Vesicular Tubular Clusters between the ER and Golgi Mediate Concentration of Soluble Secretory Proteins by Exclusion from COPI-Coated Vesicles

• Published in: Cell 1999-07, Vol.98 (1), p.81-90
• Main Authors: Martínez-Menárguez, José A., Geuze, Hans J., Slot, Jan W., Klumperman, Judith
• Format: Article
• Language: English
• Subjects: Amylases - metabolism; Animals; Carrier Proteins - metabolism; Chymotrypsinogen - metabolism; Coated Pits, Cell-Membrane - metabolism; Coated Pits, Cell-Membrane - ultrastructure; Coatomer Protein; Endoplasmic Reticulum - metabolism; Endoplasmic Reticulum - ultrastructure; Golgi Apparatus - metabolism; Golgi Apparatus - ultrastructure; Male; Membrane Proteins - metabolism; Microscopy, Immunoelectron; Pancreas - physiology; Pancreas - ultrastructure; Phosphoproteins - metabolism; Qc-SNARE Proteins; Rats; Rats, Wistar; Receptors, Peptide - metabolism; Saccharomyces cerevisiae Proteins; Vesicular Transport Proteins
• ISSN: 0092-8674; 1097-4172
• DOI: 10.1016/S0092-8674(00)80608-X

We have determined the concentrations of the secretory proteins amylase and chymotrypsinogen and the membrane proteins KDELr and rBet1 in COPII- and COPI-coated pre-Golgi compartments of pancreatic cells by quantitative immunoelectron microscopy. COPII was confined to ER membrane buds and adjacent vesicles. COPI occurred on vesicular tubular clusters (VTCs), Golgi cisternae, the trans-Golgi network, and immature secretory granules. Both secretory proteins exhibited a first, significant concentration step in noncoated segments of VTC tubules and were excluded from COPI-coated tips. By contrast, KDELr and rBet1 showed a first, significant concentration in COPII-coated ER buds and vesicles and were prominently present in COPI-coated tips of VTC tubules. These data suggest an important role of VTCs in soluble cargo concentration by exclusion from COPI-coated domains.