Recent Progress on Functional Genomics Research of Enterovirus 71

Tribbles pseudokinase 3 promotes enterovirus A71 infection via dual mechanisms

Enterovirus A71 (EV-A71) is the main pathogen causing hand, foot and mouth disease (HFMD) in children and occasionally associated with neurological diseases such as aseptic meningitis, brainstem encephalitis (BE) and acute flaccid paralysis. We report here that cellular pseudokinase tribbles 3 (TRIB3) facilitates the infection of EV-A71 via dual mechanisms. In one hand, TRIB3 maintains the metabolic stability of scavenger receptor class B member 2 (SCARB2), the bona fide receptor of EV-A71, to enhance the infectious entry and spreading of the virus. On the other hand, TRIB3 facilitates the replication of EV-A71 RNA in a SCARB2-independent manner. The critical role of TRIB3 in EV-A71 infection and pathogenesis was further demonstrated in vivo in mice. In comparison to wild-type C57BL/6 mice, EV-A71 infection in TRIB3 knockdown mice (Trib3+/-) resulted in significantly lower viral loads in muscular tissues and reduced lethality and severity of clinical scores and tissue pathology. In addition, TRIB3 also promoted the replication of coxsackievirus B3 (CVB3) and coxsackievirus A16 (CVA16) in vitro. In conclusion, our results suggest that TRIB3 is one of key host cellular proteins required for the infection and pathogenesis of EV-A71 and some other human enteroviruses and may thus be a potential therapeutic target for combating the infection of those viruses.

AIMP2 restricts EV71 replication by recruiting SMURF2 to promote the degradation of 3D polymerase

Hand, foot and mouth disease (HFMD), mainly caused by enterovirus 71 (EV71), has frequently occurred in the Asia-Pacific region, posing a significant threat to the health of infants and young children. Therefore, research on the infection mechanism and pathogenicity of enteroviruses is increasingly becoming important. The 3D polymerase, as the most critical RNA-dependent RNA polymerase (RdRp) for EV71 replication, is widely targeted to inhibit EV71 infection. In this study, we identified a novel host protein, AIMP2, capable of binding to 3D polymerase and inhibiting EV71 infection. Subsequent investigations revealed that AIMP2 recruits the E3 ligase SMURF2, which mediates the polyubiquitination and degradation of 3D polymerase. Furthermore, the antiviral effect of AIMP2 extended to the CVA16 and CVB1 serotypes. Our research has uncovered the dynamic regulatory function of AIMP2 during EV71 infection, revealing a novel antiviral mechanism and providing new insights for the development of antienteroviral therapeutic strategies.

Viroporins Manipulate Cellular Powerhouses and Modulate Innate Immunity

Viruses have a wide repertoire of molecular strategies that focus on their replication or the facilitation of different stages of the viral cycle. One of these strategies is mediated by the activity of viroporins, which are multifunctional viral proteins that, upon oligomerization, exhibit ion channel properties with mild ion selectivity. Viroporins facilitate multiple processes, such as the regulation of immune response and inflammasome activation through the induction of pore formation in various cell organelle membranes to facilitate the escape of ions and the alteration of intracellular homeostasis. Viroporins target diverse membranes (such as the cellular membrane), endoplasmic reticulum, and mitochondria. Cumulative data regarding the importance of mitochondria function in multiple processes, such as cellular metabolism, energy production, calcium homeostasis, apoptosis, and mitophagy, have been reported. The direct or indirect interaction of viroporins with mitochondria and how this interaction affects the functioning of mitochondrial cells in the innate immunity of host cells against viruses remains unclear. A better understanding of the viroporin-mitochondria interactions will provide insights into their role in affecting host immune signaling through the mitochondria. Thus, in this review, we mainly focus on descriptions of viroporins and studies that have provided insights into the role of viroporins in hijacked mitochondria.

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.

Recent Advances in Enterovirus A71 Infection and Antiviral Agents

Enterovirus A71 (EV-A71) is one of the major causative agents of hand, foot, and mouth disease (HFMD) that majorly affects children. Most of the time, HFMD is a mild disease but can progress to severe complications, such as meningitis, brain stem encephalitis, acute flaccid paralysis, and even death. HFMD caused by EV-A71 has emerged as an acutely infectious disease of highly pathogenic potential in the Asia-Pacific region. In this review, we introduced the properties and life cycle of EV-A71, and the pathogenesis and the pathophysiology of EV-A71 infection, including tissue tropism and host range of virus infection, the diseases caused by the virus, as well as the genes and host cell immune mechanisms of major diseases caused by enterovirus 71 (EV-A71) infection, such as encephalitis and neurologic pulmonary edema. At the same time, clinicopathologic characteristics of EV-A71 infection were introduced. There is currently no specific medication for EV-A71 infection, highlighting the urgency and significance of developing suitable anti-EV-A71 agents. This overview also summarizes the targets of existing anti-EV-A71 agents, including virus entry, translation, polyprotein processing, replication, assembly and release; interferons; interleukins; the mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and protein kinase B signaling pathways; the oxidative stress pathway; the ubiquitin-proteasome system; and so on. Furthermore, it overviews the effects of natural products, monoclonal antibodies, and RNA interference against EV-A71. It also discusses issues limiting the research of antiviral drugs. This review is a systematic and comprehensive summary of the mechanism and pathological characteristics of EV-A71 infection, the latest progress of existing anti-EV-A71 agents. It would provide better understanding and guidance for the research and application of EV-A71 infection and antiviral inhibitors.

Cathelicidin peptide analogues inhibit EV71 infection through blocking viral entry and uncoating

Given the serious neurological complications and deaths associated with enterovirus 71 (EV71) infection, there is an urgent need to develop effective antivirals against this viral infection. In this study, we demonstrated that two Cathelicidin-derived peptides, LL-18 and FF-18 were more potent against EV71 infection than the parent peptide LL-37, which is the mature and processed form of Cathelicidin. These peptides could directly bind to the EV71 virus particles, but not to coxsackievirus, indicative of their high specificity. The binding of peptides with the virus surface occupied the viral canyon region in a way that could block virus-receptor interactions and inhibit viral uncoating. In addition, these peptide analogues could also relieve the deleterious effect of EV71 infection in vivo. Therefore, Cathelicidin-derived peptides might be excellent candidates for further development of antivirals to treat EV71 infection.

Evaluation and mechanism study of Pien Tze Huang against EV-A71 infection

Hand, foot, and mouth disease (HFMD) caused by enterovirus A71 (EV-A71) infection, currently lacks specific preventive and therapeutic interventions. Here, we demonstrated that Pien Tze Huang (PZH) could dose-dependently inhibit EV-A71 replication at the cellular level, resulting in significant reductions in EV-A71 virus protein 1 (VP1) expression and viral yields in Vero and human rhabdomyosarcoma cells. More importantly, we confirmed that PZH could protect mice from EV-A71 infection for the first time, with Ribavirin serving as a positive control. PZH treatment reduced EV-A71 VP1 protein expression, viral yields in infected muscles, and improved muscle pathology. Additionally, we conducted a preliminary mechanism study using quantitative proteomics. The results suggested that the suppression of the PI3K/AKT/mTOR and NF-κB signaling pathways may contribute to the anti-EV-A71 activity of PZH. These findings provide strong evidence supporting the potential therapeutic application of PZH for EV-A71 infection management.

Targeting HNRNPA2B1 inhibits enterovirus 71 replication in SK-N-SH cells

OBJECTIVE

To investigate the effect of heterogeneous nuclear ribonucleoprotein A2B1 (HNRNPA2B1) on the replication of enterovirus 71 (EV-71) in SK-N-SH cells.

METHODS

The mRNA and protein expression of HNRNPA2B1 in SK-N-SH cells were detected by real-time quantitative PCR (qRT-PCR) and western blotting (WB), respectively. WB was used to detect HNRNPA2B1 protein expression in the nucleus and cytosol. The localization of HNRNPA2B1 protein in the nucleus and cytosol was detected by immunofluorescence (IF). The expression of HNRNPA2B1 was inhibited by small interfering RNA (si-HNRNPA2B1). Viral RNA, viral structural protein VP1, and viral titer were detected by qRT-PCR, WB, and viral dilution counting, respectively.

RESULTS

EV-71 infection significantly upregulates the expression of HNRNPA2B1 in SK-N-SH cells. EV-71 infection promotes HNRNPA2B1 nucleus-cytoplasm redistribution. Down-regulation of HNRNPA2B1 expression significantly inhibited EV-71 replication.

CONCLUSION

HNRNPA2B1 protein redistributed from nucleus to cytoplasm and is highly expressed in the cytoplasm during EV-71 infection. Inhibition of HNRNPA2B1 levels effectively inhibits EV-71 replication in SK-N-SH cells.

Research progress on pathogenic and therapeutic mechanisms of Enterovirus A71

In recent years, enterovirus A71 (EV-A71) infection has become a major global public health problem, especially for infants and young children. The results of epidemiological research show that EV-A71 infection can cause acute hand, foot, and mouth disease (HFMD) and complications of the nervous system in severe cases, including aseptic pediatric meningoencephalitis, acute flaccid paralysis, and even death. Many studies have demonstrated that EV-A71 infection may trigger a variety of intercellular and intracellular signaling pathways, which are interconnected to form a network that leads to the innate immune response, immune escape, inflammation, and apoptosis in the host. This article aims to provide an overview of the possible mechanisms underlying infection, signaling pathway activation, the immune response, immune evasion, apoptosis, and the inflammatory response caused by EV-A71 infection and an overview of potential therapeutic strategies against EV-A71 infection to better understand the pathogenesis of EV-A71 and to aid in the development of antiviral drugs and vaccines.

Antiviral effects and mechanisms against EV71 of the novel 2-Benzoxyl-Phenylpyridine Derivatives

A series of 2-Benzoxyl-Phenylpyridine derivatives were evaluated for their potential antiviral activities against EV71. The preliminary assays indicated that some of these compounds exhibited excellent antiviral effects on EV71, they could effectively inhibit virus-induced cytopathic effects (CPEs), reduce progeny viral yields, and present similar or better antiviral activities compared to the positive control drug ribavirin. Among these derivatives, compounds WY7, WY13 and WY14 showed the most potency against EV71. Investigation of the underlying mechanism of action revealed that these compounds target EV71 replication in cells post infection, they could profoundly inhibit viral RNA replication and protein synthesis, and inhibit virus-induced cell apoptosis. Further experiments demonstrated that compound WY7 potently inhibited the activity of the EV71 3C protease (3Cpro), and to some extent, it affected the activity of 3D polymerase (3Dpol), thus blocking viral replication, but not the activity of the 2A proteinase (2Apro). Modeling of the molecular binding of the 3Cpro-WY7 complex revealed that compound WY7 was predicted to insert into the substrate-binding pocket of EV71 3Cpro, blocking substrate recognition and thereby inhibiting EV71 3Cpro activity. These results indicate that these compounds might be feasible therapeutic agents against EV71 infection and that these compounds may provide promising lead scaffolds for the further design and synthesis of potential antiviral agents.

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.

The Bottlenecks of Preparing Virus Particles by Size Exclusion for Antibody Generation

Enterovirus 71 (EV71) is the major etiological agent contributing to the development of hand-foot-mouth disease (HFMD). There are not any global available vaccines or antibody drugs against EV71 released yet. In this study, we perform the virus immunization in a cost-effective and convenient approach by preparing virus particles from size exclusion and immunization of chicken. Polyclonal yolk-immunoglobulin (IgY) was simply purified from egg yolk and monoclonal single-chain variable fragments (scFv) were selected via phage display technology with two scFv libraries containing 6.0 × 106 and 1.3 × 107 transformants. Specific clones were enriched after 5 rounds of bio-panning and four identical genes were classified after the sequence analysis. Moreover, the higher mutation rates were revealed in the CDR regions, especially in the CDR3. IgY showed specific binding activities to both EV71-infected and Coxsackievirus 16-infected cell lysates and high infectivity inhibitory activity of EV71. However, while IgY detected a 37 kDa protein, the selected scFv seemingly detected higher size proteins which could be cell protein instead of EV71 proteins. Despite the highly effective chicken antibody generation, the purity of virus particles prepared by size exclusion is the limitation of this study, and further characterization should be carried out rigorously.

Insights into the Anti-inflammatory and Antiviral Mechanisms of Resveratrol

Resveratrol is a naturally occurring stilbene phytoalexin phenolic compound, which has been extensively studied on its biological activity. It has been widely accepted that resveratrol possesses anti-inflammatory and antiviral activities. In this review, we summarize the anti-inflammatory dosages and mechanism and antiviral mechanism of resveratrol. Since viral infections are often accompanied by inflammation, we propose that the NF-κB signaling pathway is a key and common molecular mechanism of resveratrol to exert anti-inflammatory and antiviral effects. For future studies, we believe that resveratrol's anti-inflammatory and antiviral mechanisms can consider the upstream signaling molecules of the NF-κB signaling pathway. For resveratrol antivirus, future studies can be conducted on the interaction of resveratrol with key proteins or important enzymes of the virus. In addition, we also think that the clinical application of resveratrol is very important. In short, resveratrol is a promising anti-inflammatory and antiviral drug, and research on it needs to be expanded.

Urolithin A inhibits enterovirus 71 replication and promotes autophagy and apoptosis of infected cells in vitro

Hand, foot, and mouth disease (HFMD) is a serious threat to the health of infants, and it can be caused by enterovirus 71 (EV71). The clinical symptoms are mostly self-limiting, but some infections develop into aseptic meningitis with poor prognosis and even death. In this study, urolithin A (UroA), an intestinal metabolite of ellagic acid, significantly inhibited the replication of EV71 in cells. Further evaluation showed that UroA was better than ribavirin in terms of its 50% cytopathic concentration (CC₅₀), 50% inhibitory concentration (IC₅₀), and selectivity index. Moreover, UroA inhibited the proliferation of EV71 by promoting autophagy and apoptosis of infected cells. Therefore, UroA is a candidate drug for the treatment of EV71 infection.

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.

Neddylation of Enterovirus 71 VP2 Protein Reduces Its Stability and Restricts Viral Replication

Posttranslational modifications (PTMs) of viral proteins play critical roles in virus infection. The role of neddylation in enterovirus 71 (EV71) replication remains poorly defined. Here, we showed that the structural protein VP2 of EV71 can be modified by neural precursor cell-expressed developmentally downregulated protein 8 (NEDD8) in an E3 ligase X-linked inhibitor of apoptosis protein (XIAP)-dependent manner. Mutagenesis and biochemical analyses mapped the neddylation site at lysine 69 (K69) of VP2 and demonstrated that neddylation reduced the stability of VP2. In agreement with the essential role of VP2 in viral replication, studies with EV71 reporter viruses with wild-type VP2 (enhanced green fluorescent protein [EGFP]-EV71) and a K69R mutant VP2 (EGFP-EV71-VP2 K69R) showed that abolishment of VP2 neddylation increased EV71 replication. In support of this finding, overexpression of NEDD8 significantly inhibited the replication of wild-type EV71 and EGFP-EV71, but not EGFP-EV71-VP2 K69R, whereas pharmacologic inhibition of neddylation with the NEDD8-activating enzyme inhibitor MLN4924 promoted the replication of EV71 in biologically relevant cell types. Our results thus support the notion that EV71 replication can be negatively regulated by host cellular and pathobiological cues through neddylation of VP2 protein. IMPORTANCE Neddylation is a ubiquitin-like posttranslational modification by conjugation of neural precursor cell-expressed developmentally downregulated protein 8 (NEDD8) to specific proteins for regulation of their metabolism and biological activities. In this study, we demonstrated for the first time that EV71 VP2 protein is neddylated at K69 residue to promote viral protein degradation and consequentially suppress multiplication of the virus. Our findings advance knowledge related to the roles of VP2 in EV71 virulence and the neddylation pathway in the host restriction of EV71 infection.

A Single Amino Acid Substitution in Structural Protein VP2 Abrogates the Neurotropism of Enterovirus A-71 in Mice

Enterovirus 71 (EV-A71) causes hand, foot, and mouth disease (HFMD) in children and has been associated with neurological complications. With no specific treatment and a monovalent vaccine limited to the Chinese market, HFMD remains a serious public health concern and an economic burden to affected societies. The molecular mechanisms underpinning EV-A71 neurovirulence have yet to be fully elucidated. In this work, we provide experimental evidence that a single amino acid substitution (I to K) at position 149 in structural protein VP2 of a non-mouse-adapted EV-A71 strain completely and specifically abrogated its infectivity in murine motor neuron-like NSC-34 cells. We showed that VP2 I149K mutant was impaired in murine SCARB2-mediated entry step but retained the ability to attach at the cell surface. In vivo, VP2 I149K mutant was fully attenuated in a symptomatic mouse model of progressive limb paralysis. While viral titers in limb muscles were comparable to mice infected with parental wild-type strain, significantly lower viral titers were measured in the spinal cord and brain, with minimal tissue damage, therefore indicating that VP2 I149K mutant is specifically impaired in its ability to invade the central nervous system (CNS). This study highlights the key role of amino acid at position 149 in VP2 in EV-A71 neurovirulence, and lends further support that the EF loop of VP2 represents a potential therapeutic target.

N-Acetyltransferase 8 Promotes Viral Replication by Increasing the Stability of Enterovirus 71 Nonstructural Proteins

Enterovirus 71 (EV71) is deemed as a re-emergent pathogen with recent outbreaks worldwide. EV71 infection causes hand, foot and mouth disease (HFMD) and has been associated with severe cardiac and central nervous system complications and even death. Viruses need host factors to complete their life cycle, thus the identification of the host factors for EV71 infection is pivotal to new antiviral research. Emerging evidence has highlighted the importance of protein acetylation during infection of various human viruses. The endoplasmic reticulum, as the prominent organelle of EV71 replication, also has its unique acetylation regulation mechanism. However, the pathogenesis of EV71 and its relationship with the ER-based acetylation machinery are not fully understood. In this study, we demonstrated for the first time that the ER-resident acetyltransferase NAT8 is a host factor for EV71 infection. Inhibiting NAT8 with CRISPR or a small compound significantly suppressed EV71 infection in SK-N-SH cells. NAT8 promoted EV71 replication in an acetyltransferase activity-dependent manner. Additionally, we found NAT8 facilitates EV71 infection through interacting with EV71 2B,3AB and 3C proteins and increasing the stability of these proteins. These results uncovered a novel function of NAT8 and elucidated a new mechanism underlying the regulation of EV71 replication. Importance Enterovirus 71 (EV71) is one of the most common pathogens that cause hand, foot and mouth disease in young children and some patients experience severe or fatal neurologic consequences. To ensure efficient replication, the virus must hijack multiple host factors for its own benefit. Here we show that the ER-resident acetyltransferase NAT8 is a host factor for EV71 infection. EV71 fails to complete its infection in various cells in the absence of NAT8. We further show that NAT8 benefits EV71 replication in an acetyltransferase activity-dependent manner. Finally, we show that NAT8 facilitates EV71 infection through interacting with EV71 2B,3AB and 3C proteins and increasing the stability of these proteins. These results uncovered a novel function of NAT8 in EV71 infection and elucidated a new mechanism underlying the regulation of EV71 replication.

A novel subgenotype C6 Enterovirus A71 originating from the recombination between subgenotypes C4 and C2 strains in mainland China

Recombination plays important roles in the genetic diversity and evolution of Enterovirus A71 (EV-A71). The phylogenetics of EV-A71 in mainland China found that one strain DL71 formed a new subgenotype C6 with unknown origin. This study investigated the detailed genetic characteristics of the new variant. DL71 formed a distinct cluster within genotype C based on the genome and individual genes (5′UTR, VP4, VP1, 2A, 2B, 2C, 3D, and 3′UTR). The average genetic distances of the genome and individual genes (VP3, 2A, 2B, 2C, 3A, 3C, and 3D) between DL71 and reference strains were greater than 0.1. Nine recombination events involving smaller fragments along DL71 genome were detected. The strains Fuyang-0805a (C4) and Tainan/5746/98 (C2) were identified as the parental strains of DL71. In the non-recombination regions, DL71 had higher identities with Fuyang-0805a than Tainan/5746/98, and located in the cluster with C4 strains. However, in the recombination regions, DL71 had higher identities with Tainan/5746/98 than Fuyang-0805a, and located in the cluster with C2 strains. Thus, DL71 was a novel multiple inter-subgenotype recombinant derived from the dominant subgenotype C4 and the sporadic subgenotype C2 strains. Monitoring the emergence of new variants by the whole-genome sequencing remains essential for preventing disease outbreaks and developing new vaccines.

3C protease of enterovirus 71 cleaves promyelocytic leukemia protein and impairs PML-NBs production

BACKGROUND

Enterovirus 71 (EV71) usually infects infants causing hand-foot-mouth disease (HFMD), even fatal neurological disease like aseptic meningitis. Effective drug for preventing and treating EV71 infection is unavailable currently. EV71 3C mediated the cleavage of many proteins and played an important role in viral inhibiting host innate immunity. Promyelocytic leukemia (PML) protein, the primary organizer of PML nuclear bodies (PML-NBs), can be induced by interferon and is involved in antiviral activity. PML inhibits EV71 replication, and EV71 infection reduces PML expression, but the molecular mechanism is unclear.

METHODS

The cleavage of PMLIII and IV was confirmed by co-transfection of EV71 3C protease and PML. The detailed cleavage sites were evaluated further by constructing the Q to A mutant of PML. PML knockout cells were infected with EV71 to identify the effect of cleavage on EV71 replication. Immunofluorescence analysis to examine the interference of EV71 3C on the formation of PML-NBs.

RESULTS

EV71 3C directly cleaved PMLIII and IV. Furthermore, 3C cleaved PMLIV at the sites of Q430-A431 and Q444-S445 through its protease activity. Overexpression of PMLIV Q430A/Q444A variant exhibited stronger antiviral potential than the wild type. PMLIV Q430A/Q444A formed normal nuclear bodies that were not affected by 3C, suggesting that 3C may impair PML-NBs production via PMLIV cleavage and counter its antiviral activities. PML, especially PMLIV, which sequesters viral proteins in PML-NBs and inhibits viral production, is a novel target of EV71 3C cleavage.

CONCLUSIONS

EV71 3C cleaves PMLIV at Q430-A431 and Q444-S445. Cleavage reduces the antiviral function of PML and decomposes the formation of PML-NBs, which is conducive to virus replication.

Enterovirus Infection Restricts Long Interspersed Element 1 Retrotransposition

Long interspersed element 1 (LINE-1 or L1) is the only active autonomous retrotransposon in the human genome that can serve as an endogenous upstream activator of cytoplasmic nucleic acid sensing pathways to elicit an antiviral immune response. In this study, we investigated the influence of enteroviral infection on L1 mobility. The results showed that infection with different enteroviruses, both EV-D68 and EV-A71, blocked L1 transposition. We screened diverse viral accessory proteins for L1 activity and identified EV-D68 2A, 3A, 3C, and EV-A71 ORF2p proteins as viral L1 inhibitors. EV-D68 2A suppressed L1 mobility by expression suppression of L1 proteins. Viral proteins 3A and 3C restricted ORF2p-mediated L1 reverse transcription in isolated L1 ribonucleoproteins. The newly identified enteroviral protein ORF2p inhibited the expression of L1 ORF1p. Altogether, our findings shed light on the strict modulation of L1 retrotransposons during enterovirus replication.

Inhibition of viral suppressor of RNAi proteins by designer peptides protects from enteroviral infection in vivo

RNA interference (RNAi) is the major antiviral mechanism in plants and invertebrates, but the absence of detectable viral (v)siRNAs in mammalian cells upon viral infection has questioned the functional relevance of this pathway in mammalian immunity. We designed a series of peptides specifically targeting enterovirus A71 (EV-A71)-encoded protein 3A, a viral suppressor of RNAi (VSR). These peptides abrogated the VSR function of EV-A71 in infected cells and resulted in the accumulation of vsiRNAs and reduced viral replication. These vsiRNAs were functional, as evidenced by RISC-loading and silencing of target RNAs. The effects of VSR-targeting peptides (VTPs) on infection with EV-A71 as well as another enterovirus, Coxsackievirus-A16, were ablated upon deletion of Dicer1 or AGO2, core components of the RNAi pathway. In vivo, VTP treatment protected mice against lethal EV-A71 challenge, with detectable vsiRNAs. Our findings provide evidence for the functional relevance of RNAi in mammalian immunity and present a therapeutic strategy for infectious disease.

Preparation and verification of a monoclonal antibody against a conserved linear epitope in enterovirus A protein 2C

Enterovirus A (EV-A) species are the main agents responsible for hand, foot, and mouth disease (HFMD), a serious public health concern. Lack of appropriate reagents prevents the mechanistic study of these virus infections. 2C protein, a non-structural protein of Enterovirus, is crucial for viral replication and antiviral immunity. Here, preparation and testing of a monoclonal antibody by immunizing mice with Coxsackievirus A10 protein 2C (CVA10-2C) was reported. This antibody could identify most EV-A types, both conventional and unconventional groups. We also mapped the antibody epitope SLATGIIARA, which is highly conserved in EV-A species and located in the ATPase domain. Some key amino acids include G140, I141, I142, and R144. In conclusion, we generated a recombinant monoclonal antibody against multiple EVA types and confirmed its performance, which may facilitate the future study of Enterovirus A infection and many potential applications, such as the diagnosis of pathogen or the development of antiviral therapies.

A single mutation in the cis-acting replication element identified within the EV-A71 2C-coding region causes defects in virus production in cell culture

ABSTRACTEnterovirus A71 (EV-A71) can cause hand, foot and mouth disease with neurological and systemic complications, most frequently affecting children and infants. We describe a cis-acting replication element (cre) with a conserved stem-loop structure within the EV-A71 2C-coding region. By site-directed mutagenesis and reverse genetics using the EV-A71 full-length genome and the EV-A71 replicon containing the firefly luciferase reporter gene in place of the P1 region, the stem-loop structure and the AAACA in the loop of the cre were confirmed to be required for the EV-A71 replication phenotype. EV-A71 genomes containing a mutation at the first or third A residue of AAACA could not be recovered. Insertion of a wild-type cre from EV-A71 or poliovirus in the 5'UTR led to successful recovery of the replication of nonviable mutants. Furthermore, the cre mutants showed lower binding capacity with the host cellular factor IGF2BP2, knockdown of which resulted in a significant decrease in EV-A71 production. All the available evidence shows the location independence but functional importance of the interaction of the cre with the cellular host for efficient production of EV-A71, contributing to the growing body of knowledge regarding picornavirus cres.

Viral determinants that drive Enterovirus-A71 fitness and virulence

Hand, Foot and Mouth Disease (HFMD) is usually a self-limiting, mild childhood disease that is caused mainly by Coxsackie virus A16 (CVA16) and Enterovirus A71 (EV-A71), both members of the Picornaviridae family. However, recurring HFMD outbreaks and epidemics due to EV-A71 infection in the Western Pacific region, and the propensity of EV-A71 strains to cause severe neurological complications have made this neurotropic virus a serious public health concern in afflicted countries. High mutation rate leading to viral quasispecies combined with frequent intra- and inter-typic recombination events amongst co-circulating EV-A71 strains have contributed to the great diversity and fast evolution of EV-A71 genomes, making impossible any accurate prediction of the next epidemic strain. Comparative genome sequence analyses and mutagenesis approaches have led to the identification of a number of viral determinants involved in EV-A71 fitness and virulence. These viral determinants include amino acid residues located in the structural proteins of the virus, affecting attachment to the host cell surface, receptor binding, and uncoating events. Critical residues in non-structural proteins have also been identified, including 2C, 3A, 3C proteases and the RNA-dependent RNA polymerase. Finally, mutations altering key secondary structures in the 5’ untranslated region were also found to influence EV-A71 fitness and virulence. While our current understanding of EV-A71 pathogenesis remains fragmented, these studies may help in the rational design of effective treatments and broadly protective vaccine candidates.

DEAD-Box Helicase DDX6 Facilitated RIG-I-Mediated Type-I Interferon Response to EV71 Infection

Previous studies have shown that DEAD (Glu-Asp-Ala-Glu)-box RNA helicases play important roles in viral infection, either as cytosolic sensors of pathogenic molecules or as essential host factors against viral infection. In the current study, we found that DDX6, an RNA helicase belonging to the DEAD-box family of helicase, exhibited anti-Enterovirus 71 activity through augmenting RIG-I-mediated type-I IFN response. Moreover, DDX6 binds viral RNA to form an RNA-protein complex to positively regulate the RIG-I-mediated interferon response; however, EV71 has evolved a strategy to antagonize the antiviral effect of DDX6 by proteolytic degradation of the molecule through its non-structural protein 2A, a virus-encoded protease.

Comprehensive analysis of the circRNA expression profile and circRNA-miRNA-mRNA network in the pathogenesis of EV-A71 infection

Enterovirus A71 (EV-A71) is an important emerging virus posing a threat to children under five years old. Circular RNAs (circRNAs), a novel class of endogenous RNAs, have been recognized to play important roles in the onset and development of viral diseases. However, it has not been determined which specific circRNAs are involved in the pathological mechanisms of EV-A71 infection. In this study, RNA-sequencing (RNA-seq) was conducted to characterize differentially expressed circRNAs during the process of EV-A71 infection. Overall, 8726, 10405 and 4710 circRNAs were detected in the control, EV-A71-12 h and EV-A71-24 h groups, respectively, of which 1851 and 951 circRNAs were differentially expressed in the EV-A71-12 h and EV-A71-24 h groups versus the control group. The overlapping circRNAs in the EV-A71-infected groups were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, which further demonstrated that the host genes of these circRNAs were principally implicated in activities associated with the progression of viral infection, such as immune system process, Wnt signaling pathway, etc. Additionally, qRT-PCR detection showed that six selected circRNAs were identical to the sequencing data. To excavate the key circRNAs in EV-A71 infection, we comprehensively evaluated and integrated the relationship of circRNA/miRNA/mRNA, and eventually screened 2 key circRNA regulatory axes, namely hsa_circ_0017115/hsa-miR-150-5p/EGR1 and hsa_circ_0005060/hsa-miR-4685-5p/MMP2. In summary, our findings not only provide the first comprehensive expression and functional profile of circRNAs in response to EV-A71 infection, but also offer a novel direction to elucidate the molecular mechanism underlying viral pathogenesis and the cellular immune response in host-EV-A71 interactions.

The Enterovirus Theory of Disease Etiology in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: A Critical Review

Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) is a complex, multi-system disease whose etiological basis has not been established. Enteroviruses (EVs) as a cause of ME/CFS have sometimes been proposed, as they are known agents of acute respiratory and gastrointestinal infections that may persist in secondary infection sites, including the central nervous system, muscle, and heart. To date, the body of research that has investigated enterovirus infections in relation to ME/CFS supports an increased prevalence of chronic or persistent enteroviral infections in ME/CFS patient cohorts than in healthy individuals. Nevertheless, inconsistent results have fueled a decline in related studies over the past two decades. This review covers the aspects of ME/CFS pathophysiology that are consistent with a chronic enterovirus infection and critically reviews methodologies and approaches used in past EV-related ME/CFS studies. We describe the prior sample types that were interrogated, the methods used and the limitations to the approaches that were chosen. We conclude that there is considerable evidence that prior outbreaks of ME/CFS were caused by one or more enterovirus groups. Furthermore, we find that the methods used in prior studies were inadequate to rule out the presence of chronic enteroviral infections in individuals with ME/CFS. Given the possibility that such infections could be contributing to morbidity and preventing recovery, further studies of appropriate biological samples with the latest molecular methods are urgently needed.

Antiviral activity of Mulberroside C against enterovirus A71 in vitro and in vivo

Enterovirus A71 (EV-A71) is one of the main causative agents of hand, foot and mouth disease which seriously threatens young children's health and lives. However, there is no effective therapy currently available for treating these infections. Therefore, effective drugs to prevent and treat EV-A71 infections are urgently needed. Here, we identified Mulberroside C potently against the proliferation of EV-A71. The in-vitro anti-EV-A71 activity of Mulberroside C was assessed by cytopathic effect inhibition and viral plaque reduction assays, and the results showed that Mulberroside C significantly inhibited EV-A71 infection. The downstream assays affirmed that Mulberroside C inhibited viral protein and RNA synthesis. Furthermore, Mulberroside C effectively reduced clinical symptoms in EV-A71 infected mice and reduced mortality at higher concentrations. The mechanism study indicated that Mulberroside C bound to the hydrophobic pocket of viral capsid protein VP1, thereby preventing viral uncoating and genome release. Taken together, our study indicated that Mulberroside C could be a promising EV-A71 inhibitor and worth extensive preclinical investigation as a lead compound.

Reverse Genetic Approaches for the Generation of Full Length and Subgenomic Replicon of EV71 Virus

Enterovirus 71 (EV71) is a neurotropic pathogen that causes hand, foot, and mouth disease (HFMD) and it has been consistently associated with severe neurological, cardiac, and respiratory complications. Yet there is no specific treatment for this virus and we still know little about the viral pathogenesis. In this study, we first generated an infectious cDNA clone of EV71 virus from a patient virus strain and made a full-length virus with a NanoLuc reporter gene through reverse genetic approaches. The reporter gene of this virus is genetically stable when passaging in cells and could be used for antiviral testing. In addition, we also made subgenomic replicons (SGRs) of EV71, which lacks part of the structural genes dispensable for viral replication and showed that SGR can be used for viral replication study. Overall, these reporter viral systems are useful tools for EV71 pathogenesis study and antiviral screening.

Stem II-disrupting pseudoknot does not abolish ability of Senecavirus A IRES to initiate protein expression, but inhibits recovery of virus from cDNA clone

Senecavirus A (SVA) is classified into the genus Senecavirus in the family Picornaviridae. Its genome is a positive-sense, single-stranded and nonsegmented RNA, approximately 7300 nucleotides in length. A picornaviral genome is essentially an mRNA, which, albeit unmodified with 5' cap structure, can still initiate protein expression by the internal ribosome entry site (IRES). The SVA genome contains a hepatitis C virus-like IRES, in which a pseudoknot structure plays an important role in initiating protein expression. In this study, we constructed a set of SVA (CH-LX-01-2016 strain) minigenomes with all combinations of point mutations in its pseudoknot stem II (PKS-II). The results showed that any combination of point mutations could not significantly interfere with the IRES to initiate protein expression. Further, we constructed a full-length SVA cDNA clone, in which the PKS-II-forming cDNA motif was subjected to site-directed mutagenesis for totally disrupting the PKS-II formation in IRES. Such a modified SVA cDNA clone was transfected into BSR-T7/5 cells, consequently demonstrating that the PKS-II-disrupting IRES interfered neither with protein expression nor with antigenome replication, whereas a competent SVA could not be rescued from the cDNA clone. It was speculated that the mutated motif possibly disrupted a packaging signal for virion assembly, therefore causing the failure of SVA rescue.

Molecular epidemiology and recombination of Enterovirus A71 in mainland China from 1987 to 2017

Enterovirus A71 (EV-A71) is an important pathogen of severe hand, foot, and mouth disease (HFMD) in young children. This study aimed to retrospectively analyze the molecular epidemiology and recombination of EV-A71 in mainland China during 1987–2017. Phylogenetic tree showed that besides the previously reported subgenotypes A, B5, C0, C2, C3, and C4, a new subgenotype C6 emerged in mainland China. Recombination analysis indicated that C4 EV-A71 was derived from a common ancestor as a “double-recombinant” virus by intertypic recombination between C EV-A71 and CVA4, CVA5, CVA14, and CVA16 strains in P3 region and intratypic recombination between C and B EV-A71 strains in P2 region. The B5 EV-A71 shared high similarity with C EV-A71 in P1 region while it contained an unidentified sequence in P2 and P3 regions with two possible recombination patterns: one occurred between C4 EV-A71 and CVA3, CVA5, CVA6, CVA10, and CVA12 stains with one breakpoint in 3C, and the other occurred between C1, C2, C3, and C5 EV-A71 and CVA4, CVA5, CVA14, and CVA16 strains with two breakpoints in the 2A/2B junction and 3C. The C2 EV-A71 was probably a recombinant virus between C4 EV-A71 and CVA8 strains with two breakpoints located in the 5′UTR and 2A/2B junction. Moreover, an incredible recombination of C6 EV-A71 occurred between C4 and C2 EV-A71 with multiple breakpoints. Thus, continuous studies on EV-A71 genome characteristics are still useful and essential for monitoring emergence of new viruses and preventing HFMD outbreaks.

Recent advances of enterovirus 71 [Formula: see text] targeting Inhibitors

With CA16, enterovirus-71 is the causative agent of hand foot and mouth disease (HFMD) which occurs mostly in children under 5 years-old and responsible of several outbreaks since a decade. Most of the time, HFMD is a mild disease but can progress to severe complications such as meningitis, brain stem encephalitis, acute flaccid paralysis (AFP) and even death; EV71 has been identified in all severe cases. Therefore, it is actually one of the most public health issues that threatens children's life. [Formula: see text] is a protease which plays important functions in EV71 infection. To date, a lot of [Formula: see text] inhibitors have been tested but none of them has been approved yet. Therefore, a drug screening is still an utmost importance in order to treat and/or prevent EV71 infections. This work highlights the EV71 life cycle, [Formula: see text] functions and [Formula: see text] inhibitors recently screened. It permits to well understand all mechanisms about [Formula: see text] and consequently allow further development of drugs targeting [Formula: see text]. Thus, this review is helpful for screening of more new [Formula: see text] inhibitors or for designing analogues of well known [Formula: see text] inhibitors in order to improve its antiviral activity.

Molecular epidemiology of enteroviruses associated with severe hand, foot and mouth disease in Shenzhen, China, 2014-2018

In this study, we investigated the epidemiology and molecular characteristics of enteroviruses associated with severe hand, foot and mouth disease (HFMD) in Shenzhen, China, during 2014-2018. A total of 137 fecal specimens from patients with severe HFMD were collected. Enterovirus (EV) types were determined using real-time reverse transcription polymerase chain reaction (RT-PCR), RT nested PCR, and sequencing. Sequences were analyzed using bioinformatics programs. Of 137 specimens tested, 97 (70.8%), 12 (8.8%), and 10 (7.3%) were positive for EV-A71, coxsackievirus A6 (CVA6), and CVA16, respectively. Other pathogens detected included CVA2 (2.9%, 4/137), CVA10 (2.9%, 4/137), CVA5 (0.7%, 1/137), echovirus 6 (E6) (0.7%, 1/137) and E18 (0.7%, 1/137). The most frequent complication in patients with proven EV infections was myoclonic jerk, followed by aseptic encephalitis, tachypnea, and vomiting. The frequencies of vomiting and abnormal eye movements were higher in EV-A71-infected patients than that in CVA6-infected or CVA16-infected patients. Molecular phylogeny based on the complete VP1 gene revealed no association between the subgenotype of the virus and disease severity. Nevertheless, 12 significant mutations that were likely to be associated with virulence or the clinical phenotype were observed in the 5’UTR, 2A^pro, 2C, 3A, 3D^pol and 3’UTR of CVA6. Eight significant mutations were observed in the 5’UTR, 2B, 3A, 3D^pol and 3’UTR of CVA16, and 10 significant mutations were observed in the 5’UTR, VP1, 3A and 3C^pro of CVA10. In conclusion, EV-A71 is still the main pathogen causing severe HFMD, although other EV types can also cause severe complications. Potential virulence or phenotype-associated sites were identified in the genomes of CVA6, CVA16, and CVA10.

Regulation of Apoptosis by Enteroviruses

Enterovirus infection can cause a variety of diseases and severely impair the health of humans, animals, poultry, and other organisms. To resist viral infection, host organisms clear infected cells and viruses via apoptosis. However, throughout their long-term competition with host cells, enteroviruses have evolved a series of mechanisms to regulate the balance of apoptosis in order to replicate and proliferate. In the early stage of infection, enteroviruses mainly inhibit apoptosis by regulating the PI3K/Akt pathway and the autophagy pathway and by impairing cell sensors, thereby delaying viral replication. In the late stage of infection, enteroviruses mainly regulate apoptotic pathways and the host translation process via various viral proteins, ultimately inducing apoptosis. This paper discusses the means by which these two phenomena are balanced in enteroviruses to produce virus-favoring conditions – in a temporal sequence or through competition with each other. This information is important for further elucidation of the relevant mechanisms of acute infection by enteroviruses and other members of the picornavirus family.

N6-methyladenosine modifications enhance enterovirus 71 ORF translation through METTL3 cytoplasmic distribution

During replication, numerous viral RNAs are modified by N⁶-methyladenosine (m⁶A), the most abundant internal RNA modification. m⁶A is believed to regulate elements of RNA metabolism, such as splicing, stability, translation, secondary structure formation, and viral replication. In this study, we assessed the occurrence of m⁶A modification of the EV71 genome in human cells and revealed a preferred, conserved modification site across diverse viral strains. A single m⁶A modification at the 5' UTR-VP4 junction was shown to perform a protranslational function. Depletion of the METTL3 methyltransferase or treatment with 3-deazaadenosine significantly reduced EV71 replication. Specifically, METTL3 colocalized with the viral dsRNA replication intermediate in the cytoplasm during EV71 infection. As a nuclear resident protein, METTL3 relies on the binding of the nuclear import protein karyopherin to its nuclear localization signal (NLS) for nuclear translocation. We observed that EV71 2A and METTL3 share nuclear import proteins. The results of this study revealed an inner mechanism by which EV71 2A regulates the subcellular location of METTL3 to amplify its own gene expression, providing an increased understanding of RNA epitranscriptomics during the EV71 replication cycle.

Sodium Copper Chlorophyllin Is Highly Effective against Enterovirus (EV) A71 Infection by Blocking Its Entry into the Host Cell

Human enteroviruses (HEVs) pose an ongoing threat to global public health. Particularly, enterovirus-A71 (EV-A71), the main pathogen causing hand-foot-and-mouth disease (HFMD), has caused ongoing outbreaks globally in recent years associated with severe neurological manifestations and several deaths. Currently, no effective antivirals are available for the prevention or treatment of EV-A71 infection. In this study, we found that sodium copper chlorophyllin (CHL), a health food additive and an over-the-counter anticancer medicine or treatment to reduce the odor of urine or feces, exhibited potent inhibitory activity against infection by divergent EV-A71 and coxsackievirus-A16 (CV-A16) isolates at a low micromolar concentration with excellent safety. The antiviral activity of each was confirmed by colorimetric viral infection and qRT-PCR assays. A series of mechanistic studies showed that CHL did not target the host cell but blocked the entry of EV-A71 and CV-A16 into the host cell at the postattachment stage. In the mouse model, CHL could significantly reduce the viral titer in the lungs and muscles. Since CHL has been used in clinics for many years with excellent safety, it has the potential to be further developed into a prophylactic or therapeutic to prevent or treat HFMD caused by EV-A71 or CV-A16 infection.

Enterovirus-Associated Hand-Foot and Mouth Disease and Neurological Complications in Japan and the Rest of the World

Enteroviruses (EVs) are responsible for extremely large-scale, periodic epidemics in pediatric cohorts, particularly in East and Southeast Asia. Clinical presentation includes a diverse disease spectrum, including hand-foot and mouth disease (HFMD), aseptic meningitis, encephalitis, acute flaccid paralysis, and acute flaccid myelitis. HFMD is predominantly attributable to EV-A types, including the major pathogen EV-A71, and coxsackieviruses, particularly CV-A6, CV-A16, and CV-A10. There have been multiple EV-A71 outbreaks associated with a profound burden of neurological disease and fatal outcomes in Asia since the early 1980s. Efficacious vaccines against EV-A71 have been developed in China but widespread pediatric vaccination programs have not been introduced in other countries. Encephalitis, as a consequence of complications arising from HFMD infection, leads to damage to the thalamus and medulla oblongata. Studies in Vietnam suggest that myoclonus is a significant indicator of central nervous system (CNS) complications in EV-A71-associated HFMD cases. Rapid response in HFMD cases in children is imperative to prevent the progression to a CNS infection; however, prophylactic and therapeutic agents have not been well established internationally, therefore surveillance and functional studies including development of antivirals and multivalent vaccines is critically important to reduce disease burden in pediatric populations.

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.

Synthesis and Broad Antiviral Activity of Novel 2-aryl-isoindolin-1-ones towards Diverse Enterovirus A71 Clinical Isolates

Enterovirus 71 (EV-A71) is the main causative pathogen of childhood hand, foot and mouth disease. Effective medicine is currently unavailable for the treatment of this viral disease. Using the fragment-hopping strategy, a series of 2-aryl-isoindolin-1-one compounds were designed, synthesized and investigated for their in vitro antiviral activity towards multiple EV-A71 clinical isolates (H, BrCr, Shenzhen98, Jiangsu52) in Vero cell culture in this study. The structure⁻activity relationship (SAR) studies identified 2-phenyl-isoindolin-1-ones as a new potent chemotype with potent antiviral activity against EV-A71. Ten out of the 24 tested compounds showed significant antiviral activity (EC₅₀ < 10 µM) towards four EV-A71 strains. Compounds A3 and A4 exhibited broad and potent antiviral activity with the 50% effective concentration (EC₅₀) values in the range of 1.23⁻1.76 μM. Moreover, the selectivity indices of A3 and A4 were significantly higher than those of the reference compound, pirodavir. The western blotting experiment indicated that the viral VP1 was significantly decreased at both the protein and RNA level in a dose-dependent manner following treatment with compound A3. Moreover, compound A3 inhibited the viral replication by acting on the virus entry stage. In summary, this study led to the discovery of 2-aryl-isoindolin-1-ones as a promising scaffold with potent anti-EV-A71 activities, which deserves further in-depth studies.

N6-Methyladenosine and Viral Infection

N⁶-methyladenosine (m⁶A), as a dynamic posttranscriptional RNA modification, recently gave rise to the field of viral epitranscriptomics. The interaction between virus and host is affected by m⁶A. Multiple m⁶A-modified viral RNAs have been observed. The epitranscriptome of m⁶A in host cells are altered after viral infection. The expression of viral genes, the replication of virus and the generation of progeny virions are influenced by m⁶A modifications in viral RNAs during virus infection. Meanwhile, the decorations of m⁶A in host mRNAs can make viral infections more likely to happen or can enhance the resistance of host to virus infection. However, the mechanism of m⁶A regulation in viral infection and host immune response has not been thoroughly elucidated to date. With the development of sequencing-based biotechnologies, transcriptome-wide mapping of m⁶A in viruses has been achieved, laying the foundation for expanding its functions and corresponding mechanisms. In this report, we summarize the positive and negative effects of m⁶A in distinct viral infection. Given the increasingly important roles of m⁶A in diverse viruses, m⁶A represents a novel potential target for antiviral therapy.