title: The mammalian protein (rbet1) homologous to yeast Bet1p is primarily associated with the pre-Golgi intermediate compartment and is involved in vesicular transport from the endoplasmic reticulum to the Golgi apparatus.
abstract: Yeast Bet1p participates in vesicular transport from the endoplasmic reticulum to the Golgi apparatus and functions as a soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) associated with ER-derived vesicles. A mammalian protein (rbet1) homologous to Bet1p was recently identified, and it was concluded that rbet1 is associated with the Golgi apparatus based on the subcellular localization of transiently expressed epitope-tagged rbet1. In the present study using rabbit antibodies raised against the cytoplasmic domain of rbet1, we found that the majority of rbet1 is not associated with the Golgi apparatus as marked by the Golgi mannosidase II in normal rat kidney cells. Rather, rbet1 is predominantly associated with vesicular spotty structures that concentrate in the peri-Golgi region but are also present throughout the cytoplasm. These structures colocalize with the KDEL receptor and ERGIC-53, which are known to be enriched in the intermediate compartment. When the Golgi apparatus is fragmented by nocodazole treatment, a significant portion of rbet1 is not colocalized with structures marked by Golgi mannosidase II or the KDEL receptor. Association of rbet1 in cytoplasmic spotty structures is apparently not altered by preincubation of cells at 15 degrees C. However, upon warming up from 15 to 37 degrees C, rbet1 concentrates into the peri-Golgi region. Furthermore, rbet1 colocalizes with vesicular stomatitis virus G-protein en route from the ER to the Golgi. Antibodies against rbet1 inhibit in vitro transport of G-protein from the ER to the Golgi apparatus in a dose-dependent manner. This inhibition can be neutralized by preincubation of antibodies with recombinant rbet1. EGTA is known to inhibit ER-Golgi transport at a stage after vesicle docking but before the actual fusion event. Antibodies against rbet1 inhibit ER-Golgi transport only when they are added before the EGTA-sensitive stage. These results suggest that rbet1 may be involved in the docking process of ER-derived vesicles with the cis-Golgi membrane.
authors.affiliation: Membrane Biology Laboratory, Institute of Molecular and Cell Biology, Singapore 119076, Singapore.
authors.forename: T
authors.initials: T
authors.lastname: Zhang
authors.forename: S H
authors.initials: SH
authors.lastname: Wong
authors.forename: B L
authors.initials: BL
authors.lastname: Tang
authors.forename: Y
authors.initials: Y
authors.lastname: Xu
authors.forename: F
authors.initials: F
authors.lastname: Peter
authors.forename: V N
authors.initials: VN
authors.lastname: Subramaniam
authors.forename: W
authors.initials: W
authors.lastname: Hong
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport; D015415:Biomarkers; D002451:Cell Compartmentation; D002474:Cell-Free System; D003001:Cloning, Molecular; D018076:DNA, Complementary / Q000235:genetics; D004533:Egtazic Acid / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D037241:Mannose-Binding Lectins; D008361:Mannosidases / Q000378:metabolism; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D051379:Mice; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D011233:Precipitin Tests; D011485:Protein Binding; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D018000:Receptors, Peptide / Q000302:isolation & purification; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013045:Species Specificity; D033921:Vesicular Transport Proteins; D015003:Yeasts
chemical_list: C098783:BET1 protein, rat; D015415:Biomarkers; D018076:DNA, Complementary; C490972:GOSR1 protein, human; C490971:Gosr1 protein, mouse; C064459:KDEL receptor; C084004:LMAN1 protein, human; C501458:Lman1 protein, rat; D037241:Mannose-Binding Lectins; D008565:Membrane Proteins; D050765:Qa-SNARE Proteins; D050766:Qb-SNARE Proteins; D050767:Qc-SNARE Proteins; D018000:Receptors, Peptide; D033921:Vesicular Transport Proteins; D004533:Egtazic Acid; D008361:Mannosidases; C038829:mannosyl-oligosaccharide 1,3 - 1,6-alpha-mannosidase