Binding to carboxypeptidase M mediates protective effects of fibrinopeptide Bβ 15-42 .

During fibrinolysis a 28-amino-acid peptide is generated besides other degradation products of fibrin. This peptide, called B beta(15-42), which is cleaved by plasmin from the end of the fibrin Bp-chain, is protective in myocardial and renal ischemia/reperfusion injury and improves the outcome in experimental sepsis. B beta(15-42) has been shown to mediate different beneficial effects in endothelial cells through binding to vascular endothelial-cadherin. Here, we provide in vitro and in vivo evidence that B beta(15-42) has additional cell protective activity in tubular cells, which is caused by a distinct mechanism. As vascular endothelial-cadherin is not expressed by tubular cells we used ligand-receptor capture technology LRC-TriCEPS to search for tubular cell surface receptors and identified carboxypeptidase M (CBPM) as a novel binding partner of B beta(15-42). Silencing CBPM with siRNA reduced the protective potential of B beta(15-42) against tubular cell stress. B beta(15-42) inhibited the enzymatic activity of CBPM and modified the impact of CBPM on bradykinin signaling. We conclude that beneficial properties of B beta(15-42) are not restricted to endothelial cells but are also active in epithelial cells where cytoprotection depends on CBPM binding.