Control of actin polymerization via the coincidence of phosphoinositides and high membrane curvature

Abstract

The conditional use of actin during clathrin-mediated endocytosis in mammalian cells suggests that the cell controls whether and how actin is used. Using a combination of biochemical reconstitution and mammalian cell culture, we elucidate a mechanism by which the coincidence of PI(4,5)P2 and PI(3)P in a curved vesicle triggers actin polymerization. At clathrin-coated pits, PI(3)P is produced by the INPP4A hydrolysis of PI(3,4)P2, and this is necessary for actin-driven endocytosis. Both Cdc42⋅guanosine triphosphate and SNX9 activate N-WASP–WIP- and Arp2/3-mediated actin nucleation. Membrane curvature, PI(4,5)P2, and PI(3)P signals are needed for SNX9 assembly via its PX–BAR domain, whereas signaling through Cdc42 is activated by PI(4,5)P2 alone. INPP4A activity is stimulated by high membrane curvature and synergizes with SNX9 BAR domain binding in a process we call curvature cascade amplification. We show that the SNX9-driven actin comets that arise on human disease–associated oculocerebrorenal syndrome of Lowe (OCRL) deficiencies are reduced by inhibiting PI(3)P production, suggesting PI(3)P kinase inhibitors as a therapeutic strategy in Lowe syndrome.J.L. Gallop is supported by a Wellcome Trust Research Career Development Fellowship (grant WT095829AIA). F.  Daste, A.  Walrant, J.R. Gadsby, and J. Mason are supported by an H2020 European Research Council Starting Grant (281971) awarded to J.L. Gallop. Gurdon Institute funding is provided by the Wellcome Trust (grant 092096) and Cancer Research UK (grant C6946/A14492). The Swedish Medical Research Council and the Swedish Foundation for Strategic Research supported the work of M.R. Holst and R. Lundmark. S.F. Lee is funded by a Royal Society University Research Fellowship (grant UF120277). M. Mettlen is funded by grant MH73125 to Sandra L. Schmid (University of Texas Southwestern Medical Center)