ENDOGENOUS PROTEOLYTIC CLEAVAGE OF NORMAL AND DISEASE-ASSOCIATED ISOFORMS OF THE HUMAN PRION PROTEIN IN NEURAL AND NONNEURAL TISSUES

We have investigated the proteolytic cleavage of the cellular (PrPC) a nd pathological (PrPSc) isoforms of the human prion protein (PrP) in n ormal and prion-affected brains and in tonsils and platelets from neur ologically intact individuals. The various PrP species were resolved a fter deglycosylation according to their electrophoretic mobility, immu noreactivity, Sarkosyl solubility, and, as a novel approach, resistanc e to endogenous proteases, First, our data show that PrPC proteolysis in brain originates amino-truncated peptides of 21 to 22 and 18 (C1) k d that are similar in different regions and are not modified by the Pr P codon 129 genotype, a polymorphism that affects the expression of pr ion disorders. Second, this proteolytic cleavage of PrPC in brain is b locked by inhibitors of metalloproteases. Third, differences in PrPC p roteolysis, and probably in Asn glycosylation and glycosylphosphatidyl inositol anchor composition, exist between neural and non-neural tissu es. Fourth, protease-resistant PrPSc cores in sporadic Creutzfeldt-Jak ob disease (CJD) and Gerstmann-Straussler-Scheinker F198S disease brai ns all have an intact C1 cleavage site (Met111-His112), which preclude s disruption of a domain associated with toxicity and fibrillogenesis. Fifth, the profile of endogenous proteolytic PrPSc peptides is charac teristic of each disorder studied, thus permitting the molecular class ification of these prion diseases without the use of proteinase K and even a recognition of PrPSc heterogeneity within type 2 CJD patients h aving different codon 129 genotype and neuropathological phenotype, Th is does not exclude the role of additional factors in phenotypic expre ssion; in particular, differences in glycosylation that may be especia lly relevant in the new variant CJD. Proteolytic processing of PrP may play an important role in the neurotropism and phenotypic expression of prion diseases, but it does not appear to participate in disease su sceptibility.