Paxillin is a multi-domain protein that localizes in cultured cells primarily to sites of cell adhesion to the extracellular matrix (ECM) called focal adhesions. Focal adhesions form a structural link between the ECM and the actin cytoskeleton and are also important sites of signal transduction; their components propagate signals arising from the activation of integrins following their engagement with ECM proteins, such as fibronectin, collagen and laminin. Importantly, focal adhesion proteins including paxillin also serve as a point of convergence for signals resulting from stimulation of various classes of growth factor receptor.

Paxillin localizes to focal adhesions through its LIM domains, possibly through a direct association with βintegrin tails or an intermediate protein ‘X’. In lymphoid cells it can bind directly to α4-integrin (not shown). Its primary function is as a molecular adapter or scaffold protein that provides multiple docking sites at the plasma membrane for an array of signaling and structural proteins. For example, it provides a platform for protein tyrosine kinases such as FAK and SRC, which are activated as a result of adhesion or growth factor stimulation. Phosphorylation of residues in the N-terminus of