Nucleolar and coiled-body phosphoprotein 1 enhances the induction of CYP3A4 by promoting nuclear translocation of pregnane X receptor.

Pregnane X receptor (PXR) is a xenobiotic-sensing nuclear receptor that plays a central role in the regulation of drug-metabolizing enzymes and transporters. Under basal conditions, PXR is predominantly localized in the cytoplasm. Upon activation by ligands such as rifampicin, PXR translocates into the nucleus and induces the transcription of its target genes, including CYP3A4, a major drug-metabolizing enzyme in the human liver. From our previous proteomic analysis of coimmunoprecipitated proteins obtained from lysates of rifampicin-treated ShP51 cells (a HepG2 cell line stably expressing human PXR) using an anti-PXR antibody, we identified nucleolar and coiled-body phosphoprotein 1 (NOLC1), a protein known to shuttle among the cytoplasm, nucleus, and nucleolus, as a potential PXR-interacting factor. This study aimed to clarify the role of NOLC1 in PXR nuclear translocation. Knockdown of NOLC1 in ShP51 cells or HepaSH cells (primary hepatocytes from humanized-liver mice) attenuated the rifampicin-induced expression and activity of CYP3A4, suggesting that NOLC1 positively regulates PXR-mediated CYP3A4 induction. Rifampicin significantly increased luciferase activity driven by the promoter and distal enhancer regions of the CYP3A4 gene; however, this induction was diminished by NOLC1 knockdown in ShP51 cells. Furthermore, immunofluorescence staining of HepaSH cells revealed that rifampicin promoted PXR nuclear translocation, whereas this effect was suppressed by NOLC1 knockdown. Taken together, these findings demonstrate that NOLC1 facilitates the ligand-dependent nuclear translocation and transcriptional activity of PXR, thereby functioning as a regulatory factor for drug metabolism in the human liver. SIGNIFICANCE STATEMENT: This study demonstrates that nucleolar and coiled-body phosphoprotein 1 promotes ligand-dependent pregnane X receptor (PXR) nuclear translocation, enhances PXR recruitment to chromatin, and increases PXR-mediated transactivation, thereby enhancing the induction of CYP3A4 expression. These findings provide mechanistic insight into potential strategies for mitigating PXR-mediated adverse effects.