Glucose Response Repression of the Estrogen Sulfotransferase by Nuclear Receptors PXR and RORa via Phosphorylation

Authors

• H Hu
• M Negishi

Abstract

Estrogen sulfotransferase (SULT1E1) sulfates estrogens to its inactive forms-sulfated estrogens. Its expression is tightly regulated by nuclear receptors such as RORa, PXR and HNF4a. Our preliminary results indicated that SULT1E1 was suppressed in low glucose treated HepG2 cells, which implies a cellular defense response to elevate cellular estrogen levels thereby compromising hypoglycemia induced inflammation. We hypothesized that PXR coordinates RORa to repress SULT1E1 gene expression via their conserved phosphorylation sites. First, by utilizing HepG2 cells and HepG2-derived Shp51 cells which stably express human PXR, it was observed that SULT1E1 was suppressed in low glucose (400 mg/L) medium in a PXR-dependent manner. Phosphorylation of PXR at Ser350 was detected in low glucose treated Shp51 cells. Transient transfection analysis of SULT1E1 promoter-luciferase reporter genes revealed that phosphorylated PXR and RORa repressed SULT1E1 promoter activity. Chromatin immunoprecipitation indicated that phosphorylated PXR and RORa bound to the SULT1E1 enhancer (-941 bp upstream of SULT1E1) at low glucose condition, while RORa was phosphorylated at Ser100 at high glucose condition. Co-immunoprecipitation assays elucidated a protein-protein interaction between the phosphorylated PXR and RORa. Gel shift assays showed that phosphorylated PXR interacted with RORa binding to the SULT1E1 enhancer. Phosphopeptide antibodies and phosphomimetic mutants of these nuclear receptors were utilized to examine whether phosphorylation becomes a regulatory factor determining the glucose responsive SULT1E1 gene activation. The results demonstrated that phosphorylated PXR at Ser350 mediates the dephosphosphorylation of RORa at Ser100, leading RORa binding to the SULT1E1 gene thereby suppressing its expression in low glucose treated cells.

Scientific Focus Area: Molecular Biology and Biochemistry

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