Activation of the nuclear receptor FXR induces fibrinogen expression: a new role for bile acid signaling

J Lipid Res. 2005 Mar;46(3):458-68. doi: 10.1194/jlr.M400292-JLR200. Epub 2004 Dec 16.

Abstract

Three genes, fibrinogen-alpha (FBGalpha), -beta, and -gamma, encode proteins that make up the mature FBG protein complex. This complex is secreted from the liver and plays a key role in coagulation in response to vascular disruption. We identified all three FBG genes in a screen designed to isolate genes that are regulated by the farnesoid X receptor (FXR; NR1H4). Treatment of human hepatoma cells with either naturally occurring or synthetic [3-(2,6-dichlorophenyl)-4-(3'-carboxy-2-chloro-stilben-4-yl)-oxymethyl-5-isopropyl-isoxazole] FXR ligands resulted in the induction of transcripts for all three genes. The induction of FBGbeta mRNA in response to activated FXR appears to be a primary transcriptional response, as it is blocked by actinomycin D but not by cycloheximide. Four FXR isoforms were recently identified that differ either at their N termini and/or by the presence of four amino acids in the hinge region. Interestingly, the activities of the human FBGbeta promoter-reporter constructs were highly induced by FXR isoforms that lack the four amino acid insert. The observation that all three FBG subunits are induced by specific FXR isoforms, in response to FXR ligands, suggests that bile acids and FXR modulate fibrinolytic activity.

Publication types

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

MeSH terms

  • Bile Acids and Salts / metabolism
  • Bile Acids and Salts / physiology*
  • Cell Line, Tumor
  • Cycloheximide / pharmacology
  • DNA-Binding Proteins / drug effects
  • DNA-Binding Proteins / metabolism*
  • Dactinomycin / pharmacology
  • Fibrinogen / biosynthesis*
  • Fibrinogen / genetics*
  • Gene Expression Regulation*
  • Humans
  • Isoxazoles / pharmacology
  • Ligands
  • Promoter Regions, Genetic
  • Protein Isoforms / drug effects
  • Protein Isoforms / genetics
  • RNA, Messenger / drug effects
  • RNA, Messenger / genetics
  • Receptors, Cytoplasmic and Nuclear
  • Signal Transduction / drug effects
  • Signal Transduction / physiology*
  • Transcription Factors / drug effects
  • Transcription Factors / metabolism*
  • Transcription, Genetic

Substances

  • Bile Acids and Salts
  • DNA-Binding Proteins
  • Isoxazoles
  • Ligands
  • Protein Isoforms
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • Transcription Factors
  • farnesoid X-activated receptor
  • Dactinomycin
  • Fibrinogen
  • Cycloheximide