title: The small GTPase Rab27B regulates amylase release from rat parotid acinar cells.
abstract: Small GTPase Rab is a large family of putative membrane trafficking proteins, and each member is thought to regulate a specific type(s) of membrane trafficking. However, little is known about the involvement of Rab protein(s) in secretory granule exocytosis in exocrine cells or the molecular mechanism underlying this process. We show that Rab27B, a closely related isoform of Rab27A that regulates lysosome-related granule exocytosis in cytotoxic T lymphocytes, is abundantly expressed on amylase-containing secretory granules in rat parotid gland acinar cells. We also identify the putative Rab27B effector protein, Slac2-c (Slp homologue lacking C2 domains-c)/MyRIP, which was originally described as a myosin Va/VIIa and actin binding protein, in rat parotid glands. The results of subcellular fractionation, immunoprecipitation and immunohistochemical studies indicate that the Rab27B-Slac2-c complex is formed on secretory granules in vivo. The introduction of either a specific Rab27 binding domain (i.e. a recombinant Slp homology domain of Slac2-b that specifically binds Rab27A/B but not other Rabs) or functionally blocking antibodies that specifically disrupt Rab27B-Slac2-c complex in vitro strongly inhibited isoproterenol-stimulated amylase release from streptolysin O-permeabilized parotid acinar cells. Our results indicate that the Rab27B-Slac2-c complex is an important constituent of secretory granule exocytosis in parotid acinar cells.
authors.affiliation: Department of Biochemistry, The Nippon Dental University, School of Dentistry at Niigata, 1-8, Hamaura-cho, Niigata 951-8580, Japan.
authors.forename: Akane
authors.initials: A
authors.lastname: Imai
authors.forename: Sumio
authors.initials: S
authors.lastname: Yoshie
authors.forename: Tomoko
authors.initials: T
authors.lastname: Nashida
authors.forename: Hiromi
authors.initials: H
authors.lastname: Shimomura
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
mesh_terms: D000681:Amylases / Q000378:metabolism*; D000818:Animals; D001426:Bacterial Proteins / Q000494:pharmacology; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D005089:Exocytosis; D015151:Immunoblotting; D007150:Immunohistochemistry; D047468:Immunoprecipitation; D008247:Lysosomes / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism / Q000502:physiology*; D010306:Parotid Gland / Q000166:cytology* / Q000378:metabolism*; D011485:Protein Binding; D020033:Protein Isoforms; D017434:Protein Structure, Tertiary; D050683:R-SNARE Proteins; D051381:Rats; D013301:Streptolysins / Q000494:pharmacology; D013347:Subcellular Fractions / Q000378:metabolism; D013602:T-Lymphocytes, Cytotoxic / Q000378:metabolism; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D000075745:rab27 GTP-Binding Proteins
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C501262:MYRIP protein, human; D008565:Membrane Proteins; D008840:Microfilament Proteins; D020033:Protein Isoforms; D050683:R-SNARE Proteins; C512779:SYTL4 protein, human; D013301:Streptolysins; C512778:Sytl4 protein, rat; D033921:Vesicular Transport Proteins; D000075745:rab27 GTP-Binding Proteins; C025964:streptolysin O; D000681:Amylases; C512958:Rab27b protein, mouse; C512956:Rab27b protein, rat; C512962:Rab27a protein, mouse; C512961:Rab27a protein, rat; D020691:rab GTP-Binding Proteins