Inhibition of LXRalpha signaling by vitamin D receptor: possible role of VDR in bile acid synthesis

Biochem Biophys Res Commun. 2006 Dec 8;351(1):176-84. doi: 10.1016/j.bbrc.2006.10.027. Epub 2006 Oct 19.

Abstract

The expression of cholesterol 7alpha-hydroxylase (CYP7alpha), the rate-limiting enzyme in the catabolism of cholesterol to bile acid, is stimulated by oxysterol receptor, liver X receptor alpha (LXRalpha) and negatively regulated by a bile acid receptor, farnesoid X receptor. In the current study, we demonstrated that 1,25-(OH)(2)D3 blunted the LXRalpha-mediated induction of CYP7alpha mRNA in H4IIE rat hepatoma cells. In co-transfection experiments in HepG2 cells, VDR repressed the activity of rat CYP7alpha promoter in a ligand-dependent manner through inhibition of LXRalpha signaling. We also confirmed the ability of VDR to repress LXRalpha transcriptional activation using a synthetic LXRalpha responsive reporter. Deletion analyses revealed that the ligand-binding domain of VDR was required for the suppression and the DNA-binding domain was dispensable. Given the fact that VDR can be activated by the secondary bile acid as well as 1,25-(OH)(2)D3, the crosstalk between LXRalpha and VDR signaling in regulation of bile acid metabolism provides a possible contribution of VDR to modulate bile acid and cholesterol homeostasis, and highlights a physiological function of VDR beyond calcium metabolism in the body.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bile Acids and Salts
  • COS Cells
  • Calcitriol / analogs & derivatives*
  • Calcitriol / pharmacology
  • Carcinoma, Hepatocellular / metabolism*
  • Cell Line
  • Chlorocebus aethiops
  • Cholesterol 7-alpha-Hydroxylase / metabolism*
  • DNA-Binding Proteins / metabolism*
  • Humans
  • Liver X Receptors
  • Orphan Nuclear Receptors
  • Rats
  • Receptors, Calcitriol / metabolism*
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*

Substances

  • Bile Acids and Salts
  • DNA-Binding Proteins
  • Liver X Receptors
  • NR1H3 protein, human
  • Nr1h3 protein, rat
  • Orphan Nuclear Receptors
  • Receptors, Calcitriol
  • Receptors, Cytoplasmic and Nuclear
  • 1,25-dihydroxy-23-azavitamin D3
  • Cholesterol 7-alpha-Hydroxylase
  • Calcitriol