Scrapie-like prion protein accumulates in aggresomes of cyclosporin A-treated cells

Prion diseases are infectious, sporadic and inherited fatal neurodegenerations that are propagated by an abnormal refolding of the cellular prion protein PrPC. Which chaperones assist the normal folding of PrPC is unknown. The linkage of familial Gerstmann-Straussler-Scheinker (GSS) syndrome with proline substitutions in PrP raised the prospect that peptidylprolyl cis-trans isomerases (PPlases) may play a role in normal PrP metabolism. Here we used cyclosporin A (CsA), an immunosuppressant, to inhibit the cyclophilin family of PPlases in cultured cells. CsA-treated cells accumulated proteasome-resistant, 'prion-like' PrP species, which deposited in long-lived aggresomes. PrP aggresomes also formed with disease-linked proline mutants when proteasomes were inhibited. These results suggest mechanisms whereby abnormally folded cytosolic PrP may in some cases participate in the development of spontaneous and inherited prion diseases.