PrP^CHomodimerization Stimulates the Production of PrP^CCleaved Fragments PrPN1 and PrPC1

Abstract

An endoproteolytic cleavage termed ␣-cleavage between residues 111/112 is a characteristic feature of the cellular prion protein (PrP C ). This cleavage generates a soluble N-terminal fragment (PrPN1) and a glycosylphosphatidylinositol-anchored C-terminal fragment (PrPC1). Independent studies demonstrate that modulating PrP C ␣-cleavage represents a potential therapeutic strategy in prion diseases. The regulation of PrP C ␣-cleavage is unclear. The only known domain that is essential for the ␣-cleavage to occur is a hydrophobic domain (HD). Importantly, the HD is also essential for the formation of PrP C homodimers. To explore the role of PrP C homodimerization on the ␣-cleavage, we used a well described inducible dimerization strategy whereby a chimeric PrP C composed of a modified FK506-binding protein (Fv) fused with PrP C and termed Fv-PrP is incubated in the presence of a dimerizer AP20187 ligand. We show that homodimerization leads to a considerable increase of PrP C ␣-cleavage in cultured cells and release of PrPN1 and PrPC1. Interestingly, enforced homodimerization increased PrP C levels at the plasma membrane, and preventing PrP C trafficking to the cell surface inhibited dimerization-induced ␣-cleavage. These observations were confirmed in primary hippocampal neurons from transgenic mice expressing Fv-PrP. The proteases responsible for the ␣-cleavage are still elusive, and in contrast to initial studies we confirm more recent investigations that neither ADAM10 nor ADAM17 are involved. Importantly, PrPN1 produced after PrP C homodimerization protects against toxic amyloid-␤ (A␤) oligomers. Thus, our results show that PrP C homodimerization is an important regulator of PrP C ␣-cleavage and may represent a potential therapeutic avenue against A␤ toxicity in Alzheimer's disease.

Homodimerization as a molecular switch between low and high efficiency PrPCcell surface delivery and neuroprotective activity

“…15 In this experiment, the burst in secretion of PrPN1 after PrP C dimerization resulted in levels sufficient to inhibit Aβ oligomers-mediated cell death compared with basal levels of PrPN1 that were clearly inadequate. 15 In this experimental setting, dimerization is a molecular switch between cell death and survival. Enforced dimerization of PrP of its own trafficking through the secretory pathway is possible.…”

“…Second, levels of total PrP species after dimerization were noticeably increased after dimerization. 15 Since dimerization did not change PrP C stability (Fig. 2), we hypothesize that it improves maturation efficiency and passage through protein folding quality control checkpoints.…”

“…That PrP C may have evolved a well conserved domain to stimulate the efficiency shed PrP C . 15 Other studies demonstrated that PrPC1 acts as a GPI-anchored dominant negative inhibitor of PrP Sc formation, 16 and that soluble dimeric PrP binds PrP Sc and can antagonize prion propagation. 17 Thus, increased trafficking of PrP C may be an effective mechanism to deliver protective molecules at the cell surface and in the extracellular space.…”

“…15,39,40 Specifically, Alzheimer disease is set to surge in the next future, and any potential therapeutic strategy disserves in depth investigations. In prion diseases, the N-terminal polybasic residues of PrP C bind PrP Sc and are required for efficient prion propagation.…”

The GPI-anchoring of PrP

“…91, [100][101][102][103][104][105][106][107] Thus, it is not surprising that these cleavage events are currently discussed as therapeutic targets with regard to prion diseases and other neurodegenerative proteinopathies.…”