SHIP1 partitions between cortical oscillations and membrane puncta to regulate neutrophil chemotaxis

Abstract

As frontline defenders in the innate immune system, neutrophils traffic to sites of infection by detecting chemical gradients, polarizing, and migrating towards foreign pathogens. This requires communication between small GTPases, phosphatidylinositol phosphate (PIP) lipids, and the actin cytoskeleton to generate forces that drive leading-edge membrane protrusions. Central to the coordination of these signaling events is the hematopoietic-cell-specific 5-inositol lipid phosphatase SHIP1 (or INPP5D), which shapes PIP lipid domains by dephosphorylating phosphatidylinositol-(3,4,5)-trisphosphate (PIP3) to generate PI(3,4)P2. To decipher mechanisms controlling SHIP1 membrane localization during neutrophil chemotaxis, we combined genetic manipulation of SHIP1 with live cell Total Internal Reflection Fluorescence (TIRF) microscopy. Our results reveal two modes of SHIP1 localization: (1) cortical oscillations regulated by the membrane curvature sensing protein FBP17, and (2) dynamic membrane puncta organized by the adaptor protein Nck1. Localization to both membrane structures requires the proline-rich C-terminal domain (CTD) of SHIP1. Neutrophil-differentiated HL60 cells solely expressing a cytoplasmic localized SHIP1 CTD deletion mutant exhibit chemotaxis defects that phenocopy complete SHIP1 loss of function. Overall, this work reveals a dual mechanism by which SHIP1 integrates signals from membrane curvature sensing and adaptor proteins to control neutrophil cell migration.