Biosynthesis of the prion proteins in scrapie-infected cells in culture.

Prions are small proteinaceous particles that transmit scrapie and other fatal encephalopathies of humans and animals, and that appear to be devoid of nucleic acids. The only known--and perhaps the sole--component of the scrapie prion is an abnormal host-encoded protein, the scrapie prion protein PrPSc. The biosynthesis of this pathological protein in the host cell, which is thus of paramount importance to prion replication, is still poorly understood. We are studying the biosynthesis and degradation of the scrapie prion protein PrPSc and of its normal isoform PrPC in scrapie-infected rodent cells in culture. PrPC is anchored to the plasma membrane through a glycosylphosphatidylinositol (GPI) moiety. In scrapie-infected mouse neuroblastoma N2a cells, PrPSc is formed post-translationally, probably from plasma membrane PrPC, in an unknown subcellular compartment that is readily accessible from the plasma membrane. Transport along the secretory pathway is necessary for PrPSc synthesis. In contrast to PrPC, PrPSc accumulates intracellularly, primarily in secondary lysosomes. The subcellular compartment(s) in which PrPSc is formed remain to be determined.