Restructuring of focal adhesion plaques by PI 3-kinase: Regulation by PtdIns (3,4,5)-P-3 binding to alpha-actinin

Focal adhesions are an elaborate network of interconnecting proteins linkin g actin stress fibers to the extracellular matrix substrate. Modulation of the focal adhesion plaque provides a mechanism for the regulation of cellul ar adhesive strength. Using interference reflection microscopy, we found th at activation of phosphoinositide 3-kinase (PI 3-kinase) by PDGF induces th e dissipation of focal adhesions. Loss of this close apposition between the cell membrane and the extracellular matrix coincided with a redistribution of alpha-actinin and vinculin from the focal adhesion complex to the Trito n X-100-soluble fraction. In contrast, talin and paxillin remained localize d to focal adhesions, suggesting that activation of PI 3-kinase induced a r estructuring of the plaque rather than complete dispersion. Furthermore, ph osphatidylinositol (3,4,5)-trisphosphate (PtdIns (3,4,5)-P-3), a lipid prod uct of PI 3-kinase, was sufficient to induce restructuring of the focal adh esion plaque. We also found that PtdIns (3,4,5)-P3 binds to cr-actinin in P DGF-treated cells. Further evidence demonstrated that activation of PI 3-ki nase by PDGF induced a decrease in the association of ol-actinin with the i ntegrin beta subunit, and that PtdIns (3,4,5)-P-3 could disrupt this intera ction in vitro. Modification of focal adhesion structure by PI 3-kinase and its lipid product, PtdIns (3,4,5)-P-3, has important implications for the regulation of cellular adhesive strength and motility.