Separate mechanisms act concurrently to shed and release the prion protein from the cell

Abstract

The cellular prion protein (PrP (C) ) is attached to the cell membrane via its glycosylphosphatidylinositol (GPI)-anchor and is constitutively shed into the extracellular space. Here, three different mechanisms are presented that concurrently shed PrP (C) from the cell. The fast α-cleavage released a N-terminal fragment (N1) into the medium and the extreme C-terminal cleavage shed soluble full-length (FL-S) PrP and C-terminally cleaved (C1-S) fragments outside the cell. Also, a slow exosomal release of full-length (FL) and C1-fragment (C1) was demonstrated. The three separate mechanisms acting simultaneously, but with different kinetics, have to be taken into consideration when elucidating functional roles of PrP (C) and also when processing of PrP (C) is considered as a target for intervention in prion diseases. Further, in this study it was shown that metalloprotease inhibitors affected the extreme C-terminal cleavage and shedding of PrP (C) . The metalloprotease inhibitors did not influence the α-cleavage or the exosomal release. Taken together, these results are important for understanding the different mechanisms acting in parallel in the shedding and cleavage of PrP (C) .

Physiological Functions of the Cellular Prion Protein

“…A recent study proposed that this “α” form of cleavage may also occur at alternative sites within the hydrophobic domain itself (McDonald et al, 2014). Members of the disintegrin and metalloproteinase domain-containing protein (ADAM) family may be responsible for α-cleavage (Vincent et al, 2001; Cisse et al, 2008; McDonald et al, 2014), although not all studies support this idea (Beland et al, 2012; Wik et al, 2012). α-Cleavage is thought to occur either in an acidic endosomal compartment (Shyng et al, 1993) or within the Golgi apparatus (Walmsley et al, 2009) and results in the production of the N-terminal fragment N1, which is released from the cell, and the C-terminal fragment C1, which seems to be trafficked to the cell membrane as per the full length protein (Harris et al, 1993; Vincent et al, 2000; Laffont-Proust et al, 2006).…”

The GPI-anchoring of PrP

“…110 In contrast, the role of ADAM10 as the major PrP C sheddase has been established by recent studies. 95,96,107,111 While knowledge on the concrete localization of the two cleavage events is limited 54,111-113 both processing steps seem to depend on PrP C membrane attachment. As a matter of implicitness, for a protein to be proteolytically cleaved it has to meet and interact with the relevant protease.…”

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

“…Thus, Ctm PrP may be the neurotoxic molecule in the corresponding familial forms of human prion disease. 34 Several artificial deletions of different size in this domain outside of the α-cleavage site partially or completely inhibit the α-cleavage, [35][36][37] indicating that the dimerization domain is also essential for this cleavage. Since α-cleavage occurs in the late secretory pathway, 38 PrP C mutants unable to reach the cell surface should be resistant to α-cleavage.…”