A mutation mimicking ligand-induced conformational change yields a constitutive RXR that senses allosteric effects in heterodimers.
Mutations of a single residue in the retinoid X receptor alpha (RXRalpha) ligand-binding pocket (LBP) generate constitutive, ligand-binding-competent mutants with structural and functional characteristics similar to those of agonist-bound wild-type RXR. Modelling of the mouse RXRalphaF318A LBP suggests that, like agonist binding, the mutation disrupts a cluster of van der Waals interactions that maintains helix H11 in the apo-receptor location, thereby shifting the thermodynamic equilibrium to the holo form. Heterodimerization with some apo-receptors (retinoic acid, thyroid hormone and vitamin D3 receptors) results in 'silencing' of RXRalphaF318A constitutive activity, which, on the other hand, efficiently contributes to synergistic transactivation within NGFI-B-RXR heterodimers. RAR mutants disabled for corepressor binding and/or lacking a functional AF-2 activation domain, do not relieve RXR 'silencing'. Not only RAR agonists, but also the RAR antagonist BMS614 induce conformational changes allowing RXR to exert constitutive (RXRalphaF318A) or agonist-induced (wild-type RXR) activity in heterodimers. Interestingly, the RXRalphaF318A constitutive activity generated within heterodimers in the presence of BMS614 requires the integrity of both RXR and RAR AF-2 domains. These observations suggest that, within RXR-RAR heterodimers, RAR can adopt a structure distinct from that of the active holo-RAR, thus allowing RXR to become transcriptionally responsive to agonists.
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Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC)/CNRS/INSERM/ULP/Collège de France, BP 163, 67404 Illkrich Cedex, CU de Strasbourg, France.
Zechel
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C
Wurtz
J M
JM
Bourguet
W
W
Kagechika
H
H
Umemiya
H
H
Shudo
K
K
Moras
D
D
Gronemeyer
H
H
Chambon
P
P
D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000818:Animals; D001665:Binding Sites; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D019281:Dimerization; D006801:Humans; D008024:Ligands; D051379:Mice; D008961:Models, Structural; D016297:Mutagenesis, Site-Directed; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D011487:Protein Conformation / Q000187:drug effects; D055503:Protein Multimerization; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism*; D011987:Receptors, Steroid / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D047488:Retinoid X Receptors; D012176:Retinoids / Q000494:pharmacology*; D014157:Transcription Factors / Q000737:chemistry* / Q000378:metabolism*; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology
D004268:DNA-Binding Proteins; D008024:Ligands; C539821:NR4A1 protein, human; C539818:Nr4a1 protein, mouse; D057105:Nuclear Receptor Subfamily 4, Group A, Member 1; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D011987:Receptors, Steroid; D011994:Recombinant Proteins; D047488:Retinoid X Receptors; D012176:Retinoids; D014157:Transcription Factors; D014212:Tretinoin