Effets de mélanges de xénobiotiques agissant par des voies de signalisation différentes (conséquences moléculaires dans des modèles hépatiques humains)

PARIS-BIUP (751062107) / SudocSudocFranceF

2,3,7,8-Tetrachlorodibenzo-p-Dioxin Counteracts the p53 Response to a Genotoxicant by Upregulating Expression of the Metastasis Marker AGR2 in the Hepatocarcinoma Cell Line HepG2

International audienceTCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin) is an environmental pollutant which binds the aryl hydrocarbon receptor (AhR), a transcription factor that triggers variousbiological responses. In this study, we show that TCDD treatment counteracts the p53 activation elicited by a genotoxic compound, etoposide, in the human hepatocarcinoma cell line HepG2 and we delineated the mechanisms of this interaction. Using siRNA knock-down experiments, we found that the newly described metastasis marker, anterior gradient-2 (AGR2), is involved in this effect. Both AGR2 mRNA and protein levels were increased (6-and 4-fold, respectively) by TCDD treatment and this effect was mediated by the AhR receptor. The half-life of AGR2 mRNA was unchanged by TCDD treatment. Analysis of the promoter of the AGR2 gene revealed 3 putative xenobiotic responsive elements (XRE) in the proximal 3.5 kb promoter. Transient transfection of HepG2 cells by the Gaussia luciferase reporter gene driven by various deleted and mutated fragments of the promoter indicated that only the most proximal XRE was active. These results suggest that AhR ligands such as TCDD may contribute to tumour progression by inhibiting p53 regulation by genotoxicants via the increased expression of the metastasis marker AGR2

INDUCTION OF THE RAS ACTIVATOR SON OF SEVENLESS 1 BY ENVIRONMENTAL POLLUTANTS MEDIATES THEIR EFFECTS ON CELLULAR PROLIFERATION

International audienc

Two persistent organic pollutants which act through different xenosensors (alpha-endosulfan and 2,3,7,8 tetrachlorodibenzo-p-dioxin) interact in a mixture and downregulate multiple genes involved in human hepatocyte lipid and glucose metabolism.

International audienceIndividuals, typically, are exposed to mixtures of environmental xenobiotics affecting multiple organs and acting through different xenosensors and pathways in species and cell-type specific manners. 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and α-endosulfan are Persistent Organic Pollutants (POPs) and endocrine disruptors which act through different xenosensors and accumulate in the liver. Our objective in this HEALS study was to investigate the effects of the mixture of these POPs on gene expression in a human-derived hepatocyte cell line, HepaRG. We found that, in spite of having largely uncorrelated effects, TCDD and α-endosulfan, when mixed, alter the expression of genes. The combined effects of the mixture of the POPs significantly altered the expression of 100 genes (42 up- and 58 down-regulated) whereas the same concentration of either POP alone did not alter significantly the expression of these genes. For 32 other genes, selective inhibitory crosstalk between TCDD and α-endosulfan was observed. One of the POPs inhibited the effect, on gene expression, of the other in the mixture although, when used alone, that POP did not affect expression. The expression of another 82 genes was significantly altered (up- or down-regulated) by a single POP. The addition of the second POP either increased, in the same direction, the effect on gene expression or had no further effect. At low concentrations (0.2nM TCDD and 1μM α-endosulfan), the POPs still had significant effects and the levels of expression of the corresponding proteins were found to be affected for some genes. Particularly striking was the 80-90% inhibition, by the mixture, of the expression of a number of genes of several hepatic intermediary metabolic pathways (glycerolipid metabolism, FXR/RXR activation, glycolysis/gluconeogenesis, retinoid and bile acid biosynthesis), whereas each pollutant alone had only a moderate effec

Aryl Hydrocarbon Receptor-Dependent Induction of Liver Fibrosis by Dioxin

International audienceThe contribution of environmental pollutants to liver fibrosis is an important and poorly explored issue. In vitro studies suggest that the environmental pollutant 2,3,7,8-tetrachlorodibenzo-p-dioxin(TCDD) and other Aryl hydrocarbon Receptor(AhR) ligands induce several genes that are known to be up-regulated during liver fibrosis. Our aim was to determine whether exposure to such pollutants can lead to liver fibrosis and to characterize the mechanisms of action. Mice were treated for 2, 14 or 42 days, once a week with 25µg/kg of TCDD. Gene and protein expression, in vitro and in vivo, as well as liver histology were investigated for each treatment. Treatment of mice with TCDD for 2-weeks modified the hepatic expression of markers of fibrosis such as collagen-1α1 and α-smooth-muscle-actin. Following 6-weeks of treatment, histological features of murine hepatic fibrosis became apparent. In parallel, the levels of inflammatory cytokines(interleurkin-1-beta, tumor-necrosis-factor-α) and of markers of activated fibroblasts(Fibroblast-Specific-Protein1) were found to be up-regulated. Interestingly, we also found increased expression of genes of the TGFß pathway and a concomitant decrease of miR-200a levels. Since the transcription factors of the Snail family were shown to be involved in liver fibrosis, we studied their regulation by TCDD. Two members of the Snail family were increased, whereas their negative targets, the epithelial marker E-cadherin and Claudin1, were decreased. Further, the expression of mesenchymal markers were increased. Finally, we confirmed that Snai2 is a direct transcriptional target of TCDD in the human hepatocarcinoma cell line, HepG2. The AhR ligand, TCDD, induces hepatic fibrosis by directly regulating pro-fibrotic pathways