Identification of human thrombin-activatable fibrinolysis inhibitor in vascular and inflammatory cells

Abstract

TAFI (thrombin-activatable fibrinolysis inhibitor) is a carboxypeptidase zymogen originally identified in plasma. The TAFI pathway helps to regulate the balance between the coagulation and fibrinolytic cascades. Activated TAFI (TAFIa) can also inactivate certain pro-inflammatory mediators, suggesting that the TAFI pathway may also regulate communication between coagulation and inflammation. Expression in the liver is considered to be the source of plasma TAFI. TAFI has also been identified in platelets and CPB2 (the gene encoding TAFI) mRNA has been detected in megakaryocytic cell lines as well as in endothelial cells. We have undertaken a quantitative analysis of CPB2 mRNA and TAFI protein in extrahepatic cell types relevant to vascular disease. Using RT-PCR and quantitative RT-PCR, we detected CPB2 mRNA in the human megakaryoblastic cell lines MEG-01 and Dami, the human monocytoid cell line THP-1 as well as THP-1 cells differentiated into a macrophage-like phenotype, and in primary human umbilical vein and coronary artery endothelial cells. CPB2 mRNA abundance in MEG-01, Dami, and THP-1 cells was modulated by the state of differentiation of these cells. Using a recently developed TAFIa assay, we detected TAFI protein in the lysates of the human hepatocellular carcinoma cell line HepG2 as well as in MEG-01 and Dami cells and in the conditioned medium of HepG2 cells, differentiated Dami cells, and THP-1 macrophages. We have obtained clear evidence for extrahepatic expression of TAFI, which has clear implications for the physiological and pathophysiological functions of the TAFI pathway.

Activated thrombin-activatable fibrinolysis inhibitor (TAFIa) attenuates breast cancer cell metastatic behaviors through inhibition of plasminogen activation and extracellular proteolysis

“…CPB2 mRNA was detectable in all of the examined breast cancer cell lines, albeit at a lower level in all cases compared to the positive control THP-1 macrophages (Fig. 1 ), which is correspondingly much lower than reported in liver or a cultured hepatoma cell line [ 11 ]. CPB2 mRNA levels in the highly malignant and invasive MDA-MB-231, HTB-126, and MCF10ACA1a cell lines were comparable to mRNA levels in the non-invasive [ 26 ] MCF7 cell line.…”

“…Thrombin activatable fibrinolysis inhibitor (TAFI), also known as carboxypeptidase B, U or R [ 10 ], is a plasma zymogen expressed mainly in the liver but also found in megakaryocytes (leading to a platelet pool of TAFI) and macrophages [ 11 ]. TAFI is converted to activated TAFI (TAFIa) by proteolytic cleavage at Arg92 either by thrombin, plasmin or thrombin in complex with the endothelial cofactor thrombomodulin (TM).…”

Fibrinolysis inhibitors in plaque stability: a morphological association of PAI‐1 and TAFI in advanced carotid plaque

“…The question is whether there is TAFI activity in the plaque. The main part of TAFI in plasma, as well as in EC, is not activated . Both plasmin and thrombin, which can convert TAFI into TAFIa, are present in the plaque and TAFI can be activated to TAFIa both by plasmin on the fibrin matrix and by the thrombin‐TM complex on the EC surface.…”

Identification and Characterization of Circulating Variants of CXCL12 from Human Plasma: Effects on Chemotaxis and Mobilization of Hematopoietic Stem and Progenitor Cells

“…Carboxypeptidases N and M exclusively process Lys 89 [44], whereas Cathepsin X is secreted by human osteoblasts and reveals a C-terminal exopeptidase activity for CXCL12 , which cleaves 15 amino acids up to proline P 74 [47]. A putative carboxypeptidase for C-terminal processing of CXCL12 represents a thrombin-activatable fibrinolysis inhibitor that is expressed in thrombocytes and is able to process C-terminal Lys residues [48].…”