Selective Processing and Metabolism of Disease-Causing Mutant Prion Proteins

Abstract

Prion diseases are fatal neurodegenerative disorders caused by aberrant metabolism of the cellular prion protein (PrPC). In genetic forms of these diseases, mutations in the globular C-terminal domain are hypothesized to favor the spontaneous generation of misfolded PrP conformers (including the transmissible PrPSc form) that trigger downstream pathways leading to neuronal death. A mechanistic understanding of these diseases therefore requires knowledge of the quality control pathways that recognize and degrade aberrant PrPs. Here, we present comparative analyses of the biosynthesis, trafficking, and metabolism of a panel of genetic disease-causing prion protein mutants in the C-terminal domain. Using quantitative imaging and biochemistry, we identify a misfolded subpopulation of each mutant PrP characterized by relative detergent insolubility, inaccessibility to the cell surface, and incomplete glycan modifications. The misfolded populations of mutant PrPs were neither recognized by ER quality control pathways nor routed to ER-associated degradation despite demonstrable misfolding in the ER. Instead, mutant PrPs trafficked to the Golgi, from where the misfolded subpopulation was selectively trafficked for degradation in acidic compartments. Surprisingly, selective re-routing was dependent not only on a mutant globular domain, but on an additional lysine-based motif in the highly conserved unstructured N-terminus. These results define a specific trafficking and degradation pathway shared by many disease-causing PrP mutants. As the acidic lysosomal environment has been implicated in facilitating the conversion of PrPC to PrPSc, our identification of a mutant-selective trafficking pathway to this compartment may provide a cell biological basis for spontaneous generation of PrPSc in familial prion disease.

Alternative fates of newly formed PrPSc upon prion conversion on the plasma membrane

“…This mechanism clears misfolded or aggregated protein from the Golgi and transfers them to the lysosome for degradation (Anelli and Sitia, 2008;Arvan et al, 2002). This pathway has previously been implicated in the clearance of misfolded PrP isoforms generated by inherited prion disease mutations or pharmacological manipulation of PrP trafficking in neuronal cells (Ashok and Hegde, 2009;Gilch et al, 2001). The results presented here extend these findings to infectious PrP isoforms, where PrP Sc formed following inocula exposure at the cell surface enters the Golgi via the retrograde pathway before being targeted for degradation.…”

Pathogenic Mutations within the Hydrophobic Domain of the Prion Protein Lead to the Formation of Protease-Sensitive Prion Species with Increased Lethality

“…Although some alterations in processing and cleavage were observed, the presence of the G113V or A116V mutation did not alter the localization or expression of PrP. Furthermore, similar to MoPrP C , PrP C associated with G113V and A116V was shown here to be detergent soluble (in agreement with a previous study [60]), and separation of PrP by velocity gradient sedimentation revealed no gross differences compared to MoPrP.…”

Homodimerization as a molecular switch between low and high efficiency PrPCcell surface delivery and neuroprotective activity

“…[19][20][21] In addition, PrP C familial or artificial mutants that accumulate intracellularly are also neurotoxic. 22,23 Dimerization may help preventing fatal accumulation of intracellular PrP C . According to our model, we predict that promoting PrP C dimerization in the secretory pathway may help fighting neurotoxic insults, including the neutralisation of β-sheet oligomers (Fig.…”