Integrins are /B 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 and 8 B 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 4 integrins，4B1 and 4B7，interact with VCAM-1，fibronectin，and MAdCAM-1 at cell adhesions. Gene knockout and antibody blocking research reveal that 4 integrins play important roles in embryonic liver and heart development and in fetal lymphocyte homing. Phosphorylation at Ser988 within the cytoplasmic tail of integrin 4 blocks binding to paxillin and promotes leading edge migration.
