Antiplasmin-cleaving enzyme is a soluble form of fibroblast activation protein

• Published in: Blood 2006-02, Vol.107 (4), p.1397-1404
• Main Authors: Lee, Kyung N., Jackson, Kenneth W., Christiansen, Victoria J., Lee, Chung S., Chun, Jin-Geun, McKee, Patrick A.
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Antigens, Neoplasm - blood; Antigens, Neoplasm - genetics; Antigens, Neoplasm - metabolism; Biological and medical sciences; Biomarkers, Tumor - blood; Biomarkers, Tumor - genetics; Biomarkers, Tumor - metabolism; Blood coagulation. Blood cells; Chromatography, Gel; Fundamental and applied biological sciences. Psychology; Gelatinases; General aspects, investigation methods, hemostasis, fibrinolysis; Humans; Hydrogen-Ion Concentration; Kinetics; Mass Spectrometry; Membrane Proteins; Molecular and cellular biology; Molecular Sequence Data; Peptide Fragments - chemistry; Recombinant Proteins - metabolism; Sequence Alignment; Sequence Homology, Amino Acid; Serine Endopeptidases - blood; Serine Endopeptidases - genetics; Serine Endopeptidases - metabolism; Structure-Activity Relationship
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood-2005-08-3452

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 (∈280nm1%) 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-α2-antiplasmin (Met-α2AP) and peptide substrates. APCE and rFAP cleave both Pro3-Leu4 and Pro12-Asn13 bonds of Met-α2AP, 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-α2AP as its physiologic substrate. Conversion of Met-α2AP by membrane or soluble FAP to the more easily fibrin-incorporable form, Asn-α2AP, may increase plasmin inhibition within fibrin surrounding certain neoplasms and have an impact on growth and therapeutic susceptibility.