Mouse Profilin 2 Regulates Endocytosis and Competes with SH3 Ligand Binding to Dynamin 1

Ralph Gareus,Alessia Di Nardo,Vladimir Rybin,Walter Witke

doi:10.1074/jbc.m503528200

Abstract

Mammalian profilins are abundantly expressed actin monomer-binding proteins, highly conserved with respect to their affinities for G-actin, poly-L-proline, and phosphoinositides. Profilins associate with a large number of proline-rich proteins; the physiological significance and regulation of which is poorly understood. Here we show that profilin 2 associates with dynamin 1 via the C-terminal proline-rich domain of dynamin and thereby competes with the binding of SH3 ligands such as endophilin, amphiphysin, and Grb2, thus interfering with the assembly of the endocytic machinery. We also present a novel role for the brain-specific mouse profilin 2 as a regulator of membrane trafficking. Overexpression of profilin 2 inhibits endocytosis, whereas lack of profilin 2 in neurons results in an increase in endocytosis and membrane recycling. Phosphatidylinositol 4,5-bisphosphate releases profilin 2 from the profilin 2-dynamin 1 complex as well as from the profilin 2-actin complex, suggesting that profilin 2 is diverging the phosphoinositide signaling pathway to actin polymerization as well as endocytosis.

Highlights

In addition to binding to actin, all profilins identified so far except for the profilin of Vaccinia virus [8] and the mouse profilin IIB splice form [9] have been shown to bind to poly-L-proline, an ability of profilin proven to be essential in yeast [10, 11]
We show that PtdInsP2 is a common signal to release profilin 2 from dynamin 1 as well as G-actin, providing a mechanism by which activation of the endocytic machinery and actin polymerization can be orchestrated at PtdInsP2rich membrane domains
To address this hypothesis in more detail, we focused on the biochemical aspects of the profilin 2-dynamin 1 interaction

Summary

Introduction

In addition to binding to actin, all profilins identified so far except for the profilin of Vaccinia virus [8] and the mouse profilin IIB splice form [9] have been shown to bind to poly-L-proline, an ability of profilin proven to be essential in yeast [10, 11]. Profilin 2, in particular, interacts with ligands involved in signal transduction, membrane trafficking, and vesicle recycling such as ROCK2, synapsins, POP-130/CyFIP1, and dynamin 1. These findings suggest a not yet recognized additional role for profilin 2 in membrane trafficking. To assemble the endocytic machinery, which initiates changes in membrane curvature, dynamin 1 interacts with a number of effector molecules such as amphiphysin [16] and endophilin [17]. We show that PtdInsP2 is a common signal to release profilin 2 from dynamin 1 as well as G-actin, providing a mechanism by which activation of the endocytic machinery and actin polymerization can be orchestrated at PtdInsP2rich membrane domains

Methods

Results

Conclusion