An update on enterovirus 71 infection and interferon type I response

Pathoimmunological analyses of fatal E11 infection in premature infants

E11 causes acute fulminant hepatitis in newborns. We investigated the pathological changes of different tissues from premature male twins who died due to E11 infection. The E11 expression level was higher in the liver than in other tissues. IP10 was upregulated in liver tissue in the patient group, and might be regulated by IFNAR and IRF7, whereas IFNα was regulated by IFNAR or IRF5.

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.

The EV71 2A protease occupies the central cleft of SETD3 and disrupts SETD3-actin interaction

SETD3 is an essential host factor for the replication of a variety of enteroviruses that specifically interacts with viral protease 2A. However, the interaction between SETD3 and the 2A protease has not been fully characterized. Here, we use X-ray crystallography and cryo-electron microscopy to determine the structures of SETD3 complexed with the 2A protease of EV71 to 3.5 Å and 3.1 Å resolution, respectively. We find that the 2A protease occupies the V-shaped central cleft of SETD3 through two discrete sites. The relative positions of the two proteins vary in the crystal and cryo-EM structures, showing dynamic binding. A biolayer interferometry assay shows that the EV71 2A protease outcompetes actin for SETD3 binding. We identify key 2A residues involved in SETD3 binding and demonstrate that 2A's ability to bind SETD3 correlates with EV71 production in cells. Coimmunoprecipitation experiments in EV71 infected and 2A expressing cells indicate that 2A interferes with the SETD3-actin complex, and the disruption of this complex reduces enterovirus replication. Together, these results reveal the molecular mechanism underlying the interplay between SETD3, actin, and viral 2A during virus replication.

Modulation of plasmacytoid dendritic cell and CD4+ T cell differentiation accompanied by upregulation of the cholinergic anti-inflammatory pathway induced by enterovirus 71

Enterovirus 71 (EV71) is a neurotropic enterovirus associated with hand, foot, and mouth disease (HFMD) fatalities. In this study, we investigated the impact of EV71 on plasmacytoid dendritic cells (pDCs) and CD4+ T cells. The results showed that pDCs were promptly activated, secreting interferon (IFN)-α and inducing CD4+ T cell proliferation and differentiation during early EV71 infection. This initiated adaptive immune responses and promoted proinflammatory cytokine production by CD4+ T cells. Over time, viral nucleic acids and proteins were synthesized in pDCs and CD4+ T cells. Concurrently, the cholinergic anti-inflammatory pathway (CAP) was activated, exhibiting an anti-inflammatory role. With constant viral stimulation, pDCs and CD4+ T cells showed reduced differentiation and cytokine secretion. Defects in pDCs were identified as a key factor in CD4+ T cell tolerance. CAP had a more significant regulatory effect on CD4+ T cells than on pDCs and was capable of inhibiting inflammation in these cells.

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.

Non-small cell lung cancers (NSCLCs) oncolysis using coxsackievirus B5 and synergistic DNA-damage response inhibitors

With the continuous in-depth study of the interaction mechanism between viruses and hosts, the virus has become a promising tool in cancer treatment. In fact, many oncolytic viruses with selectivity and effectiveness have been used in cancer therapy. Human enterovirus is one of the most convenient sources to generate oncolytic viruses, however, the high seroprevalence of some enteroviruses limits its application which urges to exploit more oncolytic enteroviruses. In this study, coxsackievirus B5/Faulkner (CV-B5/F) was screened for its potential oncolytic effect against non-small cell lung cancers (NSCLCs) through inducing apoptosis and autophagy. For refractory NSCLCs, DNA-dependent protein kinase (DNA-PK) or ataxia telangiectasia mutated protein (ATM) inhibitors can synergize with CV-B5/F to promote refractory cell death. Here, we showed that viral infection triggered endoplasmic reticulum (ER) stress-related pro-apoptosis and autophagy signals, whereas repair for double-stranded DNA breaks (DSBs) contributed to cell survival which can be antagonized by inhibitor-induced cell death, manifesting exacerbated DSBs, apoptosis, and autophagy. Mechanistically, PERK pathway was activated by the combination of CV-B5/F and inhibitor, and the irreversible ER stress-induced exacerbated cell death. Furthermore, the degradation of activated STING by ERphagy promoted viral replication. Meanwhile, no treatment-related deaths due to CV-B5/F and/or inhibitors occurred. Conclusively, our study identifies an oncolytic CV-B5/F and the synergistic effects of inhibitors of DNA-PK or ATM, which is a potential therapy for NSCLCs.

SHFL inhibits enterovirus A71 infection by triggering degradation of viral 3Dpol protein via the ubiquitin-proteasome pathway

Enterovirus A71 (EV-A71) is a highly contagious virus that poses a major threat to global health, representing the primary etiological agent for hand-foot and mouth disease (HFMD) and neurological complications. It has been established that interferon signaling is critical to establishing a robust antiviral state in host cells, mainly mediated through the antiviral effects of numerous interferon-stimulated genes (ISGs). The host restriction factor SHFL is a novel ISG with broad antiviral activity against various viruses through diverse underlying molecular mechanisms. Although SHFL is widely acknowledged for its broad-spectrum antiviral activity, it remains elusive whether SHFL inhibits EV-A71. In this work, we validated that EV-A71 triggers the upregulation of SHFL both in cell lines and in a mouse model. Knockdown and overexpression of SHFL in EVA71-infected cells suggested that this factor could markedly suppress EV-A71 replication. Our findings further revealed an intriguing mechanism of SHFL that it could interact with the nonstructural proteins 3Dpol of EV-A71 and promoted the degradation of 3Dpol through the ubiquitin-proteasome pathway. Furthermore, the zinc-finger domain and the 36 amino acids (164-199) of SHFL were crucial to the interaction between SHFL and EV-A71 3Dpol . Overall, these findings broadened our understanding of the pivotal roles of SHFL in the interaction between the host and EV-A71.

Inhibitory effects and mechanisms of proanthocyanidins against enterovirus 71 infection

Proanthocyanidins (PC), a natural flavonoid compound, was reported to possess a variety of pharmacological activities such as anti-tumor and anti-viral effects. In this study, the anti-Enterovirus 71 (EV71) activities and mechanisms of PC were investigated both in vitro and in vivo. The results showed that PC possessed anti-EV71 activities in different cell lines with low toxicity. PC can block both the adsorption and entry processes of EV71 via directly binding to virus VP1 protein. PC may competitively interfere with the binding of VP1 to its receptor SCARB2. PC can also regulate three different MAPK signaling pathways to reduce EV71 infection and attenuate virus induced inflammatory responses. Importantly, intramuscular therapy of EV71-infected mice with PC markedly improved their survival and attenuated the severe clinical symptoms. Therefore, the natural compound PC has potential to be developed into a novel anti-EV71 agent targeting viral VP1 protein and MAPK pathways.

Current status of hand-foot-and-mouth disease

Hand-foot-and-mouth disease (HFMD) is a viral illness commonly seen in young children under 5 years of age, characterized by typical manifestations such as oral herpes and rashes on the hands and feet. These symptoms typically resolve spontaneously within a few days without complications. Over the past two decades, our understanding of HFMD has greatly improved and it has received significant attention. A variety of research studies, including epidemiological, animal, and in vitro studies, suggest that the disease may be associated with potentially fatal neurological complications. These findings reveal clinical, epidemiological, pathological, and etiological characteristics that are quite different from initial understandings of the illness. It is important to note that HFMD has been linked to severe cardiopulmonary complications, as well as severe neurological sequelae that can be observed during follow-up. At present, there is no specific pharmaceutical intervention for HFMD. An inactivated Enterovirus A71 (EV-A71) vaccine that has been approved by the China Food and Drug Administration (CFDA) has been shown to provide a high level of protection against EV-A71-related HFMD. However, the simultaneous circulation of multiple pathogens and the evolution of the molecular epidemiology of infectious agents make interventions based solely on a single agent comparatively inadequate. Enteroviruses are highly contagious and have a predilection for the nervous system, particularly in child populations, which contributes to the ongoing outbreak. Given the substantial impact of HFMD around the world, this Review synthesizes the current knowledge of the virology, epidemiology, pathogenesis, therapy, sequelae, and vaccine development of HFMD to improve clinical practices and public health efforts.

TBK1 and IRF3 are potential therapeutic targets in Enterovirus A71-associated diseases

BACKGROUND

Enterovirus A71 (EV-A71) is an important causative agent of hand-foot-and-mouth disease (HFMD) associated with enormous healthcare and socioeconomic burden. Although a range of studies about EV-A71 pathogenesis have been well described, the underlying molecular mechanism in terms of innate immune response is still not fully understood, especially the roles of TANK-binding kinase 1 (TBK1) and interferon-regulatory factor 3 (IRF3).

METHODOLOGY/PRINCIPAL FINDINGS

Here, we applied TBK1 inhibitor and IRF3 agonist, for the first time, to evaluate the antiviral activities of TBK1 and IRF3 in vivo. We found that, through regulating EV-A71-induced type I interferon (IFN) response, IRF3 agonist effectively alleviated EV-A71-induced illness, while TBK1 inhibitor aggravated disease progression. In addition, EV-A71 replication was suppressed in EVA-71-infected mice administrated with IRF3 agonist. On the other hand, more severe pathological alterations of neuronal degeneration, muscle fiber breaks, fractured or fused alveolar walls, and diffuse congestion occurred in EVA-71-infected mice treated with TBK1 inhibitor administration. Furthermore, we determined the concentrations of interleukin (IL)-6, tumor necrosis factor-alpha (TNF-α), IL-1β, monocyte chemotactic protein-1 (MCP-1), and IL-10 in both lungs and brains of mice and found that TBK1 inhibitor promoted EV-A71-induced inflammatory response, while IRF3 agonist alleviated it, which was consistent with clinical manifestations and pathological alterations.

CONCLUSIONS

Collectively, our findings suggest that TBK1 and IRF3 are potential therapeutic targets in EV-A71-induced illness.

Cell membrane-bound toll-like receptor-1/2/4/6 monomers and -2 heterodimer inhibit enterovirus 71 replication by activating the antiviral innate response

Host immune activation is critical for enterovirus 71 (EV71) clearance and immunopathogenesis. However, the mechanism of innate immune activation, especially of cell membrane-bound toll-like receptors (TLRs), against EV71 remains unknown. We previously demonstrated that TLR2 and its heterodimer inhibit EV71 replication. In this study, we systematically investigated the effects of TLR1/2/4/6 monomers and TLR2 heterodimer (TLR2/TLR1, TLR2/TLR6, and TLR2/TLR4) on EV71 replication and innate immune activation. We found that the overexpression of human- or mouse-derived TLR1/2/4/6 monomers and TLR2 heterodimer significantly inhibited EV71 replication and induced the production of interleukin (IL)-8 via activation of the phosphoinositide 3-kinase/protein kinase B (PI3K/AKT) and mitogen-activated protein kinase (MAPK) pathways. Furthermore,human-mouse chimeric TLR2 heterodimer inhibited EV71 replication and activated innate immunity. Dominant-negative TIR-less (DN)-TLR1/2/4/6 did not exert any inhibitory effects, whereas DN-TLR2 heterodimer inhibited EV71 replication. Prokaryotic expression of purified recombinant EV71 capsid proteins (VP1, VP2, VP3, and VP4) or overexpression of EV71 capsid proteins induced the production of IL-6 and IL-8 via activation of the PI3K/AKT and MAPK pathways. Notably, two types of EV71 capsid proteins served as pathogen-associated molecular patterns for TLR monomers (TLR2 and TLR4) and TLR2 heterodimer (TLR2/TLR1, TLR2/TLR6, and TLR2/TLR4) and activated innate immunity. Collectively, our results revealed that membrane TLRs inhibited EV71 replication via activation of the antiviral innate response, providing insights into the EV71 innate immune activation mechanism.

In Silico and In Vitro Antiviral Activity Evaluation of Prodigiosin from Serratia marcescens Against Enterovirus 71

Prodigiosin, a red linear tripyrrole pigment found in Serratia marcescens, is one such naturally occurring compound that has gained wide attention owing to its numerous biological activities, including antibacterial, antifungal, antimalarial, anticancer, and immunosuppressive properties. This study was conducted to evaluate the possible antiviral activity of prodigiosin against Enterovirus 71, a causative agent of hand, foot, and mouth disease (HFMD). Preliminary studies were done in silico by analyzing the interaction of prodigiosin with amino acid residues of five EV71-target proteins. Interaction refinement analysis with FireDock revealed that 2C helicase (-48.01 kcal/moL) has the most negative global energy, followed by capsid (-36.52 kcal/moL), 3C protease (-34.16 kcal/moL), 3D RNA polymerase (-30.93 kcal/moL) and 2A protease (-20.61 kcal/moL). These values are indicative of the interaction strength. Prodigiosin was shown to form chemical bonds with specific amino acid residues in capsid (Gln-30, Asn-223), 2A protease (Trp-33, Trp-142), 2C helicase (Tyr-150, His-151, Gln-169, Ser-212), 3C protease (Glu-50), and 3D RNA polymerase (Ala-239, Tyr-237). To investigate further, prodigiosin was extracted from S. marcescens using a methanolic extraction method. In vitro studies revealed that prodigiosin, with an IC50 value of 0.5112 μg/mL, reduced virus titers by 0.17 log (32.39%) in 30 min and 0.19 log (35.43%) in 60 min. The findings suggest that prodigiosin has antiviral activity with an intermediate inhibitory effect against EV71. As a result of this research, new biological activities of prodigiosin have been identified.

IFN-β1b induces OAS3 to inhibit EV71 via IFN-β1b/JAK/STAT1 pathway

Enterovirus 71 (EV71) caused hand, foot and mouth disease (HFMD) is a serious threat to the health of young children. Although type I interferon (IFN-I) has been proven to control EV71 replication, the key downstream IFN-stimulated gene (ISG) remains to be clarified and investigated. Recently, we found that 2′-5′-oligoadenylate synthetases 3 (OAS3), as one of ISG of IFN-β1b, was antagonized by EV71 3C protein. Here, we confirm that OAS3 is the major determinant of IFN-β1b-mediated EV71 inhibition, which depends on the downstream constitutive RNase L activation. 2′-5′-oligoadenylate (2-5A) synthesis activity deficient mutations of OAS3 D816A, D818A, D888A, and K950A lost resistance to EV71 because they could not activate downstream RNase L. Further investigation proved that EV71 infection induced OAS3 but not RNase L expression by IFN pathway. Mechanically, EV71 or IFN-β1b-induced phosphorylation of STAT1, but not STAT3, initiated the transcription of OAS3 by directly binding to the OAS3 promoter. Our works elucidate the immune regulatory mechanism of the host OAS3/RNase L system against EV71 replication.

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OAS3 contributes important inhibition effect for IFN-β1b against EV71.

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OAS3 resistance to EV71 replication depends on RNase L activation.

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STAT1 initiates the transcription of OAS3 by directly binding to the OAS3 promoter.

TRAF3IP3 Is Cleaved by EV71 3C Protease and Exhibits Antiviral Activity

Enterovirus 71 (EV71) is one of the major pathogens of hand, foot, and mouth disease, which poses a major risk to public health and infant safety. 3C protease (3C^pro), a non-structural protein of EV71, promotes viral protein maturation by cleaving polyprotein precursors and facilitates viral immune escape by cleaving host proteins. In this study, we screened for human proteins that could interact with EV71 3C^pro using a yeast two-hybrid assay. Immune-associated protein TRAF3 Interacting Protein 3 (TRAF3IP3) was selected for further study. The results of co-immunoprecipitation and immunofluorescence demonstrated the interaction between TRAF3IP3 and EV71 3C^pro. A cleavage band was detected, indicating that both transfected 3C^pro and EV71 infection could cleave TRAF3IP3. 87Q-88G was identified as the only 3C^pro cleavage site in TRAF3IP3. In Jurkat and rhabdomyosarcoma (RD) cells, TRAF3IP3 inhibited EV71 replication, and 3C^pro cleavage partially resisted TRAF3IP3-induced inhibition. Additionally, the nuclear localization signal (NLS) and nuclear export signal (NES) of TRAF3IP3 were identified. The NES contributed to TRAF3IP3 alteration of 3C^pro localization and inhibition of EV71 replication. Together, these results indicate that TRAF3IP3 inhibits EV71 replication and 3C^pro resists such inhibition via proteolytic cleavage, providing a new example of virus-host interaction.

Proteolytic Activities of Enterovirus 2A Do Not Depend on Its Interaction with SETD3

Enterovirus 2A^pro is a protease that proteolytically processes the viral polyprotein and cleaves several host proteins to antagonize host responses during enteroviral infection. Recently, the host protein actin histidine methyltransferase SET domain containing 3 (SETD3) was identified to interact with 2A^pro and to be essential for virus replication. The role of SETD3 and its interaction with 2A^pro remain unclear. In this study, we investigated the potential involvement of SETD3 in several functions of 2A^pro. For this, we introduced the 2A^pro from coxsackievirus B3 (CVB3) in a mutant of encephalomyocarditis virus (EMCV) containing an inactivated Leader protein (EMCV-L^zn) that is unable to shut down host mRNA translation, to trigger nucleocytoplasmic transport disorder (NCTD), and to suppress stress granule (SG) formation and type I interferon (IFN) induction. Both in wt HeLa cells and in HeLa SETD3 knockout (SETD3^KO) cells, the virus containing active 2A^pro (EMCV-2A^pro) efficiently cleaved eukaryotic translation initiation factor 4 gamma (eIF4G) to shut off host mRNA translation, cleaved nucleoporins to trigger NCTD, and actively suppressed SG formation and IFN gene transcription, arguing against a role of SETD3 in these 2A^pro-mediated functions. Surprisingly, we observed that the catalytic activity of enteroviral 2A is not crucial for triggering NCTD, as a virus containing an inactive 2A^pro (EMCV-2A^m) induced NCTD in both wt and SETD3^KO cells, albeit delayed, challenging the idea that the NCTD critically depends on nucleoporin cleavage by this protease. Taken together, our results do not support a role of SETD3 in the proteolytic activities of enterovirus 2A^pro.

Type I Interferon-Induced TMEM106A Blocks Attachment of EV-A71 Virus by Interacting With the Membrane Protein SCARB2

Enterovirus A71 (EV-A71) and Coxsackievirus A16 (CV-A16) are the main causative agents of hand, foot and mouth disease (HFMD) worldwide. Studies showed that EV-A71 and CV-A16 antagonize the interferon (IFN) signaling pathway; however, how IFN controls this viral infection is largely unknown. Here, we identified an IFN-stimulated gene, Transmembrane Protein 106A (TMEM106A), encoding a protein that blocks EV-A71 and CV-A16 infection. Combined approaches measuring viral infection, gene expression, and protein interactions uncovered that TMEM106A is required for optimal IFN-mediated viral inhibition and interferes with EV-A71 binding to host cells on the receptor scavenger receptor class B member 2 (SCARB2). Our findings reveal a new mechanism contributing to the IFN-mediated defense against EV-A71 and CV-A16 infection and provide a potential strategy for HFMD treatment by using the antiviral role of TMEM106A against enterovirus.

Enterovirus 71 Antagonizes Antiviral Effects of Type III Interferon and Evades the Clearance of Intestinal Intraepithelial Lymphocytes

Enterovirus 71 (EV71) is the major pathogen causing severe neurological complications and hand, foot, and mouth disease. The intestinal mucosal immune system has a complete immune response and immune regulation mechanism, consisting of densely arranged monolayer intestinal epithelial cells (IECs) and intestinal intraepithelial lymphocytes (iIELs) distributed among the IECs, which constitute the first line of intestinal mucosa against infection of foreign pathogens. As an enterovirus, EV71 is transmitted by the intestinal tract; however, the mechanisms it uses to evade the immunosurveillance of the intestinal mucosal immune system are still incompletely clarified. The present study investigated how EV71 evades from recognizing and eliminating IECs, iIELs, and iNK cells. We found that EV71 infection induced a higher level of type III interferons (IFN-λ) than type I interferons (IFN-β) in IECs, and the addition of IFN-λ markedly restricted EV71 replication in IECs. These results indicate that IFN-λ plays a more important role in anti-EV71 intestinal infection. However, EV71 infection could markedly attenuate the antiviral responses of IFN-λ. Mechanistically, 2A protease (2Apro) and 3C protease (3Cpro) of EV71 inhibited the IFN-λ production and IFN-λ receptor expression and further decreased the response of IECs to IFN-λ. In addition, we found that EV71-infected IECs were less susceptible to the lysis of intestinal NK (iNK) cells and CD3⁺iIELs. We revealed that the viral 2Apro and 3Cpro could significantly reduce the expression of the ligands of natural killer group 2D (NKG2D) and promote the expression of PD-L1 on IECs, rendering them to evade the recognition and killing of iNK and CD3⁺iIELs. These results provide novel evasion mechanisms of EV71 from intestinal mucosal innate immunity and may give new insights into antiviral therapy.

Curcumin assists anti-EV71 activity of IFN-α by inhibiting IFNAR1 reduction in SH-SY5Y cells

Background and aim

Enterovirus 71(EV71) can cause severe hand, foot, and mouth disease (HFMD) with brain tissue involvement. Few effective anti-EV71 drugs are presently available in clinical practice. Interferon-α (IFN-α) was ineffective while Curcumin was effective in restricting EV71 replication in non-neuronal cells. Ubiquitin–proteasome-mediated degradation of interferon-alpha receptor 1 (IFNAR1) protein contributes to IFN-α resistance. Current study aimed to determine synergistic inhibition of EV71 by Curcumin and IFN-α in human neuroblastoma SH-SY5Y cells.

Methods

SH-SY5Y cells were infected with mock-/Curcumin-pre-incubated EV71 or transfected with plasmid containing interferon-stimulated response element (ISRE) or mRNA containing viral internal ribosomal entry site (IRES) following by post-treatment with Curcumin with or without IFN-α. Supernatant IFN-α/β was detected by ELISA. ISRE, IRSE, proteasome and deubiquitinating activity were measured by luciferase assay. EV71 RNA and viral protein or IFNAR1 were determined by qPCR and western blot, respectively.

Results

EV71 flailed to completely block IFN-α/β production but inhibited IFN-α signal. Curcumin only slightly inhibited EV71 proliferation without modulating virus attachment and internalization. However, Curcumin addition restored IFN-α-mediated ISRE activity thus significantly inhibiting EV71 replication. Furthermore, EV71 also reduced IFNAR1 protein with proteasome-dependence in SH-SY5Y cells, which can be reversed by Curcumin addition with the evidence that it lowered proteasome activity.

Conclusion

These data demonstrate that Curcumin assists anti-EV71 activity of IFN-α by inhibiting IFNAR1 reduction via ubiquitin–proteasome disruption in SH-SY5Y cells.

MiR-103/miR-107 inhibits enterovirus 71 replication and facilitates type I interferon response by regulating SOCS3/STAT3 pathway

BACKGROUND

Enterovirus71 (EV71), the major cause of hand, foot, and-mouth disease (HFMD), has increasingly become a public health challenge. Type I interferons (IFNs) can regulate innate and adaptive immune responses to pathogens. MicroRNAs (miRNAs) play regulatory roles in host innate immune responses to viral infections. However, the roles of miR-103 and miR-107 in EV71 infection remain unclear.

METHODS

Quantitative real-time polymerase chain reaction (qRT-PCR) was employed to determine the expression of miR-103, miR-107, suppressor of cytokine signaling 3 (SOCS3), VP1, IFN-α, and IFN-β. Virus titers were measured by 50% tissue culture infectious dose (TCID₅₀) assay. Western blot assay was conducted to detect the protein levels of VP1, IFN-α, IFN-β, SOCS3, signal transducer and activator of transcription 3 (STAT3), and phospho-STAT3 (p-STAT3). Immunofluorescence assay was used to detect the protein level of VP1. The concentrations of IFN-α and IFN-β were examined by Enzyme-linked immunosorbent assay (ELISA). The interaction between SOCS3 and miR-103/miR-107 was predicted by starBase and verified by dual-luciferase reporter assay and RNA pull-down assay.

RESULTS

MiR-103 and miR-107 were downregulated and SOCS3 was upregulated in serum from patients with EV71 and EV71-infected cells. Overexpression of miR-103 and miR-107 repressed EV71 replication by inhibiting EV71 titers and VP1 expression. Moreover, upregulation of miR-103 and miR-107 enhanced EV71-triggered the production of type I IFNs. In addition, miR-103 and miR-107 directly targeted SOCS3, and SOCS3 upregulation reversed the effects of miR-103 and miR-107 on EV71 replication and type I IFN response. Importantly, miR-103 and miR-107 increased STAT3 phosphorylation by targeting SOCS3 after EV71 infection.

CONCLUSION

MiR-103 and miR-107 suppressed EV71 replication and increased the production of type I IFNs by regulating SOCS3/STAT3 pathway, which might provide a novel strategy for developing effective antiviral therapy.

Global profiling of the alternative splicing landscape reveals transcriptomic diversity during the early phase of enterovirus 71 infection

The alteration of host cell splicing is a major strategy favouring viral replication; however, the interaction between human tonsillar epithelial cells (HTECs) and enterovirus 71 (EV71) has not been fully elucidated. Here, a total of 201 differentially expressed genes (DEGs) and 3266 novel genes with coding potential were identified. A total of 3479 skipped exons (SEs), 515 alternative 3' splice sites (A3SSs), 391 alternative 5' splice sites (A5SSs), 531 mutually exclusive exons (MXEs) and 825 retained introns (RIs) were identified as significantly altered alternative splicing (AS) events. The enriched DEGs were mainly related to the cell cycle, spliceosome, and Toll-like receptor (TLR) signalling pathways. Finally, the replication of EV71 was significantly inhibited by TLR2 heterodimers. Our findings suggest that AS events induced by EV71 increase the transcriptomic diversity of HTECs in response to EV71 infection. Additionally, TLR2 heterodimers have the potential to protect HTECs against EV71.

Enterovirus A71 capsid protein VP1 increases blood-brain barrier permeability and virus receptor vimentin on the brain endothelial cells

Enterovirus A71 (EV-A71) is the major cause of severe hand-foot-and-mouth diseases (HFMD), especially encephalitis and other nervous system diseases. EV-A71 capsid protein VP1 mediates virus attachment and is the important virulence factor in the EV-A71pathogenesis. In this study, we explored the roles of VP1 in the permeability of blood-brain barrier (BBB). Sera albumin, Evans blue, and dextran leaked into brain parenchyma of the 1-week-old C57BL/6J mice intracranially injected with VP1 recombinant protein. VP1 also increased the permeability of the brain endothelial cells monolayer, an in vitro BBB model. Tight junction protein claudin-5 was reduced in the brain tissues or brain endothelial cells treated with VP1. In contrast, VP1 increased the expression of virus receptor vimentin, which could be blocked with VP1 neutralization antibody. Vimentin expression in the VP1-treated brain endothelial cells was regulated by TGF-β/Smad-3 and NF-κB signal pathways. Moreover, vimentin over-expression was accompanied with compromised BBB. From these studies, we conclude that EV-A71 virus capsid protein VP1 disrupted BBB and increased virus receptor vimentin, which both may contribute to the virus entrance into brain and EV-A71 CNS infection.

Downregulation of miR-155-5p facilitates enterovirus 71 replication through suppression of type I IFN response by targeting FOXO3/IRF7 pathway

Enterovirus 71 (EV71), the major cause of hand-foot-and-mouth disease (HFMD), has evolved diverse strategies to counter the type I interferon (IFN-I) response during infection. Recently, microRNAs have regulatory roles in host innate immune responses to viral infections; however, whether EV71 escapes the IFN-I antiviral response through regulation of miRNAs remains unclear. Using a microarray assay, microRNA-155-5p (miR-155-5p) was found to be significantly up-regulated in serum from patients with EV71 infection and the increased expression of miR-155-5p was further confirmed in vivo and in vitro in response to EV71 infection. miR-155-5p overexpression suppressed EV71 titers and VP1 protein level, while miR-155-5p inhibition had an opposite result. Moreover, we found that miR-155-5p overexpression enhanced EV71 triggered IFN I production and the expressions of IFN-stimulated genes (ISGs), while inhibition of miR-155-5p suppressed these processes. Furthermore, bioinformatics analysis and luciferase reporter assay demonstrated that miR-155-5p directly targeted forkhead box protein O3 (FOXO3) and negatively regulated FOXO3/IRF7 axis, an important regulatory pathway for type I IFN production during EV71 infection. Inhibition of FOXO3 reversed the effects of miR-155-5p inhibitor on EV71 replication and the type I IFN production. Importantly, in EV71 infection mice, agomir-155-5p injection resulted in a significant reduction of viral VP1 protein expressions in brain and lung tissues, increased IFN-α/β production and increased mice survival rate. In contrast, antagomir-155-5p enhanced EV71 induced these effects. Collectively, our study indicates that weaken miR-155-5p facilitates EV71 replication through suppression of type I IFN response by FOXO3/IRF7 pathway, thereby suggesting a novel strategy for developing effective antiviral therapy.

EV71 Infection Induces IFNβ Expression in Neural Cells

Enterovirus 71 (EV71) can invade the central nervous system (CNS) and cause neurological disease. Accumulating evidence indicates that EV71 can directly infect neurons in the CNS. Innate immune responses in the CNS have been known to play an essential role in limiting pathogen infections. Thus, investigating the effects of EV71 infection of neural cells is important for understanding disease pathogenesis. In this study, human neural cells were infected with EV71, and interferonβ (IFNβ) expression was examined. Our results show that IFNβ expression was upregulated in EV71-infected neural cells via pattern recognition receptors (PRRs) sensing of virus RNA. The PRRs Toll-like receptor 3 (TLR3), Toll-like receptor 8 (TLR8), and melanoma differentiation-associated gene-5 (MDA-5), but not retinoic acid-inducible gene-I (RIG-I) and Toll-like receptor 7 (TLR7), were found to be EV71-mediated IFNβ induction. Although viral proteins exhibited the ability to cleave mitochondrial antiviral signaling protein (MAVS) and Toll/IL-1 receptor (TIR) domain-containing adaptor-inducing IFN-β (TRIF) in neural cells, levels of viral protein expression were low in these cells. Furthermore, neural cells efficiently produced IFNβ transcripts upon EV71 vRNA stimulation. Treating infected cells with anti-IFNβ antibodies resulted in increased virus replication, indicating that IFNβ release may play a role in limiting viral growth. These results indicate that EV71 infection can induce IFNβ expression in neural cells through PRR pathways.

Cellular Caspase-3 Contributes to EV-A71 2Apro-Mediated Down-Regulation of IFNAR1 at the Translation Level

Enterovirus A71 (EV-A71) is the major pathogen responsible for the severe hand, foot and mouth disease worldwide, for which few effective antiviral drugs are presently available. Interferon-α (IFN-α) has been used in antiviral therapy for decades; it has been reported that EV-A71 antagonizes the antiviral activity of IFN-α based on viral 2A^pro-mediated reduction of the interferon-alpha receptor 1 (IFNAR1); however, the mechanism remains unknown. Here, we showed a significant increase in IFNAR1 protein induced by IFN-α in RD cells, whereas EV-A71 infection caused obvious down-regulation of the IFNAR1 protein and blockage of IFN-α signaling. Subsequently, we observed that EV-A71 2A^pro inhibited IFNAR1 translation by cleavage of the eukaryotic initiation factor 4GI (eIF4GI), without affecting IFNAR1 mRNA levels induced by IFN-α. The inhibition of IFNAR1 translation also occurred in puromycin-induced apoptotic cells when caspase-3 cleaved eIF4GI. Importantly, we verified that 2A^pro could activate cellular caspase-3, which was subsequently involved in eIF4GI cleavage mediated by 2A^pro. Furthermore, inhibition of caspase-3 activation resulted in the partial restoration of IFNAR1 in cells transfected with 2A or infected with EV-A71, suggesting the pivotal role of both viral 2A^pro and caspase-3 activation in the disturbance of IFN-α signaling. Collectively, we elucidate a novel mechanism by which cellular caspase-3 contributes to viral 2A^pro-mediated down-regulation of IFNAR1 at the translation level during EV-A71 infection, indicating that caspase-3 inhibition could be a potential complementary strategy to improve clinical anti-EV-A71 therapy with IFN-α.

An update on enterovirus 71 infection and interferon type I response

Enteroviruses are members of Pichornaviridae family consisting of human enterovirus group A, B, C, and D as well as nonhuman enteroviruses. Hand, foot, and mouth disease (HFMD) is a serious disease which is usually seen in the Asia-Pacific region in children. Enterovirus 71 and coxsackievirus A16 are two important viruses responsible for HFMD which are members of group A enterovirus. IFN α and β are two cytokines, which have a major activity in the innate immune system against viral infections. Most of the viruses have some weapons against these cytokines. EV71 has two main proteases called 2A and 3C, which are important for polyprotein processing and virus maturation. Several studies have indicated that they have a significant effect on different cellular pathways such as interferon production and signaling pathway. The aim of this study was to investigate the latest findings about the interaction of 2A and 3C protease of EV71 and IFN production/signaling pathway and their inhibitory effects on this pathway.