Truncated Forms of the Human Prion Protein in Normal Brain and in Prion Diseases

Abstract

The cellular form of the prion protein (PrPc) is a glycoprotein anchored to the cell membrane by a glycosylphosphatidylinositol moiety. An aberrant form of PrPc that is partially resistant to proteases, PrPres, is a hallmark of prion diseases, which in humans include Cruetzfeldt-Jakob disease (CJD), Gerstmann-Sträussler-Scheinker syndrome, and fatal familial insomnia. We have characterized the major forms of PrP in normal and pathological human brains. A COOH-terminal fragment of PrPc, designated C1, is abundant in normal and CJD brains as well as in human neuroblastoma cells. Sequence analysis revealed that C1 contains alternative NH2 termini starting at His-111 or Met-112. Like PrPc, C1 is glycosylated, anchored to the cell membrane, and is heat-stable. Consistent with the lack of the NH2-terminal region of PrPc, C1 is more acidic than PrPc and does not bind heparin. An additional fragment longer than C1, designated C2, is present in substantial amounts in CJD brains. Like PrPres, C2 is resistant to proteases and is detergent-insoluble. Our data indicate that C1 is a major product of normal PrPc metabolism, generated by a cleavage that disrupts the neurotoxic and amyloidogenic region of PrP comprising residues 106-126. This region remains intact in C2, suggesting a role for C2 in prion diseases.

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

“…Thus, truncated Ctm PrP must use an alternative mechanism for neurotoxicity in our cell model. Because this fragment includes the amyloidogenic region of PrP, comprising residues 106 -126, that is normally disrupted during recycling of PrP from the cell surface (38), the truncated Ctm PrP may initiate aggregation of additional PrP C molecules at the cell surface by acting as a nidus, or it may function as a novel surface receptor. Although the precise mechanism by which Ctm PrP mediates neurotoxicity is not clear from our data, this study demonstrates a direct correlation between aggregation of PrP C and induction of Ctm PrP and clarifies the downstream pathway of Ctm PrP transport and metabolism, thus laying the groundwork for future investigations on the cellular pathways of Ctm PrP-mediated neurodegeneration.…”

“…Step 7, during the normal re-cycling of PrP, full-length PrP C is cleaved at residue 111 or 112, resulting in a truncated 18-kDa C-terminal fragment that accumulates on the cell surface (38). PM, plasma membrane; E, endosomes; L, lysosomes; N, nucleus.…”

“…Cell lysates and PI-PLC-released proteins in the medium were subjected to immunoprecipitation with anti-PrP antibody 3F4 or 8H4 as described (17,37). Metabolic labeling at 15°C was performed in a refrigerated CO 2 incubator for 2 h, and lysates were immunoprecipitated with anti-PrP antibody 2301 specific for C-terminal residues 220 -230 of PrP (17,37,38). Anti-PrP antibody 3F4 binds to residues 109 and 112 of PrP and therefore detects truncated Ctm PrP and the conventional PK-resistant 20-kDa fragment of PrP.…”

New insights into cellular prion protein (PrPc) functions: The “ying and yang” of a relevant protein

“…However, a protein similar to F35 is generated in the healthy human brain when PrP c is endoproteolized into 110/111 residues through ADAMs in a Protein kinase C (PKC)-dependent way, thereby generating a C-terminal fragment termed C1 (Cisse et al, 2005;Chen et al, 1995;Harris et al, 1993;Vincent et al, 2000;Vincent et al, 2001). A shorter fragment, within the OR region (residues 90/91), the C2, is generated in pathological conditions and poor data have yet been provided about this cleavage (Chen et al, 1995). A recent study by Sunyach and coworkers established that stable C1 expression, but not C2, sensitizes HEK293 to apoptotic stimuli like staurosporine and that this effect is fully dependent on p53 activity (Sunyach et al, 2007).…”

Molecular biology of prion protein and its first homologous protein

“…However, PrPLP/Dpl itself is unlikely to be involved in the pathogenesis of prion diseases because PrPLP/Dpl could not be detected in the brains affected by experimental prion diseases (6,8). Instead, PrP Sc is markedly accumulated and its fragmented C-terminal products are often observed in the affected brains (58). It is therefore very interesting to speculate that PrP Sc or its fragmented products possess a neurotoxic potential equivalent to that of PrPLP/Dpl, PrP!32-121, or PrP!32-134.…”