Involvement of ezrin/moesin in de novo actin assembly on phagosomal membranes

• DOI: 10.1093/emboj/19.2.199
• Publication Date: 2002-07-26T22:45:25Z
• Authors: Hélène Defacque; Morten Egeberg; Anja Habermann; Maria Diakonova; Christian Roy; Paul Mangeat; Wolfgang Voelter; Gerard Marriott; Jens Pfannstiel; Heinz Faulstich; Gareth Griffiths
• Keywords: 0301 basic medicine; Cytochalasin D; Molecular Sequence Data; Transfection; Membrane Fusion; Cell Line; Ezrin–Radixin–Moesin Family; Mice; 03 medical and health sciences; Phagocytosis; Phagosomes; Health Sciences; Animals; Cellular and Developmental Biology; Microscopy, Immunoelectron; Cytoskeleton; Macrophages; Microfilament Proteins; Molecular; Intracellular Membranes; Phosphoproteins; Actins; Recombinant Proteins; Thymosin; Cytoskeletal Proteins; Kinetics; Latex Beads; Actin Assembly

The current study focuses on the molecular mechanisms responsible for actin assembly on a defined membrane surface: the phagosome. Mature phagosomes were surrounded by filamentous actin in vivo in two different cell types. Fluorescence microscopy was used to study in vitro actin nucleation/polymerization (assembly) on the surface of phagosomes isolated from J774 mouse macrophages. In order to prevent non-specific actin polymerization during the assay, fluorescent G-actin was mixed with thymosin beta4. The cytoplasmic side of phagosomes induced de novo assembly and barbed end growth of actin filaments. This activity varied cyclically with the maturation state of phagosomes, both in vivo and in vitro. Peripheral membrane proteins are crucial components of this actin assembly machinery, and we demonstrate a role for ezrin and/or moesin in this process. We propose that this actin assembly process facilitates phagosome/endosome aggregation prior to membrane fusion.