Cell Surface Accumulation of a Truncated Transmembrane Prion Protein in Gerstmann-Straussler-Scheinker Disease P102L

Abstract

A familial prion disorder with a proline to leucine substitution at residue 102 of the prion protein (PrP102L) is typically associated with protease-resistant PrP fragments (PrPSc) in the brain parenchyma that are infectious to recipient animals. When modeled in transgenic mice, a fatal neurodegenerative disease develops, but, unlike the human counterpart, PrPSc is lacking and transmission to recipient animals is questionable. Alternate mice expressing a single copy of PrP102L (mouse PrP101L) do not develop spontaneous disease, but show dramatic susceptibility to PrPSc isolates from different species. To understand these discrepant results, we studied the biogenesis of human PrP102L in a cell model. Here, we report that cells expressing PrP102L show decreased expression of the normal 18-kDa fragment on the plasma membrane. Instead, a 20-kDa fragment, probably derived from transmembrane PrP (CtmPrP), accumulates on the cell surface. Because the 20-kDa fragment includes an amyloidogenic region of PrP that is disrupted in the 18-kDa form, increased surface expression of 20-kDa fragment may enhance the susceptibility of these cells to PrPSc infection by providing an optimal substrate, or by amplifying the neurotoxic signal of PrPSc. Thus, altered susceptibility of PrP101L mice to exogenous PrPSc may be mediated by the 20-kDa CtmPrP fragment, rather than PrP102L per se. A familial prion disorder with a proline to leucine substitution at residue 102 of the prion protein (PrP102L) is typically associated with protease-resistant PrP fragments (PrPSc) in the brain parenchyma that are infectious to recipient animals. When modeled in transgenic mice, a fatal neurodegenerative disease develops, but, unlike the human counterpart, PrPSc is lacking and transmission to recipient animals is questionable. Alternate mice expressing a single copy of PrP102L (mouse PrP101L) do not develop spontaneous disease, but show dramatic susceptibility to PrPSc isolates from different species. To understand these discrepant results, we studied the biogenesis of human PrP102L in a cell model. Here, we report that cells expressing PrP102L show decreased expression of the normal 18-kDa fragment on the plasma membrane. Instead, a 20-kDa fragment, probably derived from transmembrane PrP (CtmPrP), accumulates on the cell surface. Because the 20-kDa fragment includes an amyloidogenic region of PrP that is disrupted in the 18-kDa form, increased surface expression of 20-kDa fragment may enhance the susceptibility of these cells to PrPSc infection by providing an optimal substrate, or by amplifying the neurotoxic signal of PrPSc. Thus, altered susceptibility of PrP101L mice to exogenous PrPSc may be mediated by the 20-kDa CtmPrP fragment, rather than PrP102L per se. Gerstmann-Straussler-Scheinker disease mutant PrP normal cell-associated PrP conformationally transformed scrapie form of PrP transmembrane PrP with the C terminus in the endoplasmic reticulum lumen transmembrane PrP with the N terminus in the ER lumen PrP with a Pro to Leu mutation at codon 102 of the prion protein proteinase K N-glycosidase F glycosyl phosphatidylinositol phosphatidylinositol-specific phospholipase C endoplasmic reticulum fluorescein isothiocyanate phosphate-buffered saline Tris-buffered saline Dulbecco's modified Eagle's medium phenylmethylsulfonyl fluoride tetramethyl rhodamine isothiocyanate Familial prion disorders of humans segregate with mutations in the prion protein gene (PRNP). Based on the clinicopathological presentation, these disorders are categorized as Gerstmann-Straussler-Scheinker disease (GSS),1 Creutzfeldt-Jakob disease, and fatal familial insomnia (reviewed in Refs. 1Prusiner S.B. Cold Spring Harbor Symp. Quant. Biol. 1996; LXI: 473-493Google Scholar, 2Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 13363-13383Crossref PubMed Scopus (5221) Google Scholar, 3Weissmann C. J. Biol. Chem. 1999; 274: 3-6Abstract Full Text Full Text PDF PubMed Scopus (148) Google Scholar, 4Collinge J. Annu. Rev. Neurosci. 2001; 24: 519-550Crossref PubMed Scopus (1119) Google Scholar). A proline to leucine substitution at codon 102 of PRNP is one of the most frequent mutations associated with GSS, and also one of the earliest prion disorders to be ascribed a genetic etiology (5Hsiao K. Baker H.F. Crow T.J. Poulter M. Owen F. Terwilliger J.D. Westaway D Ott J. Prusiner S.B. Nature. 1989; 338: 342-345Crossref PubMed Scopus (704) Google Scholar, 10Hsiao K. Dlouhy S.R. Farlow M.R. Cass C., Da Costa M. Conneally P.M. Hodes M.E. Ghetti B. Prusiner S.B. Nat. Genet. 1992; 1: 68-71Crossref PubMed Scopus (218) Google Scholar). Most GSS cases present with cerebellar ataxia and dementia, and a prominent pathological feature is the presence of multicentric amyloid plaques composed of protease resistant PrP fragments of 8, 15, and 21–30 kDa. Although the 21-kDa fragment has also been observed in Creutzfeldt-Jakob disease, the 8-kDa fragment appears specific to GSS (6Barbanti P. Fabbrini G. Salvatore M. Petraroli R. Cardone F. Maras B. Equestre M. Macchi G. Lenzi G.L. Pocchiari M. Neurology. 1996; 47: 734-741Crossref PubMed Scopus (70) Google Scholar, 7Piccardo P. Dlouhy S.R. Lievens P.M.J. Young K. Bird T.D. Nochlin D. Dickson D.W. Vinters H.V. Zimmerman T.R. Mackenzie I.R.A. Kish S.J. Ang L.-C., De Carli C. Pocchiari M. Brown P. Gibbs C.J., Jr. Gajdusek D.C. Bugiani O. Ironside J. Tagliavini F. Ghetti B. J. Neuropathol. Exp. Neurol. 1998; 57: 979-988Crossref PubMed Scopus (188) Google Scholar, 8Parchi P. Chen S.G. Brown P. Zou W. Capellari S. Budka H. Hainfellner J. Reyes P.F. Golden G.T. Hauw J.J. Gajdusek D.C. Gambetti P. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 8322-8327Crossref PubMed Scopus (187) Google Scholar). The 21–30-kDa fragments are more prominent in GSS102L with a spongiform change, and low molecular mass fragments of 8 or 7–15 kDa are predominant in cases with multicentric amyloid plaques (7Piccardo P. Dlouhy S.R. Lievens P.M.J. Young K. Bird T.D. Nochlin D. Dickson D.W. Vinters H.V. Zimmerman T.R. Mackenzie I.R.A. Kish S.J. Ang L.-C., De Carli C. Pocchiari M. Brown P. Gibbs C.J., Jr. Gajdusek D.C. Bugiani O. Ironside J. Tagliavini F. Ghetti B. J. Neuropathol. Exp. Neurol. 1998; 57: 979-988Crossref PubMed Scopus (188) Google Scholar, 8Parchi P. Chen S.G. Brown P. Zou W. Capellari S. Budka H. Hainfellner J. Reyes P.F. Golden G.T. Hauw J.J. Gajdusek D.C. Gambetti P. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 8322-8327Crossref PubMed Scopus (187) Google Scholar, 9Yamada M. Tomimitsu H. Yokota T. Tomi H. Sunohara N. Mukoyama M. Itoh Y. Suematsu N. Otomo E. Okeda R. Matsushita M. Mizusawa H. Neurology. 1999; 52: 260-265Crossref PubMed Google Scholar, 10Hsiao K. Dlouhy S.R. Farlow M.R. Cass C., Da Costa M. Conneally P.M. Hodes M.E. Ghetti B. Prusiner S.B. Nat. Genet. 1992; 1: 68-71Crossref PubMed Scopus (218) Google Scholar). These fragments are generated in vivo and are believed to contribute to the neuropathology observed in these disorders. Modeling of GSS102L in transgenic mice expressing the corresponding PrP mutation (MoPrP P101L) has produced unusual and provocative observations. Animals expressing high levels of the transgene showed spontaneous neurodegeneration at 85–300 days of age without the presence of detectable PK-resistant PrPSc (11Hsiao K.K. Groth D. Scott M. Yang S.L. Serban H. Rapp D. Foster D. Torchia M. DeArmond S.J. Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 9126-9130Crossref PubMed Scopus (276) Google Scholar). The observed neurodegeneration in these mice is believed to result from adverse effects of the mutant PrP rather than overexpression of the transgene (12Telling G.C. Haga T. Torchia M. Tremblay P. DeArmond S.J. Prusiner S.B. Genes Dev. 1996; 10: 1736-1750Crossref PubMed Scopus (238) Google Scholar). Intracerebral inoculation of tissue from diseased animals transmitted the disease to healthy P101L mice expressing low levels of the transgene, but not to mice expressing normal PrP (11Hsiao K.K. Groth D. Scott M. Yang S.L. Serban H. Rapp D. Foster D. Torchia M. DeArmond S.J. Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 9126-9130Crossref PubMed Scopus (276) Google Scholar,12Telling G.C. Haga T. Torchia M. Tremblay P. DeArmond S.J. Prusiner S.B. Genes Dev. 1996; 10: 1736-1750Crossref PubMed Scopus (238) Google Scholar). Subsequently, mice expressing a single copy of the P101L allele generated by to of transgene These mice also but of the animals spontaneous disease, susceptibility to exogenous PrPSc infection altered E. H. R. R. Ironside J. D.W. J. C. J. 1999; PubMed Scopus Google Scholar, E. D.W. Ironside J. R. J. 2001; PubMed Scopus Google Scholar). Thus, appears that PrP102L or of cells that the or of PrPSc. The these discrepant are the biogenesis of PrP102L in human cells in an to the that in and the of in we show that the of PrP102L is in of a 20-kDa fragment of PrP on the cell with a in the expression of 18-kDa fragment, a of normal of PrP from the plasma S.G. P. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The 20-kDa fragment is derived from a transmembrane form of PrP that has been as a of neurodegeneration in and infectious prion disorders Scott M.R. P. Torchia M. S.J. Prusiner S.B. 1998; PubMed Scopus Google Scholar, Tremblay P. Groth D. DeArmond S.J. Prusiner S.B. Nature. 1999; PubMed Scopus Google Scholar). that the in of fragments on PrP102L cells may to PrPSc by the effects of PrP102L in The human cell from J. and Dulbecco's modified Eagle's medium and from and from from protein and N-glycosidase F from phosphatidylinositol-specific phospholipase C from from cells expressing or mutant (PrP102L) prion protein generated as in a report N. G. Chen S.G. H. S. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, G. T. Y. R. S. Gambetti P. N. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). at in with and in a of cells with to the the PrP on cells at different cells and at The in in and S. of and in The is specific and of to an of and to of a cells of protein from cells expressing or with and in a and in Tris-buffered saline of and fluoride by at and protein in the with of at by and to at at in and at and with or in normal as G. T. Y. R. S. Gambetti P. N. J. Biol. Chem. 1999; 274: Full Text Full Text PDF PubMed Scopus Google Scholar). with to and on an by To PrP in the cells with as and the PrP and as a cells expressing PrP102L as N. G. Chen S.G. H. S. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar, Y. M. A. M. Gambetti P. N. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). in in the presence or of the and with in the medium or the medium with normal medium in a of cells with and as by at and to with the in the presence of and to protein with of and the protein by in and by cells with and in normal the the cells with and to as To the glycosyl phosphatidylinositol cells with in medium and as or cells with and in the medium at with or at in a or at in the or presence of and to as at or with with without and with in medium at The medium and at at to in the with of at by and or as with the to or with of and in and with in at with of at in and by or and cells and on in a and with of a The cell and to The at to These in of and and with proteinase K on to the in and with expressing PrP102L on of and PrP102L cells with in medium on and of cells with the at the or at in a the of cells with and with at with and with and by in with to the to PrP on the cell surface. Subsequently, the cells with to the on the cell and with The cells in and the with to that been from the cell surface. a in cells in and observed a The expression of and PrP102L in cells by cell-associated PrP with specific to PrP and or with as of the form of of and of kDa with in the of a of and a at kDa. of PrP102L showed of PrP and the 20-kDa fragment, but in to the PrP102L and the 20-kDa fragment kDa on and and the 20-kDa fragment is more in as with with in to the of observed at and kDa These fragments of the and that are a of normal of PrP from the cell surface S.G. P. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). with a form of kDa and the fragment of kDa. A of the 20-kDa fragment also of PrP102L the of but the 18-kDa fragment and form of kDa detectable showed the PrP as observed as with the 18-kDa fragment and the 20-kDa fragment more in PrP102L the 20-kDa fragment, of 18-kDa fragment of and PrP102L and A 20-kDa observed in as a result of of as with The in of PrP in the and is a result of the in to the PrP that result from at residue of PrP normal from the plasma membrane. The fragments of and kDa that from been in the and do not with of of at residue S.G. P. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). The 20-kDa fragment is by and that is a fragment of The as with not The increased of 20-kDa fragment in be the result of increased from of PrP102L decreased of the 20-kDa fragment by or probably includes the PrP102L The decreased of 18-kDa fragment, on the be by expression of PrP102L on the cell surface of in an normal surface expression but decreased to the plasma membrane. These in the To of the 20-kDa fragment is the result of increased as a result of of and cells with and to with or The of PrP and the 20-kDa fragment with in and PrP102L and as observed in PrP102L and the 20-kDa fragment kDa than and The 20-kDa fragment prominent in but in to the in at the 20-kDa fragment not in PrP102L and with A of 18-kDa fragment be in but in the in and PrP102L and Because the in the of and 20-kDa fragments in and PrP102L at but not a probably as a result of a that and not of an in the of To the results, the and of and PrP102L in a with and and the of surface with at and the medium Subsequently, cell and the to with and by with the show the of and the 20-kDa fragment the of and the 20-kDa fragment decreased in the and a corresponding observed in the and PrP102L showed of and of and 20-kDa to the plasma a in PrP102L of in the and and a form in the PrP102L the decreased with Although the form of not in the with showed that the medium The of the 20-kDa is generated and not with that is not a of is to the cell surface and is by and not or on the cell surface of these show that the 20-kDa fragment from an form of probably the transmembrane PrP (CtmPrP), and the of fragment observed in PrP102L in is not the result of increased or in an but of the 20-kDa fragment from be B. Biol. 2001; PubMed Scopus Google Scholar). To and PrP102L cells with the with and with to The on a to the in of the 20-kDa fragment from and PrP102L the form and the 20-kDa fragment of PrP102L kDa on the 20-kDa fragment from and PrP102L with that is with the observed in the 20-kDa more in PrP102L as with To the 20-kDa fragment from and PrP102L cells with the and to with a in the 20-kDa fragment the PrP and is and by the B. Biol. 2001; PubMed Scopus Google an in a 20-kDa fragment A in a also in The of PrP form is To the of 20-kDa fragment from from and PrP102L cells with on and to with or Because the N terminus of CtmPrP the be by a fragment of kDa in the the PrP in the ER lumen be from protease and show in or Scott M.R. P. Torchia M. S.J. Prusiner S.B. 1998; PubMed Scopus Google Scholar, Tremblay P. Groth D. DeArmond S.J. Prusiner S.B. Nature. 1999; PubMed Scopus Google Scholar). in a but in the 20-kDa fragment protease of and PrP102L the PrP and of cell from cells with the showed increased expression of the and 20-kDa fragments in and PrP102L PrP102L in showed a in the region of kDa of from these cells showed an in the 20-kDa fragment in and PrP102L the fragment and PrP of by to a lacking the the of and of the in and The that the 20-kDa fragment in cell is a of The in the of 20-kDa fragment is with that of PrP is in the transmembrane in cells J. Biol. Chem. 2001; Full Text Full Text PDF PubMed Scopus Google Scholar). To of CtmPrP in PrP102L cells the of 20-kDa fragment, and PrP102L cells in the or presence of the at or at to of from the to with and by a in PrP in the presence of at and at with a report that of is by the Y. S. A. A. J. 2001; PubMed Scopus Google Scholar). at as showed with high The that are in and The 20-kDa fragment at in and PrP102L that is generated in the ER and an fragment of kDa at in PrP102L the and 20-kDa fragments increased in in the presence of the increased by a of or decreased of these fragments by the of the in of of kDa in to PrP increased of the 20-kDa fragment at and in the presence of in and The of kDa in PrP102L than at or and in the or presence of The fragment appears to be at or in the presence of and increased in PrP102L fragment not in of from the form of PrP Scott M.R. P. Torchia M. S.J. Prusiner S.B. 1998; PubMed Scopus Google Scholar, Tremblay P. Groth D. DeArmond S.J. Prusiner S.B. Nature. 1999; PubMed Scopus Google Scholar). The of fragment is the show the 20-kDa fragment is generated in the most from at the ER by in an in the of 20-kDa fragment, an fragment of kDa is in PrP102L the of is and increased of 20-kDa fragment in PrP102L is not of increased of but rather of decreased of fragment, probably at the cell surface. the cell surface expression and of the 20-kDa fragment to understand the that to in PrP102L in not is the 20-kDa in PrP102L at but the 18-kDa fragment of PrP is To the of and 20-kDa fragments and cells with in a of and normal of the medium to and cells with and with to cell surface The cells and the and medium to with or and by in the and the the and The 20-kDa fragment in the rather than the and PrP102L showed of the form as with and the PrP102L kDa than observed in the the 20-kDa fragment in the and in PrP102L as with The in the of 20-kDa fragment and PrP102L more prominent of that a of fragment on the cell surface is and at kDa are and a fragment in from PrP102L cells with showed and PrP102L as observed with the 18-kDa fragment of PrP that with but not with observed in but the of fragment present in the in the 18-kDa fragment and the 20-kDa fragment in PrP102L 8 and of showed 18-kDa and more 20-kDa fragment in PrP102L with of medium from and PrP102L cells with showed the presence of fragment in PrP102L that fragment is the A of the and PrP102L also the medium and Thus, at or observed in the 18-kDa fragment is and the 20-kDa fragment is increased in PrP102L the is that to the plasma The in 18-kDa may of or of PrP102L at the plasma membrane. is from the that the of kDa in PrP102L is not the result of or of an in the of Instead, the 20-kDa may at the plasma of decreased probably as a result of and These The of and PrP102L and by and PrP102L cells with in medium on or and at in a the of cells with and with to on the plasma membrane. on the cell surface with and the cells and with with Thus, with PrP on the cell surface the the of with on of the and PrP102L on the cell surface and the the cells at most of the in probably the in PrP102L in a rather than to the plasma a that more of with of the at a to the of with and or PrP102L and are in the of and PrP102L at the cell surface. of at the surface expression of and PrP102L is and the surface expression of and PrP102L on the surface of cells showed and that of the to the plasma membrane. PrP102L the that a of PrP102L not of at and that that not to the plasma A and To the surface expression of by of to the and PrP102L cells with as with a and or a to a of observed in PrP102L not the as to PrP102L is probably by the and not to the plasma membrane. The of and PrPSc in GSS102L has been to with the that PrPSc is the in prion disorders. we a of the of PrP102L mutation in show that the and of PrP102L is in decreased expression of the normal 18-kDa fragment, and increased of the fragment on the surface of these in may PrP102L cells more to exogenous PrPSc infection and by the 20-kDa fragment may be more to a in to PrPSc includes an amyloidogenic region of PrP that is disrupted in the 18-kDa the 20-kDa may the neurotoxic signal of exogenous PrPSc as observed in the of CtmPrP Tremblay P. Groth D. DeArmond S.J. Prusiner S.B. Nature. 1999; PubMed Scopus Google without as a PrPSc. A in the of PrP101L transgenic mice may the effects of mutation in cell of the surface of 20-kDa CtmPrP fragment is and the 18-kDa as with that from of the cell surface. cell surface the plasma and is at and a fragment of kDa is to the cell surface S.G. P. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, of on the plasma the 18-kDa fragment rather than has the 18-kDa is disrupted at and in the of to PrPSc K. D. T. H. R. Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. Scopus Google Scholar, J. B. B. J. Biol. Chem. 1998; Full Text Full Text PDF PubMed Scopus Google Scholar, C. H. A. J. 1998; PubMed Google Scholar, J. Prusiner PubMed Scopus Google Scholar). The of these is by the in mice that are resistant to scrapie PrP with to residue but not susceptibility of the animals to PrPSc infection M. T. A. A. M. B. S. A. C. J. 1996; PubMed Scopus Google Scholar). Because the 20-kDa fragment, but not the 18-kDa fragment, includes most of a in the of to 18-kDa fragment on the surface of cells PrPSc and in cell PrP102L is Although is with on transgenic mice that develop disease in the of detectable PrPSc (11Hsiao K.K. Groth D. Scott M. Yang S.L. Serban H. Rapp D. Foster D. Torchia M. DeArmond S.J. Prusiner S.B. Proc. Natl. Acad. Sci. U. S. A. 1994; 91: 9126-9130Crossref PubMed Scopus (276) Google Scholar, E. H. R. R. Ironside J. D.W. J. C. J. 1999; PubMed Scopus Google Scholar, E. D.W. Ironside J. R. J. 2001; PubMed Scopus Google the by mutant PrP neurodegeneration is to are on transgenic mice expressing a single allele of and the mice with an that to develop spontaneous neurodegenerative disease, but increased to exogenous PrPSc infection E. H. R. R. Ironside J. D.W. J. C. J. 1999; PubMed Scopus Google Scholar, E. D.W. Ironside J. R. J. 2001; PubMed Scopus Google Scholar, R. 2001; PubMed Scopus Google Scholar). When in with is to that susceptibility of PrP101L mice to PrPSc infection may be the result of increased expression of the amyloidogenic 20-kDa fragment on the cell providing an optimal the PrPSc. a of PrPSc is on the cell the 20-kDa fragment, of PrP and 20-kDa fragments as in Y. H. R. N. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). a the increased susceptibility of PrP101L transgenic mice to exogenous PrPSc as by E. D.W. Ironside J. R. J. 2001; PubMed Scopus Google Scholar). the 20-kDa fragment may the neurotoxic signal by exogenous PrPSc without a change, by The is by an PrPSc and CtmPrP has been in mice with as the of Tremblay P. Groth D. DeArmond S.J. Prusiner S.B. Nature. 1999; PubMed Scopus Google Scholar). Based on the and in a the 20-kDa fragment is generated in the ER probably from CtmPrP Y. H. R. N. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google the 18-kDa fragment is produced from the cell surface S.G. P. Gambetti P. J. Biol. Chem. Full Text Full Text PDF PubMed Scopus Google Scholar). Although of from and PrP102L cells in an in the of 20-kDa fragment, result the of 20-kDa fragment from The of 20-kDa fragment generated in the cell is not altered and the increased of 20-kDa fragment in PrP102L cells be to an in the or increased of Instead, we that the of 20-kDa fragment on the surface of PrP102L cells is by decreased on the of and of and PrP102L show in to the plasma and is to the cell most of PrP102L accumulates in probably and is These the decreased expression of 18-kDa fragment on the surface of 18-kDa fragment to the plasma in an The to of 20-kDa fragment on the surface of PrP102L cells is not from Because of fragment are observed at or appears to probably of Because the 20-kDa fragment in PrP102L cells on than the corresponding fragment from probably includes the PrP102L The in the 20-kDa and not the 18-kDa fragment of PrP102L is probably a result of the to to than is a is that the 20-kDa fragment with the PrP102L mutation is of the may a in A in may the of PrP102L rather than to the plasma membrane. an in the and of PrP102L and 20-kDa fragment the of to 18-kDa fragment on the surface of these in a PrP102L and 20-kDa fragment be from the cell surface by the that these are or on the cell surface. Although the 20-kDa fragment from is by B. Biol. 2001; PubMed Scopus Google the of fragment is show that is an fragment and is the medium normal and more is S. and N. observations. is that the from transmembrane form of PrP with the in the and the in the unlike the 20-kDa fragment, of not result in an in the of fragment, on the of fragment are report in the of PrP102L as with the 20-kDa of CtmPrP in the of Although the of the is report the to the of mutation in P. Gambetti M. S. and R. and J. of the