title: Transition of galactosyltransferase 1 from trans-Golgi cisterna to the trans-Golgi network is signal mediated.
abstract: The Golgi apparatus (GA) is the organelle where complex glycan formation takes place. In addition, it is a major sorting site for proteins destined for various subcellular compartments or for secretion. Here we investigate beta1,4-galactosyltransferase 1 (galT) and alpha2,6-sialyltransferase 1 (siaT), two trans-Golgi glycosyltransferases, with respect to their different pathways in monensin-treated cells. Upon addition of monensin galT dissociates from siaT and the GA and accumulates in swollen vesicles derived from the trans-Golgi network (TGN), as shown by colocalization with TGN46, a specific TGN marker. We analyzed various chimeric constructs of galT and siaT by confocal fluorescence microscopy and time-lapse videomicroscopy as well as Optiprep density gradient fractionation. We show that the first 13 amino acids of the cytoplasmic tail of galT are necessary for its localization to swollen vesicles induced by monensin. We also show that the monensin sensitivity resulting from the cytoplasmic tail can be conferred to siaT, which leads to the rapid accumulation of the galT-siaT chimera in swollen vesicles upon monensin treatment. On the basis of these data, we suggest that cycling between the trans-Golgi cisterna and the trans-Golgi network of galT is signal mediated.
authors.affiliation: Institute of Physiology, University of Zurich, CH-8057 Zurich, Switzerland.
authors.forename: Beat E
authors.initials: BE
authors.lastname: Schaub
authors.forename: Bea
authors.initials: B
authors.lastname: Berger
authors.forename: Eric G
authors.initials: EG
authors.lastname: Berger
authors.forename: Jack
authors.initials: J
authors.lastname: Rohrer
mesh_terms: D000595:Amino Acid Sequence; D020126:Brefeldin A / Q000494:pharmacology; D022162:Cytoplasmic Vesicles / Q000187:drug effects; D005700:Galactosyltransferases / Q000737:chemistry / Q000378:metabolism*; D000077614:Golgi Matrix Proteins; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism; D008954:Models, Biological; D008969:Molecular Sequence Data; D008985:Monensin / Q000494:pharmacology; D050505:Mutant Proteins / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012799:Sialyltransferases / Q000737:chemistry / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D021601:trans-Golgi Network / Q000187:drug effects / Q000378:metabolism*; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
chemical_list: D000077614:Golgi Matrix Proteins; D008562:Membrane Glycoproteins; D008565:Membrane Proteins; D050505:Mutant Proteins; D011993:Recombinant Fusion Proteins; C072237:TGOLN2 protein, human; C087574:macrogolgin; D049452:Green Fluorescent Proteins; D020126:Brefeldin A; D008985:Monensin; D005700:Galactosyltransferases; C493310:beta1,4-galactosyltransferase, human; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase