Biosynthesis and Processing of the Cytoadhesins, GPIIb/IIIa and Vitronectin Receptor

Integrins are heterodimers comprised of non covalently associated α and β subunits (1, 2). This family has been divided into four groups of adhesion receptors, according to their β subunit. Each group is composed of glycoproteins sharing the same β subunit and different α subunits. This includes the VLA family (3), the leukocyte adhesion proteins LFA-1, Mac-1 and p 150,95 (4), the cytoadhesin family (5), and the newly identified epithelial integrin (6). The platelet GPIIb/IIIa and the vitronectin receptor (VNR) belong to the cytoadhesin family (5) and share the same β subunit, i.e. GPIIIa or VNRβ (7), according to its primary sequence (8–10) and distinct a subunits, i.e. GPIIb or VNRα (11–13).