Surachai Supattapone

Prion Protein of 106 Residues Creates an Artificial Transmission Barrier for Prion Replication in Transgenic Mice

A redacted prion protein (PrP) of 106 amino acids with two large deletions was expressed in transgenic (Tg) mice deficient for wild-type (wt) PrP (Prnp0/0) and supported prion propagation. RML prions containing full-length PrP(Sc)produced disease in Tg(PrP106)Prnp0/0 mice after approximately 300 days, while transmission of RML106 prions containing PrP(Sc)106 created disease in Tg(PrP106) Prnp0/0 mice after only approximately 66 days on repeated passage. This artificial transmission barrier for the passage of RML prions was diminished by the coexpression of wt MoPrPc in Tg(PrP106)Prnp+/0 mice that developed scrapie in approximately 165 days, suggesting that wt MoPrP acts in trans to accelerate replication of RML106 prions. Purified PrP(Sc)106 was protease resistant, formed filaments, and was insoluble in nondenaturing detergents. The unique features of RML106 prions offer insights into the mechanism of prion replication, and the small size of PrP(Sc)106 should facilitate structural analysis.

Branched Polyamines Cure Prion-Infected Neuroblastoma Cells

ABSTRACT Branched polyamines, including polyamidoamine and polypropyleneimine (PPI) dendrimers, are able to purge PrPSc, the disease-causing isoform of the prion protein, from scrapie-infected neuroblastoma (ScN2a) cells in culture (S. Supattapone, H.-O. B. Nguyen, F. E. Cohen, S. B. Prusiner, and M. R. Scott, Proc. Natl. Acad. Sci. USA 96:14529–14534, 1999). We now demonstrate that exposure of ScN2a cells to 3 μg of PPI generation 4.0/ml for 4 weeks not only reduced PrPSc to a level undetectable by Western blot but also eradicated prion infectivity as determined by a bioassay in mice. Exposure of purified RML prions to branched polyamines in vitro disaggregated the prion rods, reduced the β-sheet content of PrP 27-30, and rendered PrP 27-30 susceptible to proteolysis. The susceptibility of PrPSc to proteolytic digestion induced by branched polyamines in vitro was strain dependent. Notably, PrPSc from bovine spongiform encephalopathy-infected brain was susceptible to PPI-mediated denaturation in vitro, whereas PrPSc from natural sheep scrapie-infected brain was resistant. Fluorescein-labeled PPI accumulated specifically in lysosomes, suggesting that branched polyamines act within this acidic compartment to mediate PrPSc clearance. Branched polyamines are the first class of compounds shown to cure prion infection in living cells and may prove useful as therapeutic, disinfecting, and strain-typing reagents for prion diseases.