Role of PIP2-Dependent Membrane Interactions in Vinculin Activation, Motility and Force Transmission

Abstract

Vinculin is an essential and abundant cytoskeletal protein localized to focal adhesions and cell-cell contacts, where it participates in the linkage of transmembrane receptors to the actin cytoskeleton to control cell survival and migration. Loss of vinculin results in increased cell migration, apoptotic resistance, and the acquisition of tumorigenic properties. Mutations in vinculin and its splice variant, metavinculin, are associated with cardiac disease. Vinculin consists of a head domain (Vh) and a tail domain (Vt) that form autoinhibitory interactions in its inactive state, but release upon activation, exposing phosphorylation, protein and phosphoinositol 4,5-bisphosphate (PIP2) binding sites. The interaction of vinculin with PIP2 is believed critical for its function, however, it is currently unclear how vinculin specifically recognizes PIP2 and regulates vinculin. Vt forms an antiparallel five-helix bundle with amino-terminal (NT) and carboxyl terminal (CT) extensions. While a crystal structure of an oligomerized Vt mutant complexed to a short chain PIP2 has recently been published (Chinthalapudi et al. (JCB, 2014)), the structure is incompatible with membrane insertion. We propose an alternative model using experimental data, molecular docking and dynamics simulations and provide validation of the model through biophysical and biochemical analyses. In our model, the PIP2 head group binds to the Vt basic collar, and promotes release of Vt's strap and CT to facilitate membrane insertion. The role of vinculin/PIP2 interaction in mediating vinculin activation, localization, cell migration, force sensing and transmission has also been characterized using cell microscopy, including super-resolution microscopy approaches, by examining WT and PIP2-deficient full length vinculin in knockout cells. Information derived from these analyses will result in an unprecedented understanding of vinculin function from the molecular to the cellular level and will enable us to build more comprehensive models of vinculin membrane interactions.