title: Free ricin A chain reaches an early compartment of the secretory pathway before it enters the cytosol.
abstract: During the intoxication of mammalian cells by ricin, the catalytically active A chain must cross the membrane of an intracellular compartment in order to reach its ribosomal substrates in the cytosol. The actual site of ricin A chain translocation is unclear, and conflicting views hold that it enters the cytosol from endosomes or from an early compartment of the secretory pathway, possibly the lumen of the endoplasmic reticulum. Here we show that treating cells with brefeldin A, or transiently overexpressing mutant GTPases known to inhibit biochemical complexes mediating anterograde and retrograde transport between the endoplasmic reticulum and the Golgi complex, protected cells from intoxication by free ricin A chain. These data indicate that ricin A chain, either free or as part of intact ricin, reaches an early compartment of the secretory pathway before translocation into the cytosol occurs.
authors.affiliation: Department of Biological Sciences, University of Warwick, Coventry, CV4 7AL, United Kingdom.
authors.forename: J C
authors.initials: JC
authors.lastname: Simpson
authors.forename: L M
authors.initials: LM
authors.lastname: Roberts
authors.forename: J M
authors.initials: JM
authors.lastname: Lord
mesh_terms: D000595:Amino Acid Sequence; D001693:Biological Transport, Active; D020126:Brefeldin A; D002451:Cell Compartmentation; D003517:Cyclopentanes / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012276:Ricin / Q000737:chemistry / Q000493:pharmacokinetics* / Q000633:toxicity*
chemical_list: D003517:Cyclopentanes; D011500:Protein Synthesis Inhibitors; D020126:Brefeldin A; D012276:Ricin; D020558:GTP Phosphohydrolases