Farnesoid X receptor induces murine scavenger receptor Class B type I via intron binding

PLoS One. 2012;7(4):e35895. doi: 10.1371/journal.pone.0035895. Epub 2012 Apr 23.

Abstract

Farnesoid X receptor (FXR) is a nuclear receptor and a key regulator of liver cholesterol and triglyceride homeostasis. Scavenger receptor class B type I (SR-BI) is critical for reverse cholesterol transport (RCT) by transporting high-density lipoprotein (HDL) into liver. FXR induces SR-BI, however, the underlying molecular mechanism of this induction is not known. The current study confirmed induction of SR-BI mRNA by activated FXR in mouse livers, a human hepatoma cell line, and primary human hepatocytes. Genome-wide FXR binding analysis in mouse livers identified 4 putative FXR response elements in the form of inverse repeat separated by one nucleotide (IR1) at the first intron and 1 IR1 at the downstream of the mouse Sr-bi gene. ChIP-qPCR analysis revealed FXR binding to only the intronic IR1s, but not the downstream one. Luciferase assays and site-directed mutagenesis further showed that 3 out of 4 IR1s were able to activate gene transcription. A 16-week high-fat diet (HFD) feeding in mice increased hepatic Sr-bi gene expression in a FXR-dependent manner. In addition, FXR bound to the 3 bona fide IR1s in vivo, which was increased following HFD feeding. Serum total and HDL cholesterol levels were increased in FXR knockout mice fed the HFD, compared to wild-type mice. In conclusion, the Sr-bi/SR-BI gene is confirmed as a FXR target gene in both mice and humans, and at least in mice, induction of Sr-bi by FXR is via binding to intronic IR1s. This study suggests that FXR may serve as a promising molecular target for increasing reverse cholesterol transport.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Cells, Cultured
  • Cholesterol / metabolism
  • Diet, High-Fat
  • Female
  • Hep G2 Cells
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism
  • Humans
  • Introns
  • Isoxazoles / pharmacology
  • Lipoproteins, HDL / metabolism
  • Liver / drug effects
  • Liver / metabolism
  • Mice
  • Mice, Inbred C57BL
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • RNA, Messenger / metabolism
  • Receptors, Cytoplasmic and Nuclear / deficiency
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Scavenger Receptors, Class B / genetics
  • Scavenger Receptors, Class B / metabolism*

Substances

  • Isoxazoles
  • Lipoproteins, HDL
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • Scavenger Receptors, Class B
  • farnesoid X-activated receptor
  • Cholesterol
  • GW 4064