Activation of the activator protein-1 by the peroxisome proliferator clofibric acid in rat H4IIEC3 hepatoma cells.
Clofibric acid (CA), a potent peroxisome proliferator (PP), has been shown to cause tumor formation in rat liver. The precise mechanism of action of PPs remains largely unknown. However, it has been proposed that they act by increasing reactive oxygen species (ROS), leading to a cellular oxidative stress. In the present study, we have investigated the effect of CA on the activator protein-1 (AP-1) expression in PP-responsive H4IIEC3 rat hepatoma cells. Electrophoretic mobility shift assays demonstrated that AP-1 activation was induced in cells treated with CA for 24 h at all concentrations of the fibrate. This activation was prolonged up to 48 h. Using transfection experiments with H4IIEC3 cells, we found that CA induced the expression of a reporter gene driven by AP-1 and that of the glutathione S-transferase P target gene. By supershift experiments, jun and fos proteins were identified as components of the CA-activated AP-1 complexes. Western blot analyses revealed that the induction of the AP-1 activity was not dependent to an increase in the levels of jun and fos proteins. Cotreatment of H4IIEC3 cells with CA and the antioxidant N-acetylcysteine or calphostin C, a specific inhibitor of protein kinase C (PKC), blocked the AP-1 activation and the expression of the AP-1-driven luciferase reporter gene. These results demonstrate that CA activates AP-1 in H4IIEC3 cells and that this induction is mediated via ROS and PKC.
Bécuwe
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Laboratory of Cell Biology of Development, University Henri Poincaré-Nancy I, Faculty of Sciences, Vandoeuvre-les-Nancy Cedex, 54506, France. becuwe@ciril.fr
Bianchi
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A
Dauça
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D042962:Acyl-CoA Oxidase; D000818:Animals; D002457:Cell Extracts; D002995:Clofibric Acid / Q000494:pharmacology*; D004586:Electrophoresis; D015870:Gene Expression; D017930:Genes, Reporter; D018384:Oxidative Stress / Q000187:drug effects; D010088:Oxidoreductases / Q000378:metabolism; D020025:Peroxisome Proliferators / Q000494:pharmacology*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism; D018808:Transcription Factor AP-1 / Q000378:metabolism*; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D002457:Cell Extracts; D020025:Peroxisome Proliferators; D017382:Reactive Oxygen Species; D018808:Transcription Factor AP-1; D002995:Clofibric Acid; D010088:Oxidoreductases; D042962:Acyl-CoA Oxidase; D011493:Protein Kinase C