The human organic anion transporter 2 gene is transactivated by hepatocyte nuclear factor-4 alpha and suppressed by bile acids

Mol Pharmacol. 2005 May;67(5):1629-38. doi: 10.1124/mol.104.010223. Epub 2005 Feb 3.


The human organic anion transporter 2 (hOAT2, SLC22A7) mediates the sodium-independent uptake of numerous drugs, including cephalosporins, salicylates, dicarboxylates, and prostaglandins, and is mainly expressed in hepatocytes. Because the regulation of hOAT2 expression is poorly understood, we characterized cis-acting elements in the 5'-flanking region that regulate hOAT2 transcription. A consensus binding motif for the hepatocyte nuclear factor-4 alpha (HNF-4 alpha), arranged as a direct repeat (DR)-1, is located at nucleotides -329/-317 relative to the transcription initiation site. This element specifically binds HNF-4 alpha in electrophoretic mobility shift assays. A luciferase-linked hOAT2 promoter fragment containing the HNF-4 alpha binding site was transactivated upon cotransfection of an HNF-4 alpha expression vector in Huh7 cells, whereas site-directed mutagenesis of the DR-1 element abolished activation by HNF-4 alpha. Short interfering RNAs inhibiting endogenous HNF-4 alpha expression markedly reduced endogenous expression of hOAT2 in Huh7 cells. Because HNF-4 alpha is a known target for bile acid-mediated repression of gene transcription, we studied whether chenodeoxycholic acid (CDCA) suppresses hOAT2 gene expression by inhibiting HNF-4 alpha-mediated transactivation. Treatment of Huh7 cells with CDCA or the synthetic farnesoid X receptor (FXR) agonist GW4064 decreased mRNA and protein levels and also nuclear binding activity of HNF-4 alpha. The FXR-inducible transcriptional repressor small heterodimer partner inhibited transactivation of hOAT2 promoter constructs and of endogenous hOAT2 expression by HNF-4 alpha. We conclude that the hOAT2 gene is critically dependent on HNF-4 alpha and that bile acids repress the hOAT2 gene by inhibiting HNF-4 alpha. Hepatic uptake of hOAT2 substrates may thus be decreased in disease conditions associated with elevated intracellular levels of bile acids.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Bile Acids and Salts / genetics
  • Bile Acids and Salts / metabolism
  • Bile Acids and Salts / physiology*
  • Cell Line, Tumor
  • DNA-Binding Proteins / genetics
  • DNA-Binding Proteins / physiology*
  • Hepatocyte Nuclear Factor 4
  • Humans
  • Molecular Sequence Data
  • Organic Anion Transporters, Sodium-Independent / genetics
  • Organic Anion Transporters, Sodium-Independent / metabolism*
  • Phosphoproteins / genetics
  • Phosphoproteins / physiology*
  • Trans-Activators / physiology*
  • Transcription Factors / genetics
  • Transcription Factors / physiology*
  • Transcriptional Activation / physiology*


  • Bile Acids and Salts
  • DNA-Binding Proteins
  • Hepatocyte Nuclear Factor 4
  • Organic Anion Transporters, Sodium-Independent
  • Phosphoproteins
  • SLC22A7 protein, human
  • Trans-Activators
  • Transcription Factors