Membrane Lipids in Migrating Cells Illuminated by Molecular Sensors and Chemical Actuators

Abstract

Cell motility plays a vital role in both normal physiology and the pathogenesis of many diseases. We have recently shown that cell motility requires the signal transduction network serving as a pacemaker to drive cytoskeletal activities. This network features spontaneous firing that promotes the formation of sustained protrusions which govern random cell migration. However, a molecular identity of the signal excitability remains unknown. Phosphatidylinositol 4,5‐bisphosphate (PIP2) is one of the eight phosphoinositide species consisting of the cellular membrane structures, and well characterized as a substrate of PI3K that produces phosphatidylinositol 3,4,5‐trisphosphate (PIP3). PIP2 has long been viewed as a general source of negative charges, offering docking sites for cytosolic proteins through electrostatic interactions. Here, we examine the roles of PIP2 in this signal transduction network using a Dictyostelium cell as a model. To specifically manipulate PIP2 levels with high spatiotemporal precision, we rapidly recruited a yeast‐derived PIP2‐specific 5‐phosphotase, Inp54p, to the plasma membrane using the chemically‐induced dimerization (CID) system. Following the Inp54p recruitment, the cells went into a heterogeneous oscillation between a spreading and a crunching morphology. While a PIP3 phosphatase PTEN fell off the membrane when cells spread, it rebounded to the membrane as cells crunched. Other signaling events such as Ras activation, PIP3 production, and actin polymerization are largely induced along the periphery as cells spread. Together with a series of pharmacological experiments, our results indicate that PIP2 impedes protrusion events through multiple redundant pathways, providing a driving force for the excitable signaling network.