SPECIFIC INHIBITOR FOR PROLYL ENDOPEPTIDASE SUPPRESSES THE GENERATIONOF AMYLOID-BETA PROTEIN IN NG108-15 CELLS

A potent and specific prolyl endopeptidase inhibitor, JTP-4819, was us ed to investigate the role of prolyl endopeptidase in the generation o f 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-termi nal and N-terminal portions of A beta, were cleaved by NG108-15 cell l ysates. Cleavage of the C-terminal portion, but not the N-terminal, wa s 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 incr eased by serum deprivation. JTP-4819 caused concentration (>10(-9) M)- and time-dependent inhibition of this serum deprivation-induced incre ase 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 co nfirmed to be A beta (1-40), suggesting that it might be produced by c onversion of A beta (1-42) to A beta (1-40), These findings indicate t hat prolyl endopeptidase may be a key enzyme in the production of A be ta by NG108-15 cells and that A beta secretion can be modulated by a p rolyl endopeptidase inhibitor. (C) 1997 Academic Press.