title: The protease inhibitor, MG132, blocks maturation of the amyloid precursor protein Swedish mutant preventing cleavage by beta-Secretase.
abstract: Amyloid (Abeta) 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 Abeta peptide secretion by interfering with gamma-secretase cleavage. Using a novel, specific, and sensitive enzyme-linked immunosorbent assay for the beta-secretase-cleaved fragment of the Swedish mutant of APP (APPSw), we determined that the peptide aldehyde, MG132, prevented beta-secretase cleavage. This block in beta-secretase cleavage was not observed with clasto-lactacystin beta-lactone and thus, cannot be attributed to proteasomal inhibition. MG132 inhibition 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 affect alpha-secretase cleavage. With MG132, inhibition was delayed and it decreased secretion of alpha-cleaved APPSw as well. Furthermore, MG132 treatment 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 processing 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 explain the previously reported peptide aldehyde-induced decrease in Abeta peptide secretion.
authors.affiliation: Institute of Gerontology, Department of Biological Chemistry, University of Michigan, Ann Arbor, Michigan 48109, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Steinhilb
authors.forename: R S
authors.initials: RS
authors.lastname: Turner
authors.forename: J R
authors.initials: JR
authors.lastname: Gaut
mesh_terms: D000595:Amino Acid Sequence; D053829:Amyloid Precursor Protein Secretases; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D010450:Endopeptidases / Q000378:metabolism*; D004797:Enzyme-Linked Immunosorbent Assay; D006056:Golgi Apparatus / Q000378:metabolism; D006868:Hydrolysis; D007976:Leupeptins / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009154:Mutation
chemical_list: D016564:Amyloid beta-Protein Precursor; D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D053829:Amyloid Precursor Protein Secretases; D010450:Endopeptidases; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde