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

Abstract

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 (E64c), 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.

Spreading of prions from the immune to the peripheral nervous system: a potential implication of dendritic cells

“…SD: 10,641.04 (free medium) and 10,786.49 (PrP Sc -loaded medium). The experiment was repeated four times (Luhr et al 2002(Luhr et al , 2004 our model used peripheral primary neurons that were infected in vivo after oral scrapie challenge (Beekes and McBride 2007). Thus our model speciWcally targeted a cell-to-cell transmission of PrP Sc (Caughey and Baron 2006) from the immune system to the PNS, hypothetically at the genesis of the prion peripheral neuroinvasion (Kimberlin and Walker 1989).…”

“…The role of DCs in prion disease appears to be ambiguous. Some authors have shown, through in vitro models, that DCs can impair prion dissemination and that they are able to process PrP Sc , by cysteine protease, and to decrease the amount of infectivity associated with scrapie (Luhr et al 2002(Luhr et al , 2004 or BSE (Rybner-Barnier et al 2006). Several studies have demonstrated that DCs act in the spreading of prions.…”

Inhibitors of the Mitogen-Activated Protein Kinase Kinase 1/2 Signaling Pathway Clear Prion-Infected Cells from PrPSc

“…Thus, when formation of PrP Sc was blocked by PPS (Caughey and Raymond, 1993) during the BDNF treatment, no effect on PrP Sc levels was seen, which makes it unlikely that the BDNF effect is attributable to a decrease in PrP Sc degradation. In contrast, when degradation of PrP Sc was inhibited with leupeptin (Luhr et al, 2004a), BDNF caused an increase in PrP…”

Polymorphisms in genes <i>CTSB, CTSD, CAPN2, KLK1</i> and <i>TGFB1</i> not associated with susceptibility to atypical or classical ovine scrapie

“…The results of ARNOLD et al (1995) and SUPATTAPONE et al (1999SUPATTAPONE et al ( , 2001 give evidence for a potential involvement of the endosomal cysteine protease cathepsin B (CTSB) in degradation of the abnormal prion protein isoform (PrP Sc ), which is underlined by the investigations of LUHR et al (2004aLUHR et al ( , 2004b who found out that degradation of PrP Sc in scrapie infected neurons is carried out by cysteine proteases at a sour pH and that addition of a selective CTSB inhibitor leads to a significant increase of the PrP Sc content. Concerning the lysosomal aspartate protease cathepsin D (CTSD), several expression studies reported an elevated concentration of the respective enzyme within the course of scrapie infection in mice (BROWN et al 2004, RIEMER et al 2004, XIANG et al 2004.…”