CHARACTERIZATION OF DETERGENT-INSOLUBLE COMPLEXES CONTAINING THE CELLULAR PRION PROTEIN AND ITS SCRAPIE ISOFORM

Cells infected with prions contain both prion protein isoforms cellula r prion protein (PrPC) and scrapie prion protein (PrPSc). PrPSc is for med posttranslationally through the pathological refolding of PrPC. In scrapie-infected ScN2a cells, the metabolism of both PrP isoforms inv olves cholesterol-dependent pathways. We show here that both PrPC and PrPSc are attached to Triton X-100-insoluble, low density complexes or ''rafts.'' These complexes are sensitive to saponin and thus probably contain cholesterol. This finding suggests that the transformation Pr PC --> PrPSc occurs within rafts. It also reveals the existence of raf ts in late compartments of the endocytic pathway, where most PrPSc res ides. When Triton X-100 lysates of cells were incubated at 37 degrees C prior to density analysis, PrPC was still found in buoyant complexes , although it now failed to sediment at high speed. This property was shared by another glycophosphatidyl inositol protein, Thy-1, and also by the raft resident GM1. In one ScN2a clone and in the brain of a Syr ian hamster with scrapie, Triton X-100 extraction at 37 degrees C perm itted resolution of PrPC and PrPSc into two distinct peaks of differen t densities. This suggests that there are two populations of PrP-conta ining rafts and may permit isolation of PrPC-specific rafts from those containing PrPSc. Our findings reinforce the contention that rafts ar e involved in various aspects of PrP metabolism and in the ''life cycl e'' of prions.