Coxsackievirus B3 proteases 2A and 3C induce apoptotic cell death through mitochondrial injury and cleavage of eIF4GI but not DAP5/p97/NAT1

Non-Polio Enterovirus Inhibitors: Scaffolds, Targets, and Potency─What's New?

Enterovirus (EV) is a genus that includes a large diversity of viruses spread around the world. They are the main cause of numerous diseases with seasonal clusters, like hand-foot-mouth disease (HFMD). A vaccine is marketed in China for the prevention of HFMD caused by EV-A71. Despite the need, no antiviral is marketed to date. Therefore, several compounds have been currently evaluated to inhibit non-polio Enterovirus (NPEV), namely direct antiviral agents and host target inhibitor. We propose to make a review of the latest molecules evaluated as NPEV inhibitors and to summarize structure-activity relationships between these inhibitors and their target. We provide access to all recent information on Enterovirus inhibitors, regardless of the species, to facilitate the design of future broad-spectrum drugs.

From the "One-Molecule, One-Target, One-Disease" Concept towards Looking for Multi-Target Therapeutics for Treating Non-Polio Enterovirus (NPEV) Infections

Non-polio enteroviruses (NPEVs), namely coxsackieviruses (CV), echoviruses (E), enteroviruses (EV), and rhinoviruses (RV), are responsible for a wide variety of illnesses. Some infections can progress to life-threatening conditions in children or immunocompromised patients. To date, no treatments have been approved. Several molecules have been evaluated through clinical trials without success. To overcome these failures, the multi-target directed ligand (MTDL) strategy could be applied to tackle enterovirus infections. This work analyzes registered clinical trials involving antiviral drugs to highlight the best candidates and develops filters to apply to a selection for MTDL synthesis. We explicitly stated the methods used to answer the question: which solution can fight NPEVs effectively? We note the originality and relevance of this proposal in relation to the state of the art in the enterovirus-inhibitors field. Several combinations are possible to broaden the antiviral spectrum and potency. We discuss data related to the virus and data related to each LEAD compound identified so far. Overall, this study proposes a perspective on different strategies to overcome issues identified in clinical trials and evaluate the "MTDL" potential to improve the efficacy of drugs, broaden the antiviral targets, possibly reduce the adverse effects, drug design costs and limit the selection of drug-resistant virus variants.

Baicalein suppresses Coxsackievirus B3 replication by inhibiting caspase-1 and viral protease 2A

Myocarditis is an inflammatory disease of the cardiac muscle and one of the primary causes of dilated cardiomyopathy. Group B coxsackievirus (CVB) is one of the leading causative pathogens of viral myocarditis, which primarily affects children and young adults. Due to the lack of vaccines, the development of antiviral medicines is crucial to controlling CVB infection and the progression of myocarditis. In this study, we investigated the antiviral effect of baicalein, a flavonoid extracted from Scutellaria baicaleinsis. Our results demonstrated that baicalein treatment significantly reduced cytopathic effect and increased cell viability in CVB3-infected cells. In addition, significant reductions in viral protein 3D, viral RNA, and viral particles were observed in CVB3-infected cells treated with baicalein. We found that baicalein exerted its inhibitory effect in the early stages of CVB3 infection. Baicalein also suppressed viral replication in the myocardium and effectively alleviated myocarditis induced by CVB3 infection. Our study revealed that baicalein exerts its antiviral effect by inhibiting the activity of caspase-1 and viral protease 2A. Taken together, our findings demonstrate that baicalein has antiviral activity against CVB3 infection and may serve as a potential therapeutic option for the myocarditis caused by enterovirus infection.

Ferroptosis, from the virus point of view: opportunities and challenges

Ferroptosis is a new type of cell death, which is mainly dependent on the formation and accumulation of reactive oxygen species and lipid peroxides mediated by iron. It is distinct from other forms of regulation of cell death in morphology, immunology, biochemistry, and molecular biology. Various cell death mechanisms have been observed in many viral infections, and virus-induced cell death has long been considered as a double-edged sword that can inhibit or aggravate viral infections. However, understanding of the role of ferroptosis in various viral infections is limited. Special attention will be paid to the mechanisms of ferroptosis in mediating viral infection and antiviral treatment associated with ferroptosis. In this paper, we outlined the mechanism of ferroptosis. Additionally, this paper also review research on ferroptosis from the perspective of the virus, discussed the research status of ferroptosis in virus infection and classified and summarized research on the interaction between viral infections and ferroptosis.

Enterovirus D68 3C protease antagonizes type I interferon signaling by cleaving signal transducer and activator of transcription 1

Following the successful control of poliovirus, the re-emergence of respiratory enterovirus D68 (EV-D68), a prominent non-polio enterovirus, has become a serious public health concern worldwide. Host innate immune responses are the primary defense against EV-D68 invasion; however, the mechanism underlying viral evasion of the antiviral activity of interferons (IFN) remains unclear. In this study, we found that EV-D68 inhibited type I IFN signaling by cleaving signal transducer and activator of transcription 1 (STAT1), a crucial factor in cellular responses to interferons and other cytokines. We observed that the prototype and circulating EV-D68 strains conserved their ability to induce STAT1 cleavage and attenuate IFN signal transduction. Further investigation revealed that EV-D68 3C protease cleaves STAT1 at the 131Q residue. Interestingly, not all enterovirus-encoded 3C proteases exhibited this ability. EV-D68 and poliovirus 3C proteases efficiently induced STAT1 cleavage; whereas, 3C proteases from EV-A71, coxsackievirus A16, and echoviruses did not. STAT1 cleavage also abolished the nuclear translocation capacity of STAT1 in response to IFN stimulation to activate downstream signaling elements. Overall, these results suggest that STAT1, targeted by viral protease 3C, is utilized by EV-D68 to subvert the host's innate immune response.IMPORTANCEEnterovirus D68 (EV-D68) has significantly transformed over the past decade, evolving from a rare pathogen to a potential pandemic pathogen. The interferon (IFN) signaling pathway is an important defense mechanism and therapeutic target for the host to resist viral invasion. Previous studies have reported that the EV-D68 virus blocks or weakens immune recognition and IFN production in host cells through diverse strategies; however, the mechanisms of EV-D68 resistance to IFN signaling have not been fully elucidated. Our study revealed that EV-D68 relies on its own encoded protease, 3C, to directly cleave signal transducer and activator of transcription 1 (STAT1), a pivotal transduction component in the IFN signaling pathway, disrupting the IFN-mediated antiviral response. Previous studies on human enteroviruses have not documented direct cleavage of the STAT1 protein to evade cellular immune defenses. However, not all enteroviral 3C proteins can cleave STAT1. These findings highlight the diverse evolutionary strategies different human enteroviruses employ to evade host immunity.

Identification of amentoflavone as a potent SARS-CoV-2 Mpro inhibitor: a combination of computational studies and in vitro biological evaluation

Small-molecule inhibitors of SARS-CoV-2 Mpro that block the active site pocket of the viral main protease have been considered potential therapeutics for the development of drugs against SARS-CoV-2. Here, we report the identification of amentoflavone (a biflavonoid) through docking-based virtual screening of a library comprised of 231 compounds consisting of flavonoids and isoflavonoids. The docking results were further substantiated through extensive analysis of the data obtained from all-atom 150 ns MD simulation. End-state effective free energy calculations using MM-PBSA calculations further suggested that (Ra)-amentoflavone (C3'-C8''-atropisomer) may show a greater binding affinity towards the Mpro than (Sa)-amentoflavone. In vitro cytotoxicity assay established that amentoflavone showed a high CC50 value indicating much lower toxicity. Further, potent inhibition of the Mpro by amentoflavone was established by studying the effect on HEK293T cells treated with SARS-CoV-2 Mpro expressing plasmid.Communicated by Ramaswamy H. Sarma.

[The role of the encephalomyocarditis virus type 1 proteins L and 2A in the inhibition of the synthesis of cellular proteins and the accumulation of viral proteins during infection]

INTRODUCTION

Infection of cells with encephalomyocarditis virus type 1 (EMCV-1, Cardiovirus A: Picornaviridae) is accompanied by suppression of cellular protein synthesis. The main role in the inhibition of cellular translation is assigned to the L and 2A «security» proteins. The mechanism of the possible influence of the L protein on cellular translation is unknown. There are hypotheses about the mechanism of influence of 2A protein on the efficiency of cap-dependent translation, which are based on interaction with translation factors and ribosome subunits. However, the available experimental data are contradictory, obtained using different approaches, and do not form a unified model of the interaction between the L and 2A proteins and the cellular translation machinery.

AIM

To study the role of L and 2A «security» proteins in the suppression of translation of cellular proteins and the efficiency of translation and processing of viral proteins in infected cells.

MATERIALS AND METHODS

Mutant variants of EMCV-1 were obtained to study the properties of L and 2A viral proteins: Zfmut, which has a defective L; Δ2A encoding a partially deleted 2A; Zfmut&Δ2A containing mutations in both proteins. Translational processes in infected cells were studied by Western-blot and the pulse method of incorporating radioactively labeled amino acids (14C) into newly synthesized proteins, followed by radioautography.

RESULTS

The functional inactivation of the 2A protein does not affect the inhibition of cellular protein synthesis. A direct correlation was found between the presence of active L protein and specific inactivation of cellular protein synthesis at an early stage of viral infection. Nonspecific suppression of the translational processes of the infected cell, accompanied by phosphorylation of eIF2α, occurs at the late stage of infection. Partial removal of the 2A protein from the EMCV-1 genome does not affect the development of this process, while inactivation of the L protein accelerates the onset of complete inhibition of protein synthesis. Partial deletion of the 2A disrupts the processing of viral capsid proteins. Suppression of L protein functions leads to a decrease in the efficiency of viral translation.

CONCLUSION

A study of the role of EMCV-1 L and 2A proteins during the translational processes of an infected cell, first performed using infectious viral pathogens lacking active L and 2A proteins in one experiment, showed that 2A protein is not implicated in the inhibition of cellular translation in HeLa cells; L protein seems to play an important role not only in the specific inhibition of cellular translation but also in maintaining the efficient synthesis of viral proteins; 2A protein is involved not only in primary but also in secondary processing of EMCV-1 capsid proteins.

Critical roles of parkin and PINK1 in coxsackievirus B3-induced viral myocarditis

Viral myocarditis is an inflammatory disease of the myocardium, often leads to cardiac dysfunction and death. PARKIN (PRKN) and PINK1, well known as Parkinson's disease-associated genes, have been reported to be involved in innate immunity and mitochondrial damage control. Therefore, we investigated the role of parkin and PINK1 in coxsackievirus B3 (CVB3)-induced viral myocarditis because the etiology of myocarditis is related to abnormal immune response to viral infection and mitochondrial damage. After viral infection, the survival was significantly lower and myocardial damage was more severe in parkin knockout (KO) and PINK1 KO mice compared to wild-type (WT) mice. Parkin KO and PINK1 KO showed defective immune cell recruitment and impaired production of antiviral cytokines such as interferon-gamma, allowing increased viral replication. In addition, parkin KO and PINK1 KO mice were more susceptible to CVB3-induced mitochondrial damage than WT mice, resulting in susceptibility to viral-induced cardiac damage. Finally, using publicly available RNA-seq data, we found that pathogenic mutants of the PRKN gene are more common in patients with dilated cardiomyopathy and myocarditis than in controls or the general population. This study will help elucidate the molecular mechanism of CVB3-induced viral myocarditis.

Experimental infection of foot and mouth disease virus (FMDV) upregulates the expression of Coxsackie and adenovirus receptor (CAR) in the myocardium of suckling mice

The relative overexpression of Coxsackie and adenoviral receptor (CAR) predisposes children to viral myocarditis. As the foot and mouth disease virus (FMDV) causes fatal myocarditis in calves, lambs, and piglets and belongs to the same family as the Coxsackie virus, we investigated the role of CAR in FMDV induced myocarditis in the suckling mice model. Swiss albino suckling mice of 5 days (n = 24) were divided into two equal groups. One group was inoculated with suckling mice adapted FMDV serotype O at 10 LD50, while the other group served as uninfected control. In addition, adult mice (n = 12) served as the control for age related CAR expression and lack of pathogenicity to FMDV. The establishment of myocarditis was confirmed by histopathological changes typical of myocarditis along with immunolocalization of FMDV antigens in the heart of suckling mice. The FMDV inoculated suckling mice group showed a significant upregulation of CAR transcripts by 2.5 folds, overexpression of CAR protein by densitometric analysis of immunoblots, and intense immunolocalization of CAR in the sarcolemma and intercalated discs of cardiomyocytes as compared to the uninfected suckling mice group and adult mice. It was concluded that FMDV infection induced overexpression of CAR in the myocardium of suckling mice.

Roles of inflammasomes in viral myocarditis

Viral myocarditis (VMC), characterized by viral infection-induced inflammation, is a life-threatening disease associated with dilated cardiomyopathy or heart failure. Innate immunity plays a crucial role in the progression of inflammation, in which inflammasomes provide a platform for the secretion of cytokines and mediate pyroptosis. Inflammasomes are rising stars gaining increasing attention. The nucleotide oligomerization domain-, leucine-rich repeat-, and pyrin domain-containing protein 3 (NLRP3) inflammasome, the caspase recruitment domain-containing protein 8 (CARD8) inflammasome, and the caspase-11 inflammasome are three inflammasomes that were reported to affect the process and prognosis of VMC. These inflammasomes can be activated by a wide range of cellular events. Accumulating evidence has suggested that inflammasomes are involved in different stages of VMC, including the trigger and progression of myocardial injury and remodeling after infection. In this review, we summarized the pathways involving inflammasomes in VMC and discussed the potential therapies targeting inflammasomes and related pathways.

Inhibitor of CD147 Suppresses T Cell Activation and Recruitment in CVB3-Induced Acute Viral Myocarditis

Viral myocarditis (VMC) is a common disease characterized by cardiac inflammation. AC-73, an inhibitor of CD147, disrupts the dimerization of CD147, which participates in the regulation of inflammation. To explore whether AC-73 could alleviate cardiac inflammation induced by CVB3, mice were injected intraperitoneally with AC-73 on the fourth day post-infection (dpi) and sacrificed on the seventh dpi. Pathological changes in the myocardium, T cell activation or differentiation, and expression of cytokines were analyzed using H&E staining, flow cytometry, fluorescence staining and multiplex immunoassay. The results showed that AC-73 alleviated cardiac pathological injury and downregulated the percentage of CD45⁺CD3⁺ T cells in the CVB3-infected mice. The administration of AC-73 reduced the percentage of activated CD4⁺ and CD8⁺ T cells (CD69⁺ and/or CD38⁺) in the spleen, while the percentage of CD4⁺ T cell subsets in the spleen was not changed in the CVB3-infected mice. In addition, the infiltration of activated T cells (CD69⁺) and macrophages (F4/80⁺) in the myocardium also decreased after the AC-73 treatment. The results also showed that AC-73 inhibited the release of many cytokines and chemokines in the plasma of the CVB3-infected mice. In conclusion, AC-73 mitigated CVB3-induced myocarditis by inhibiting the activation of T cells and the recruitment of immune cells to the heart. Thus, CD147 may be a therapeutic target for virus-induced cardiac inflammation.

Enterovirus D68 Infection Induces TDP-43 Cleavage, Aggregation, and Neurotoxicity

Enterovirus D68 (EV-D68), which causes severe respiratory diseases and irreversible central nervous system damage, has become a serious public health problem worldwide. However, the mechanisms by which EV-D68 exerts neurotoxicity remain unclear. Thus, we aimed to analyze the effects of EV-D68 infection on the cleavage, subcellular translocation, and pathogenic aggregation of TAR DNA-binding protein 43 kDa (TDP-43) in respiratory or neural cells. The results showed that EV-D68-encoded proteases 2A and 3C induced TDP-43 translocation and cleavage, respectively. Specifically, 3C cleaved residue 327Q of TDP-43. The 3C-mediated cleaved TDP-43 fragments had substantially decreased protein solubility compared with the wild-type TDP-43. Hence, 3C activity promoted TDP-43 aggregation, which exerted cytotoxicity to diverse human cells, including glioblastoma T98G cells. The effects of commercially available antiviral drugs on 3C-mediated TDP-43 cleavage were screened, and the results revealed lopinavir as a potent inhibitor of EV-D68 3C protease. Overall, these results suggested TDP-43 as a conserved host target of EV-D68 3C. This study is the first to provide evidence on the involvement of TDP-43 dysregulation in EV-D68 pathogenesis. IMPORTANCE Over the past decade, the incidence of enterovirus D68 (EV-D68) infection has increased worldwide. EV-D68 infection can cause different respiratory symptoms and severe neurological complications, including acute flaccid myelitis. Thus, elucidating the mechanisms underlying EV-D68 toxicity is important to develop novel methods to prevent EV-D68 infection-associated diseases. This study shows that EV-D68 infection triggers the translocalization, cleavage, and aggregation of TDP-43, an intracellular protein closely related to degenerative neurological disorders. The viral protease 3C decreased TDP-43 solubility, thereby exerting cytotoxicity to host cells, including human glioblastoma cells. Thus, counteracting 3C activity is an effective strategy to relieve EV-D68-triggered cell death. Cytoplasmic aggregation of TDP-43 is a hallmark of degenerative diseases, contributing to neural cell damage and central nervous system (CNS) disorders. The findings of this study on EV-D68-induced TDP-43 formation extend our understanding of virus-mediated cytotoxicity and the potential risks of TDP-43 dysfunction-related cognitive impairment and neurological symptoms in infected patients.

Role of Coxsackievirus B3-Induced Immune Responses in the Transition from Myocarditis to Dilated Cardiomyopathy and Heart Failure

Dilated cardiomyopathy (DCM) is a cardiac disease marked by the stretching and thinning of the heart muscle and impaired left ventricular contractile function. While most patients do not develop significant cardiac diseases from myocarditis, disparate immune responses can affect pathological outcomes, including DCM progression. These altered immune responses, which may be caused by genetic variance, can prolong cytotoxicity, induce direct cleavage of host protein, or encourage atypical wound healing responses that result in tissue scarring and impaired mechanical and electrical heart function. However, it is unclear which alterations within host immune profiles are crucial to dictating the outcomes of myocarditis. Coxsackievirus B3 (CVB3) is a well-studied virus that has been identified as a causal agent of myocarditis in various models, along with other viruses such as adenovirus, parvovirus B19, and SARS-CoV-2. This paper takes CVB3 as a pathogenic example to review the recent advances in understanding virus-induced immune responses and differential gene expression that regulates iron, lipid, and glucose metabolic remodeling, the severity of cardiac tissue damage, and the development of DCM and heart failure.

Potential Therapeutic Value of the STING Inhibitors

The stimulator of interferon genes (STING) is a critical protein in the activation of the immune system in response to DNA. It can participate the inflammatory response process by modulating the inflammation-preferred translation program through the STING-PKR-like endoplasmic reticulum kinase (PERK)-eIF2α pathway or by inducing the secretion of type I interferons (IFNs) and a variety of proinflammatory factors through the recruitment of TANK-binding kinase 1 (TBK1) and interferon regulatory factor 3 (IRF3) or the regulation of the nuclear factor kappa-B (NF-κB) pathway. Based on the structure, location, function, genotype, and regulatory mechanism of STING, this review summarizes the potential value of STING inhibitors in the prevention and treatment of infectious diseases, psoriasis, systemic lupus erythematosus, non-alcoholic fatty liver disease, and other inflammatory and autoimmune diseases.

Specific mechanisms of translation initiation in higher eukaryotes: the eIF4G2 story

The eukaryotic initiation factor 4G2 (eIF4G2, DAP5, Nat1, p97) was discovered in 1997. Over the past two decades, dozens of papers have presented contradictory data on eIF4G2 function. Since its identification, eIF4G2 has been assumed to participate in noncanonical translation initiation mechanisms, but recent results indicate that it can be involved in scanning as well. In particular, eIF4G2 provides leaky scanning through some upstream open reading frames (uORFs), which are typical for long 5' UTRs of mRNAs from higher eukaryotes. It is likely the protein can also help the ribosome overcome other impediments during scanning of the 5' UTRs of animal mRNAs. This may explain the need for eIF4G2 in higher eukaryotes, as many mRNAs that encode regulatory proteins have rather long and highly structured 5' UTRs. Additionally, they often bind to various proteins, which also hamper the movement of scanning ribosomes. This review discusses the suggested mechanisms of eIF4G2 action, denotes obscure or inconsistent results, and proposes ways to uncover other fundamental mechanisms in which this important protein factor may be involved in higher eukaryotes.

Eukaryotic translation initiation factor eIF4G2 opens novel paths for protein synthesis in development, apoptosis and cell differentiation

Protein translation is a critical regulatory event involved in nearly all physiological and pathological processes. Eukaryotic translation initiation factors are dedicated to translation initiation, the most highly regulated stage of protein synthesis. Eukaryotic translation initiation factor 4G2 (eIF4G2, also called p97, NAT1 and DAP5), an eIF4G family member that lacks the binding sites for 5' cap binding protein eIF4E, is widely considered to be a key factor for internal ribosome entry sites (IRESs)-mediated cap-independent translation. However, recent findings demonstrate that eIF4G2 also supports many other translation initiation pathways. In this review, we summarize the role of eIF4G2 in a variety of cap-independent and -dependent translation initiation events. Additionally, we also update recent findings regarding the role of eIF4G2 in apoptosis, cell survival, cell differentiation and embryonic development. These studies reveal an emerging new picture of how eIF4G2 utilizes diverse translational mechanisms to regulate gene expression.

Mitochondria Dysfunction at the Heart of Viral Myocarditis: Mechanistic Insights and Therapeutic Implications

The myocardium/heart is the most mitochondria-rich tissue in the human body with mitochondria comprising approximately 30% of total cardiomyocyte volume. As the resident "powerhouse" of cells, mitochondria help to fuel the high energy demands of a continuously beating myocardium. It is no surprise that mitochondrial dysfunction underscores the pathogenesis of many cardiovascular ailments, including those of viral origin such as virus-induced myocarditis. Enteroviruses have been especially linked to injuries of the myocardium and its sequelae dilated cardiomyopathy for which no effective therapies currently exist. Intriguingly, recent mechanistic insights have demonstrated viral infections to directly damage mitochondria, impair the mitochondrial quality control processes of the cell, such as disrupting mitochondrial antiviral innate immune signaling, and promoting mitochondrial-dependent pathological inflammation of the infected myocardium. In this review, we briefly highlight recent insights on the virus-mitochondria crosstalk and discuss the therapeutic implications of targeting mitochondria to preserve heart function and ultimately combat viral myocarditis.

Enterovirus 3C Protease Cleaves TRIM7 To Dampen Its Antiviral Activity

Mammalian TRIM7 is an antiviral protein that inhibits multiple human enteroviruses by degrading the viral 2BC protein. Whether TRIM7 is reciprocally targeted by enteroviruses is not known. Here, we report that the 3C protease (3Cpro) from two enteroviruses, coxsackievirus B3 (CVB3) and poliovirus, targets TRIM7 for cleavage. CVB3 3Cpro cleaves TRIM7 at glutamine 24 (Q24), resulting in a truncated TRIM7 that fails to inhibit CVB3 due to dampened E3 ubiquitin ligase activity. TRIM7 Q24 is highly conserved across mammals, except in marsupials, which instead have a naturally occurring histidine (H24) that is not subject to 3Cpro cleavage. Marsupials also express two isoforms of TRIM7, and the two proteins from koalas have distinct antiviral activities. The longer isoform contains an additional exon due to alternate splice site usage. This additional exon contains a unique 3Cpro cleavage site, suggesting that certain enteroviruses may have evolved to target marsupial TRIM7 even if the canonical Q24 is missing. Combined with computational analyses indicating that TRIM7 is rapidly evolving, our data raise the possibility that TRIM7 may be targeted by enterovirus evasion strategies and that evolution of TRIM7 across mammals may have conferred unique antiviral properties. IMPORTANCE Enteroviruses are significant human pathogens that cause viral myocarditis, pancreatitis, and meningitis. Knowing how the host controls these viruses and how the viruses may evade host restriction is important for understanding fundamental concepts in antiviral immunity and for informing potential therapeutic interventions. In this study, we demonstrate that coxsackievirus B3 uses its virally encoded protease to target the host antiviral protein TRIM7 for cleavage, suggesting a potential mechanism of viral immune evasion. We additionally show that TRIM7 has evolved in certain mammalian lineages to express protein variants with distinct antiviral activities and susceptibilities to viral protease-mediated cleavage.

Advances in cell death mechanisms involved in viral myocarditis

Viral myocarditis is an acute inflammatory disease of the myocardium. Although many etiopathogenic factors exist, coxsackievirus B3 is a the leading cause of viral myocarditis. Abnormal cardiomyocyte death is the underlying problem for most cardiovascular diseases and fatalities. Various types of cell death occur and are regulated to varying degrees. In this review, we discuss the different cell death mechanisms in viral myocarditis and the potential interactions between them. We also explore the role and mechanism of cardiomyocyte death with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection. Exploring the mechanisms may help in the early identification and the development of effective treatments, thus improving the quality of life of patients with viral myocarditis. We believe that the inhibition of cardiomyocyte death has immense therapeutic potential in increasing the longevity and health of the heart.

Virus-induced inhibition of cardiac pacemaker channel HCN4 triggers bradycardia in human-induced stem cell system

The enterovirus Coxsackievirus B3 (CVB3) is known to be a major source for the development of cardiac dysfunctions like viral myocarditis (VMC) and dilatative cardiomyopathy (DCM), but also results in bradycardia and fatal cardiac arrest. Besides clinical reports on bradycardia and sudden cardiac death, very little is known about the influence of CVB3 on the activity of human cardiac pacemaker cells. Here, we address this issue using the first human induced pluripotent stem cell (hiPSC)-derived pacemaker-like cells, in which the expression of a transgenic non-infectious variant of CVB3 can be controlled dose- and time-dependently. We found that CVB3 drastically changed hyperpolarization-activated cyclic nucleotide-gated channel 4 (HCN4) distribution and function in hiPSC-derived pacemaker-like tissue. In addition, using HCN4 cell expression systems, we found that HCN4 currents were decreased with altered voltage dependency of activation when CVB3 was expressed. Increased autophagosome formation and autophagosomal HCN4 insertion was observed in hiPSC-derived pacemaker-like cells under CVB3 expression as well. Individual effects of single, non-structural CVB3 proteins were analyzed and demonstrated that CVB3 proteins 2C and 3A had the most robust effect on HCN4 activity. Treatment of cells with the Rab7 inhibitor CID 106770 or the CVB3-3A inhibitor GW5074 led to the recovery of the cytoplasmatic HCN4 accumulation into a healthy appearing phenotype, indicating that malfunctioning Rab7-directed autophagosome transport is involved in the disturbed, cytoplasmatic HCN4 accumulation in CVB3-expressing human pacemaker-like cells. Summarizing, the enterovirus CVB3 inhibits human cardiac pacemaker function by reducing the pacemaker channel plasma membrane density, an effect that can be corrected by pharmacological intervention of endocytic vesicle trafficking.

The SARS-CoV-2 main protease doesn't induce cell death in human cells in vitro

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the cause of coronavirus disease 2019 (COVID-19) which has extremely rapidly spread worldwide. In order to develop the effective antiviral therapies, it is required to understand the molecular mechanisms of the SARS-CoV-2 pathogenesis. The main protease, or 3C-like protease (3CLpro), plays the essential role in the coronavirus replication that makes the enzyme a promising therapeutic target. Viral enzymes are known to be multifunctional. Particularly, 3CLpro of SARS-CoV was shown to induce apoptosis in addition to its main function. In the present study we analyzed the cytotoxicity of active SARS-CoV-2 3CLpro and its inactivated form upon their individual expression in four human cell lines. For this purpose, we constructed a protein biosensor which allows to detect the proteolytic activity of SARS-CoV-2 3CLpro and confirmed the expression of the active protease in all cell lines used. We studied viability and morphology of the cells and found that both active and inactivated enzyme variants induce no cell death in contrast to the homologous 3CL protease of SARS-CoV. These results indicate that SARS-CoV-2 3CLpro is unlikely contribute to the cytopathic effect observed during viral infection directly.

When Poly(A) Binding Proteins Meet Viral Infections, Including SARS-CoV-2

Viruses have evolved diverse strategies to hijack the cellular gene expression system for their replication. The poly(A) binding proteins (PABPs), a family of critical gene expression factors, are viruses' common targets. PABPs act not only as a translation factor but also as a key factor of mRNA metabolism. During viral infections, the activities of PABPs are manipulated by various viruses, subverting the host translation machinery or evading the cellular antiviral defense mechanism. Viruses harness PABPs by modifying their stability, complex formation with other translation initiation factors, or subcellular localization to promote viral mRNAs translation while shutting off or competing with host protein synthesis. For the past decade, many studies have demonstrated the PABPs' roles during viral infection. This review summarizes a comprehensive perspective of PABPs' roles during viral infection and how viruses evade host antiviral defense through the manipulations of PABPs.

Degradation of Host Proteins and Apoptosis Induced by Foot-and-Mouth Disease Virus 3C Protease

Foot-and-mouth disease (FMD), induced by the foot-and-mouth disease virus (FMDV), is a highly contagious disease of cloven-hoofed animals. Previous studies have reported that FMDV 3C protease could degrade multiple host proteins; however, the degradation mechanism mediated by FMDV 3C is still unclear. Here, we found that transient expression of FMDV 3C degraded various molecules in NF-κB signaling in a dose-dependent manner, and the proteolytic activity of FMDV 3C is important for inducing degradation. Additionally, 3C-overexpression was associated with the induction of apoptosis. In this study, we showed that an apoptosis inhibitor CrmA abolished the ability of 3C to degrade molecules in NF-κB signaling. Further experiments using specific caspase inhibitors confirmed the irrelevance of caspase3, caspase8, and caspase9 activity for degradation induced by 3C. Altogether, these results suggest that FMDV 3C induces the widespread degradation of host proteins through its proteolytic activity and that the apoptosis pathway might be an important strategy to mediate this process. Further exploration of the relationship between apoptosis and degradation induced by 3C could provide novel insights into the pathogenic mechanisms of FMDV.

The molecular mosaic of regulated cell death in the cardiovascular system

Cell death is now understood to be a highly regulated process that contributes to normal development and tissue homeostasis, alongside its role in the etiology of various pathological conditions. Through detailed molecular analysis, we have come to know that all cells do not always die in the same way, and that there are at least 7 processes involved, including: apoptosis, mitochondrial permeability transition (MPT)-driven necrosis, necroptosis, ferroptosis, pyroptosis, parthanatos, and autophagy-mediated cell death. These processes act as pieces in the mosaic of cardiomyocyte cell death, which come together depending on context and stimulus. This review details each individual process, as well as highlights how they come together to produce various cardiac pathologies. By knowing how the pieces go together we can aim towards the development of efficacious therapeutics, which will enable us to prevent cardiomyocyte loss in the face of stress, both reducing mortality and improving quality of life.

Identification of Potential Drug Targets of Broad-Spectrum Inhibitors with a Michael Acceptor Moiety Using Shotgun Proteomics

The Michael addition reaction is a spontaneous and quick chemical reaction that is widely applied in various fields. This reaction is performed by conjugating an addition of nucleophiles with α, β-unsaturated carbonyl compounds, resulting in the bond formation of C-N, C-S, C-O, and so on. In the development of molecular materials, the Michael addition is not only used to synthesize chemical compounds but is also involved in the mechanism of drug action. Several covalent drugs that bond via Michael addition are regarded as anticarcinogens and anti-inflammatory drugs. Although drug development is mainly focused on pharmaceutical drug discovery, target-based discovery can provide a different perspective for drug usage. However, considerable time and labor are required to define a molecular target through molecular biological experiments. In this review, we systematically examine the chemical structures of current FDA-approved antiviral drugs for potential Michael addition moieties with α, β-unsaturated carbonyl groups, which may exert an unidentified broad-spectrum inhibitory mechanism to target viral or host factors. We thus propose that profiling the targets of antiviral agents, such as Michael addition products, can be achieved by employing a high-throughput LC-MS approach to comprehensively analyze the interaction between drugs and targets, and the subsequent drug responses in the cellular environment to facilitate drug repurposing and/or identify potential adverse effects, with a particular emphasis on the pros and cons of this shotgun proteomic approach.

Individual Expression of Hepatitis A Virus 3C Protease Induces Ferroptosis in Human Cells In Vitro

Regulated cell death (RCD) is a fundamental process common to nearly all living beings and essential for the development and tissue homeostasis in animals and humans. A wide range of molecules can induce RCD, including a number of viral proteolytic enzymes. To date, numerous data indicate that picornaviral 3C proteases can induce RCD. In most reported cases, these proteases induce classical caspase-dependent apoptosis. In contrast, the human hepatitis A virus 3C protease (3Cpro) has recently been shown to cause caspase-independent cell death accompanied by previously undescribed features. Here, we expressed 3Cpro in HEK293, HeLa, and A549 human cell lines to characterize 3Cpro-induced cell death morphologically and biochemically using flow cytometry and fluorescence microscopy. We found that dead cells demonstrated necrosis-like morphological changes including permeabilization of the plasma membrane, loss of mitochondrial potential, as well as mitochondria and nuclei swelling. Additionally, we showed that 3Cpro-induced cell death was efficiently blocked by ferroptosis inhibitors and was accompanied by intense lipid peroxidation. Taken together, these results indicate that 3Cpro induces ferroptosis upon its individual expression in human cells. This is the first demonstration that a proteolytic enzyme can induce ferroptosis, the recently discovered and actively studied type of RCD.

Inhibitors of Coronavirus 3CL Proteases Protect Cells from Protease-Mediated Cytotoxicity

We describe a mammalian cell-based assay to identify coronavirus 3CL protease (3CLpro) inhibitors. This assay is based on rescuing protease-mediated cytotoxicity and does not require live virus. By enabling the facile testing of compounds across a range of 15 distantly related coronavirus 3CLpro enzymes, we identified compounds with broad 3CLpro-inhibitory activity. We also adapted the assay for use in compound screening and in doing so uncovered additional severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) 3CLpro inhibitors. We observed strong concordance between data emerging from this assay and those obtained from live-virus testing. The reported approach democratizes the testing of 3CLpro inhibitors by developing a simplified method for identifying coronavirus 3CLpro inhibitors that can be used by the majority of laboratories, rather than the few with extensive biosafety infrastructure. We identified two lead compounds, GC376 and compound 4, with broad activity against all 3CL proteases tested, including 3CLpro enzymes from understudied zoonotic coronaviruses. IMPORTANCE Multiple coronavirus pandemics have occurred over the last 2 decades. This has highlighted a need to be proactive in the development of therapeutics that can be readily deployed in the case of future coronavirus pandemics. We developed and validated a simplified cell-based assay for the identification of chemical inhibitors of 3CL proteases encoded by a wide range of coronaviruses. This assay is reporter free, does not require specialized biocontainment, and is optimized for performance in high-throughput screening. By testing reported 3CL protease inhibitors against a large collection of 3CL proteases with variable sequence similarity, we identified compounds with broad activity against 3CL proteases and uncovered structural insights into features that contribute to their broad activity. Furthermore, we demonstrated that this assay is suitable for identifying chemical inhibitors of proteases from families other than 3CL proteases.

Autophagy Receptor Protein Tax1-Binding Protein 1/TRAF6-Binding Protein Is a Cellular Substrate of Enteroviral Proteinase

Enteroviruses (EVs) usurp the host autophagy pathway for pro-viral functions; however, the consequence of EV-induced diversion of autophagy on organelle quality control is poorly defined. Using coxsackievirus B3 (CVB3) as a model EV, we explored the interplay between EV infection and selective autophagy receptors, i.e., Tax1-binding protein 1/TRAF6-binding protein (T6BP), optineurin (OPTN), and nuclear dot 10 protein 52 (NDP52), known to be involved in regulating the clearance of damaged mitochondria, a process termed as mitophagy. Following CVB3 infection, we showed significant perturbations of the mitochondrial network coincident with degradation of the autophagy receptor protein T6BP, similar phenomenon to what we previously observed on NDP52. Notably, protein levels of OPTN are not altered during early infection and slightly reduced upon late infection. Cell culture studies revealed that T6BP degradation occurs independent of the function of host caspases and viral proteinase 3C, but requires the proteolytic activity of viral proteinase 2A. Further investigation identified the cleavage site on T6BP after the amino acid 621 that separates the C-terminal ubiquitin-binding domain from the other functional domains at the N-terminus. Genetic silencing of T6BP and OPTN results in the attenuation of CVB3 replication, suggesting a pro-viral activity for these two proteins. Finally, functional assessment of cleaved fragments from NDP52 and T6BP revealed abnormal binding affinity and impaired capacity to be recruited to depolarized mitochondria. Collectively, these results suggest that CVB3 targets autophagy receptors to impair selective autophagy.

Coxsackievirus B3-Its Potential as an Oncolytic Virus

Oncolytic virotherapy represents one of the most advanced strategies to treat otherwise untreatable types of cancer. Despite encouraging developments in recent years, the limited fraction of patients responding to therapy has demonstrated the need to search for new suitable viruses. Coxsackievirus B3 (CVB3) is a promising novel candidate with particularly valuable features. Its entry receptor, the coxsackievirus and adenovirus receptor (CAR), and heparan sulfate, which is used for cellular entry by some CVB3 variants, are highly expressed on various cancer types. Consequently, CVB3 has broad anti-tumor activity, as shown in various xenograft and syngeneic mouse tumor models. In addition to direct tumor cell killing the virus induces a strong immune response against the tumor, which contributes to a substantial increase in the efficiency of the treatment. The toxicity of oncolytic CVB3 in healthy tissues is variable and depends on the virus strain. It can be abrogated by genetic engineering the virus with target sites of microRNAs. In this review, we present an overview of the current status of the development of CVB3 as an oncolytic virus and outline which steps still need to be accomplished to develop CVB3 as a therapeutic agent for clinical use in cancer treatment.

Picornavirus 3C - a protease ensuring virus replication and subverting host responses

The protease 3C is encoded by all known picornaviruses, and the structural features related to its protease and RNA-binding activities are conserved; these contribute to the cleavage of viral polyproteins and the assembly of the viral RNA replication complex during virus replication. Furthermore, 3C performs functions in the host cell through its interaction with host proteins. For instance, 3C has been shown to selectively 'hijack' host factors involved in gene expression, promoting picornavirus replication, and to inactivate key factors in innate immunity signaling pathways, inhibiting the production of interferon and inflammatory cytokines. Importantly, 3C maintains virus infection by subtly subverting host cell death and modifying critical molecules in host organelles. This Review focuses on the molecular mechanisms through which 3C mediates physiological processes involved in virus-host interaction, thus highlighting the picornavirus-mediated pathogenesis caused by 3C.

Egress of non-enveloped enteric RNA viruses

A long-standing paradigm in virology was that non-enveloped viruses induce cell lysis to release progeny virions. However, emerging evidence indicates that some non-enveloped viruses exit cells without inducing cell lysis, while others engage both lytic and non-lytic egress mechanisms. Enteric viruses are transmitted via the faecal-oral route and are important causes of a wide range of human infections, both gastrointestinal and extra-intestinal. Virus cellular egress, when fully understood, may be a relevant target for antiviral therapies, which could minimize the public health impact of these infections. In this review, we outline lytic and non-lytic cell egress mechanisms of non-enveloped enteric RNA viruses belonging to five families: Picornaviridae, Reoviridae, Caliciviridae, Astroviridae and Hepeviridae. We discuss factors that contribute to egress mechanisms and the relevance of these mechanisms to virion stability, infectivity and transmission. Since most data were obtained in traditional two-dimensional cell cultures, we will further attempt to place them into the context of polarized cultures and in vivo pathogenesis. Throughout the review, we highlight numerous knowledge gaps to stimulate future research into the egress mechanisms of these highly prevalent but largely understudied viruses.

Modulation of IGF2 Expression in the Murine Thymus and Thymic Epithelial Cells Following Coxsackievirus-B4 Infection

Coxsackievirus B4 (CV-B4) can infect human and murine thymic epithelial cells (TECs). In a murine TEC cell line, CV-B4 can downregulate the transcription of the insulin-like growth factor 2 (Igf2) gene coding for the self-peptide of the insulin family. In this study, we show that CV-B4 infections of a murine TEC cell line decreased Igf2 P3 promoter activity by targeting a region near the transcription start site; however, the stability of Igf2 transcripts remained unchanged, indicating a regulation of Igf2 transcription. Furthermore, CV-B4 infections decreased STAT3 phosphorylation in vitro. We also showed that mice infected with CV-B4 had an altered expression of Igf2 isoforms as detected in TECs, followed by a decrease in the pro-IGF2 precursor in the thymus. Our study sheds new light on the intrathymic regulation of Igf2 transcription during CV-B4 infections and supports the hypothesis that a viral infection can disrupt central self-tolerance to insulin by decreasing Igf2 transcription in the thymic epithelium.

Innate immune evasion mediated by picornaviral 3C protease: Possible lessons for coronaviral 3C-like protease?

Severe acute respiratory syndrome coronavirus-2 is the etiological agent of the ongoing pandemic of coronavirus disease-2019, a multi-organ disease that has triggered an unprecedented global health and economic crisis. The virally encoded 3C-like protease (3CL^pro ), which is named after picornaviral 3C protease (3C^pro ) due to their similarities in substrate recognition and enzymatic activity, is essential for viral replication and has been considered as the primary drug target. However, information regarding the cellular substrates of 3CL^pro and its interaction with the host remains scarce, though recent work has begun to shape our understanding more clearly. Here we summarized and compared the mechanisms by which picornaviruses and coronaviruses have evolved to evade innate immune surveillance, with a focus on the established role of 3C^pro in this process. Through this comparison, we hope to highlight the potential action and mechanisms that are conserved and shared between 3C^pro and 3CL^pro . In this review, we also briefly discussed current advances in the development of broad-spectrum antivirals targeting both 3C^pro and 3CL^pro .

Inhibition of Type III Interferon Expression in Intestinal Epithelial Cells-A Strategy Used by Coxsackie B Virus to Evade the Host's Innate Immune Response at the Primary Site of Infection?

Increasing evidence highlights the importance of the antiviral activities of the type III interferons (IFNλs; IL-28A, IL-28B, IL29, and IFNλ4) in the intestine. However, many viruses have developed strategies to counteract these defense mechanisms by preventing the production of IFNs. Here we use infection models, a clinical virus isolate, and several molecular biology techniques to demonstrate that both type I and III IFNs induce an antiviral state and attenuate Coxsackievirus group B (CVB) replication in human intestinal epithelial cells (IECs). While treatment of IECs with a viral mimic (poly (I:C)) induced a robust expression of both type I and III IFNs, no such up-regulation was observed after CVB infection. The blunted IFN response was paralleled by a reduction in the abundance of proteins involved in the induction of interferon gene transcription, including TIR-domain-containing adapter-inducing interferon-β (TRIF), mitochondrial antiviral-signaling protein (MAVS), and the global protein translation initiator eukaryotic translation initiation factor 4G (eIF4G). Taken together, this study highlights a potent anti-Coxsackieviral effect of both type I and III IFNs in cells located at the primary site of infection. Furthermore, we show for the first time that the production of type I and III IFNs in IECs is blocked by CVBs. These findings suggest that CVBs evade the host immune response in order to successfully infect the intestine.

Pathogenesis of non-epithelial foot-and-mouth disease in neonatal animals

Foot-and-mouth disease virus (FMDV), which causes a highly contagious viral disease of cloven-hoofed animals, is notable for epithelial cell tropism, resulting in the appearance of vesicles on the feet and in and around the mouth in infected animals, while FMDV infection in neonatal animals is also associated with not only epithelial lesions, but also muscle-associated lesions, which leads to myocarditis, resulting in high-mortality. However, critical knowledge about the non-epithelial tropism of FMDV is still lacking. In this paper, the current progress of the FMDV non-epithelial tropisms is summarized and the possible role of the key viral and cellular components involved is discussed.

IL6-mediated HCoV-host interactome regulatory network and GO/Pathway enrichment analysis

During these days of global emergency for the COVID-19 disease outbreak, there is an urgency to share reliable information able to help worldwide life scientists to get better insights and make sense of the large amount of data currently available. In this study we used the results presented in [1] to perform two different Systems Biology analyses on the HCoV-host interactome. In the first one, we reconstructed the interactome of the HCoV-host proteins, integrating it with highly reliable miRNA and drug interactions information. We then added the IL-6 gene, identified in recent publications [2] as heavily involved in the COVID-19 progression and, interestingly, we identified several interactions with the reconstructed interactome. In the second analysis, we performed a Gene Ontology and a Pathways enrichment analysis on the full set of the HCoV-host interactome proteins and on the ones belonging to a significantly dense cluster of interacting proteins identified in the first analysis. Results of the two analyses provide a compact but comprehensive glance on some of the current state-of-the-art regulations, GO, and pathways involved in the HCoV-host interactome, and that could support all scientists currently focusing on SARS-CoV-2 research.

A simplified cell-based assay to identify coronavirus 3CL protease inhibitors

We describe a mammalian cell-based assay capable of identifying coronavirus 3CL protease (3CLpro) inhibitors without requiring the use of live virus. By enabling the facile testing of compounds across a range of coronavirus 3CLpro enzymes, including the one from SARS-CoV-2, we are able to quickly identify compounds with broad or narrow spectra of activity. We further demonstrate the utility of our approach by performing a curated compound screen along with structure-activity profiling of a series of small molecules to identify compounds with antiviral activity. Throughout these studies, we observed concordance between data emerging from this assay and from live virus assays. By democratizing the testing of 3CL inhibitors to enable screening in the majority of laboratories rather than the few with extensive biosafety infrastructure, we hope to expedite the search for coronavirus 3CL protease inhibitors, to address the current epidemic and future ones that will inevitably arise.

The Role of Non-coding RNAs in Viral Myocarditis

Viral myocarditis (VMC) is a disease characterized as myocardial parenchyma or interstitium inflammation caused by virus infection, especially Coxsackievirus B3 (CVB3) infection, which has no accurate non-invasive examination for diagnosis and specific drugs for treatment. The mechanism of CVB3-induced VMC may be related to direct myocardial damage of virus infection and extensive damage of abnormal immune response after infection. Non-coding RNA (ncRNA) refers to RNA that is not translated into protein and plays a vital role in many biological processes. There is expanding evidence to reveal that ncRNAs regulate the occurrence and development of VMC, which may provide new treatment or diagnosis targets. In this review, we mainly demonstrate an overview of the potential role of ncRNAs in the pathogenesis, diagnosis and treatment of CVB3-induced VMC.

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.

Structural Biology of the Enterovirus Replication-Linked 5'-Cloverleaf RNA and Associated Virus Proteins

Although enteroviruses are associated with a wide variety of diseases and conditions, their mode of replication is well conserved. Their genome is carried as a single, positive-sense RNA strand. At the 5' end of the strand is an approximately 90-nucleotide self-complementary region called the 5' cloverleaf, or the oriL. This noncoding region serves as a platform upon which host and virus proteins, including the 3B, 3C, and 3D virus proteins, assemble in order to initiate replication of a negative-sense RNA strand. The negative strand in turn serves as a template for synthesis of multiple positive-sense RNA strands. Building on structural studies of individual RNA stem-loops, the structure of the intact 5' cloverleaf from rhinovirus has recently been determined via nuclear magnetic resonance/small-angle X-ray scattering (NMR/SAXS)-based methods, while structures have also been determined for enterovirus 3A, 3B, 3C, and 3D proteins. Analysis of these structures, together with structural and modeling studies of interactions between host and virus proteins and RNA, has begun to provide insight into the enterovirus replication mechanism and the potential to inhibit replication by blocking these interactions.

Inhibition of microRNA-15 protects H9c2 cells against CVB3-induced myocardial injury by targeting NLRX1 to regulate the NLRP3 inflammasome

Background

Viral myocarditis (VMC) is a type of cardiac inflammation that is generally caused by coxsackievirus B3 (CVB3) infection. Several MicroRNAs (miRNAs) are known to play crucial roles in VMC pathogenesis. MiR-15 is reportedly associated with myocardial injury, inflammatory responses and viral infection. Whether miR-15 affects the occurrence and development of VMC remains largely unknown. The roles of miR-15 and their underlying mechanisms in CVB3-stimulated H9c2 cells were assessed in this study.

Methods

We infected H9c2 cells with CVB3 to establish a VMC cellular model. We then determined the effects of miR-15 inhibition on three cardiomyocyte injury markers: lactate dehydrogenase (LDH), creatine kinase-MB (CK-MB) and cardiac troponin-I (cTn-I). The impact on CVB3-induced cell apoptosis and pro-inflammatory cytokines was also investigated. The effects of miR-15 inhibition on NLRP3 inflammasome activation were also assessed. The target relationship between miR-15 and NOD-like receptor X1 (NLRX1) was determined using a luciferase reporter assay.

Results

MiR-15 expression was significantly upregulated in H9c2 cells after CVB3 infection. Inhibition of miR-15 significantly decreased the CVB3-induced levels of LDH, CK-MB and cTn-I. It also elevated cell viability, reduced CVB3-induced cell apoptosis and decreased the generation of the interleukins IL-1β, IL-6 and IL-18. Furthermore, we determined that miR-15 inhibition suppressed NLRP3 inflammasome activation by downregulating NLRP3 and caspase-1 p20 expression. We found a direct target relationship between miR-15 and NLRX1. Additionally, inhibition of NLRX1 reversed the protective effects of miR-15 inhibition against CVB3-induced myocardial cell injury by regulating the NLRP3 inflammasome.

Conclusion

Our results indicate that miR-15 inhibition alleviates CVB3-induced myocardial inflammation and cell injury. This may be partially due to NLRX1-mediated NLRP3 inflammasome inactivation.

Human Enterovirus Group B Viruses Rely on Vimentin Dynamics for Efficient Processing of Viral Nonstructural Proteins

We report that several viruses from the human enterovirus group B cause massive vimentin rearrangements during lytic infection. Comprehensive studies suggested that viral protein synthesis was triggering the vimentin rearrangements. Blocking the host cell vimentin dynamics with β, β'-iminodipropionitrile (IDPN) did not significantly affect the production of progeny viruses and only moderately lowered the synthesis of structural proteins such as VP1. In contrast, the synthesis of the nonstructural proteins 2A, 3C, and 3D was drastically lowered. This led to attenuation of the cleavage of the host cell substrates PABP and G3BP1 and reduced caspase activation, leading to prolonged cell survival. Furthermore, the localization of the proteins differed in the infected cells. Capsid protein VP1 was found diffusely around the cytoplasm, whereas 2A and 3D followed vimentin distribution. Based on protein blotting, smaller amounts of nonstructural proteins did not result from proteasomal degradation but from lower synthesis without intact vimentin cage structure. In contrast, inhibition of Hsp90 chaperone activity, which regulates P1 maturation, lowered the amount of VP1 but had less effect on 2A. The results suggest that the vimentin dynamics regulate viral nonstructural protein synthesis while having less effect on structural protein synthesis or overall infection efficiency. The results presented here shed new light on differential fate of structural and nonstructural proteins of enteroviruses, having consequences on host cell survival.IMPORTANCE A virus needs the host cell in order to replicate and produce new progeny viruses. For this, the virus takes over the host cell and modifies it to become a factory for viral proteins. Irrespective of the specific virus family, these proteins can be divided into structural and nonstructural proteins. Structural proteins are the building blocks for the new progeny virions, whereas the nonstructural proteins orchestrate the takeover of the host cell and its functions. Here, we have shown a mechanism that viruses exploit in order to regulate the host cell. We show that viral protein synthesis induces vimentin cages, which promote production of specific viral proteins that eventually control apoptosis and host cell death. This study specifies vimentin as the key regulator of these events and indicates that viral proteins have different fates in the cells depending on their association with vimentin cages.

Regulation of cell death in the cardiovascular system

The adult heart is a post-mitotic terminally differentiated organ; therefore, beyond development, cardiomyocyte cell death is maladaptive. Heart disease is the leading cause of death in the world and aberrant cardiomyocyte cell death is the underlying problem for most cardiovascular-related diseases and fatalities. In this chapter, we will discuss the different cell death mechanisms that engage during normal cardiac development, aging, and disease states. The most abundant loss of cardiomyocytes occurs during a myocardial infarction, when the blood supply to the heart is obstructed, and the affected myocardium succumbs to cell death. Originally, this form of cell death was considered to be unregulated; however, research from the last half a century clearly demonstrates that this form of cell death is multifaceted and employees various degrees of regulation. We will explore all of the cell death pathways that have been implicated in this disease state and the potential interplay between them. Beyond myocardial infarction, we also explore the role and mechanisms of cardiomyocyte cell death in heart failure, myocarditis, and chemotherapeutic-induced cardiotoxicity. Inhibition of cardiomyocyte cell death has extensive therapeutic potential that will increase the longevity and health of the human heart.

Apoptosis and Autophagy in Picornavirus Infection

Cell death is a fundamental process in maintaining cellular homeostasis, which can be either accidental or programed. Programed cell death depends on the specific signaling pathways, resulting in either lytic or non-lytic morphology. It exists in two primary forms: apoptosis and autophagic cell death. Apoptosis is a non-lytic and selective cell death program, which is executed by caspases in response to non-self or external stimuli. In contrast, autophagy is crucial for maintaining cellular homeostasis via the degradation and recycling of cellular components. These two mechanisms also function in the defense against pathogen attack. However, picornaviruses have evolved to utilize diverse strategies and target critical components to regulate the apoptotic and autophagic processes for optimal replication and the release from the host cell. Although an increasing number of investigations have shown that the apoptosis and autophagy are altered in picornavirus infection, the mechanism by which viruses take advantage of these two processes remains unknown. In this review, we discuss the mechanisms of picornavirus executes cellular apoptosis and autophagy at the molecular level and the relationship between these interactions and viral pathogenesis.

Cleavage and Sub-Cellular Redistribution of Nuclear Pore Protein 98 by Coxsackievirus B3 Protease 2A Impairs Cardioprotection

Myocarditis, inflammation of the heart muscle, affects all demographics and is a major cause of sudden and unexpected death in young people. It is most commonly caused by viral infections of the heart, with coxsackievirus B3 (CVB3) being among the most prevalent pathogens. To understand the molecular pathogenesis of CVB3 infection and provide strategies for developing treatments, we examined the role of a key nuclear pore protein 98 (NUP98) in the setting of viral myocarditis. NUP98 was cleaved as early as 2 h post-CVB3 infection. This cleavage was further verified through both the ectopic expression of viral proteases and in vitro using purified recombinant CVB3 proteases (2A and 3C), which demonstrated that CVB3 2A but not 3C is responsible for this cleavage. By immunostaining and confocal imaging, we observed that cleavage resulted in the redistribution of NUP98 to punctate structures in the cytoplasm. Targeted siRNA knockdown of NUP98 during infection further increased viral protein expression and viral titer, and reduced cell viability, suggesting a potential antiviral role of NUP98. Moreover, we discovered that expression levels of neuregulin-1 (NRG1), a cardioprotective gene, and presenilin-1 (PSEN1), a cellular protease processing the tyrosine kinase receptor ERBB4 of NRG1, were reliant upon NUP98 and were downregulated during CVB3 infection. In addition, expression of these NUP98 target genes in myocardium tissue not only occurred at an earlier phase of infection, but also appeared in areas away from the initial inflammatory regions. Collectively, CVB3-induced cleavage of NUP98 and subsequent impairment of the cardioprotective NRG1-ERBB4/PSEN1 signaling cascade may contribute to increased myocardial damage in the context of CVB3-induced myocarditis. To our knowledge, this is the first study to demonstrate the link between NUP98 and the NRG1 signaling pathway in viral myocarditis.

The Capsid Protein VP1 of Coxsackievirus B Induces Cell Cycle Arrest by Up-Regulating Heat Shock Protein 70

Manipulating cell cycle is one of the common strategies used by viruses to generate favorable cellular environment to facilitate viral replication. Coxsackievirus B (CVB) is one of the major viral pathogens of human myocarditis and cardiomyopathy. Because of its small genome, CVB depends on cellular machineries for productive replication. However, how the structural and non-structural components of CVB would manipulate cell cycle is not clearly understood. In this study, we demonstrated that the capsid protein VP1 of CVB type 3 (CVB3) induced cell cycle arrest at G1 phase. G1 arrest was the result of the decrease level of cyclin E and the accumulation of p27^Kip1. Study on the gene expression profile of the cells expressing VP1 showed that the expression of both heat shock protein 70-1 (Hsp70-1) and Hsp70-2 was significantly up-regulated. Knockdown of Hsp70 resulted in the increased level of cyclin E and the reduction of p27^Kip1. We further demonstrated that the phosphorylation of the heat shock factor 1, which directly promotes the expression of Hsp70, was also increased in the cell expressing VP1. Moreover, we show that CVB3 infection also induced G1 arrest, likely due to dysregulating Hsp70, cyclin E, and p27, while knockdown of Hsp70 dramatically inhibited viral replication. Cell cycle arrest at G1 phase facilitated CVB3 infection, since viral replication in the cells synchronized at G1 phase dramatically increased. Taken together, this study demonstrates that the VP1 of CVB3 induces cell cycle arrest at G1 phase through up-regulating Hsp70. Our findings suggest that the capsid protein VP1 of CVB is capable of manipulating cellular activities during viral infection.

The Saffold Virus-Penang 2B and 3C Proteins, but not the L Protein, Induce Apoptosis in HEp-2 and Vero Cells

Our previous work has shown that Saffold virus (SAFV) induced several rodent and primate cell lines to undergo apoptosis (Xu et al. in Emerg Microb Infect 3:1-8, 2014), but the essential viral proteins of SAFV involved in apoptotic activity lack study. In this study, we individually transfected the viral proteins of SAFV into HEp-2 and Vero cells to assess their ability to induce apoptosis, and found that the 2B and 3C proteins are proapoptotic. Further investigation indicated the transmembrane domain of the 2B protein is essential for the apoptotic activity and tetramer formation of the 2B protein. Our research provides clues for the possible mechanisms of apoptosis induced by SAFV in different cell lines. It also opens up new directions to study viral proteins (the 2B, 3C protein), and sets the stage for future exploration of any possible link between SAFV, inclusive of its related uncultivable genotypes, and multiple sclerosis.

Senecavirus A 3C Protease Mediates Host Cell Apoptosis Late in Infection

Senecavirus A (SVA), an oncolytic picornavirus used for cancer treatment in humans, has recently emerged as a vesicular disease (VD)-causing agent in swine worldwide. Notably, SVA-induced VD is indistinguishable from foot-and-mouth disease (FMD) and other high-consequence VDs of pigs. Here we investigated the role of apoptosis on infection and replication of SVA. Given the critical role of the nuclear factor-kappa B (NF-κB) signaling pathway on modulation of cell death, we first assessed activation of NF-κB during SVA infection. Results here show that while early during infection SVA induces activation of NF-κB, as evidenced by nuclear translocation of NF-κB-p65 and NF-κB-mediated transcription, late in infection a cleaved product corresponding to the C-terminus of NF-κB-p65 is detected in infected cells, resulting in lower NF-κB transcriptional activity. Additionally, we assessed the potential role of SVA 3C protease (3Cpro) in SVA-induced host-cell apoptosis and cleavage of NF-κB-p65. Transient expression of SVA 3Cpro was associated with cleavage of NF-κB-p65 and Poly (ADP-ribose) polymerase (PARP), suggesting its involvement in virus-induced apoptosis. Most importantly, we showed that while cleavage of NF-κB-p65 is secondary to caspase activation, the proteolytic activity of SVA 3Cpro is essential for induction of apoptosis. Experiments using the pan-caspase inhibitor Z-VAD-FMK confirmed the relevance of late apoptosis for SVA infection, indicating that SVA induces apoptosis, presumably, as a mechanism to facilitate virus release and/or spread from infected cells. Together, these results suggest an important role of apoptosis for SVA infection biology.