title: Dislocation of ricin toxin A chains in human cells utilizes selective cellular factors.
abstract: Ricin is a potent A-B toxin that is transported from the cell surface to the cytosol, where it inactivates ribosomes, leading to cell death. Ricin enters cells via endocytosis, where only a minute number of ricin molecules reach the endoplasmic reticulum (ER) lumen. Subsequently, the ricin A chain traverses the ER bilayer by a process referred to as dislocation or retrograde translocation to gain access to the cytosol. To study the molecular processes of ricin A chain dislocation, we have established, for the first time, a human cell system in which enzymatically attenuated ricin toxin A chains (RTA(E177D) and RTA(Δ177-181)) are expressed in the cell and directed to the ER. Using this human cell-based system, we found that ricin A chains underwent a rapid dislocation event that was quite distinct from the dislocation of a canonical ER soluble misfolded protein, null Hong Kong variant of α(1)-antitrypsin. Remarkably, ricin A chain dislocation occurred via a membrane-integrated intermediate and utilized the ER protein SEL1L for transport across the ER bilayer to inhibit protein synthesis. The data support a model in which ricin A chain dislocation occurs via a novel strategy of utilizing the hydrophobic nature of the ER membrane and selective ER components to gain access to the cytosol.
authors.affiliation: Department of Microbiology, Mount Sinai School of Medicine, New York, New York 10029, USA.
authors.forename: Veronika
authors.initials: V
authors.lastname: Redmann
authors.forename: Kristina
authors.initials: K
authors.lastname: Oresic
authors.forename: Lori L
authors.initials: LL
authors.lastname: Tortorella
authors.forename: Jonathan P
authors.initials: JP
authors.lastname: Cook
authors.forename: Michael
authors.initials: M
authors.lastname: Lord
authors.forename: Domenico
authors.initials: D
authors.lastname: Tortorella
mesh_terms: D002460:Cell Line; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000939:Epitopes / Q000737:chemistry; D006026:Glycoside Hydrolases / Q000737:chemistry; D006801:Humans; D007525:Isoelectric Focusing; D008051:Lipid Bilayers / Q000737:chemistry*; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase / Q000737:chemistry; D017510:Protein Folding; D012276:Ricin / Q000737:chemistry*; D000515:alpha 1-Antitrypsin / Q000737:chemistry
chemical_list: D000939:Epitopes; D008051:Lipid Bilayers; D000515:alpha 1-Antitrypsin; D012276:Ricin; D006026:Glycoside Hydrolases; D043524:Peptide-N4-(N-acetyl-beta-glucosaminyl) Asparagine Amidase