Recrutement des kinases PI4KIII aux organelles de réplication virale au cours de l'infection par le poliovirus et d'autres virus à ARN de polarité positive.

One characteristic of infections with RNA viruses of positive polarity is the generation of new specialized membrane structures acting as platforms accommodating the complexes involved in replication of the viral genome. The functionality of these "replication organelles" is dependent on interactions between viral nonstructural proteins, recruited host factors and viral RNAs. Poliovirus, the causal agent of paralytic poliomyelitis, is the model most frequently used for identification of the viral and cellular components involved in this process. Several recent studies have suggested that the efficiency of genome replication for poliovirus and other members of the Picornaviridæ family results from the recruitment of a phosphatidylinositol (PI) kinase, PI4KIIIß (phosphatidylinositol-4-kinase IIIß), which generates a lipid membrane microenvironment rich in PI4P (phosphatidylinositol-4-phosphate) at sites of replication. The nonstructural protein 3A of these viruses has been shown to play a role in the enrichment of replication organelle membranes in PI4KIIIß, but the mechanisms of kinase recruitment seem to differ between members of this family of viruses. Hepatitis C, from the Flaviviridæ family, recruits another PI4KIII kinase, PI4KIIIα, to sites of replication, through another nonstructural protein, NS5A. In this review, we will describe the various recently proposed models and the potential role of PI4P lipids. Finally, we will show that PI4KIII kinases are potential targets for the development of antiviral drugs targeting many positive-polarity RNA viruses.

[Eradication of poliomyelitis and emergence of pathogenic vaccine-derived polioviruses: from Madagascar to Cameroon]. / Éradication de la poliomyélite et émergence de poliovirus pathogènes dérivés du vaccin - De Madagascar au Cameroun.

The oral poliovaccine, a live vaccine made of attenuated poliovirus strains, is the main tool of the vaccination campaigns organised for eradicating poliomyelitis. these campaigns had led to the decline and, thereafter, to the disappearance of wild poliovirus strains of the three serotypes (1-3) in most parts of the world. However, when the poliovaccine coverage becomes too low, vaccine polioviruses can circulate in insufficiently immunized populations and become then pathogenic by mutations and genetic recombination with other enteroviruses of the same species, in particular some coxsackievirus A. These mutated and recombinant vaccine strains have been implicated in several epidemics of paralytic poliomyelitis. Two polio outbreaks associated with these pathogenic circulating vaccine-derived poliovirus (cVDPV) occurred in 2001-2002 and 2005 in the South of Madagascar where vaccine coverage was low. These cVDPV, of serotype 2 or 3, were isolated from paralyzed children and some of their healthy contacts. Other cVDPV were isolated in the same region from healthy children in 2011, indicating that these viruses were circulating again. Vaccination campaigns could stop the outbreaks in 2002 and 2005, and most probably prevent another one in 2011. Therefore, the genetic plasticity of poliovaccine strains that threatens the benefit of vaccination campaigns is the target of an accurate surveillance and an important theme of studies in the virology laboratories of the Institut Pasteur international network.

Recombination between poliovirus and coxsackie A viruses of species C: a model of viral genetic plasticity and emergence.

Genetic recombination in RNA viruses was discovered many years ago for poliovirus (PV), an enterovirus of the Picornaviridae family, and studied using PV or other picornaviruses as models. Recently, recombination was shown to be a general phenomenon between different types of enteroviruses of the same species. In particular, the interest for this mechanism of genetic plasticity was renewed with the emergence of pathogenic recombinant circulating vaccine-derived polioviruses (cVDPVs), which were implicated in poliomyelitis outbreaks in several regions of the world with insufficient vaccination coverage. Most of these cVDPVs had mosaic genomes constituted of mutated poliovaccine capsid sequences and part or all of the non-structural sequences from other human enteroviruses of species C (HEV-C), in particular coxsackie A viruses. A study in Madagascar showed that recombinant cVDPVs had been co-circulating in a small population of children with many different HEV-C types. This viral ecosystem showed a surprising and extensive biodiversity associated to several types and recombinant genotypes, indicating that intertypic genetic recombination was not only a mechanism of evolution for HEV-C, but an usual mode of genetic plasticity shaping viral diversity. Results suggested that recombination may be, in conjunction with mutations, implicated in the phenotypic diversity of enterovirus strains and in the emergence of new pathogenic strains. Nevertheless, little is known about the rules and mechanisms which govern genetic exchanges between HEV-C types, as well as about the importance of intertypic recombination in generating phenotypic variation. This review summarizes our current knowledge of the mechanisms of evolution of PV, in particular recombination events leading to the emergence of recombinant cVDPVs.

Calcium flux between the endoplasmic reticulum and mitochondrion contributes to poliovirus-induced apoptosis.

We show that poliovirus (PV) infection induces an increase in cytosolic calcium (Ca(2+)) concentration in neuroblastoma IMR5 cells, at least partly through Ca(2+) release from the endoplasmic reticulum lumen via the inositol 1,4,5-triphosphate receptor (IP(3)R) and ryanodine receptor (RyR) channels. This leads to Ca(2+) accumulation in mitochondria through the mitochondrial Ca(2+) uniporter and the voltage-dependent anion channel (VDAC). This increase in mitochondrial Ca(2+) concentration in PV-infected cells leads to mitochondrial dysfunction and apoptosis.

Enhanced gene silencing in cells cured of persistent virus infection by RNA interference.

We compared HEp-2-derived cells cured of persistent poliovirus infection by RNA interference (RNAi) with parental cells, to investigate possible changes in the efficiency of RNAi. Lower levels of poliovirus replication were observed in cured cells, possibly facilitating virus silencing by antiviral small interfering RNAs (siRNAs). However, green fluorescent protein (GFP) produced from a measles virus vector and also GFP and luciferase produced from plasmids that do not replicate in human cells were more effectively silenced by specific siRNAs in cured than in control cells. Thus, cells displaying enhanced silencing were selected during curing by RNAi. Our results strongly suggest that the RNAi machinery of cured cells is more efficient than that of parental cells.

Recombination between polioviruses and co-circulating Coxsackie A viruses: role in the emergence of pathogenic vaccine-derived polioviruses.

Ten outbreaks of poliomyelitis caused by pathogenic circulating vaccine-derived polioviruses (cVDPVs) have recently been reported in different regions of the world. Two of these outbreaks occurred in Madagascar. Most cVDPVs were recombinants of mutated poliovaccine strains and other unidentified enteroviruses of species C. We previously reported that a type 2 cVDPV isolated during an outbreak in Madagascar was co-circulating with coxsackieviruses A17 (CA17) and that sequences in the 3' half of the cVDPV and CA17 genomes were related. The goal of this study was to investigate whether these CA17 isolates can act as recombination partners of poliovirus and subsequently to evaluate the major effects of recombination events on the phenotype of the recombinants. We first cloned the infectious cDNA of a Madagascar CA17 isolate. We then generated recombinant constructs combining the genetic material of this CA17 isolate with that of the type 2 vaccine strain and that of the type 2 cVDPV. Our results showed that poliovirus/CA17 recombinants are viable. The recombinant in which the 3' half of the vaccine strain genome had been replaced by that of the CA17 genome yielded larger plaques and was less temperature sensitive than its parental strains. The virus in which the 3' portion of the cVDPV genome was replaced by the 3' half of the CA17 genome was almost as neurovirulent as the cVDPV in transgenic mice expressing the poliovirus cellular receptor gene. The co-circulation in children and genetic recombination of viruses, differing in their pathogenicity for humans and in certain other biological properties such as receptor usage, can lead to the generation of pathogenic recombinants, thus constituting an interesting model of viral evolution and emergence.

Apoptotic signaling cascades operating in poliovirus-infected cells.

The flaccid paralyses characteristic of poliomyelitis are a direct consequence of the infection of motor neurons with poliovirus (PV). In PV-infected mice, motor neurons die by apoptosis. However, the mechanisms by which PV induces cell death in neurons remain unclear. Analyses of the apoptotic pathways induced by PV infection in several cell lines have demonstrated that mitochondria play a key role in PV-induced apoptosis. Furthermore, mitochondrial dysfunction results from an imbalance between pro- and anti-apoptotic pathways. We present here an overview of the many studies of PV-induced apoptosis carried out in recent years and discuss the contribution of these studies to our understanding of poliomyelitis.

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.

Prevention and treatment of enteric viral infections: possible benefits of probiotic bacteria.

The structure and function of the intestinal epithelium is briefly described, with the principal mechanisms involved in diarrhea. Human enteric viruses and probiotics are presented. We then review how probiotic bacteria could interfere with virus-induced pathology, we present our own view and describe specific interactions that would be valuable targets for future studies.

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.

Inhibition of hepatitis C virus infection in cell culture by small interfering RNAs.

Hepatitis C virus (HCV) infection is a major cause of chronic liver disease and hepatocellular carcinoma, yet fully efficacious treatments are missing. In this study, we investigated RNA interference (RNAi), a specific gene silencing process mediated by small interfering RNA (siRNA) duplexes, as an antiviral strategy against HCV. Synthetic siRNAs were designed to target conserved sequences of the HCV 5' nontranslated region (NTR) located in a functional, stem-loop structured domain of the HCV internal ribosome entry site (IRES), which is crucial for initiation of polyprotein translation. Several siRNAs dramatically reduced or even abrogated the replication of selectable subgenomic HCV replicons upon cotransfection of human hepatoma cells with viral target and siRNAs, or upon transfection of cells supporting autonomous replication of HCV replicon with siRNAs. Importantly, three siRNAs also proved capable of strongly inhibiting virus production in cell culture. One siRNA, targeting a sequence that is highly conserved across all genotypes and forms a critical pseudoknot structure involved in translation, was identified as the most promising therapeutic candidate. These results indicate that the HCV life cycle can be efficiently blocked by using properly-designed siRNAs that target functionally important, highly conserved sequences of the HCV IRES. This finding offers a novel approach towards developing IRES-based antiviral treatment for chronic HCV infections.

Bax is activated during rotavirus-induced apoptosis through the mitochondrial pathway.

Rotaviruses are the leading cause of infantile viral gastroenteritis worldwide. Mature enterocytes of the small intestine infected by rotavirus undergo apoptosis, and their replacement by less differentiated dividing cells probably leads to defective absorptive function of the intestinal epithelium, which, in turn, contributes to osmotic diarrhea and rotavirus pathogenesis. Here we show that infection of MA104 cells by the simian rhesus rotavirus strain RRV induced caspase-3 activation, DNA fragmentation, and cleavage of poly(ADP-ribose) polymerase; all three phenomena are features of apoptosis. RRV induced the release of cytochrome c from mitochondria to the cytosol, indicating that the mitochondrial apoptotic pathway was activated. RRV infection of MA104 cells activated Bax, a proapoptotic member of the Bcl-2 family, as revealed by its conformational change. Most importantly, Bax-specific small interfering RNAs partially inhibited cytochrome c release in RRV-infected cells. Thus, mitochondrial dysfunction induced by rotavirus is Bax dependent. Apoptosis presumably leads to impaired intestinal functions, so our findings contribute to improving our understanding of rotavirus pathogenesis at the cellular level.

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.

Complete cure of persistent virus infections by antiviral siRNAs.

Small interfering RNAs (siRNAs) have been developed as antiviral agents for mammalian cells. The capacity of specific siRNAs to prevent virus infections has been demonstrated, and there is evidence that these new antiviral agents could have a partial therapeutic effect a few days after infection. We investigated the possibility of curing a persistent infection, several months after becoming established, using an in vitro model of persistent poliovirus (PV) infection in HEp-2 cells. Despite high virus titers and the presence of PV mutants, repeated treatment with a mixture of two siRNAs targeting both noncoding and coding regions, one of them in a highly conserved region, resulted in the complete cure of the majority of persistently infected cultures. No escape mutants emerged in treated cultures. The antiviral effect of specific siRNAs, consistent with a mechanism of RNA interference, correlated with a decrease in the amount of viral RNA, until its complete disappearance, resulting in cultures cured of virions and viral RNA.

Silencing viruses by RNA interference.

Post-transcriptional gene silencing (PTGS) makes possible new approaches for studying the various steps of the viral cycle. Plus-strand RNA viruses appear to be attractive targets for small interfering RNAs (siRNAs), as their genome functions as both mRNA and replication template. PTGS creates an alternative to classic reverse genetics for viruses with either negative-strand or double-stranded RNA genomes and for those with a large genome. PTGS allows modification of the expression of a given cellular gene as a means to elucidate its role in the viral cycle and in virus-host cell interactions, and to investigate cellular pathways involved in viral pathogenesis. It also allows the creation of new animal models of human diseases. In addition, PTGS already appears to be a promising new therapeutic tool to fight viral multiplication and dissemination through the host and to prevent inflammation and virus-induced pathogenesis, including virus-induced tumorigenesis.

Poliovirus mutants excreted by a chronically infected hypogammaglobulinemic patient establish persistent infections in human intestinal cells.

Immunodeficient patients whose gut is chronically infected by vaccine-derived poliovirus (VDPV) may excrete large amounts of virus for years. To investigate how poliovirus (PV) establishes chronic infections in the gut, we tested whether it is possible to establish persistent VDPV infections in human intestinal Caco-2 cells. Four type 3 VDPV mutants, representative of the viral evolution in the gut of a hypogammaglobulinemic patient over almost 2 years [J. Virol. 74 (2000) 3001], were used to infect both undifferentiated, dividing cells, and differentiated, polarized enterocytes. A VDPV mutant excreted 36 days postvaccination by the patient was lytic in both types of intestinal cell cultures, like the parental Sabin 3 (S3) strain. In contrast, three VDPVs excreted 136, 442, and 637 days postvaccination, established persistent infections both in undifferentiated cells and in enterocytes. Thus, viral determinants selected between day 36 and 136 conferred on VDPV mutants the capacity to infect intestinal cells persistently. The percentage of persistently VDPV-infected cultures was higher in enterocytes than in undifferentiated cells, implicating cellular determinants involved in the differentiation of enterocytes in persistent VDPV infections. The establishment of persistent infections in enterocytes was not due to poor replication of VDPVs in these cells, but was associated with reduced viral adsorption to the cell surface.

Characterization of the poliovirus 147S particle: new insights into poliovirus uncoating.

A Sabin 1 strain poliovirus (PV) mutant, S1(2Y-1I), carrying a Tyr at amino acid position VP2(142) and an Ile at position VP1(160), can establish persistent infections in HEp-2c cells. This mutant forms atypical 147S particles upon interaction at 0 degrees C with either cells expressing PV receptor (PVR) CD155, or PVR-IgG2a, a chimeric molecule consisting of an extracellular moiety of PVR and the hinge and Fc portion of a mouse IgG2a. Upon interaction with PVR at 37 degrees C, S1(2Y-1I), similar to the parental strain, forms both 135S A particles and 80S empty capsids. At 0 degrees C, surprisingly, at a concentration equal to or greater than 5 nM, PVR-IgG2a induced both the extrusion of VP4 from the capsid of S1(2Y-1I) and the formation of 80S particles. The same transitions were observed at 0 degrees C with the parental strain Sabin 1 at 40 nM PVR-IgG2a. Thus, the formation of 80S particles and VP4 extrusion, considered as one of the steps of PV uncoating, can be temperature-independent at high PVR concentration. This implies that structural changes of the PV capsid occurred following adsorption at low temperature.