Evidence for a COP-I-independent transport route from the Golgi complex to the endoplasmic reticulum.
The cytosolic coat-protein complex COP-I interacts with cytoplasmic 'retrieval' signals present in membrane proteins that cycle between the endoplasmic reticulum (ER) and the Golgi complex, and is required for both anterograde and retrograde transport in the secretory pathway. Here we study the role of COP-I in Golgi-to-ER transport of several distinct marker molecules. Microinjection of anti-COP-I antibodies inhibits retrieval of the lectin-like molecule ERGIC-53 and of the KDEL receptor from the Golgi to the ER. Transport to the ER of protein toxins, which contain a sequence that is recognized by the KDEL receptor, is also inhibited. In contrast, microinjection of anti-COP-I antibodies or expression of a GTP-restricted Arf-1 mutant does not interfere with Golgi-to-ER transport of Shiga toxin/Shiga-like toxin-1 or with the apparent recycling to the ER of Golgi-resident glycosylation enzymes. Overexpression of a GDP-restricted mutant of Rab6 blocks transport to the ER of Shiga toxin/Shiga-like toxin-1 and glycosylation enzymes, but not of ERGIC-53, the KDEL receptor or KDEL-containing toxins. These data indicate the existence of at least two distinct pathways for Golgi-to-ER transport, one COP-I dependent and the other COP-I independent. The COP-I-independent pathway is specifically regulated by Rab6 and is used by Golgi glycosylation enzymes and Shiga toxin/Shiga-like toxin-1.
Girod
A
A
Cell Biology and Biophysics Programme, EMBL Heidelberg, Meyerhofstrasse 1, 69117 Heidelberg, Germany.
Storrie
B
B
Simpson
J C
JC
Johannes
L
L
Goud
B
B
Roberts
L M
LM
Lord
J M
JM
Nilsson
T
T
Pepperkok
R
R
D020823:ADP-Ribosylation Factor 1 / Q000235:genetics / Q000378:metabolism; D020816:Amino Acid Motifs; D000818:Animals; D002522:Chlorocebus aethiops; D020755:Coat Protein Complex I / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D037241:Mannose-Binding Lectins; D008565:Membrane Proteins / Q000378:metabolism; D008845:Microinjections; D008856:Microscopy, Fluorescence; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D021382:Protein Sorting Signals; D021381:Protein Transport / Q000502:physiology*; D018000:Receptors, Peptide / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins; D022621:Shiga Toxin / Q000378:metabolism*; D022622:Shiga Toxin 1 / Q000378:metabolism*; D014709:Vero Cells; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000378:metabolism
D020755:Coat Protein Complex I; C064459:KDEL receptor; C084004:LMAN1 protein, human; D037241:Mannose-Binding Lectins; D008565:Membrane Proteins; D021382:Protein Sorting Signals; C094135:Rab6 protein; D018000:Receptors, Peptide; D029701:Saccharomyces cerevisiae Proteins; D022622:Shiga Toxin 1; D033921:Vesicular Transport Proteins; D022621:Shiga Toxin; D020823:ADP-Ribosylation Factor 1; D020559:Monomeric GTP-Binding Proteins; C077395:SAR1 protein, S cerevisiae; D020691:rab GTP-Binding Proteins