A role for CCAAT/enhancer-binding protein in hepatic expression of thrombin-activable fibrinolysis inhibitor.
Thrombin-activable fibrinolysis inhibitor (TAFI) is a procarboxypeptidase B-like zymogen that upon activation by thrombin, thrombin-thrombomodulin, or plasmin attenuates fibrin clot lysis by inhibiting positive feedback in the fibrinolytic cascade. The concentration of TAFI in plasma varies in the human population and thus may constitute a risk factor for thrombotic disorders. In addition, TAFI has been reported to be a positive acute phase reactant in mice. We have initiated molecular analysis of the human TAFI promoter to understand the mechanisms underlying regulation of TAFI gene expression. We identified a putative C/EBP-binding site between -53 and -40 of the promoter. Mutations in this site that abolish C/EBP binding decrease TAFI promoter activity in human hepatoma (HepG2) cells by approximately 80%. Gel mobility shift analyses indicated that C/EBP-beta present in HepG2 nuclear extracts and C/EBP-alpha and -beta present in adult rat liver nuclear extracts bind to the C/EBP site. C/EBP-alpha, -beta, and -delta isoforms are all capable of binding to the C/EBP site and activating the TAFI promoter. The identification of a functional C/EBP-binding site in the human TAFI promoter may have important implications for the regulation of expression of this gene during development and in response to inflammatory stimuli.
Boffa
Michael B
MB
Department of Biochemistry, Queen's University, Kingston, Ontario K7L 3N6, Canada.
Hamill
Jeffrey D
JD
Bastajian
Nazareth
N
Dillon
Rebecca
R
Nesheim
Michael E
ME
Koschinsky
Marlys L
ML
D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D025901:Carboxypeptidase B2 / Q000378:metabolism*; D006224:Cricetinae; D006801:Humans; D008099:Liver / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D051381:Rats; D014407:Tumor Cells, Cultured
D022762:CCAAT-Enhancer-Binding Proteins; D025901:Carboxypeptidase B2