INHIBITION OF PP125(FAK) IN CULTURED FIBROBLASTS RESULTS IN APOPTOSIS

The tyrosine kinase called pp125(FAK) is believed to play an important role in integrin-mediated signal transduction. pp125(FAK) is associat ed both functionally and spatially with integrins, which are the cell surface receptors for extracellular matrix components. Although the pr ecise function of pp125(FAK) is not known, two possibilities have been proposed: pp125(FAK) may regulate the assembly of focal adhesions in spreading or migrating cells, or pp125(FAK) may participate in a signa l transduction cascade to inform the nucleus that the cell is anchored . To test these models in living cells, a peptide representing the foc al adhesion kinase (FAK)-binding site of the beta(1) tail was coupled to carrier protein and injected into cultured cells to competitively i nhibit the binding of pp125(FAK) to endogenous integrin, thus inhibiti ng activation of pp125(FAK) On a cell-by-cell basis. In addition, an a ntibody directed against an epitope adjacent to the focal adhesion tar geting sequence on pp125(FAK) was microinjected, as an alternative mea ns of inhibiting pp125(FAK) activation. It was observed that when roun ded cells were injected with either the integrin peptide or the anti-F AK antibody, the cells rapidly began to apoptose, within 4 h after inj ection. These results indicate that pp125(FAK) may play a critical rol e in suppressing apoptosis in fibroblasts.