Interactions of foot-and-mouth disease virus with soluble bovine V3 and V6

At least four members of the integrin family of receptors, V1, V3, V6, and V8, have been identified as receptors for foot-and-mouth disease virus (FMDV) in vitro. Our investigators have recently shown that the efficiency of receptor usage appears to be related to the viral serotype and may be influenced by structural differences on the viral surface (H. Duque and B. Baxt, J. Virol. 77:2500-2511, 2003). To further examine these differences, we generated soluble V3 and V6 integrins. cDNA plasmids encoding the individual complete integrin V, 3, and 6 subunits were used to amplify sequences encoding the subunits ’ signal peptide and ectodomain, resulting in subunits lacking transmembrane and cytoplasmic domains. COS-1 cells were trans-fected with plasmids encoding the soluble V subunit and either the soluble 3 or 6 subunit and labeled with [35S]methionine-cysteine. Complete subunit heterodimeric integrins were secreted into the medium, as deter-mined by radioimmunoprecipitation with specific monoclonal and polyclonal antibodies. For the examination of the integrins ’ biological activities, stable cell lines producing the soluble integrins were generated in HEK 293A cells. In the presence of divalent cations, soluble V6 bound to representatives of type A or O viruses, immobilized on plastic dishes, and significantly inhibited viral replication, as determined by plaque reduction assays. In contrast, soluble V3 was unable to bind to immobilized virus of either serotype; however, virus bound to the immobilized integrin, suggesting that FMDV binding to V3 is a low-affinity interaction. I