Prion Peptide 106–126 Modulates the Aggregation of Cellular Prion Protein and Induces the Synthesis of Potentially Neurotoxic Transmembrane PrP

Abstract

In infectious and familial prion disorders, neurodegeneration is often seen without obvious deposits of the scrapie prion protein (PrPSc), the principal cause of neuronal death in prion disorders. In such cases, neurotoxicity must be mediated by alternative pathways of cell death. One such pathway is through a transmembrane form of PrP. We have investigated the relationship between intracellular accumulation of prion protein aggregates and the consequent up-regulation of transmembrane prion protein in a cell model. Here, we report that exposure of neuroblastoma cells to the prion peptide 106–126 catalyzes the aggregation of cellular prion protein to a weakly proteinase K-resistant form and induces the synthesis of transmembrane prion protein, the proposed mediator of neurotoxicity in certain prion disorders. The N terminus of newly synthesized transmembrane prion protein is cleaved spontaneously on the cytosolic face of the endoplasmic reticulum, and the truncated C-terminal fragment accumulates on the cell surface. Our results suggest that neurotoxicity in prion disorders is mediated by a complex pathway involving transmembrane prion protein and not by deposits of aggregated and proteinase K-resistant PrP alone. In infectious and familial prion disorders, neurodegeneration is often seen without obvious deposits of the scrapie prion protein (PrPSc), the principal cause of neuronal death in prion disorders. In such cases, neurotoxicity must be mediated by alternative pathways of cell death. One such pathway is through a transmembrane form of PrP. We have investigated the relationship between intracellular accumulation of prion protein aggregates and the consequent up-regulation of transmembrane prion protein in a cell model. Here, we report that exposure of neuroblastoma cells to the prion peptide 106–126 catalyzes the aggregation of cellular prion protein to a weakly proteinase K-resistant form and induces the synthesis of transmembrane prion protein, the proposed mediator of neurotoxicity in certain prion disorders. The N terminus of newly synthesized transmembrane prion protein is cleaved spontaneously on the cytosolic face of the endoplasmic reticulum, and the truncated C-terminal fragment accumulates on the cell surface. Our results suggest that neurotoxicity in prion disorders is mediated by a complex pathway involving transmembrane prion protein and not by deposits of aggregated and proteinase K-resistant PrP alone. normal cell-associated prion protein PrP peptide including residues 106–126 biotin-tagged at the N terminus PrP peptide with a scrambled 106–126 sequence biotin-tagged at the N terminus conformationally transformed scrapie form of PrP β-amyloid peptide of amyloid precursor protein proteinase K phosphatidylinositol-specific phospholipase C endoplasmic reticulum 3,3′-diaminobenzidine glycosylphosphatidylinositol N-glycosidase F transmembrane PrP lysosomes nucleus endosomes Prion disorders manifest when the prion protein (PrPC),1 a normal cell surface glycoprotein, undergoes a conformational change from a predominantly α-helical to a β-sheet-rich structure that is pathogenic (PrPSc). This transformation is initiated by an exogenous source of PrPSc in cases acquired by infection, triggered by mutation(s) in the prion protein gene in inherited forms, and is a random, spontaneous event in sporadic cases. Following the initial conversion, subsequent transformation of additional PrPC molecules progresses autocatalytically, resulting in deposits of PrPSc in the brain parenchyma. Unlike PrPC, PrPSc aggregates easily, is insoluble in nonionic detergents, and is partially resistant to limited digestion by proteinase K. Deposits of PrPSc in the brain parenchyma are believed to be the principal cause of neuronal toxicity in prion disorders (1Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13363-13383Crossref PubMed Scopus (5168) Google Scholar, 2Cohen F.E. Prusiner S.B. Annu. Rev. Biochem. 1998; 67: 793-819Crossref PubMed Scopus (473) Google Scholar, 3Caughey B. Nat. Med. 2000; 6: 751-754Crossref PubMed Scopus (68) Google Scholar). Although PrPSc is believed to be responsible for both transmission and pathogenicity in all prion disorders, the molecular events leading to PrPSc-induced transformation of additional PrPC molecules and the consequent neuronal toxicity are poorly understood. Because neurodegenerative changes typical of prion disorders are often seen without detectable PrPSc, alternative mechanisms of neuronal death besides PrPSc deposition have been suggested (4Brown P. Gibbs C.J. Rodgers-Johnson P. Asher D.M. Sulima M.P. Bacote A. Goldfarb L.G. Gajdusek D.C. Ann. Neurol. 1994; 35: 513-529Crossref PubMed Scopus (731) Google Scholar, 5Tateishi J. Kitamoto T. Brain Pathol. 1995; 5: 53-59Crossref PubMed Scopus (94) Google Scholar, 6Tateishi J. Kitamoto T. Hoque M.Z. Furukawa H. Neurology. 1996; 40: 1578-1581Crossref Google Scholar). One such mechanism is through the preferred synthesis of CtmPrP, a transmembrane form of PrP that spans the endoplasmic reticulum (ER) membrane at residues 113–135 with its N terminus in the cytosol, rather than the normal glycolipid-linked PrPC that is translocated co-translationally into the ER lumen. Mice carrying the mutant PrP transgene A117V that has an increased predilection forCtmPrP synthesis show spontaneous neurodegeneration without detectable PrPSc and, when challenged with infectious prions, show neurodegeneration earlier and with smaller amounts of accumulated PrPSc than the corresponding animals with a deleted transmembrane domain. In fact, in these cases the extent of neurodegeneration correlates directly with the amount ofCtmPrP rather than PrPSc load, indicating thatCtmPrP, and not accumulated PrPSc, is responsible for the observed neurodegeneration (7Hegde R.S. Mastrianni J.A. Scott M.R. DeFea K.A. Tremblay P. Torchia M. DeArmond S.J. Prusiner S.B. Lingappa V.R. Science. 1998; 279: 827-834Crossref PubMed Scopus (617) Google Scholar, 8Hegde R.S. Trembly P. Groth D. DeArmond S.J. Prusiner S.B. Lingappa V.R. Nature. 1999; 402: 822-826Crossref PubMed Scopus (269) Google Scholar). We have examined the initial events of PrPC aggregation in a cell model, and the correlation between intracellular accumulation of aggregated PrPC and CtmPrP generation. To initiate the aggregation of endogenous PrPC, we have used an internal peptide of PrP comprising residues 106–126 (PrP106–126) instead of the proteinase K (PK)-resistant core of PrPSc that constitutes the infectious prion particle. PrP106–126 offers the advantage of being similar to PrPSc in several and at the is and to for cell PrPSc, PrP106–126 is in aggregates that are and and is to of J. 2000; PubMed Scopus Google Scholar, M. J. J. 2000; PubMed Scopus Google Scholar, Biochem. J. 2000; PubMed Google Scholar). residues of PrP have been to be for the transformation of PrPC, these the principal of of PrPSc to PrPC the K. D. T. H. F.E. Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. 1995; Scopus Google Scholar, J. F.E. Prusiner 1995; PubMed Scopus Google Scholar, J. B. B. J. 1998; PubMed Scopus Google Scholar, H. A. J. 1998; PubMed Google Scholar). This be to residues are for the and Biochem. J. 2000; PubMed Google Scholar, J. B. B. J. 1998; PubMed Scopus Google Scholar). In we that when neuroblastoma cells are to of of the aggregation of cellular deposits that in the is increased synthesis of the transmembrane CtmPrP in these Our the for transformation of PrPC into aggregated and weakly in a cell model. show a correlation between intracellular PrPC aggregation and CtmPrP indicating that is mediated by complex cellular and not by deposits of cell from from and from PrP106–126 and biotin-tagged scrambled PrP106–126 synthesized and from to PrP residues from for in to a between residues of in D. S. A. S. S. P. P. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). including to the protein and from neuroblastoma cells H. S. P. J. PubMed Scopus Google and in the of B. brain cells from the of brain from with and by through a from aggregates of by a at for The cells and the cells on in and for The with To for neuronal the to the of the cells on rather than in and to the The synthesized for the biotin-tagged PrP106–126 and biotin-tagged scrambled of PrP106–126 not its Biochem. J. 2000; PubMed Google Scholar, A. H. J. PubMed Scopus Google Scholar). in and the of PrP106–126 in and at for to The used to neuroblastoma cells brain the neuroblastoma cells and with peptide Brain cells in the of peptide for all used to cellular PrP. This is to residues of PrP and not with The of has been in several by H. J. J. J. 1999; PubMed Scopus Google Scholar, D. J. PubMed Scopus Google Scholar, D. S. A. S. S. P. P. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar). biotin-tagged PrP106–126 biotin-tagged used of the of with cell surface of the membrane with cells in normal in and with by intracellular cells with to cells with for to and in observed with a and a of several in cells with with and and endogenous by cells to The cells with by and to 3,3′-diaminobenzidine to an and with the cells in in and for with and to the for the intracellular cells with cells by and examined with a with for H. S. P. J. PubMed Scopus Google Scholar, T. S. P. J. 1999; PubMed Scopus Google Scholar). with by on an by with with of in with of in cells with in for at and in the to with H. S. P. J. PubMed Scopus Google Scholar, T. S. P. J. 1999; PubMed Scopus Google Scholar). at in a for and with for C-terminal residues of PrP H. S. P. J. PubMed Scopus Google Scholar, T. S. P. J. 1999; PubMed Scopus Google Scholar, P. P. J. 1995; PubMed Scopus Google Scholar). to residues and of PrP and and the fragment of PrP. and to both the and of PrP with in a nonionic and aggregates and by at and the at in a for at The and and by of and with the is all of the aggregated PrPC and PrP106–126 in the and rather than in the observed for aggregated PrP. of proteinase K of (PrP106–126) cells to for at The with and and with H. S. P. J. PubMed Scopus Google Scholar, T. S. P. J. 1999; PubMed Scopus Google Scholar). F H. S. P. J. PubMed Scopus Google Scholar, T. S. P. J. 1999; PubMed Scopus Google Scholar). with and on in a and by of a The for cell and to The resulting at to membrane The in of and and with proteinase K on for the of to the membrane in and with with for and and with the cells with a of for and with by with with with the to the to and In a we that exposure of neuroblastoma cells to of PrP106–126 to intracellular accumulation of aggregated scrambled PrP106–126 is A. H. J. PubMed Scopus Google Scholar). To the of exposure of cells to neuroblastoma cells of PrPC for in at the N The cells and the peptide for the by with the and the of cell by the of cells the peptide in at and is not to neuroblastoma cells of of PrP106–126 and the corresponding scrambled peptide with cells by used to cellular PrPC and to biotin-tagged PrP106–126 the corresponding scrambled Because the for between residues of not to and a of between PrPC and of exposure to cells with and for PrP106–126 To surface with to at including of the to aggregates of PrP106–126 are at the cell surface of with and aggregates to be and are and cells with show for the peptide a surface for PrPC with and and cells show with induces the aggregation and of cell surface surface of cells with for with to PrPC by to of PrPC and PrP106–126 aggregates on the membrane and aggregates of that for PrPC and PrP106–126 and smaller aggregates that to be are and of cells with for a similar of with a normal of PrP on the cell surface and in the and cells with with show PrP and of the cells a of the surface of cells with In cells with show aggregates of PrPC on the cell surface that are in In the aggregates to the nucleus The in in a membrane of cells with with normal of PrP in cells with PrP106–126 show with PrP106–126 and aggregates similar with normal PrP in cells cells show intracellular aggregates of PrPC with the aggregates PrP106–126 aggregates in of cells similar of PrPC be on the membrane of cells with In cells show intracellular aggregates of PrPC cells with PrP106–126 show PrP of cells with for of lysosomes in cells with the are obvious of cellular such of in cells results by with PrP106–126 and with without The with the and to an with and to a with in the of scrambled peptide show a of PrPC on the cell surface cells show aggregation of PrPC at the membrane and The aggregates in and are in In cases the aggregates are to the membrane The intracellular of aggregated PrPC by of with scrambled peptide PrP106–126 for with and to the aggregates at in the cells with scrambled peptide show the intracellular of PrPC in the cells show aggregates of PrP106–126 and complex aggregates PrP106–126 at the cell surface and in intracellular with an similar cells show normal PrP cells show intracellular aggregates with for and to PrP106–126 residues and the aggregates with a be aggregates of the aggregated peptide a of PrPC on the membrane of cells with scrambled peptide In cells show intracellular aggregates of PrPC by a membrane in cases to the cells with PrP106–126 and in show for PrPC The results show that PrP106–126 induces the aggregation and of cell surface PrPC in The aggregates and cause a of lysosomes in cells with PrP106–126 with to in is of the changes observed the of PrPC to is by cell in a and and the at to at PrP is in the of To aggregated PrPC is insoluble in detergents, cells with scrambled peptide and cells to PrP106–126 for to the and the and from and with to PrP106–126 PrPC, Because of the aggregates in the and the at is in with and normal PrP for both cells with biotin-tagged and cells in the of biotin-tagged PrP106–126 In protein that with both and are in the of cells and and the with indicating that the protein aggregates in cells are to be by the the and that these are complex aggregates of PrPC and PrP106–126 and amount of PrP106–126 is at in that with that PrP106–126 to the is not into the in cells are and insoluble in and The aggregated PrP constitutes than of the cellular is in the exposure is in to show aggregates in the To the cells with for on and with for on to with The insoluble with and aggregates of and PrP106–126 are in cell of to be membrane the of cellular that have been by the with scrambled peptide show membrane aggregates To intracellular aggregates of and PrPC the cells with for in with and with the by the S. of aggregates be seen in intracellular similar to the observed in with by that of the aggregates for and of the aggregates not show PrPC and are to by aggregated PrPC aggregates not with the PrP106–126 not that the for these are not of aggregation change in of in cells in cells with scrambled peptide not of cells with a intracellular that with in the of the exposure of cells to the aggregates of both PrP106–126 and PrPC of the of Although the neuroblastoma cells used intracellular aggregates of PrP106–126 without toxicity by these are cells that in and not the of neuronal To similar aggregation of PrPC be in of brain cells from and for with for The cells to and for PrPC and PrP106–126 with protein and to cell in the brain of PrPC and PrP106–126 be seen in neuronal cell neuronal and of the intracellular deposits for PrPC and PrP106–126 indicating the of aggregates seen for neuroblastoma of the cells in brain show of PrP106–126 to cells with are for to not To the of aggregated PrPC in cells with of cells with PrP106–126 for with and with to cell surface the and to with to residues by PrP in the of cells with indicating that of the intracellular accumulated PrPC is and aggregates The amount of PrPC from the cell surface is similar in and for a in the fragment in cells and This fragment with and indicating the of of on the cell in with the and with that the fragment is and C-terminal and of the of fragment in with PrP that in constitutes of the than of is at the cell surface and with the amount of to than of is at the cell surface and of surface with that the amount of fragment on the surface of cells is at to cells and similar of PrP is observed in and have that PrPC in at the synthesis of of the transmembrane is believed to the neurodegeneration observed in certain inherited and infectious prion disorders (7Hegde R.S. Mastrianni J.A. Scott M.R. DeFea K.A. Tremblay P. Torchia M. DeArmond S.J. Prusiner S.B. Lingappa V.R. Science. 1998; 279: 827-834Crossref PubMed Scopus (617) Google Scholar, 8Hegde R.S. Trembly P. Groth D. DeArmond S.J. Prusiner S.B. Lingappa V.R. Nature. 1999; 402: 822-826Crossref PubMed Scopus (269) Google Scholar). to PrPC, CtmPrP is in the ER membrane through its including residues with its N terminus in the and C terminus in the ER lumen. of an C-terminal is increased in brain from animals (7Hegde R.S. Mastrianni J.A. Scott M.R. DeFea K.A. Tremblay P. Torchia M. DeArmond S.J. Prusiner S.B. Lingappa V.R. Science. 1998; 279: 827-834Crossref PubMed Scopus (617) Google Scholar). Because fragment to the must To the fragment observed in cells is the cleaved CtmPrP, from cells in the of PrP106–126 for with on for in (7Hegde R.S. Mastrianni J.A. Scott M.R. DeFea K.A. Tremblay P. Torchia M. DeArmond S.J. Prusiner S.B. Lingappa V.R. Science. 1998; 279: 827-834Crossref PubMed Scopus (617) Google Scholar, 8Hegde R.S. Trembly P. Groth D. DeArmond S.J. Prusiner S.B. Lingappa V.R. Nature. 1999; 402: 822-826Crossref PubMed Scopus (269) Google Scholar). The with and the in and to with of PrPC are from the in both and cells and In is a in the fragment digestion of cells indicating that the fragment is by limited ofCtmPrP and, that the of PrP molecules in the CtmPrP is in cells than in of to a the cytosolic C-terminal the of and the of the and Because the of PrPC molecules in the than of the PrPC in and cells R.S. J. PubMed Scopus Google the observed in peptide cells is of the of fragment with PrP a in the fragment in cells with the of the results in an of in the amount of with a in the and is to the fragment in cells by is by To that the fragment in the and cells for at to of from the to with and by Because of PrP the is these PrP with core are The form and the C-terminal fragment that is a of normal of PrP from the membrane are and is a accumulation of the is in cells with the Because is for the C-terminal residues of these results that the is a C-terminal fragment of and in the the fragment constitutes of PrP in with in an of to of the cells with PrP106–126 To the that is a of PrP in the PrPC cells for at and for at the in the of to of from the The fragment is the not with indicating that not from PrPC not the is and are to the the with the PrPC forms, be from the cell surface by of and similar of not the results show that the fragment is not a of PrPC in the from an form of is in The fragment is of spontaneous of CtmPrP at the cytosolic face of the and is the to the to limited digestion by is the of PrPSc, and is of the at for Although the amount of used for PrP in cell is of and the than the used to PrPSc in the an of a change in of PrPC, an the transformation to To aggregated PrPC in cell is of and cells to of for The in the with and by with In the with scrambled PrPC is of with of the form In a amount of PrP from cells with PrP106–126 is resistant to at of with that the resistant in cells of PrPC and a C-terminal fragment of both of are at in cells with the Because the fragment of PrPSc has a N terminus is cleaved at in (7Hegde R.S. Mastrianni J.A. Scott M.R. DeFea K.A. Tremblay P. Torchia M. DeArmond S.J. Prusiner S.B. Lingappa V.R. Science. 1998; 279: 827-834Crossref PubMed Scopus (617) Google both have a similar molecular of on to between the from the of to and its in not not to be aggregated the fragment the of aggregated PrPC rather than truncated In a amount of PrP is resistant to digestion in the of its of This report the of mechanisms of PrPSc-induced aggregation of consequent neurodegeneration in we show that a β-sheet-rich peptide of PrP catalyzes the aggregation of endogenous PrPC in a cell model, the of PrP we that intracellular accumulation of PrP aggregates to up-regulation of the synthesis of CtmPrP, and we show that of CtmPrP accumulates a C-terminal fragment on the cell surface. results suggest that the mediator of neurotoxicity in prion disorders is the of intracellular aggregated PrP by the aggregation of additional PrPC molecules at the cell a for that the neurodegenerative This report is the of a change in of endogenous PrPC into an partially form by an peptide of PrP. Although the cellular and of PrPSc and neuronal toxicity that transmission of PrPSc by the of PrPC into the PrPSc have been proposed to the mechanism of conformational of endogenous PrPC to PrPSc, and the PubMed Scopus Google Scholar, PubMed Scopus Google Scholar). We show that a β-sheet-rich internal fragment of PrP106–126 the aggregation of PrPC on the membrane of and catalyzes its accumulation in an We that PrP106–126 the the induces its Here, a for the deposition of additional PrPC Because have an for J. 2000; PubMed Scopus Google Scholar, T. M. H. M. K. J. 1999; PubMed Scopus Google aggregated in of the is the preferred for endogenous PrPC and the for PrPC to PrPSc J. T. M. T. J. J. J. Pathol. PubMed Scopus Google Scholar, A. Scott M. A. D. Prusiner S.B. J. 1995; PubMed Scopus Google Scholar, A. A. J. PubMed Scopus Google an for the of PrP106–126 and PrPC, and subsequent aggregation of the Following the initial aggregation of PrPC at the the complex aggregates of PrPC and PrP106–126 are to the and the membrane a in transformation to an accumulation of PrPC and PrP106–126 aggregates the of lysosomes observed in cell model, and the of PrP lysosomes in the of animals and J. T. M. T. J. J. J. Pathol. PubMed Scopus Google Scholar, F.E. J. P. 1999; PubMed Scopus Google Scholar). similar change in from an α-helical to a structure has been for and for certain when to an T. M. H. M. K. J. 1999; PubMed Scopus Google Scholar, S. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google and is with the that the accumulation and the of PrPSc in cells S. F.E. Prusiner S.B. Scott M.R. Proc. Natl. Acad. Sci. U. S. A. 1999; PubMed Scopus Google Scholar, K. B. J. 2000; PubMed Scopus Google Scholar). The intracellular aggregates of PrPC several of the typical of to digestion by proteinase K and by of the aggregated PrPC is insoluble in and be by to PrPSc that the similar of PrPC aggregates observed in cell a conformational of PrPC rather than conformational into PrP leading to PrPSc is is to that of prion have been in with peptide without correlation with PrPSc deposition K. H. H. Groth D. Torchia M. Tremblay P. J. Prusiner S.B. DeArmond S.J. F.E. J. 2000; PubMed Scopus Google in the results in similar aggregation of PrPC in brain cells to results in neuroblastoma and the of a similar sequence of events of animals and to exogenous PrPSc The aggregates of PrP106–126 and PrPC in brain cells are not in neuronal and cell in neuronal and is that these aggregates to cells by are into the and are by intracellular PrP aggregates be directly to the cells and that in the observed in the of show similar accumulates in lysosomes and is from the cell without H. J. 1999; PubMed Scopus Google Scholar). Because PrPSc in is in and to with the of PrPSc through PrP106–126 that are resistant to and have the to into with the membrane The of such a the of PrPSc in the brain in an This for the that intracellular accumulation of aggregated PrPC the synthesis of CtmPrP, the proposed mediator of neurodegeneration in certain inherited and infectious prion disorders (7Hegde R.S. Mastrianni J.A. Scott M.R. DeFea K.A. Tremblay P. Torchia M. DeArmond S.J. Prusiner S.B. Lingappa V.R. Science. 1998; 279: 827-834Crossref PubMed Scopus (617) Google Scholar, 8Hegde R.S. Trembly P. Groth D. DeArmond S.J. Prusiner S.B. Lingappa V.R. Nature. 1999; 402: 822-826Crossref PubMed Scopus (269) Google Scholar). of that the C-terminal fragment of PrP that accumulates on the surface of PrP106–126 cells from of from cells a in the C-terminal and a in peptide its transmembrane with N terminus in the In and PrP has been to in the transmembrane R.S. J. PubMed Scopus Google with the in the fragment observed in cell model. is at a in the surface of fragment in cells that is similar in molecular and to the fragment ofCtmPrP The amount of and not PrP in the of a and with its from CtmPrP, is by the R.S. B. PubMed Scopus Google Scholar). The fragment is for and is to the membrane of This fragment not with in of PrP from the ER is its from in a cell mutant the and aggregates in the a similar fragment is an in Because is the of its transmembrane is in a to the the at the the that the fragment is from CtmPrP and not from translocated PrP in the Although the of CtmPrP in neurotoxicity has been by an in with PrPSc R.S. Trembly P. Groth D. DeArmond S.J. Prusiner S.B. Lingappa V.R. Nature. 1999; 402: 822-826Crossref PubMed Scopus (269) Google is the of a correlation between intracellular accumulation of PrP aggregates and up-regulation of CtmPrP The that of CtmPrP is cleaved spontaneously on the cytosolic face of the ER and the truncated C-terminal fragment is on the cell surface and the of CtmPrP and mechanisms of neuronal its through cell membrane S. D. 2000; PubMed Scopus Google Scholar). truncated CtmPrP in cell is and not to be through the transmembrane is into the by of the ofCtmPrP at the ER membrane its with the membrane at residues 113–135 of the membrane of the truncated CtmPrP has been to into the of of the R.S. J. PubMed Scopus Google the transmembrane not to be to membrane by truncated CtmPrP must an alternative mechanism for neurotoxicity in cell model. Because fragment the of comprising residues that is of PrP from the cell surface P. P. J. 1995; PubMed Scopus Google the truncated CtmPrP initiate aggregation of additional PrPC molecules at the cell surface by a a surface Although the mechanism by CtmPrP neurotoxicity is not from a correlation between aggregation of PrPC and ofCtmPrP and the pathway ofCtmPrP and the for on the cellular pathways Although truncated CtmPrP similar in molecular to the fragment from of the in the limited of PrP observed in the of a change in the of PrPC of its conformational to on the results from a of transmembrane PrP in the ER and is to in the of PrPSc accumulates in intracellular truncated CtmPrP is on the cell surface and is by the fragment in from aggregated and conformationally transformed PrPC and not truncated is intracellular aggregated PrPC, truncated CtmPrP is the in the of prion disorders. In suggest the sequence of events when cells are to an peptide of in in a cell of PrP106–126 to the membrane and initiate the aggregation of PrPC, is and to into β-sheet-rich The intracellular PrP aggregates the synthesis of CtmPrP, an the of CtmPrP is cleaved by a cytosolic and the C-terminal fragment of CtmPrP accumulates on the cell to the membrane by the these that aggregated and PrPSc is not the of neurotoxicity and that several through complex and to the of neuronal death in the cell not of the mechanism of the cellular pathways of We P. for M. S. for the J. for the of for in and of the and for with