title: Cdc42 and RhoB activation are required for mannose receptor-mediated phagocytosis by human alveolar macrophages.
abstract: Human alveolar macrophages (AMs) phagocytose Pneumocystis (Pc) organisms predominantly through mannose receptors, although the molecular mechanism mediating this opsonin-independent process is not known. In this study, using AMs from healthy individuals, Pc phagocytosis was associated with focal F-actin polymerization and Cdc42, Rac1, and Rho activation in a time-dependent manner. Phagocytosis was primarily dependent on Cdc42 and RhoB activation (as determined by AM transfection with Cdc42 and RhoB dominant-negative alleles) and mediated predominantly through mannose receptors (as determined by siRNA gene silencing of AM mannose receptors). Pc also promoted PAK-1 phosphorylation, which was also dependent on RhoGTPase activation. HIV infection of AMs (as a model for reduced mannose receptor expression and function) was associated with impaired F-actin polymerization, reduced Cdc42 and Rho activation, and markedly reduced PAK-1 phosphorylation in response to Pc organisms. In healthy AMs, Pc phagocytosis was partially dependent on PAK activation, but dependent on the Rho effector molecule ROCK. These data provide a molecular mechanism for AM mannose receptor-mediated phagocytosis of unopsonized Pc organisms that appears distinct from opsonin-dependent phagocytic receptors. Reduced AM mannose receptor-mediated Cdc42 and Rho activation in the context of HIV infection may represent a mechanism that contributes to the pathogenesis of opportunistic pneumonia.
authors.affiliation: Division of Pulmonary and Critical Care Medicine, Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA 02115, USA.
authors.forename: Jianmin
authors.initials: J
authors.lastname: Zhang
authors.forename: Jinping
authors.initials: J
authors.lastname: Zhu
authors.forename: Xia
authors.initials: X
authors.lastname: Bu
authors.forename: Melanie
authors.initials: M
authors.lastname: Cushion
authors.forename: T Bernard
authors.initials: TB
authors.lastname: Kinane
authors.forename: Hava
authors.initials: H
authors.lastname: Avraham
authors.forename: Henry
authors.initials: H
authors.lastname: Koziel
mesh_terms: D000199:Actins / Q000378:metabolism; D048868:Adaptor Proteins, Signal Transducing; D015153:Blotting, Western; D001992:Bronchoalveolar Lavage Fluid / Q000166:cytology; D001999:Bronchoscopy; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins; D004789:Enzyme Activation; D004797:Enzyme-Linked Immunosorbent Assay; D016650:Fluorescein-5-isothiocyanate; D005456:Fluorescent Dyes; D020868:Gene Silencing; D015658:HIV Infections / Q000150:complications / Q000276:immunology* / Q000821:virology; D015497:HIV-1 / Q000302:isolation & purification; D006801:Humans; D007113:Immunity, Innate; D037181:Lectins, C-Type / Q000378:metabolism*; D008262:Macrophage Activation; D016676:Macrophages, Alveolar / Q000276:immunology* / Q000382:microbiology; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins / Q000378:metabolism*; D018613:Microscopy, Confocal; D010587:Phagocytosis / Q000187:drug effects / Q000502:physiology; D011010:Pneumocystis / Q000502:physiology; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D034741:RNA, Small Interfering / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000378:metabolism*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection; D015054:Zymosan / Q000494:pharmacology; D020764:cdc42 GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*; D054462:p21-Activated Kinases; D020741:rho GTP-Binding Proteins; D020743:rhoB GTP-Binding Protein / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D003598:Cytoskeletal Proteins; D005456:Fluorescent Dyes; D037181:Lectins, C-Type; D000090323:Mannose Receptor; D037241:Mannose-Binding Lectins; D034741:RNA, Small Interfering; D011956:Receptors, Cell Surface; C075598:CDC42EP1 protein, human; D015054:Zymosan; C515903:PAK1 protein, human; D017346:Protein Serine-Threonine Kinases; D054462:p21-Activated Kinases; D020764:cdc42 GTP-Binding Protein; D020741:rho GTP-Binding Proteins; D020743:rhoB GTP-Binding Protein; D016650:Fluorescein-5-isothiocyanate; D013755:Tetradecanoylphorbol Acetate