Specific inhibitor for prolyl endopeptidase suppresses the generation of amyloid beta protein in NG108-15 cells.

A potent and specific prolyl endopeptidase inhibitor, JTP-4819, was used to investigate the role of prolyl endopeptidase in the generation of amyloid beta protein (A beta) from APP by NG108-15 cells. Synthetic substrates, 7-(succinyl-Ile-Ala)-4-methylcoumarinamide and Z(Val-Lys-Met)-4-methylcoumarinamide, respectively, corresponding to the C-terminal and N-terminal portions of A beta, were cleaved by NG108-15 cell lysates. Cleavage of the C-terminal portion, but not the N-terminal, was inhibited by JTP-4819 (IC50 = 0.6 nM). Western blot analysis showed that the A beta level in the culture medium of NG108-15 cells was increased by serum deprivation. JTP-4819 caused concentration (>10(-9) M)- and time-dependent inhibition of this serum deprivation-induced increase of A beta without having any effect on the level of the secretory form of APP. Using both specific anti-A beta (1-40) and anti-A beta (1-42) antisera, the A beta that increased with serum deprivation was confirmed to be A beta (1-40), suggesting that it might be produced by conversion of A beta (1-42) to A beta (1-40). These findings indicate that prolyl endopeptidase may be a key enzyme in the production of A beta by NG108-15 cells and that A beta secretion can be modulated by a prolyl endopeptidase inhibitor.