title: Pro-inflammatory cytokines reduce human TAFI expression via tristetraprolin-mediated mRNA destabilisation and decreased binding of HuR.
abstract: Thrombin activatable fibrinolysis inhibitor (TAFI) is the zymogen form of a basic carboxypeptidase (TAFIa) with both anti-fibrinolytic and anti-inflammatory properties. The role of TAFI in inflammatory disease is multifaceted and involves modulation both of specific inflammatory mediators as well as of the behaviour of inflammatory cells. Moreover, as suggested by in vitro studies, inflammatory mediators are capable of regulating the expression of CPB2, the gene encoding TAFI. In this study we addressed the hypothesis that decreased TAFI levels observed in inflammation are due to post-transcriptional mechanisms. Treatment of human HepG2 cells with pro-inflammatory cytokines TNFα, IL-6 in combination with IL-1β, or with bacterial lipopolysaccharide (LPS) decreased TAFI protein levels by approximately two-fold over 24 to 48 hours of treatment. Conversely, treatment of HepG2 cells with the anti-inflammatory cytokine IL-10 increased TAFI protein levels by two-fold at both time points. We found that the mechanistic basis for this modulation of TAFI levels involves binding of tristetraprolin (TTP) to the CPB2 3'-UTR, which mediates CPB2 mRNA destabilisation. In this report we also identified that HuR, another ARE-binding protein but one that stabilises transcripts, is capable of binding the CBP2 3'UTR. We found that pro-inflammatory mediators reduce the occupancy of HuR on the CPB2 3'-UTR and that the mutation of the TTP binding site in this context abolishes this effect, although TTP and HuR appear to contact discrete binding sites. Interestingly, all of the mediators tested appear to increase TAFI protein expression in THP-1 macrophages, likewise through effects on CPB2 mRNA stability.
authors.forename: D
authors.initials: D
authors.lastname: Komnenov
authors.forename: C A
authors.initials: CA
authors.lastname: Scipione
authors.forename: Z A
authors.initials: ZA
authors.lastname: Bazzi
authors.forename: J J W
authors.initials: JJ
authors.lastname: Garabon
authors.forename: M L
authors.initials: ML
authors.lastname: Koschinsky
authors.affiliation: Michael B. Boffa, PhD, Department of Chemistry & Biochemistry, University of Windsor, Windsor, Ontario, Canada, Tel.: +1 519 253 3000 ext 3537, Fax: +1 519 973 7098, E-mail: mboffa@uwindsor.ca.
authors.forename: M B
authors.initials: MB
authors.lastname: Boffa
mesh_terms: D020413:3' Untranslated Regions / Q000235:genetics*; D001665:Binding Sites; D025901:Carboxypeptidase B2 / Q000096:biosynthesis* / Q000235:genetics; D045744:Cell Line, Tumor; D000067780:ELAV-Like Protein 1 / Q000502:physiology*; D005342:Fibrinolysis; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D017930:Genes, Reporter; D056945:Hep G2 Cells; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D018836:Inflammation Mediators / Q000494:pharmacology*; D007378:Interleukins / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000378:metabolism; D009154:Mutation; D009363:Neoplasm Proteins / Q000502:physiology; D011485:Protein Binding; D020871:RNA Stability / Q000187:drug effects* / Q000502:physiology; D012333:RNA, Messenger / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D051816:Tristetraprolin / Q000502:physiology*; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
chemical_list: D020413:3' Untranslated Regions; D000067780:ELAV-Like Protein 1; C098770:ELAVL1 protein, human; D018836:Inflammation Mediators; D007378:Interleukins; D008070:Lipopolysaccharides; D009363:Neoplasm Proteins; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins; D051816:Tristetraprolin; D014409:Tumor Necrosis Factor-alpha; C497552:ZFP36 protein, human; C585364:CPB2 protein, human; D025901:Carboxypeptidase B2
keywords: Fibrinolysis inhibitors; gene regulation; inflammatory mediators; liver