Nuclear Pregnane X Receptor Transduces Glucose Signal to Suppress Estrogen Sulfotransferase Gene in Human Liver Cells

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Estrogen sulfotransferase (SULT1E1) metabolically inactivates estrogen and SULT1E1 expression is tightly regulated by multiple nuclear receptors. Previously, it was found that nuclear receptors HNF4a and RORa form as complexes binding to the SULT1E1 enhancer (−943/−922 bp) to activate gene expression in high glucose (450 mg/dL) treated human liver cells. However, the mechanism by which low glucose signal (40 mg/dL) mediated SULT1E1 suppression in human liver cells remain mysterious. Here, we have demonstrated that low glucose signal stimulates PXR phosphorylation at Ser350 on its ligand binding domain, preventing its heterodimerization with RXR and enabling it to interact with the HNF4a/RORa binding complexes on the enhancer, thereby suppressing SULT1E1 gene transcription. SULT1E1 was significantly repressed at both mRNA and protein levels in low glucose cultured human liver cells and this suppression was found to be PXR dependent. Vaccinia‐related kinase 1 (VRK1) was found to phosphorylate PXR at Ser350 in low glucose treated cells. Transient transfection analysis of SULT1E1 promoter‐luciferase reporter genes revealed that phosphorylated PXR significantly suppressed SULT1E1 promoter activity via the enhancer. Chromatin immunoprecipitation and gel shift assays elucidated that phosphorylated PXR bound to the SULT1E1 enhancer and disrupted the formation of the HNF4a/RORa binding complexes on it at low glucose condition. The physical interactions among these nuclear receptors were subsequently demonstrated by a series of co‐immunoprecipitation assays. Our study has shown that xenobiotic sensing nuclear receptor PXR transduces low glucose signal by its conserved phosphorylation to suppress SULT1E1 expression in human liver cells.Support or Funding InformationThis work was supported by National Institutes of Health intramural research program Z01ES1005‐01.