Integrins are ?/? heterodimeric cell surface receptors that play a pivotal role in cell adhesion and migration, as well as in growth and survival. The integrin family contains at least 18 ? and 8 ? subunits that form 24 known integrins with distinct tissue distribution and overlapping ligand specificities. Integrins not only transmit signals to cells in response to the extracellular environment (outside-in signaling), but also sense intracellular cues to alter their interaction with the extracellular environment (inside-out signaling).
Integrin ?2b is a cell-surface adhesion molecule that undergoes proteolytic cleavage to yield disulfide-linked heavy and light chains, which together with glycoprotein IIIb, forms a major fibrinogen receptor in activated platelets. Mutations in the corresponding ITGA2B gene can result in Glanzmann thrombasthenia, a bleeding disorder characterized by lack of platelet aggregation.