Genome sequence of foot-and-mouth disease virus outside the 3A region is also responsible for virus replication in bovine cells

Substitution 3A protein of foot-and-mouth disease virus of attenuated ZB strain rescued the viral replication and infection in bovine cells

The non-structural protein 3A of foot-and-mouth disease virus (FMDV) plays an important role in viral replication, virulence and determination of host range. Previously we identified genomic changes in gene encoding 3A protein between the attenuated ZBatt strain and its parental virulent strain during the attenuation process. However, the effects of changes in 3A protein on viral replication and infection of the rabbit-attenuated ZBatt virus during the attenuation process are poorly understood. In this study, a chimeric virus, rZBatt-3A, was constructed by introducing the 3A gene of virulent ZB virus into its attenuated vaccine ZB strain. Subsequently, the biological characteristics between rZBatt-3A and its parental virus (rZBatt) were compared. The relative expression level of four host cell proteins that interact with FMDV 3A were also analyzed. The results showed that the chimeric virus rZBatt-3A exhibited significantly different growth properties and plaque phenotypes from rZBatt in primary fetal bovine kidney (BK) cells. Cytopathic effect (CPE) of the rZBatt-3A was observed in BK cells with smaller plaque size, but CPE from the rZBatt could not be observed. The viral RNA replication was higher in rZBatt-3A-infected BK cells than in rZBatt-infected cells at 24 hpi (P < .05). In addition, the relative mRNA expression level of Ubiquilin 1 (UBQLN1) was significantly increased in rZBatt-3A-infected BK cells than in rZBatt-infected cells (P < .01) suggesting that UBQLN1 may be associated with 3A protein changes. Thus, the substitution of 3A protein altered the replication efficiency of attenuated ZB virus in bovine cells. Our data suggested that changes in 3A protein might be associated with the attenuation of ZB virus, which shed more lights in molecular mechanisms about attenuation of FMDV.

Type I Interferon Induced and Antagonized by Foot-and-Mouth Disease Virus

Viral infections trigger the innate immune system, serving as the first line of defense, and are characterized by the production of type I interferon (IFN). Type I IFN is expressed in a broad spectrum of cells and tissues in the host and includes various subtypes (IFN-α, IFN-β, IFN-δ, IFN-ε, IFN-κ, IFN-τ, IFN-ω, IFN-ν, and IFN-ζ). Since the discovery of type I IFN, our knowledge of the biology of type I IFN has accumulated immensely, and we now have a substantial amount of information on the molecular mechanisms of the response and induction of type I IFN, as well as the strategies utilized by viruses to evade the type I IFN response. Foot-and-mouth disease virus (FMDV) can selectively alter cellular pathways to promote viral replication and evade antiviral immune activation of type I IFN. RNA molecules generated by FMDV are sensed by the cellular receptor for pathogen-associated molecular patterns (PAMPs). FMDV preferentially activates different sensor molecules and various signal transduction pathways. Based on knowledge of the virus or RNA pathogen specificity as well as the function-structure relationship of RNA sensing, it is necessary to summarize numerous signaling adaptors that are reported to participate in the regulation of IFN gene activation.

Relevance of the N-terminal and major hydrophobic domains of non-structural protein 3A in the replicative process of a DNA-launched foot-and-mouth disease virus replicon

A foot-and-mouth disease virus (FMDV) DNA-launched reporter replicon containing a luciferase gene was used to assess the impact of non-structural (NS) protein 3A on viral replication. Independent deletions within the N-terminal region (amino acid [aa] residues 6 to 24) and the central hydrophobic region (HR, aa 59 to 76) of FMDV NS protein 3A were engineered, and luciferase activity in lysates of control and mutated replicon-transfected cells was measured. Triple alanine replacements of the N-terminal triplet Arg 18- His 19 -Glu 20 and a single alanine substitution of the highly charged Glu 20 residue both resulted in a 70-80% reduction in luciferase activity when compared with wild-type controls. Alanine substitution of the 17 aa present in the central HR, on the other hand, resulted in complete inhibition of luciferase activity and in the accumulation of the mutated 3A within the cell nucleus according to immunofluorescence analysis. Our results suggest that both the aa sequence around the putatively exposed hydrophilic E20 residue at the N-terminus of the protein and the hydrophobic tract located between aa 59 and 76 are of major relevance for maintaining the functionality of the 3A protein and preventing its mislocalization into the cell nucleus.