Variability in apoptotic response to poliovirus infection

Comprehensive Elucidation of the Role of L and 2A Security Proteins on Cell Death during EMCV Infection

The EMCV L and 2A proteins are virulence factors that counteract host cell defense mechanisms. Both L and 2A exhibit antiapoptotic properties, but the available data were obtained in different cell lines and under incomparable conditions. This study is aimed at checking the role of these proteins in the choice of cell death type in three different cell lines using three mutants of EMCV lacking functional L, 2A, and both proteins together. We have found that both L and 2A are non-essential for viral replication in HeLa, BHK, and RD cell lines, as evidenced by the viability of the virus in the absence of both functional proteins. L-deficient infection led to the apoptotic death of HeLa and RD cells, and the necrotic death of BHK cells. 2A-deficient infection induced apoptosis in BHK and RD cells. Infection of HeLa cells with the 2A-deficient mutant was finalized with exclusive caspase-dependent death with membrane permeabilization, morphologically similar to pyroptosis. We also demonstrated that inactivation of both proteins, along with caspase inhibition, delayed cell death progression. The results obtained demonstrate that proteins L and 2A play a critical role in choosing the path of cell death during infection, but the result of their influence depends on the properties of the host cells.

Silver nanoparticles biosynthesized from secondary metabolite producing marine actinobacteria and evaluation of their biomedical potential

Biosynthesis of silver nanoparticles (AgNPs) from marine actinobacteria offers a promising avenue for exploring bacterial extracts as reducing and stabilizing agents. We report extracellular extracts of Rhodococcus rhodochrous (MOSEL-ME29) and Streptomyces sp. (MOSEL-ME28), identified by 16S rRNA gene sequencing for synthesis of AgNPs. Ultrafine silver nanoparticles were biosynthesized using the extracts of R. rhodochrous and Streptomyces sp. and their possible therapeutic applications were studied. The physicochemical properties of nanoparticles were established by HR-SEM/TEM, SAED, UV-Vis, EDS, XRD, and FTIR. UV-Vis spectra displayed characteristic absorption at 430 nm and 412 nm for AgNPs from Streptomyces sp. (S-AgNPs) and Rhodococcus sp. (R-AgNPs), respectively. HR-SEM/TEM, XRD, EDS analysis confirmed the spherical shape, crystalline nature, and elemental formation of silver. Crystallite or grain size was deduced as 5.52 nm for R-AgNPs and 35 nm for S-AgNPs. Zeta-potential indicated electrostatic negative charge for AgNPs, while FTIR revealed the presence of diverse functional groups. Disc diffusion assay indicated the broad-spectrum antibacterial potential of S-AgNPs with the maximum inhibition of B. subtilis while R-AgNPs revealed potency against P. aeruginosa at 10 µg/mL concentration. Biogenic AgNPs revealed antileishmanial activity and the IC₅₀ was calculated as 164 µg/mL and 184 µg/mL for R-AgNPs and S-AgNPs respectively. Similarly, the R-AgNPs and S-AgNPs revealed anti-cancer potential against HepG2 and the IC₅₀ was calculated as 49 µg/mL and 69 µg/mL for R-AgNPs and S-AgNPs, respectively. Moreover, the antioxidant activity showed significant results. MTT assay on RD cells, L20B cells, and Hep-2C indicated intensification in viability by reducing the concentration of R-AgNPs and S-AgNPs. The R-AgNPs and S-AgNPs inhibited sabin-like poliovirus (1TCID₅₀ infection in RD cells). Furthermore, hemocompatibility at low concentrations has been confirmed. Hence, it is concluded that biogenic-AgNPs has the potential to be used in diverse biological applications and that the marine actinobacteria are an excellent resource for fabrication of AgNPs.

Phyto-fabricated Cr2O3 nanoparticle for multifunctional biomedical applications

Aim: The biosynthesis of chromium oxide nanoparticles (Cr₂O₃ NPs), using Hyphaene thebaica as a bioreductant, for assessment of their potential nanomedicinal applications. Materials & methods: Biosynthesized Cr₂O₃ NPs were characterized by x-ray diffraction, Fourier-transform infrared spectroscopy, energy dispersive x-ray spectroscopy, scanning and transmission electron microscopy, selected area electron diffraction, UV-Vis spectroscopy and ζ-potential measurement. In vitro assays were used to assess the biological properties of Cr₂O₃ NPs. Results: Nanoparticles with size approximately 25-38 nm were obtained with a characteristic Cr-O vibration at 417 cm^-1. A broad spectrum antimicrobial potential and antioxidant nature is reported. Slight inhibition of polio virus and biocompatibility at low doses was observed. Conclusion: We conclude a multifunctional nature of biogenic Cr₂O₃ NPs.

In pursuit of intriguing puzzles

This Invited Review is a kind of scientific autobiography based on the presentation at the Symposium "Viruses: Discovering Big in Small" held in honor of the author's 90th birthday (Moscow, March 2019).

Human tryptophanyl-tRNA synthetase is an IFN-γ-inducible entry factor for Enterovirus

Enterovirus A71 (EV-A71) receptors that have been identified to date cannot fully explain the pathogenesis of EV-A71, which is an important global cause of hand, foot, and mouth disease and life-threatening encephalitis. We identified an IFN-γ-inducible EV-A71 cellular entry factor, human tryptophanyl-tRNA synthetase (hWARS), using genome-wide RNAi library screening. The importance of hWARS in mediating virus entry and infectivity was confirmed by virus attachment, in vitro pulldown, antibody/antigen blocking, and CRISPR/Cas9-mediated deletion. Hyperexpression and plasma membrane translocation of hWARS were observed in IFN-γ-treated semipermissive (human neuronal NT2) and cDNA-transfected nonpermissive (mouse fibroblast L929) cells, resulting in their sensitization to EV-A71 infection. Our hWARS-transduced mouse infection model showed pathological changes similar to those seen in patients with severe EV-A71 infection. Expression of hWARS is also required for productive infection by other human enteroviruses, including the clinically important coxsackievirus A16 (CV-A16) and EV-D68. This is the first report to our knowledge on the discovery of an entry factor, hWARS, that can be induced by IFN-γ for EV-A71 infection. Given that we detected high levels of IFN-γ in patients with severe EV-A71 infection, our findings extend the knowledge of the pathogenicity of EV-A71 in relation to entry factor expression upon IFN-γ stimulation and the therapeutic options for treating severe EV-A71-associated complications.

Neurotropic Enterovirus Infections in the Central Nervous System

Enteroviruses are a group of positive-sense single stranded viruses that belong to the Picornaviridae family. Most enteroviruses infect humans from the gastrointestinal tract and cause mild symptoms. However, several enteroviruses can invade the central nervous system (CNS) and result in various neurological symptoms that are correlated to mortality associated with enteroviral infections. In recent years, large outbreaks of enteroviruses occurred worldwide. Therefore, these neurotropic enteroviruses have been deemed as re-emerging pathogens. Although these viruses are becoming large threats to public health, our understanding of these viruses, especially for non-polio enteroviruses, is limited. In this article, we review recent advances in the trafficking of these pathogens from the peripheral to the central nervous system, compare their cell tropism, and discuss the effects of viral infections in their host neuronal cells.

Cytopathic effects: virus-modulated manifestations of innate immunity?

The capacity to injure infected cells is a widespread property of viruses. Usually, this cytopathic effect (CPE) is ascribed to viral hijacking of cellular resources to fulfill viral needs. However, evidence is accumulating that CPE is not necessarily directly coupled to viral reproduction but may largely be due to host defensive and viral antidefensive activities. A major part in this virus–cell interaction appears to be played by a putative host-encoded program with multiple competing branches, leading to necrotic, apoptotic, and, possibly, other types of cell suicide. Manifestations of this program are controlled and modulated by host, viral, and environmental factors.

Suppression of injuries caused by a lytic RNA virus (mengovirus) and their uncoupling from viral reproduction by mutual cell/virus disarmament

Viruses often elicit cell injury (cytopathic effect [CPE]), a major cause of viral diseases. CPE is usually considered to be a prerequisite for and/or consequence of efficient viral growth. Recently, we proposed that viral CPE may largely be due to host defensive and viral antidefensive activities. This study aimed to check the validity of this proposal by using as a model HeLa cells infected with mengovirus (MV). As we showed previously, infection of these cells with wild-type MV resulted in necrosis, whereas a mutant with incapacitated antidefensive ("security") viral leader (L) protein induced apoptosis. Here, we showed that several major morphological and biochemical signs of CPE (e.g., alterations in cellular and nuclear shape, plasma membrane, cytoskeleton, chromatin, and metabolic activity) in cells infected with L(-) mutants in the presence of an apoptosis inhibitor were strongly suppressed or delayed for long after completion of viral reproduction. These facts demonstrate that the efficient reproduction of a lytic virus may not directly require development of at least some pathological alterations normally accompanying infection. They also imply that L protein is involved in the control of many apparently unrelated functions. The results also suggest that the virus-activated program with competing necrotic and apoptotic branches is host encoded, with the choice between apoptosis and necrosis depending on a variety of intrinsic and extrinsic conditions. Implementation of this defensive suicidal program could be uncoupled from the viral reproduction. The possibility of such uncoupling has significant implications for the pathogenesis and treatment of viral diseases.

Bypass suppression of small-plaque phenotypes by a mutation in poliovirus 2A that enhances apoptosis

The rate of protein secretion in host cells is inhibited during infection with several different picornaviruses, with consequences likely to have significant effects on viral growth, spread, and pathogenesis. This Sin(+) (secretion inhibition) phenotype has been documented for poliovirus, foot-and-mouth disease virus, and coxsackievirus B3 and can lead to reduced cell surface expression of major histocompatibility complex class I and tumor necrosis factor receptor as well as reduced extracellular secretion of induced cytokines such as interleukin-6 (IL-6), IL-8, and beta interferon. The inhibition of protein secretion is global, affecting the movement of all tested cargo proteins through the cellular secretion apparatus. To test the physiological significance of the Sin(-) and Sin(+) phenotypes in animal models, Sin(-) mutant viruses are needed that fail to inhibit host protein secretion and also exhibit robust growth properties. To identify such Sin(-) mutant polioviruses, we devised a fluorescence-activated cell sorter-based screen to select virus-infected cells that nevertheless expressed newly synthesized surface proteins. After multiple rounds of selection, candidate Sin(-) mutant viruses were screened for genetic stability, increased secretion of cargo molecules and wild-type translation and growth properties. A newly identified Sin(-) mutant poliovirus that contained coding changes in nonstructural proteins 2A (N32D) and 2C (E253G) was characterized. In this virus, the 2C mutation is responsible for the Sin(-) phenotype and the 2A mutation suppresses a resulting growth defect by increasing the rate of cell death and therefore the rate of viral spread. The 2A-N32D suppressor mutation was not allele specific and, by increasing the rate of cellular apoptosis, affected a completely different pathway than the 2C-E253G Sin(-) mutation. Therefore, the 2A mutation suppresses the 2C-E253G mutant phenotype by a bypass suppression mechanism.

Interactions between viral and prokaryotic pathogens in a mixed infection with cardiovirus and mycoplasma

In the natural environment, animal and plant viruses often share ecological niches with microorganisms, but the interactions between these pathogens, although potentially having important implications, are poorly investigated. The present report demonstrates, in a model system, profound mutual effects of mycoplasma and cardioviruses in animal cell cultures. In contrast to mycoplasma-free cells, cultures contaminated with Mycoplasma hyorhinis responded to infection with encephalomyocarditis virus (EMCV), a picornavirus, but not with poliovirus (also a picornavirus), with a strong activation of a DNase(s), as evidenced by the TUNEL (terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling) immunofluorescence assay and electrophoretic analysis of host DNA. This degradation was reminiscent of that observed upon apoptosis but was caspase independent, judging by the failure of the specific pan-caspase inhibitor Q-VD-OPh to prevent it. The electrophoretic mobility of the enzyme responsible for DNA degradation and dependence of its activity on ionic conditions strongly suggested that it was represented by a DNase(s) of mycoplasma origin. In cells not infected with EMCV, the relevant DNase was dormant. The possibility is discussed that activation of the mycoplasma DNase might be linked to a relatively early increase in permeability of plasma membrane of the infected cells caused by EMCV. This type of unanticipated virus-mycoplasma "cooperation" may exemplify the complexity of pathogen-host interactions under conditions when viruses and microorganisms are infecting the same host. In the course of the present study, it was also demonstrated that pan-caspase inhibitor zVAD(OMe).fmk strongly suppressed cardiovirus polyprotein processing, illustrating an additional pitfall in investigations of viral effects on the apoptotic system of host cells.

Antiapoptotic activity of the cardiovirus leader protein, a viral "security" protein

Apoptosis is a common antiviral defensive mechanism that potentially limits viral reproduction and spread. Many viruses possess apoptosis-suppressing tools. Here, we show that the productive infection of HeLa cells with encephalomyocarditis virus (a cardiovirus) was not accompanied by full-fledged apoptosis (although the activation of caspases was detected late in infection) but rather elicited a strong antiapoptotic state, as evidenced by the resistance of infected cells to viral and nonviral apoptosis inducers. The development of the antiapoptotic state appeared to depend on a function(s) of the viral leader (L) protein, since its mutational inactivation resulted in the efflux of cytochrome c from mitochondria, the early activation of caspases, and the appearance of morphological and biochemical signs of apoptosis in a significant proportion of infected cells. Infection with both wild-type and L-deficient viruses induced the fragmentation of mitochondria, which in the former case was not accompanied with cytochrome c efflux. Although the exact nature of the antiapoptotic function(s) of cardioviruses remains obscure, our results suggested that it includes previously undescribed mechanisms operating upstream and possibly downstream of the mitochondrial level, and that L is involved in the control of these mechanisms. We propose that cardiovirus L belongs to a class of viral proteins, dubbed here security proteins, whose roles consist solely, or largely, in counteracting host antidefenses. Unrelated L proteins of other picornaviruses as well as their highly variable 2A proteins also may be security proteins. These proteins appear to be independent acquisitions in the evolution of picornaviruses, implying multiple cases of functional (though not structural) convergence.

Theiler's murine encephalomyelitis virus leader protein is the only nonstructural protein tested that induces apoptosis when transfected into mammalian cells

Theiler's murine encephalomyelitis virus (TMEV) induces two distinct cell death programs, necrosis and apoptosis. The apoptotic pathway is of particular interest because TMEV persists in the central nervous system of mice, largely in infiltrating macrophages, which undergo apoptosis. Infection of murine macrophages in culture induces apoptosis that is Bax dependent through the intrinsic or mitochondrial pathway, restricting infectious-virus yields and raising the possibility that apoptosis represents a mechanism to attenuate TMEV yet promote macrophage-to-macrophage spread during persistent infection. To help define the cellular stressors and upstream signaling events leading to apoptosis during TMEV infection, we screened baby hamster kidney (BHK-21) cells transfected to express individual nonstructural genes (except 3B) of the low-neurovirulence BeAn virus strain for cell death. Only expression of the leader protein led to apoptosis, as assessed by fluorescence-activated cell sorting analysis of propidium iodide- and annexin V-stained transfected cells, immunoblot analysis of poly(ADP-ribose) polymerase and caspase cleavages, electron microscopy, and inhibition of apoptosis by the pancaspase inhibitor qVD-OPh. After transfection, Bak and not Bax expression increased, suggesting that the apical pathway leading to activation of these Bcl-2 multi-BH-domain proapoptotic proteins differs in BeAn virus infection versus L transfection. Mutation to remove the CHCC Zn finger motif from L, a motif required by L to mediate inhibition of nucleocytoplasmic trafficking, significantly reduced L-protein-induced apoptosis in both BHK-21 and M1-D macrophages.

The pathogenesis of poliomyelitis: what we don't know

Poliomyelitis has long served as a model for studies of viral pathogenesis, but there remain many important gaps in our understanding of this disease. It is the intent of this review to highlight these residual but important questions, in light of a possible future moratorium on research with polioviruses. Salient questions include: (1) What cells in the gastrointestinal tract are initially infected and act as the source of excreted virus? (2) What is the receptor used by mouse-adapted strains of poliovirus and how can some polioviruses use both mouse and primate receptors? (3) What determines species differences in susceptibility of the gastrointestinal tract to polioviruses? Why cannot PVR transgenic mice be infected by the natural enteric route? (4) Why are neuroadapted polioviruses unable to infect nonneural cells? (5) What is the role of postentry blocks in replication as determinants of neurovirulence? (6) What route(s) does poliovirus take to enter the central nervous system and how does it cross the blood-brain barrier? (7) Why does poliovirus preferentially attack lower motor neurons in contrast to many other neuronal types within the central nervous system? (8) Does cellular immunity play any role in recovery from acute infection or in vaccine-induced protection? (9) In which cells does poliovirus persist in patients with gamma-globulin deficiencies? (10) Is there any evidence that poliovirus genomes can persist in immunocompetent hosts? (11) Why has type 2 poliovirus been eradicated while types 1 and 3 have not? (12) Can transmission of vaccine-derived polioviruses be prevented with inactivated poliovirus vaccine? (13) What is the best strategy to control and eliminate vaccine-derived polioviruses?

Early phosphatidylinositol 3-kinase/Akt pathway activation limits poliovirus-induced JNK-mediated cell death

Poliovirus (PV)-induced apoptosis seems to play a major role in tissue injury in the central nervous system (CNS). We have previously shown that this process involves PV-induced Bax-dependent mitochondrial dysfunction mediated by early JNK activation in IMR5 neuroblastoma cells. We showed here that PV simultaneously activates the phosphatidylinositol 3-kinase (PI3K)/Akt survival signaling pathway in these cells, limiting the extent of JNK activation and thereby cell death. JNK inhibition is associated with PI3K-dependent negative regulation of the apoptosis signal-regulating kinase 1, which acts upstream from JNK in PV-infected IMR5 cells. In poliomyelitis, this survival pathway may limit the spread of PV-induced damage in the CNS.

Viroporins from RNA viruses induce caspase-dependent apoptosis

The virus‐encoded viroporins are known to modify membrane permeability and play an essential role in virus budding. Here, a comparative analysis of the membrane permeabilization capacity of a number of viroporins was performed in baby hamster kidney cells. Synthesis of 6K protein from Sindbis virus, E from mouse hepatitis virus, M2 from influenza A virus, and 2B and 3A from poliovirus enhanced membrane permeability to different extents. We show that two proteins from hepatitis C virus, p7 and NS4A, also display viroporin activity to a level comparable to 6K protein. In addition to their capacity to disrupt ionic cellular homeostasis and promote bacterial cell lysis, the expressed viroporins were able to induce cell death. Degradation of internucleosomal DNA and generation of apoptotic bodies were observed upon viroporin expression. Consistently, cleavage of translation initiation factor 4GI and poly‐(ADP‐ribose) polymerase indicated activation of effector caspase‐3. We found that poliovirus 2B localizes partially in mitochondria and induces an anomalous perinuclear distribution of these organelles. Mitochondria morphology was also altered after expression of other viroporins. Finally, detection of cytochrome c release from mitochondria suggests involvement of the mitochondrial pathway in viroporin‐induced apoptosis. These findings suggest that viroporins induce caspase‐dependent programmed cell death.

Poliovirus induces Bax-dependent cell death mediated by c-Jun NH2-terminal kinase

Poliovirus (PV) is the causal agent of paralytic poliomyelitis, a disease that involves the destruction of motor neurons associated with PV replication. In PV-infected mice, motor neurons die through an apoptotic process. However, mechanisms by which PV induces cell death in neuronal cells remain unclear. Here, we demonstrate that PV infection of neuronal IMR5 cells induces cytochrome c release from mitochondria and loss of mitochondrial transmembrane potential, both of which are evidence of mitochondrial outer membrane permeabilization. PV infection also activates Bax, a proapoptotic member of the Bcl-2 family; this activation involves its conformational change and its redistribution from the cytosol to mitochondria. Neutralization of Bax by vMIA protein expression prevents cytochrome c release, consistent with a contribution of PV-induced Bax activation to mitochondrial outer membrane permeabilization. Interestingly, we also found that c-Jun NH(2)-terminal kinase (JNK) is activated soon after PV infection and that the PV-cell receptor interaction alone is sufficient to induce JNK activation. Moreover, the pharmacological inhibition of JNK by SP600125 inhibits Bax activation and cytochrome c release. This is, to our knowledge, the first demonstration of JNK-mediated Bax-dependent apoptosis in PV-infected cells. Our findings contribute to our understanding of poliomyelitis pathogenesis at the cellular level.

A phylogenetically conserved RNA structure in the poliovirus open reading frame inhibits the antiviral endoribonuclease RNase L

RNase L is an antiviral endoribonuclease that cleaves viral mRNAs after single-stranded UA and UU dinucleotides. Poliovirus (PV) mRNA is surprisingly resistant to cleavage by RNase L due to an RNA structure in the 3C(Pro) open reading frame (ORF). The RNA structure associated with the inhibition of RNase L is phylogenetically conserved in group C enteroviruses, including PV type 1 (PV1), PV2, PV3, coxsackie A virus 11 (CAV11), CAV13, CAV17, CAV20, CAV21, and CAV24. The RNA structure is not present in other human enteroviruses (group A, B, or D enteroviruses). Coxsackievirus B3 mRNA and hepatitis C virus mRNA were fully sensitive to cleavage by RNase L. HeLa cells expressing either wild-type RNase L or a dominant-negative mutant RNase L were used to examine the effects of RNase L on PV replication. PV replication was not inhibited by RNase L activity, but rRNA cleavage characteristic of RNase L activity was detected late during the course of PV infection, after assembly of intracellular virus. Rather than inhibiting PV replication, RNase L activity was associated with larger plaques and better cell-to-cell spread. Mutations in the RNA structure associated with the inhibition of RNase L did not affect the magnitude of PV replication in HeLa cells expressing RNase L, consistent with the absence of observed RNase L activity until after virus assembly. Thus, PV carries an RNA structure in the 3C protease ORF that potently inhibits the endonuclease activity of RNase L, but this RNA structure does not prevent RNase L activity late during the course of infection, as virus assembly nears completion.

Infection and direct injury in human hepatocyte explants and a hepatoblastoma cell line due to hepatiticomimetic (non-hepatitis) viruses

Hepatitis is caused by hepatitis viruses, but hepatitis or hepatocellular enzyme abnormalities is sometimes associated with infection by the hepatiticomimetic viruses. The direct and indirect effects of infection with hepatiticomimetic viruses were examined in two human hepatocyte systems. Poliovirus, adenovirus, and herpes simplex virus (HSV) induced cytopathology in Hep G2 cells. Measles virus caused no change in hepatocytes. Poliovirus infection did not affect cellular protein synthesis, and the peak of hepatocellular enzyme release coincided with the peak of virus release. The increase in adenovirus protein synthesis correlated with the decrease of transferrin synthesis, and enzyme release was not prominent. HSV induced viral protein synthesis with enhanced processing and inhibition of synthesis of alpha1-antitrypsin. The peak of enzyme release was later than the peak of virus release. In primary hepatocytes, poliovirus, adenovirus, and induced extensive cytopathology and enzyme release, and VZV caused cytopathology and significant but minute enzyme release. The ratio of lactate dehydrogenase to aspartate aminotransferase release was larger in poliovirus infection in both hepatocytes than in HSV or VZV infection. Although poliovirus and adenovirus are released by cytolysis and HSV and VZV are secreted by exocytosis of cytoplasmic vacuoles, enzyme release was independent of the type of virus release. Adenovirus showed strong cytotoxicity but did not modify the membrane nor cause enzyme release. Enzyme release was associated with modification of the surface membrane due to apoptosis with poliovirus and necrosis with HSV. Consequently hepatocellular injury by viral infection did not reflect the amount or pattern of hepatocellular enzyme release.

Reduced apoptosis in human intestinal cells cured of persistent poliovirus infection

Cells cured of persistent virus infection can be used to investigate cellular pathways of resistance to viral cytopathic effects. Persistent poliovirus (PV) infections were established in human intestinal Caco-2 cells, and spontaneously cured cell cultures were obtained. Two cell clones, cl6 and b13, cured of type 3 PV mutant infection and their parental Caco-2 cells were compared for susceptibility to PV infection, PV receptor CD155 expression, capacity to differentiate into polarized enterocytes, and PV-, staurosporine-, and actinomycin D-induced apoptosis. Our results strongly suggest that cells that are partially resistant to apoptosis can be selected during persistent virus infection.

Effects on isolated human pancreatic islet cells after infection with strains of enterovirus isolated at clinical presentation of type 1 diabetes

Enterovirus (EV) infections have been associated with the pathogenesis of type 1 diabetes (T1D). They may cause beta-cell destruction either by cytolytic infection of the cells or indirectly by triggering the autoimmune response. Evidence for EV involvement have been presented in several studies, EV-IgM antibodies have been reported in T1D patients, EV-RNA has been found in the blood from T1D patients at onset, and EV have been isolated from newly diagnosed T1D. Our aim was to study infections with EV isolates from newly diagnosed T1D patients in human pancreatic islets in vitro. Two of them (T1 and T2) originated from a mother and her son diagnosed with T1D on the same day, the other two (A and E) were isolated from a pair of twins at the time of diagnosis of T1D in one of them. Isolated human pancreatic islets were infected and viral replication, viability and degree of cytolysis as well as insulin release in response to high glucose were measured. All four EV isolates replicated in the islet cells and virus particles and virus-induced vesicles were seen in the cytoplasm of the beta-cells. The isolates varied in their ability to induce cytolysis and to cause destruction of the islets and infection with two of the isolates (T1 and A) caused more pronounced destruction of the islets. Infection with the isolate from the healthy twin boy (E) was the least cytolytic. The ability to secrete insulin in response to high glucose was reduced in all infected islets as early as 3 days post infection, before any difference in viability was observed. To conclude, strains of EV isolated from T1D patients at clinical presentation of T1D revealed beta-cell tropism, and clearly affected the function of the beta-cell. In addition, the infection caused a clear increase in the number of dead cells.

Quantitative analysis of poliomyelitis-like paralysis in mice induced by a poliovirus replicon

Poliovirus (PV) infection causes severe paralysis, typically of the legs, by destruction of the motor neurons in the spinal cord. In this study, the relationship between PV replication in the spinal cord, damage in the motor neurons and poliomyelitis-like paralysis was analysed in transgenic mice expressing the human PV receptor (TgPVR21). First, a PV replicon encoding firefly luciferase in place of the capsid genes (PV-Fluc mc) was trans-encapsidated in 293T cells and the trans-encapsidated PV-Fluc mc (TE-PV-Fluc mc) was then inoculated into the spinal cords of TgPVR21 mice. TE-PV-Fluc mc was recovered with a titre of 6.3 x 10(7) infectious units ml(-1), which was comparable to those of PV1 strains. TgPVR21 mice inoculated with TE-PV-Fluc mc showed non-lethal paralysis of the hindlimbs, with severity ranging from a decline in grip strength to complete flaccid paralysis. The replication of TE-PV-Fluc mc in the spinal cord reached peak levels at 10 h post-inoculation (p.i.), followed by the appearance of paralysis at as early as 12 h p.i., reaching a plateau at 16 h p.i. Histological analysis showed a correlation between the lesion and the severity of the clinical symptoms in most mice. However, severe paralysis could also be observed with an apparently low lesion score, where as few as 5.3 x 10(2) motor neurons (1.4 % of the susceptible cells in the lumbar cord) were infected by TE-PV-Fluc mc. These results indicate that PV replication in a small population of the motor neurons was critical for severe residual poliomyelitis-like paralysis in TgPVR21 mice.

Cross talk between PML and p53 during poliovirus infection: implications for antiviral defense

PML nuclear bodies (NBs) are dynamic intranuclear structures harboring numerous transiently or permanently localized proteins. PML, the NBs' organizer, is directly induced by interferon, and its expression is critical for antiviral host defense. We describe herein the molecular events following poliovirus infection that lead to PML-dependent p53 activation and protection against virus infection. Poliovirus infection induces PML phosphorylation through the extracellular signal-regulated kinase pathway, increases PML SUMOylation, and induces its transfer from the nucleoplasm to the nuclear matrix. These events result in the recruitment of p53 to PML NBs, p53 phosphorylation on Ser15, and activation of p53 target genes leading to the induction of apoptosis. Moreover, the knock-down of p53 by small interfering RNA results in higher poliovirus replication, suggesting that p53 participates in antiviral defense. This effect, which requires the presence of PML, is transient since poliovirus targets p53 by inducing its degradation in a proteasome- and MDM2-dependent manner. Our results provide evidence of how poliovirus counteracts p53 antiviral activity by regulating PML and NBs, thus leading to p53 degradation.

Glutathione is required for efficient production of infectious picornavirus virions

Glutathione is an intracellular reducing agent that helps maintain the redox potential of the cell and is important for immune function. The drug L-buthionine sulfoximine (BSO) selectively inhibits glutathione synthesis. Glutathione has been reported to block replication of HIV, HSV-1, and influenza virus, whereas cells treated with BSO exhibit increased replication of Sendai virus. Pre-treatment of HeLa cell monolayers with BSO inhibited replication of CVB3, CVB4, and HRV14 with viral titers reduced by approximately 6, 5, and 3 log10, respectively. The addition of glutathione ethyl ester, but not dithiothreitol or 2-mercaptoethanol, to the culture medium reversed the inhibitory effect of BSO. Viral RNA and protein synthesis were not inhibited by BSO treatment. Fractionation of lysates from CVB3-infected BSO-treated cells on cesium chloride and sucrose gradients revealed that empty capsids but not mature virions were being produced. The levels of the 5S and 14S assembly intermediates, however, were not affected by BSO treatment. These results demonstrate that glutathione is important for production of mature infectious picornavirus virions.

Transcriptomic and proteomic analyses of rhabdomyosarcoma cells reveal differential cellular gene expression in response to enterovirus 71 infection

Insights into the host antiviral strategies as well as viral disease manifestations can be achieved through the elucidation of host- and virus-mediated transcriptional responses. An oligo-based microarray was employed to analyse mRNAs from rhabdomyosarcoma cells infected with the MS/7423/87 strain of enterovirus 71 (EV71) at 20 h post infection. Using Acuity software and LOWESS normalization, 152 genes were found to be downregulated while 39 were upregulated by greater than twofold. Altered transcripts include those encoding components of cytoskeleton, protein translation and modification; cellular transport proteins; protein degradation mediators; cell death mediators; mitochondrial-related and metabolism proteins; cellular receptors and signal transducers. Changes in expression profiles of 15 representative genes were authenticated by real-time reverse transcription polymerase chain reaction (RT-PCR), which also compared the transcriptional responses of cells infected with EV71 strain 5865/Sin/000009 isolated from a fatal case during the Singapore outbreak in 2000. Western blot analyses of APOB, CLU, DCAMKL1 and ODC1 proteins correlated protein and transcript levels. Two-dimensional proteomic maps highlighted differences in expression of cellular proteins (CCT5, CFL1, ENO1, HSPB1, PSMA2 and STMN1) following EV71 infection. Expression of several apoptosis-associated genes was modified, coinciding with apoptosis attenuation observed in poliovirus infection. Interestingly, doublecortin and CaM kinase-like 1 (DCAMKL1) involved in brain development, was highly expressed during infection. Thus, microarray, real-time RT-PCR and proteomic analyses can elucidate the global view of the numerous and complex cellular responses that contribute towards EV71 pathogenesis.

Coxsackievirus protein 2BC blocks host cell apoptosis by inhibiting caspase-3

Virus infection may induce host cell death by apoptosis, but some DNA viruses are capable of preventing this process. RNA viruses were thought not to display anti-apoptotic activities, as their spread appears to benefit from a rapid induction of cell death. Here, we report an antiapoptotic activity in the Picornavirus Coxsackievirus B4 (CVB4). CVB4 infection of HeLa cells induced negligible apoptosis over a period of 10 h. However, infected cells developed resistance to drug-induced apoptosis using staurosporine and actinomycin D and to death receptor-induced apoptosis using tumor necrosis factor-related apoptosis-inducing ligand. Despite this resistance, the apoptotic machinery was nonetheless fully activated in these drug-treated infected cells because the levels of pro-caspase-3 processing to its active form were similar to control cells. However, the DEVDase (Asp-Glu-Val-Asp protease) activity of the processed caspase was significantly inhibited in the virus-infected staurosporine-treated cells compared with drug treatment alone. Likewise, extracts of CVB4-infected cells suppressed recombinant caspase-3 activity in vitro. Immunoprecipitation of activated caspase-3 from radiolabeled virus-infected cells revealed the co-precipitation of a 48-kDa protein that was tentatively identified as viral protein 2BC. Recombinant caspase-3 was found to co-precipitate with virus protein 2BC. Finally, when protein 2BC was expressed in HeLa cells, both staurosporine-induced apoptosis and in vitro caspase-3 DEVDase activity were significantly reduced. Taken together these data imply that CVB4 infection suppresses apoptosis through virus protein 2BC associating with caspase-3 and inhibiting its function. Thus, 2BC is the first reported RNA virus inhibitor of apoptosis protein.

Picornaviruses and cell death

Members of the picornavirus family, including poliovirus and foot-and-mouth disease virus, are widespread pathogens of humans and domestic animals. Recent global developments in the resurgence of poliovirus infection and in the control of foot-and-mouth disease infection highlight the problems caused by the ability of picornaviruses to alter the apoptotic machinery of host cells and establish persistent infections. Despite the medical, economic and social impact of this family of viruses, little information exists that integrates the mechanisms of cell death and damage induced by related family members. Fortunately, examination of the reported roles and functions of individual viral proteins from multiple picornaviruses makes it possible to surmise canonical functions for these proteins. This review analyzes the canonical function of picornavirus proteins involved in the alteration of apoptotic homeostasis in infected host cells.

Translational control by viral proteinases

Most RNA viruses have evolved strategies to regulate cellular translation in order to promote preferential expression of the viral genome. Positive strand RNA viruses express large portions, or all of their proteome via translation of large polyproteins that are processed by embedded viral proteinases or host proteinases. Several of these viral proteinases are known to interact with host proteins, particularly with the host translation machinery, and thus, encompass the dual functions of processing of viral polyproteins and exerting translation control. Picornaviruses are perhaps the best characterized in regards to interaction of their proteinases with the host translation machinery and will be emphasized here. However, new findings have shown that similar paradigms exist in other viral systems which will be discussed.