Monoacylated cellular prion protein modifies cell membranes, inhibits cell signaling, and reduces prion formation

Prion diseases occur following the conversion of the cellular prion protein (PrP(C)) into a disease related, protease-resistant isoform (PrP(Sc)). In these studies, a cell painting technique was used to introduce PrP(C) to prion-infected neuronal cell lines (ScGT1, ScN2a, or SMB cells). The addition of PrP(C) resulted in increased PrP(Sc) formation that was preceded by an increase in the cholesterol content of cell membranes and increased activation of cytoplasmic phospholipase A(2) (cPLA(2)). In contrast, although PrP(C) lacking one of the two acyl chains from its glycosylphosphatidylinositol (GPI) anchor (PrP(C)-G-lyso-PI) bound readily to cells, it did not alter the amount of cholesterol in cell membranes, was not found within detergent-resistant membranes (lipid rafts), and did not activate cPLA(2). It remained within cells for longer than PrP(C) with a conventional GPI anchor and was not converted to PrP(Sc). Moreover, the addition of high amounts of PrP(C)-G-lyso-PI displaced cPLA(2) from PrP(Sc)-containing lipid rafts, reduced the activation of cPLA(2), and reduced PrP(Sc) formation in all three cell lines. In addition, ScGT1 cells treated with PrP(C)-G-lyso-PI did not transmit infection following intracerebral injection to mice. We propose that that the chemical composition of the GPI anchor attached to PrP(C) modified the local membrane microenvironments that control cell signaling, the fate of PrP(C), and hence PrP(Sc) formation. In addition, our observations raise the possibility that pharmacological modification of GPI anchors might constitute a novel therapeutic approach to prion diseases.