Integrin αvβ8 Functions as a Receptor for Foot-and-Mouth Disease Virus: Role of the β-Chain Cytodomain in Integrin-Mediated Infection

ABSTRACT Field isolates of foot-and-mouth disease virus (FMDV) have been shown to use three αv integrins, αvβ1, αvβ3, and αvβ6, as cellular receptors. Binding to the integrin is mediated by a highly conserved RGD motif located on a surface-exposed loop of VP1. The RGD tripeptide is recognized by several other members of the integrin family, which therefore have the potential to act as receptors for FMDV. Here we show that SW480 cells are made susceptible to FMDV following transfection with human β8 cDNA and expression of αvβ8 at the cell surface. The involvement of αvβ8 in infection was confirmed by showing that virus binding and infection of the transfected cells are inhibited by RGD-containing peptides and by function-blocking monoclonal antibodies specific for either the αvβ8 heterodimer or the αv chain. Similar results were obtained with a chimeric αvβ8 including the β6 cytodomain (αvβ8/6), showing that the β6 cytodomain can substitute efficiently for the corresponding region of β8. In contrast, virus binding to αvβ6 including the β8 cytodomain (αvβ6/8) was lower than that of the wild-type integrin, and this binding did not lead to infection. Further, the αvβ6 chimera was recognized poorly by antibodies specific for the ectodomain of αvβ6 and displayed a relaxed sequence-binding specificity relative to that of wild-type integrin. These data suggest that the β6 cytodomain is important for maintaining αvβ6 in a conformation required for productive infection by FMDV.