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

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental pollutant that binds the aryl hydrocarbon receptor (AhR), a transcription factor that triggers various biological responses. In this study, we show that TCDD treatment counteracts the p53 activation (phosphorylation and acetylation) elicited by a genotoxic compound, etoposide, in the human hepatocarcinoma cell line HepG2 and we delineated the mechanisms of this interaction. Using small interfering RNA knockdown experiments, we found that the newly described metastasis marker, anterior gradient-2 (AGR2), is involved in this effect. Both AGR2 messenger RNA (mRNA) and protein levels were increased (sixfold and fourfold, 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 three putative xenobiotic-responsive elements (XREs) 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. Binding of the AhR to the endogenous AGR2 promoter was also triggered by TCDD treatment. These results suggest that AhR ligands such as TCDD might contribute to tumor progression by inhibiting p53 regulation (phosphorylation and acetylation) triggered by genotoxicants via the increased expression of the metastasis marker AGR2.