title: Involvement of syntaxin 18, an endoplasmic reticulum (ER)-localized SNARE protein, in ER-mediated phagocytosis.
abstract: The endoplasmic reticulum (ER) is thought to play an important structural and functional role in phagocytosis. According to this model, direct membrane fusion between the ER and the plasma or phagosomal membrane must precede further invagination, but the exact mechanisms remain elusive. Here, we investigated whether various ER-localized SNARE proteins are involved in this fusion process. When phagosomes were isolated from murine J774 macrophages, we found that ER-localized SNARE proteins (syntaxin 18, D12, and Sec22b) were significantly enriched in the phagosomes. Fluorescence and immuno-EM analyses confirmed the localization of syntaxin 18 in the phagosomal membranes of J774 cells stably expressing this protein tagged to a GFP variant. To examine whether these SNARE proteins are required for phagocytosis, we generated 293T cells stably expressing the Fc gamma receptor, in which phagocytosis occurs in an IgG-mediated manner. Expression in these cells of dominant-negative mutants of syntaxin 18 or D12 lacking the transmembrane domain, but not a Sec22b mutant, impaired phagocytosis. Syntaxin 18 small interfering RNA (siRNA) selectively decreased the efficiency of phagocytosis, and the rate of phagocytosis was markedly enhanced by stable overexpression of syntaxin 18 in J774 cells. Therefore, we conclude that syntaxin 18 is involved in ER-mediated phagocytosis, presumably by regulating the specific and direct fusion of the ER and plasma or phagosomal membranes.
authors.affiliation: Department of Cell Science, Institute of Biomedical Sciences, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan. hatsu@fmu.ac.jp
authors.forename: Kiyotaka
authors.initials: K
authors.lastname: Hatsuzawa
authors.forename: Taku
authors.initials: T
authors.lastname: Tamura
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Hiromi
authors.initials: H
authors.lastname: Hashimoto
authors.forename: Sachihiko
authors.initials: S
authors.lastname: Yokoya
authors.forename: Megumi
authors.initials: M
authors.lastname: Miura
authors.forename: Hisao
authors.initials: H
authors.lastname: Nagaya
authors.forename: Ikuo
authors.initials: I
authors.lastname: Wada
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015703:Antigens, CD / Q000276:immunology; D022181:COP-Coated Vesicles / Q000378:metabolism; D002462:Cell Membrane / Q000378:metabolism; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D008264:Macrophages / Q000166:cytology / Q000648:ultrastructure; D051379:Mice; D008969:Molecular Sequence Data; D009842:Oligopeptides; D010455:Peptides / Q000378:metabolism; D010587:Phagocytosis / Q000502:physiology*; D010588:Phagosomes / Q000648:ultrastructure; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D050765:Qa-SNARE Proteins / Q000737:chemistry / Q000378:metabolism*; D050683:R-SNARE Proteins / Q000378:metabolism; D034741:RNA, Small Interfering; D017452:Receptors, IgG / Q000276:immunology
chemical_list: D015703:Antigens, CD; C080568:Fc gamma receptor IIA; D009842:Oligopeptides; D010455:Peptides; D050765:Qa-SNARE Proteins; D050683:R-SNARE Proteins; D034741:RNA, Small Interfering; D017452:Receptors, IgG; C432415:Sec22b protein, mouse; C085706:FLAG peptide