Neurodegenerative Diseases and

downstate.edu The susceptibility of the normal cellular prion protein isoform, cellular prion protein (PrPC), to proteolytic digestion has been well documented. In addition, a link between PrPC and the cytosolic protease, calpain, has been reported although the specifics of the interaction remain unclear.We performed in vitro and in cell-based studies to examine this relationship. We observed that human recombinant PrP (HrPrP) was readily cleaved by calpain-1 and-2, and we have identified and defined the targeted cleavage sites. In contrast, HrPrP was resis-tant to caspase-3 digestion. Unexpectedly, when brain lysates from PrPC-expressing mice were treated with calpain, no appreciable loss of the intact PrPC, nor the appearance of PrPC breakdown products (BDPs) were observed, even though alpha II-spectrin was converted to its signature calpain-induced BDPs. In addition, when rat cerebrocortical neuronal cul-tures (RtCNC) were subjected to the two neurotoxins at subacute levels, maitotoxin (MTX) and N-methyl-D-aspartate (NMDA), PrPC-BDPs were also not detectable. However, a novel finding from these cell-based studies is that apparently full-length, mature PrPC is released into culture media from RtCNC challenged with subacute doses of MTX and NMDA. Cal