Thapsigargin-induced transport of cholera toxin to the endoplasmic reticulum.
Cholera toxin is normally observed only in the Golgi apparatus and not in the endoplasmic reticulum (ER) although the enzymatically active A subunit of cholera toxin has a KDEL sequence. Here we demonstrate transport of horseradish peroxidase-labeled cholera toxin to the ER by electron microscopy in thapsigargin-treated A431 cells. Thapsigargin treatment strongly increased cholera toxin-induced cAMP production, and the formation of the catalytically active A1 fragment was somewhat increased. Binding of cholera toxin to the cell surface and transport of toxin to the Golgi apparatus were not changed in thapsigargin-treated cells, suggesting increased retrograde transport of cholera toxin from the Golgi apparatus to the ER. The data demonstrate that retrograde transport of cholera toxin can take place and that the transport is under regulation. The results are consistent with the idea that retrograde transport can be important for the action of cholera toxin.
Institute for Cancer Research, Norwegian Radium Hospital, Montebello, Oslo, Norway.
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K
Sandvig
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O
Garred
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B
van Deurs
D002118:Calcium / Q000378:metabolism; D002294:Carcinoma, Squamous Cell / Q000378:metabolism; D002772:Cholera Toxin / Q000378:metabolism*; D000242:Cyclic AMP / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006056:Golgi Apparatus / Q000378:metabolism; D006801:Humans; D008854:Microscopy, Electron; D009842:Oligopeptides / Q000378:metabolism; D021382:Protein Sorting Signals; D019284:Thapsigargin / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
D009842:Oligopeptides; D021382:Protein Sorting Signals; C073762:lysyl-aspartyl-glutamyl-leucine; D019284:Thapsigargin; D002772:Cholera Toxin; D000242:Cyclic AMP; D002118:Calcium