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Mol. Cell. Biol., 02 1997, 644-655, Vol 17, No. 2
S Minucci, M Leid, R Toyama, JP Saint-Jeannet, VJ Peterson, V Horn, JE Ishmael, N Bhattacharyya, A Dey, IB Dawid and K Ozato
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.
Copyright © 1997, American Society for Microbiology
Retinoid X receptor (RXR) within the RXR-retinoic acid receptor heterodimer binds its ligand and enhances retinoid-dependent gene expression
Laboratory of Molecular Growth Regulation, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland 20892, USA.
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