The Ero1alpha-PDI redox cycle regulates retro-translocation of cholera toxin.
Cholera toxin (CT) is transported from the plasma membrane of host cells to the endoplasmic reticulum (ER) where the catalytic CTA1 subunit retro-translocates to the cytosol to induce toxicity. Our previous analyses demonstrated that the ER oxidoreductase protein disulfide isomerase (PDI) acts as a redox-dependent chaperone to unfold CTA1, a reaction postulated to initiate toxin retro-translocation. In its reduced state, PDI binds and unfolds CTA1; subsequent oxidation of PDI by Ero1alpha enables toxin release. Whether this in vitro model describes events in cells that control CTA1 retro-translocation is unknown. Here we show that down-regulation of Ero1alpha decreases retro-translocation of CTA1 by increasing reduced PDI and blocking efficient toxin release. Overexpression of Ero1alpha also attenuates CTA1 retro-translocation, an effect due to increased PDI oxidation, which prevents PDI from engaging the toxin effectively. Interestingly, Ero1alpha down-regulation increases interaction between PDI and Derlin-1, an ER membrane protein that is a component of the retro-translocation complex. These findings demonstrate that an appropriate Ero1alpha-PDI ratio is critical for regulating the binding-release cycle of CTA1 by PDI during retro-translocation, and implicate PDI's redox state in targeting it to the retro-translocon.
Moore
Paul
P
Department of Cell and Developmental Biology, University of Michigan Medical School, Ann Arbor, MI 48109, USA.
Bernardi
Kaleena M
KM
Tsai
Billy
B
D017398:Alternative Splicing; D020134:Catalytic Domain; D002460:Cell Line; D002772:Cholera Toxin / Q000378:metabolism*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006801:Humans; D008562:Membrane Glycoproteins / Q000378:metabolism*; D008954:Models, Biological; D016296:Mutagenesis; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000378:metabolism*; D010100:Oxygen / Q000737:chemistry; D019704:Protein Disulfide-Isomerases / Q000378:metabolism*; D020033:Protein Isoforms; D021381:Protein Transport
D003432:Cross-Linking Reagents; D008562:Membrane Glycoproteins; D020033:Protein Isoforms; D002772:Cholera Toxin; C405327:ERO1A protein, human; D010088:Oxidoreductases; D019704:Protein Disulfide-Isomerases; D010100:Oxygen