title: Expression of mutant or cytosolic PrP in transgenic mice and cells is not associated with endoplasmic reticulum stress or proteasome dysfunction.
abstract: The cellular pathways activated by mutant prion protein (PrP) in genetic prion diseases, ultimately leading to neuronal dysfunction and degeneration, are not known. Several mutant PrPs misfold in the early secretory pathway and reside longer in the endoplasmic reticulum (ER) possibly stimulating ER stress-related pathogenic mechanisms. To investigate whether mutant PrP induced maladaptive responses, we checked key elements of the unfolded protein response (UPR) in transgenic mice, primary neurons and transfected cells expressing two different mutant PrPs. Because ER stress favors the formation of untranslocated PrP that might aggregate in the cytosol and impair proteasome function, we also measured the activity of the ubiquitin proteasome system (UPS). Molecular, biochemical and immunohistochemical analyses found no increase in the expression of UPR-regulated genes, such as Grp78/Bip, CHOP/GADD153, or ER stress-dependent splicing of the mRNA encoding the X-box-binding protein 1. No alterations in UPS activity were detected in mutant mouse brains and primary neurons using the Ub(G76V)-GFP reporter and a new fluorogenic peptide for monitoring proteasomal proteolytic activity in vivo. Finally, there was no loss of proteasome function in neurons in which endogenous PrP was forced to accumulate in the cytosol by inhibiting cotranslational translocation. These results indicate that neither ER stress, nor perturbation of proteasome activity plays a major pathogenic role in prion diseases.
authors.affiliation: Dulbecco Telethon Institute, Milan, Italy.
authors.forename: Elena
authors.initials: E
authors.lastname: Quaglio
authors.forename: Elena
authors.initials: E
authors.lastname: Restelli
authors.forename: Anna
authors.initials: A
authors.lastname: Garofoli
authors.forename: Sara
authors.initials: S
authors.lastname: Dossena
authors.forename: Ada
authors.initials: A
authors.lastname: De Luigi
authors.forename: Luigina
authors.initials: L
authors.lastname: Tagliavacca
authors.forename: Daniele
authors.initials: D
authors.lastname: Imperiale
authors.forename: Antonio
authors.initials: A
authors.lastname: Migheli
authors.forename: Mario
authors.initials: M
authors.lastname: Salmona
authors.forename: Roberto
authors.initials: R
authors.lastname: Sitia
authors.forename: Gianluigi
authors.initials: G
authors.lastname: Forloni
authors.forename: Roberto
authors.initials: R
authors.lastname: Chiesa
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D003600:Cytosol / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008822:Mice, Transgenic; D009154:Mutation; D009474:Neurons / Q000378:metabolism; D016716:PC12 Cells; D010455:Peptides / Q000737:chemistry; D011328:Prions / Q000096:biosynthesis* / Q000235:genetics; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D014176:Protein Biosynthesis; D051381:Rats
chemical_list: D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; C000717248:Hspa5 protein, mouse; D010455:Peptides; D011328:Prions; D049452:Green Fluorescent Proteins; D046988:Proteasome Endopeptidase Complex