NR1I2 Gene (PXR): Function, Expression, Mutations, and Clinical Significance

The NR1I2 gene encodes the pregnane X receptor (PXR), a ligand-activated transcription factor belonging to the nuclear receptor superfamily. PXR is primarily expressed in the liver and intestine, where it acts as a xenobiotic sensor. Upon binding to a wide range of endogenous and exogenous ligands, PXR heterodimerizes with the retinoid X receptor (RXR) and binds to response elements in the promoter regions of target genes, thereby regulating the expression of phase I and phase II drug-metabolizing enzymes (e.g., CYP3A4, CYP2B6, UGT1A1) and drug transporters (e.g., MDR1, MRP2). This adaptive response enhances the clearance of xenobiotics and protects the body from toxic compounds. PXR also plays roles in bile acid homeostasis, glucose and lipid metabolism, and inflammation. Genetic variations in NR1I2 can affect drug metabolism and are associated with inter-individual differences in drug response and susceptibility to certain diseases.

Tissue Expression

Cell Line Expression

Hotspot Mutations

Mutation functional classification

• Pregnane X receptor pathway

• Nuclear receptor transcription pathway

• Drug metabolism - cytochrome P450

• Bile acid metabolism

• Xenobiotic metabolism signaling

The NR1I2 protein, known as the pregnane X receptor (PXR), is a 434-amino acid nuclear receptor with a conserved domain structure: an N-terminal activation function 1 (AF-1) domain, a DNA-binding domain (DBD) with two zinc fingers, a hinge region, and a C-terminal ligand-binding domain (LBD) that also contains the activation function 2 (AF-2). PXR is predominantly cytoplasmic in the absence of ligand; upon ligand binding, it translocates to the nucleus, heterodimerizes with RXRα, and binds to xenobiotic response elements (XREs) in target gene promoters. PXR regulates a broad array of genes involved in drug metabolism, including CYP3A4, CYP2B6, CYP2C9, UGT1A1, and ABCB1 (MDR1). Its ligand-binding pocket is large and flexible, allowing it to interact with structurally diverse compounds. Post-translational modifications, such as phosphorylation and ubiquitination, modulate its stability and activity. PXR also interacts with coactivators (e.g., SRC-1) and corepressors (e.g., NCoR) to fine-tune transcriptional output.