FMDV 3A Antagonizes the Effect of ANXA1 to Positively Modulate Viral Replication.

The RIG-I-like receptor signaling pathway is crucial for producing type I interferon (IFN-I) against RNA viruses. The present study observed that viral infection increased annexin-A1 (ANXA1) expression, and ANXA1 then promoted RNA virus-induced IFN-I production. Compared to ANXA1 wild-type cells, ANXA1-/- knockout cells showed IFN-ß production decreasing after viral stimulation. RNA virus stimulation induced ANXA1 to regulate IFN-ß production through the TBK1-IRF3 axis but not through the NF-κB axis. ANXA1 also interacted with JAK1 and STAT1 to increase signal transduction induced by IFN-ß or IFN-γ. We assessed the effect of ANXA1 on the replication of foot-and-mouth disease virus (FMDV) and found that ANXA1 inhibits FMDV replication dependent on IFN-I production. FMDV 3A plays critical roles in viral replication and host range. The results showed that FMDV 3A interacts with ANXA1 to inhibit its ability to promote IFN-ß production. We also demonstrated that FMDV 3A inhibits the formation of ANXA1-TBK1 complex. These results indicate that ANXA1 positively regulates RNA virus-stimulated IFN-ß production and FMDV 3A antagonizes ANXA1-promoted IFN-ß production to modulate viral replication. IMPORTANCE FMDV is a pathogen that causes one of the world's most destructive and highly contagious animal diseases. The FMDV 3A protein plays a critical role in viral replication and host range. Although 3A is one of the viral proteins that influences FMDV virulence, its underlying mechanisms remain unclear. ANXA1 is involved in immune activation against pathogens. The present study demonstrated that FMDV increases ANXA1 expression, while ANXA1 inhibits FMDV replication. The results also showed that ANXA1 promotes RNA virus-induced IFN-I production through the IRF3 axis at VISA and TBK1 levels. ANXA1 was also found to interact with JAK1 and STAT1 to strengthen signal transduction induced by IFN-ß and IFN-γ. 3A interacted with ANXA1 to inhibit ANXA1-TBK1 complex formation, thereby antagonizing the inhibitory effect of ANXA1 on FMDV replication. This study helps to elucidate the mechanism underlying the effect of the 3A protein on FMDV replication.

Foot-and-Mouth Disease Virus Structural Protein VP1 Destroys the Stability of TPL2 Trimer by Degradation TPL2 to Evade Host Antiviral Immunity.

Tumor progression locus 2 (TPL2) is a serine/threonine kinase that belongs to the mitogen-activated protein 3 kinase (MAP3K) family, and it plays an important role in pathogen infection. The trimer complex of TPL2, p105, and ABIN2 is essential for maintenance of TPL2 steady-state levels and host cell response to pathogens. Foot-and-mouth disease virus (FMDV) is a positive-strand RNA virus of the family Picornaviridae that encodes proteins capable of antagonizing host immune responses to achieve infection. The VP1 protein of FMDV is a multifunctional protein that can bind host cells and induce an immune response as well as cell apoptosis. However, the role and mechanisms of TPL2 in FMDV infection remain unknown. Here, we determined that FMDV infection could inhibit TPL2, p105, and ABIN2 at the transcription and protein levels, while VP1 could only inhibit TPL2, p105 and ABIN2 at protein level. TPL2 inhibited the replication of FMDV in vivo and in vitro, the 268 to 283 amino-acid region in the TPL2 kinase domain was essential for interaction with VP1. Moreover, VP1 promoted K48-linked polyubiquitination of TPL2 and degraded TPL2 by the proteasome pathway. However, VP1-induced degradation of p105 and ABIN2 was independent of proteasome, autophagy, lysosome, and caspase-dependent pathways. Further studies showed that VP1 destroyed the stability of the TPL2-p105-ABIN2 complex. Taken together, these results revealed that VP1 antagonized TPL2-meditated antivirus activity by degrading TPL2 and destroying its complex. These findings may contribute to understand FMDV-host interactions and improve development of a novel vaccine to prevent FMDV infection.Importance Virus-host interactions are critical for virus infection. This study was the first to demonstrate the antiviral effect of host TPL2 during FMDV replication by increasing production of interferons and antiviral cytokines. Both FMDV and VP1 protein can reduce host TPL2, ABIN2 and p105 to destroy TPL2-p105-ABIN2 trimer complex. VP1 interacted with TPL2 and degrade TPL2 via proteasome pathway to repress TPL2-mediated antivirus activity. This study provided new insights into FMDV immune evasion mechanisms, elucidating new informations regarding FMDV counteraction of host antivirus activity.

Profiling and functional analysis of differentially expressed circular RNAs identified in foot-and-mouth disease virus infected PK-15 cells.

Circular RNAs (circRNAs) are a new type of endogenous noncoding RNA that exhibit a variety of biological functions. However, it is not clear whether they are involved in foot-and-mouth disease virus (FMDV) infection and host response. In this study, we established circRNA expression profiles in FMDV-infected PK-15 cells using RNA-seq (RNA-sequencing) technology analysis. The biological function of the differentially expressed circRNAs was determined by protein interaction network, Gene Ontology (GO), and Kyoto Encyclopedia of Gene and Genome (KEGG) pathway enrichment. We found 1100 differentially expressed circRNAs (675 downregulated and 425 upregulated) which were involved in various biological processes such as protein ubiquitination modification, cell cycle regulation, RNA transport, and autophagy. We also found that circRNAs identified after FMDV infection may be involved in the host cell immune response. RNA-Seq results were validated by circRNAs qRT-PCR. In this study, we analyzed for the first time circRNAs expression profile and the biological function of these genes after FMDV infection of host cells. The results provide new insights into the interactions between FMDV and host cells.

Foot-and-Mouth Disease Virus Capsid Protein VP1 Interacts with Host Ribosomal Protein SA To Maintain Activation of the MAPK Signal Pathway and Promote Virus Replication.

Foot-and-mouth disease virus (FMDV) is the causative agent of foot-and-mouth disease, a highly contagious, economically important viral disease. The structural protein VP1 plays significant roles during FMDV infection. Here, we identified that VP1 interacted with host ribosomal protein SA (RPSA). RPSA is a viral receptor for dengue virus and classical swine fever virus infections. However, the incubation of susceptible cells using the anti-RPSA antibodies did not block the infection of FMDV. Overexpression of porcine RPSA in the insusceptible cells could not trigger FMDV infection, suggesting that RPSA was not responsible for FMDV entry and infection. On the contrary, we found that overexpression of RPSA suppressed FMDV replication, and knockdown of RPSA enhanced FMDV replication. We further determined that FMDV infection activated the mitogen-activated protein kinase (MAPK) pathway and demonstrated that MAPK pathway activation was critically important for FMDV replication. RPSA negatively regulated MAPK pathway activation during FMDV infection and displayed an antiviral function. FMDV VP1 interacted with RPSA to abrogate the RPSA-mediated suppressive role in MAPK pathway activation. Together, our study indicated that MAPK pathway activation was required for FMDV replication and that host RPSA played a negatively regulatory role on MAPK pathway activation to suppress FMDV replication. FMDV VP1 bound to RPSA to promote viral replication by repressing RPSA-mediated function and maintaining the activation of MAPK signal pathway.IMPORTANCE Identification of virus-cell interactions is essential for making strategies to limit virus replication and refine the models of virus replication. This study demonstrated that FMDV utilized the MAPK pathway for viral replication. The host RPSA protein inhibited FMDV replication by suppressing the activation of the MAPK pathway during FMDV infection. FMDV VP1 bound to RPSA to repress the RPSA-mediated regulatory effect on MAPK pathway activation. This study revealed an important implication of the MAPK pathway for FMDV infection and identified a novel mechanism by which FMDV VP1 has evolved to interact with RPSA and maintain the activation of the MAPK pathway, elucidating new information regarding the signal reprogramming of host cells by FMDV.

Genetic Determinants of Altered Virulence of Type O Foot-and-Mouth Disease Virus.

Under different circumstances, the alteration of several viral genes may give an evolutionary advantage to the virus to maintain its prevalence in nature. In this study, a 70-nucleotide deletion in the small fragment (S fragment) of the viral 5'-untranslated region (5'-UTR) together with one amino acid insertion in the leader protein (Lpro) that naturally occurred in several serotype O foot-and-mouth disease virus (FMDV) strains in China was identified. The properties of two field serotype O FMDV strains, with or without the 70-nucleotide deletion in the S fragment and the amino acid insertion in Lpro, were compared in vitro and in vivo Clinical manifestations of FMD were clearly observed in cattle and pigs infected by the virus without the mutations. However, the virus with the mentioned mutations caused FMD outcomes only in pigs, not in cattle. To determine the role of the 70-nucleotide deletion in the S fragment and the single amino acid insertion in Lpro in the pathogenicity and host range of FMDV, four recombinant viruses, with complete genomes and a 70-nucleotide deletion in the S fragment, a single amino acid insertion in Lpro, or both mutations, were constructed and rescued. It showed that deletion of 70 nucleotides in the S fragment or insertion of one amino acid (leucine) at position 10 of Lpro partly decreased the viral pathogenicity of Mya-98 lineage virus in cattle and pigs. However, the virus with dual mutations caused clinical disease only in pigs, not in cattle. This suggested that the S fragment and Lpro are significantly associated with the virulence and host specificity of FMDV. The naturally occurring dual mutation in the S fragment and Lpro is a novel determinant of viral pathogenicity and host range for serotype O FMDV.IMPORTANCE FMD is probably the most important livestock disease in the world due to the severe economic consequences caused. The alteration of several viral genes may give the virus selective advantage to maintain its prevalence in nature. Here, we identified that a 70-nucleotide deletion in the S fragment combined with a single leucine insertion in the leader protein (Lpro) is a novel determinant of restricted growth on bovine cells, which significantly contributes to the altered virulence of serotype O FMDV in cattle. A synergistic and additive effect of the 70-nucleotide deletion in the S fragment and the single leucine insertion in Lpro on the virulence and host specificity of the virus was determined. These results will benefit efforts to understand the vial pathogenicity mechanism and molecular characteristics of FMDV.

Foot-and-Mouth Disease Virus Antagonizes NOD2-Mediated Antiviral Effects by Inhibiting NOD2 Protein Expression.

The role of nucleotide-binding oligomerization domain 2 (NOD2) in foot-and-mouth disease virus (FMDV)-infected cells remains unknown. Here, we showed that FMDV infection activated NOD2-mediated beta interferon (IFN-ß) and nuclear factor-κB (NF-ĸB) signaling pathways. NOD2 inhibited FMDV replication in the infected cells. FMDV infection triggered NOD2 transcription, while it reduced the abundance of NOD2 protein. Our results revealed that FMDV 2B, 2C, and 3C proteinase (3Cpro) were responsible for the decrease in NOD2 protein levels. 3Cpro is a viral proteinase that can cleave multiple host proteins and limit protein synthesis. Our previous studies determined that FMDV 2B suppressed protein expression of RIG-I and LGP2. Here, we found that 3Cpro and 2B also decreased NOD2 expression. However, this is the first report that 2C induced the reduction of NOD2 protein levels. We determined that both 2B- and 2C-induced decreases in NOD2 were independent of the cleavage of host eukaryotic translation initiation factor 4 gamma (eIF4G), induction of cellular apoptosis, or proteasome, lysosome, and caspase pathways. The interactions between NOD2 and 2B or 2C were observed in the context of viral infection. The carboxyl-terminal amino acids 105 to 114 and 135 to 144 of 2B were essential for the reduction of NOD2, while the residues 105 to 114 were required for the interaction. Amino acids 116 to 260 of the carboxyl terminus of 2C were essential for the interaction, while truncated 2C mutants did not reduce NOD2. These data suggested novel antagonistic mechanisms of FMDV that were mediated by 2B, 2C, and 3Cpro proteins.IMPORTANCE NOD2 was identified as a cytoplasmic viral pattern recognition receptor in 2009. Subsequently, many viruses were reported to activate NOD2-mediated signaling pathways. This study demonstrated that FMDV infection activated NOD2-mediated IFN-ß and NF-ĸB signaling pathways. Host cells have developed multiple strategies against viral infection; however, viruses have evolved many strategies to escape host defenses. FMDV has evolved multiple mechanisms to inhibit host type I IFN production. Here, we showed that NOD2 suppressed FMDV replication during viral infection. FMDV 2B, 2C, and 3Cpro decreased NOD2 protein expression by different mechanisms to promote viral replication. This study provided new insight into the immune evasion mechanisms mediated by FMDV and identified 2B, 2C, and 3Cpro as antagonistic factors for FMDV to evade host antiviral responses.

The Pseudoknot Region of the 5' Untranslated Region Is a Determinant of Viral Tropism and Virulence of Foot-and-Mouth Disease Virus.

Foot-and-mouth disease virus (FMDV) is the causative agent of foot-and-mouth disease. It is characterized by genetic instability and different antigenic properties. The nonstructural protein 3A is a primary determinant of the tropism and virulence of Cathay topotype FMDVs. However, several other determinants are also speculated to be involved in viral tropism and virulence. Deletion of 43 nucleotides (nt) in the pseudoknot (PK) region of the 5' untranslated region (UTR) has been found to coexist with the identified 3A deletion in Cathay topotype FMDV genomes. In this study, we isolated an O/ME-SA/PanAsia lineage FMDV strain, O/GD/CHA/2015, that includes an 86-nt deletion in the PK region and shows a porcinophilic phenotype. To investigate the potential role of the PK region in viral pathogenicity, we generated a recombinant FMDV strain with an incomplete PK region and compared its virulence and pathogenesis to the intact FMDV strain in swine and bovines. Deletion of the 86 nt in the PKs had no major effects on the pathogenicity of the virus in swine but significantly attenuated its ability to infect bovine cells and cattle, indicating that the PK region is a newly discovered determinant of viral tropism and virulence. The role of the 43-nt deletion existing in the Cathay topotype FMDV was also investigated by evaluating the infection properties of genetically engineered viruses. Consistently, the 43-nt deletion in the PK region significantly decreased the pathogenicity of the virus in bovines. Overall, our findings suggest that the PK region deletion occurred naturally in the FMDV genome and that the PK region is highly associated with viral host range and functions as a novel determinant for FMDV pathogenesis.IMPORTANCE This study demonstrates that the deletion in the PK region occurred naturally in the FMDV genome. The isolated O/ME-SA/PanAsia lineage FMDV with an 86-nt deletion in the PK region showed a pig-adapted characteristic that could cause clinical signs in swine but not bovines. Compared to the wild-type FMDV strain, which possesses full infection capacity in both swine and bovines, the recombinant virus with the 86-nt deletion in the PK region is deficient in causing disease in bovines. Deletion of the previously reported 43 nt in the PK region also led to significantly decreased pathogenicity of FMDV in bovines. This study indicates that the PK region is a novel determinant of the tropism and virulence of FMDV.

Cellular DNAJA3, a Novel VP1-Interacting Protein, Inhibits Foot-and-Mouth Disease Virus Replication by Inducing Lysosomal Degradation of VP1 and Attenuating Its Antagonistic Role in the Beta Interferon Signaling Pathway.

DnaJ heat shock protein family (Hsp40) member A3 (DNAJA3) plays an important role in viral infections. However, the role of DNAJA3 in replication of foot-and-mouth-disease virus (FMDV) remains unknown. In this study, DNAJA3, a novel binding partner of VP1, was identified using yeast two-hybrid screening. The DNAJA3-VP1 interaction was further confirmed by coimmunoprecipitation and colocalization in FMDV-infected cells. The J domain of DNAJA3 (amino acids 1 to 168) and the lysine at position 208 (K208) of VP1 were shown to be critical for the DNAJA3-VP1 interaction. Overexpression of DNAJA3 dramatically dampened FMDV replication, whereas loss of function of DNAJA3 elicited opposing effects against FMDV replication. Mechanistical study demonstrated that K208 of VP1 was critical for reducing virus titer caused by DNAJA3 using K208A mutant virus. DNAJA3 induced lysosomal degradation of VP1 by interacting with LC3 to enhance the activation of lysosomal pathway. Meanwhile, we discovered that VP1 suppressed the beta interferon (IFN-ß) signaling pathway by inhibiting the phosphorylation, dimerization, and nuclear translocation of IRF3. This inhibitory effect was considerably boosted in DNAJA3-knockout cells. In contrast, overexpression of DNAJA3 markedly attenuated VP1-mediated suppression on the IFN-ß signaling pathway. Poly(I⋅C)-induced phosphorylation of IRF3 was also decreased in DNAJA3-knockout cells compared to that in the DNAJA3-WT cells. In conclusion, our study described a novel role for DNAJA3 in the host's antiviral response by inducing the lysosomal degradation of VP1 and attenuating the VP1-induced suppressive effect on the IFN-ß signaling pathway.IMPORTANCE This study pioneeringly determined the antiviral role of DNAJA3 in FMDV. DNAJA3 was found to interact with FMDV VP1 and trigger its degradation via the lysosomal pathway. In addition, this study is also the first to clarify the mechanism by which VP1 suppressed IFN-ß signaling pathway by inhibiting the phosphorylation, dimerization, and nuclear translocation of IRF3. Moreover, DNAJA3 significantly abrogated VP1-induced inhibitive effect on the IFN-ß signaling pathway. These data suggested that DNAJA3 plays an important antiviral role against FMDV by both degrading VP1 and restoring of IFN-ß signaling pathway.

Foot-and-mouth disease virus nonstructural protein 2B interacts with cyclophilin A, modulating virus replication.

Foot-and-mouth disease (FMD) is a highly contagious virus that affects cloven-hoofed animals. To understand better the role of nonstructural protein 2B of the causative agent FMD virus (FMDV) in the process of virus replication, we identified a porcine host protein, cyclophilin A (CypA), which interacts with FMDV 2B. The 2B-CypA interaction was confirmed by coimmunoprecipitation and GST pull-down assays. CypA showed antiviral functions during FMDV infection. Overexpression of CypA decreased FMDV leader protein (Lpro) and 3A at protein levels. CypA-induced reduction of Lpro enhanced the synthesis of host proteins and increased the integrality of host eukaryotic translation initiation factor (eIF)-4γ (eIF4G). The reduction of Lpro and 3A was dependent on the proteasome pathway. No interaction was identified between CypA and Lpro or 3A. However, CypA-induced reduction of Lpro and 3A was suppressed by 2B, and disruption of 2B-CypA interaction impaired this inhibitive effect induced by 2B. In summary, our findings identify the antiviral role of CypA against FMDV and provide key insights into how FMDV antagonizes host antiviral response by 2B protein.-Liu, H., Xue, Q., Cao, W., Yang, F., Ma, L., Liu, W., Zhang, K., Liu, X., Zhu, Z., Zheng, H. Foot-and-mouth disease virus nonstructural protein 2B interacts with cyclophilin A, modulating virus replication.

Foot-and-Mouth Disease Virus Viroporin 2B Antagonizes RIG-I-Mediated Antiviral Effects by Inhibition of Its Protein Expression.

The role of retinoic acid-inducible gene I (RIG-I) in foot-and-mouth disease virus (FMDV)-infected cells remains unknown. Here, we showed that RIG-I inhibits FMDV replication in host cells. FMDV infection increased the transcription of RIG-I, while it decreased RIG-I protein expression. A detailed analysis revealed that FMDV leader proteinase (Lpro), as well as 3C proteinase (3Cpro) and 2B protein, decreased RIG-I protein expression. Lpro and 3Cpro are viral proteinases that can cleave various host proteins and are responsible for several of the viral polyprotein cleavages. However, for the first time, we observed 2B-induced reduction of host protein. Further studies showed that 2B-mediated reduction of RIG-I is specific to FMDV, but not other picornaviruses, including encephalomyocarditis virus, enterovirus 71, and coxsackievirus A16. Moreover, we found the decreased protein level of RIG-I is independent of the cleavage of eukaryotic translation initiation factor 4 gamma, the induction of cellular apoptosis, or the association of proteasome, lysosome, and caspase pathways. A direct interaction was observed between RIG-I and 2B. The carboxyl-terminal amino acids 105 to 114 and amino acids 135 to 144 of 2B were essential for the reduction of RIG-I, while residues 105 to 114 were required for the interaction. These data suggest the antiviral role of RIG-I against FMDV and a novel antagonistic mechanism of FMDV that is mediated by 2B protein. IMPORTANCE: This study demonstrated that RIG-I could suppress FMDV replication during virus infection. FMDV infection increased the transcriptional expression of RIG-I, while it decreased RIG-I protein expression. FMDV 2B protein interacted with RIG-I and induced reduction of RIG-I. 2B-induced reduction of RIG-I was independent of the induction of the cleavage of eukaryotic translation initiation factor 4 gamma or cellular apoptosis. In addition, proteasome, lysosome, and caspase pathways were not involved in this process. This study provides new insight into the immune evasion mediated by FMDV and identifies 2B as an antagonistic factor for FMDV to evade the antiviral response.

Comparative Proteomic Analysis of Wild-Type and SAP Domain Mutant Foot-and-Mouth Disease Virus-Infected Porcine Cells Identifies the Ubiquitin-Activating Enzyme UBE1 Required for Virus Replication.

Leader protein (L(pro)) of foot-and-mouth disease virus (FMDV) manipulates the activities of several host proteins to promote viral replication and pathogenicity. L(pro) has a conserved protein domain SAP that is suggested to subvert interferon (IFN) production to block antiviral responses. However, apart from blocking IFN production, the roles of the SAP domain during FMDV infection in host cells remain unknown. Therefore, we identified host proteins associated with the SAP domain of L(pro) by a high-throughput quantitative proteomic approach [isobaric tags for relative and absolute quantitation (iTRAQ) in conjunction with liquid chromatography/electrospray ionization tandem mass spectrometry]. Comparison of the differentially regulated proteins in rA/FMDVΔmSAP- versus rA/FMDV-infected SK6 cells revealed 45 down-regulated and 32 up-regulated proteins that were mostly associated with metabolic, ribosome, spliceosome, and ubiquitin-proteasome pathways. The results also imply that the SAP domain has a function similar to SAF-A/B besides its potential protein inhibitor of activated signal transducer and activator of transcription (PIAS) function. One of the identified proteins UBE1 was further analyzed and displayed a novel role for the SAP domain of L(pro). Overexpression of UBE1 enhanced the replication of FMDV, and knockdown of UBE1 decreased FMDV replication. This shows that FMDV manipulates UBE1 for increased viral replication, and the SAP domain was involved in this process.

Picornavirus VP3 protein induces autophagy through the TP53-BAD-BAX axis to promote viral replication.

Macroautophagy/autophagy and apoptosis are pivotal interconnected host cell responses to viral infection, including picornaviruses. Here, the VP3 proteins of picornaviruses were determined to trigger autophagy, with the autophagic flux being triggered by the TP53-BAD-BAX axis. Using foot-and-mouth disease virus (FMDV) as a model system, we unraveled a novel mechanism of how picornavirus hijacks autophagy to bolster viral replication and enhance pathogenesis. FMDV infection induced both autophagy and apoptosis in vivo and in vitro. FMDV VP3 protein facilitated the phosphorylation and translocation of TP53 from the nucleus into the mitochondria, resulting in BAD-mediated apoptosis and BECN1-mediated autophagy. The amino acid Gly129 in VP3 is essential for its interaction with TP53, and crucial for induction of autophagy and apoptosis. VP3-induced autophagy and apoptosis are both essential for FMDV replication, while, autophagy plays a more important role in VP3-mediated pathogenesis. Mutation of Gly129 to Ala129 in VP3 abrogated the autophagic regulatory function of VP3, which significantly decreased the viral replication and pathogenesis of FMDV. This suggested that VP3-induced autophagy benefits viral replication and pathogenesis. Importantly, this Gly is conserved and showed a common function in various picornaviruses. This study provides insight for developing broad-spectrum antivirals and genetic engineering attenuated vaccines against picornaviruses.Abbreviations: 3-MA, 3-methyladenine; ATG, autophagy related; BAD, BCL2 associated agonist of cell death; BAK1, BCL2 antagonist/killer 1; BAX, BCL2 associated X, apoptosis regulator; BBC3/PUMA, BCL2 binding component 3; BCL2, BCL2 apoptosis regulator; BID, BH3 interacting domain death agonist; BIP-V5, BAX inhibitor peptide V5; CFLAR/FLIP, CASP8 and FADD like apoptosis regulator; CPE, cytopathic effects; CQ, chloroquine; CV, coxsackievirus; DAPK, death associated protein kinase; DRAM, DNA damage regulated autophagy modulator; EV71, enterovirus 71; FMDV, foot-and-mouth disease virus; HAV, hepatitis A virus; KD, knockdown; MAP1LC3/LC3, microtubule associated protein 1 light chain 3; MOI, multiplicity of infection; MTOR, mechanistic target of rapamycin kinase; PML, promyelocytic leukemia; PV, poliovirus; SVA, Seneca Valley virus; TCID50, 50% tissue culture infectious doses; TOR, target of rapamycin. TP53/p53, tumor protein p53; WCL, whole-cell lysate.

Comparative analysis of cloned cDNAs encoding Chinese yellow cattle and Gansu black swine integrin receptors for foot-and-mouth disease virus.

To analyze foot-and-mouth disease virus tropism and host range with respect to the integrin receptor, we cloned cDNAs encoding the integrin αν, ß1, ß3, ß6 and ß8 subunits from Chinese yellow cattle and Gansu black swine and carried out comparative analysis of their molecular characteristics. The lengths of the mature proteins and the functional domains of the four integrin ß subunits were the same between bovine and swine; however, the number of putative N-linked glycosylation sites and cysteine residues and their arrangement varied. Homology analysis of the nucleotide and amino acid sequences showed that FMDV integrin receptors of Chinese yellow cattle and Gansu black swine are highly conserved. Phylogenetic analysis showed that all FMDV integrin receptor subunits of cattle and swine are clustered into the Artiodactyla group; however, Chinese yellow cattle are phylogenetically closer to sheep than to Gansu black swine. We postulate that the host tropism of FMDV may, in part, be related to the divergence of integrin subunits among different species.

Component Identification and Analysis of Vesicular Fluid From Swine Infected by Foot-and-Mouth Disease Virus.

Foot-and-mouth disease (FMD) is induced by FMD virus (FMDV) and characterized by fever and vesicular (blister-like) lesions. However, the exact composition of the vesicular fluid in pigs infected with FMDV remains unclear. To identify and analyze the components of the vesicular fluid in FMDV-infected domestic pigs, the fluid was collected and subjected to mass spectrometry. Further analyses were conducted using Gene Ontology (GO), Kyoto Encyclopedia of Genes and Genome (KEGG), and protein-protein interaction (PPI). Quantitative ELISA kit for TNF-α, and IFN-α, IFN-ß, IL-6, IL-10, IL-1ß, and IFN-γ were used to verify the mass spectrometry results. Results showed that 937 proteins were identified in the vesicular fluid from swine after FMDV infection, and bioinformatics analysis indicated that these proteins are related to the innate immune and inflammation pathways. The levels of cytokines involved in the disease-related pathways, tumor necrosis factors, and IL-6 in the fluid samples were significantly increased. This study identified and analyzed the composition of vesicular fluid in pigs after FMD infection for the first time and provided interesting information that help understand the infection and pathogenesis mechanism of FMD. These information will eventually contribute to the prevention and control of FMD.

Corrigendum: Foot-and-Mouth Disease Virus Capsid Protein VP1 Antagonizes TPL2-Mediated Activation of the IRF3/IFN-ß Signaling Pathway to Facilitate the Virus Replication.

[This corrects the article .].

Corrigendum: Foot-and-Mouth Disease Virus Counteracts on Internal Ribosome Entry Site Suppression by G3BP1 and Inhibits G3BP1-Mediated Stress Granule Assembly via Post-Translational Mechanisms.

[This corrects the article DOI: 10.3389/fimmu.2018.01142.].

Foot-and-mouth disease virus degrades Rab27a to suppress the exosome-mediated antiviral immune response.

Foot-and-mouth disease (FMD) is a highly contagious infection caused by foot-and-mouth disease virus (FMDV). Exosomes are extracellular vesicles that mediate antiviral immune responses in host cells and could be used by pathogens to evade host cell immune responses. Whether FMDV affects exosome secretion or whether exosomes derived from FMDV-infected cells mediate host cell antiviral immune responses is not yet clarified. In this study, the exosomes were identified and extracted from FMDV-infected PK-15 cells, and it was found that FMDV inhibits exosome secretion. Further investigation revealed that FMDV suppresses exosomes by degrading Rab27a via the autophagy-lysosome pathway. Also, microRNA (miRNA) differential analysis was performed in exosomes, which revealed that miRNA-136 was highly differentially expressed in exosomes and may be the key miRNA that inhibits the proliferation of FMDV. In summary, these results showed that host cells take advantage of exosomes to mediate their antiviral immune response, while FMDV evades exosome-mediated immune responses by degrading the exosome molecular switch, Rab27a.

Foot-and-Mouth Disease Virus Capsid Protein VP1 Antagonizes TPL2-Mediated Activation of the IRF3/IFN-ß Signaling Pathway to Facilitate the Virus Replication.

Foot-and-mouth disease (FMD) is a severe, highly contagious viral disease of cloven-hoofed animals. In order to establish an infection, the FMD virus (FMDV) needs to counteract host antiviral responses. Tumor progression locus 2 (TPL2), a mitogen-activated protein kinase, can regulate innate and adaptive immunity; however, its exact mechanisms underlying TPL2-mediated regulation of the pathogenesis of FMDV infection remain unknown. In this study, we confirmed that TPL2 could inhibit FMDV replication in vitro and in vivo. The virus replication increased in Tpl2-deficient suckling mice in association with reduced expression of interferon-stimulated genes interferon-α (IFN-α) and myxovirus resistance (MX2) and significantly reduced expression of C-X-C motif chemokine ligand 10 (CXCL10), interferon regulatory factor 3 (IRF3), and IRF7, while the phosphorylation of IRF3 was not detected. Moreover, the interactions between TPL2 and VP1 were also confirmed. The overexpression of TPL2 promoted IRF3-mediated dose-dependent activation of the IFN-ß signaling pathway in association with interactions between IRF3 and TPL2. VP1 also inhibited phosphorylation of TPL2 at Thr290, while Thr290 resulted as the key functional site associated with the TPL2-mediated antiviral response. Taken together, this study indicated that FMDV capsid protein VP1 antagonizes TPL2-mediated activation of the IRF3/IFN-ß signaling pathway for immune escape and facilitated virus replication.

Molecular Mechanisms of Immune Escape for Foot-and-Mouth Disease Virus.

Foot-and-mouth disease virus (FMDV) causes a highly contagious vesicular disease in cloven-hoofed livestock that results in severe consequences for international trade, posing a great economic threat to agriculture. The FMDV infection antagonizes the host immune responses via different signaling pathways to achieve immune escape. Strategies to escape the cell immune system are key to effective infection and pathogenesis. This review is focused on summarizing the recent advances to understand how the proteins encoded by FMDV antagonize the host innate and adaptive immune responses.