Structure, signal transduction, activation, and inhibition of integrin αIIbß3.

ABSTRACT

Integrins are heterodimeric receptors comprising α and ß subunits. They are expressed on the cell surface and play key roles in cell adhesion, migration, and growth. Several types of integrins are expressed on the platelets, including αvß3, αIIbß3, α2ß1, α5ß1, and α6ß1. Among these, physically αIIbß3 is exclusively expressed on the platelet surface and their precursor cells, megakaryocytes. αIIbß3 adopts at least three conformations i) bent-closed, ii) extended-closed, and iii) extended-open. The transition from conformation i) to iii) occurs when αIIbß3 is activated by stimulants. Conformation iii) possesses a high ligand affinity, which triggers integrin clustering and platelet aggregation. Platelets are indispensable for maintaining vascular system integrity and preventing bleeding. However, excessive platelet activation can result in myocardial infarction (MI) and stroke. Therefore, finding a novel strategy to stop bleeding without accelerating the risk of thrombosis is important. Regulation of αIIbß3 activation is vital for this strategy. There are a large number of molecules that facilitate or inhibit αIIbß3 activation. The interference of these molecules can accurately control the balance between hemostasis and thrombosis. This review describes the structure and signal transduction of αIIbß3, summarizes the molecules that directly or indirectly affect integrin αIIbß3 activation, and discusses some novel antiαIIbß3 drugs. This will advance our understanding of the activation of αIIbß3 and its essential role in platelet function and tumor development.