Disintegrin Interaction with αvβ3Integrin on Human Umbilical Vein Endothelial Cells: Expression of Ligand-Induced Binding Site on β3Subunit☆

Abstract The effect of seven disintegrins (albolabrin, barbourin, bitistatin, echistatin, eristostatin, flavoridin, and kistrin) and the neurotoxin analogue, mambin, on the adhesion of human umbilical vein endothelial cells (HUVEC) to immobilized vitronectin and fibronectin has been studied. Adhesion to vitronectin was significantly inhibited by echistatin, kistrin, flavoridin, and mambin. Echistatin, flavoridin, and kistrin bound with high affinity to immobilized α v β 3 in solid phase assay; other disintegrins bound at a much lower level. Echistatin and flavoridin had a modest inhibitory effect on HUVEC adhesion to fibronectin. HUVEC adhered to disintegrins with a high selectivity toward bitistatin, echistatin, flavoridin, kistrin, and mambin. Adhesion of HUVEC to fibronectin and vitronectin resulted in cell spreading, whereas cells adhering to immobilized echistatin remained globular and cells adhering to kistrin showed abnormal morphology. Echistatin and kistrin potently inhibited the binding of monoclonal antibody (Mab) 7E3, which recognizes the α v β 3 complex, to HUVEC. Echistatin and kistrin also induced the binding to HUVEC of Mab 62, which recognizes the ligand-induced binding site (LIBS) epitope on the β 3 subunit, enhancing HUVEC binding to immobilized Mab 62. Similar results with both antibodies were obtained in Chinese hamster ovary cells transfected with α v β 3 genes. In conclusion, disintegrin interaction with HUVEC appears to be selectively mediated by α v β 3 receptors, and it results in an expression of LIBS epitope that may play a role in the regulation of ligand-binding affinity and intracellular signaling.