Proteasomes and ubiquitin are involved in the turnover of the wild-type prion protein.
Prion diseases propagate by converting a normal glycoprotein of the host, PrP(C), into a pathogenic "prion" conformation. Several misfolding mutants of PrP(C) are degraded through the ER-associated degradation (ERAD)-proteasome pathway. In their infectious form, prion diseases such as bovine spongiform encephalopathy involve PrP(C) of wild-type sequence. In contrast to mutant PrP, wild-type PrP(C) was hitherto thought to be stable in the ER and thus immune to ERAD. Using proteasome inhibitors, we now show that approximately 10% of nascent PrP(C) molecules are diverted into the ERAD pathway. Cells incubated with N-acetyl-leucinal-leucinal-norleucinal (ALLN), lactacystin or MG132 accumulated both detergent-soluble and insoluble PrP species. The insoluble fraction included an unglycosylated 26 kDa PrP species with a protease-resistant core, and a M(r) "ladder" that contained ubiquitylated PrP. Our results show for the first time that wild-type PrP(C) molecules are subjected to ERAD, in the course of which they are dislocated into the cytosol and ubiquitylated. The presence of wild-type PrP molecules in the cytosol may have potential pathogenic implications.
Yedidia
Y
Y
Department of Molecular Biology, The Hebrew University-Hadassah Medical School, PO Box 12272, Jerusalem 91120, Israel.
Horonchik
L
L
Tzaban
S
S
Yanai
A
A
Taraboulos
A
A
D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D016466:CHO Cells; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000378:metabolism; D007976:Leupeptins / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018621:PrPC Proteins / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex; D011499:Protein Processing, Post-Translational; D012995:Solubility; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism*
D007976:Leupeptins; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D018621:PrPC Proteins; D011480:Protease Inhibitors; D025801:Ubiquitin; C063261:acetylleucyl-leucyl-norleucinal; D020126:Brefeldin A; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex