title: The host cell chaperone Hsp90 is essential for translocation of the binary Clostridium botulinum C2 toxin into the cytosol.
abstract: Clostridium botulinum C2 toxin is the prototype of the binary actin-ADP-ribosylating toxins and consists of the binding component C2II and the enzyme component C2I. The activated binding component C2IIa forms heptamers, which bind to carbohydrates on the cell surface and interact with the enzyme component C2I. This toxin complex is taken up by receptor-mediated endocytosis. In acidic endosomes, heptameric C2IIa forms pores and mediates the translocation of C2I into the cytosol. We report that the heat shock protein (Hsp) 90-specific inhibitors, geldanamycin or radicicol, block intoxication of Vero cells, rat astrocytes, and HeLa cells by C2 toxin. ADP-ribosylation of actin in the cytosol of toxin-treated cells revealed that less active C2I was translocated into the cytosol after treatment with Hsp90 inhibitors. Under control conditions, C2I was localized in the cytosol of toxin-treated rat astrocytes, whereas geldanamycin blocked the cytosolic distribution of C2I. At low extracellular pH (pH 4.5), which allows the direct translocation of C2I via C2IIa heptamers across the cell membrane into the cytosol, Hsp90 inhibitors retarded intoxication by C2I. Geldanamycin did not affect toxin binding, endocytosis, and pore formation by C2IIa. The ADP-ribosyltransferase activity of C2I was not affected by Hsp90 inhibitors in vitro. The cytotoxic actions of the actin-ADP-ribosylating Clostridium perfringens iota toxin and the Rho-ADP-ribosylating C2-C3 fusion toxin was similarly blocked by Hsp90 inhibitors. In contrast, radicicol and geldanamycin had no effect on anthrax lethal toxin-induced cytotoxicity of J774-A1 macrophage-like cells or on cytotoxic effects of the glucosylating Clostridium difficile toxin B in Vero cells. The data indicate that Hsp90 is essential for the membrane translocation of ADP-ribosylating toxins delivered by C2II.
authors.affiliation: Institut für Experimentelle und Klinische Pharmakologie und Toxikologie der Albert-Ludwigs-Universität Freiburg, Albertstrasse 25 (Otto-Krayer-Haus), D-79104 Freiburg, Germany.
authors.forename: Gerd
authors.initials: G
authors.lastname: Haug
authors.forename: Jost
authors.initials: J
authors.lastname: Leemhuis
authors.forename: Dirk
authors.initials: D
authors.lastname: Tiemann
authors.forename: Dieter K
authors.initials: DK
authors.lastname: Meyer
authors.forename: Klaus
authors.initials: K
authors.lastname: Aktories
authors.forename: Holger
authors.initials: H
authors.lastname: Barth
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D016227:Benzoquinones; D001905:Botulinum Toxins / Q000378:metabolism*; D002460:Cell Line; D003600:Cytosol / Q000378:metabolism*; D004705:Endocytosis / Q000187:drug effects; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D006801:Humans; D007150:Immunohistochemistry; D047029:Lactams, Macrocyclic; D018942:Macrolides; D011485:Protein Binding; D021381:Protein Transport; D011809:Quinones / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D018942:Macrolides; D011809:Quinones; C040929:bafilomycin A1; D001905:Botulinum Toxins; C096324:botulinum toxin type C; C001277:geldanamycin