Prion protein “gamma-cleavage”: characterizing a novel endoproteolytic processing event

Abstract

The cellular prion protein (PrP C ) is a ubiquitously expressed protein of currently unresolved but potentially diverse function. Of putative relevance to normal biological activity, PrP C is recognized to undergo both a-and b-endoproteolysis, producing the cleavage fragment pairs N1/C1 and N2/C2, respectively. Experimental evidence suggests the likelihood that these processing events serve differing cellular needs. Through the engineering of a C-terminal c-myc tag onto murine PrP C , as well as the selective use of a far-Cterminal anti-PrP antibody, we have identified a new PrP C fragment, nominally 'C3', and elaborating existing nomenclature, 'c-cleavage' as the responsible proteolysis. Our studies indicate that this novel c-cleavage event can occur during transit through the secretory pathway after exiting the endoplasmic reticulum, and after PrP C has reached the cell surface, by a matrix metalloprotease.We found that C3 is GPI-anchored like other C-terminal and full length PrP C species, though it does not localize primarily at the cell surface, and is preferentially cleaved from an unglycosylated substrate. Importantly, we observed that C3 exists in diverse cell types as well as mouse and human brain tissue, and of possible pathogenic significance, c-cleavage may increase in human prion diseases. Given the likely relevance of PrP C processing to both its normal function, and susceptibility to prion disease, the potential importance of this previously underappreciated and overlooked cleavage event warrants further consideration.

The biological function of the cellular prion protein: an update

“…1). These cleavage events release the so-called N1 + C1, N2 + C2, and C3 fragments, respectively [17–20]. These events may be important for both physiology and pathology.…”

Secreted cellular prion protein binds doxorubicin and correlates with anthracycline resistance in breast cancer

“…Cellular prion protein (PrP C ) is a small glycoprotein that is anchored to the cell membrane outer leaflet via a glycosylphosphatidylinositol (GPI) tail (4). PrP C comprises a structured globular α-helical C-terminal domain and a less structured octarepeat-containing N-terminus and is regulated by proteolytic processing at 3 sites (α, β, and γ) (4). PrP C can be secreted into the extracellular environment through GPI anchor cleavage and/or modified glycosylation (4).…”

“…PrP C comprises a structured globular α-helical C-terminal domain and a less structured octarepeat-containing N-terminus and is regulated by proteolytic processing at 3 sites (α, β, and γ) (4). PrP C can be secreted into the extracellular environment through GPI anchor cleavage and/or modified glycosylation (4). By acting as a multivalent scaffold protein, it has been implicated in a variety of normal biological processes that buffer cells from internal and environmental stresses (5), though its precise molecular functions are still incompletely defined.…”

Prion protein—Semisynthetic prion protein (PrP) variants with posttranslational modifications

“…Lastly, γ‐cleavages restricted to unglycosylated PrP generate a large soluble N3 and a short C3 part by taking place in a region between aas 170 and 200. While prevalence and relevance of this cleavage requires further investigation, increased amounts of C3 in CJD brain samples suggest a pathophysiological role …”

“…While prevalence and relevance of this cleavage requires further investigation, increased amounts of C3 in CJD brain samples suggest a pathophysiological role. 135 Despite multiple evidence of PrP in physiological processes, the functional diversity based on its manifold binding partners and proteolytic fragments complicate an exact definition of its physiological function. Yet successful elucidation of pathways and roles of PrP could help to understand its linkage to toxicity in prion diseases and to other neurodegenerative diseases.…”