Phorbol ester-regulated cleavage of normal prion protein in HEK293 human cells and murine neurons

Cellular prion protein (PrPc) undergoes a proteolytic attach at the 110/111 down arrow 112 peptide bond, whereas the PrP isoform (PrPres) that accumul ates in the brain tissue in Creutzfeldt-Jakob disease reveals an alternate cleavage site at about residue 90. Interestingly, the normal processing of PrP occurs inside the 106-126 amino acid region thought to be responsible f or the neurotoxicity of the pathogenic prions, whereas PrPres cleavage pres erves this potentially toxic domain, Therefore, any molecular mechanisms le ading to enhanced cleavage at the 110/111 down arrow 112 peptide bond Could be of potential interest, We set up TSM1 neurons and HEK293 stable transfe ctants overexpressing the wild-type or 3F4-tagged murine PrPc, respectively , Both mock-transfected and PrPc-expressing cell Lines produced an 11-12-kD a PrP fragment (referred to as N1), the immunological: characterization of which strongly suggests that it corresponds to the N-terminal PrPc fragment derived hom normal processing. We have established that the recovery of se creted N1 is increased by the protein kinase C agonists PDBu and PMA in a t ime- and dose-dependent manner in both cell lines. In contrast, secretion o f N1 remains unaffected by the inactive PDBu analog alpha PDD and by the pr otein kinase A effecters dibutyryl cAMP and forskolin. Overall, our data in dicate that the normal processing of PrPc is up-regulated by protein kinase C but not protein kinase A in human cells and murine neurons.