Coupling Arp2/3 Complex-Mediated Actin Branching and Membrane Deformation by the Exocyst Component Exo70

Abstract

Directional cell migration requires tight coordination of actin assembly and membrane remodeling. However, the molecular mechanism underlying this coordination remains elusive. Here we report that Exo70, a component of the exocyst complex, couples actin assembly and membrane curvature induction for leading edge protrusion and cell migration. Using in vitro pyrene actin assay and dual-color total internal reflection fluorescence (TIRF) microscopy, we found that Exo70 kinetically stimulates the Arp2/3 complex-mediated actin polymerization and branching. This effect of Exo70 on actin is mediated by promoting the interaction of the Arp2/3 complex with WAVE2, a member of the N-WASP/WAVE family of nucleation promoting factors. We also found that Exo70 induces tubular membrane invaginations toward the lumen of synthetic vesicles in vitro and generates protrusions on the surface of cells. Biochemical analyses using Exo70 mutants and independent molecular dynamics simulations based on Exo70 structure reveal that Exo70 generates negative membrane curvature through an oligomerization-based scaffolding mechanism. At the cellular level, both the stimulatory effect of Exo70 on the Arp2/3 complex and the membrane-deformation activity of Exo70 are required for generating lamellipodia and maintaining directional persistence during cell migration. Exo70 thus represents a novel Arp2/3 regulator and membrane-bending protein that couples actin dynamics and plasma membrane remodeling for migration.