Search

West Nile virus (WNV) is a worldwide (re)emerging mosquito-transmitted Flavivirus causing fatal neurological diseases in humans. However, no human vaccine has been yet approved. One of the most effective live-attenuated vaccines was empirically obtained by serial passaging of wild-type yellow fever Flavivirus. However, such an approach is not acceptable nowadays, and the development of a rationally designed vaccine is necessary. Generating molecular infectious clones and mutating specific residues known to be involved in Flavivirus virulence constitute a powerful tool to promote viral attenuation. WNV membrane glycoprotein is thought to carry such essential determinants. Here, we identified two residues of this protein whose substitutions are key to the full and stable attenuation of WNV in vivo, most likely through inhibition of secretion and possible alteration of morphology. Applied to other flaviviruses, this approach should help in designing new vaccines against these viruses, which are an increasing threat to global human health., West Nile virus (WNV), a member of the Flavivirus genus and currently one of the most common arboviruses worldwide, is associated with severe neurological disease in humans. Its high potential to reemerge and rapidly disseminate makes it a bona fide global public health problem. The surface membrane glycoprotein (M) has been associated with Flavivirus-induced pathogenesis. Here, we identified a key amino acid residue at position 36 of the M protein whose mutation impacts WNV secretion and promotes viral attenuation. We also identified a compensatory site at position M-43 whose mutation stabilizes M-36 substitution both in vitro and in vivo. Moreover, we found that introduction of the two mutations together confers a full attenuation phenotype and protection against wild-type WNV lethal challenge, eliciting potent neutralizing-antibody production in mice. Our study thus establishes the M protein as a new viral target for rational design of attenuated WNV strains. IMPORTANCE West Nile virus (WNV) is a worldwide (re)emerging mosquito-transmitted Flavivirus causing fatal neurological diseases in humans. However, no human vaccine has been yet approved. One of the most effective live-attenuated vaccines was empirically obtained by serial passaging of wild-type yellow fever Flavivirus. However, such an approach is not acceptable nowadays, and the development of a rationally designed vaccine is necessary. Generating molecular infectious clones and mutating specific residues known to be involved in Flavivirus virulence constitute a powerful tool to promote viral attenuation. WNV membrane glycoprotein is thought to carry such essential determinants. Here, we identified two residues of this protein whose substitutions are key to the full and stable attenuation of WNV in vivo, most likely through inhibition of secretion and possible alteration of morphology. Applied to other flaviviruses, this approach should help in designing new vaccines against these viruses, which are an increasing threat to global human health.

Emerging Flaviviruses pose an increasing threat to global human health. To date, human vaccines against yellow fever virus (YFV), Japanese encephalitis virus (JEV), dengue virus (DV), and tick-borne encephalitis virus (TBEV) exist. However, there is no human vaccine against other Flaviviruses such as Zika virus (ZIKV) and West Nile virus (WNV). In order to restrict their spread and to protect populations against the diseases they induce, vaccines against these emerging viruses must be designed. Obtaining new live attenuated Flavivirus vaccines using molecular biology methods is now possible. Molecular infectious clones of the parental viruses are relatively easy to generate. Key mutations present in live attenuated vaccines or mutations known to have a key role in the Flavivirus life cycle and/or interactions with their hosts can be identified by sequencing, and are then inserted in infectious clones by site-directed mutagenesis. More recently, the use of chimeric viruses and large-scale reencoding and introduction of microRNA target sequences have also been tested. Indeed, a combination of these methods will help in designing new generations of vaccines against emerging and reemerging Flaviviruses.

Japanese encephalitis virus (JEV) is the major cause of viral encephalitis in South East Asia. It has been suggested that JEV gets access to the central nervous system (CNS) as a consequence of a preceding inflammatory process which leads to the blood-brain barrier (BBB) disruption and viral neuroinvasion. However, what happens at early times of JEV contact with the BBB is poorly understood. In the present work, we evaluated the ability of both a virulent and a vaccine strain of JEV (JEV RP9 and SA14-14-2, respectively) to cross anin cellulohuman BBB model consisting of hCMEC/D3 human endothelial cells cultivated on permeable inserts above SK-N-SH human neuroblastoma cells. Using this system, we demonstrated that both JEV RP9 and SA14-14-2 are able to cross the BBB without disrupting it at early times post-addition. Furthermore, this BBB model was able to discriminate between the virulent RP9 and the vaccine SA14-14-2 strains, as demonstrated by the presence of almost 10 times more RP9 infectious particles that crossed the BBB than SA14-14 particles at a high MOI. Besides contributing to the understanding of early events in JEV neuroinvasion, thisin celluloBBB model represents a suitable and useful system to study the viral determinants of JEV neuroinvasiveness and the molecular mechanisms by which this flavivirus crosses the BBB at early times of neuroinvasion.

International audience; Live attenuated vaccines have proved to be mostly valuable in the prevention of infectious diseases in humans, especially in developing countries. The safety and potency of vaccine, and the consistency of vaccine batch-to-batch manufacturing, must be proven before being administrated to humans. For now, the tests used to control vaccine safety largely involve animal testing. For live viral vaccines, regulations require suppliers to demonstrate the absence of neurovirulence in animals, principally in non-human primates and mice. In a search to reduce the use of animals and embracing the 3Rs principles (Replacement, Reduction, Refinement in the use of laboratory animals), we developed a new Blood-Brain Barrier Minibrain (BBB-Minibrain) in cellulo device to evaluate the neuroinvasiveness/neurovirulence of live Yellow Fever virus (YFV) vaccines. A pilot study was performed using the features of two distinct YFV strains, with the ultimate goal of proposing a companion test to characterize YFV neurovirulence. Here, we demonstrate that the BBB-Minibrain model is a promising alternative to consider for future replacement of YFV vaccine in vivo neurovirulence testing (see graphical abstract).

RNA viruses present an extraordinary threat to human health, given their sudden and unpredictable appearance, the potential for rapid spread among the human population, and their ability to evolve resistance to antiviral therapies. The recent emergence of chikungunya virus, Zika virus, and Ebola virus highlights the struggles to contain outbreaks. A significant hurdle is the availability of antivirals to treat the infected or protect at-risk populations. While several compounds show promise in vitro and in vivo , these outbreaks underscore the need to accelerate drug discovery. The replication of several viruses has been described to rely on host polyamines, small and abundant positively charged molecules found in the cell. Here, we describe the antiviral effects of two molecules that alter polyamine levels: difluoromethylornithine (DFMO; also called eflornithine), which is a suicide inhibitor of ornithine decarboxylase 1 (ODC1), and diethylnorspermine (DENSpm), an activator of spermidine/spermine N 1 -acetyltransferase (SAT1). We show that reducing polyamine levels has a negative effect on diverse RNA viruses, including several viruses involved in recent outbreaks, in vitro and in vivo . These findings highlight the importance of the polyamine biosynthetic pathway to viral replication, as well as its potential as a target in the development of further antivirals or currently available molecules, such as DFMO. IMPORTANCE RNA viruses present a significant hazard to human health, and combatting these viruses requires the exploration of new avenues for targeting viral replication. Polyamines, small positively charged molecules within the cell, have been demonstrated to facilitate infection for a few different viruses. Our study demonstrates that diverse RNA viruses rely on the polyamine pathway for replication and highlights polyamine biosynthesis as a promising drug target.

The recent Zika outbreak in South America and French Polynesia was associated with an epidemic of microcephaly, a disease characterized by a reduced size of the cerebral cortex. Other members of the Flavivirus genus, including West Nile virus (WNV), can cause encephalitis but were not demonstrated to cause microcephaly. It remains unclear whether Zika virus (ZIKV) and other flaviviruses may infect different cell populations in the developing neocortex and lead to distinct developmental defects. Here, we describe an assay to infect mouse E15 embryonic brain slices with ZIKV, WNV and dengue virus serotype 4 (DENV-4). We show that this tissue is able to support viral replication of ZIKV and WNV, but not DENV-4. Cell fate analysis reveals a remarkable tropism of ZIKV infection for neural stem cells. Closely related WNV displays a very different tropism of infection, with a bias towards neurons. We further show that ZIKV infection, but not WNV infection, impairs cell cycle progression of neural stem cells. Both viruses inhibited apoptosis at early stages of infection. This work establishes a powerful comparative approach to identify ZIKV-specific alterations in the developing neocortex and reveals specific preferential infection of neural stem cells by ZIKV., Highlights • Mouse embryonic brain slices sustain Zika and West Nile, but not Dengue-4, virus replication. • Zika virus, but not West Nile virus, exhibits a selective tropism of infection for neural stem cells. • Zika virus, but not West Nile virus, alters cell cycle progression of neural stem cells. A Zika virus outbreak in South America is currently responsible for a large burst of microcephaly cases, a congenital brain malformation characterized by a reduced brain size. We describe here an assay to infect cultured mouse embryonic brain slices with Zika virus as well as other closely related flaviviruses not demonstrated to cause microcephaly. We show that Zika virus displays a specific pattern of infection in the developing brain, almost exclusively infecting neural stem cells. Zika virus impairs neural stem cell proliferation, an effect not seen for other flaviviruses and that may participate in the induction of microcephaly.

West Nile virus (WNV) is the most widespread arbovirus in the world. Several recent outbreaks and epizootics have been reported in Europe and the Mediterranean basin with increased virulence. In contrast to the well-characterized American and Australian strains, little is known about the virulence determinants of the WNV European-Mediterranean strains. To investigate the viral factors involved in the virulence of these strains, we generated chimeras between the highly neuropathogenic Israel 1998 (IS-98-ST1, IS98) strain and the non-pathogenic Malaysian Kunjin virus (KJMP-502). In vivo analyses in a mouse model of WNV pathogenesis shows that chimeric virus where KJMP-502 E glycoprotein was replaced by that of IS98 is neuropathogenic, demonstrating that this protein is a major virulence determinant. Presence of the N-glycosylation site had limited impact on virus virulence and the 5'UTR does not seem to influence pathogenesis. Finally, mice inoculated with KJMP-502 virus were protected against lethal IS98 infection.

International audience; The role of the membrane protein (prM/M) in flavivirus life cycle remains unclear. Here, we identified a cellular interactor to the 40-residue-long ectodomain of prM/M (ectoM) using a yeast two-hybrid screen against a human cDNA library and GST pull-down assays. We showed that dynein light chain Tctex-1 interacts with the ectoM of dengue 1-4, West Nile, and Japanese encephalitis flaviviruses. No interaction was found with yellow fever and tick-borne flaviviruses. This interaction is highly specific since a single amino-acid change in the ectoM abrogates the interaction with Tctex-1. To understand the role of this interaction, silencing of Tctex-1 using siRNA was performed prior to infection. A significant decrease in progeny production was observed for dengue and West Nile viruses. Silencing Tctex-1 inhibited the production of recombinant dengue subviral particles (RSPs). Thus Tctex-1 may play a role in late stages of viral replication through its interaction with the membrane protein.

International audience; Intestinal CD8αα intraepithelial T lymphocytes (T-IELs) have a key role in mucosal immunity and, unlike other T cells, were proposed to differentiate locally. In apparent contradiction, these cells were also shown to originate from a wave of thymus migrants colonizing the gut in the first 3 weeks after birth. We here identify previously uncharacterized very immature CD4(-)CD8(-)CD3(-)CD44(+)CD25(int) thymocytes, which have not yet rearranged their T-cell antigen receptor (TCR), as having the capacity to leave the thymus, migrate to the blood, colonize the gut, and reconstitute CD8αα T-IEL, and show that this cell set is fully responsible for the generation of the CD8αα T-IEL pool. Thus, although the thymus may be fundamental for efficient T-cell commitment, CD8αα T-IEL' complete TCR rearrangements and TCR-αβ/γδ lineage commitment must occur in the gut. These results demonstrate a major role of the gut environment as a primary lymphoid organ.

Japanese encephalitis virus (JEV) membrane (M) protein plays important structural roles in the processes of fusion and maturation of progeny virus during cellular infection. The M protein is anchored in the viral membrane, and its ectodomain is composed of a flexible N-terminal loop and a perimembrane helix. In this study, we performed site-directed mutagenesis on residue 36 of JEV M protein and showed that the resulting mutation had little or no effect on the entry process but greatly affected virus assembly in mammalian cells. Interestingly, this mutant virus had a host-dependent phenotype and could develop a wild-type infection in insect cells. Experiments performed on infectious virus as well as in a virus-like particle (VLP) system indicate that the JEV mutant expresses structural proteins but fails to form infectious particles in mammalian cells. Using a mouse model for JEV pathogenesis, we showed that the mutation conferred complete attenuation in vivo . The production of JEV neutralizing antibodies in challenged mice was indicative of the immunogenicity of the mutant virus in vivo . Together, our results indicate that the introduction of a single mutation in the M protein, while being tolerated in insect cells, strongly impacts JEV infection in mammalian hosts. IMPORTANCE JEV is a mosquito-transmitted flavivirus and is a medically important pathogen in Asia. The M protein is thought to be important for accommodating the structural rearrangements undergone by the virion during viral assembly and may play additional roles in the JEV infectious cycle. In the present study, we show that a sole mutation in the M protein impairs the JEV infection cycle in mammalian hosts but not in mosquito cells. This finding highlights differences in flavivirus assembly pathways among hosts. Moreover, infection of mice indicated that the mutant was completely attenuated and triggered a strong immune response to JEV, thus providing new insights for further development of JEV vaccines.

International audience; The two-signal model states that activation of naive T cells requires a signal 1 stimulus through the TCR and a co-stimulatory signal 2. By contrast, signal 1 alone is sufficient for pre-activated T cells. Recently, however, it has been shown that under certain conditions T cells can bypass the requirement for co-stimulation. For example, CD28-deficient mice, when immunized with lymphocytic choriomeningitis virus, mount a vigorous cytotoxic T lymphocyte response and clear the virus. As a continuous effort to unravel the mechanisms of T cell activation, we previously reported activation of hybridoma T cells by recombinant single-chain MHC molecules in the absence of antigen-presenting cells. In such reconstitution experiments, since the signals delivered to the T cells are well controlled, the contribution of any known or unknown signals can be ruled out. In the present study, we analyzed the requirements for activation of naive T cells by using splenocytes from TCR transgenic mice as a source of responding cells. We observed that naive CD8+ T cells are fully activated by signal 1 alone, but that co-stimulation lowers their activation threshold. Previously activated T cells are fully responsive, even when the first stimulation was performed in the absence of co-stimulation. They display a low activation threshold and are insensitive to co-stimulation. The physiological relevance of this finding and its consequences for immunotherapy as well as for our understanding of self-tolerance are discussed.

International audience; Infectious clones of West Nile virus (WNV) have previously been generated and used to decipher the role of viral proteins in WNV virulence. The majority of molecular clones obtained to date have been derived from North American, Australian, or African isolates. Here, we describe the construction of an infectious cDNA clone of a Mediterranean WNV strain, IS-98-ST1. We characterized the biological properties of the recovered recombinant virus in cell culture and in mice. The growth kinetics of recombinant and parental WNV were similar in Vero cells. Moreover, the phenotype of recombinant and parental WNV was indistinguishable as regards viremia, viral load in the brain, and mortality in susceptible and resistant mice. Finally, the pathobiology of the infectious clone was examined in embryonated chicken eggs. The capacity of different WNV strains to replicate in embryonated chicken eggs closely paralleled their ability to replicate in mice, suggesting that inoculation of embryonated chicken eggs could provide a practical in vivo model for the study of WNV pathogenesis. In conclusion, the IS-98-ST1 infectious clone will allow assessment of the impact of selected mutations and novel genomic changes appearing in emerging European strains pathogenicity and endemic or epidemic potential. This will be invaluable in the context of an increasing number of outbreaks and enhanced severity of infections in the Mediterranean basin and Eastern Europe.

This article is available open access through the publisher’s website. Identification and characterization of virus-host interactions are very important steps toward a better understanding of the molecular mechanisms responsible for disease progression and pathogenesis. To date, very few cellular factors involved in the life cycle of flaviviruses, which are important human pathogens, have been described. In this study, we demonstrate a crucial role for class II Arf proteins (Arf4 and Arf5) in the dengue flavivirus life cycle. We show that simultaneous depletion of Arf4 and Arf5 blocks recombinant subviral particle secretion for all four dengue serotypes. Immunostaining analysis suggests that class II Arf proteins are required at an early pre-Golgi step for dengue virus secretion. Using a horseradish peroxidase protein fused to a signal peptide, we show that class II Arfs act specifically on dengue virus secretion without altering the secretion of proteins through the constitutive secretory pathway. Co-immunoprecipitation data demonstrate that the dengue prM glycoprotein interacts with class II Arf proteins but not through its C-terminal VXPX motif. Finally, experiments performed with replication-competent dengue and yellow fever viruses demonstrate that the depletion of class II Arfs inhibits virus secretion, thus confirming their implication in the virus life cycle, although data obtained with West Nile virus pointed out the differences in virus-host interactions among flaviviruses. Our findings shed new light on a molecular mechanism used by dengue viruses during the late stages of the life cycle and demonstrate a novel function for class II Arf proteins. Research Fund for Control of Infectious Diseases of Hong Kong and BNP Paribas Corporate and Investment Banking.

Thymic leukemia (TL) is a MHC class Ib molecule that interacts with CD8αα homodimers. CD8αα is abundantly expressed by intraepithelial T lymphocytes (IELs) located in close proximity to TL-expressing intestinal epithelial cells. In this study, we show that CD8αα+ IELs “snatch” TL from the plasma membrane of TL-expressing cells and express TL in its proper orientation on their own cell surface. TL snatching is enhanced by cross-linking of IEL TCRs in a phosphatidylinositol kinase-dependent manner, and results in overall alterations to the IEL cell surface detected by enhanced binding of peanut agglutinin lectin. Induction of bowel inflammation results in the presence of TL on IELs, probably via in vivo snatching, providing the initial evidence for the interaction of CD8αα IELs with intestinal cells.

International audience; Thymus leukemia antigen (TL) is an MHC class Ib molecule that is highly conserved in rats and mice with no obvious human homolog. TL is expressed in mouse small intestinal epithelial cells and is known to interact with CD8alphaalpha homodimers, which are expressed by intraepithelial lymphocytes (IELs), some other T cell subsets and some non-T cells such as a subset of dendritic cells. We show here that TL is abundantly expressed on the basolateral surface of mouse small intestinal epithelial cells and that expression is abrogated in beta2m-/- mice but unaffected in TCR-/- mice or CD8alpha chain-/- mice. We demonstrate that the interaction between TL and CD8alphaalpha is not necessary for IEL survival in vitro or in vivo and does not modulate IEL trafficking in vivo. TL co-stimulation of alpha-CD3 antibody-activated IELs resulted in modestly enhanced production of IFN-gamma in one subset of IELs. The lack of effect on IEL survival and trafficking and the modest effect on IFN-gamma production suggest that the functional consequences of TL interaction with CD8alphaalpha as well as the more general biological role of TL in mucosal immunity remains to be discovered.

International audience; Using male and female RAG(-/-) mutant mice expressing TCR transgenes specific for MHC class I- or II-presented HY peptides, we performed quantitative and phenotypic comparisons between the TCR(+) lymphocytes present in the lymphoid organs and the gut mucosa in euthymic versus athymic (nude) animals. These comparisons suggest that only a minority of the TCR(+) CD8alpha alpha (+) intraepithelial lymphocytes (IEL) of the transgenic euthymic mice originate from hematopoietic precursors acquiring a TCR in the gut wall, while a majority of these CD8alpha alpha(+) IEL appear to be of thymic origin (as were all TCR(+) CD8alpha beta (+) or CD4(+) in any location); these last cells are released from the thymus as double-negative thymocytes, which are at a more immature stage (CD44(+)CD25(+)) in female mice than in males (CD44(-)). In view of previous observations that in non-transgenic athymic mice the CD8alpha alpha (+) TCR(+) IEL populations are also markedly reduced quantitatively, the possibility of a thymic contribution to these ontogenically peculiar populations may also exist in normal mice. At which stage of differentiation such precursors might leave the thymus of normal adult mice remains to be explored.

CD8+ T cells are important effectors, as well as regulators, of organ-specific autoimmunity. Compared with Tc1-type CD8+ cells, Tc2 cells have impaired anti-viral and anti-tumor effector functions, although no data are yet available on their pathogenic role in autoimmunity. Our aim was to explore the role of autoreactive Tc1 and Tc2 cells in autoimmune diabetes. We set up an adoptive transfer model in which the recipients were transgenic mice expressing influenza virus hemagglutinin (HA) specifically in their pancreatic β islet cells (rat insulin promoter-HA mice) and islet-specific Tc1 and Tc2 cells were generated in vitro from HA-specific CD8+ cells of TCR transgenic mice (CL4-TCR mice). One million Tc1 cells, differentiated in vitro in the presence of IL-12, transferred diabetes in 100% of nonirradiated adult rat insulin promoter-HA recipients; the 50% diabetogenic dose was 5 × 105. Highly polarized Tc2 cells generated in the presence of IL-4, IL-10, and anti-IFN-γ mAb had a relatively low, but definite, diabetogenic potential. Thus, 5 × 106 Tc2 cells caused diabetes in 6 of 18 recipients, while the same dose of naive CD8+ cells did not cause diabetes. Looking for the cause of the different diabetogenic potential of Tc1 and Tc2 cells, we found that Tc2 cells are at least as cytotoxic as Tc1 cells but their accumulation in the pancreas is slower, a possible consequence of differential chemokine receptor expression. The diabetogenicity of autoreactive Tc2 cells, most likely caused by their cytotoxic activity, precludes their therapeutic use as regulators of autoimmunity.

Although the two-signal model for T cell activation states that a signal-1 through the TCR and a costimulatory signal-2 are required for optimal stimulation, it is now clear that the requirement for costimulation can be bypassed under certain conditions. We previously reported that this is the case for naive CD8+ T cells in vitro. In the present study we tested the effect of signal-2 when delivered after signal-1 has been disrupted. Naive CD8+ T cells from TCR transgenic mice were stimulated in vitro by using immobilized recombinant single-chain MHC molecules alone as signal-1. This signal was then stopped after different lengths of time, and anti-CD28 mAb as signal-2 was given either immediately or after a time lag. We found that signal-2 can potentiate a short signal-1 when added sequentially. Moreover, a time lag between the two signals does not abolish this potentiation. If the strength of signal-1, but not its duration, is increased, then the time lag between the delivery of signals 1 and 2 can be lengthen without loss of potentiation. Together, our results indicate that the two signals do not need to be delivered concomitantly to get optimal T cell activation. We suggest that the CD8+ T cells can reach a transient “excited” state after being stimulated with signal-1 alone, characterized by the cell’s ability to respond to separate and delayed signal-2.

International audience; Numerous studies have focused on characterizing and monitoring antigen-specific T cells during the course of an immune response. Mostly indirect methods were used to circumvent the low frequency of T cell precursors and the inherent complexity of T cell receptor (TcR)-MHC-peptide interactions. Here, we took advantage of peptide-specific adhesion induced by immobilized MHC-peptide complexes. We describe a simple technique which allows enrichment in antigen-specific T lymphocytes among a heterogeneous CD8+ T cell population. Enrichment of T cells according to their specificity should facilitate their characterization and provide an attractive tool for immunotherapy.

International audience; We have isolated a 50-kDa mosquito protein that binds with high affinity to a riboprobe representing the 3' end of the minus strand of Sindbis virus RNA. The isolated protein has been used to obtain cDNA clones encoding this protein that have been sequenced and used to express the protein in large amounts. Sequence comparisons make clear that this protein is the mosquito homolog of the La autoantigen. The N-terminal half of the protein shares considerable sequence identity with the human La protein, the rat La protein, and the recently identified Drosophila melanogaster homolog. There is one stretch of 100 amino acids in the N-terminal domain in which 48 residues are identical in all four proteins. In contrast, the C-terminal domain of the mosquito protein shares little identity with any of the other three proteins. We have also shown that the mosquito protein, the human protein, and a putative chicken homolog of the La protein cross-react immunologically and, thus, all share antigenic epitopes. The mosquito La protein is primarily nuclear in location, but significant amounts are present in the cytoplasm, as is the case for the La proteins of other species. The equilibrium constant for the binding of the expressed mosquito La protein to the Sindbis virus riboprobe is 15.4 nM, and thus the affinity of binding is high enough to be physiologically relevant. Furthermore, the conservation of this protein in the animal kingdom may be significant, because Sindbis virus utilizes mosquitoes, birds, and mammals as hosts. We propose that the interactions we observe between the La protein and toes, birds, and mammals as hosts. We propose that the interactions we observe between the La protein and a putative promoter in the Sindbis virus genome are significant for Sindbis virus RNA replication.

International audience; The 3' end of Sindbis virus minus-sense RNA was tested for its ability to bind proteins in mosquito cell extracts, using labeled riboprobes that represented different parts of this region. We found four domains in the first 250 nucleotides that could bind the same 50- and 52-kDa proteins, three with high affinity and one with low affinity, whereas tested domains outside this region did not bind these proteins. The first binding domain was found in the first 60 nucleotides, which represents the complement of the 5'-nontranslated region, the second in the next 60 nucleotides, the third in the following 60 nucleotides, and the fourth between nucleotides 194 and 249 (all numbering is 3' to 5'). The relative binding constants, Kr, of the first, second, and fourth sites were similar, whereas that of domain 2 was fivefold less. Deletion mapping of the first domain showed that the first 10 nucleotides were critical for binding. Deletion of nucleotides 2 to 4, deletion or replacement of nucleotide 5, or deletion of the first 15 nucleotides was deleterious for binding, deletion of nucleotides 10 to 15, 26 to 40, or 41 to 55 had little effect on the binding, and deletion of nucleotides 15 to to 25 increased the binding affinity. We also found that the corresponding riboprobes derived from two other alphaviruses, Ross River virus and Semliki Forest virus, and from rubella virus were also able to interact with the 50- and 52-kDa proteins. The Kr value for the Semliki Forest virus probe was similar to that for the Sindbis virus probe, while that for the Ross River virus probe was four times greater. The rubella virus probe was bound only weakly, consistent with the fact that mosquito cells are not permissive for rubella virus replication. We suggest that the binding of the 50- and 52-kDa proteins to the 3' end of alphavirus minus-sense RNA represents an important step in the initiation of RNA replication.

International audience; We describe the construction of plasmids which express fusion proteins representing various regions of Germiston virus M polyprotein. The fusion proteins were purified and inoculated into rabbits to produce antisera. The N- and C-terminal regions of the polyprotein induced specific antibodies which reacted with glycoproteins G2 and G1, respectively, and the intermediate region induced antibodies against the NSM polypeptide. This enabled us to determine the gene order: G2-NSM-G1. Glycoproteins G1 and G2 form the spikes on the surface of the virion. We attempted to determine the structural organization of the glycoproteins by using a membrane-permeable cross-linking reagent, dimethyl suberimidate, but were unable to demonstrate that G1 and/or G2 form oligomeric structures. We analysed the glycoproteins further and showed that, like peripheral membrane proteins, the G2 and NSM proteins are almost completely extracted into the aqueous phase of detergent Triton X114-treated cellular extracts, whereas glycoprotein G1 is distributed in almost equal proportions between the aqueous and the detergent fractions. This indicates that G1 is a membrane-associated protein, but its presence in the aqueous phase suggests that it is less hydrophobic than a typical membrane protein. We have also characterized the intracellular transport of the envelope glycoproteins from the endoplasmic reticulum to the Golgi complex. Pulse-chase labelling followed by immunoprecipitation and treatment with endoglycosidase H (endo H) showed that both G1 and G2 are transported from the endoplasmic reticulum to the Golgi complex. Conversion to the endo H-resistant form is a rather slow process which takes more than 2 h. The mature G1 and G2 proteins present in the virion particle contain almost completely endo-H-resistant glycans.

Forty-four nucleotides at the 5' terminus of the genomic RNA of Sindbis virus can form a stable stem-loop structure and have been shown previously to be important for viral replication. The structure formed by the complement of this sequence at the 3' end of the minus-strand RNA has been proposed to be a promoter for RNA replication and as such might be bound in a specific fashion by proteins of either cellular or viral origin. Short oligonucleotide probes (either 62 or 132 nucleotides) representing the 3'-terminal sequence of the minus strand were prepared. When added to extracts from infected or uninfected cells, these probes were bound by cellular proteins, as evidenced by a shift in the electrophoretic mobility of the (labeled) oligonucleotide. Competition experiments confirmed the specificity of the interaction. Proteins of apparent molecular sizes 42 and 44 kDa, and to a lesser extent 52 kDa, could be cross-linked to the minus-sense probes by UV irradiation. A mutant minus-strand probe identical to the longer probe except for a single-nucleotide deletion corresponding to nucleotide 5 in the genomic RNA, which is lethal for the virus, was also found to bind the same proteins as the wild-type probe. The half-life of the mutant probe-cellular protein complex was threefold longer than that of the wild-type complex, however, indicating that the mutant probe was bound more tightly than the wild-type probe. We hypothesize that the binding of cellular factors may be transiently required for initiation of transcription of plus-strand RNA from the minus-strand template and that overly tight binding of such factors is deleterious for RNA replication.

International audience; The 3' ends of the S and M messenger RNAs isolated from BHK21 cells infected with Germiston virus were analyzed by mapping with RNase T2 or nuclease S1. The transcription termination signal was found to be located approximately 115 and 80 nucleotides upstream from the 3' end of the S and M genomic RNA templates, respectively. Both mRNAs were found to possess several adenosine residues at their 3' ends, but were not polyadenylated. They have acquired at their 5' end a heterologous 12- to 18-nucleotide-long sequence, which is not coded for by the virus. Sequencing of the 5' terminal region from single molecules cloned into pBR327 revealed that these primers are rich in C and G residues and possess a U or a C adjacent to the viral sequence.

Summary The three genomic RNA segments of the Germiston virus (Bunyaviridae) were analysed by electrophoresis in denaturing gels. A variety of gel types and denaturing agents were tested. Best separation of the three RNA species was achieved using 1% agarose gels in the presence of methylmercuric hydroxide. Under these conditions, the L, M and S RNA segments migrated with apparent molecular weights of 2.8×106, 1.6×106 and 0.34×106 daltons, respectively. The RNA species were isolated from the gel using low-melting temperature agarose, after which they were digested with RNase-T1, and the resulting oligonucleotides were labelled in vitro using T4 polynucleotide-kinase and γ-32P-ATP. The RNase-T1-resistant oligonucleotide fingerprints obtained after two-dimensional electrophoresis show that each of the three viral RNA segments is unique.

International audience; The complete sequence of the S segment of Germiston bunyavirus has been determined from plasmids containing S cDNA inserts. The S segment is 980 nucleotides long with the first 15 bases at the 3' end complementary to the first 15 bases at the 5' end. Three overlapping open reading frames (ORF) were identified in the viral complementary RNA strand. The first ORF codes for a polypeptide of 233 amino acids (Mr 26,600) which is the nucleoprotein N. The second ORF codes for a polypeptide of 109 amino acids (Mr 11,800) which corresponds to the NSS protein, also called p12. Following this ORF, in the same frame, a third ORF which could encode a polypeptide of 75 amino acids was identified. Such a polypeptide has not yet been detected in infected cells. The N and NSS proteins of Germiston virus were compared with the corresponding proteins of La Crosse, snowshoe hare, and Aino viruses, and show a high extent of homology.

International audience; The complete nucleotide sequence of the M RNA segment of Germiston bunyavirus was determined from plasmids containing overlapping M cDNA inserts. The M segment is 4534 nucleotides long and contains a 50-base-long inverted terminal repeat which can form a stable hydrogen-bonded secondary structure with a delta G of -45.8 kcal/mol. The RNA molecule complementary to viral RNA contains a single large open reading frame that encodes a 1437 amino acid-long protein with hydrophobic amino and carboxy terminal regions, which could represent signal and anchor sequences, respectively. It is presumed that this gene product is the polyprotein precursor to glycoproteins G1 and G2 and to the nonstructural polypeptide NSM. The nucleotide and amino acid sequences of the M RNA of Bunyamwera virus (prototype of the serogroup) and snowshow hare and La Crosse viruses (California serogroup) (Lees et al., 1986; Eshita and Bishop, 1984; Grady et al., 1987) were compared to those of Germiston virus. An overall amino acid sequence homology of 44% was found between Germiston and snowshoe hare viruses and of 61% between Germiston and Bunyamwera viruses. Most of the cysteines, three out of seven of the potential glycosylation sites, as well as the N and C terminal hydrophobic domains, are conserved between the four viruses.

Publisher Summary Germiston virus is a member of the Bunyamwera Serogroup of bunyaviridae. Its genome consists of three single-stranded RNA molecules of negative polarity: large (L), medium (M), and small (S). Each bunyavirus RNA subunit is associated with two polypeptides: a major one, the nucleoprotein N, and a minor one, the large polypeptide L. This chapter discusses an experiment to analyze the proteins synthesized in BHK21 cells infected by Germiston virus after labeling with 35S methionine from 4 to 6 hr after infection. In the experiment, germiston virus infected BHK21 cells were exposed to ( 3H) adenosine or (3H) uridine in the presence of actinomycin D, which does not block the replication of Bunyaviruses. Cytoplasmic extracts were prepared and the polysomes and viral ribonucleoproteins (RNP) were separated on sucrose gradients. The RNAs were analyzed by electrophoresis on a 2.8% polyacrylamide gel containing Murea. The presence of two transcripts from the S RNA Segment of Germiston virus was readily detected in infected BHK21 cells by the electrophoresis of the RNAs in polyacrylamide-urea gels. The transcript S1 is a full length cRNA copy of the S segment, whereas transcript S2 is about100 nucleotides shorter.

The nucleotide sequences at the 5′ and 3′ ends of the S RNA segment of Germiston virus have been determined. The first 15 nucleotides at the 5′ and 3′ ends are complementary to each other. In agreement with the sequence data, we have isolated the 5′ and 3′ terminal nucleotide structures in the form of short duplex molecules after self annealing and RNase digestion. The panhandle structures from the S RNA segment are 4, 13, 15, and 20 bases long. Two models are proposed. We favor one in which the first 11 nucleotides at the 3′ and 5′ ends of the S RNA segment form a double hairpin structure followed by a stem.

International audience; Analysis of the RNAs present in BHK-21 cells infected with Germiston virus showed that the transcripts from the L and M segments have a size similar to that of their template, whereas two types of complementary RNA are transcribed from the S segment. One, S1, is a full-length "plus" RNA strand (antigenome), and the other, S2, is an incomplete plus RNA strand which serves as mRNA for at least the synthesis of the N protein and a virus-specific nonstructural polypeptide, p12. The 5' ends of these two transcripts appeared to be identical and complementary to the 3' ends of the viral RNA. Our results suggest that transcription of the S fragment either stops 100 to 150 nucleotides from the 5' end of the template, generating an S2 molecule, or continues, generating an S1 molecule. Neither the S1 antigenome nor the S2 mRNA molecules were polyadenylated at their 3' ends or capped at their 5' ends.

Because of their highly transmission potential, their speed of dissemination that can be dazzling, and the disease severity they might induced, flaviviruses are of great concern. West Nile virus (WNV) is currently one of the most common arboviruses (arthropod-borne virus) in the world and its high ability to (re-)emerge causes a global public health problem. This virus is responsible for many cases of severe neurological diseases, sometimes fatal, especially in humans and horses. No human anti-WNV treatment or vaccine is currently available. The role(s) of the Flavivirus membrane protein (M) is/are still poorly characterized. This glycoprotein is anchored in the viral membrane and plays an important structural role in the processes of fusion and maturation of viral particles. In addition, the M protein has recently been associated with Japanese Encephalitis and Zika-induced pathogenesis (de Wispelaere et al., 2016; Yuan et al., 2017), suggesting that this protein contains viral determinants essential for virulence. In order to study the underlying mechanisms, we substituted the isoleucine residue located in position 36 of the ectodomain of the M protein with a phenylalanine (M-I36F), and demonstrated that this mutation causes a steric hindrance that directly affects the structure of the M protein. The introduction of a second mutation (substitution of the alanine residue at position 43 with a glycine which has no side chain) in the same protein allowed stabilization of the M-I36F mutation. If the M-I36F mutation alone or associated with the M-A43G mutation does not affect the early stages (entry, translation, replication) of the viral cycle, it is however at the origin of a change in the morphology of viral particles in the mammalian host. In addition, our study strongly suggests that the secretion of newly formed WNV particles from the endoplasmic reticulum, a still poorly described stage of the viral cycle, directly depends on their morphology. Finally, this study allowed us to develop a rationally designed WNV attenuation model, which was tested in vivo in a previously described mouse model of WNV-induced encephalitis. The complete protection against a lethal challenge with the wild-type virus of mice previously infected with the double mutant virus makes this mutant virus a potential candidate vaccine. This study is being filed for a patent application.; En raison de leur potentiel élevé de transmission, de leur vitesse de dissémination qui peut être fulgurante et des maladies parfois sévères qu’ils induisent, les Flavivirus sont considérablement préoccupants. Le virus West Nile (WNV) est actuellement l'un des arbovirus (arthropod-borne virus)le plus répandu dans le monde et sa forte capacité de (ré)émergence pose un problème de santé publique important. Ce virus est responsable de nombreux cas de maladies neurologiques sévères, parfois mortelles, notamment chez l’Homme et les chevaux. Aucun traitement ou vaccin humain anti-WNV n’est actuellement disponible sur le marché. Le(s) rôle(s) de la protéine de membrane (M) des Flavivirus est/sont encore peu caractérisé(s). Cette glycoprotéine est ancrée dans la membrane virale et joue un rôle structural important dans les processus de fusion et de maturation des particules virales. De plus, la protéine M a récemment été associée à la pathogénèse induite par les virus de l’encéphalite japonaise et du Zika (de Wispelaere et al., 2016; Yuanet al., 2017), suggérant que cette protéine contient des déterminants viraux essentiels à la virulence. Afin d’étudier les mécanismes sous-jacents, nous avons substitué le résidu isoleucine localisé en position 36de l’ectodomaine de la protéine M par une phénylalanine (M-I36F), et démontré que cette mutation provoque un encombrement allostérique qui affecte directement la structure de la protéine M.L’introduction d’une seconde mutation (substitution de l’alanine en position 43 par une glycine, résidu ne possédant pas de chaine latérale) dans la même protéine nous a permis de stabiliser la mutation MI36F. Si la mutation M-I36F seule ou associée à la mutation M-A43G n’affecte pas les étapes précoces (entrée,traduction, réplication) du cycle viral, elle est cependant à l’origine d’une modification de la morphologie des particules virales chez l’hôte mammifère. De plus, notre étude suggère que la sécrétion des particules de WNV néo-formées hors du réticulum endoplasmique, une étape encore peu caractérisée du cycle viral, dépend directement de leur morphologie. Enfin, cette étude nous a permis de mettre au point un modèle d’atténuation du WNV rationnellement dessiné, qui a été testé in vivo dans un modèle murin décrit d’encéphalite induite par le WNV. La protection complète induite par le virus double mutant, que nous observons lors d’une épreuve létale avec le virus sauvage, fait de ce virus mutant un potentiel candidat vaccin. Cette étude fait l’objet d’un dépôt de brevet.

Although members of the Flaviviridae display high incidence, morbidity, and mortality rates, the development of specific antiviral drugs for each virus is unlikely. Cyclophilins, a family of host peptidyl-prolyl cis-trans isomerases (PPIases), play a pivotal role in the life cycles of many viruses and therefore represent an attractive target for broad-spectrum antiviral development. We report here the pangenotypic anti-hepatitis C virus (HCV) activity of a small-molecule cyclophilin inhibitor (SMCypI). Mechanistic and modeling studies revealed that the SMCypI bound to cyclophilin A in competition with cyclosporine (CsA), inhibited its PPIase activity, and disrupted the CypA-nonstructural protein 5A (NS5A) interaction. Resistance selection showed that the lead SMCypI hardly selected amino acid substitutions conferring low-level or no resistance in vitro . Interestingly, the SMCypI selected D320E and Y321H substitutions, located in domain II of the NS5A protein. These substitutions were previously associated with low-level resistance to cyclophilin inhibitors such as alisporivir. Finally, the SMCypI inhibited the replication of other members of the Flaviviridae family with higher 50% effective concentrations (EC 50 s) than for HCV. Thus, because of its chemical plasticity and simplicity of synthesis, our new family of SMCypIs represents a promising new class of drugs with the potential for broad-spectrum anti- Flaviviridae activity as well as an invaluable tool to explore the role of cyclophilins in viral life cycles.