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.
Highlights
Parotid gland acinar cells are typical exocrine cells that secrete serous saliva containing amylase
To investigate the possible involvement of small GTPase Rab27A/B and its effectors (Slp and Slac2) in amylase release from parotid acinar cells, we first investigated their expression in rat parotid glands by immunoblot analyses using specific antibodies against Rab27A, Rab27B, Slp1-5 or Slac2-a/b/c
Control IgG had no significant effect on either IPR-stimulated or basal amylase release when applied at concentrations up to 100 μg/ml. These results strongly indicate that the interaction of small GTPase Rab27B with Slac2-c is a crucial process for regulating granule exocytosis (i.e. IPR-stimulated amylase release) in rat parotid acinar cells
Summary
Parotid gland acinar cells are typical exocrine cells that secrete serous saliva containing amylase. The cells have many secretory granules containing proteins such as amylase, and the exocytosis of these proteins is induced by both the sympathetic and the parasympathetic nervous stimulation systems. Normal amylase release kinetics has been observed in response to secretory stimulation even in Rab3D-deficient mice; Rab3D seems to control the size of the secretory granules, rather than exocytosis itself (Riedel et al, 2002). This finding strongly indicates the presence of additional Rab(s) that regulate secretory granule exocytosis in the parotid gland
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
