The interaction between human enteroviruses and type I IFN signaling pathway

A mouse model and pathogenesis study for CVA19 first isolated from hand, foot, and mouth disease

ABSTRACTCoxsackievirus A19 (CVA19) is a member of Enterovirus (EV) C group in the Picornaviridae family. Recently, we reported a case of CVA19-infected hand, foot, and mouth disease (HFMD) for the first time. However, the current body of knowledge on the CVA19 infection, particularly the pathogenesis of encephalomyelitis and diarrhoea is still very limited, due to the lack of suitable animal models. Here, we successfully established a CVA19 mouse model via oral route based on 7-day-old ICR mice. Our results found the virus strain could directly infect the neurons, astrocytes of brain, and motor neurons of spinal cord causing neurological complications, such as acute flaccid paralysis. Importantly, viruses isolated from the spinal cords of infected mice caused severe illness in suckling mice, fulfilling Koch's postulates to some extent. CVA19 infection led to diarrhoea with typical pathological features of shortened intestinal villi, increased number of secretory cells and apoptotic intestinal cells, and inflammatory cell infiltration. Much higher concentrations of serum cytokines and more peripheral blood inflammatory cells in CVA19-infected mice indicated a systematic inflammatory response induced by CVA19 infection. Finally, we found ribavirin and CVA19 VP1 monoclonal antibody could not prevent the disease progression, but higher concentrations of antisera and interferon alpha 2 (IFN-α2) could provide protective effects against CVA19. In conclusion, this study shows that a natural mouse-adapted CVA19 strain leads to diarrhoea and encephalomyelitis in a mouse model via oral infection, which provides a useful tool for studying CVA19 pathogenesis and evaluating the efficacy of vaccines and antivirals.

Suppression of innate and acquired immunity in severe hand foot and mouth disease caused by EV71 infections in children

Hand, foot, and mouth disease (HFMD) is a common children infectious disease caused by human enteroviruses. Most of the cases have minimal symptoms, however, some patients may develop serious neurological, cardiac complications, or even death. The pathological mechanism leading to severe HFMD is not clearly understood, and the immunological status of the individual patient may play an important role. Transcriptomes of peripheral blood mononuclear cells from EV71-infected patients (n = 45) and healthy controls (n = 36) were examined. Immune pathways were up-regulated in patients with mild disease symptoms (n = 11, M) compared to the healthy controls (n = 36, H), demonstrating an effective anti-viral response upon EV71 infection. However, in patients with severe symptoms (n = 23, S) as well as severe patients following treatment (n = 11, A), their innate and acquired immune pathways were down-regulated, indicating a global immunity suppression. Such immune suppression characteristics could thus provide an opportunity for early EV-71 infection prognosis prediction. Based on our cohort, an SVM model using RNA-seq expression levels of five genes (MCL1, ZBTB37, PLEKHM1P, IFNAR2 and YEATS2) was developed and achieved a high ROC-AUC (91·3%) in predicting severe HFMD. Meanwhile, qPCR fold-changes method was performed based three genes (MCL1, IFNAR2 and YEATS2) on additional cohort. This qPCR method achieved a ROC-AUC of 78.6% in predicting severe HFMD, which the patients could be distinguished in 2-3 h. Therefore, our models demonstrate the possibility of HFMD severity prediction based on the selected biomarkers that predict severe HFMD effectively.

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

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

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

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OAS3 resistance to EV71 replication depends on RNase L activation.

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

EV71 3C protease cleaves host anti-viral factor OAS3 and enhances virus replication

The global spread of enteroviruses (EVs) has become more frequent, severe and life-threatening. Intereron (IFN) I has been proved to control EVs by regulating IFN-stimulated genes (ISG) expression. 2'-5'-oligoadenylate synthetases 3 (OAS3) is an important ISG in the OAS/RNase L antiviral system. The relationship between OAS3 and EVs is still unclear. Here, we reveal that OAS3, superior to OAS1 and OAS2, significantly inhibited EV71 replication in vitro. However, EV71 utilized autologous 3C protease (3Cpro) to cleave intracellular OAS3 and enhance viral replication. Rupintrivir, a human rhinovirus 3C protease inhibitor, completely abolished the cleavage of EV71 3Cpro on OAS3. And the proteolytically deficient mutants H40G, E71A, and C147G of EV71 3Cpro also lost the ability of OAS3 cleavage. Mechanistically, the Q982-G983 motif in C-terminal of OAS3 was identified as a crucial 3Cpro cutting site. Further investigation indicated that OAS3 inhibited not only EV71 but also Coxsackievirus B3 (CVB3), Coxsackievirus A16 (CA16), Enterovirus D68 (EVD68), and Coxsackievirus A6 (CA6) subtypes. Notably, unlike other four subtypes, CA16 3Cpro could not cleave OAS3. Two key amino acids variation Ile36 and Val86 in CA16 3Cpro might result in weak and delayed virus replication of CA16 because of failure of OAS and 3AB cleavage. Our works elucidate the broad anti-EVs function of OAS3, and illuminate a novel mechanism by which EV71 use 3Cpro to escape the antiviral effect of OAS3. These findings can be an important entry point for developing novel therapeutic strategies for multiple EVs infection.

Influence of Nonpolio Enteroviruses and the Bacterial Gut Microbiota on Oral Poliovirus Vaccine Response: A Study from South India

Background

Oral poliovirus vaccine (OPV) is less immunogenic in low- or middle-income than in high-income countries. We tested whether bacterial and viral components of the intestinal microbiota are associated with this phenomenon.

Methods

We assessed the prevalence of enteropathogens using TaqMan array cards 14 days before and at vaccination in 704 Indian infants (aged 6–11 months) receiving monovalent type 3 OPV (CTRI/2014/05/004588). Nonpolio enterovirus (NPEV) serotypes were identified by means of VP1 sequencing. In 120 infants, the prevaccination bacterial microbiota was characterized using 16S ribosomal RNA sequencing.

Results

We detected 56 NPEV serotypes on the day of vaccination. Concurrent NPEVs were associated with a reduction in OPV seroconversion, consistent across species (odds ratio [95% confidence interval], 0.57 [.36–.90], 0.61 [.43–.86], and 0.69 [.41–1.16] for species A, B, and C, respectively). Recently acquired enterovirus infections, detected at vaccination but not 14 days earlier, had a greater interfering effect on monovalent type 3 OPV seroresponse than did persistent infections, with enterovirus detected at both time points (seroconversion in 44 of 127 infants [35%] vs 63 of 129 [49%]; P = .02). The abundance of specific bacterial taxa did not differ significantly according to OPV response, although the microbiota was more diverse in nonresponders at the time of vaccination.

Conclusion

Enteric viruses have a greater impact on OPV response than the bacterial microbiota, with recent enterovirus infections having a greater inhibitory effect than persistent infections.

Coxsackievirus Type B3 Is a Potent Oncolytic Virus against KRAS-Mutant Lung Adenocarcinoma

KRAS mutant (KRAS^mut) lung adenocarcinoma is a refractory cancer without available targeted therapy. The current study explored the possibility to develop coxsackievirus type B3 (CVB3) as an oncolytic agent for the treatment of KRAS^mut lung adenocarcinoma. In cultured cells, we discovered that CVB3 selectively infects and lyses KRAS^mut lung adenocarcinoma cells (A549, H2030, and H23), while sparing normal lung epithelial cells (primary, BEAS2B, HPL1D, and 1HAEo) and EGFR^mut lung adenocarcinoma cells (HCC4006, PC9, H3255, and H1975). Using stable cells expressing a single driver mutation of either KRAS^G12V or EGFR^L858R in normal lung epithelial cells (HPL1D), we further showed that CVB3 specifically kills HPL1D-KRAS^G12V cells with minimal harm to HPL1D-EGFR^L858R and control cells. Mechanistically, we demonstrated that aberrant activation of extracellular signal-regulated kinase 1/2 (ERK1/2) and compromised type I interferon immune response in KRAS^mut lung adenocarcinoma cells serve as key factors contributing to the sensitivity to CVB3-induced cytotoxicity. Lastly, we conducted in vivo xenograft studies using two immunocompromised mouse models. Our results revealed that intratumoral injection of CVB3 results in a marked tumor regression of KRAS^mut lung adenocarcinoma in both non-obese diabetic (NOD) severe combined immunodeficiency (SCID) gamma (NSG) and NOD-SCID xenograft models. Together, our findings suggest that CVB3 is an excellent candidate to be further developed as a targeted therapy for KRAS^mut lung adenocarcinoma.

Hijacking of multiple phospholipid biosynthetic pathways and induction of membrane biogenesis by a picornaviral 3CD protein

RNA viruses induce specialized membranous structures for use in genome replication. These structures are often referred to as replication organelles (ROs). ROs exhibit distinct lipid composition relative to other cellular membranes. In many picornaviruses, phosphatidylinositol-4-phosphate (PI4P) is a marker of the RO. Studies to date indicate that the viral 3A protein hijacks a PI4 kinase to induce PI4P by a mechanism unrelated to the cellular pathway, which requires Golgi-specific brefeldin A-resistance guanine nucleotide exchange factor 1, GBF1, and ADP ribosylation factor 1, Arf1. Here we show that a picornaviral 3CD protein is sufficient to induce synthesis of not only PI4P but also phosphatidylinositol-4,5-bisphosphate (PIP2) and phosphatidylcholine (PC). Synthesis of PI4P requires GBF1 and Arf1. We identified 3CD derivatives: 3CD^m and 3C^mD, that we used to show that distinct domains of 3CD function upstream of GBF1 and downstream of Arf1 activation. These same 3CD derivatives still supported induction of PIP2 and PC, suggesting that pathways and corresponding mechanisms used to induce these phospholipids are distinct. Phospholipid induction by 3CD is localized to the perinuclear region of the cell, the outcome of which is the proliferation of membranes in this area of the cell. We conclude that a single viral protein can serve as a master regulator of cellular phospholipid and membrane biogenesis, likely by commandeering normal cellular pathways.

Picornaviruses replicate their genomes in association with host membranes. Early during infection, existing membranes are used but remodeled to contain a repertoire of lipids best suited for virus multiplication. Later, new membrane synthesis occurs, which requires biosynthesis of phosphatidylcholine in addition to the other more specialized lipids. We have learned that a single picornaviral protein is able to induce membrane biogenesis and decorate these membranes with some of the specialized lipids induced by the virus. A detailed mechanism of induction has been elucidated for one of these lipids. The ability of a single viral protein to commandeer host pathways that lead to membrane biogenesis was unexpected. This discovery reveals a new target for antiviral therapy with the potential to completely derail all aspects of the viral lifecycle requiring membrane biogenesis.

Oblongifolin M, an active compound isolated from a Chinese medical herb Garcinia oblongifolia, potently inhibits enterovirus 71 reproduction through downregulation of ERp57

There is no effective drug to treat EV71 infection yet. Traditional Chinese herbs are great resources for novel antiviral compounds. Here we showed that Oblongifolin M (OM), an active compound isolated from Garcinia oblongifolia, potently inhibited EV71 infection in a dose dependent manner. To identify its potential effectors in the host cells, we successfully identified 18 proteins from 52 differentially expressed spots by comparative proteomics studies. Further studies showed that knockdown of ERp57 inhibited viral replication through downregulating viral IRES (internal ribosome entry site) activities, whereas ectopic expression of ERp57 increased IRES activity and partly rescued the inhibitory effects of OM on viral replication. We demonstrated that OM is an effective antiviral agent; and that ERp57 is one of its cellular effectors against EV71 infection.

Diverse Strategies Used by Picornaviruses to Escape Host RNA Decay Pathways

To successfully replicate, viruses protect their genomic material from degradation by the host cell. RNA viruses must contend with numerous destabilizing host cell processes including mRNA decay pathways and viral RNA (vRNA) degradation resulting from the antiviral response. Members of the Picornaviridae family of small RNA viruses have evolved numerous diverse strategies to evade RNA decay, including incorporation of stabilizing elements into vRNA and re-purposing host stability factors. Viral proteins are deployed to disrupt and inhibit components of the decay machinery and to redirect decay machinery to the advantage of the virus. This review summarizes documented interactions of picornaviruses with cellular RNA decay pathways and processes.