Reactive Oxygen Species-mediated β-Cleavage of the Prion Protein in the Cellular Response to Oxidative Stress

Abstract

The cellular prion protein (PrP C ) is critical for the development of prion diseases. However, the physiological role of PrP C is less clear, although a role in the cellular resistance to oxidative stress has been proposed. PrP C is cleaved at the end of the copper-binding octapeptide repeats through the action of reactive oxygen species (ROS), a process termed ␤-cleavage. Here we show that ROS-mediated ␤-cleavage of cell surface PrP C occurs within minutes and was inhibited by the hydroxyl radical quencher dimethyl sulfoxide and by an antibody against the octapeptide repeats. A construct of PrP lacking the octapeptide repeats, PrP⌬oct, failed to undergo ROSmediated ␤-cleavage, as did two mutant forms of PrP, PG14 and A116V, associated with human prion diseases. As compared with cells expressing wild type PrP, when challenged with H 2 O 2 and Cu 2؉ , cells expressing PrP⌬oct, PG14, or A116V had reduced viability and glutathione peroxidase activity and increased intracellular free radicals. Thus, lack of ROS-mediated ␤-cleavage of PrP correlated with the sensitivity of the cells to oxidative stress. These data indicate that the ␤-cleavage of PrP C is an early and critical event in the mechanism by which PrP protects cells against oxidative stress.

New insights into cellular prion protein (PrPc) functions: The “ying and yang” of a relevant protein

“…Accordingly, the insertion of three octarepeats alters the conformation of PrP c , thereby promoting greater cell susceptibility to oxidative insults in vitro (Yin et al, 2006). Indeed, PrP c lacking the OR fails to undergo oxidative-mediated -cleavage, thereby promoting an in vitro increase in cell susceptibility to oxidative radicals (Watt et al, 2005). In PrP c knockout mice, the OR domain contributes to pathologies induced by N-terminal truncation.…”

Deconvoluting the Cu2+ Binding Modes of Full-length Prion Protein

“…Copper has been shown to promote the endocytosis of PrP C (33,34), but PrP expression levels do not seem to affect copper delivery (35,36). Copper-induced cleavage of the PrP C main chain has also been reported (37,38) and PrP C can act as an antioxidant by sacrificially quenching hydroxyl radicals produced via Cu 2ϩ /Cu ϩ Fenton's cycling (15). PrP knock-out mice show highlighted sensitivity to Cu 2ϩ -induced oxidative stress (12,39).…”

“…Copper has been shown to promote the endocytosis of PrP C (33, 34), but PrP expression levels do not seem to affect copper delivery (35,36). Copper-induced cleavage of the PrP C main chain has also been reported (37,38) (22), and mass spectrometry (30).There have been numerous Cu 2ϩ binding studies of fragments of PrP centered on two regions within the unstructured N-terminal domain of PrP. These studies include the octarepeat region, residues 58 -91, and a second Cu 2ϩ binding region between the octarepeats and the C-terminal structured domain, between residues 90 and 126.…”

“…Copper has been shown to promote the endocytosis of PrP C (33, 34), but PrP expression levels do not seem to affect copper delivery (35,36). Copper-induced cleavage of the PrP C main chain has also been reported (37,38) (22), and mass spectrometry (30).…”

Redox Control of Prion and Disease Pathogenesis

“…It is likely that compromised function of this enzyme in prion disease-affected brains (245) increases the susceptibility of neurons to toxic signals that are generated as a by-product of normal cellular metabolic processes. It has also been proposed that PrP C is a free radical-scavenging protein, and loss of this activity in mutant PrP forms increases the susceptibility of neurons to toxicity (236). The protective function of PrP C is further exemplified by the fact that expression of a single copy of PrP C can rescue the ataxic phenotype of transgenic mice expressing a deletion construct of PrP (PrP~32-121=134) (199), slow neurodegeneration in transgenic mice expressing a pathogenic mutation of PrP (217), rescue neurons from Doppel-induced toxicity (149), and protect brain tissue from ischemia-and traumainduced insult (210,238).…”