Integrins are transmembrane receptors that are the bridges for cell-cell and cell-extracellular matrix (ECM) interactions. When triggered, integrins trigger chemical pathways to the interior (signal transduction), such as the chemical composition and mechanical status of the ECM. This results in a response (activation of transcription) like the regulation of the cell cycle, cell shape, and/or motility; or adding new receptors to the cell membrane. This allows rapid and flexible responses to events at the cell surface, for example to signal platelets to initiate an interaction with coagulation factors.

Integrins come in several types. One cell may have several types on its surface. Integrins are found in all animals.

Integrins work alongside other receptors such as cadherins, the immunoglobulin superfamily cell adhesion molecules, selectins and syndecans to mediate cell–cell and cell–matrix interaction. Ligands for integrins include fibronectin, vitronectin, collagen and laminin.

Integrins are obligate heterodimers, meaning that they have two subunits: α (alpha) and β (beta). Integrins in mammals have eighteen α and eight β subunits, in Drosophila five α and two β subunits, and in Caenorhabditis nematodes two α subunits and one β subunit. The α and β subunits each penetrate the plasma membrane and possess small cytoplasmic domains.

Variants of some subunits are formed by differential RNA splicing; for example, four variants of the beta-1 subunit exist. Through different combinations of the α and β subunits, around 24 unique integrins are generated.

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