title: Agonist ligands mediate the transcriptional response of nuclear receptor heterodimers through distinct stoichiometric assemblies with coactivators.
abstract: The constitutive androstane (CAR) and retinoid X receptors (RXR) are ligand-mediated transcription factors of the nuclear receptor protein superfamily. Functional CAR:RXR heterodimers recruit coactivator proteins, such as the steroid receptor coactivator-1 (SRC1). Here, we show that agonist ligands can potentiate transactivation through both coactivator binding sites on CAR:RXR, which distinctly bind two SRC1 molecules. We also observe that SRC1 transitions from a structurally plastic to a compact form upon binding CAR:RXR. Using small angle x-ray scattering (SAXS) we show that the CAR(tcp):RXR(9c)·SRC1 complex can encompass two SRC1 molecules compared with the CAR(tcp):RXR·SRC1, which binds only a single SRC1. Moreover, sedimentation coefficients and molecular weights determined by analytical ultracentrifugation confirm the SAXS model. Cell-based transcription assays show that disrupting the SRC1 binding site on RXR alters the transactivation by CAR:RXR. These data suggest a broader role for RXR within heterodimers, whereas offering multiple strategies for the assembly of the transcription complex.
authors: From the Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996 and.
authors: Mark Remec
authors: MR
authors: Pavlin
authors: the Department of Molecular Pharmacology and Biological Chemistry, Life Sciences Collaborative Access Team, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611.
authors: Joseph S
authors: JS
authors: Brunzelle
authors: From the Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996 and elias.fernandez@utk.edu.
authors: Elias J
authors: EJ
authors: Fernandez
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D000090702:Constitutive Androstane Receptor; D006801:Humans; D008024:Ligands; D051379:Mice; D008958:Models, Molecular; D008970:Molecular Weight; D009154:Mutation; D056920:Nuclear Receptor Coactivator 1 / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D047490:Retinoid X Receptor alpha / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D053838:Scattering, Small Angle; D015533:Transcriptional Activation; D014961:X-Ray Diffraction
chemical_list: D000090702:Constitutive Androstane Receptor; D008024:Ligands; D018160:Receptors, Cytoplasmic and Nuclear; D047490:Retinoid X Receptor alpha; D056920:Nuclear Receptor Coactivator 1
keywords: Analytical Ultracentrifugation; Heterodimer; Nuclear Receptor; Protein Assembly; Small Angle X-ray Scattering (SAXS); Stoichiometry; Transactivation; Transcription Coactivator