Expression of recombinant platelet glycoprotein IIbIIIa results in a functional fibrinogen-binding complex

The ability of cDNAs encoding the human platelet glycoprotein IIbIIIa to be expressed and assembled into a functional integrin receptor was assessed by transient transfection into a human cell line. Transfection of full length cDNAs resulted in synthesis of high levels of integrin subunits which appear to be stable within the cell for several days. Coexpression of both subunits resulted in a proteolytically processed form of GPIIb that associated with GPIIIa as a heterodimeric complex as the cell surface. Transport to the cell surface required association of these subunits with each other or with endogenous integrin subunits. When expressed alone, the GPIIb subunit remained intracellular, while the GPIIIa subunit was found to complex with endogenous proteins and was mobilized to the cell surface. The GPIIbIIIa receptor complex facilitated attachment of cells to known ligands for GPIIbIIIa: fibrinogen, vitronectin, and von Willebrand factor. This adhesion was sensitive to inhibition by the peptide GRGDV and the monoclonal antibody AP2, known inhibitors of platelet aggregation