The retention of prion protein in the endoplasmic reticulum prevents N2A cells from proteasome inhibition-induced cytotoxicity.

Prion disease is a fatal neurodegenerative disease that may result from the conversion of normal cellular prion protein (PrP) to the pathogenic scrapie PrP isoform (PrP), however, how proliferation of prion leads to neuronal apoptosis is still not clear. In this study, to explore the role of the endoplasmic reticulum (ER) in prion diseases, we engineered the KDEL ER-retention motif to the C-terminus of PrP and studied its effect on N2A cell toxicity. The KDEL retention signal led to the accumulation of PrP in the ER, and KDEL signal could effectively deplete PrP from the cell surface and trap PrP in the ER/Cis-Golgi compartment. PrP molecules were delayed in their transit along the early pathway of the secretory compartment, however, they did not aggregate, and were not resistant to Proteinase K (PK) or become detergent-insoluble. Moreover, we found that the ER was not the site where PrP became detergent-insoluble and acquired PK resistance. In addition, an MTT assay indicated cells expressing PrP/N2A were sensitive to proteasome inhibition, but not N2A cells expressing PrP. Our findings suggest that the ER is not a compartment in which wild type PrP is able to initiate aggregation, protease resistance or other scapie-like properties of PrP.