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Department of Cell Biology, Sciences III, University of Geneva, Geneva, Switzerland, and * Cell Biology Program, European
Molecular Biology Laboratory, Heidelberg, Germany
Addition of brefeldin A (BFA) to mammalian cells rapidly results in the removal of coatomer
from membranes and subsequent delivery of Golgi enzymes to the endoplasmic reticulum (ER). Microinjected anti-EAGE (intact IgG or Fab-fragments), antibodies against the "EAGE"-peptide of 
-COP, inhibit
BFA-induced redistribution of -COP in vivo and
block transfer of resident proteins of the Golgi complex
to the ER; tubulo-vesicular clusters accumulate and
Golgi membrane proteins concentrate in cytoplasmic
patches containing -COP. These patches are devoid of
marker proteins of the ER, the intermediate compartment (IC), and do not contain KDEL receptor. Interestingly, relocation of KDEL receptor to the IC, where
it colocalizes with ERGIC53 and ts-O45-G, is not inhibited under these conditions. While no stacked Golgi cisternae remain in these injected cells, reassembly of
stacks of Golgi cisternae following BFA wash-out is inhibited to only ~50%. Mono- or divalent anti-EAGE stabilize binding of coatomer to membranes in vitro, at
least as efficiently as GTP
S. Taken together these results suggest that enhanced binding of coatomer to
membranes completely inhibits the BFA-induced retrograde transport of Golgi resident proteins to the ER,
probably by inhibiting fusion of Golgi with ER membranes, but does not interfere with the disassembly of
the stacked Golgi cisternae and recycling of KDEL receptor to the IC. These results confirm our previous results suggesting that COPI is involved in anterograde
membrane transport from the ER/IC to the Golgi complex (), and corroborate that
COPI regulates retrograde membrane transport between the Golgi complex and ER in mammalian cells.
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