Retinoids increase human apolipoprotein A-11 expression through activation of the retinoid X receptor but not the retinoic acid receptor

Mol Cell Biol. 1996 Jul;16(7):3350-60. doi: 10.1128/MCB.16.7.3350.

Abstract

Considering the link between plasma high-density lipoprotein (HDL) cholesterol levels and a protective effect against coronary artery disease as well as the suggested beneficial effects of retinoids on the production of the major HDL apolipoprotein (apo), apo A-I, the goal of this study was to analyze the influence of retinoids on the expression of apo A-II, the other major HDL protein. Retinoic acid (RA) derivatives have a direct effect on hepatic apo A-II production, since all-trans (at) RA induces apo A-II mRNA levels and apo A-II secretion in primary cultures of human hepatocytes. In the HepG2 human hepatoblastoma cell line, both at-RA and 9-cis RA as well as the retinoid X receptor (RXR)-specific agonist LGD 1069, but not the RA receptor (RAR) agonist ethyl-p-[(E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-l-pro penyl]-benzoic acid (TTNPB), induce apo A-II mRNA levels. Transient-transfection experiments with a reporter construct driven by the human apo A-II gene promoter indicated that 9-cis RA and at-RA, as well as the RXR agonists LGD 1069 and LG 100268, induced apo A-II gene expression at the transcriptional level. Only minimal effects of the RAR agonist TTNPB were observed on the apo A-II promoter reporter construct. Unilateral deletions and site-directed mutagenesis identified the J site of the apo A-II promoter mediating the responsiveness to RA. This element contains two imperfect half-sites spaced by 1 oligonucleotide. Cotransfection assays in combination with the use of RXR or RAR agonists showed that RXR but not RAR transactivates the apo A-II promoter through this element. By contrast, RAR inhibits the inductive effects of RXR on the apo A-II J site in a dose-dependent fashion. Gel retardation assays demonstrated that RXR homodimers bind, although with a lower affinity than RAR-RXR heterodimers, to the AH-RXR response element. In conclusion, retinoids induce hepatic apo A-II production at the transcriptional level via the interaction of RXR with an element in the J site containing two imperfect half-sites spaced by 1 oligonucleotide, thereby demonstrating an important role of RXR in controlling human lipoprotein metabolism. Since the J site also confers responsiveness of the apo A-II gene to fibrates and fatty acids via the activation of peroxisome proliferator-activated receptor-RXR heterodimers, this site can be considered a plurimetabolic response element.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Apolipoprotein A-II / biosynthesis*
  • Apolipoprotein A-II / genetics
  • Apolipoproteins E / biosynthesis
  • Base Sequence
  • Benzoates / pharmacology
  • Bexarotene
  • Carcinoma, Hepatocellular
  • Cloning, Molecular
  • DNA-Binding Proteins / metabolism
  • Female
  • Gene Expression Regulation / drug effects*
  • Genomic Library
  • HeLa Cells
  • Humans
  • Kinetics
  • Liver Neoplasms
  • Molecular Sequence Data
  • Nicotinic Acids / pharmacology
  • Oligodeoxyribonucleotides
  • Placenta / metabolism
  • Pregnancy
  • RNA, Messenger / biosynthesis
  • Receptors, Retinoic Acid / metabolism*
  • Regulatory Sequences, Nucleic Acid
  • Retinoid X Receptors
  • Retinoids / pharmacology*
  • Tetrahydronaphthalenes / pharmacology
  • Transcription Factors / metabolism*
  • Transcription, Genetic / drug effects
  • Transfection
  • Tretinoin / pharmacology
  • Tumor Cells, Cultured

Substances

  • Apolipoprotein A-II
  • Apolipoproteins E
  • Benzoates
  • DNA-Binding Proteins
  • Nicotinic Acids
  • Oligodeoxyribonucleotides
  • RNA, Messenger
  • Receptors, Retinoic Acid
  • Retinoid X Receptors
  • Retinoids
  • Tetrahydronaphthalenes
  • Transcription Factors
  • Tretinoin
  • ethyl-p-((E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-1-propenyl)benzoic acid
  • Bexarotene
  • LG 100268