title: The amyloid precursor protein/protease nexin 2 Kunitz inhibitor domain is a highly specific substrate of mesotrypsin.
abstract: The amyloid precursor protein (APP) is a ubiquitously expressed transmembrane adhesion protein and the progenitor of amyloid-beta peptides. The major splice isoforms of APP expressed by most tissues contain a Kunitz protease inhibitor domain; secreted APP containing this domain is also known as protease nexin 2 and potently inhibits serine proteases, including trypsin and coagulation factors. The atypical human trypsin isoform mesotrypsin is resistant to inhibition by most protein protease inhibitors and cleaves some inhibitors at a substantially accelerated rate. Here, in a proteomic screen to identify potential physiological substrates of mesotrypsin, we find that APP/protease nexin 2 is selectively cleaved by mesotrypsin within the Kunitz protease inhibitor domain. In studies employing the recombinant Kunitz domain of APP (APPI), we show that mesotrypsin cleaves selectively at the Arg(15)-Ala(16) reactive site bond, with kinetic constants approaching those of other proteases toward highly specific protein substrates. Finally, we show that cleavage of APPI compromises its inhibition of other serine proteases, including cationic trypsin and factor XIa, by 2 orders of magnitude. Because APP/protease nexin 2 and mesotrypsin are coexpressed in a number of tissues, we suggest that processing by mesotrypsin may ablate the protease inhibitory function of APP/protease nexin 2 in vivo and may also modulate other activities of APP/protease nexin 2 that involve the Kunitz domain.
authors.affiliation: Department of Cancer Biology, Mayo Clinic Cancer Center, Jacksonville, Florida 32224, USA.
authors.forename: Moh'd A
authors.initials: MA
authors.lastname: Salameh
authors.forename: Jessica L
authors.initials: JL
authors.lastname: Robinson
authors.forename: Duraiswamy
authors.initials: D
authors.lastname: Navaneetham
authors.forename: Dipali
authors.initials: D
authors.lastname: Sinha
authors.forename: Benjamin J
authors.initials: BJ
authors.lastname: Madden
authors.forename: Peter N
authors.initials: PN
authors.lastname: Walsh
authors.forename: Evette S
authors.initials: ES
authors.lastname: Radisky
mesh_terms: D000595:Amino Acid Sequence; D016564:Amyloid beta-Protein Precursor / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D000818:Animals; D045744:Cell Line, Tumor; D015945:Factor XIa / Q000037:antagonists & inhibitors; D006801:Humans; D007700:Kinetics; D051379:Mice; D008969:Molecular Sequence Data; D011480:Protease Inhibitors / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D058255:Protease Nexins; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000737:chemistry* / Q000378:metabolism*; D013379:Substrate Specificity; D014357:Trypsin / Q000378:metabolism*
chemical_list: C545487:APP protein, human; D016564:Amyloid beta-Protein Precursor; D011480:Protease Inhibitors; D058255:Protease Nexins; D011956:Receptors, Cell Surface; D015945:Factor XIa; C040749:PRSS3 protein, human; D014357:Trypsin