Objective
The type-II transmembrane extracellular serine protease matriptase was shown to cleave at Arg-102 in the amino-terminal region of the amyloid precursor protein (APP). In this study we determined matriptase cleavage sites in the amyloid-beta (Aβ) peptide region of APP (Asp-597 to Ala-638 in the APP695 isoform). A recombinant human matriptase protease domain was used to cleave a synthetic human Aβ1-42 peptide. The human APP695 or mutants at the candidate matriptase cleavage sites was co-expressed with the human matriptase or its protease-dead mutant in HEK293 cells to evaluate matriptase cleavage of APP. Overexpression of matriptase in the M17 human neuroblastoma cells was performed to determine the effect of matriptase expression on endogenous APP.
Results
The human Aβ1-42 peptide can be cleaved by the matriptase serine protease domain, at Arg-5, Lys-16, and Lys-28, as determined by matrix-assisted laser desorption ionization time-of-flight mass spectrometry. Co-expression of matriptase but not its protease-dead mutant with APP695 resulted in site-specific cleavages of the latter. Replacement of Arg-601 (Arg-5 in Aβ1-42) by Ala in APP695 prevented matriptase cleavage at this site. Overexpression of matriptase but not its protease-dead mutant in the M17 cells resulted in a significant reduction of the endogenous APP quantity.