title: Sec6/8 complexes on trans-Golgi network and plasma membrane regulate late stages of exocytosis in mammalian cells.
abstract: Sec6/8 complex regulates delivery of exocytic vesicles to plasma membrane docking sites, but how it is recruited to specific sites in the exocytic pathway is poorly understood. We identified an Sec6/8 complex on trans-Golgi network (TGN) and plasma membrane in normal rat kidney (NRK) cells that formed either fibroblast- (NRK-49F) or epithelial-like (NRK-52E) intercellular junctions. At both TGN and plasma membrane, Sec6/8 complex colocalizes with exocytic cargo protein, vesicular stomatitis virus G protein (VSVG)-tsO45. Newly synthesized Sec6/8 complex is simultaneously recruited from the cytosol to both sites. However, brefeldin A treatment inhibits recruitment to the plasma membrane and other treatments that block exocytosis (e.g., expression of kinase-inactive protein kinase D and low temperature incubation) cause accumulation of Sec6/8 on the TGN, indicating that steady-state distribution of Sec6/8 complex depends on continuous exocytic vesicle trafficking. Addition of antibodies specific for TGN- or plasma membrane-bound Sec6/8 complexes to semiintact NRK cells results in cargo accumulation in a perinuclear region or near the plasma membrane, respectively. These results indicate that Sec6/8 complex is required for several steps in exocytic transport of vesicles between TGN and plasma membrane.
authors.affiliation: Department of Molecular and Cellular Physiology, Beckman Center for Molecular and Genetic Medicine, Stanford University School of Medicine, Stanford, CA 94305, USA.
authors.forename: C
authors.initials: C
authors.lastname: Yeaman
authors.forename: K K
authors.initials: KK
authors.lastname: Grindstaff
authors.forename: J R
authors.initials: JR
authors.lastname: Wright
authors.forename: W J
authors.initials: WJ
authors.lastname: Nelson
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004847:Epithelial Cells / Q000166:cytology; D005089:Exocytosis / Q000502:physiology*; D005347:Fibroblasts / Q000166:cytology; D008322:Mammals; D008565:Membrane Proteins; D051379:Mice; D021601:trans-Golgi Network / Q000378:metabolism*
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; C490683:Sec6l1 protein, mouse; C489608:Sec8l1 protein, mouse