title: Ezrin promotes actin assembly at the phagosome membrane and regulates phago-lysosomal fusion.
abstract: Phagosome maturation is defined as the process by which phagosomes fuse sequentially with endosomes and lysosomes to acquire an acidic pH and hydrolases that degrade ingested particles. While the essential role of actin cytoskeleton remodeling during particle internalization is well established, its role during the later stages of phagosome maturation remains largely unknown. We have previously shown that purified mature phagosomes assemble F-actin at their membrane, and that the ezrin-radixin-moesin (ERM) proteins ezrin and moesin participate in this process. Moreover, we provided evidence that actin assembly on purified phagosomes stimulates their fusion with late endocytic compartments in vitro. In this study, we further investigated the role of ezrin in phagosome maturation. We engineered a structurally open form of ezrin and demonstrated that ezrin binds directly to the actin assembly promoting factor N-WASP (Neural Wiskott-Aldrich Syndrome Protein) by its FERM domain. Using a cell-free system, we found that ezrin stimulates F-actin assembly on purified phagosomes by recruiting the N-WASP-Arp2/3 machinery. Accordingly, we showed that the down-regulation of ezrin activity in macrophages by a dominant-negative approach caused reduced F-actin accumulation on maturing phagosomes. Furthermore, using fluorescence and electron microscopy, we found that ezrin is required for the efficient fusion between phagosomes and lysosomes. Live-cell imaging analysis supported the notion that ezrin is necessary for the fusogenic process itself, promoting the transfer of the lysosome content into the phagosomal lumen.
authors.affiliation: Department of Cell Biology and Biophysics, European Molecular Biology Laboratory, Heidelberg, Germany. sabrina.marion@inserm.fr
authors.forename: Sabrina
authors.initials: S
authors.lastname: Marion
authors.forename: Eik
authors.initials: E
authors.lastname: Hoffmann
authors.forename: Daniela
authors.initials: D
authors.lastname: Holzer
authors.forename: Christophe
authors.initials: C
authors.lastname: Le Clainche
authors.forename: Marianne
authors.initials: M
authors.lastname: Martin
authors.forename: Martin
authors.initials: M
authors.lastname: Sachse
authors.forename: Iva
authors.initials: I
authors.lastname: Ganeva
authors.forename: Paul
authors.initials: P
authors.lastname: Mangeat
authors.forename: Gareth
authors.initials: G
authors.lastname: Griffiths
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000378:metabolism; D000199:Actins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D002460:Cell Line; D045744:Cell Line, Tumor; D002474:Cell-Free System; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000378:metabolism*; D003599:Cytoskeleton / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D008247:Lysosomes / Q000378:metabolism / Q000502:physiology*; D008264:Macrophages / Q000378:metabolism; D008561:Membrane Fusion / Q000502:physiology*; D051379:Mice; D010588:Phagosomes / Q000378:metabolism / Q000502:physiology*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D051316:Wiskott-Aldrich Syndrome Protein / Q000378:metabolism; D000099149:Ezrin
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D003598:Cytoskeletal Proteins; D051316:Wiskott-Aldrich Syndrome Protein; D000099149:Ezrin