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Negative Regulation of Human Fibrinogen Gene Expression by Peroxisome Proliferator-activated Receptor α Agonists via Inhibition of CCAAT Box/Enhancer-binding Protein β

Author: Gervois, P. · Vu-Dac, N. · Kleemann, R. · Kockx, M. · Dubois, G. · Laine, B. · Kosykh, V. · Fruchart, J.C. · Kooistra, T. · Staels, B.
Type:article
Date:2001
Institution: Gaubius Instituut TNO
Source:Journal of Biological Chemistry, 36, 276, 33471-33477
Identifier: 236214
doi: doi:10.1074/jbc.M102839200
Keywords: Western blotting · Blotting, Northern · Blotting, Western · CCAAT-Enhancer-Binding Protein-alpha · Cell Line · Dose-Response Relationship, Drug · Down-Regulation · Fibrinogen · Hepatocytes · Humans · Inflammation · Interleukin-6 · Liver · Mutagenesis, Site-Directed · Nuclear Receptor Coactivator 2 · Peroxisome Proliferators · Plasmids · Precipitin Tests · Promoter Regions (Genetics) · Pyrimidines · Receptors, Cytoplasmic and Nuclear · Transcription Factors · Transcription, Genetic · Transfection · Tumor Cells, Cultured

Abstract

Fibrinogen is a coagulation factor and an acute phase reactant up-regulated by inflammatory cytokines, such as interleukin 6 (IL-6). Elevated plasma fibrinogen levels are associated with coronary heart diseases. Fibrates are clinically used hypolipidemic drugs that act via the nuclear receptor peroxisome proliferator-activated receptor α (PPARα). In addition, most fibrates also reduce plasma fibrinogen levels, but the molecular mechanism is unknown. In this study, we demonstrate that fibrates decrease basal and IL-6-stimulated expression of the human fibrinogen-β gene in human primary hepatocytes and hepatoma HepG2 cells. Fibrates diminish basal and IL-6-induced fibrinogen-β promoter activity, and this effect is enhanced in the presence of co-transfected PPARα. Site-directed mutagenesis experiments demonstrate that PPARα activators decrease human fibrinogen-β promoter activity via the CCAAT box/enhancer-binding protein (C/EBP) response element. Co-transfection of the transcriptional intermediary factor glucocorticoid receptor-interacting protein 1/transcriptional intermediary factor 2 (GRIP1/TIF2) enhances fibrinogen-β gene transcription and alleviates the repressive effect of PPARα. Co-immunoprecipitation experiments demonstrate that PPARα and GRIP1/TIF2 physically interact in vivo in human liver. These data demonstrate that PPARα agonists repress human fibrinogen gene expression by interference with the C/EBPβ pathway through titration of the coactivator GRIP1/TIF2. We observed that the anti-inflammatory action of PPARα is not restricted to fibrinogen but also applies to other acute phase genes containing a C/EBP response element; it also occurs under conditions in which the stimulating action of IL-6 is potentiated by dexamethasone. These findings identify a novel molecular mechanism of negative gene regulation by PPARα and reveal the direct implication of PPARα in the modulation of the inflammatory gene response in the liver. Chemicals/CAS: fibrinogen, 9001-32-5; peroxisome proliferator activated receptor alpha, 147258-70-6; CCAAT-Enhancer-Binding Protein-alpha; Fibrinogen, 9001-32-5; Interleukin-6; NCOA2 protein, human; Nuclear Receptor Coactivator 2; Peroxisome Proliferators; pirinixic acid, 50892-23-4; Pyrimidines; Receptors, Cytoplasmic and Nuclear; Transcription Factors