title: Rab27 effector granuphilin promotes the plasma membrane targeting of insulin granules via interaction with syntaxin 1a.
abstract: Secretory vesicle exocytosis is a highly regulated process involving vesicle targeting, priming, and membrane fusion. Rabs and SNAREs play a central role in executing these processes. We have shown recently that Rab27a and its effector, granuphilin, are involved in the exocytosis of insulin-containing secretory granules through a direct interaction with the plasma membrane syntaxin 1a in pancreatic beta cells. Here, we demonstrate that fluorescence-labeled insulin granules are peripherally accumulated in cells overexpressing granuphilin. The peripheral location of granules is well overlapped with both localizations of granuphilin and syntaxin 1a. The plasma membrane targeting of secretory granules is promoted by wild-type granuphilin but not by granuphilin mutants that are defective in binding to either Rab27a or syntaxin 1a. Granuphilin directly binds to the H3 domain of syntaxin 1a containing its SNARE motif. Moreover, introduction of the H3 domain into beta cells induces a dissociation of the native granuphilin-syntaxin complex and a marked reduction of newly docked granules. These results indicate that granuphilin plays a role in tethering insulin granules to the plasma membrane by an interaction with both Rab27a and syntaxin 1a. The complex formation of these three proteins may contribute to the specificity of the targeting process during the exocytosis of insulin granules.
authors.affiliation: Laboratory of Gene Analysis and Laboratory of Gene Engineering, Institute for Molecular and Cellular Regulation, Gunma University, Maebashi, Gunma 371-8512, Japan.
authors.forename: Seiji
authors.initials: S
authors.lastname: Torii
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Takeuchi
authors.forename: Shinya
authors.initials: S
authors.lastname: Nagamatsu
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Izumi
mesh_terms: D000818:Animals; D000954:Antigens, Surface / Q000737:chemistry*; D002352:Carrier Proteins / Q000737:chemistry* / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism*; D004247:DNA / Q000737:chemistry; D018076:DNA, Complementary / Q000378:metabolism; D005089:Exocytosis; D019084:Fluorescent Antibody Technique, Indirect; D007328:Insulin / Q000378:metabolism*; D007700:Kinetics; D051379:Mice; D008856:Microscopy, Fluorescence; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000737:chemistry*; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D013347:Subcellular Fractions; D050827:Syntaxin 1; D014162:Transfection; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D000954:Antigens, Surface; D002352:Carrier Proteins; D018076:DNA, Complementary; D007328:Insulin; D009419:Nerve Tissue Proteins; C512779:SYTL4 protein, human; C494214:Stx1a protein, mouse; D050827:Syntaxin 1; C122015:Sytl4 protein, mouse; D033921:Vesicular Transport Proteins; D000075745:rab27 GTP-Binding Proteins; D004247:DNA; C512962:Rab27a protein, mouse; D020691:rab GTP-Binding Proteins