Expression of mutant or cytosolic PrP in transgenic mice and cells is not associated with endoplasmic reticulum stress or proteasome dysfunction

• Published in: PloS one Vol. 6; no. 4; p. e19339
• Main Authors: Quaglio, Elena, Restelli, Elena, Garofoli, Anna, Dossena, Sara, De Luigi, Ada, Tagliavacca, Luigina, Imperiale, Daniele, Migheli, Antonio, Salmona, Mario, Sitia, Roberto, Forloni, Gianluigi, Chiesa, Roberto
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 29.04.2011; Public Library of Science (PLoS)
• Subjects: Analysis; Animals; Apoptosis; Biochemistry; Biology; Brain research; Cells, Cultured; CHOP protein; Creutzfeldt-Jakob disease; Cytosol; Cytosol - metabolism; Degeneration; Endoplasmic reticulum; Endoplasmic Reticulum - metabolism; Gene expression; Genetic engineering; Genetic research; Green Fluorescent Proteins - metabolism; Homeostasis; Humans; Kinases; Lymphatic system; Medicine; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Transgenic; mRNA; Mutation; Neurons; Neurons - metabolism; Neurophysiology; Neurosciences; Neurotoxicity; PC12 Cells; Peptides - chemistry; Prion protein; Prions (Proteins); Prions - biosynthesis; Prions - genetics; Proteasome Endopeptidase Complex - metabolism; Proteasomes; Protein binding; Protein Biosynthesis; Protein expression; Protein folding; Proteins; Proteolysis; Rats; RNA; Signal transduction; Splicing; Stress; Stress (Physiology); Stresses; Tonna; Transcription factors; Transgenic mice; Translocation; Ubiquitin; Italy
• ISSN: 1932-6203; 1932-6203
• DOI: 10.1371/journal.pone.0019339

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.