Scrapie Protein Degradation by Cysteine Proteases in CD11c+ Dendritic Cells and GT1-1 Neuronal Cells

摘要

Dendritic cells (DC) of the CD11c⁺ myeloid phenotype have been implicated in the spread of scrapie in the host. Previously, we have shown that CD11c⁺ DC can cause a rapid degradation of proteinase K-resistant prion proteins (PrP^Sc) in vitro, indicating a possible role of these cells in the clearance of PrP^Sc. To determine the mechanisms of PrP^Sc degradation, CD11c⁺ DC that had been exposed to PrP^Sc derived from a neuronal cell line (GT1-1) infected with scrapie (ScGT1-1) were treated with a battery of protease inhibitors. Following treatment with the cysteine protease inhibitors (2S,3S)-trans-epoxysuccinyl-l-leucylamido-3-methylbutane (E-64c), its ethyl ester (E-64d), and leupeptin, the degradation of PrP^Sc was inhibited, while inhibitors of serine and aspartic and metalloproteases (aprotinin, pepstatin, and phosphoramidon) had no effect. An endogenous degradation of PrP^Sc in ScGT1-1 cells was revealed by inhibiting the expression of cellular PrP (PrP^C) by RNA interference, and this degradation could also be inhibited by the cysteine protease inhibitors. Our data show that PrP^Sc is proteolytically cleaved preferentially by cysteine proteases in both CD11c⁺ DC and ScGT1-1 cells and that the degradation of PrP^Sc by proteases is different from that of PrP^C. Interference by protease inhibitors with DC-induced processing of PrP^Sc has the potential to modify prion spread, clearance, and immunization in a host.