REGULATION OF VINCULIN BINDING TO TALIN AND ACTIN BY PHOSPHATIDYL-INOSITOL-4-5-BISPHOSPHATE

VINCULIN, a prominent cytoskeletal protein at cell-substrate adhesions (focal adhesions) and cell-cell adhesions (adherens junctions)(1), in teracts with other cytoskeletal proteins, including talin and actin(2, 3). An intramolecular interaction between the head and tail domains of vinculin masks the binding sites for both proteins(4,5). The exposure of cryptic binding sites may be important for promoting focal adhesio n assembly. Several agents that induce the formation of focal adhesion s act through the GTP-binding protein Rho(6-9), which elevates phospha tidylinositol-4,5-bisphosphate (PtdInsP(2)) levels by activating phosp hatidylinositol-4-phosphate-5-OH kinase (PtdIns-5-OH kinase)(10). PtdI nsP(2) regulates several actin-binding proteins, including profilin(11 ), gelsolin(12) and alpha-actinin(13), and interacts with vinculin(14, 15). Here we report that PtdInsP(2) dissociates vinculin's head-tail i nteraction, unmasking its talin- and actin-binding sites. Microinjecti on of antibodies against PtdInsP(2) inhibit assembly of stress fibres and focal adhesions.