[Show abstract][Hide abstract] ABSTRACT: E2 is one of the envelope glycoproteins of pestiviruses, including classical swine fever virus (CSFV) and bovine viral diarrhea virus (BVDV). E2 is involved in several critical functions, including virus entry into target cells, induction of a protective immune response and virulence in swine. However, there is no information regarding any host binding partners for the E2 proteins. Here, we utilized the yeast two-hybrid system and identified fifty-seven host proteins as positive binding partners which bound E2 from both CSFV and BVDV with the exception of two proteins that were found to be positive for binding only to CSFV E2. Alanine scanning of CSFV E2 demonstrated that the binding sites for these cellular proteins on E2 are likely non-linear binding sites. The possible roles of the identified host proteins are discussed as the results presented here will be important for future studies to elucidate mechanisms of host protein-virus interactions during pestivirus infection. However, due to the limitations of the yeast two hybrid system, the proteins identified is not exhaustive and each interaction identified needs to be confirmed by independent experimental approaches in the context of virus-infected cells before any definitive conclusion can be drawn on relevance for the virus life cycle.
PLoS ONE 01/2014; 9(1):e85324. · 3.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Non-structural protein 3A of foot-and-mouth disease virus (FMDV) is a partially conserved protein of 153 amino acids in most FMDVs examined to date. The role of 3A in virus growth and virulence within the natural host is not well understood. Using a yeast two-hybrid approach, we identified cellular protein DCTN3 as a specific host binding partner for 3A. DCTN3 is a subunit of the dynactin complex, a co-factor for dynein, a motor protein. The dynactin-dynein duplex has been implicated in several subcellular functions involving intracellular organelle transport. The 3A-DCTN3 interaction identified by the yeast two-hybrid approach was further confirmed in mammalian cells. Over-expression of DCTN3 or proteins known to disrupt dynein, p150/Glued and 50/dynamitin, resulted in decreased FMDV replication in infected cells. We mapped the critical amino acid residues in the 3A protein that mediate the protein interaction with DCTN3 by mutational analysis and, based on that information, we developed a mutant harboring the same mutations in O1 Campos FMDV (O1C3A-PLDGv). Although O1C3A-PLDGv FMDV and its parental virus (O1Cv) grew equally well in LFBK-αvβ6, O1C3A-PLDGv virus exhibited a decreased ability to replicate in primary bovine cell cultures. Importantly, O1C3A-PLDGv virus exhibited a delayed disease in cattle compared to the virulent parental O1Campus (O1Cv). Virus isolated from lesions of animals inoculated with O1C3A-PLDGv virus contained amino acid substitutions in the area of 3A mediating binding to DCTN3. Importantly, 3A protein harboring similar amino acid substitutions regained interaction with DCTN3, supporting the hypothesis that DCTN3 interaction likely contributes to virulence in cattle.The objective of this work was to understand the possible role of a FMD virus protein 3A, in causing disease in cattle. We have found that the cellular protein, DCTN3, is a specific binding partner for 3A. It was shown that manipulation of DCTN3 has a profound effect in virus replication. We developed a FMDV mutant virus that could not bind DCTN3. This mutant virus exhibited a delayed disease in cattle compared to the parental strain highlighting the role of the 3A-DCTN3 interaction in virulence in cattle. Interestingly, virus isolated from lesions of animals inoculated with mutant virus contained mutations in the area of 3A that allowed binding to DCTN3. This highlights the importance of the 3A-DCTN3 interaction in FMD virus virulence and provides possible mechanisms of virus attenuation for the development of improved FMD vaccines.
[Show abstract][Hide abstract] ABSTRACT: The role of non-structural protein 3A of foot-and-mouth disease virus (FMDV) on the virulence in cattle has received significant attention. Particularly, a characteristic 10-20 amino acid deletion has been implicated as responsible for virus attenuation in cattle: a 10 amino acid deletion in the naturally occurring, porcinophilic FMDV O1 Taiwanese strain, and an approximately 20 amino acid deletion found in egg-adapted derivatives of FMDV serotypes O1 and C3. Previous reports using chimeric viruses linked the presence of these deletions to an attenuated phenotype in cattle although results were not conclusive. We report here the construction of a FMDV O1Campos variant differing exclusively from the highly virulent parental virus in a 20 amino acid deletion between 3A residues 87-106, and its characterization in vitro and in vivo. We describe a direct link between a deletion in the FMDV 3A protein and disease attenuation in cattle.
[Show abstract][Hide abstract] ABSTRACT: To investigate the pathogenesis of African swine fever virus (ASFV), domestic pigs (n=18) were challenged with a range (10(2)-10(6) 50% hemadsorbing doses (HAD50)) of the highly virulent ASFV-Malawi strain by inoculation via the intraoropharyngeal (IOP), intranasopharyngeal (INP), or intramuscular (IM) routes. A subsequent contact challenge experiment was performed in which six IOP-inoculated donor pigs were allowed to have direct contact (DC) with six naïve pigs for exposure times that varied from 24-72h. All challenge routes resulted in clinical progression and postmortem lesions similar to those previously described in experimental and natural infection. The onset of clinical signs occurred between 1-7 days post inoculation (dpi) and included pyrexia with variable progression to obtundation, hematochezia, melena, moribundity and death with a duration of 4-11 days. Viremia was first detected between 4-5 dpi in all inoculation groups whereas ASFV shedding from the nasal cavity and tonsil was first detected at 3-9 dpi. IM and DC were the most consistent modes of infection, with 12/12 (100%) of pigs challenged by these routes becoming infected. Several clinical and virological parameters were significantly different between IM and DC groups indicating dissimilarity between these modes of infection. Amongst the simulated natural routes, INP inoculation resulted in the most consistent progression of disease across the widest range of doses whilst preserving simulation of natural exposure and therefore may provide a superior system for pathogenesis and vaccine efficacy investigation.
[Show abstract][Hide abstract] ABSTRACT: Foot-and-mouth disease virus (FMDV), the causative agent of foot-and-mouth disease, is an Aphthovirus within the Picornaviridae family. During infection with FMDV, several host cell membrane rearrangements occur to form sites of viral replication. FMDV protein 2C is part of the replication complex, and thought to have multiple roles during virus replication. To better understand the role of 2C in the process of virus replication, we have been using a yeast two-hybrid approach to identify host proteins that interact with 2C. We recently reported that cellular Beclin1 is a natural ligand of 2C and that it is involved in the autophagy pathway which was shown to be important for FMDV replication. Here, we report that cellular vimentin is also a specific host binding partner for 2C. The 2C-vimentin interaction was further confirmed by co-immunoprecipitation and immunofluorescence staining to occur in FMDV-infected cells. It was shown that upon infection a vimentin structure forms around 2C, and that this structure is later resolved or disappears. Interestingly, over-expression of vimentin had no effect on virus replication; however, over-expression of a truncated dominant-negative form of vimentin resulted in a significant decrease in viral yield. Acrylamide, which causes disruption of vimentin filaments, also inhibited viral yield. Alanine scanning mutagenesis was used to map the specific amino acid residues in 2C critical for vimentin binding. Using reverse genetics, we identified 2C residues that are necessary for virus growth, suggesting that the interaction between FMDV 2C and cellular vimentin is essential for virus replication.
[Show abstract][Hide abstract] ABSTRACT: Foot-and-mouth disease virus (FMDV), the causative agent of foot-and-mouth disease, is an Apthovirus within the Picornaviridae family. Replication of the virus occurs in association with replication complexes that are formed by host cell membrane rearrangements. The largest viral protein in the replication complex, 2C, is thought to have multiple roles during virus replication. However, studies examining the function of FMDV 2C have been rather limited. To better understand the role of 2C in the process of virus replication, we used a yeast two-hybrid approach to identify host proteins that interact with 2C. We report here that cellular Beclin1 is a specific host binding partner for 2C. Beclin1 is a regulator of the autophagy pathway, a metabolic pathway required for efficient FMDV replication. The 2C-Beclin1 interaction was further confirmed by coimmunoprecipitation and confocal microscopy to actually occur in FMDV-infected cells. Overexpression of either Beclin1 or Bcl-2, another important autophagy factor, strongly affects virus yield in cell culture. The fusion of lysosomes to autophagosomes containing viral proteins is not seen during FMDV infection, a process that is stimulated by Beclin1; however, in FMDV-infected cells overexpressing Beclin1 this fusion occurs, suggesting that 2C would bind to Beclin1 to prevent the fusion of lysosomes to autophagosomes, allowing for virus survival. Using reverse genetics, we demonstrate here that modifications to the amino acids in 2C that are critical for interaction with Beclin1 are also critical for virus growth. These results suggest that interaction between FMDV 2C and host protein Beclin1 could be essential for virus replication.
Journal of Virology 08/2012; 86(22):12080-90. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The nonstructural protein p7 of classical swine fever virus (CSFV) is a small hydrophobic polypeptide with an apparent molecular mass of 6 to 7 kDa. The protein contains two hydrophobic stretches of amino acids interrupted by a short charged segment that are predicted to form transmembrane helices and a cytosolic loop, respectively. Using reverse genetics, partial in-frame deletions of p7 were deleterious for virus growth, demonstrating that CSFV p7 function is critical for virus production in cell cultures. A panel of recombinant mutant CSFVs was created using alanine scanning mutagenesis of the p7 gene harboring sequential three- to six-amino-acid residue substitutions spanning the entire protein. These recombinant viruses allowed the identification of the regions within p7 that are critical for virus production in vitro. In vivo, some of these viruses were partially or completely attenuated in swine relative to the highly virulent parental CSFV Brescia strain, indicating a significant role of p7 in CSFV virulence. Structure-function analyses in model membranes emulating the endoplasmic reticulum lipid composition confirmed that CSFV p7 is a pore-forming protein, and that pore-forming activity resides in the C-terminal transmembrane helix. Therefore, p7 is a viroporin which is clearly involved in the process of CSFV virulence in swine.
Journal of Virology 04/2012; 86(12):6778-91. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: E1, along with E(rns) and E2, is one of the three envelope glycoproteins of classical swine fever virus (CSFV). E1 and E2 are anchored to the virus envelope at their carboxyl termini, and E(rns) loosely associates with the viral envelope. In infected cells, E2 forms homodimers and heterodimers with E1 mediated by disulfide bridges between cysteine residues. The E1 protein of CSFV strain Brescia contains six cysteine residues at positions 5, 20, 24, 94, 123, and 171. The role of these residues in the formation of E1-E2 heterodimers and their effect on CSFV viability in vitro and in vivo remain unclear. Here we observed that recombinant viruses harboring individual cysteine-to-serine substitutions within the E1 envelope protein still have formation of E1-E2 heterodimers which are functional in terms of allowing efficient virus progeny yields in infected primary swine cells. Additionally, these single cysteine mutant viruses were virulent in infected swine. However, a double mutant harboring Cys24Ser and Cys94Ser substitutions within the E1 protein altered formation of E1-E2 heterodimers in infected cells. This recombinant virus, E1ΔCys24/94v, showed delayed growth kinetics in primary swine macrophage cultures and was attenuated in swine. Furthermore, despite the observed diminished growth in vitro, infection with E1ΔCys24/94v protected swine from challenge with virulent CSFV strain Brescia at 3 and 28 days postinfection.
Journal of Virology 07/2011; 85(14):7264-72. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Classical swine fever (CSF) is a highly contagious and often fatal disease of swine caused by CSF virus (CSFV), a positive-sense single-stranded RNA virus within the Pestivirus genus of the Flaviviridae family. Here, we have identified conserved sequence elements observed in nucleotide-binding motifs (NBM) that hydrolyze NTPs within the CSFV non-structural (NS) protein NS4B. Expressed NS4B protein hydrolyzes both ATP and GTP. Substitutions of critical residues within the identified NS4B NBM Walker A and B motifs significantly impair the ATPase and GTPase activities of expressed proteins. Similar mutations introduced into the genetic backbone of a full-length cDNA copy of CSFV strain Brescia rendered no infectious viruses or viruses with impaired replication capabilities, suggesting that this NTPase activity is critical for the CSFV cycle. Recovered mutant viruses retained a virulent phenotype, as parental strain Brescia, in infected swine. These results have important implications for developing novel antiviral strategies against CSFV infection.
[Show abstract][Hide abstract] ABSTRACT: Foot-and-mouth disease virus (FMDV) is the type species of the Aphthovirus genus within the Picornaviridae family. Infection of cells with positive-strand RNA viruses results in a rearrangement of intracellular membranes into viral replication complexes. The origin of these membranes remains unknown; however induction of the cellular process of autophagy is beneficial for the replication of poliovirus, suggesting that it might be advantageous for other picornaviruses. By using confocal microscopy we showed in FMDV-infected cells co-localization of non-structural viral proteins 2B, 2C and 3A with LC3 (an autophagosome marker) and viral structural protein VP1 with Atg5 (autophagy-related protein), and LC3 with LAMP-1. Importantly, treatment of FMDV-infected cell with autophagy inducer rapamycin, increased viral yield, and inhibition of autophagosomal pathway by 3-methyladenine or small-interfering RNAs, decreased viral replication. Altogether, these studies strongly suggest that autophagy may play an important role during the replication of FMDV.
[Show abstract][Hide abstract] ABSTRACT: Here we show that IQGAP1, a cellular protein that plays a pivotal role as a regulator of the cytoskeleton interacts with Classical Swine Fever Virus (CSFV) Core protein. Sequence analyses identified residues within CSFV Core protein (designated as areas I, II, III and IV) that maintain homology to regions within the matrix protein of Moloney Murine Leukemia Virus (MMLV) that mediate binding to IQGAP1 [EMBO J, 2006 25:2155]. Alanine-substitution within Core regions I, II, III and IV identified residues that specifically mediate the Core-IQGAP1 interaction. Recombinant CSFV viruses harboring alanine substitutions at residues (207)ATI(209) (I), (210)VVE(212) (II), (213)GVK(215) (III), or (232)GLYHN(236) (IV) have defective growth in primary swine macrophage cultures. In vivo, substitutions of residues in areas I and III yielded viruses that were completely attenuated in swine. These data shows that the interaction of Core with an integral component of cytoskeletal regulation plays a role in the CSFV cycle.
[Show abstract][Hide abstract] ABSTRACT: Infection of domestic swine with highly virulent, classical swine fever virus (CSFV) strain Brescia, causes lethal disease in all infected animals. However, the molecular mechanisms involved in modulating the host cellular processes and evasion of the immune response have not been clearly established. To gain insight into, the early host response to CSFV, we analyzed the pattern of gene expression in infected swine macrophages, using custom designed swine microarrays. Macrophages, the target cell for CSFV infection, were isolated from primary cultures of peripheral blood mononuclear cells, allowing us to utilize identical uninfected macrophages at the same time points as CSFV-infected macrophages, allowing only genes induced by CSFV to be identified. First, microarray probes were optimized by screening 244,000 probes for hybridization with RNA from infected and uninfected macrophages. Probes that hybridized and passed quality control standards were used to design a 44,000 probe microarray for this study. Changes in expression levels of 79 genes (48 up- and 31 down-regulated) during the first 48h post-infection were observed. As expected many of the genes with an altered pattern of expression are involved in the development of an innate immune response. Several of these genes had differential expression in an attenuated strain NS4B.VGIv, suggesting that some of these differences are responsible for virulence. The observed gene expression profile might help to explain the immunological and pathological changes associated with infection of pigs with CSFV Brescia.
Virus Research 03/2010; 151(1):10-8. · 2.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: NS4B is one of the nonstructural proteins of classical swine fever virus (CSFV), the etiological agent of a severe, highly lethal disease of swine. Protein domain analysis of the predicted amino acid sequence of the NS4B protein of highly pathogenic CSFV strain Brescia (BICv) identified a putative Toll/interleukin-1 receptor (TIR)-like domain. This TIR-like motif harbors two conserved domains, box 1 and box 2, also observed in other members of the TIR superfamily, including Toll-like receptors (TLRs). Mutations within the BICv NS4B box 2 domain (V2566A, G2567A, I2568A) produced recombinant virus NS4B.VGIv, with an altered phenotype displaying enhanced transcriptional activation of TLR-7-induced genes in swine macrophages, including a significant sustained accumulation of interleukin-6 (IL-6) mRNA. Transfection of swine macrophages with the wild-type NS4B gene partially blocked the TLR-7-activating effect of imiquimod (R837), while transfection with the NS4B gene harboring mutations in either of the putative boxes displayed decreased blocking activity. NS4B.VGIv showed an attenuated phenotype in swine, displaying reduced replication in the oronasal cavity and limited spread from the inoculation site to secondary target organs. Furthermore, the level and duration of IL-6 production in the tonsils of pigs intranasally inoculated with NS4B.VGIv were significantly higher than those for animals infected with BICv. The peak of IL-6 production in infected animals paralleled the ability of animals infected with NS4B.VGIv to resist challenge with virulent BICv. Interestingly, treatment of peripheral blood mononuclear cell cultures with recombinant porcine IL-6 results in a significant decrease in BICv replication.
Journal of Virology 11/2009; 84(3):1536-49. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Foot-and-mouth disease (FMD) is a highly contagious viral disease of cloven-hoofed animals principally affecting cattle, pigs and sheep. FMD virus (FMDV) uses the alpha(V)beta(1), alpha(V)beta(3), alpha(V)beta(6), and alpha(V)beta(8) integrins as receptors in vitro via a highly conserved arginine-glycine-aspartic acid amino acid sequence motif located within the betaG-betaH loop of VP1. Immunofluorescence and confocal microscopy were used to study the expression of two major FMDV receptors, alpha(V)beta(3) and alpha(V)beta(6), within epithelial tissues from FMDV-infected and uninfected cattle in order to understand the role of these receptors in tissue tropism. Integrin alpha(V)beta(6) was expressed by epithelial cells in tissues that are important sites for FMDV replication (i.e. tongue and coronary band). Integrin alpha(V)beta(3) was detected in epithelium of all tissues examined except tongue. In addition, alpha(V)beta(3) expression was associated with blood vessels in all tissues examined. In infected tissues, alpha(V)beta(6) integrin was distributed on the surface of those epithelial cells also expressing FMDV antigen. Although integrin alpha(V)beta(3) has been shown to be a receptor for FMDV, no expression of alpha(V)beta(3) was associated with FMDV-positive keratinocytes in the tongue. In contrast, podal epithelial cells containing FMDV antigen also expressed alpha(V)beta(3) integrin. Thus, at the cellular level the expression of these two integrins correlates with susceptibility to infection and may contribute substantially to viral tropism in FMD pathogenesis.
Journal of comparative pathology 07/2009; 141(2-3):98-112. · 1.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Until recently strategies for controlling Classical Swine Fever Virus (CSFV) involve either prophylactic vaccination or non-vaccination with elimination of infected herds depending on the epidemiological situation of the affected geographical area. Marker vaccines allowing distinction between naturally infected from vaccinated swine could complement "stamping out" measures. Here we developed a double antigenic marker live attenuated CSFV strain FlagT4v obtained by combining two genetic determinants of attenuation. FlagT4v harbors a positive antigenic marker, synthetic Flag(R) epitope, introduced via a 19mer insertion in E1 glycoprotein; and a negative marker resulting from mutations of the binding site of monoclonal antibody WH303 (mAbWH303) epitope in E2 glycoprotein. Intranasal or intramuscular administration of FlagT4v protected swine against virulent CSFV Brescia strain at early (2 or 3 days), and late (28 days) time post-inoculation. FlagT4v induced antibody response in pigs reacted strongly against the Flag(R) epitope but failed to inhibit binding of mAbWH303 to a synthetic peptide representing the WH303 epitope. These results constitute a proof-of-concept for rationally designing a CSFV antigenically marked live attenuated virus.
[Show abstract][Hide abstract] ABSTRACT: Foot-and-mouth disease virus (FMDV) utilizes different cell surface macromolecules to facilitate infection of cultured cells. Virus, which is virulent for susceptible animals, infects cells via four members of the alpha(V) subclass of cellular integrins. In contrast, tissue culture adaptation of some FMDV serotypes results in the loss of viral virulence in the animal, accompanied by the loss of virus' ability to use integrins as receptors. These avirulent viral variants acquire positively charged amino acids on surface-exposed structural proteins, resulting in the utilization of cell surface heparan sulfate (HS) molecules as receptors. We have recently shown that FMDV serotypes utilizing integrin receptors enter cells via a clathrin-mediated mechanism into early endosomes. Acidification within the endosome results in a breakdown of the viral capsid, releasing the RNA, which enters the cytoplasm by a still undefined mechanism. Since there is evidence that HS internalizes bound ligands via a caveola-mediated mechanism, it was of interest to analyze the entry of FMDV by cell-surface HS. Using a genetically engineered variant of type O(1)Campos (O(1)C3056R) which can utilize both integrins and HS as receptors and a second variant (O(1)C3056R-KGE) which can utilize only HS as a receptor, we followed viral entry using confocal microscopy. After virus bound to cells at 4 degrees C, followed by a temperature shift to 37 degrees C, type O(1)C3056R-KGE colocalized with caveolin-1, while O(1)C3056R colocalized with both clathrin and caveolin-1. Compounds which either disrupt or inhibit the formation of lipid rafts inhibited the replication of O(1)C3056R-KGE. Furthermore, a caveolin-1 knockdown by RNA interference also considerably reduced the efficiency of O(1)C3056R-KGE infection. These results indicate that HS-binding FMDV enters the cells via the caveola-mediated endocytosis pathway and that caveolae can associate and traffic with endosomes. In addition, these results further suggest that the route of FMDV entry into cells is a function solely of the viral receptor.
Journal of Virology 08/2008; 82(18):9075-85. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Inoculation of vesicular stomatitis New Jersey virus (VSNJV) by skin scarification of the coronary-band in cattle, a natural host of VSNJV, resulted in vesicular lesions and 6-8 log(10) TCID(50) increase in skin virus titers over a 72 h period. Virus infection was restricted to the lesion sites and lymph nodes draining those areas but no virus or viral RNA was found in the blood or in 20 other organs and tissues sampled at necropsy. Scarification of flank skin did not result in lesions or a significant increase in viral titer indicating that viral clinical infection is restricted to skin inoculation at sites where lesions naturally occur. Viral antigens co-localized primarily with keratinocytes in the coronary band, suggesting these cells are the primary site of viral replication. Viral antigen also co-localized with few MHC-II positive cells, but no co-localization was observed in cells positive for macrophage markers. Although granulocyte infiltration was observed in lesions, little viral antigen co-localized with these cells. This is the first detailed description of VSNJV tissue distribution and infected cell characterization in a natural host. The pathogenesis model shown herein could be useful for in-vivo tracking of virus infection and local immune responses.
Veterinary Research 01/2007; 38(3):375-90. · 3.43 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: It has been demonstrated that foot-and-mouth disease virus (FMDV) can utilize at least four members of the alpha(V) subgroup of the integrin family of receptors in vitro. The virus interacts with these receptors via a highly conserved arginine-glycine-aspartic acid amino acid sequence motif located within the betaG-betaH loop of VP1. While there have been extensive studies of virus-receptor interactions at the cell surface, our understanding of the events during viral entry into the infected cell is still not clear. We have utilized confocal microscopy to analyze the entry of two FMDV serotypes (types A and O) after interaction with integrin receptors at the cell surface. In cell cultures expressing both the alphaVbeta3 and alphaVbeta6 integrins, virus adsorbed to the cells at 4 degrees C appears to colocalize almost exclusively with the alphaVbeta6 integrin. Upon shifting the infected cells to 37 degrees C, FMDV capsid proteins were detected within 15 min after the temperature shift, in association with the integrin in vesicular structures that were positive for a marker of clathrin-mediated endocytosis. In contrast, virus did not colocalize with a marker for caveola-mediated endocytosis. Virus remained associated with the integrin until about 1 h after the temperature shift, when viral proteins appeared around the perinuclear region of the cell. By 15 min after the temperature shift, viral proteins were seen colocalizing with a marker for early endosomes, while no colocalization with late endosomal markers was observed. In the presence of monensin, which raises the pH of endocytic vesicles and has been shown to inhibit FMDV replication, viral proteins were not released from the recycling endosome structures. Viral proteins were not observed associated with the endoplasmic reticulum or the Golgi. These data indicate that FMDV utilizes the clathrin-mediated endocytosis pathway to infect the cells and that viral replication begins due to acidification of endocytic vesicles, causing the breakdown of the viral capsid structure and release of the genome by an as-yet-unidentified mechanism.
Journal of Virology 08/2005; 79(13):8506-18. · 5.08 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Flaviviruses are emerging threats to public health worldwide. Recently, one flavivirus, West Nile virus (WNV), has caused the largest epidemic of viral encephalitis in US history. Like other flaviviruses, WNV is thought to cause a persistent infection in insect cells, but an acute cytopathic infection of mammalian cells. To study adaptation of WNV to persistently replicate in cell culture and generate a system capable of detecting antiviral compounds in the absence of live virus, we generated subgenomic replicons of WNV and adapted these to persistently replicate in mammalian cells. Here we report that adaptation of these replicons to cell culture results in a reduction of genome copy number, and demonstrate that hamster, monkey, and human cells that stably carry the replicons can be used as surrogates to detect the activity of anti-WNV compounds. Additionally, we have used these cells to investigate the interaction of WNV genomes with interferon (IFN). These studies demonstrated that IFN can cure cells of replicons and that replicon-bearing cells display lower responses to IFN than their IFN-cured derivatives.
[Show abstract][Hide abstract] ABSTRACT: The genome of foot-and-mouth disease virus (FMDV) differs from that of other picornaviruses in that it encodes a larger 3A protein (>50% longer than poliovirus 3A), as well as three copies of protein 3B (also known as VPg). Previous studies have shown that a deletion of amino acids 93 to 102 of the 153-codon 3A protein is associated with an inability of a Taiwanese strain of FMDV (O/TAW/97) to cause disease in bovines. Recently, an Asian virus with a second 3A deletion (amino acids 133 to 143) has also been detected (N. J. Knowles et al., J. Virol. 75:1551-1556, 2001). Genetically engineered viruses harboring the amino acids 93 to 102 or 133 to 143 grew well in porcine cells but replicated poorly in bovine cells, whereas a genetically engineered derivative of the O/TAW/97 virus expressing a full-length 3A (strain A12) grew well in both cell types. Interestingly, a virus with a deletion spanning amino acid 93 to 144 also grew well in porcine cells and caused disease in swine. Further, genetically engineered viruses containing only a single copy of VPg were readily recovered with the full-length 3A, the deleted 3A (amino acids 93 to 102), or the "super" deleted forms of 3A (missing amino acids 93 to 144). All of the single-VPg viruses were attenuated in porcine cells and replicated poorly in bovine cells. The single-VPg viruses produced a mild disease in swine, indicating that the VPg copy number is an important determinant of host range and virulence. The association of VPg copy number with increased virulence in vivo may help to explain why all naturally occurring FMDVs have retained three copies of VPg.
Journal of Virology 12/2003; 77(24):13017-27. · 5.08 Impact Factor