| Background |
Integrins are α/β 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 α and 8 β 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).A pair of important α4 integrins, α4β1 and α4β7, interact with VCAM-1, fibronectin, and MAdCAM-1 at cell adhesions. Gene knockout and antibody blocking research reveal that α4 integrins play important roles in embryonic liver and heart development and in fetal lymphocyte homing. Phosphorylation at Ser988 within the cytoplasmic tail of integrin α4 blocks binding to paxillin and promotes leading edge migration.On SDS-PAGE, integrin α4 can migrate at several different apparent molecular sizes, a 150 kDa mature protein and a 140 kDa precursor protein (a 180 kDa protein also exists under mild non-reducing conditions). Integrin α4 has a cleavage site at Arg558, which results in a small portion of the protein as either an 80 kDa N-terminal or 70 kDa C-terminal fragment.
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