Reactive oxygen species (ROS)-mediated beta-cleavage of the prion protein in the mechanism of the cellular response to oxidative stress.

The PrP(C) [cellular isoform of PrP (prion protein)] can undergo a conformational conversion to produce a proteinase-resistant form PrP(Sc) (scrapie isoform of PrP), a step critical for the development of prion disease. Although essential for disease progression, the normal cellular function of PrP(C) remains unknown. Suggestions to date have centred on a protective role against oxidative stress. We have demonstrated that ROS (reactive oxygen species)-mediated beta-cleavage of PrP(C) occurs at the cell surface, can be inhibited following hydroxyl radical quenching and has a prerequisite for the octarepeat region in the N-terminus of the protein. Significantly, two disease-associated mutants of PrP, namely PG14 and A116V (Ala(116)-->Val), were unable to undergo beta-cleavage and this lack of proteolysis was accompanied by functional consequences in cells expressing these mutant proteins. The cells were found to be less viable following exposure to copper and H2O2, had reduced levels of glutathione peroxidase and increased amounts of intracellular oxygen radicals. These results suggest that beta-cleavage of PrP(C) is an initial consequence following exposure to ROS in the extracellular environment contributing to a pathway involved in antioxidant protection of neuronal cells.