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Reverse Yeast Two-hybrid System to Identify Mammalian Nuclear Receptor Residues that Interact with Ligands and/or Antagonists
10:51

Reverse Yeast Two-hybrid System to Identify Mammalian Nuclear Receptor Residues that Interact with Ligands and/or Antagonists

Published on: November 15, 2013

Androstane metabolites bind to and deactivate the nuclear receptor CAR-beta

B M Forman1, I Tzameli, H S Choi

  • 1The City of Hope National Medical Center, Duarte, California 91010, USA. bforman@gte.net

Nature
|October 23, 1998
PubMed

Insights

Constitutive Androstane Receptor-beta (CAR-beta) activity is inhibited by specific androstane steroids. These steroids act as inverse agonists, reversing CAR-beta

Area of Science:

  • Molecular Endocrinology
  • Steroid Signaling Pathways
  • Nuclear Receptor Research

Background:

  • The orphan receptor CAR-beta (constitutive androstane receptor-beta) forms heterodimers with the retinoid-X receptor.
  • CAR-beta constitutively activates gene transcription independently of ligand binding.
  • Classical nuclear receptors typically require ligand binding for transcriptional activation.

Purpose of the Study:

  • To investigate the mechanism behind CAR-beta's constitutive activity.
  • To identify potential ligands that modulate CAR-beta activity.
  • To characterize the nature of identified ligands and their mechanism of action.

Main Methods:

  • Screening for potential ligands of CAR-beta.
  • Assessing the effect of identified steroids on CAR-beta's constitutive transcriptional activity.
  • Evaluating the stereospecificity of the steroid interaction.
  • Analyzing the impact of steroids on CAR-beta heterodimerization, DNA binding, and co-activator recruitment/release.

Main Results:

  • Androstanol and androstenol were identified as inhibitors of CAR-beta's constitutive activity.
  • The inhibitory effect was stereospecific, requiring a 3alpha-hydroxy, 5alpha-reduced androstane structure.
  • These androstanes do not affect heterodimerization or DNA binding but promote co-activator release from CAR-beta.

Conclusions:

  • CAR-beta functions via ligand-independent co-activator recruitment.
  • Specific androstanes act as naturally occurring inverse agonists for CAR-beta.
  • This defines a novel steroidal signaling pathway opposing conventional nuclear receptor mechanisms.

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