Subclassification, molecular structure, function and ligand in integrin superfamily

Integrins are the major family of cell surface receptors that mediate adhesion to the extracellular matrix and sometimes cell-cell adhesive interactions. These integrin-mediated adhesive interactions are involved in the regulation of many cellular functions, including embryonic development, tumor cell growth and metastasis, programmed cell death, hemostasis, inflammation, immune reaction, bone reabsorption, etc. Integrins are composed of alpha and beta transmembrane subunits selected from among 16 alpha and 8 beta subunits that heterodimerize to produce more than 20 different receptors which bind specific ligands. Ligand binding sites have been clarified by chimera integrin protein in some integrins. Integrins link to intracellular cytoskeletal complexes and bundles of actin filaments. There have been many reports about intracellular signaling pathways activated by integrin-ligand interactions.