poorly understood. Herein, proteomics and metabonomics studies were conducted to uncover the mechanism of EV71 infection in rhabdomyosarcoma (RD) cells and identify potential drug targets. Differential expressed proteins from enriched membrane were analyzed by isobaric tags for relative and absolute quantitation (iTRAQ)-based proteomics technology. Twenty-six differential proteins with 1.5-fold (p < 0.05) change were detected, including 14 upregulated proteins and 12 downregulated proteins. The upregulated proteins are mainly involved in metabolic process, especially in the glycolysis pathway. Alpha-enolase (ENO1) protein was found to increase with temporal dependence following EV71 infection. The targeted metabolomics analysis revealed that glucose absorption and glycolysis metabolites were increased after EV71 infection. The glycolysis pathway was inhibited by knocking down ENO1 or the use of a glycolysis inhibitor (dichloroacetic acid [DCA]); and we found that EV71 infection was inhibited by depleting ENO1 or using DCA. Our study indicates that EV71 may reprogram glucose metabolism by activating glycolysis, and EV71 infection can be inhibited by interrupting the glycolysis pathway. ENO1 may be a potential target against EV71, and DCA could act as an inhibitor of EV71.

Insight into the role of clathrin-mediated endocytosis inhibitors in SARS-CoV-2 infection

Emergence of SARS-CoV-2 variants warrants sustainable efforts to upgrade both the diagnostic and therapeutic protocols. Understanding the details of cellular and molecular basis of the virus-host cell interaction is essential for developing variant-independent therapeutic options. The internalization of SARS-CoV-2, into lung epithelial cells, is mediated by endocytosis, especially clathrin-mediated endocytosis (CME). Although vaccination is the gold standard strategy against viral infection, selective inhibition of endocytic proteins, complexes, and associated adaptor proteins may present a variant-independent therapeutic strategy. Although clathrin and/or dynamins are the most important proteins involved in CME, other endocytic mechanisms are clathrin and/or dynamin independent and rely on other proteins. Moreover, endocytosis implicates some subcellular structures, like plasma membrane, actin and lysosomes. Also, physiological conditions, such as pH and ion concentrations, represent an additional factor that mediates these events. Accordingly, endocytosis related proteins are potential targets for small molecules that inhibit endocytosis-mediated viral entry. This review summarizes the potential of using small molecules, targeting key proteins, participating in clathrin-dependent and -independent endocytosis, as variant-independent antiviral drugs against SARS-CoV-2 infection. The review takes two approaches. The first outlines the potential role of endocytic inhibitors in preventing endocytosis-mediated viral entry and its mechanism of action, whereas in the second computational analysis was implemented to investigate the selectivity of common inhibitors against endocytic proteins in SARS-CoV-2 endocytosis. The analysis revealed that remdesivir, methyl-β-cyclodextrin, rottlerin, and Bis-T can effectively inhibit clathrin, HMG-CoA reductase, actin, and dynamin I GTPase and are more potent in inhibiting SARS-CoV-2 than chloroquine. CME inhibitors for SARS-CoV-2 infection remain understudied.

Excipient-Free Ionizable Polyester Nanoparticles for Lung-Selective and Innate Immune Cell Plasmid DNA and mRNA Transfection

Extrahepatic nucleic acid delivery using polymers typically requires the synthesis and purification of custom monomers, post-synthetic modifications, and incorporation of additional excipients to augment their stability, endosomal escape, and in vivo effectiveness. Here, we report the development of a single-component and excipient-free, polyester-based nucleic acid delivery nanoparticle platform comprising ionizable N-methyldiethanolamine (MDET) and various hydrophobic alkyl diols (Cp) that achieves lung-selective nucleic acid transfection in vivo. PolyMDET and polyMDET-Cp polyplexes displayed high serum and enzymatic stability, while delivering pDNA or mRNA to "hard-to-transfect" innate immune cells. PolyMDET-C4 and polyMDET-C6 mediated high protein expression in lung alveolar macrophages and dendritic cells without inducing tissue damage or systemic inflammatory responses. Improved strategies using readily available starting materials to produce a simple, excipient-free, non-viral nucleic acid delivery platform with lung-selective and innate immune cell tropism has the potential to expedite clinical deployment of polymer-based genetic medicines.

The endocytosis of foot-and mouth disease virus requires clathrin and caveolin and is dependent on the existence of Rab5 and Rab7 in CHO-677 cells

Foot-and-mouth disease virus (FMDV) is a highly contagious virus that causes severe vesicular disease of cloven-hoofed animals. Various endocytosis mechanisms are involved in the entry of FMDV after binding to the integrin and heparan sulfate (HS) receptors. However, the mechanism of FMDV using other unknown receptors to enter the cells remains unclear. Here, we reported that the endocytosis and endosomal pathways are employed by FMDV to invade the Chinese hamster ovary cell line (CHO-677) without the integrin and HS receptors. We demonstrated that the internalization of FMDV into CHO-677 cells was abrogated by chlorpromazine, an inhibitor of clathrin-mediated endocytosis. Knockdown of the clathrin heavy chain decreased the viral protein abundance. Incubation of the CHO-677 cells with the inhibitors of caveolae-mediated endocytosis or transfection by caveolin-1 siRNA also limited FMDV replication. In addition, we determined that the acidic environment and the existence of dynamin were essential for FMDV infection in CHO-677 cells. The endosomal proteins Rab5 (early endosome) and Rab7 (late endosome), but not Rab11 (recycling endosome), were utilized by FMDV during infection. These data provide a new entry model of FMDV by unknown receptors which will help to better understand the pathogenesis mediated by FMDV.

Respiratory syncytial virus infection changes the piwi-interacting RNA content of airway epithelial cells

Piwi-interacting RNAs (piRNAs) are small non-coding RNAs (sncRNAs) of about 26–32 nucleotides in length and represent the largest class of sncRNA molecules expressed in animal cells. piRNAs have been shown to play a crucial role to safeguard the genome, maintaining genome complexity and integrity, as they suppress the insertional mutations caused by transposable elements. However, there is growing evidence for the role of piRNAs in controlling gene expression in somatic cells as well. Little is known about changes in piRNA expression and possible function occurring in response to viral infections. In this study, we investigated the piRNA expression profile, using a human piRNA microarray, in human small airway epithelial (SAE) cells infected with respiratory syncytial virus (RSV), a leading cause of acute respiratory tract infections in children. We found a time-dependent increase in piRNAs differentially expressed in RSV-infected SAE cells. We validated the top piRNAs upregulated and downregulated at 24 h post-infection by RT-qPCR and identified potential targets. We then used Gene Ontology (GO) tool to predict the biological processes of the predicted targets of the most represented piRNAs in infected cells over the time course of RSV infection. We found that the most significant groups of targets of regulated piRNAs are related to cytoskeletal or Golgi organization and nucleic acid/nucleotide binding at 15 and 24 h p.i. To identify common patterns of time-dependent responses to infection, we clustered the significantly regulated expression profiles. Each of the clusters of temporal profiles have a distinct set of potential targets of the piRNAs in the cluster Understanding changes in piRNA expression in RSV-infected airway epithelial cells will increase our knowledge of the piRNA role in viral infection and might identify novel therapeutic targets for viral lung-mediated diseases.

Interaction network of African swine fever virus structural protein p30 with host proteins

African swine fever virus (ASFV) is a complex nucleocytoplasmic large DNA virus (NCLDV) that causes a lethal hemorrhagic disease that is currently threatening the global pig industry. ASFV structural protein p30 is a membrane phosphoprotein that suggests it may play a regulatory role, possibly in signal transduction. Despite its significance in internalization into host cells, the interaction between p30 and host proteins is relatively unknown. In this study, we describe the application of a DUALmembrane yeast two-hybrid assay to screen a primary porcine alveolar macrophages cDNA library and analyze the interactome of p30 protein. Our data identify seven host cellular proteins (DAB2, RPSA, OAS1, PARP9, CAPG, ARPC5, and VBP1) that putatively interact with the p30. We further verified the interaction between p30 and host proteins by laser confocal microscopy, co-immunoprecipitation, and GST-pulldown assay. To further understand the relationship between host proteins and p30, we drew the interaction network diagram and analyzed the functional enrichment of each host protein. Enrichment analysis of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes indicated that host proteins were mainly related to endocytosis, actin cytoskeleton regulation, and innate immunity. Collectively, we identified the interaction between p30 and host cell protein using a membrane protein yeast two-hybrid system, which increases our knowledge of the interaction between ASFV and the host and informs future research on antiviral strategies.

The uncoating of EV71 in mature late endosomes requires CD-M6PR

Enterovirus 71 (EV71) is one of the causative agents of hand-foot-and-mouth disease, which in some circumstances could lead to severe neurological diseases. Despite of its importance for human health, little is known about the early stages of EV71 infection. EV71 starts uncoating with its receptor, human scavenger receptor B2 (hSCARB2), at low pH. We show that EV71 was not targeted to lysosomes in human rhabdomyosarcoma cells overexpressing hSCARB2 and that the autophagic pathway is not essential for EV71 productive uncoating. Instead, EV71 was efficiently uncoated 30 minutes after infection in late endosomes (LEs) containing hSCARB2, mannose-6-phosphate receptor (M6PR), RAB9, bis(monoacylglycero)phosphate and lysosomal associated membrane protein 2 (LAMP2). Furthering the notion that mature LEs are crucial for EV71 uncoating, cation-dependent (CD)-M6PR knockdown impairs EV71 infection. Since hSCARB2 interacts with cation-independent (CI)-M6PR through M6P-binding sites and CD-M6PR also harbor a M6P-binding site, CD-M6PR is likely to play important roles in EV71 uncoating in LEs.

Dabie bandavirus Nonstructural Protein Interacts with Actin to Induce F-Actin Rearrangement and Inhibit Viral Adsorption and Entry

Dabie bandavirus (DBV) is an emerging Bandavirus that causes multiorgan failure with a high fatality rate in humans. While many viruses can manipulate the actin cytoskeleton to facilitate viral growth, the regulation pattern of the actin cytoskeleton and the molecular mechanisms involved in DBV entry into the host cells remain unclear. In this study, we demonstrate that expression of nonstructural protein (NSs) or infection with DBV induces actin rearrangement, which presents a point-like distribution, and this destruction is dependent on inclusion bodies (IBs). Further experiments showed that NSs inhibits viral adsorption by destroying the filopodium structure. In addition, NSs also compromised the viral entry by inhibiting clathrin aggregation on the cell surface and capturing clathrin into IBs. Furthermore, NSs induced clathrin light chain B (CLTB) degradation through the K48-linked ubiquitin proteasome pathway, which could negatively regulate clathrin-mediated endocytosis, inhibiting the viral entry. Finally, we confirmed that this NSs-induced antiviral mechanism is broadly applicable to other viruses, such as enterovirus 71 (EV71) and influenza virus, A/PR8/34 (PR8), which use the same clathrin-mediated endocytosis to enter host cells. In conclusion, our study provides new insights into the role of NSs in inhibiting endocytosis and a novel strategy for treating DBV infections. IMPORTANCEDabie bandavirus (DBV), a member of the Phenuiviridae family, is a newly emerging tick-borne pathogen that causes multifunctional organ failure and even death in humans. The actin cytoskeleton is involved in various crucial cellular processes and plays an important role in viral life activities. However, the relationship between DBV infection and the actin cytoskeleton has not been described in detail. Here, we show for the first time the interaction between NSs and actin to induce actin rearrangement, which inhibits the viral adsorption and entry. We also identify a key mechanism underlying NSs-induced entry inhibition in which NSs prevents clathrin aggregation on the cell surface by hijacking clathrin into the inclusion body and induces CLTB degradation through the K48-linked ubiquitination modification. This paper is the first to reveal the antiviral mechanism of NSs and provides a theoretical basis for the search for new antiviral targets.

SLC35B2 Acts in a Dual Role in the Host Sulfation Required for EV71 Infection

As an important neurotropic enterovirus, enterovirus 71 (EV71) is occasionally associated with severe neurological diseases and high mortality rates in infants and young children. Understanding the interaction between host factors and EV71 will play a vital role in developing antivirals and optimizing vaccines. Here, we performed a genome-wide CRISPR-Cas9 knockout screen and revealed that scavenger receptor class B member 2 (SCARB2), solute carrier family 35 member B2 (SLC35B2), and beta-1,3-glucuronyltransferase 3 (B3GAT3) are essential in facilitating EV71 replication. Subsequently, the exploration of molecular mechanisms suggested that the knockout of SLC35B2 or B3GAT3, not SCARB2, led to a remarkable decrease in the binding of EV71 to cells and internalization into cells. Furthermore, we found that the infection efficiency for EV71 was positively correlated with the level of host cell sulfation, not simply with the amount of heparan sulfate, suggesting that an unidentified sulfated protein(s) must contribute to EV71 infection. In support of this idea, we screened possible sulfated proteins among the proteinous receptors for EV71 and confirmed that SCARB2 could uniquely interact with both tyrosyl protein sulfotransferases in humans. We then performed mass spectrometric analysis of SCARB2, identifying five sites with tyrosine sulfation. The function verification test indicated that there were more than five tyrosine-sulfated sites on SCARB2. Finally, we constructed a model for EV71 entry in which both heparan sulfate and SCARB2 are regulated by SLC35B2 and act cooperatively to support viral binding, internalization, and uncoating. Taken together, this is the first time that we performed the pooled CRISPR-Cas9 genetic screening to investigate the interplay of host cells and EV71. Furthermore, we found that a novel host factor, SLC35B2, played a dual role in regulating the overall sulfation comprising heparan sulfate sulfation and protein tyrosine sulfation, which are critical for EV71 entry. IMPORTANCE As the most important nonpolio neurotropic enterovirus lacking specific treatments, EV71 can transmit to the central nervous system, leading to severe and fatal neurological complications in infants and young children. The identification of new factors that facilitate or inhibit EV71 replication is crucial to uncover the mechanisms of viral infection and pathogenesis. To date, only a few host factors involved in EV71 infection have been characterized. Herein, we conducted a genome-wide CRISPR-Cas9 functional knockout (GeCKO) screen for the first time to study EV71 in HeLa cells. The screening results are presented as a ranked list of candidates, including 518 hits in the positive selection that facilitate EV71 replication and 1,044 hits in the negative selection that may be essential for cell growth and survival or for suppressing EV71 infection. We subsequently concentrated on the top three hits in the positive selection: SCARB2, SLC35B2, and B3GAT3. The knockout of any of these three genes confers strong resistance against EV71 infection. We confirmed that EV71 infection is codependent on two receptors, heparan sulfate and SCARB2. We also identified a host entry factor, SLC35B2, indirectly facilitating EV71 infection through regulation of the host cell sulfation, and determined a novel posttranslational modification, protein tyrosine sulfation existing in SCARB2. This study revealed that EV71 infectivity exhibits a significant positive correlation with the level of cellular sulfation regulated by SLC35B2. Due to the sulfation pathway being required for many distinct viruses, including but not limited to EV71 and respiratory syncytial virus (RSV), which were tested in this study, SLC35B2 represents a target of broad-spectrum antiviral therapy.

Insight into the Enterovirus A71: A review

Enterovirus A71 is a major causative pathogen of hand, foot and mouth disease. It has become a global public health threat, and is especially important for infants and young children in the Asian-Pacific countries. The enterovirus A71 is a non-enveloped virus of the Picornaviridae family having a single-stranded positive-sense RNA genome of about 7.4 kb which encodes the structural and nonstructural proteins. Currently there are no US FDA-approved vaccines or antiviral therapy available against enterovirus A71 infection. Although enterovirus A71 vaccines have been licenced in China, clinically approved vaccines for widespread vaccination programs are lacking. Substantial progress has recently been achieved on understanding the structure and function of enterovirus A71 proteins together with information on the viral genetic diversity and geographic distribution. The present review is intended to provide an overview on our current understanding of the molecular biology and epidemiology of enterovirus A71 which will aid the development of vaccines, therapeutics and other control strategies so as to bolster the preparedness for future enterovirus A71 outbreaks.

Antidepressant Sertraline Is a Broad-Spectrum Inhibitor of Enteroviruses Targeting Viral Entry through Neutralization of Endolysosomal Acidification

Enterovirus 71 (EV71) is an etiological agent of hand foot and mouth disease and can also cause neurological complications in young children. However, there are no approved drugs as of yet to treat EV71 infections. In this study, we conducted antiviral drug screening by using a Food and Drug Administration (FDA)-approved drug library. We identified five drugs that showed dose-dependent inhibition of viral replication. Sertraline was further characterized because it exhibited the most potent antiviral activity with the highest selectivity index among the five hits. The antiviral activity of sertraline was noted for other EV serotypes. The drug’s antiviral effect is not likely associated with its approved indications as an antidepressant and its mode-of-action as a selective serotonin reuptake inhibitor. The time-of-addition assay revealed that sertraline inhibited an EV71 infection at the entry stage. We also showed that sertraline partitioned into acidic compartments, such as endolysosomes, to neutralize the low pH levels. In agreement with the findings, the antiviral effect of sertraline could be greatly relieved by exposing virus-infected cells to extracellular low-pH culture media. Ultimately, we have identified a use for an FDA-approved antidepressant in broad-spectrum EV inhibition by blocking viral entry through the alkalization of the endolysosomal route.

Role of adaptin protein complexes in intracellular trafficking and their impact on diseases

Adaptin proteins (APs) play a crucial role in intracellular cell trafficking. The 'classical' role of APs is carried out by AP1‒3, which bind to clathrin, cargo, and accessory proteins. Accordingly, AP1-3 are crucial for both vesicle formation and sorting. All APs consist of four subunits that are indispensable for their functions. In fact, based on studies using cells, model organism knockdown/knock-out, and human variants, each subunit plays crucial roles and contributes to the specificity of each AP. These studies also revealed that the sorting and intracellular trafficking function of AP can exert varying effects on pathology by controlling features such as cell development, signal transduction related to the apoptosis and proliferation pathways in cancer cells, organelle integrity, receptor presentation, and viral infection. Although the roles and functions of AP1‒3 are relatively well studied, the functions of the less abundant and more recently identified APs, AP4 and AP5, are still to be investigated. Further studies on these APs may enable a better understanding and targeting of specific diseases.APs known or suggested locations and functions.

Involvement of adaptor proteins in clathrin-mediated endocytosis of virus entry

The first step in the initiation of effective viral infection is breaking through the cytomembrane to enter the cell. Clathrin-mediated endocytosis is a key vesicular trafficking process in which a variety of cargo molecules are transported from the outside to the inside of the cell. This process is hijacked by numerous families of enveloped or non-enveloped viruses, which use it to enter host cells, followed by trafficking to their replicating sites. Various adaptor proteins that assist in cargo selection, coat assembly, and clathrin-coated bud maturation are important in this process. Research data documented on the involvement of adaptor proteins, such as AP-2, Eps-15, Epsin1, and AP180/CALM, in the invasion of viruses via the clathrin-mediated endocytosis have provided novel insights into understanding the viral life cycle and have led to the development of novel therapeutics. Here, we summarize the latest discoveries on the role of these adaptor proteins in clathrin-mediated endocytosis of virus entry and also discuss the future trends in this field.

Heat Shock Protein A6, a Novel HSP70, Is Induced During Enterovirus A71 Infection to Facilitate Internal Ribosomal Entry Site-Mediated Translation

Enterovirus A71 (EV-A71) is a human pathogen causing hand, foot, and mouth disease (HFMD) in children. Its infection can lead to severe neurological diseases or even death in some cases. While being produced in a large quantity during infection, viral proteins often require the assistance from cellular chaperones for proper folding. In this study, we found that heat shock protein A6 (HSPA6), whose function in viral life cycle is scarcely studied, was induced and functioned as a positive regulator for EV-A71 infection. Depletion of HSPA6 led to the reductions of EV-A71 viral proteins, viral RNA and virions as a result of the downregulation of internal ribosomal entry site (IRES)-mediated translation. Unlike other HSP70 isoforms such as HSPA1, HSPA8, and HSPA9, which regulate all phases of the EV-A71 life, HSPA6 was required for the IRES-mediated translation only. Unexpectedly, the importance of HSPA6 in the IRES activity could be observed in the absence of viral proteins, suggesting that HSPA6 facilitated IRES activity through cellular factor(s) instead of viral proteins. Intriguingly, the knockdown of HSPA6 also caused the reduction of luciferase activity driven by the IRES from coxsackievirus A16, echovirus 9, encephalomyocarditis virus, or hepatitis C virus, supporting that HSPA6 may assist the function of a cellular protein generally required for viral IRES activities.

Strategy, Progress, and Challenges of Drug Repurposing for Efficient Antiviral Discovery

Emerging or re-emerging viruses are still major threats to public health. Prophylactic vaccines represent the most effective way to prevent virus infection; however, antivirals are more promising for those viruses against which vaccines are not effective enough or contemporarily unavailable. Because of the slow pace of novel antiviral discovery, the high disuse rates, and the substantial cost, repurposing of the well-characterized therapeutics, either approved or under investigation, is becoming an attractive strategy to identify the new directions to treat virus infections. In this review, we described recent progress in identifying broad-spectrum antivirals through drug repurposing. We defined the two major categories of the repurposed antivirals, direct-acting repurposed antivirals (DARA) and host-targeting repurposed antivirals (HTRA). Under each category, we summarized repurposed antivirals with potential broad-spectrum activity against a variety of viruses and discussed the possible mechanisms of action. Finally, we proposed the potential investigative directions of drug repurposing.

Recent advances in the understanding of enterovirus A71 infection: a focus on neuropathogenesis

Introduction: Hand, foot, and mouth disease caused by enterovirus A71 (EV-A71) is more frequently associated with neurological complications and deaths compared to other enteroviruses.Areas covered: The authors discuss current understanding of the neuropathogenesis of EV-A71 based on various clinical, human, and animal model studies. The authors discuss the important advancements in virus entry, virus dissemination, and neuroinvasion. The authors highlight the role of host immune system, host genetic factors, viral quasispecies, and heparan sulfate in EV-A71 neuropathogenesis.Expert opinion: Comparison of EV-A71 with EV-D68 and PV shows similarity in primary target sites and dissemination to the central nervous system. More research is needed to understand cellular tropisms, persistence of EV-A71, and other possible invasion routes. EV-A71 infection has varied clinical manifestations which may be attributed to multiple receptors usage. Future development of antivirals and vaccines should target neurotropic enteroviruses. Repurposing drug and immunomodulators used in combination could reduce the severity of EV-A71 infection. Only a few drugs have been tested in clinical trials, and in the absence of antiviral and vaccines (except China), active virus surveillance, good hand hygiene, and physical distancing should be advocated. A better understanding of EV-A71 neuropathogenesis is critical for antiviral and multivalent vaccines development.

Honeysuckle Aqueous Extracts Induced let-7a Suppress EV71 Replication and Pathogenesis In Vitro and In Vivo and Is Predicted to Inhibit SARS-CoV-2

Honeysuckle (Lonicera japonica Thunb) is a traditional Chinese medicine (TCM) with an antipathogenic activity. MicroRNAs (miRNAs) are small non-coding RNA molecules that are ubiquitously expressed in cells. Endogenous miRNA may function as an innate response to block pathogen invasion. The miRNA expression profiles of both mice and humans after the ingestion of honeysuckle were obtained. Fifteen overexpressed miRNAs overlapped and were predicted to be capable of targeting three viruses: dengue virus (DENV), enterovirus 71 (EV71) and SARS-CoV-2. Among them, let-7a was examined to be capable of targeting the EV71 RNA genome by reporter assay and Western blotting. Moreover, honeysuckle-induced let-7a suppression of EV71 RNA and protein expression as well as viral replication were investigated both in vitro and in vivo. We demonstrated that let-7a targeted EV71 at the predicted sequences using luciferase reporter plasmids as well as two infectious replicons (pMP4-y-5 and pTOPO-4643). The suppression of EV71 replication and viral load was demonstrated in two cell lines by luciferase activity, RT-PCR, real-time PCR, Western blotting and plaque assay. Furthermore, EV71-infected suckling mice fed honeysuckle extract or inoculated with let-7a showed decreased clinical scores and a prolonged survival time accompanied with decreased viral RNA, protein expression and virus titer. The ingestion of honeysuckle attenuates EV71 replication and related pathogenesis partially through the upregulation of let-7a expression both in vitro and in vivo. Our previous report and the current findings imply that both honeysuckle and upregulated let-7a can execute a suppressive function against the replication of DENV and EV71. Taken together, this evidence indicates that honeysuckle can induce the expression of let-7a and that this miRNA as well as 11 other miRNAs have great potential to prevent and suppress EV71 replication.

Surface functionalization of zeolite-based drug delivery systems enhances their antitumoral activity in vivo

Zeolites have attractive features making them suitable carriers for drug delivery systems (DDS). As such, we loaded the anticancer drug 5-fluorouracil (5-FU), into two different zeolite structures, faujasite (NaY) and Linde Type L (LTL), to obtain different DDS. The prepared DDS were tested in vitro using breast cancer, colorectal carcinoma, and melanoma cell lines and in vivo using the chick embryo chorioallantoic membrane model (CAM). Both assays showed the best results for the Hs578T breast cancer cells, with a higher potentiation for 5-FU encapsulated in the zeolite LTL. To unveil the endocytic mechanisms involved in the internalization of the zeolite nanoparticles, endocytosis was inhibited pharmacologically in breast cancer and epithelial mammary human cells. The results suggest that a caveolin-mediated process was responsible for the internalized zeolite nanoparticles. Aiming to boost the DDS efficacy, the disc-shaped zeolite LTL outer surface was functionalized using amino (NH₂) or carboxylic acid (COOH) groups and coated with poly-l-lysine (PLL). Positively functionalized surface LTL nanoparticles revealed to be non-toxic to human cells and, importantly, their internalization was faster and led to a higher tumor reduction in vivo. Overall, our results provide further insights into the mechanisms of interaction between zeolite-based DDS and cancer cells, and pave the way for future studies aiming to improve DDS anticancer activity.

Enterovirus D68 molecular and cellular biology and pathogenesis

In recent years, enterovirus D68 (EV-D68) has advanced from a rarely detected respiratory virus to a widespread pathogen responsible for increasing rates of severe respiratory illness and acute flaccid myelitis (AFM) in children worldwide. In this review, we discuss the accumulating data on the molecular features of EV-D68 and place these into the context of enterovirus biology in general. We highlight similarities and differences with other enteroviruses and genetic divergence from own historical prototype strains of EV-D68. These include changes in capsid antigens, host cell receptor usage, and viral RNA metabolism collectively leading to increased virulence. Furthermore, we discuss the impact of EV-D68 infection on the biology of its host cells, and how these changes are hypothesized to contribute to motor neuron toxicity in AFM. We highlight areas in need of further research, including the identification of its primary receptor and an understanding of the pathogenic cascade leading to motor neuron injury in AFM. Finally, we discuss the epidemiology of the EV-D68 and potential therapeutic approaches.

Echovirus-30 Infection Alters Host Proteins in Lipid Rafts at the Cerebrospinal Fluid Barrier In Vitro

Echovirus-30 (E-30) is a non-polio enterovirus responsible for meningitis outbreaks in children worldwide. To gain access to the central nervous system (CNS), E-30 first has to cross the blood-brain barrier (BBB) or the blood-cerebrospinal fluid barrier (BCSFB). E-30 may use lipid rafts of the host cells to interact with and to invade the BCSFB. To study enteroviral infection of the BCSFB, an established in vitro model based on human immortalized brain choroid plexus papilloma (HIBCPP) cells has been used. Here, we investigated the impact of E-30 infection on the protein content of the lipid rafts at the BCSFB in vitro. Mass spectrometry analysis following E-30 infection versus uninfected conditions revealed differential abundancy in proteins implicated in cellular adhesion, cytoskeleton remodeling, and endocytosis/vesicle budding. Further, we evaluated the blocking of endocytosis via clathrin/dynamin blocking and its consequences for E-30 induced barrier disruption. Interestingly, blocking of endocytosis had no impact on the capacity of E-30 to induce loss of barrier properties in HIBCPP cells. Altogether, these data highlight the impact of E-30 on HIBCPP cells microdomain as an important factor for host cell alteration.

Rac1-dependent endocytosis and Rab5-dependent intracellular trafficking are required by Enterovirus A71 and Coxsackievirus A10 to establish infections

Enterovirus A71 (EVA71) and Coxsackievirus A10 (CVA10) are representative types of Enterovirus A. Dependent on the host cell types, the EVA71 entry may utilize clathrin-, caveola-, and endophilin-A2-mediated endocytosis. However, the cell-entry and intracellular trafficking pathways of CVA10, using KREMEN1 as its receptor, are unclear. Here, we tested the relevant mechanisms through RNA interference (RNAi) and chemical inhibitors. We found that endocytosis of EVA71 and CVA10 in rhabdomyosarcoma (RD) cells engaged multiple pathways, and both viruses required Rac1. Interestingly, while CDC42 and Pak1 participated in EVA71 infection, PI3K played a role in CVA10 infection. The functions of Rab proteins in intracellular trafficking of CVA10 and EVA71 were examined by RNAi. Knockdown of Rab5 and Rab21 significantly reduced CVA10 infectivity, while knockdown of Rab5, Rab7 and Rab9 reduced EVA71 infectivity. Confocal microscopy confirmed the colocalization of CVA10 virions with Rab5 or Rab21, and colocalization of EVA71 virions with Rab5 or Rab7. Additionally, we observed that both CVA10 and EVA71 infections were inhibited by endosome acidification inhibitors, bafilomycin-A1 and NH₄Cl. Together, our findings comparatively illustrate the entry and intracellular trafficking processes of representative Enterovirus A types and revealed novel enterovirus intervention targets.

Entry of Epidemic Keratoconjunctivitis-Associated Human Adenovirus Type 37 in Human Corneal Epithelial Cells

Purpose

Ocular infection by human adenovirus species D type 37 (HAdV-D37) causes epidemic keratoconjunctivitis, a severe, hyperacute condition. The corneal component of epidemic keratoconjunctivitis begins upon infection of corneal epithelium, and the mechanism of viral entry dictates subsequent proinflammatory gene expression. Therefore, it is important to understand the specific pathways of adenoviral entry in these cells.

Methods

Transmission electron microscopy of primary and tert-immortalized human corneal epithelial cells infected with HAdV-D37 was performed to identify the means of viral entry. Confocal microscopy was used to determine intracellular trafficking. The results of targeted small interfering RNA and specific chemical inhibitors were analyzed by quantitative PCR, and Western blot.

Results

By transmission electron microscopy, HAdV-D37 was seen to enter by both clathrin-coated pits and macropinocytosis; however, entry was both pH and dynamin 2 independent. Small interfering RNA against clathrin, AP2A1, and lysosome-associated membrane protein 1, but not early endosome antigen 1, decreased early viral gene expression. Ethyl-isopropyl amiloride, which blocks micropinocytosis, did not affect HAdV-D37 entry, but IPA, an inhibitor of p21-activated kinase, and important to actin polymerization, decreased viral entry in a dose-dependent manner.

Conclusions

HAdV-D37 enters human corneal epithelial cells by a noncanonical clathrin-mediated pathway involving lysosome-associated membrane protein 1 and PAK1, independent of pH, dynamin, and early endosome antigen 1. We showed earlier that HAdV-D37 enters human keratocytes through caveolae. Therefore, epidemic keratoconjunctivitis-associated viruses enter different corneal cell types via disparate pathways, which could account for a relative paucity of proinflammatory gene expression upon infection of corneal epithelial cells compared with keratocytes, as seen in prior studies.

Molecular basis of Coxsackievirus A10 entry using the two-in-one attachment and uncoating receptor KRM1

KREMEN1 (KRM1) has been identified as a functional receptor for Coxsackievirus A10 (CV-A10), a causative agent of hand-foot-and-mouth disease (HFMD), which poses a great threat to infants globally. However, the underlying mechanisms for the viral entry process are not well understood. Here we determined the atomic structures of different forms of CV-A10 viral particles and its complex with KRM1 in both neutral and acidic conditions. These structures reveal that KRM1 selectively binds to the mature viral particle above the canyon of the viral protein 1 (VP1) subunit and contacts across two adjacent asymmetry units. The key residues for receptor binding are conserved among most KRM1-dependent enteroviruses, suggesting a uniform mechanism for receptor binding. Moreover, the binding of KRM1 induces the release of pocket factor, a process accelerated under acidic conditions. Further biochemical studies confirmed that receptor binding at acidic pH enabled CV-A10 virion uncoating in vitro. Taken together, these findings provide high-resolution snapshots of CV-A10 entry and identify KRM1 as a two-in-one receptor for enterovirus infection.

The Heat Shock Protein 70 Family of Chaperones Regulates All Phases of the Enterovirus A71 Life Cycle

Enterovirus A71 (EV-A71) is one of the major etiologic agents causing hand, foot, and mouth disease (HFMD) in children and occasionally causes severe neurological diseases or even death. EV-A71 replicates rapidly in host cells. For a successful infection, viruses produce large quantities of viral proteins in a short period, which requires cellular chaperone proteins for viral protein folding and viral particle assembly. In this study, we explored the roles of the heat shock protein 70 (HSP70) chaperone subnetwork in the EV-A71 life cycle. Our results revealed that EV-A71 exploits multiple HSP70s at each step of the viral life cycle, i.e., viral entry, translation, replication, assembly and release, and that each HSP70 typically functions in several stages of the life cycle. For example, the HSP70 isoforms HSPA1, HSPA8, and HSPA9 are required for viral entry and the translational steps of the infection. HSPA8 and HSPA9 may facilitate folding and stabilize viral proteins 3D and 2C, respectively, thus contributing to the formation of a replication complex. HSPA8 and HSPA9 also promote viral particle assembly, whereas HSPA1 and HSPA8 are involved in viral particle release. Because of the importance of various HSP70s at distinct steps of the viral life cycle, an allosteric inhibitor, JG40, which targets all HSP70s, significantly blocks EV-A71 infection. JG40 also blocks the replication of several other enteroviruses, such as coxsackievirus (CV) A16, CVB1, CVB3, and echovirus 11. Thus, targeting HSP70s may be a means of providing broad-spectrum antiviral therapy.

Hsv-1 Endocytic Entry into a Human Oligodendrocytic Cell Line is Mediated by Clathrin and Dynamin but Not Caveolin

Endocytosis is a pathway used by viruses to enter cells that can be classified based on the proteins involved, such as dynamin, clathrin or caveolin. Although the entry of herpes simplex type 1 (HSV-1) by endocytosis has been documented in different cell types, its dependence on clathrin has not been described whereas its dependence on dynamin has been shown according to the cell line used. The present work shows how clathrin-mediated endocytosis (CME) is one way that HSV-1 infects the human oligodendroglial (HOG) cell line. Partial dynamin inhibition using dynasore revealed a relationship between decrease of infection and dynamin inhibition, measured by viral titration and immunoblot. Co-localization between dynamin and HSV-1 was verified by immunofluorescence at the moment of viral entry into the cell. Inhibition by chlorpromazine revealed that viral progeny also decreased when clathrin was partially inhibited in our cell line. RT-qPCR of immediately early viral genes, specific entry assays and electron microscopy all confirmed clathrin's participation in HSV-1 entry into HOG cells. In contrast, caveolin entry assays showed no effect on the entry of this virus. Therefore, our results suggest the participation of dynamin and clathrin during endocytosis of HSV-1 in HOG cells.

Silicon-Nanotube-Mediated Intracellular Delivery Enables Ex Vivo Gene Editing

Engineered nano-bio cellular interfaces driven by vertical nanostructured materials are set to spur transformative progress in modulating cellular processes and interrogations. In particular, the intracellular delivery-a core concept in fundamental and translational biomedical research-holds great promise for developing novel cell therapies based on gene modification. This study demonstrates the development of a mechanotransfection platform comprising vertically aligned silicon nanotube (VA-SiNT) arrays for ex vivo gene editing. The internal hollow structure of SiNTs allows effective loading of various biomolecule cargoes; and SiNTs mediate delivery of those cargoes into GPE86 mouse embryonic fibroblasts without compromising their viability. Focused ion beam scanning electron microscopy (FIB-SEM) and confocal microscopy results demonstrate localized membrane invaginations and accumulation of caveolin-1 at the cell-NT interface, suggesting the presence of endocytic pits. Small-molecule inhibition of endocytosis suggests that active endocytic process plays a role in the intracellular delivery of cargo from SiNTs. SiNT-mediated siRNA intracellular delivery shows the capacity to reduce expression levels of F-actin binding protein (Triobp) and alter the cellular morphology of GPE86. Finally, the successful delivery of Cas9 ribonucleoprotein (RNP) to specifically target mouse Hprt gene is achieved. This NT-enhanced molecular delivery platform has strong potential to support gene editing technologies.

Efficient cellular uptake of click nucleic acid modified proteins

Efficient intracellular delivery of biomacromolecules such as proteins continues to remain a challenge despite its potential for medicine. In this work, we show that mScarlet, a non cytotoxic red fluorescent protein (RFP) conjugated to Click Nucleic Acid (CNA), a synthetic analog of DNA, undergo cell uptake significantly more than either native proteins or proteins conjugated with similar amounts of DNA in MDA-MB-468 cells. We further demonstrate that the process of cell uptake is metabolically driven and that scavenger receptors and caveolae mediated endocytosis play a significant role. Co-localization studies using anti-scavenger receptor antibodies suggest that scavenger receptors are implicated in the mechanism of uptake of CNA modified proteins.

Molecular Pathogenicity of Enteroviruses Causing Neurological Disease

Enteroviruses are single-stranded positive-sense RNA viruses that primarily cause self-limiting gastrointestinal or respiratory illness. In some cases, these viruses can invade the central nervous system, causing life-threatening neurological diseases including encephalitis, meningitis and acute flaccid paralysis (AFP). As we near the global eradication of poliovirus, formerly the major cause of AFP, the number of AFP cases have not diminished implying a non-poliovirus etiology. As the number of enteroviruses linked with neurological disease is expanding, of which many had previously little clinical significance, these viruses are becoming increasingly important to public health. Our current understanding of these non-polio enteroviruses is limited, especially with regards to their neurovirulence. Elucidating the molecular pathogenesis of these viruses is paramount for the development of effective therapeutic strategies. This review summarizes the clinical diseases associated with neurotropic enteroviruses and discusses recent advances in the understanding of viral invasion of the central nervous system, cell tropism and molecular pathogenesis as it correlates with host responses.

PEDV enters cells through clathrin-, caveolae-, and lipid raft-mediated endocytosis and traffics via the endo-/lysosome pathway

With the emergence of highly pathogenic variant strains, porcine epidemic diarrhea virus (PEDV) has led to significant economic loss in the global swine industry. Many studies have described how coronaviruses enter cells, but information on PEDV invasion strategies remains insufficient. Given that the differences in gene sequences and pathogenicity between classical and mutant strains of PEDV may lead to diverse invasion mechanisms, this study focused on the cellular entry pathways and cellular transport of the PEDV GI and GII subtype strains in Vero cells and IPEC-J2 cells. We first characterized the kinetics of PEDV entry into cells and found that the highest invasion rate of PEDV was approximately 33% in the IPEC-J2 cells and approximately 100% in the Vero cells. To clarify the specific endocytic pathways, systematic research methods were used and showed that PEDV enters cells via the clathrin- and caveolae-mediated endocytosis pathways, in which dynamin II, clathrin heavy chain, Eps15, cholesterol, and caveolin-1 were indispensably involved. In addition, lipid raft extraction assay showed that PEDV can also enter cells through lipid raft-mediated endocytosis. To investigate the trafficking of internalized PEDV, we found that PEDV entry into cells relied on low pH and internalized virions reached lysosomes through the early endosome-late endosome-lysosome pathway. The results concretely revealed the entry mechanisms of PEDV and provided an insightful theoretical basis for the further understanding of PEDV pathogenesis and guidance for new targets of antiviral drugs.

Bioorthogonal Metabolic Labeling Utilizing Protein Biosynthesis for Dynamic Visualization of Nonenveloped Enterovirus 71 Infection

Bioorthogonal metabolic labeling through the endogenous cellular metabolic pathways (e.g., phospholipid and sugar) is a promising approach for effectively labeling live viruses. However, it remains a big challenge to label nonenveloped viruses due to lack of host-derived envelopes. Herein, a novel bioorthogonal labeling strategy is developed utilizing protein synthesis pathway to label and trace nonenveloped viruses. The results show that l-azidohomoalanine (Aha), an azido derivative of methionine, is more effective than azido sugars to introduce azido motifs into viral capsid proteins by substituting methionine residues during viral protein biosynthesis and assembly. The azide-modified EV71 (N₃-EV71) particles are then effectively labeled with dibenzocyclooctyl (DBCO)-functionalized fluorescence probes through an in situ bioorthogonal reaction with well-preserved viral infectivity. Dual-labeled imaging clearly clarifies that EV71 virions primarily bind to scavenger receptors and are internalized through clathrin-mediated endocytosis. The viral particles are then transported into early and late endosomes where viral RNA is released in a low-pH dependent manner at about 70 min postinfection. These results first reveal viral trafficking and uncoating mechanisms, which may shed light on the pathogenesis of EV71 infection and contribute to antiviral drug discovery.

Endophilin-A2-mediated endocytic pathway is critical for enterovirus 71 entry into caco-2 cells

Enterovirus 71 (EV71) is typically transmitted by the oral-faecal route and initiates infection upon crossing the intestinal mucosa. Our limited understanding of the mechanisms by which it crosses the intestinal mucosa has hampered the development of effective therapeutic options. Here, using an RNA interference screen combined with chemical inhibitors or the overexpression of dominant negative proteins, we found that EV71 entry into Caco-2 cells, a polarized human intestinal epithelial cell line, does not involve clathrin- and caveolae-dependent endocytic pathways or macropinocytosis but requires GTP-binding protein dynamin 2 and cytoskeleton remodelling. The use of siRNAs targeting endophilin family members revealed that endophlin-A2 is essential for the uptake of EV71 particles by Caco-2 cells. Subcellular analysis revealed that internalized EV71 virions largely colocalized with endophilin-A2 at cytomembrane ruffles and in the perinuclear area. Combined with viral entry kinetics, these data suggest that EV71 enters Caco-2 cells mainly via an endophilin-A2-mediated endocytic (EME) pathway. Finally, we showed that internalized EV71 virions were transported to endosomal sorting complex required for transport (ESCRT)-related multivesicular bodies (MVBs). These data provide attractive therapeutic targets to block EV71 infection.

The life cycle of non-polio enteroviruses and how to target it

The genus Enterovirus (EV) of the family Picornaviridae includes poliovirus, coxsackieviruses, echoviruses, numbered enteroviruses and rhinoviruses. These diverse viruses cause a variety of diseases, including non-specific febrile illness, hand-foot-and-mouth disease, neonatal sepsis-like disease, encephalitis, paralysis and respiratory diseases. In recent years, several non-polio enteroviruses (NPEVs) have emerged as serious public health concerns. These include EV-A71, which has caused epidemics of hand-foot-and-mouth disease in Southeast Asia, and EV-D68, which recently caused a large outbreak of severe lower respiratory tract disease in North America. Infections with these viruses are associated with severe neurological complications. For decades, most research has focused on poliovirus, but in recent years, our knowledge of NPEVs has increased considerably. In this Review, we summarize recent insights from enterovirus research with a special emphasis on NPEVs. We discuss virion structures, host-receptor interactions, viral uncoating and the recent discovery of a universal enterovirus host factor that is involved in viral genome release. Moreover, we briefly explain the mechanisms of viral genome replication, virion assembly and virion release, and describe potential targets for antiviral therapy. We reflect on how these recent discoveries may help the development of antiviral therapies and vaccines.

Bypassing pan-enterovirus host factor PLA2G16

Enteroviruses are a major cause of human disease. Adipose-specific phospholipase A2 (PLA2G16) was recently identified as a pan-enterovirus host factor and potential drug target. In this study, we identify a possible mechanism of PLA2G16 evasion by employing a dual glycan receptor-binding enterovirus D68 (EV-D68) strain. We previously showed that this strain does not strictly require the canonical EV-D68 receptor sialic acid. Here, we employ a haploid screen to identify sulfated glycosaminoglycans (sGAGs) as its second glycan receptor. Remarkably, engagement of sGAGs enables this virus to bypass PLA2G16. Using cryo-EM analysis, we reveal that, in contrast to sialic acid, sGAGs stimulate genome release from virions via structural changes that enlarge the putative openings for genome egress. Together, we describe an enterovirus that can bypass PLA2G16 and identify additional virion destabilization as a potential mechanism to circumvent PLA2G16.

Recent advances on the role of host factors during non-poliovirus enteroviral infections

Non-polio enteroviruses are emerging viruses known to cause outbreaks of polio-like infections in different parts of the world with several cases already reported in Asia Pacific, Europe and in United States of America. These outbreaks normally result in overstretching of health facilities as well as death in children under the age of five. Most of these infections are usually self-limiting except for the neurological complications associated with human enterovirus A 71 (EV-A71). The infection dynamics of these viruses have not been fully understood, with most inferences made from previous studies conducted with poliovirus.Non-poliovirus enteroviral infections are responsible for major outbreaks of hand, foot and mouth disease (HFMD) often associated with neurological complications and severe respiratory diseases. The myriad of disease presentations observed so far in children calls for an urgent need to fully elucidate the replication processes of these viruses. There are concerted efforts from different research groups to fully map out the role of human host factors in the replication cycle of these viral infections. Understanding the interaction between viral proteins and human host factors will unravel important insights on the lifecycle of this groups of viruses.This review provides the latest update on the interplay between human host factors/processes and non-polio enteroviruses (NPEV). We focus on the interactions involved in viral attachment, entry, internalization, uncoating, replication, virion assembly and eventual egress of the NPEV from the infected cells. We emphasize on the virus- human host interplay and highlight existing knowledge gaps that needs further studies. Understanding the NPEV-human host factors interactions will be key in the design and development of vaccines as well as antivirals against enteroviral infections. Dissecting the role of human host factors during NPEV infection cycle will provide a clear picture of how NPEVs usurp the human cellular processes to establish an efficient infection. This will be a boost to the drug and vaccine development against enteroviruses which will be key in control and eventual elimination of the viral infections.