title: EDEM is involved in retrotranslocation of ricin from the endoplasmic reticulum to the cytosol.
abstract: The plant toxin ricin is transported retrogradely from the cell surface to the endoplasmic reticulum (ER) from where the enzymatically active part is retrotranslocated to the cytosol, presumably by the same mechanism as used by misfolded proteins. The ER degradation enhancing alpha-mannosidase I-like protein, EDEM, is responsible for directing aberrant proteins for ER-associated protein degradation. In this study, we have investigated whether EDEM is involved in ricin retrotranslocation. Overexpression of EDEM strongly protects against ricin. However, when the interaction between EDEM and misfolded proteins is inhibited by kifunensin, EDEM promotes retrotranslocation of ricin from the ER to the cytosol. Furthermore, puromycin, which inhibits synthesis and thereby transport of proteins into the ER, counteracted the protection seen in EDEM-transfected cells. Coimmunoprecipitation studies revealed that ricin can interact with EDEM and with Sec61alpha, and both kifunensin and puromycin increase these interactions. Importantly, vector-based RNA interference against EDEM, which leads to reduction of the cellular level of EDEM, decreased retrotranslocation of ricin A-chain to the cytosol. In conclusion, our results indicate that EDEM is involved in retrotranslocation of ricin from the ER to the cytosol.
authors.affiliation: Department of Biochemistry, Institute for Cancer Research, Faculty Division The Norwegian Radium Hospital, University of Oslo, Montebello, N-0310 Oslo, Norway.
authors.forename: Monika
authors.initials: M
authors.lastname: Slominska-Wojewodzka
authors.forename: Tone F
authors.initials: TF
authors.lastname: Gregers
authors.forename: Sébastien
authors.initials: S
authors.lastname: Wälchli
authors.forename: Kirsten
authors.initials: K
authors.lastname: Sandvig
mesh_terms: D000470:Alkaloids / Q000494:pharmacology; D000818:Animals; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D047468:Immunoprecipitation; D008565:Membrane Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D017510:Protein Folding; D021381:Protein Transport / Q000235:genetics; D011691:Puromycin / Q000494:pharmacology; D034622:RNA Interference; D012276:Ricin / Q000378:metabolism*; D000069816:SEC Translocation Channels; D015533:Transcriptional Activation
chemical_list: D000470:Alkaloids; C487709:DERL1 protein, human; C513305:DERL2 protein, human; C513304:Derl2 protein, mouse; C434526:Edem1 protein, mouse; D004791:Enzyme Inhibitors; D008565:Membrane Proteins; D009363:Neoplasm Proteins; D000069816:SEC Translocation Channels; C000613244:SEC61A1 protein, human; C065629:kifunensine; D011691:Puromycin; D012276:Ricin