Biosynthesis of the Scrapie Prion Protein in Scrapie-Infected Cells

Abstract

Compelling evidence argues that the major component of the scrapie prion is a host- encoded protein, the scrapie prion protein (PrP^Sc) (reviewed in Prusiner, 1991). The events of PrP^Sc biosynthesis are thus of central importance to understanding the biology of scrapie. PrP^Sc is the abnormal isoform of a normal phosphoinositol glycolipid (GPI)-anchored plasma membrane sialoglycoprotein PrP^C. While the two PrP isoforms differ strikingly in many of their properties, their structural differences have not yet been elucidated. PrP^Sc is insoluble in detergents and possesses a protease-resistant core, while PrP^C is readily soluble in most detergents and is completely degraded by proteases. In infected cells in culture, PrP^Sc becomes protease-resistant as a result of an as yet unidentified post-translational event (Borchelt et al., 1990) unrelated to PrP N-linked glycosylation (Taraboulos et al., 1990a). In scrapie infected cells in culture, PrP^Sc accumulates primarily within secondary lysosomes (Taraboulos et al., 1990b; McKinley et al., 1991). All PrP antibodies described to date react equally well with both PrP^C and denatured PrP^Sc, but are much less reactive with native PrP^Sc. To study further the biosynthesis of protease-resistant PrP^Sc, we have used scrapie-infected ScN2a and ScHaB cells in pulse-chase radiolabeling experiments.