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CAR and PXR: the xenobiotic-sensing receptors

Yoav E Timsit1, Masahiko Negishi

  • 1Pharmacogenetics Section, Laboratory of Reproductive and Developmental Toxicology, National Institute of Environmental Health Sciences, 111 T.W. Alexander Drive, Research Triangle Park, NC 27709, USA.

Steroids
|February 8, 2007
PubMed

Insights

Xenobiotic receptors Constitutive Androstane Receptor (CAR) and Pregnane X Receptor (PXR) differ from steroid receptors like estrogen receptor (ER) and glucocorticoid receptor (GR). These differences evolved for distinct roles in metabolism and homeostasis.

Area of Science:

  • Molecular Endocrinology
  • Nuclear Receptor Signaling
  • Xenobiotic Metabolism

Background:

  • Constitutive Androstane Receptor (CAR) and Pregnane X Receptor (PXR) are key members of the NR1I nuclear receptor family.
  • These receptors act as sensors for endogenous metabolic byproducts and exogenous chemicals, facilitating their elimination.
  • This function contrasts with steroid hormone receptors like estrogen receptor (ER) and glucocorticoid receptor (GR), which maintain homeostasis.

Purpose of the Study:

  • To compare and contrast the xenobiotic receptors CAR and PXR with prototypical steroid hormone receptors ER and GR.
  • To explore the structural differences that contribute to the divergence in function and activation mechanisms.
  • To review the physiological roles of CAR and PXR, including their interactions with endocrine signaling pathways.

Main Methods:

  • Review of existing literature on nuclear receptor structure, function, and regulation.
  • Comparative analysis of CAR/PXR and ER/GR based on published data.
  • Discussion of physiological roles and endocrine pathway interactions.

Main Results:

  • CAR and PXR possess distinct structural features compared to ER and GR, leading to different activation mechanisms.
  • The divergence in sensing functions (xenobiotics vs. hormones) evolved to ensure endocrine regulation fidelity and metabolic clearance.
  • CAR and PXR play crucial roles in handling metabolic byproducts and foreign compounds, reflecting metabolic complexity in higher organisms.

Conclusions:

  • Structural and functional differences between CAR/PXR and ER/GR highlight specialized evolutionary pathways for xenobiotic sensing and steroid hormone regulation.
  • Understanding these nuclear receptors is vital for comprehending xenobiotic metabolism and potential cross-talk with endocrine systems.
  • Further research into CAR and PXR interactions with endocrine pathways can reveal new insights into metabolic and hormonal regulation.

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