Andes Virus Recognition of Human and Syrian Hamster β3 Integrins Is Determined by an L33P Substitution in the PSI Domain

Hantaviruses persistently infect specific small mammal hosts and are spread to humans by the inhalation of aerosolized excreted virus (41, 42). Hantaviruses predominantly infect endothelial cells and cause one of two vascular leak-based diseases: hemorrhagic fever with renal syndrome (HFRS) and hantavirus pulmonary syndrome (HPS) (41). Hantavirus diseases are characterized by increased vascular permeability and acute thrombocytopenia in the absence of endothelial cell lysis (36, 41, 42, 54). In general, hantaviruses are not spread from person to person; however, the Andes hantavirus (ANDV) is an exception, since there are several reports of person-to-person transmission of ANDV infection (11, 37, 47, 52). ANDV is also unique in its ability to cause an HPS-like disease in Syrian hamsters and serves as the best-characterized hantavirus disease model with a long onset, symptoms, and pathogenesis nearly identical to that of HPS patients (20, 21, 50). Hantavirus infection of the endothelium alters endothelial cell barrier functions through direct and immunological responses (8, 14). Although the means by which hantaviruses cause pulmonary edema or hemorrhagic disease has been widely conjectured, the mechanisms by which hantaviruses elicit pathogenic human responses have yet to be defined. Hantaviruses coat the surface of infected VeroE6 cells days after infection (17), and this further suggests that dynamic hantavirus interactions with immune and endothelial cells are likely to contribute to viral pathogenesis. Hantavirus pathogenesis has been suggested to involve CD8+ T cells, tumor necrosis factor alpha or other cytokines, viremia, and the dysregulation of β3 integrins (7, 8, 13-16, 25-28, 32, 34, 38, 44-46). However, these responses have not been demonstrated to contribute to hantavirus pathogenesis, and in some cases there are conflicting data on their involvement (18, 25-28, 34, 35, 44, 45, 48). Immune complex deposition clearly contributes to HFRS patient disease and renal sequelae (4, 7), but it is unclear what triggers vascular permeability in HPS and HFRS diseases or why hemorrhage occurs in HFRS patients but not in HPS patients (8, 36, 54). Acute thrombocytopenia is common to both diseases, and platelet dysfunction resulting from defective platelet aggregation is reported in HFRS patients (7, 8). Pathogenic hantaviruses have in common their ability to interact with αIIbβ3 and αvβ3 integrins present on platelets and endothelial cells (13, 16), and β3 integrins have primary roles in regulating vascular integrity (1, 2, 6, 19, 22, 39, 40). Consistent with the presence of cell surface displayed virus (17), pathogenic hantaviruses uniquely block αvβ3 directed endothelial cell migration and enhance endothelial cell permeability for 3 to 5 days postinfection (14, 15). Pathogenic hantaviruses dysregulate β3 integrin functions by binding domains present at the apex of inactive β3 integrin conformers (38). αvβ3 forms a complex with vascular endothelial cell growth factor receptor 2 (VEGFR2) and normally regulates VEGF-directed endothelial cell permeability (2, 3, 10, 39, 40). However, both β3 integrin knockouts and hantavirus-infected endothelial cells result in increased VEGF-induced permeability, presumably by disrupting VEGFR2-β3 integrin complex formation (2, 14, 19, 39, 40). This suggests that at least one means for hantaviruses to increase vascular permeability occurs through interactions with β3 integrins that are required for normal platelet and endothelial cell functions. αvβ3 and αIIbβ3 integrins exist in two conformations: an active extended conformation where the ligand binding head domain is present at the apex of the heterodimer and a basal, inactive bent conformation where the globular head of the integrin is folded toward the cell membrane (30, 53, 55). Pathogenic HTN and NY-1 hantaviruses bind to the N-terminal plexin-semaphorin-integrin (PSI) domain of β3 integrin subunits and are selective for bent, inactive αvβ3 integrin conformers (38). Pathogenic hantavirus binding to inactive αvβ3 integrins is consistent with the selective inhibitory effect of hantaviruses on αvβ3 function and endothelial cell permeability (14, 15, 38). Although the mechanism of hantavirus induced vascular permeability has yet to be defined, there is a clear role for β3 integrin dysfunction in vascular permeability deficits (5, 6, 22, 29, 39, 40, 51) which make an understanding of hantavirus interactions with β3 subunits important for both entry and disease processes. The similarity between HPS disease in humans and Syrian hamsters (20, 21) suggests that pathogenic mechanisms of ANDV disease are likely to be coincident. Curiously, other hantaviruses (Sin Nombre virus [SNV] and Hantaan virus [HTNV]) are restricted in Syrian hamsters and fail to cause disease in this animal, even though they are prominent causes of human disease (50). Although the host range restriction for SNV and HTNV in Syrian hamsters has not been defined (33), the pathogenesis of ANDV in Syrian hamsters suggests that both human and Syrian hamster β3 integrins may similarly be used by ANDV and contribute to pathogenesis. We demonstrate here that ANDV infection of the Syrian hamster BHK-21 cell line and human endothelial cells is dependent on αvβ3 and inhibited by αvβ3 specific ligands and antibodies. Further, polypeptides expressing the N-terminal 53 residues of human and Syrian hamster β3 subunits block ANDV infection. This further indicates that ANDV interaction with the N-terminal 53 residues of both human and Syrian hamster β3 integrins is required for viral entry. We also demonstrate that ANDV recognition of human and Syrian hamster β3 integrins is determined by proline substitutions at residues 32/33 within the β3 integrin PSI domain. These results define unique ANDV interactions with human and Syrian hamster β3 integrins.