title: Trafficking of green fluorescent protein-tagged SNARE proteins in HSY cells.
abstract: SNARE proteins are widely accepted to be involved in the docking and fusion process of intracellular vesicle trafficking. VAMP-2, syntaxin-4, and SNAP-23 are plausible candidate SNARE proteins for non-neuronal exocytosis. Thus, we examined the localization, protein-protein interaction, and intracellular trafficking of these proteins by expressing them as green fluorescent protein (GFP)- and FLAG-tagged fusion proteins in various cells, including HSY cells, a human parotid epithelial cell line. GFP-VAMP-2 was ex-pressed strongly in the Golgi area and weakly on the plasma membrane. Although GFP-SNAP-23 seemed to be expressed universally in the cytosol, the GFP signal was clearly seen on the plasma membrane, when soluble GFP-SNAP-23 was removed by treatment with saponin. GFP-syntaxin-4 was undetectable on the plasma membrane but was strongly expressed on unidentified unusually large vesicles. GFP-syntaxin-4 without its transmembrane domain was still incompletely soluble and observed as aggregates. When syntaxin-4 and munc18c were coexpressed, syntaxin-4 was translocated at least in part to the plasma membrane. The protein-protein interaction between syntaxin-4 and VAMP-2 with their transmembrane domains was markedly inhibited on coexpression of munc18c. These results suggest that munc18c plays an important role in the trafficking of syntaxin-4 to its proper destination by preventing premature interactions with other proteins, including SNARE proteins.
authors.affiliation: Department of Oral Biochemistry, School of Dentistry, Health Sciences University of Hokkaido, Tobetsu, Hokkaido 061-0293. takuma@hoku-iryo-u.ac.jp
authors.forename: Taishin
authors.initials: T
authors.lastname: Takuma
authors.forename: Toshiya
authors.initials: T
authors.lastname: Arakawa
authors.forename: Miki
authors.initials: M
authors.lastname: Okayama
authors.forename: Itaru
authors.initials: I
authors.lastname: Mizoguchi
authors.forename: Akihiko
authors.initials: A
authors.lastname: Tanimura
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Tajima
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D049452:Green Fluorescent Proteins; D006801:Humans; D066298:In Vitro Techniques; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism*; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D011233:Precipitin Tests; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000378:metabolism; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism*; D033921:Vesicular Transport Proteins
chemical_list: D002352:Carrier Proteins; D008164:Luminescent Proteins; D008565:Membrane Proteins; D051938:Munc18 Proteins; D009419:Nerve Tissue Proteins; D011506:Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D050683:R-SNARE Proteins; D011993:Recombinant Fusion Proteins; C100493:SNAP23 protein, human; D033921:Vesicular Transport Proteins; D049452:Green Fluorescent Proteins