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

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 (PIP 2 ) 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 (PIP 3 ). PIP 2 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 PIP 2 in this signal transduction network using a Dictyostelium cell as a model. To specifically manipulate PIP 2 levels with high spatiotemporal precision, we rapidly recruited a yeast‐derived PIP 2 ‐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 PIP 3 phosphatase PTEN fell off the membrane when cells spread, it rebounded to the membrane as cells crunched. Other signaling events such as Ras activation, PIP 3 production, and actin polymerization are largely induced along the periphery as cells spread. Together with a series of pharmacological experiments, our results indicate that PIP 2 impedes protrusion events through multiple redundant pathways, providing a driving force for the excitable signaling network.