Beta-COP localizes mainly to the cis-Golgi side in exocrine pancreas.
We examined the distribution of the non-clathrin-coated vesicle-associated coat protein beta-COP in rat exocrine pancreatic cells by immunogold cytochemistry. Labeling for beta-COP was found in the Golgi region (48%) where it was associated with vesicles and buds of approximately 50 nm, showing a characteristic approximately 10-nm-thick coat. The other half of the label was present in the cytoplasm, not associated with visible coats or membranes, with a minor fraction present on small clusters of tubules and vesicles. Clathrin-coated vesicles were typically located at the trans-side of the Golgi complex, and showed a thicker coat of approximately 18 nm. Of the total beta-COP labeling over the Golgi region, 68% occurred on the cis-side, 6% on the cisternae, 17% on the rims of the cisternae, and only 9% on the trans-side. For clathrin these figures were 16, 2, 4, and 78%, respectively. At the cis-Golgi side beta-COP was present in transitional areas (TA), on so-called peripheral elements (PE), consisting of tubules and vesicles located between the cup-shaped transitional elements (TE) of the RER and the cis-most Golgi cisternae. Label for Sec23p was also present in TA but was located closer to the TE, while beta-COP labeled PE were located near the cis-Golgi cisternae. Upon energy depletion, Golgi associated beta-COP was almost exclusively (86%) in spherical aggregates of 200-500 nm in diameter, whereas the cis-side (6%), the cisternae (1%), the rims (4%) and trans-side (3%) of the Golgi complex, were barely labeled; 50% of the total label remained in the cytoplasm. The aggregates were predominantly located at the cis-side of the Golgi stack, next to, but distinct from the Sec23p positive TA, that were devoid of beta-COP and had only a few recognizable vesicles left. Incubation with aluminum fluoride resulted in fragmentation of the Golgi complex into large clusters of beta-COP positive vesicles, while 50% of the label remained in the cytoplasm, as in control cells. After 10 min of Brefeldin A treatment 91% of beta-COP was cytoplasmic and only 7% associated with membranes of the Golgi complex. The total label for beta-COP over exocrine cells remained unchanged during the incubation with either of the drugs, indicating that the drugs induce reallocation of beta-COP. Our data suggest that beta-COP plays a role in membrane transport at the cis-side of the Golgi complex.
Oprins
A
A
Department of Cell Biology, Medical School, Utrecht University, The Netherlands.
Duden
R
R
Kreis
T E
TE
Geuze
H J
HJ
Slot
J W
JW
D000535:Aluminum / Q000494:pharmacology; D017607:Aluminum Compounds; D000818:Animals; D001692:Biological Transport; D020126:Brefeldin A; D002966:Clathrin / Q000032:analysis; D020756:Coatomer Protein; D003517:Cyclopentanes / Q000494:pharmacology; D004734:Energy Metabolism; D005459:Fluorides / Q000494:pharmacology; D006056:Golgi Apparatus / Q000737:chemistry*; D008297:Male; D008565:Membrane Proteins / Q000032:analysis*; D016253:Microscopy, Immunoelectron; D008869:Microtubule-Associated Proteins / Q000032:analysis*; D010179:Pancreas / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D051381:Rats; D017208:Rats, Wistar
D017607:Aluminum Compounds; D002966:Clathrin; D020756:Coatomer Protein; D003517:Cyclopentanes; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D020126:Brefeldin A; D000535:Aluminum; D005459:Fluorides; C032311:aluminum fluoride