Enterovirus 71 VP1 Protein Regulates Viral Replication in SH-SY5Y Cells via the mTOR Autophagy Signaling Pathway

Mitochondrial transfer of α-synuclein mediates carbon disulfide-induced mitochondrial dysfunction and neurotoxicity

Exposure to carbon disulfide (CS2) is a recognized risk factor in the pathogenesis of Parkinson's disease, yet the underlying mechanisms of deleterious effects on mitochondrial integrity have remained elusive. Here, through establishing CS2 exposure models in rat and SH-SY5Y cells, we demonstrated that highly expressed α-synuclein (α-Syn) is transferred to mitochondria via membrane proteins such as Tom20 and leads to mitochondrial dysfunction and mitochondrial oxidative stress, which ultimately causes neuronal injury. We first found significant mitochondrial damage and oxidative stress in CS2-exposed rat midbrain and SH-SY5Y cells and showed that mitochondrial oxidative stress was the main factor of mitochondrial damage by Mitoquinone intervention. Further experiments revealed that CS2 exposure led to the accumulation of α-Syn in mitochondria and that α-Syn co-immunoprecipitated with mitochondrial membrane proteins. Finally, the use of an α-Syn inhibitor (ELN484228) and small interfering RNA (siRNA) effectively mitigated the accumulation of α-Syn in neurons, as well as the inhibition of mitochondrial membrane potential, caused by CS2 exposure. In conclusion, our study identifies the translocation of α-Syn to mitochondria and the impairment of mitochondrial function, which has important implications for the broader understanding and treatment of neurodegenerative diseases associated with environmental toxins.

TLR4 signalling: the key to controlling EV71 replication and inflammatory response

Hand, foot, and mouth disease (HFMD) is a common infectious disease caused by enterovirus 71 (EV71) that frequently affects children, leading to severe infections in some cases. In general, when infection occurs, the body upregulates inflammatory responses to eliminate pathogenic microorganisms to protect the host from infection. However, EV71 may inhibit host's innate immunity to promote virus infection. At present, it is not fully understood how EV71 hijack the host cells for its own replication. Toll-like receptor 4 (TLR4), a natural immune receptor, historically associated with bacterial endotoxin-induced inflammatory responses. However, it is still unclear whether and how TLR4 is altered during EV71 infection. In this study, we observed a reduction in both TLR4 protein and gene transcript levels in RD, GES-1, and Vero cells following EV71 infection, as detected by RT-qPCR, immunofluorescence staining and western blot. Furthermore, we observed that the TLR4 downstream molecules of MYD88, p-NF-κB p65, p-TBK1 and related inflammatory cytokines were also reduced, suggesting that antiviral innate immune and inflammatory response were suppressed. To determine the impact of TLR4 changes on EV71 infection, we interfered EV71-infected RD cells with TLR4 agonist or inhibitor and the results showed that activation of TLR4 inhibited EV71 replication, while inhibition of TLR4 promote EV71 replication. Besides, EV71 replication was also promoted in TLR4 siRNA-transfected and EV71-infected RD cells. This suggests that down-regulation the expression of TLR4 by EV71 can inhibit host immune defense to promote EV71 self-replication. This novel mechanism may be a strategy for EV71 to evade host immunity.

EV71 5'UTR interacts with 3D protein affecting replication through the AKT-mTOR pathway

BACKGROUND

EV71 is one of the important pathogens of Hand-foot-and-mouth disease (HFMD), which causes serious neurological symptoms. Several studies have speculated that there will be interaction between 5'UTR and 3D protein. However, whether 5'UTR interacts with the 3D protein in regulating virus replication has not been clarified.

METHODS

Four 5'UTR mutation sites (nt88C/T, nt90-102-3C, nt157G/A and nt574T/A) and two 3D protein mutation sites (S37N and R142K) were mutated or co-mutated using virulent strains as templates. The replication of these mutant viruses and their effect on autophagy were determined.

RESULTS

5'UTR single-point mutant strains, except for EGFP-EV71(nt90-102-3C), triggered replication attenuation. The replication ability of them was weaker than that of the parent strain the virulent strain SDLY107 which is the fatal strain that can cause severe neurological complications. While the replication level of the co-mutant strains showed different characteristics. 5 co-mutant strains with interaction were screened: EGFP-EV71(S37N-nt88C/T), EGFP-EV71(S37N-nt574T/A), EGFP-EV71(R142K-nt574T/A), EGFP-EV71(R142K-nt88C/T), and EGFP-EV71(R142K-nt157G/A). The results showed that the high replicative strains significantly promoted the accumulation of autophagosomes in host cells and hindered the degradation of autolysosomes. The low replicative strains had a low ability to regulate the autophagy of host cells. In addition, the high replicative strains also significantly inhibited the phosphorylation of AKT and mTOR.

CONCLUSIONS

EV71 5'UTR interacted with the 3D protein during virus replication. The co-mutation of S37N and nt88C/T, S37N and nt574T/ A, R142K and nt574T/A induced incomplete autophagy of host cells and promoted virus replication by inhibiting the autophagy pathway AKT-mTOR. The co-mutation of R142K and nt88C/T, and R142K and nt157G/A significantly reduced the inhibitory effect of EV71 on the AKT-mTOR pathway and reduced the replication ability of the virus.

Molecular Mechanisms Associated with Neurodegeneration of Neurotropic Viral Infection

Viral infections of the central nervous system (CNS) cause variable outcomes from acute to severe neurological sequelae with increased morbidity and mortality. Viral neuroinvasion directly or indirectly induces encephalitis via dysregulation of the immune response and contributes to the alteration of neuronal function and the degeneration of neuronal cells. This review provides an overview of the cellular and molecular mechanisms of virus-induced neurodegeneration. Neurotropic viral infections influence many aspects of neuronal dysfunction, including promoting chronic inflammation, inducing cellular oxidative stress, impairing mitophagy, encountering mitochondrial dynamics, enhancing metabolic rewiring, altering neurotransmitter systems, and inducing misfolded and aggregated pathological proteins associated with neurodegenerative diseases. These pathogenetic mechanisms create a multidimensional injury of the brain that leads to specific neuronal and brain dysfunction. The understanding of the molecular mechanisms underlying the neurophathogenesis associated with neurodegeneration of viral infection may emphasize the strategies for prevention, protection, and treatment of virus infection of the CNS.

Severe pneumonia and pathogenic damage in human airway epithelium caused by Coxsackievirus B4

Coxsackievirus B4 (CVB4) has one of the highest proportions of fatal outcomes of other enterovirus serotypes. However, the pathogenesis of severe respiratory disease caused by CVB4 infection remains unclear. In this study, 3 of 42 (7.2%, GZ-R6, GZ-R7 and GZ-R8) patients with severe pneumonia tested positive for CVB4 infection in southern China. Three full-length genomes of pneumonia-derived CVB4 were sequenced and annotated for the first time, showing their high nucleotide similarity and clustering within genotype V. To analyze the pathogenic damage caused by CVB4 in the lungs, a well-differentiated human airway epithelium (HAE) was established and infected with the pneumonia-derived CVB4 isolate GZ-R6. The outcome was compared with that of a severe hand-foot-mouth disease (HFMD)-derived CVB4 strain GZ-HFM01. Compared with HFMD-derived CVB4, pneumonia-derived CVB4 caused more intense and rapid disruption of HAE polarity, leading to tight-junction barrier disruption, loss of cilia, and airway epithelial cell hypertrophy. More pneumonia-derived CVB4 were released from the basolateral side of the HAE than HFMD-derived CVB4. Of the 18 cytokines tested, only IL-6 and IL-1b secretion significantly increased on bilateral sides of HAE during the early stage of pneumonia-derived CVB4 infection, while multiple cytokine secretions significantly increased in HFMD-derived CVB4-infected HAE. HFMD-derived CVB4 exhibited stronger neurovirulence in the human neuroblastoma cells SH-SY5Y than pneumonia-derived CVB4, which is consistent with the clinical manifestations of patients infected with these two viruses. This study has increased the depth of our knowledge of severe pneumonia infection caused by CVB4 and will benefit its prevention and treatment.

Chronic carbon disulfide exposure induces parkinsonian pathology via α-synuclein aggregation and necrosome complex interaction

Exposure to carbon disulfide (CS2) has been associated with an increased incidence of parkinsonism in workers, but the mechanism underlying this association remains unclear. Using a rat model, we investigated the effects of chronic CS2 exposure on parkinsonian pathology. Our results showed that CS2 exposure leads to significant motor impairment and neuronal damage, including loss of dopaminergic neurons and degeneration of the substantia nigra pars compacta (SNpc). The immunoassays revealed that exposure to CS2 induces aggregation of α-synuclein and phosphorylated α-synuclein, as well as activation of necroptosis in the SNpc. Furthermore, in vitro and in vivo experiments demonstrated that the interaction between α-synuclein and the necrosome complex (RIP1, RIP3, and MLKL) is responsible for the loss of neuronal cells after CS2 exposure. Taken together, our results demonstrate that CS2-mediated α-synuclein aggregation can induce dopaminergic neuron damage and parkinsonian behavior through interaction with the necrosome complex.

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

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

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.

Candida albicans-enteric viral interactions-The prostaglandin E2 connection and host immune responses

The human microbiome comprises trillions of microorganisms residing within different mucosal cavities and across the body surface. The gut microbiota modulates host susceptibility to viral infections in several ways, and microbial interkingdom interactions increase viral infectivity within the gut. Candida albicans, a frequently encountered fungal species in the gut, produces highly structured biofilms and eicosanoids such as prostaglandin E₂ (PGE₂), which aid in viral protection and replication. These biofilms encompass viruses and provide a shield from antiviral drugs or the immune system. PGE₂ is a key modulator of active inflammation with the potential to regulate interferon signaling upon microbial invasion or viral infections. In this review, we raise the perspective of gut interkingdom interactions involving C. albicans and enteric viruses, with a special focus on biofilms, PGE₂, and viral replication. Ultimately, we discuss the possible implications of C. albicans-enteric virus associations on host immune responses, particularly the interferon signaling pathway.

SLC1A3 facilitates Newcastle disease virus replication by regulating glutamine catabolism

As obligate intracellular parasites, viruses rely completely on host metabolic machinery and hijack host nutrients for viral replication. Newcastle disease virus (NDV) causes acute, highly contagious avian disease and functions as an oncolytic agent. NDV efficiently replicates in both chicken and tumour cells. However, how NDV reprograms host cellular metabolism for its efficient replication is still ill-defined. We previously identified a significantly upregulated glutamate transporter gene, solute carrier family 1 member 3 (SLC1A3), during NDV infection via transcriptome analysis. To investigate the potential role of SLC1A3 during NDV infection, we first confirmed the marked upregulation of SLC1A3 in NDV-infected DF-1 or A549 cells through p53 and NF-κB pathways. Knockdown of SLC1A3 inhibited NDV infection. Western blot analysis further confirmed that glutamine, but not glutamate, asparagine, or aspartate, was required for NDV replication. Metabolic flux data showed that NDV promotes the decomposition of glutamine into the tricarboxylic acid cycle. Importantly, the level of glutamate and glutaminolysis were reduced by SLC1A3 knockdown, indicating that SLC1A3 propelled glutaminolysis for glutamate utilization and NDV replication in host cells. Taken together, our data identify that SLC1A3 serves as an important regulator for glutamine metabolism and is hijacked by NDV for its efficient replication during NDV infection. These results improve our understanding of the interaction between NDV and host cellular metabolism and lay the foundation for further investigation of efficient vaccines.

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.

Enterovirus 71 VP1 promotes 5-HT release by upregulating the expression of ERICH3 and methyltransferase ZC3H13: VP1 promotes 5-HT release by ERICH3 and ZC3H13 upregulation

BACKGROUND AND AIM

The effect of structural viral protein 1 (VP1) on neurological damage caused by enterovirus 71 (EV71) infection is unclear. This study aimed to explore the transcriptome changes in EV infected patients and the role of VP1 on the cell secretion pathway of neuron cells.

METHODS

In our cohort, EV infected patients were enrolled, and RNA-seq analysis was used to evaluate the distinct transcript patterns of cerebrospinal fluid (CSF). The EV71 VP1-overexpressing vector (pEGFP-c3-VP1) was generated and transfected into neuron cells. The relationship between Glutamate Rich 3 (ERICH3) and methyltransferase Zinc Finger CCCH-Type Containing 13 (ZC3H13) and their effect on the serotonin (5-HT) release of neuron cells were explored using small interfering RNA. The expression of ERICH3 and ZC3H13 and concentration of 5-HT were determined using real-time PCR, Western blot, and ELISA, respectively.

RESULT

The expression of ERICH3 and ZC3H13 were significantly upregulated in EV infected patients with neurological symptoms compared to those without (P<0.05). The ERICH3 gene had many N6-methyladenosine (m6A) binding sites that can be regulated by m6A modification. Further, the expression of ERICH3 and ZC3H13 were elevated significantly in EV71-VP1 overexpressing neuron cells (P<0.05). Moreover, ERICH3 or ZC3H13 deficiency could significantly downregulate the release of 5-HT in VP1-overexpressing cells (P<0.05). Nonetheless, ERICH3 expression was significantly suppressed when ZC3H13 was silenced in neuron cells and vice versa (P<0.05).

CONCLUSIONS

EV71-VP1 can promote 5-HT release by upregulating the expression of ERICH3 and ZC3H13. 5-HT might be a novel therapeutic target for EV71 infection-induced fatal neuronal damage.

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.

Novel putative pathogenic viruses identified in pangolins by mining metagenomic data

The pangolin is the only scaly mammal in the world and also an important reservoir of pathogenic viruses. Habitat loss and poaching have been shrinking the survival range of pangolins. More information on pangolin virus populations is needed to better understand and assess potential disease risks. In this study, viral metagenomic data were used to reinvestigate the virome in pangolin lung tissue. Complete genome sequences of two novel anelloviruses were acquired and clustered with the referenced feline strains belonging to genus Tettorquevirus and genus Etatorquevirus, respectively. Two genomes belonging to the genus Gemykibivirus, and species Bat-associated cyclovirus 9 were detected, respectively. One genome with a large contig belonging to the genus Senecavirus were also characterized, according to phylogenetic analysis, which can be presumed to be a novel species. In addition, a full genome of endogenous retroviruse (ERV) was assembled from the lungs of pangolin, and this virus may have the possibility of cross-species transmission during the evolution. This virological investigation has increased our understanding of the virome carried by pangolins and provided a reference baseline for possible zoonotic infectious diseases in the future.

Fish ACE2 is not susceptible to SARS-CoV-2

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SARS-CoV-2 cannot use fish ACE2 to entry cells.

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Fish cell lines (EPC, CIK, BF-2) were not susceptible to SARS-CoV-2 infection.

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Proper disinfection of frozen food surfaces could prevent cold-chain transimission of SARS-CoV-2.

Molecular dynamic simulation analysis of SARS-CoV-2 spike mutations and evaluation of ACE2 from pets and wild animals for infection risk

Coronavirus Disease 2019 (COVID-19) is an ongoing global health emergency that has caused tremendous stress and loss of life worldwide. The viral spike glycoprotein is a critical molecule mediating transmission of SARS-CoV-2 by interacting with human ACE2. However, through the course of the pandemics, there has not been a thorough analysis of the spike protein mutations, and on how these mutants influence the transmission of SARS-CoV-2. Besides, cases of SARS-CoV-2 infection among pets and wild animals have been reported, so the susceptibility of these animals requires great attention to investigate, as they may also link to the renewed question of a possible intermediate host for SARS-CoV-2 before it was transmitted to humans. With over 226,000 SARS-CoV-2 sequences obtained, we found 1573 missense mutations in the spike gene, and 226 of them were within the receptor-binding domain (RBD) region that directly interacts with human ACE2. Modeling the interactions between SARS-CoV-2 spike mutants and ACE2 molecules showed that most of the 74 missense mutations in the RBD region of the interaction interface had little impact on spike binding to ACE2, whereas several within the spike RBD increased the binding affinity toward human ACE2 thus making the virus likely more contagious. On the other hand, modeling the interactions between animal ACE2 molecules and SARS-CoV-2 spike revealed that many pets and wild animals' ACE2 had a variable binding ability. Particularly, ACE2 of bamboo rat had stronger binding to SARS-CoV-2 spike protein, whereas that of mole, vole, Mus pahari, palm civet, and pangolin had a weaker binding compared to human ACE2. Our results provide structural insights into the impact on interactions of the SARS-CoV-2 spike mutants to human ACE2, and shed light on SARS-CoV-2 transmission in pets and wild animals, and possible clues to the intermediate host(s) for SARS-CoV-2.

Integrative analysis of lncRNA-miRNA-mRNA-associated competing endogenous RNA regulatory network involved in EV71 infection

The competing endogenous RNA (ceRNA) axis has been shown to play a critical role in the pathogenesis of various viral infections. Generally, the ceRNA network involves long non-coding RNAs (lncRNAs) that act as sponges for miRNA to regulate mRNA expression. However, no information is available regarding the involvement of ceRNA networks in Enterovirus type 71 (EV71) infections. In the present study, data obtained from Gene Expression Omnibus (GEO) database was analyzed using various bioinformatics tools. EV71 infection in rhabdomyosarcoma (RD) cells was associated with differential expression of six lncRNAs, 28 miRNAs, and 349 mRNAs. Gene function enrichment analysis suggested induction of cytoplasmic vesicle process upon EV71 infection. The ceRNA networks were constructed, in which 20 hub genes were predicted by protein-protein interaction. To confirm the MALAT1/miR-194-5p/DUSP1 ceRNA regulatory axis in EV71 infection, real-time quantitative polymerase chain reaction (qRT-PCR) and luciferase reporter assay were performed. The results of the study also revealed the involvement of the MALAT1/miR-194-5p axis in apoptosis induced by EV71 infection, while no association with autophagy was observed. Thus, the present study provided novel insights into the pathogenic mechanism of EV71 infection.

Comparative genetic analyses of Korean bat coronaviruses with SARS-CoV and the newly emerged SARS-CoV-2

Background

Bats have been considered natural reservoirs for several pathogenic human coronaviruses (CoVs) in the last two decades. Recently, a bat CoV was detected in the Republic of Korea; its entire genome was sequenced and reported to be genetically similar to that of the severe acute respiratory syndrome CoV (SARS-CoV).

Objectives

The objective of this study was to compare the genetic sequences of SARS-CoV, SARS-CoV-2, and the two Korean bat CoV strains 16BO133 and B15-21, to estimate the likelihood of an interaction between the Korean bat CoVs and the human angiotensin-converting enzyme 2 (ACE2) receptor.

Methods

The phylogenetic analysis was conducted with the maximum-likelihood (ML) method using MEGA 7 software. The Korean bat CoVs receptor binding domain (RBD) of the spike protein was analyzed by comparative homology modeling using the SWISS-MODEL server. The binding energies of the complexes were calculated using PRODIGY and MM/GBGA.

Results

Phylogenetic analyses of the entire RNA-dependent RNA polymerase, spike regions, and the complete genome revealed that the Korean CoVs, along with SARS-CoV and SARS-CoV-2, belong to the subgenus Sarbecovirus, within BetaCoVs. However, the two Korean CoVs were distinct from SARS-CoV-2. Specifically, the spike gene of the Korean CoVs, which is involved in host infection, differed from that of SARS-CoV-2, showing only 66.8%–67.0% nucleotide homology and presented deletions within the RBD, particularly within regions critical for cross-species transmission and that mediate interaction with ACE2. Binding free energy calculation revealed that the binding affinity of Korean bat CoV RBD to hACE2 was drastically lower than that of SARS-CoV and SARS-CoV-2.

Conclusions

These results suggest that Korean bat CoVs are unlikely to bind to the human ACE2 receptor.

Regulation of the proteostasis network during enterovirus infection: A feedforward mechanism for EV-A71 and EV-D68

The proteostasis network guarantees successful protein synthesis, folding, transportation, and degradation. Mounting evidence has revealed that this network maintains proteome integrity and is linked to cellular physiology, pathology, and virus infection. Human enterovirus A71 (EV-A71) and EV-D68 are suspected causative agents of acute flaccid myelitis, a severe poliomyelitis-like neurologic syndrome with no known cure. In this context, further clarification of the molecular mechanisms underlying EV-A71 and EV-D68 infection is paramount. Here, we summarize the components of the proteostasis network that are intercepted by EV-A71 and EV-D68, as well as antivirals that target this network and may help develop improved antiviral drugs.

Dysregulated autophagy contributes to the pathogenesis of enterovirus A71 infection

Enterovirus A71 (EVA71) infection continues to remain a vital threat to global public health, especially in the Asia–Pacific region. It is one of the most predominant pathogens that cause hand, foot, and mouth disease (HFMD), which occurs mainly in children below 5 years old. Although EVA71 prevalence has decreased sharply in China with the use of vaccines, epidemiological studies still indicate that EVA71 infection involves severe and even fatal HFMD cases. As a result, it remains more fundamental research into the pathogenesis of EVA71 as well as to develop specific anti-viral therapy. Autophagy is a conserved, self-degradation system that is critical for maintaining cellular homeostasis. It involves a variety of biological functions, such as development, cellular differentiation, nutritional starvation, and defense against pathogens. However, accumulating evidence has indicated that EVA71 induces autophagy and hijacks the process of autophagy for their optimal infection during the different stages of life cycle. This review provides a perspective on the emerging evidence that the “positive feedback” between autophagy induction and EVA71 infection, as well as its potential mechanisms. Furthermore, autophagy may be involved in EVA71-induced nervous system impairment through mediating intracranial viral spread and dysregulating host regulator involved self-damage. Autophagy is a promising therapeutic target in EVA71 infection.

Identifying SARS-CoV-2-related coronaviruses in Malayan pangolins

The ongoing outbreak of viral pneumonia in China and across the world is associated with a new coronavirus, SARS-CoV-2¹. This outbreak has been tentatively associated with a seafood market in Wuhan, China, where the sale of wild animals may be the source of zoonotic infection². Although bats are probable reservoir hosts for SARS-CoV-2, the identity of any intermediate host that may have facilitated transfer to humans is unknown. Here we report the identification of SARS-CoV-2-related coronaviruses in Malayan pangolins (Manis javanica) seized in anti-smuggling operations in southern China. Metagenomic sequencing identified pangolin-associated coronaviruses that belong to two sub-lineages of SARS-CoV-2-related coronaviruses, including one that exhibits strong similarity in the receptor-binding domain to SARS-CoV-2. The discovery of multiple lineages of pangolin coronavirus and their similarity to SARS-CoV-2 suggests that pangolins should be considered as possible hosts in the emergence of new coronaviruses and should be removed from wet markets to prevent zoonotic transmission.

Inhibition of Enterovirus 71 by Selenium Nanoparticles Loaded with siRNA through Bax Signaling Pathways

Enterovirus 71 (EV71) is the principal pathogen leading to severe cases of hand, foot, and mouth disease (HFMD). Specific drugs for EV71 are not discovered currently. Small interfering RNA (siRNA) provides a promising antiviral treatment pathway, but it is difficult to cross cell membranes and is easy to degrade. Nanoparticles are promising for their carrying capacity currently. In this study, the siRNA targeting EV71 VP1 gene was loaded with selenium nanoparticles (SeNPs) and surface decorated with polyethylenimine (PEI) (Se@PEI@siRNA). Se@PEI@siRNA showed a remarkable interference efficiency in the nerve cell line SK-N-SH and prevented the cells to be infected. The mechanism study revealed that Se@PEI@siRNA could lighten the extent of SK-N-SH cells for staying in the sub-G1 phase. Activation of Bax apoptosis signaling was restrained either. Taken together, this study demonstrated that Se@PEI@siRNA is a promising drug against EV71 virus.

Interaction between PHB2 and Enterovirus A71 VP1 Induces Autophagy and Affects EV-A71 Infection

Enterovirus A71 (EV-A71) is a major pathogen that causes severe and fatal cases of hand-foot-and-mouth disease (HFMD). HFMD caused by EV-A71 seriously endangers children’s health. Although autophagy is an important antiviral defense mechanism, some viruses have evolved strategies to utilize autophagy to promote self-replication. EV-A71 can utilize autophagy vesicles as replication scaffolds, indicating that EV-A71 infection is closely related to its autophagy induction mechanism. VP1, a structural protein of EV-A71, has been reported to induce autophagy, but the underlying mechanism is still unclear. In this study, we found that the C-terminus (aa 251–297) of VP1 induces autophagy. Mass spectrometry analysis suggested that prohibitin 2 (PHB2) interacts with the C-terminus of the EV-A71 VP1 protein, and this was further verified by coimmunoprecipitation assays. After PHB2 knockdown, EV-A71 replication, viral particle release, and viral protein synthesis were reduced, and autophagy was inhibited. The results suggest that PHB2 interaction with VP1 is essential for induction of autophagy and the infectivity of EV-A71. Furthermore, we confirmed that EV-A71 induced complete autophagy that required autolysosomal acidification, thus affecting EV-A71 infection. In summary, this study revealed that the host protein PHB2 is involved in an autophagy mechanism during EV-A71 infection.

Viral infection dampens human fetal membrane type I interferon responses triggered by bacterial LPS

The maternal-fetal interface possesses innate immune strategies to protect against infections. We previously reported that prior viral infection of human fetal membranes (FMs) in vitro and mouse FMs in vivo sensitized the tissue to low dose bacterial LPS leading to augmented inflammation. The objective of this study was to examine FM production of type I interferons (IFNs) and IFN-stimulated genes (ISGs) in the context of this polymicrobial model. Human FM explants and pregnant C57BL/6 mice were treated with or without low dose LPS following exposure to media or the γ-herpes virus, MHV-68. FM RNA was analyzed by qRT-PCR for type I IFNs, ISGs, upstream signaling, and MHV-68 open reading frames (ORFs). Pre-exposure to MHV-68 followed by LPS treatment inhibited the ability of LPS to induce human FM type I IFNs (IFNA, IFNB); ISGs (OAS, MxA, APOBEC3G) and upstream signaling mediators (RIG-I, TBK-1). Signaling mediators IRF-3 and IRF-7 were also reduced. In mouse FMs, pre-exposure to MHV-68 followed by LPS treatment reduced the ability of LPS to upregulate Ifna, Ifnb, Mxa, Irf7, and also reduced Irf3. MHV-68 infection of FMs induced ORF45 which targets IRF-7, and this was further augmented in response to a combination of MHV-68 and LPS. Together, these findings indicate that a viral infection blunts FM type I IFN production and signaling in response to LPS leading to a suppressed ISG response. Our studies suggest that a viral infection inhibits this protective FM response by negatively regulating IRF-7 through ORF45, leaving the maternal-fetal interface vulnerable to further viral attack.

Identifying SARS-CoV-2-related coronaviruses in Malayan pangolins

The ongoing outbreak of viral pneumonia in China and across the world is associated with a new coronavirus, SARS-CoV-2¹. This outbreak has been tentatively associated with a seafood market in Wuhan, China, where the sale of wild animals may be the source of zoonotic infection². Although bats are probable reservoir hosts for SARS-CoV-2, the identity of any intermediate host that may have facilitated transfer to humans is unknown. Here we report the identification of SARS-CoV-2-related coronaviruses in Malayan pangolins (Manis javanica) seized in anti-smuggling operations in southern China. Metagenomic sequencing identified pangolin-associated coronaviruses that belong to two sub-lineages of SARS-CoV-2-related coronaviruses, including one that exhibits strong similarity in the receptor-binding domain to SARS-CoV-2. The discovery of multiple lineages of pangolin coronavirus and their similarity to SARS-CoV-2 suggests that pangolins should be considered as possible hosts in the emergence of new coronaviruses and should be removed from wet markets to prevent zoonotic transmission.