Inhibition of prolylendopeptidase does not affect γ-secretase processing of amyloid precursor protein in a human neuroblastoma cell line

AP peptides are major components of the amyloid plaques that characterize Alzheimer's disease. The enzyme activities (beta- and gamma-secretases) involved in generating AP from amyloid precursor protein (APP) are unidentified. It has been suggested that prolylendopeptidase (PEP), an oligopeptidase that normally cleaves after proline residues, could also cleave after the alanine at position 42 of A beta to generate A beta(42) We investigated whether inhibition of PEP activity in human neuroblastoma cells affected A beta levels in cell culture media. An SH SY5Y cell line expressing SPA4CT, encoding the C-terminal 100 residues of APP and the signal sequence, was used. Only gamma-secretase activity is required for AP production in this cell line. The PEP inhibitor Fmoc-AlaPro-CN (10 mu M) reduced PEP activity in these cells by approximately 95% in the absence of significant toxicity, but had no effect on A beta(40) Or A beta(42) levels in cell culture media. We conclude that PEP is unlikely to be involved in gamma-secretase processing of APP. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.