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 ␣v integrins, ␣v␤1, ␣v␤3, and ␣v␤6, 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 ␤8 cDNA and expression of ␣v␤8 at the cell surface. The involvement of ␣v␤8 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 ␣v␤8 heterodimer or the ␣v chain. Similar results were obtained with a chimeric ␣v␤8 including the ␤6 cytodomain (␣v␤8/6), showing that the ␤6 cytodomain can substitute efficiently for the corresponding region of ␤8. In contrast, virus binding to ␣v␤6 including the ␤8 cytodomain (␣v␤6/8) was lower than that of the wild-type integrin, and this binding did not lead to infection. Further, the ␣v␤6 chimera was recognized poorly by antibodies specific for the ectodomain of ␣v␤6 and displayed a relaxed sequence-binding specificity relative to that of wild-type integrin. These data suggest that the ␤6 cytodomain is important for maintaining ␣v␤6 in a conformation required for productive infection by FMDV.Foot-and-mouth disease virus (FMDV) is the etiological agent of foot-and-mouth disease, a severe vesicular disease of cloven-hoofed animals including domesticated ruminants and pigs. The virus exists as seven serotypes, which are members of the genus Aphthovirus of the family Picornaviridae (35). The virion consists of an 8.5-kb strand of RNA enclosed within an icosahedral capsid formed from 60 copies each of four proteins, VP1 to VP4 (1).Two classes of cell surface receptors that mediate FMDV infection have been identified (30). Theses are the integrins (7, 31, 33) and heparan sulfate (HS) proteoglycans (HSPGs) (29). The ability to use HSPGs as receptors appears to be restricted to strains of FMDV that have been multiply passaged through cultured cell lines (4,5,22,41,52,58), and presently there is no convincing evidence of a role for HS in cell entry by field viruses. Instead, field viruses are dependent on integrin receptors to initiate infection in vitro, and integrins are believed to be the receptors used in the infected animal. Recently, two independent studies have shown that certain strains of FMDV can infect cultured cells via an entry pathway that is independent of both integrins and cellular HS, implying the existence of a third, as yet unidentified receptor family (4, 65).Integrins are a family of integral membrane receptors with distinct ligand-binding specificities and tissue distributions. They contribute to a variety of cellular functions, including cell-cell and cell-matrix adhesion, and exist in alternative lowand high-affinity states, enab...

Positively Charged Residues at the Five-Fold Symmetry Axis of Cell Culture-Adapted Foot-and-Mouth Disease Virus Permit Novel Receptor Interactions

“…To investigate this possibility, we carried out competition experiments using RGD-containing peptides, a short GRGDSP peptide and two longer peptides (a 12-mer and 17-mer) that have sequences derived from the FMDV integrin-binding loop (and their control RGE counterparts), along with function-blocking antibodies to ␣5␤1 (PB1) (46) and ␣v␤5 (P1F6) (40). The peptides have been shown to block binding to a number of RGD-dependent integrins, including ␣v␤1, ␣v␤3, ␣v␤5, ␣v␤6, ␣v␤8, and ␣5␤1 (10,14,15,(47)(48)(49)(50), and the antibodies are known to be cross-reactive for hamster integrins (45,46). CHO cells were pretreated with these reagents prior to incubation with virus (O1K-A/VP1-Q 110 K / BHK1) for 1 h at 37°C.…”

“…Integrin binding is mediated by a highly conserved arginine-glycine-aspartic acid (RGD) motif located at the apex of a structurally disordered loop (the GH loop of VP1). The integrin specificity of FMDV has been the subject of several studies, and three other RGD-dependent integrins (␣v␤1, ␣v␤3, and ␣v␤8) have also been reported to be receptors for field strains of the virus (13)(14)(15); however, the role of these integrins in pathogenesis is unclear, and we have found that ␣v␤3 is a poor receptor for FMDV in vitro (16). Furthermore, despite recognizing their ligands via the RGD motif, two other RGD-dependent integrins (␣v␤5 and ␣5␤1) do not appear to serve as receptors for FMDV (17).…”

Analysis of a Foot-and-Mouth Disease Virus Type A 24 Isolate Containing an SGD Receptor Recognition Site In Vitro and Its Pathogenesis in Cattle

“…The intrinsic genetic variability of FMDV, which has been manifested by changes in antigenicity in FMDV escape mutants (14, 35, 50, 51), and diversity in cellular receptor usage (5,8,21,24,26,31,34,40) pose concerns for control strategies based on vaccination. The fact that current FMDV vaccines are prepared from virus grown in large amounts in cell cultures generates potential problems in vaccine manufacturing, due to the occasional outgrowth and dominance of mutant viruses.…”

Inhibition of viral replication by small interfering RNA targeting of the foot-and-mouth disease virus receptor integrin β6

“…Indeed, αvβ6 is currently considered to function as a primary FMDV receptor that contributes to FMDV tropism and viral invasion (24). Furthermore, αvβ6 exerts regulatory functions in the process of coagulation (25). Jacobsen et al (26) documented that β6-knockout mice exhibit significantly delayed wound healing at the early stage of disease when compared with wild-type diabetic mice.…”