Mechanism of vitamin D receptor inhibition of cholesterol 7alpha-hydroxylase gene transcription in human hepatocytes.

Mechanism of vitamin D receptor inhibition of cholesterol 7alpha-hydroxylase gene transcription in human hepatocytes.

Han Shuxin; Chiang John Y L

Drug metabolism and disposition: the biological fate of chemicals

2009

2009-03

Lithocholic acid (LCA) is a potent endogenous vitamin D receptor (VDR) ligand. In cholestasis, LCA levels increase in the liver and intestine. The objective of this study is to test the hypothesis that VDR plays a role in inhibiting cholesterol 7alpha-hydroxylase (CYP7A1) gene expression and bile acid synthesis in human hepatocytes. Immunoblot analysis has detected VDR proteins in the nucleus of the human hepatoma cell line HepG2 and human primary hepatocytes. 1alpha, 25-Dihydroxy-vitamin D(3) or LCA acetate-activated VDR inhibited CYP7A1 mRNA expression and bile acid synthesis, whereas small interfering RNA to VDR completely abrogated VDR inhibition of CYP7A1 mRNA expression in HepG2 cells. Electrophoretic mobility shift assay and mutagenesis analyses have identified the negative VDR response elements that bind VDR/retinoid X receptor alpha in the human CYP7A1 promoter. Mammalian two-hybrid, coimmunoprecipitation, glutathione

Base Sequence; Calcitriol/drug effects/genetics/*physiology; Cell Line; Cells; Cholesterol 7-alpha-Hydroxylase/*genetics; Cultured; DNA Primers; Electrophoretic Mobility Shift Assay; Gene Knockdown Techniques; Genetic/*physiology; Hepatocytes/*drug effects/enzymology; Humans; Immunoprecipitation; Lithocholic Acid/pharmacology; Messenger/genetics; Polymerase Chain Reaction; Receptors; RNA; Small Interfering; Transcription; Tumor; Two-Hybrid System Techniques

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