Essential role of the prion protein N terminus in subcellular trafficking and half-life of cellular prion protein

Aberrant metabolism and conformational alterations of the cellular prion protein (PrPc) are the underlying causes of transmissible spongiform encephalopathies in humans and animals. In cells, PrPc is modified post-translationally and transported along the secretory pathway to the plasma membrane, where it is attached to the cell surface by a glycosylphosphatidylinositol anchor. In surface biotinylation assays we observed that deletions within the unstructured N terminus of murine PrPc led to a significant reduction of internalization of PrP after transfection of murine neuroblastoma cells. Truncation of the entire N terminus most significantly inhibited internalization of PrPc. The same deletions caused a significant prolongation of cellular half-life of PrPc and a delay in the transport through the secretory pathway to the cell surface. There was no difference in the glycosylation kinetics, indicating that all PrP constructs equally passed endoplasmic reticulum-based cellular quality control. Addition of the N terminus of the Xenopus laevis PrP, which does not encode a copper-binding repeat element, to N-terminally truncated mouse PrP restored the wild type phenotype. These results provide deeper insight into the life cycle of the PrPc, raising the novel possibility of a targeting function of its N-proximal part by interacting with the secretory and the endocytic machinery. They also indicate the conservation of this targeting property in evolution.