Production of Soluble Integrin Α2β1 Heterodimer Complex Functionally Active in Vitro and in Vivo

Integrin α2β1, which is a membrane protein consisting of noncovalently bound α2 and β1 chains, mediates cell binding to collagen and plays a role in platelet functions. DNAs encoding the chimeric proteins in which the extracellular domains of each α2 and β1 chain was fused to hinge and Fc regions of human IgG1γ chain were cotransfected into CHO cells. Soluble integrin α2β1 (sα2β1) in which α2 and β1 chains were covalently bound by disulfide bonds was recovered from the culture supernatant. sα2β1 maintained functional characteristics of cell surface α2β1 as indicated by cation-dependent binding to collagen and conformational changes induced by cations or ligand. Intravenously administered sα2β1 in rats colocalized with collagen in inflamed microvessels. Moreover, sα2β1-conjugated liposome administered intravenously reduced bleeding time of the thrombocytopenic mice. These results indicated that sα2β1 has pharmaceutical utilities as an agent for detecting injured vessels and a component of platelet substitute.