title: Compartmentation of the Golgi complex: brefeldin-A distinguishes trans-Golgi cisternae from the trans-Golgi network.
abstract: The Golgi complex is composed of at least four distinct compartments, termed the cis-, medial, and trans-Golgi cisternae and the trans-Golgi network (TGN). It has recently been reported that the organization of the Golgi complex is disrupted in cells treated with the fungal metabolite, brefeldin-A. Under these conditions, it was shown that resident enzymes of the cis-, medial, and trans-Golgi return to the ER. We report here that 300-kD mannose 6-phosphate receptors, when pulse-labeled within the ER of brefeldin-A-treated cells, acquired numerous N-linked galactose residues with a half time of approximately 2 h, as measured by their ability to bind to RCA-I lectin affinity columns. In contrast, Limax flavus lectin chromatography revealed that less than 10% of these receptors acquired sialic acid after 8 h in brefeldin-A. Two lines of evidence suggested that proteins within and beyond the TGN did not return to the ER in the presence of brefeldin-A. First, the majority of 300-kD mannose 6-phosphate receptors present in the TGN and endosomes did not return to the ER after up to 6 h in brefeldin-A, as determined by their failure to contact galactosyltransferase that had relocated there. Moreover, although mannose 6-phosphate receptors did not acquire sialic acid when present in the ER of brefeldin-A-treated cells, they were readily sialylated when labeled at the cell surface and transported to the TGN. These experiments indicate that galactosyltransferase, a trans-Golgi enzyme, returns to the endoplasmic reticulum in the presence of brefeldin-A, while the bulk of sialyltransferase, a resident of the TGN, does not. Our findings support the proposal that the TGN is a distinct, fourth compartment of the Golgi apparatus that is insensitive to brefeldin-A.
authors.affiliation: Department of Biochemistry, Stanford University School of Medicine, California 94305-5307.
authors.forename: N W
authors.initials: NW
authors.lastname: Chege
authors.forename: S R
authors.initials: SR
authors.lastname: Pfeffer
mesh_terms: D000818:Animals; D020126:Brefeldin A; D002451:Cell Compartmentation / Q000187:drug effects; D002460:Cell Line; D003517:Cyclopentanes / Q000494:pharmacology*; D004721:Endoplasmic Reticulum / Q000378:metabolism; D005700:Galactosyltransferases / Q000378:metabolism*; D006056:Golgi Apparatus / Q000187:drug effects / Q000378:metabolism*; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface / Q000378:metabolism; D012799:Sialyltransferases / Q000378:metabolism*; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase
chemical_list: D003517:Cyclopentanes; D017527:Receptor, IGF Type 2; D011956:Receptors, Cell Surface; D020126:Brefeldin A; D005700:Galactosyltransferases; D012799:Sialyltransferases; D000094802:beta-D-Galactoside alpha 2-6-Sialyltransferase