Potential roles for focal adhesion kinase in development

Focal adhesion kinase (pp125(FAK) Or FAK) is a protein tyrosine kinase whic h is associated with intracellular signalling cascades which are initiated when the integrin family of cell adhesion molecules engage extracellular ma trix molecules. In cultured cells, this molecule is physically associated w ith focal adhesions, which are well-defined regions of intimate cell-to-sub stratum adhesion. In this location, it interacts with other proteins of the focal adhesion to activate intracellular signalling events associated with cell adhesion. The in vitro expression of FAK and its level of phosphoryla tion appear to be related to several physiological phenomena, including cel l spreading, cell differentiation, cell locomotion and cell death. Because these phenomena are all of critical importance during morphogenesis, and be cause FAK is expressed in embryonic cells, evidence has been accumulating t o indicate that FAK may be an important modulator of developmental processe s. In this review, this evidence is surveyed together with evidence from an alogous situations, such as tumour cell migration and invasiveness. Althoug h evidence suggesting a role for FAK in morphogenesis is accumulating, curr ent uncertainties regarding its cytoplasmic location and its molecular inte ractions in vivo make it difficult to reach definitive conclusions regardin g the significance of its contributions to developmental processes.