THE INTERACTION OF THE CELL-CONTACT PROTEINS VASP AND VINCULIN IS REGULATED BY PHOSPHATIDYLINOSITOL-4,5-BISPHOSPHATE

Background: Focal adhesion sites are cell-matrix contacts that are reg ulated by phosphatidylinositol-4,5-bisphosphate (PIP2)-dependent pathw ays. Vinculin is a major structural component of these sites and is th ought to be engaged in multiple ligand interactions at the cytoplasmic face of these contacts. Cytoplasmic vinculin is considered to be, ina ctive due to its closed conformation involving intramolecular head-tai l interactions. Recently, the vasodilator-stimulated phosphoprotein (V ASP), a substrate of cyclic AMP-dependent or cyclic GMP-dependent kina ses and a component of focal adhesion sites, was shown to bind to vinc ulin. Results: VASP-vinculin complexes could be immunoprecipitated fro m cell lysates and, using immunofluorescence, both proteins were found to colocalize in nascent focal adhesions. Consistent with the view th at vinculin must be activated at these sites, we found that PiP(2), le vels of which are elevated during the early stages of adhesion, bound to two discrete regions in the vinculin tail, disrupting the intramole cular head-tail interaction and inducing vinculin oligomerization. Vin culin-VASP complex formation was greatly enhanced by PIP, and both the EVH1 and EVH2 domains of VASP participated in vinculin binding. Concl usions: Focal contact assembly involves interaction between VASP and v inculin, which is enhanced by PIP2-induced vinculin activation and oli gomerization. Given that vinculin and VASP both bind to F-actin, vincu lin-VASP complexes might bundle the distal ends of actin filaments in focal contacts. We propose that PIP2-dependent signalling modulates mi crofilament organization at cellular adhesion sites by regulating vinc ulin-VASP complexes. (C) Current Biology Ltd ISSN 0960-9822.