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J Biol Chem. 2014 Sep 5;289(36):24771-8. doi: 10.1074/jbc.M114.575423. Epub 2014 Jul 22.

Agonist ligands mediate the transcriptional response of nuclear receptor heterodimers through distinct stoichiometric assemblies with coactivators.

Author information

1
From the Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996 and.
2
the Department of Molecular Pharmacology and Biological Chemistry, Life Sciences Collaborative Access Team, Northwestern University Feinberg School of Medicine, Chicago, Illinois 60611.
3
From the Department of Biochemistry, Cellular and Molecular Biology, The University of Tennessee, Knoxville, Tennessee 37996 and elias.fernandez@utk.edu.

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.

KEYWORDS:

Analytical Ultracentrifugation; Heterodimer; Nuclear Receptor; Protein Assembly; Small Angle X-ray Scattering (SAXS); Stoichiometry; Transactivation; Transcription Coactivator

PMID:
25053412
PMCID:
PMC4155646
DOI:
10.1074/jbc.M114.575423
[Indexed for MEDLINE]
Free PMC Article

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