Trivalent iron-induced conversion of prion protein to a proteinase K resistant form in vesicular trafficking

Abstract

however, some studies have shown that PrPC may be involved in metal ion homeostasis. In diseased brains, iron levels are increased, which is possible because of the coaggregation of PrP with ferritin. Although iron is known to be involved in the generation of abnormal PrP, little is known about the contribution of oxidation state-dependent iron to PrP conversion and the conversion mechanism in neural cells. In this study, murine PrPC-deficient cells (HpL3-4) were exposed to divalent [Fe (II)] or trivalent [Fe (III)] iron and then treated with exogenous recombinant PrP (rPrP). After the internalization of rPrP by the cells, we analyzed the accumulation of intracellular rPrP and its biochemical properties in combination with PK resistance and detergent insolubility. U18666A and NH4Cl were used to inhibit vesicular trafficking and endolysosomal acidification, respectively. We found that Fe (III) induced an increase of internalized rPrP in a time- and dose-dependent manner. Moreover, the accumulated rPrP was converted to detergent-insoluble and PK-resistant PrP (PrPres) in part. The generation of PrPres was hindered by U18666A, but not by NH4Cl, indicating that Fe (III)-mediated PrPres conversion possibly occurred during endosomal vesicular trafficking and not in the acidic environment of lysosomes. These results suggest that Fe (III), and not Fe (II), has a role in the generation of PrPres during endosomal vesicular trafficking.

Prion disorders belong to the group of neurodegenerative diseases involving protein misfolding. Prion protein (PrP) aggregation and neurotoxicity are believed to result from the accumulation of infectious PrP (PrPSc), a particular misfolded form of the normal PrP (PrPC). The biochemical features of PrPSc are resistance to proteinase K (PK) digestion and detergent insolubility. The physiological roles of PrPC are yet to be defined