Xenobiotic-sensing receptor (None standardized for the general term; specific receptors include CAR (Constitutive androstane receptor) and PXR (Pregnane X receptor))

A xenobiotic-sensing receptor, also known as a xenobiotic nuclear sensor or simply “xenoreceptor,” refers collectively to certain nuclear hormone receptors that detect foreign chemicals (“xenobiotics”) within an organism. The most prominent examples are the Constitutive Androstane Receptor (CAR) and the Pregnane X Receptor (PXR)—both members of the NR1I subfamily—which play central roles in regulating genes responsible for metabolizing drugs and other exogenous compounds. Upon binding their ligands—often pharmaceuticals or environmental chemicals—these receptors translocate to the nucleus where they dimerize with retinoid X receptors and bind DNA at response elements upstream from key metabolic genes such as those encoding cytochrome P450 enzymes. This process enhances cellular capacity for detoxification but also underlies many clinically relevant drug-drug interactions due to altered rates of biotransformation. While essential for host defense against toxins, dysregulation can contribute to adverse effects including hepatotoxicity or interference with normal steroid/hormone balance.

Other names

Xenobiotic sensorXenobiotic nuclear receptorNuclear xenobiotic sensorConstitutive androstane receptor (CAR)Pregnane X receptor (PXR)Steroid and xenobiotic sensing nuclear receptor (SXR)

Drugs act as agonists or antagonists by binding to the ligand-binding domain: - Agonists activate transcriptional upregulation of detoxifying enzymes like CYP3A4. - Antagonists block this activation pathway. The activated xenobiotic-sensing receptors heterodimerize with RXR to regulate gene expression involved in metabolism/excretion.