title: Redistribution of Rab27-specific effector Slac2-c, but not Slp4-a, after isoproterenol-stimulation in rat parotid acinar cells.
abstract: Small GTPase Rab27 has been implicated in the regulation of different types of membrane trafficking, including melanosome transport and various regulated secretion events. We have previously shown that Rab27 and its effectors, Slac2-c/MyRIP and Slp4-a/granuphilin-a, are involved in the control of isoproterenol (IPR)-induced amylase release from rat parotid acinar cells. The ability of Rab to interact with the specific effectors is important. However, little is known about the fate of these effectors after beta-adrenergic stimulation in parotid acinar cells. The present study investigated changes in intracellular redistribution of Slac2-c and Slp4-a in parotid acinar cells after IPR treatment. Subcellular fractionation studies detected Slac2-c and Slp4-a in the apical plasma membrane (APM) and secretory granules under resting conditions. After 5min of IPR treatment, Slac2-c was rapidly recruited to the luminal site, but after 30 min, the amount of Slac2-c in the APM fraction was reduced by approximately 80% compared to the increased level after 5 min of IPR treatment. Such reductions in Slac2-c are likely caused by the translocation of Slac2-c from the APM to the cytosol. In addition, we found that Slac2-c in the cytosolic fraction, but not other fractions, disappeared in the presence of Ca(2+). Since Slac2-c contains multiple PEST-like sequences (i.e., potential signals for rapid protein degradation), we suggest that Slac2-c is Ca(2+)-dependently proteolyzed in the cytosol after exocytosis. In contrast, intracellular localization and expression levels of Slp4-a in parotid acinar cells were unaltered even after beta-stimulation, indicating completely different fates for the two Rab27 effectors after beta-stimulation.
authors.affiliation: Department of Biochemistry, School of Life Dentistry at Niigata, The Nippon Dental University, 1-8, Hamaura-cho, Chuo-ku, Niigata 951-8580, Japan. imaiak@ngt.ndu.ac.jp
authors.forename: Akane
authors.initials: A
authors.lastname: Imai
authors.forename: Mitsunori
authors.initials: M
authors.lastname: Fukuda
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
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology*; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects; D002478:Cells, Cultured; D007545:Isoproterenol / Q000494:pharmacology*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D010306:Parotid Gland / Q000187:drug effects* / Q000378:metabolism; D015221:Potassium Channels / Q000378:metabolism*; D000081033:Potassium Channels, Sodium-Activated; D051381:Rats; D033921:Vesicular Transport Proteins / Q000378:metabolism*; D020691:rab GTP-Binding Proteins / Q000378:metabolism*
chemical_list: D000318:Adrenergic beta-Agonists; D009419:Nerve Tissue Proteins; D015221:Potassium Channels; D000081033:Potassium Channels, Sodium-Activated; C512778:Sytl4 protein, rat; D033921:Vesicular Transport Proteins; C000626167:kcnt1 protein, rat; C512956:Rab27b protein, rat; D020691:rab GTP-Binding Proteins; D007545:Isoproterenol