PrPC Homodimerization Stimulates the Production of PrPC Cleaved Fragments PrPN1 and PrPC1

An endoproteolytic cleavage termed alpha-cleavage between residues 111/112 is a characteristic feature of the cellular prion protein (PrPC). This cleavage generates a soluble N-terminal fragment (PrPN1) and a glycosylphosphatidylinositol-anchored C-terminal fragment (PrPC1). Independent studies demonstrate that modulating PrPC alpha-cleavage represents a potential therapeutic strategy in prion diseases. The regulation of PrPC alpha-cleavage is unclear. The only known domain that is essential for the alpha-cleavage to occur is a hydrophobic domain (HD). Importantly, the HD is also essential for the formation of PrPC homodimers. To explore the role of PrPC homodimerization on the alpha-cleavage, we used a well described inducible dimerization strategy whereby a chimeric PrPC composed of a modified FK506-binding protein (Fv) fused with PrPC and termed Fv-PrP is incubated in the presence of a dimerizer AP20187 ligand. We show that homodimerization leads to a considerable increase of PrPC alpha-cleavage in cultured cells and release of PrPN1 and PrPC1. Interestingly, enforced homodimerization increased PrPC levels at the plasma membrane, and preventing PrPC trafficking to the cell surface inhibited dimerization-induced alpha-cleavage. These observations were confirmed in primary hippocampal neurons from transgenic mice expressing Fv-PrP. The proteases responsible for the alpha-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 PrPC homodimerization protects against toxic amyloid-beta (A beta) oligomers. Thus, our results show that PrPC homodimerization is an important regulator of PrPC alpha-cleavage and may represent a potential therapeutic avenue against A beta toxicity in Alzheimer's disease.