Integrins are ?/? 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 ? 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, ?4?1 and ?4?7, 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 .On SDS-PAGE, integrin ?4 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 ?4 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.