Transport of an external Lys-Asp-Glu-Leu (KDEL) protein from the plasma membrane to the endoplasmic reticulum: studies with cholera toxin in Vero cells.
The A2 chain of cholera toxin (CTX) contains a COOH-terminal Lys-Asp-Glu-Leu (KDEL) sequence. We have, therefore, analyzed by immunofluorescence and by subcellular fractionation in Vero cells whether CTX can used to demonstrate a retrograde transport of KDEL proteins from the Golgi to the ER. Immunofluorescence studies reveal that after a pulse treatment with CTX, the CTX-A and B subunits (CTX-A and CTX-B) reach Golgi-like structures after 15-20 min (maximum after 30 min). Between 30 and 90 min, CTX-A (but not CTX-B) appear in the intermediate compartment and in the ER, whereas the CTX-B are translocated to the lysosomes. Subcellular fractionation studies confirm these results: after CTX uptake for 15 min, CTX-A is associated only with endosomal and Golgi compartments. After 30 min, a small amount of CTX-A appears in the ER in a trypsin-resistant form, and after 60 min, a significant amount appears. CTX-A seems to be transported mainly in its oxidized form (CTX-A1-S-S-CTX-A2) from the Golgi to the ER, where it becomes slowly reduced to form free CTX A1 and CTX-A2, as indicated by experiments in which cells were homogenized 30 and 90 min after the onset of CTX uptake in the presence of N-ethylmaleimide. Nocodazol applied after accumulation of CTX in Golgi inhibits the appearance of CTX-A in the ER and delays the increase of 3',5'cAMP, indicating the participation of microtubules in the retrograde Golgi-ER transport.
Majoul
I V
IV
Abteilung Klinische Biochemie, Universität Göttingen, Germany.
Bastiaens
P I
PI
Söling
H D
HD
D000595:Amino Acid Sequence; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002462:Cell Membrane / Q000378:metabolism*; D002522:Chlorocebus aethiops; D002772:Cholera Toxin / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006168:Guinea Pigs; D008969:Molecular Sequence Data; D015739:Nocodazole / Q000494:pharmacology; D009842:Oligopeptides / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism; D011817:Rabbits; D013347:Subcellular Fractions; D013997:Time Factors; D014709:Vero Cells
D009842:Oligopeptides; D021382:Protein Sorting Signals; C073762:lysyl-aspartyl-glutamyl-leucine; D002772:Cholera Toxin; D000242:Cyclic AMP; D015739:Nocodazole