Integrins are a family of heterodimeric membrane glycoproteins consisting of non-covalently associated alpha and beta subunits. More than 18 alpha and 8 beta subunits with numerous splice variant isoforms have been identified in mammals. In general, integrins function as receptors for extracellular matrix proteins. Certain integrins can also bind to soluble ligands or to counter-receptors on adjacent cells, such as the intracellular adhesion molecules (ICAMs), resulting in aggregation of cells. Signals transduced by integrins play a role in many biological processes, including cell growth, differentiation, migration and apoptosis. For integrin subunits alpha3 and alpha6, two cytoplasmic variants, A and B, have been identified.