Platelet membrane glycoprotein Integrin beta-3 (GP IIIa) forms a Ca2+-dependent heterodimer complex with GP IIb. The GP IIb-IIIa complex constitutes the fibrinogen and fibronectin receptor on stimulated platelets. A biochemically and immunologically similar membrane glycoprotein complex is present on endothelial cells. Homology suggests that GP IIIa is a member of a family of cell-surface adhesion receptors. (1) Data provide further support for the key role of the cytoplasmic domain of the beta3 integrin in cell adhesion and suggest a potential role for the beta3C integrin subunit in modulating cell-matrix interactions (2). It has been demonstrated that the beta 3 subunit of alpha IIb beta 3 was phosphorylated on tyrosine residues in response to thrombin-induced platelet aggregation. Data suggest that tyrosine phosphorylation of an integrin beta subunit may be important in initiating outside-in signaling cascades by inducing association of signaling components directly with the integrin (3). be important in initiating outside-in signaling cascades by inducing association of signaling components directly with the integrin (3).
