Virtually all cells of multicellular animals express integrins, and most cells of adult mammals constitutively express multiple different integrins. These cell surface receptors play an important role in mediating cell adhesionto adjacent connective tissue proteins. Integrins are transmembrane heterodimers that consist of noncovalently bound glycoprotein subunits. Each heterodimer is composed of a single α- and a single β-subunit, both of which participate in ligand recognition. A total of 18 α- and β-subunits have been identified, some of which have multiple splice variants, and these combine to form 24 distinct integrin heterodimers. Most integrins (with the notable exception of α6β4) have small cytoplasmic domains that are connected to the cytoskeleton by multiple...