Conversion of the normal membrane-bound
prion protein (
PrP-sen) to its pathological
isoform (
PrP-res) is a key event in the pathogenesis of
transmissible spongiform encephalopathies. Although the subcellular sites of conversion are poorly characterized, several lines of evidence have suggested the involvement of
membrane lipid rafts in the conversion process. Here we report that
copper stimulates the endocytosis of
PrP-sen via a
caveolin-dependent pathway in both microglia and
neuroblastoma cells. We show that the polyene
antibiotic filipin both limits endocytosis of
PrP-sen and dramatically reduces the amount of membrane-bound
PrP-sen. This reduction results from a rapid and massive release of full matured
PrP-sen into the culture medium. Finally, we demonstrate that
filipin is a potent inhibitor of
PrP-res formation into chronically infected
neuroblastoma cells. Our results reinforce the role of rafts in PrP trafficking and raise the possibility that the release of
PrP-sen from the plasma membrane decreases the amount of available substrate
PrP-sen at the conversion sites.