Panaxytriol upregulates CYP3A4 expression based on the interaction of PXR, CAR, HSP90α, and RXRα

Background: Cytochrome P450 3A4 (CYP3A4) is one of the most important drug-metabolizing enzymes in the human body, mainly existing in the liver, small intestine, and kidney. Panaxytriol is one of the key active components in red ginseng and Shenmai injection. Our previous study demonstrated that panaxytriol regulates CYP3A4 expression mainly by activating pregnancy X receptor (PXR). At a high concentration of panaxytriol (80 mu M), the constitutive androstane receptor (CAR) is also involved in the upregulation of CYP3A4 Purpose: This study investigated how the cofactors heat shock protein 90 alpha (HSP90 alpha) and retinoid X receptor alpha (RXR alpha) interact with PXR and CAR to participate in the regulation of CYP3A4 by panaxytriol from the perspective of the PXR and CAR interaction. Methods: The mRNA and protein expressions of PXR, CAR, CYP3A4, RXR alpha, and HSP90 alpha in HepG2 cells and Huh-7 cells were detected by quantitative PCR and western blot analysis, respectively. The binding levels of PXR and CAR to RXR alpha and HSP90 alpha were determined by co-immunoprecipitation analysis. The nuclear translocation of PXR and RXR alpha into HepG2 cells and human (hCAR)-silenced HepG2 cells were measured by immunofluorescence. Results: In HepG2 cells and Huh-7 cells, panaxytriol (10-80 mu M) upregulated CYP3A4 expression in a concentration-dependent manner by decreasing PXR binding to HSP90 alpha and increasing PXR binding to RXR alpha. When hCAR was silenced, panaxytriol further enhanced CYP3A4 expression by strengthening PXR binding to RXR alpha, but it had no significant effect on the binding level of PXR and HSP90 alpha. Additionally, at the high con-centration of 80 mu M panaxytriol, CAR binding to HSP90 alpha was weakened while binding to RXR alpha was enhanced. Conclusion: Panaxytriol can upregulate CYP3A4 expression by promoting PXR dissociation from HSP90 alpha and enhancing PXR binding to RXR alpha in HepG2 cells and Huh-7 cells. At high concentrations of panaxytriol, CAR also participates in the induction of CYP3A4 through a similar mechanism. However, in general, CAR antagonizes PXR binding to RXR alpha, thereby attenuating the upregulation of CYP3A4 by panaxytriol.

Automated summary

In this study, the mechanism by which panaxytriol upregulates CYP3A4 expression through the interaction of PXR and CAR was investigated. The results showed that panaxytriol promotes the dissociation of PXR from HSP90α and enhances the binding of PXR to RXRα, thereby upregulating CYP3A4 expression.