title: Microglia/macrophage-specific protein Iba1 binds to fimbrin and enhances its actin-bundling activity.
abstract: Ionized calcium binding adaptor molecule 1 (Iba1) is a microglia/macrophage-specific calcium-binding protein. Iba1 has the actin-bundling activity and participates in membrane ruffling and phagocytosis in activated microglia. In order to understand the Iba1-related intracellular signalling pathway in greater detail, we employed a yeast two-hybrid screen to isolate an Iba1-interacting molecule and identified another actin-bundling protein, L-fimbrin. In response to stimulation, L-fimbrin accumulated and co-localized with Iba1 in membrane ruffles induced by M-CSF-stimulation and phagocytic cups formed by IgG-opsonized beads in microglial cell line MG5. L-fimbrin was shown to associate with Iba1 in cell lysate of COS-7 expressing L-fimbrin and Iba1. By using purified proteins, direct binding of Iba1 to L-fimbrin was demonstrated by immunoprecipitation, glutathione S-transferase pull-down assays and ligand overlay assays. The binding of Iba1 was also found to increase the actin-bundling activity of L-fimbrin. These results indicate that Iba1 forms complexes with L-fimbrin in membrane ruffles and phagocytic cups, and suggest that Iba1 co-operates with L-fimbrin in modulating actin reorganization to facilitate cell migration and phagocytosis by microglia.
authors.affiliation: Department of Neurochemistry, National Institute of Neuroscience, Tokyo, Japan. kohsaka@ncnp.go.jp
authors.forename: Keiko
authors.initials: K
authors.lastname: Ohsawa
authors.forename: Yoshinori
authors.initials: Y
authors.lastname: Imai
authors.forename: Yo
authors.initials: Y
authors.lastname: Sasaki
authors.forename: Shinichi
authors.initials: S
authors.lastname: Kohsaka
mesh_terms: D000199:Actins / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD; D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D030161:Avian Proteins; D019771:Axotomy / Q000379:methods; D051926:Basigin; D001798:Blood Proteins; D015153:Blotting, Western; D001921:Brain / Q000166:cytology / Q000378:metabolism / Q000473:pathology; D019556:COS Cells; D002118:Calcium / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D002478:Cells, Cultured; D002522:Chlorocebus aethiops; D004268:DNA-Binding Proteins; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000494:pharmacology; D005154:Facial Nerve; D049452:Green Fluorescent Proteins; D007074:Immunoglobulin G / Q000494:pharmacology; D007150:Immunohistochemistry; D008164:Luminescent Proteins / Q000378:metabolism; D016173:Macrophage Colony-Stimulating Factor / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000737:chemistry / Q000378:metabolism*; D008840:Microfilament Proteins; D017628:Microglia / Q000378:metabolism; D008845:Microinjections; D009154:Mutation; D010957:Plasmids / Q000737:chemistry; D011233:Precipitin Tests; D011506:Proteins / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011994:Recombinant Proteins / Q000096:biosynthesis; D013997:Time Factors; D020798:Two-Hybrid System Techniques
chemical_list: C112986:AIF1 protein, human; D000199:Actins; C100745:Aif1 protein, rat; D015703:Antigens, CD; D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D030161:Avian Proteins; D001798:Blood Proteins; C102624:Bsg protein, Gallus gallus; C079432:Bsg protein, rat; D002135:Calcium-Binding Proteins; D004268:DNA-Binding Proteins; D007074:Immunoglobulin G; D008164:Luminescent Proteins; D008562:Membrane Glycoproteins; D008840:Microfilament Proteins; D011506:Proteins; D011994:Recombinant Proteins; C026742:plastin; D051926:Basigin; D049452:Green Fluorescent Proteins; D004533:Egtazic Acid; D016173:Macrophage Colony-Stimulating Factor; D002118:Calcium