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Commentary & View

The cellular prion protein with a monoacylated glycosylphosphatidylinositol anchor modifies cell membranes, inhibits cell signaling and reduces prion formation

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Pages 65-68 | Received 07 Apr 2011, Accepted 06 May 2011, Published online: 01 Apr 2011
 

Abstract

The prion diseases occur following the conversion of the cellular prion protein (PrPC) into a disease-related isoform (PrPSc). In this study a cell painting technique was used to examine the role of the glycosylphosphatidylinositol (GPI) anchor attached to PrPC in prion formation. The introduction of PrPC to infected neuronal cells increased the cholesterol content of cell membranes, increased activation of cytoplasmic phospholipase A2 (cPLA2) and increased PrPSc formation. In contrast, PrPC with a monoacylated GPI anchor did not alter the amount of cholesterol in cell membranes, was not found within lipid rafts and did not activate cPLA2. Although monoacylated PrPC remains within cells for longer than native PrPC it was not converted to PrPSc. Moreover, the presence of monoacylated PrPC displaced cPLA2 from PrPSc-containing lipid rafts, reducing the activation of cPLA2 and PrPSc formation. We conclude that acylation of the GPI anchor attached to PrPC modifies the local membrane microenvironments that control some cell signaling pathways, the trafficking of PrPC and PrPSc formation. In addition, such observations raise the possibility that the pharmacological modification of GPI anchors might constitute a novel therapeutic approach to prion diseases.

Acknowledgments

This work was supported by a grant from the European Commission FP6 “Neuroprion” Network of Excellence.

Figures and Tables

Figure 1 Phospholipase digestion of PrPC affects the acylation of the GPI anchor. Cartoon showing the putative GPI anchor attached to PrPC, monoacylated PrPC and deacylated PrPC. Glycan residues shown include inositol (Inos), mannose (Man), sialic acid (SA), galactose (Gal), N-acetyl galactosamine (GalNAc) and glucosamine (GlcN) as well as phosphate (P).

Figure 1 Phospholipase digestion of PrPC affects the acylation of the GPI anchor. Cartoon showing the putative GPI anchor attached to PrPC, monoacylated PrPC and deacylated PrPC. Glycan residues shown include inositol (Inos), mannose (Man), sialic acid (SA), galactose (Gal), N-acetyl galactosamine (GalNAc) and glucosamine (GlcN) as well as phosphate (P).

Figure 2 Acylation of PrPC affects the underlying cell membrane. Cartoon showing the proposed membranes surrounding native PrPC and monoacylated PrPC, including cholesterol (), lyso-phospholipids (

), saturated phospholipids () and unsaturated phospholipids (). Monoacylated PrPC is not directed to lipid rafts and the membrane surrounding contains less cholesterol and more unsaturated phospholipids.

Figure 2 Acylation of PrPC affects the underlying cell membrane. Cartoon showing the proposed membranes surrounding native PrPC and monoacylated PrPC, including cholesterol (), lyso-phospholipids (Display full size), saturated phospholipids () and unsaturated phospholipids (). Monoacylated PrPC is not directed to lipid rafts and the membrane surrounding contains less cholesterol and more unsaturated phospholipids.

Figure 3 Monoacylated PrPC affects the capture of cPLA2 in PrPSc-containing lipid rafts. (A) Cartoon showing the proposed membranes surrounding PrPSc and PrPC including the capture of cPLA2 in lipid rafts that are dense in cholesterol (

) and saturated phospholipids (
). (B) Cartoon showing the proposed interactions between PrPSc and monoacylated PrPC which reduces the solubility of membranes to cholesterol, increases the concentration of unsaturated phospholipids (
) and prevents the capture of cPLA2 into PrPSc-containing lipid rafts.

Figure 3 Monoacylated PrPC affects the capture of cPLA2 in PrPSc-containing lipid rafts. (A) Cartoon showing the proposed membranes surrounding PrPSc and PrPC including the capture of cPLA2 in lipid rafts that are dense in cholesterol (Display full size) and saturated phospholipids (Display full size). (B) Cartoon showing the proposed interactions between PrPSc and monoacylated PrPC which reduces the solubility of membranes to cholesterol, increases the concentration of unsaturated phospholipids (Display full size) and prevents the capture of cPLA2 into PrPSc-containing lipid rafts.

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