title: Antiplasmin-cleaving enzyme is a soluble form of fibroblast activation protein.
abstract: Circulating antiplasmin-cleaving enzyme (APCE) has a role in fibrinolysis and appears structurally similar to fibroblast activation protein (FAP), a cell-surface proteinase that promotes invasiveness of certain epithelial cancers. To explore this potential relationship, we performed comparative structure/function analyses of the 2 enzymes. APCE from human plasma and recombinant FAP (rFAP) exhibited identical pH optima of 7.5, extinction coefficients (in(280 nm)(1%)) of 20.2 and 20.5, common sequences of tryptic peptides, and cross-reactivity with FAP antibody. APCE and rFAP are homodimers with monomeric subunits of 97 and 93 kDa. Only homodimers appear to have enzymatic activity, with essentially identical kinetics toward Met-alpha2-antiplasmin (Met-alpha2AP) and peptide substrates. APCE and rFAP cleave both Pro3-Leu4 and Pro12-Asn13 bonds of Met-alpha2AP, but relative kcat/Km values for Pro12-Asn13 are about 16-fold higher than for Pro3-Leu4. APCE and rFAP demonstrate higher kcat/Km values toward a peptide modeled on P4-P4' sequence surrounding the Pro12-Asn13 primary cleavage site than for Z-Gly-Pro-AMC and Ala-Pro-AFC substrates. These data support APCE as a soluble derivative of FAP and Met-alpha2AP as its physiologic substrate. Conversion of Met-alpha2AP by membrane or soluble FAP to the more easily fibrin-incorporable form, Asn-alpha2AP, may increase plasmin inhibition within fibrin surrounding certain neoplasms and have an impact on growth and therapeutic susceptibility.
authors.affiliation: W. K. Warren Medical Research Center, PO Box 26901, BSEB-306, Oklahoma City, OK 73190, USA. kyung-lee@ouhsc.edu
authors.forename: Kyung N
authors.initials: KN
authors.lastname: Lee
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Jackson
authors.forename: Victoria J
authors.initials: VJ
authors.lastname: Christiansen
authors.forename: Chung S
authors.initials: CS
authors.lastname: Lee
authors.forename: Jin-Geun
authors.initials: JG
authors.lastname: Chun
authors.forename: Patrick A
authors.initials: PA
authors.lastname: McKee
mesh_terms: D000595:Amino Acid Sequence; D000951:Antigens, Neoplasm / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D014408:Biomarkers, Tumor / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D002850:Chromatography, Gel; D010450:Endopeptidases; D018093:Gelatinases; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D013058:Mass Spectrometry; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012697:Serine Endopeptidases / Q000097:blood / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D000099167:Fibroblast Activation Protein Alpha
chemical_list: D000951:Antigens, Neoplasm; D014408:Biomarkers, Tumor; D010450:Endopeptidases; D018093:Gelatinases; D008565:Membrane Proteins; D010446:Peptide Fragments; D011994:Recombinant Proteins; D012697:Serine Endopeptidases; D000099167:Fibroblast Activation Protein Alpha; C487177:antiplasmin-cleaving enzyme, human