Coxsackievirus A10 impairs nail regeneration and induces onychomadesis by mimicking DKK1 to attenuate Wnt signaling.

Coxsackievirus A10 (CV-A10) infection, a prominent cause of childhood hand-foot-and-mouth disease (HFMD), frequently manifests with the intriguing phenomenon of onychomadesis, characterized by nail shedding. However, the underlying mechanism is elusive. Here, we found that CV-A10 infection in mice could suppress Wnt/ß-catenin signaling by restraining LDL receptor-related protein 6 (LRP6) phosphorylation and ß-catenin accumulation and lead to onychomadesis. Mechanistically, CV-A10 mimics Dickkopf-related protein 1 (DKK1) to interact with Kringle-containing transmembrane protein 1 (KRM1), the CV-A10 cellular receptor. We further found that Wnt agonist (GSK3ß inhibitor) CHIR99021 can restore nail stem cell differentiation and protect against nail shedding. These findings provide novel insights into the pathogenesis of CV-A10 and related viruses in onychomadesis and guide prognosis assessment and clinical treatment of the disease.

Mouse Scarb2 Modulates EV-A71 Pathogenicity in Neonatal Mice.

Enterovirus A71 (EV-A71) is a human pathogen that causes hand, foot, and mouth disease, which can progress to severe neurological disease. EV-A71 infects humans via the human scavenger receptor B2 (hSCARB2). It can also infect neonatal mice experimentally. Wild-type (WT) EV-A71 strains replicate primarily in the muscle of neonatal mice; however, susceptibility lasts only for a week after birth. Mouse-adapted (MA) strains, which can be obtained by serial passages in neonatal mice, are capable of infecting both muscle and neurons of the central nervous system. It is not clear how the host range and tropism of EV-A71 are regulated and why neonatal mice lose their susceptibility during development. We hypothesized that EV-A71 infection in neonatal mice is mediated by mouse Scarb2 (mScarb2) protein. Rhabdomyosarcoma (RD) cells expressing mScarb2 were prepared. Both WT and MA strains infected mScarb2-expressing cells, but the infection efficiency of the WT strain was much lower than that of the MA strain. Infection by WT and MA strains in vivo was abolished completely in Scarb2-/- mice. Scarb2+/- mice, in which Scarb2 expression was approximately half of that in Scarb2+/+ mice, showed a milder pathology than Scarb2+/+ mice after infection with the WT strain. The Scarb2 expression level in muscle decreased with aging, which was consistent with the reduced susceptibility of aged mice to infection. These results indicated that EV-A71 infection is mediated by mScarb2 and that the severity of the disease, the spread of virus, and the susceptibility period are modulated by mScarb2 expression. IMPORTANCE EV-A71 infects humans naturally but can also infect neonatal mice. The tissue tropism and severity of EV-A71 disease are determined by several factors, among which the virus receptor is thought to be important. We show that EV-A71 can infect neonatal mice using mScarb2. However, the infection efficiency of WT strains via mScarb2 is so low that an elevated virus-receptor interaction associated with mouse adaptation mutation and decrease in mScarb2 expression level during development modulate the severity of the disease, the spread of virus, and the susceptibility period in the artificial neonatal mice model.

Enterovirus 71 Activates GADD34 via Precursor 3CD to Promote IRES-Mediated Viral Translation.

Enterovirus 71 (EV71) is the major pathogen of hand, foot, and mouth disease. In severe cases, it can cause life-threatening neurological complications, such as aseptic meningitis and polio-like paralysis. There are no specific antiviral treatments for EV71 infections. In a previous study, the host protein growth arrest and DNA damage-inducible protein 34 (GADD34) expression was upregulated during EV71 infection determined by ribosome profiling and RNA-sequencing. Here, we investigated the interactions of host protein GADD34 and EV71 during infections. Rhabdomyosarcoma (RD) cells were infected with EV71 resulting in a significant increase in expression of GADD34 mRNA and protein. Through screening of EV71 protein we determined that the non-structural precursor protein 3CD is responsible for upregulating GADD34. EV71 3CD increased the RNA and protein levels of GADD34, while the 3CD mutant Y441S could not. 3CD upregulated GADD34 translation via the upstream open reading frame (uORF) of GADD34 5'untranslated regions (UTR). EV71 replication was attenuated by the knockdown of GADD34. The function of GADD34 to dephosphorylate eIF2α was unrelated to the upregulation of EV71 replication, but the PEST 1, 2, and 3 regions of GADD34 were required. GADD34 promoted the EV71 internal ribosome entry site (IRES) activity through the PEST repeats and affected several other viruses. Finally, GADD34 amino acids 563 to 565 interacted with 3CD, assisting GADD34 to target the EV71 IRES. Our research reveals a new mechanism by which GADD34 promotes viral IRES and how the EV71 non-structural precursor protein 3CD regulates host protein expression to support viral replication. IMPORTANCE Identification of host factors involved in viral replication is an important approach in discovering viral pathogenic mechanisms and identifying potential therapeutic targets. Previously, we screened host proteins that were upregulated by EV71 infection. Here, we report the interaction between the upregulated host protein GADD34 and EV71. EV71 non-structural precursor protein 3CD activates the RNA and protein expression of GADD34. Our study reveals that 3CD regulates the uORF of the 5'-UTR to increase GADD34 translation, providing a new explanation for how viral proteins regulate host protein expression. GADD34 is important for EV71 replication, and the key functional domains of GADD34 that promote EV71 are PEST 1, 2, and 3 regions. We report that GADD34 promotes viral IRES for the first time and this process is independent of its eIF2α phosphatase activity.

Low-frequency, exhausted immune status of CD56dim NK cells and disordered inflammatory cytokine secretion of CD56bright NK cells associated with progression of severe HFMD, especially in EV71-infected patients.

BACKGROUND: The roles of CD56bright and CD56dim natural killer (NK) subsets in the viral clearance and inflammatory processes of hand, foot, and mouth disease (HFMD) remain undefined. METHODS: A total of 39 HCs and 55 patients were enrolled to analyze peripheral CD56bright and CD56dim NK cells according to cell number, surface receptors, cytotoxic activities, and cytokine production. The plasma concentrations of IL-2, IL-6, IL-10, IFN-γ, TNF-α,and MCP-1 were detected using ELSA. RESULTS: Peripheral blood NK cells was significantly lower in severe patients than in HCs due to the dramatic loss of CD56dim NK cells with no changes in the cell count of CD56bright NK cells. For mild patients, decreased NKp46 expression coincided with enhanced cytolysis (CD107a, GNLY, and GrB) in CD56dim NK cells and decreased NKG2A expression with enhanced IL-10 production in CD56bright NK cells. In contrast, severe patients showed the dominant expression of NKG2A and decreased expression of NKG2D accompanied by cytotoxic dysfunction in CD56dim NK cells. Imbalanced receptor expression coincided with the increased concentrations of TNF-α in CD56bright NK cells. Moreover, EV71+ patients showed significantly decreased counts of CD56dim NK cells with cytolysis dysfunction, displayed cytokine hypersecretion in CD56bright NK cells, while the EV71- patients displayed significantly higher plasma cytokine concentrations. The changes in the immune function of NK subsets and their subpopulations were closely related to clinical inflammatory parameters. CONCLUSIONS: Low-frequency, exhausted immune status of CD56dim NK cells and disordered inflammatory cytokine secretion of CD56bright NK cells were associated with the progression of severe HFMD, especially in EV71-infected patients. This promoted the severity of inflammatory disorders, leading to enhanced disease pathogenesis.

IFI27 as a potential indicator for severe Enterovirus 71-infected hand foot and mouth disease.

The pathogenesis of Enterovirus 71 (EV71)-induced severe hand foot and mouth disease (HFMD) has not yet been clearly established. Further study into the mechanisms underlying host immune responses to EV71 infection and identifying important predictors will be crucial to antiviral treatment and early recognition of severe HFMD. The present study establishes that T help (Th)1 type, Th2 type, and Th17 type cytokine levels in serum of peripheral blood from patients with severe HFMD is higher than in peripheral blood from healthy subjects. The most significant increase occurred as the IL-6. In order to identify the important molecules in peripheral blood mononuclear cells (PBMCs) from severe HFMD patients, we performed transcriptome sequencing analysis of PBMC from severe HFMD patients and compared them to healthy controls. Interferon α-inducible protein 27 (IFI27) and cluster of differentiation 27 (CD27) were found to be the most significant differentially expressed gene. Finally, IFI27 was proved to be present at higher levels in patients with severe HFMD than in patients with mild HFMD. Our results suggest that IFI27 may be an indicator of the severity of cases EV71-induced HFMD.

Vitamin D receptor gene methylation in patients with hand, foot, and mouth disease caused by enterovirus 71.

To evaluate the epigenetic regulation of the VDR gene in enterovirus 71 (EV71)-associated severe hand, foot, and mouth disease (HFMD), a total of 116 patients with EV71-HFMD, including 58 with mild EV71-HFMD and 58 with severe EV71-HFMD, as well as 60 healthy controls, were enrolled in this study. Quantitative real-time PCR was used to measure the relative levels of VDR mRNA expression, and the methylation status of the VDR promoter was assessed using a MethylTarget™ assay. The DNA methylation levels of the VDR promoter in children with EV71-associated severe HFMD were lower than those in the healthy controls and in children with mild HFMD (P < 0.05). Hypomethylation at CpG site 133 and hypermethylation at the CpG 42 sites and 68 downregulated VDR expression. Moreover, the methylation level of VDR could be used for differential diagnosis of mild and severe EV71-associated HFMD (AUC56, 0.73; AUC68, 0.699; AUC42, 0.694; AUC66, 0.693). VDR expression and promoter methylation were associated with the progression of EV71 infection. Determining the VDR promoter status might help clinicians initiate the appropriate strategy for treatment of EV71-associated HFMD.

Aquaporin­4 deletion ameliorates enterovirus 71 infection in mice.

Aquaporin-4 (AQP4) is a major water channel of the central nervous system. The present study was designed to determine whether AQP4 deletion could ameliorate enterovirus (EV) 71 infection­induced hand, foot and mouth disease (HFMD) by inhibiting inflammation and apoptosis in mice. EV 71 strains were injected into neonatal BALB/c mice to induce HFMD. Western blotting and ELISA were used to measure the protein expression and cytokine levels. The levels of AQP4 mRNA and protein in the brain were increased in EV 71­infected mice, while the survival rate and health score were improved in AQP4­knockout (KO) mice with EV 71 infection. The EV 71 infection­induced increases of tumor necrosis factor­α, interleukin (IL)­1ß, IL­6, monocyte chemotactic protein­1, interferon (IFN)­α and IFN­Î³ in plasma and brain were inhibited in AQP4­KO mice. AQP4 deletion reversed the decreased levels of Bcl2 and Bcl2/Bax, and the increased levels of Bax induced by EV 71 infection in the brain. These results demonstrated that AQP4 deletion ameliorated EV 71 induced­HFMD via inhibiting inflammation and apoptosis in mice.

Heparan sulfate attachment receptor is a major selection factor for attenuated enterovirus 71 mutants during cell culture adaptation.

Enterovirus 71 (EV71) is a causative agent of hand, foot, and mouth disease (HFMD). However, this infection is sometimes associated with severe neurological complications. Identification of neurovirulence determinants is important to understand the pathogenesis of EV71. One of the problems in evaluating EV71 virulence is that its genome sequence changes rapidly during replication in cultured cells. The factors that induce rapid mutations in the EV71 genome in cultured cells are unclear. Here, we illustrate the population dynamics during adaptation to RD-A cells using EV71 strains isolated from HFMD patients. We identified a reproducible amino acid substitution from glutamic acid (E) to glycine (G) or glutamine (Q) in residue 145 of the VP1 protein (VP1-145) after adaptation to RD-A cells, which was associated with attenuation in human scavenger receptor B2 transgenic (hSCARB2 tg) mice. Because previous reports demonstrated that VP1-145G and Q mutants efficiently infect cultured cells by binding to heparan sulfate (HS), we hypothesized that HS expressed on the cell surface is a major factor for this selection. Supporting this hypothesis, selection of the VP1-145 mutant was prevented by depletion of HS and overexpression of hSCARB2 in RD-A cells. In addition, this mutation promotes the acquisition of secondary amino acid substitutions at various positions of the EV71 capsid to increase its fitness in cultured cells. These results indicate that attachment receptors, especially HS, are important factors for selection of VP1-145 mutants and subsequent capsid mutations. Moreover, we offer an efficient method for isolation and propagation of EV71 virulent strains with minimal selection pressure for attenuation.

Predicting Severe Enterovirus 71-Infected Hand, Foot, and Mouth Disease: Cytokines and Chemokines.

Enterovirus 71 (EV71) is one of the most common intestinal virus that causes hand, foot, and mouth disease (HFMD) in infants and young children (mostly ≤5 years of age). Generally, children with EV71-infected HFMD have mild symptoms that resolve spontaneously within 7-14 days without complications. However, some EV71-infected HFMD cases lead to severe complications such as aseptic meningitis, encephalitis, acute flaccid paralysis, pulmonary edema, cardiorespiratory complication, circulatory disorders, poliomyelitis-like paralysis, myocarditis, meningoencephalitis, neonatal sepsis, and even death. The mechanism of EV71 pathogenesis has been studied extensively, and the regulation of host immune responses is suspected to aggravate EV71-induced severe complications. Recently, several cytokines or chemokines such as TNF-α, IFN-γ, IL-1ß, IL-18, IL-33, IL-37, IL-4, IL-13, IL-6, IL-12, IL-23, IL-27, IL-35, IL-10, IL-22, IL-17F, IL-8, IP-10, MCP-1, G-CSF, and HMGB1 have been reported to be associated with severe EV71 infection by numerous research teams, including our own. This review is aimed at summarizing the pathophysiology of the cytokines and chemokines with severe EV71 infection.

Cellular receptors for enterovirus A71.

Enterovirus 71 (EV-A71) is one of the major causative agents of hand, foot, and mouth disease. EV-A71 infection is sometimes associated with severe neurological diseases such as acute encephalitis, acute flaccid paralysis, and cardiopulmonary failure. Therefore, EV-A71 is a serious public health concern. Scavenger receptor class B, member 2 (SCARB2) is a type III transmembrane protein that belongs to the CD36 family and is a major receptor for EV-A71. SCARB2 supports attachment and internalization of the virus and initiates conformational changes that lead to uncoating of viral RNA in the cytoplasm. The three-dimensional structure of the virus-receptor complex was elucidated by cryo-electron microscopy. Two α-helices in the head domain of SCARB2 bind to the G-H loop of VP1 and the E-F loop of VP2 capsid proteins of EV-A71. Uncoating takes place in a SCARB2- and low pH-dependent manner. In addition to SCARB2, other molecules support cell surface binding of EV-A71. Heparan sulfate proteoglycans, P-selectin glycoprotein ligand-1, sialylated glycan, annexin II, vimentin, fibronectin, and prohibitin enhance viral infection by retaining the virus on the cell surface. These molecules are known as "attachment receptors" because they cannot initiate uncoating. In vivo, SCARB2 expression was observed in EV-A71 antigen-positive neurons and epithelial cells in the crypts of the palatine tonsils in patients that died of EV-A71 infection. Adult mice are not susceptible to infection by EV-A71, but transgenic mice that express human SCARB2 become susceptible to EV-A71 infection and develop neurological diseases similar to those observed in humans. Attachment receptors may also be involved in EV-A71 infection in vivo. Although heparan sulfate proteoglycans are expressed by many cultured cell lines and enhance infection by a subset of EV-A71 strains, they are not expressed by cells that express SCARB2 at high levels in vivo. Thus, heparan sulfate-positive cells merely adsorb the virus and do not contribute to replication or dissemination of the virus in vivo. In addition to these attachment receptors, cyclophilin A and human tryptophanyl aminoacyl-tRNA synthetase act as an uncoating regulator and an entry mediator that can confer susceptibility to non-susceptibile cells in the absence of SCARB2, respectively. The roles of attachment receptors and other molecules in EV-A71 pathogenesis remain to be elucidated.

Hand-foot-and-mouth disease virus receptor KREMEN1 binds the canyon of Coxsackie Virus A10.

Coxsackievirus A10 (CV-A10) is responsible for an escalating number of severe infections in children, but no prophylactics or therapeutics are currently available. KREMEN1 (KRM1) is the entry receptor for the largest receptor-group of hand-foot-and-mouth disease causing viruses, which includes CV-A10. We report here structures of CV-A10 mature virus alone and in complex with KRM1 as well as of the CV-A10 A-particle. The receptor spans the viral canyon with a large footprint on the virus surface. The footprint has some overlap with that seen for the neonatal Fc receptor complexed with enterovirus E6 but is larger and distinct from that of another enterovirus receptor SCARB2. Reduced occupancy of a particle-stabilising pocket factor in the complexed virus and the presence of both unbound and expanded virus particles suggests receptor binding initiates a cascade of conformational changes that produces expanded particles primed for viral uncoating.

Association of polymorphisms in the vitamin D receptor gene with susceptibility to and severity of hand, foot, and mouth disease caused by coxsackievirus A16.

Coxsackievirus A16 (CA16) remains the most common causative agent of hand, foot, and mouth disease (HFMD), and is related to high incidence and critical complications. Vitamin D receptor (VDR) activity might affect the outcome of CA16 infection. Our case-control research aims to evaluate the relationship between VDR polymorphisms in the gene encoding and susceptibility to and severity of HFMD due to CA16. Three single-nucleotide polymorphisms (SNPs) of VDR gene were selected according to functional prediction and linkage disequilibrium, and were examined utilizing the SNPscan method to identify possible associations with HFMD caused by CA16. A significant relationship was found in the HFMD cases of polymorphism rs11574129 (GA vs GG: odds ratio (OR) = 0.068, 95% confidence interval (CI) = 0.007-0.693, P = .023; GA + AA vs GG: OR = 0.322, 95%CI = 0.106-0.984, P = .047), and vitamin D levels in genotype AA were significantly higher than those in genotype GG (P < .05). These results suggest that VDR rs11574129 may influence genetic susceptibility to CA16-associated HFMD.

Clinical features and phylogenetic analysis of severe hand-foot-and-mouth disease caused by Coxsackievirus A6.

BACKGROUND: Coxsackievirus A6 (CA6) infection may lead to high hand-foot-and-mouth disease (HFMD) aggregation in children. We aimed to analyze the clinical and phylogenetic features of severe CA6-associated pediatric HFMD. METHODS: The clinical and laboratory features of 206 and 55 children with mild and severe CA6-associated HFMD, respectively, were summarized. The CA6 phylogenetic tree was depicted using combinatorial analysis of the VP1-encoding regions and neighbor-joining method. RESULTS: CA6 was the major pathogen both in mild and severe HFMD in 2017. Most CA6-associated severe HFMD cases showed high fever, skin rash, age younger than 36 months, and elevated white blood cell and C-reactive protein levels, and there were no significant differences compared to the mild cases (p > 0.05). The severe cases were significantly more likely (p < 0.05) to show male sex, long fever duration, decreased oral intake, tonsil enlargement, diarrhea, vomiting, elevated levels of creatine kinase and blood glucose, and positive fecal occult-blood test results. Severe complications included aseptic meningitis (29/55, 52.7%) and pulmonary edema (6/55, 10.9%) were observed in severe cases. Furthermore, genetic analyses showed all CA6 isolates belonged to lineage E2, and two amino acid changes of V174I and T283A in VP1 may be associated with the severity of HFMD. CONCLUSIONS: CA6 has become a major cause of HFMD with severe systemic disorders. V174I and T283A of VP1 may be associated with the severity of CA6 infection. These findings could raise awareness of the clinical importance of CA6 infection among practitioners.

Scavenger receptor class a, member 3 is associated with severity of hand, foot, and mouth disease in a case-control study.

Hand, foot, and mouth disease (HFMD) spreads rapidly and has been recognized as a public health problem in recent years in China. Unfortunately, there is no effective vaccine or antiviral drug currently for EV71 infection. In this study, we aim to identify biomarker which are associated with for severity of EV71 infection cases using high-throughput RNA sequencing approach.RNA sequencing of samples from severe HFMD (S) patients group (n = 10) and control HFMD (C) patients group (n = 10) were performed and the results were verified by qPCR. mRNA with the highest expression level was selected to be validated in an independent cohort comprising of 45 severe EV71 infected patients and 45 control by qPCR assay.Seventeen significant differentially expressed genes were identified. Scavenger receptor class A, member 3 (SCARA3) was one of the significantly upregulated genes with the highest expression level and was selected for validation. The mean relative expression levels in severe HFMD and control HFMD patients were 10.1-fold and 5.0-fold, respectively, P value <.001.We found that SCARA3 is associated with severity of HFMD, and it may be a potential prognostic marker to predict the HFMD progression in EV71 infected patients.

A VP1 mutation acquired during an enterovirus 71 disseminated infection confers heparan sulfate binding ability and modulates ex vivo tropism.

Enterovirus 71 (EV71) causes hand, foot and mouth disease, a mild and self-limited illness that is sometimes associated with severe neurological complications. EV71 neurotropic determinants remain ill-defined to date. We previously identified a mutation in the VP1 capsid protein (L97R) that was acquired over the course of a disseminated infection in an immunocompromised host. The mutation was absent in the respiratory tract but was present in the gut (as a mixed population) and in blood and cerebrospinal fluid (as a dominant species). In this study, we demonstrated that this mutation does not alter the dependence of EV71 on the human scavenger receptor class B2 (SCARB2), while it enables the virus to bind to the heparan sulfate (HS) attachment receptor and modifies viral tropism in cell lines and in respiratory, intestinal and neural tissues. Variants with VP197L or VP197R were able to replicate to high levels in intestinal and neural tissues and, to a lesser extent, in respiratory tissues, but their preferred entry site (from the luminal or basal tissue side) differed in respiratory and intestinal tissues and correlated with HS expression levels. These data account for the viral populations sequenced from the patient's respiratory and intestinal samples and suggest that improved dissemination, resulting from an acquired ability to bind HS, rather than specific neurotropism determinants, enabled the virus to reach and infect the central nervous system. Finally, we showed that iota-carrageenan, a highly sulfated polysaccharide, efficiently blocks the replication of HS-dependent variants in cells and 2D neural cultures. Overall, the results of this study emphasize the importance of HS binding in EV71 pathogenesis and open new avenues for the development of antiviral molecules that may prevent this virus's dissemination.

Circulating Salivary miRNA hsa-miR-221 as Clinically Validated Diagnostic Marker for Hand, Foot, and Mouth Disease in Pediatric Patients.

Enhancements in the diagnostic capabilities using host biomarkers are currently much needed where sensitivity and specificity issues plague the diagnosis of Hand, Foot and Mouth Disease (HFMD) in pediatrics clinical samples. We investigated miRNome profiles of HFMD saliva samples against healthy children and developed miRNA-based diagnosis models. Our 6-miRNA scoring model predicted HFMD with an overall accuracy of 85.11% in the training set and 92.86% in the blinded test set of Singapore cohort. Blinded evaluation of the model in Taiwan HFMD cases resulted in 77.08% accuracy with the 6-miRNA model and 68.75% with the 4-miRNA model. The strongest predictor of HFMD in all of the panels, hsa-miR-221 was found to be consistently and significantly downregulated in all of our HFMD cohorts. This is the first study to prove that HFMD infection could be diagnosed by circulating miRNAs in patient's saliva. Moreover, this study also serves as a stepping stone towards the future development of other infectious disease diagnosis workflows using novel biomarkers.

Prokaryotic expression and identification of scavenger receptor B2.

There is still no effective clinical antiviral drug against human enterovirus 71 (EV71) infection, which causes hand, foot and mouth disease (HFMD) in children. Scavenger receptor class B member 2 (SCARB2) is an important receptor of EV71 as it plays a vital role in the early steps of viral infection. In this study, recombinant SCARB2 protein was expressed and purified in a prokaryotic expression system, and was identified by western blot with a monoclonal antibody and mass spectrometry analysis. Detection of the sera from mice immunized with the recombinant SCARB2 protein using ELISA and western blot showed good immunogenicity of the recombinant protein. Furthermore, in the neutralization test cytopathic effect was significantly decreased when EV71 was incubated with the immune sera before infection. In summary, the SCARB2 protein was expressed successfully, and the immune sera showed obvious antiviral effect against EV71. This study provides useful information about the interaction mechanism between SCARB2 and EV71, and is also helpful for further clinical treatment research of HFMD.

Enhanced human enterovirus 71 infection by endocytosis inhibitors reveals multiple entry pathways by enterovirus causing hand-foot-and-mouth diseases.

BACKGROUND: Human enterovirus 71 (EV71) was previously known to enter cells through clathrin or caveolar mediated endocytic pathways. However, we observed chlorpromazine (CPZ) or dynasore (DNS), which inhibit clathrin and dynamin mediated endocytosis, did not suppress EV71 cell entry in particular cell types. So the current knowledge of entry mechanisms by EV71 is not complete. METHODS: Viral infection was examined by flow cytometry or end-point dilution assays. Viral entry was monitored by immunofluorescence or pseudoviral infections. Various inhibitors were utilized for manipulating endocytic pathways. Cellular proteins were knockdown by siRNA. RESULTS: CPZ and DNS did not inhibit but rather enhance viral infection in A549 cells, while they inhibited infections in other cells tested. We further found CPZ did not affect EV71 binding to target cells and failed to affect viral translation and replication, but enhanced viral entry in A549 cells. Immunofluorescence microscopy further confirmed this increased entry. Using siRNA experiment, we found that the enhancement of EV71 infection by CPZ did not require the components of clathrin mediated endocytosis. Finally, CPZ also enhanced infection by Coxackivirus A16 in A549 cells. CONCLUSIONS: CPZ and DNS, previously reported as EV71 entry inhibitors, may rather lead to increased viral infection in particular cell types. CPZ and DNS increased viral entry and not other steps of viral life cycles. Therefore, our study indicated an unknown dynamin-independent entry pathway utilized by enteroviruses that cause Hand-Foot-and-Mouth Diseases.

Inhibition of EV71 by curcumin in intestinal epithelial cells.

EV71 is a positive-sense single-stranded RNA virus that belongs to the Picornaviridae family. EV71 infection may cause various symptoms ranging from hand-foot-and-mouth disease to neurological pathological conditions such as aseptic meningitis, ataxia, and acute transverse myelitis. There is currently no effective treatment or vaccine available. Various compounds have been examined for their ability to restrict EV71 replication. However, most experiments have been performed in rhabdomyosarcoma or Vero cells. Since the gastrointestinal tract is the entry site for this pathogen, we anticipated that orally ingested agents may exert beneficial effects by decreasing virus replication in intestinal epithelial cells. In this study, curcumin (diferuloylmethane, C21H20O6), an active ingredient of turmeric (Curcuma longa Linn) with anti-cancer properties, was investigated for its anti-enterovirus activity. We demonstrate that curcumin treatment inhibits viral translation and increases host cell viability. Curcumin does not exert its anti-EV71 effects by modulating virus attachment or virus internal ribosome entry site (IRES) activity. Furthermore, curcumin-mediated regulation of mitogen-activated protein kinase (MAPK) signaling pathways is not involved. We found that protein kinase C delta (PKCδ) plays a role in virus translation in EV71-infected intestinal epithelial cells and that curcumin treatment decreases the phosphorylation of this enzyme. In addition, we show evidence that curcumin also limits viral translation in differentiated human intestinal epithelial cells. In summary, our data demonstrate the anti-EV71 properties of curcumin, suggesting that ingestion of this phytochemical may protect against enteroviral infections.

Isochlorogenic acid C prevents enterovirus 71 infection via modulating redox homeostasis of glutathione.

Enterovirus 71 (EV71) is a key pathogen of hand, foot and mouth disease (HFMD) in children under 6 years of age. The antiviral potency of antioxidant isochlorogenic acid C (ICAC) extracted from foods was evaluated in cellular and animal models. First, the cytotoxicity of ICAC on Vero cells was investigated. The viral plaques, cytopathic effects and yield induced by EV71 infection were obviously reduced by ICAC, which was consistent with the investigation of VP1 transcripts and protein expression. Moreover, the mortality, weight loss and limb paralysis of mice caused by EV71 challenge were remarkably relieved by ICAC injection, which was achieved through decreases in the viral load and cytokine secretion in the mouse brain. Further biochemical assays showed that ICAC modulated several antioxidant enzymes involved in reduced and oxidized glutathione (GSH and GSSG) homeostasis, including glutathione reductase (GR), glutathione peroxidase (GPX), and glucose-6-phosphate dehydrogenase (G6PD), resulting in restoration of the GSH/GSSG ratio and reactive oxygen species (ROS) level. Finally, the antiviral effects of ICAC were dose-dependently disrupted by BSO, a biosynthesis inhibitor of GSH. This study indicated that ICAC acted as an antioxidant and prevented EV71 infection by modulating the redox homeostasis of glutathione.