Abstract

Engagement of integrin receptors with extracellular ligands gives rise to the formation of complex multiprotein structures that link the ECM to the cytoplasmic actin cytoskeleton. These adhesive complexes are dynamic, often heterogeneous structures, varying in size and organization. In motile cells, sites of adhesion within filopodia and lamellipodia are relatively small and transient and are referred to as 'focal complexes,' whereas adhesions underlying the body of the cell and localized to the ends of actin stress fibers are referred to as 'focal adhesions'. Signal transduction through focal complexes and focal adhesions has been implicated in the regulation of a number of key cellular processes, including growth factor induced mitogenic signals, cell survival and cell locomotion. The formation and remodeling of focal contacts is a dynamic process under the regulation of protein tyrosine kinases and small GTPases of the Rho family. In this review, we consider the role of the focal complex associated protein tyrosine kinase, Focal Adhesion Kinase (FAK), in the regulation of cell movement with the emphasis on how FAK regulates the flow of signals from the ECM to the actin cytoskeleton.