Fibrates down-regulate IL-1-stimulated C-reactive protein gene expression in hepatocytes by reducing nuclear p50-NFkappa B-C/EBP-beta complex formation.
C-reactive protein (CRP) is a major acute-phase protein in humans. Elevated plasma CRP levels are a risk factor for cardiovascular disease. CRP is predominantly expressed in hepatocytes and is induced by interleukin-1 (IL-1) and IL-6 under inflammatory situations, such as the acute phase. Fibrates are hypolipidemic drugs that act through the nuclear receptor peroxisome proliferator-activated receptor-alpha (PPAR-alpha). Fibrates have been shown to reduce elevated CRP levels in humans, but the molecular mechanism is unknown. In this study, we demonstrate that different PPAR-alpha activators suppress IL-1-induced, but not IL-6-induced, expression of CRP in primary human hepatocytes and HuH7 hepatoma cells. Induction of CRP expression by IL-1 occurs at the transcriptional level. Site-directed mutagenesis experiments show that IL-1 induces CRP expression through 2 overlapping response elements, the binding sites for CCAAT-box/enhancer-binding protein-beta (C/EBP-beta) and p50-nuclear factor-kappaB (p50-NFkappaB). Cotransfection of C/EBP-beta and p50-NFkappaB enhances CRP promoter activity, and coimmunoprecipitation experiments indicate that the increase in CRP promoter activity by IL-1 is related to the generation and nuclear accumulation of C/EBP-beta-p50-NFkappaB complexes. Interestingly, PPAR-alpha activators reduce the formation of nuclear C/EBP-beta-p50-NFkappaB complexes, and thereby CRP promoter activity, by 2 mechanisms. First, PPAR-alpha increases IkappaB-alpha expression and thus prevents p50-NFkappaB translocation to the nucleus. Second, fibrates decrease hepatic C/EBP-beta and p50-NFkappaB protein levels in mice in a PPAR-alpha-dependent way. Our findings identify C/EBP-beta and p50-NFkappaB as novel targets for PPAR-alpha and provide a molecular explanation for the reduction of plasma CRP levels by fibrates.
Kleemann
Robert
R
Gaubius Laboratory Nederlandse Organisatie voor toegepast natuurwetenschappelijk onderzoek (TNO) Prevention and Health, Leiden, The Netherlands. r.kleemann@pg.tno.nl
Gervois
Philippe P
PP
Verschuren
Lars
L
Staels
Bart
B
Princen
Hans M G
HM
Kooistra
Teake
T
D000818:Animals; D001629:Bezafibrate / Q000494:pharmacology*; D002097:C-Reactive Protein / Q000187:drug effects / Q000235:genetics*; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D002995:Clofibric Acid / Q000031:analogs & derivatives* / Q000494:pharmacology*; D015536:Down-Regulation / Q000187:drug effects; D058607:Fibric Acids; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D000960:Hypolipidemic Agents / Q000494:pharmacology*; D007375:Interleukin-1 / Q000494:pharmacology*; D051379:Mice; D018345:Mice, Knockout; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism*; D052002:NF-kappa B p50 Subunit; D011485:Protein Binding / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
D022782:CCAAT-Enhancer-Binding Protein-beta; D058607:Fibric Acids; D000960:Hypolipidemic Agents; D007375:Interleukin-1; D016328:NF-kappa B; D052002:NF-kappa B p50 Subunit; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D002995:Clofibric Acid; D002097:C-Reactive Protein; C019304:ciprofibrate; D001629:Bezafibrate