Single-molecule imaging of PI(4,5)P and PTEN in vitro reveals a positive feedback mechanism for PTEN membrane binding.

PTEN, a 3-phosphatase of phosphoinositide, regulates asymmetric PI(3,4,5)P signaling for the anterior-posterior polarization and migration of motile cells. PTEN acts through posterior localization on the plasma membrane, but the mechanism for this accumulation is poorly understood. Here we developed an in vitro single-molecule imaging assay with various lipid compositions and use it to demonstrate that the enzymatic product, PI(4,5)P, stabilizes PTEN's membrane-binding. The dissociation kinetics and lateral mobility of PTEN depended on the PI(4,5)P density on artificial lipid bilayers. The basic residues of PTEN were responsible for electrostatic interactions with anionic PI(4,5)P and thus the PI(4,5)P-dependent stabilization. Single-molecule imaging in living Dictyostelium cells revealed that these interactions were indispensable for the stabilization in vivo, which enabled efficient cell migration by accumulating PTEN posteriorly to restrict PI(3,4,5)P distribution to the anterior. These results suggest that PI(4,5)P-mediated positive feedback and PTEN-induced PI(4,5)P clustering may be important for anterior-posterior polarization.