Retinoids increase human apolipoprotein A-11 expression through activation of the retinoid X receptor but not the retinoic acid receptor.
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.
Vu-Dac
N
N
Unite 325 Institut National de la Santé et de la Recherche Médicale, Département d'Athérosclerose, Institut Pasteur de Lille, France.
Schoonjans
K
K
Kosykh
V
V
Dallongeville
J
J
Heyman
R A
RA
Staels
B
B
Auwerx
J
J
D016633:Apolipoprotein A-II / Q000096:biosynthesis* / Q000235:genetics; D001057:Apolipoproteins E / Q000096:biosynthesis; D001483:Base Sequence; D001565:Benzoates / Q000494:pharmacology; D000077610:Bexarotene; D006528:Carcinoma, Hepatocellular; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D015698:Genomic Library; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008113:Liver Neoplasms; D008969:Molecular Sequence Data; D009539:Nicotinic Acids / Q000494:pharmacology; D009838:Oligodeoxyribonucleotides; D010920:Placenta / Q000378:metabolism; D011247:Pregnancy; D012333:RNA, Messenger / Q000096:biosynthesis; D018168:Receptors, Retinoic Acid / Q000378:metabolism*; D012045:Regulatory Sequences, Nucleic Acid; D047488:Retinoid X Receptors; D012176:Retinoids / Q000494:pharmacology*; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D016633:Apolipoprotein A-II; D001057:Apolipoproteins E; D001565:Benzoates; D004268:DNA-Binding Proteins; D009539:Nicotinic Acids; D009838:Oligodeoxyribonucleotides; D012333:RNA, Messenger; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D012176:Retinoids; D013764:Tetrahydronaphthalenes; D014157:Transcription Factors; D014212:Tretinoin; C034814:ethyl-p-((E)-2-(5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthyl)-1-propenyl)benzoic acid; D000077610:Bexarotene; C095104:LG 100268