Transcriptional Regulation of the Apolipoprotein A-IV Gene Involves Synergism Between a Proximal Orphan Receptor Response Element and a Distant Enhancer Located in the Upstream Promoter Region of the Apolipoprotein C-III Gene

Nucleic Acids Res. 1994 Nov 11;22(22):4689-96. doi: 10.1093/nar/22.22.4689.

Abstract

Apolipoprotein A-IV expression is limited to intestinal and hepatic cells, suggesting a tissue specific transcriptional regulation of its gene. To investigate the mechanism controlling apo A-IV transcription we have analysed its promoter region by in vitro DNA binding and transient transfection experiments. DNase I footprinting analysis of the proximal promoter with rat liver nuclear extracts revealed four protected regions: AIVA (-32 to -22), AIVB (-84 to -42), AIVC (-148 to -92) and AIVD (-274 to -250). Element AIVC which is necessary for maximal promoter activity, binds HNF-4, Arp-1 and Ear-3 with similar affinity in a mutually exclusive manner. HNF-4 transactivated chimeric constructs containing intact AIVC site in the context of either the apo A-IV promoter or the heterologous thymidine kinase minimal promoter, while Arp-1 and Ear-3 repressed this activation. Increasing amounts of HNF-4 alleviated Arp-1 or Ear-3 mediated repression, suggesting that the observed opposing effects is a result of direct competition of these factors for the same recognition site. In transient transfection assays the apo A-IV promoter region (-700 to +10) had a very low activity in cells of hepatic (HepG2) and intestinal (CaCo2) origin. This activity was increased 13 to 18-fold when the upstream elements of the distantly linked apo C-III gene were fused to the proximal promoter. Results obtained with different 5' and 3' deletion constructs indicated that the cis-acting elements F to J between the nucleotides -500 and -890 of the apo C-III promoter were absolutely necessary to drive maximal enhancement in HepG2 and CaCo2 cells. The apo C-III upstream elements enhanced the activity of the minimal AdML promoter or the apo A-IV site C mutant less efficiently than the intact apo A-IV or AdML promoter constructs containing single HNF-4 sites. The findings suggest that the enhancer effect is mediated by synergistic interactions between the trans-acting factors which recognize the apo C-III regulatory elements and HNF-4 which binds to the proximal apo A-IV promoter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Apolipoprotein C-III
  • Apolipoproteins A / genetics*
  • Apolipoproteins C / genetics*
  • Base Sequence
  • COUP Transcription Factor I
  • COUP Transcription Factor II
  • COUP Transcription Factors
  • Cells, Cultured
  • DNA-Binding Proteins / metabolism
  • Enhancer Elements, Genetic / genetics
  • Gene Expression Regulation / physiology*
  • Hepatocyte Nuclear Factor 4
  • Intestines / cytology
  • Liver / chemistry
  • Liver / cytology
  • Molecular Sequence Data
  • Organ Specificity
  • Phosphoproteins*
  • Promoter Regions, Genetic / genetics
  • Rats
  • Receptors, Steroid / metabolism
  • Regulatory Sequences, Nucleic Acid / genetics*
  • Trans-Activators / physiology*
  • Transcription Factors / metabolism
  • Transcription, Genetic*

Substances

  • Apolipoprotein C-III
  • Apolipoproteins A
  • Apolipoproteins C
  • COUP Transcription Factor I
  • COUP Transcription Factor II
  • COUP Transcription Factors
  • DNA-Binding Proteins
  • Hepatocyte Nuclear Factor 4
  • Nr2f1 protein, rat
  • Nr2f2 protein, rat
  • Phosphoproteins
  • Receptors, Steroid
  • Trans-Activators
  • Transcription Factors
  • apolipoprotein A-IV