title: Hsp90 is required for transfer of the cholera toxin A1 subunit from the endoplasmic reticulum to the cytosol.
abstract: Cholera toxin (CT) is an AB(5) toxin that moves from the cell surface to the endoplasmic reticulum (ER) by retrograde vesicular transport. In the ER, the catalytic A1 subunit dissociates from the rest of the toxin and enters the cytosol by exploiting the quality control system of ER-associated degradation (ERAD). The driving force for CTA1 dislocation into the cytosol is unknown. Here, we demonstrate that the cytosolic chaperone Hsp90 is required for CTA1 passage into the cytosol. Hsp90 bound to CTA1 in an ATP-dependent manner that was blocked by geldanamycin (GA), an established Hsp90 inhibitor. CT activity against cultured cells and ileal loops was also blocked by GA, as was the ER-to-cytosol export of CTA1. Experiments using RNA interference or N-ethylcarboxamidoadenosine, a drug that inhibits ER-localized GRP94 but not cytosolic Hsp90, confirmed that the inhibitory effects of GA resulted specifically from the loss of Hsp90 activity. This work establishes a functional role for Hsp90 in the ERAD-mediated dislocation of CTA1.
authors.affiliation: Burnett School of Biomedical Sciences, College of Medicine, University of Central Florida, Orlando, Florida 32826, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Taylor
authors.forename: Fernando
authors.initials: F
authors.lastname: Navarro-Garcia
authors.forename: Jazmin
authors.initials: J
authors.lastname: Huerta
authors.forename: Helen
authors.initials: H
authors.lastname: Burress
authors.forename: Shane
authors.initials: S
authors.lastname: Massey
authors.forename: Keith
authors.initials: K
authors.lastname: Ireton
authors.forename: Ken
authors.initials: K
authors.lastname: Teter
mesh_terms: D000255:Adenosine Triphosphate / Q000235:genetics / Q000378:metabolism; D000818:Animals; D016227:Benzoquinones / Q000494:pharmacology; D016466:CHO Cells; D002772:Cholera Toxin / Q000235:genetics / Q000378:metabolism*; D006224:Cricetinae; D003412:Cricetulus; D003600:Cytosol / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000235:genetics / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D047029:Lactams, Macrocyclic / Q000494:pharmacology; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D016227:Benzoquinones; D004791:Enzyme Inhibitors; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D008562:Membrane Glycoproteins; C053387:endoplasmin; D000255:Adenosine Triphosphate; D002772:Cholera Toxin; C001277:geldanamycin