The Role of Focal Adhesion Kinase (FAK) in Contact Inhibition.

Non-transformed cells cultivated in vitro become contact inhibited (stop growing) when they reach confluence at the level which is called a saturation density. Our previous study documented that in contact inhibited C3H10T1/2 fibroblasts MAP kinase (MAPK) has not been activated by serum or fibronectin, whereas in fast growing (sparse) MAPK was evidently stimulated. The same schedule of the reactivity where observed for focal adhesion kinase (FAK). Altogether it suggested the role of FAK in the mechanism of contact inhibition. To confirm the role of FAK in the saturation dependent growth inhibition C3H10T1/2 cells was stably transfected with antisense FAK vector. The transfected cells thereafter called C3H10T1/2 (FAK-) possesing only 40-60% of FAK protein as compared to the original line and displayed higher saturation density than original C3H10T1/2 cells. They also showed activation of FAK following FCS or fibronectin stimulation independently of the stage ofgrowth, whereas in original cell line FAK was only activated in sparse cells. Phosphorylation activity of ERK in both sublines follows the changes in FAK activity. RT PCR study performed in C3H10T1/2 cells and their (FAK-) transfectants displayed Id-1 mRNA only in sparse C3H10T1/2 cells, in their transfectants Id-1 could be observed in sparse as well as in confluent cells. Altogether it may prove the hypothesis on the involvement of FAK in the mechanism of contact inhibition.