Ml. Steinhilb et al., The protease inhibitor, MG132, blocks maturation of the amyloid precursor protein Swedish mutant preventing cleavage by beta-secretase, J BIOL CHEM, 276(6), 2001, pp. 4476-4484
Amyloid (AP) peptides found aggregated into plaques in Alzheimer's disease
are derived from the sequential cleavage of the amyloid precursor protein (
APP) first by beta- and then by gamma -secretases. Peptide aldehydes, which
inhibit cysteine proteases and proteasomes, reportedly block AP peptide se
cretion by interfering with gamma -secretase cleavage. Using a novel, speci
fic, and sensitive enzyme-linked immunosorbent assay for the beta -secretas
e-cleaved fragment of the Swedish mutant of APP (APPSw), we determined that
the peptide aldehyde, MG132, prevented beta -secretase cleavage. This bloc
k in beta -secretase cleavage was not observed with clasto-lactacystin beta
-lactone and thus, cannot be attributed to proteasomal inhibition. MG132 i
nhibition of beta -secretase cleavage was compared with the serine protease
inhibitor, 4-(2-aminoethyl)benzenesulfonyl fluoride hydrochloride (AEBSF).
AEBSF inhibition of beta -secretase cleavage was immediate and did not aff
ect alpha -secretase cleavage. With MG132, inhibition was delayed and it de
creased secretion of alpha -cleaved APPSw as well. Furthermore, MG132 treat
ment impaired maturation of full-length APPSw. Both inhibited intracellular
formation of the beta -cleaved product. These results suggest that peptide
aldehydes such as MG132 have multiple effects on the maturation and proces
sing of APP. We conclude that the MG132-induced decrease in beta -secretase
cleavage of APPSw is due to a block in maturation. This is sufficient to e
xplain the previously reported peptide aldehyde-induced decrease in AP pept
ide secretion.