Retinoid X receptor (RXR) within the RXR-retinoic acid receptor heterodimer binds its ligand and enhances retinoid-dependent gene expression.
Retinoic acid receptor (RAR) and retinoid X receptor (RXR) form heterodimers and regulate retinoid-mediated gene expression. We studied binding of RXR- and RAR-selective ligands to the RXR-RAR heterodimer and subsequent transcription. In limited proteolysis analyses, both RXR and RAR in the heterodimer bound their respective ligands and underwent a conformational change in the presence of a retinoic acid-responsive element. In reporter analyses, the RAR ligand (but not the RXR ligand), when added singly, activated transcription, but coaddition of the two ligands led to synergistic activation of transcription. This activation required the AF-2 domain of both RXR and RAR. Genomic footprinting analysis was performed with P19 embryonal carcinoma cells, in which transcription of the RARbeta gene is induced upon retinoid addition. Paralleling the reporter activation data, only the RAR ligand induced in vivo occupancy of the RARbeta2 promoter when added singly. However, at suboptimal concentrations of RAR ligand, coaddition of the RXR ligand increased the stability of promoter occupancy. Thus, liganded RXR and RAR both participate in transcription. Finally, when these ligands were tested for teratogenic effects on zebra fish and Xenopus embryos, we found that coadministration of the RXR and RAR ligands caused more severe abnormalities in these embryos than either ligand alone, providing biological support for the synergistic action of the two ligands.
Minucci
S
S
Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
Leid
M
M
Toyama
R
R
Saint-Jeannet
J P
JP
Peterson
V J
VJ
Horn
V
V
Ishmael
J E
JE
Bhattacharyya
N
N
Dey
A
A
Dawid
I B
IB
Ozato
K
K
D000818:Animals; D001755:Blastocyst; D004247:DNA / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000187:drug effects; D054278:Embryonal Carcinoma Stem Cells; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D008024:Ligands; D051379:Mice; D014411:Neoplastic Stem Cells; D010446:Peptide Fragments; D011401:Promoter Regions, Genetic / Q000235:genetics; D011487:Protein Conformation / Q000187:drug effects; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D012176:Retinoids / Q000494:pharmacology*; D013723:Teratogens / Q000494:pharmacology; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism*; D015533:Transcriptional Activation; D014981:Xenopus / Q000196:embryology; D015027:Zebrafish / Q000196:embryology
D008024:Ligands; D010446:Peptide Fragments; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D012176:Retinoids; D013723:Teratogens; D014157:Transcription Factors; C082925:retinoic acid receptor beta; D004247:DNA