FOCAL ADHESION KINASE PP125(FAK) IS ASSOCIATED WITH BOTH INTERCELLULAR-JUNCTIONS AND MATRIX ADHESION SITES IN-VIVO

Previous studies have characterized pp125(FAK) as a focal adhesion (FA )-associated non-receptor tyrosine kinase. However, there are few data available on the expression and localization of this kinase in tissue s. In this study we show that in human tissues the highest expression of pp125(FAK) is found in some developing epithelia, where pp125(FAK) is associated with either intercellular junctions or with sites of adh esion to the basement membrane, whereas the same adult tissues show on ly a faint reactivity. Connective tissue cells do not show any reactiv ity for pp125(FAK) in vivo, but developing arterial smooth muscle expr esses pp125(FAK) at high levels. The expression pattern in malignant t issues is variable, but most carcinomas do not express this kinase. In primary cultures of human amnion epithelial cells pp125(FAK) first be comes associated with the polarized adhesion lamellae, but is subseque ntly translocated to the forming adherens junctions (AJs). Later upon culturing pp125(FAK) becomes associated with prominent FAs, as in cult ured cell lines. Taken together, our results suggest that the associat ion of pp125(FAK) With FAs in cultured cells is principally due to a p rocess of adaptation, whereas in vivo pp125(FAK) mainly functions as a regulatory component of intercellular AJs and cell-matrix adhesions o f developing epithelia and also in developing arterial smooth muscle.