Identification of alpha v beta 3 as a heterotypic ligand for CD31/PECAM-1

CD31 (PECAM-1) is a member of the immunoglobulin gene superfamily (IgSF) and has an important role in a number of endothelial cell functions including angiogenesis, inflammation, integrin activation and cell-cell adhesion. CD31 has both homotypic and heterotypic adhesive properties and in common with other IgSF members contains multiple functional domains. Using chimaeric fusion proteins of CD31 and a panel of haematopoietic cell lines we show that CD31 can bind cells in a predominantly homotypic or heterotypic manner depending on the cell line used. Heterotypic binding was found to be cation and temperature dependent and enhanced by Mn2+: all features of integrin mediated binding. Using a panel of anti-CD31 and anti-integrin antibodies we show that alpha v beta 3 is a ligand for CD31 on the monocytic cell line U937. The specificity of the interaction between alpha v beta 3 and CD31 was further confirmed by solid phase binding assays and the use of alpha v beta 3 transfected cells which bound CD31 specifically. Furthermore, we have mapped the binding site for alpha v beta 3 to domains 1 and 2 of CD31. The interaction of CD31 with alpha v beta 3 may be important in many aspects of endothelial function including leukocyte-endothelial transmigration and angiogenesis.