Bile acids reduce SR-BI expression in hepatocytes by a pathway involving FXR/RXR, SHP, and LRH-1

Biochem Biophys Res Commun. 2005 Nov 4;336(4):1096-105. doi: 10.1016/j.bbrc.2005.08.237.

Abstract

Hepatic SR-BI mediates uptake of circulating cholesterol into liver hepatocytes where a part of the cholesterol is metabolised to bile acids. In the hepatocytes, bile acids reduce their own synthesis by a negative feedback loop to prevent toxic high levels of bile acids. Bile acid-activated FXR/RXR represses expression of CYP7A1, the rate-limiting enzyme during bile acid synthesis, by inducing the expression of SHP, which inhibits LXR/RXR and LRH-1-transactivation of CYP7A1. The present paper presents data indicating that CDCA suppresses SR-BI expression by the same pathway. As previously reported, LRH-1 induces SR-BI promoter activity. Here we show that CDCA or over-expression of SHP inhibit this transactivation. No FXR-response element was identified in the bile acid-responsive region of the SR-BI promoter (-1200bp/-937bp). However, a binding site for LRH-1 was characterised and shown to specifically bind LRH-1. The present study shows that also the SR-BI-mediated supply of cholesterol, the substrate for bile acid synthesis, is feedback regulated by bile acids.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Cells, Cultured
  • Chenodeoxycholic Acid / physiology*
  • Chlorocebus aethiops
  • Cholesterol, HDL / metabolism
  • DNA-Binding Proteins / metabolism*
  • Gene Expression Regulation
  • Genes, Reporter
  • Hepatocytes / metabolism*
  • Humans
  • Male
  • Mice
  • Promoter Regions, Genetic
  • Rats
  • Rats, Wistar
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Retinoid X Receptor alpha / agonists
  • Retinoid X Receptor alpha / metabolism*
  • Scavenger Receptors, Class B / biosynthesis*
  • Signal Transduction
  • Transcription Factors / metabolism*

Substances

  • Cholesterol, HDL
  • DNA-Binding Proteins
  • NR5A2 protein, human
  • Receptors, Cytoplasmic and Nuclear
  • Retinoid X Receptor alpha
  • SCARB1 protein, human
  • Scavenger Receptors, Class B
  • Transcription Factors
  • nuclear receptor subfamily 0, group B, member 2
  • farnesoid X-activated receptor
  • Chenodeoxycholic Acid