Mutant Prion Protein Expression Is Associated with an Alteration of the Rab GDP Dissociation

The prion protein (PrP) is a glycosylphosphatidylinositol-anchored membrane glycoprotein that plays a vital role in prion diseases, a class of fatal neurodegenerative disor-ders of humans and animals. Approximately 20 % of hu-man prion diseases display autosomal dominant inherit-ance and are linked to mutations in the PrP gene on chromosome 20. PrP mutations are thought to favor the conformational conversion of PrP into a misfolded iso-form that causes disease by an unknown mechanism. The PrP mutation D178N/Met-129 is linked to fatal familial insomnia, which causes severe sleep abnormalities and autonomic dysfunction. We showed by immunoelectron microscopy that this mutant PrP accumulates abnormally in the endoplasmic reticulum and Golgi of transfected neuroblastoma N2a cells. To investigate the impact of intracellular PrP accumulation on cellular homeostasis, we did a two-dimensional gel-based differential proteom-ics analysis. We used wide range immobilized pH gradient strips, pH 4–7 and 6–11, to analyze a large number of proteins. We found changes in proteins involved in energy metabolism, redox regulation, and vesicular transport. Rab GDP dissociation inhibitor (GDI) was one of the proteins that changed most. GDI regulates vesicular pro-tein trafficking by acting on the activity of several Rab proteins. We found a specific reduction in the level of functional Rab11 in mutant PrP-expressing cells associ-ated with impaired post-Golgi trafficking. Our data are consistent with a model by which mutant PrP induces overexpression of GDI, activating a cytotoxic feedback loop that leads to protein accumulation in the secretor