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

The cellular prion protein (PrPC) 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 PrPC from the cell. The fast alpha-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 PrPC and also when processing of PrPC 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 PrPC. The metalloprotease inhibitors did not influence the alpha-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 PrPC.