Clinical Pharmacology Institute, Nanchang University, Nanchang 330006, PR China.
Clinical Pharmacology Institute, Nanchang University, Nanchang 330006, PR China.
Biochem Pharmacol. 2019 Jan;159:32-39. doi: 10.1016/j.bcp.2018.11.009. Epub 2018 Nov 9.
Nuclear receptors pregnane X receptor (PXR; NR1I2) and constitutive androstane receptor (CAR; NR1I3) play a vital role in regulating CYP3A4. Our previous studies have demonstrated that panaxytriol (PXT) upregulates the expression of CYP3A4 via the PXR regulatory pathway. This study aimed to explore how CAR mediates the regulation of CYP3A4 in the presence of PXT using HepG2 cell, hCAR-overexpressing HepG2 cell and hCAR-silenced HepG2 cell models. In HepG2 cells, PXT induced the expression of CYP3A4 in a concentration-dependent manner (10-80 μM) and the high concentration of PXT (80 μM) upregulated the expression of CAR. The concentrations of PXT (10-40 μM) had no impact on the expression of CAR, but could significantly induce the expression of CYP2B6 target gene by activating CAR. The dual-luciferase reporter gene assay also showed that CAR-mediated CYP3A4 luciferase activity can be promoted by 80 μM of PXT (1.54-fold), while 5, 10, 20, and 40 μM of PXT had no influence on CAR-mediated CYP3A4 luciferase activity. In hCAR-overexpressing HepG2 cells, PXT concentrations (10-40 μM) that significantly induced PXR and CYP3A4 in HepG2 cells had no impact on the expression of CYP3A4, CAR and PXR, whereas a high concentration of PXT (80 µM) could weakly induce the mRNA and protein levels of CAR and CYP3A4. Moreover, the expression of PXR and CYP3A4 in hCAR-silenced HepG2 cells was markedly elevated compared with the blank control or with normal HepG2 cells treated with 10-80 μM of PXT. In conclusion, CAR significantly weakens the ability of PXT to induce CYP3A4 expression by repressing the activation of PXR. There may be a cross-talk mechanism between PXR and CAR on the regulation of CYP3A4 in the presence of PXT. Additionally, a high concentration of PXT (80 μM) induced CYP3A4 via the CAR regulatory pathway.
核受体孕烷 X 受体 (PXR; NR1I2) 和组成型雄烷受体 (CAR; NR1I3) 在调节 CYP3A4 方面发挥着重要作用。我们之前的研究表明，人参三醇 (PXT) 通过 PXR 调节途径上调 CYP3A4 的表达。本研究旨在使用 HepG2 细胞、hCAR 过表达 HepG2 细胞和 hCAR 沉默 HepG2 细胞模型，探讨在 PXT 存在的情况下，CAR 如何介导 CYP3A4 的调节。在 HepG2 细胞中，PXT 以浓度依赖的方式诱导 CYP3A4 的表达(10-80 μM)，高浓度的 PXT(80 μM)上调 CAR 的表达。PXT 的浓度(10-40 μM)对 CAR 的表达没有影响，但可以通过激活 CAR 显著诱导 CYP2B6 靶基因的表达。双荧光素酶报告基因检测也表明，80 μM 的 PXT(1.54 倍)可促进 CAR 介导的 CYP3A4 荧光素酶活性，而 5、10、20 和 40 μM 的 PXT 对 CAR 介导的 CYP3A4 荧光素酶活性没有影响。在 hCAR 过表达 HepG2 细胞中，显著诱导 HepG2 细胞中 PXR 和 CYP3A4 的 PXT 浓度(10-40 μM)对 CYP3A4、CAR 和 PXR 的表达没有影响，而高浓度的 PXT(80 μM)可弱诱导 CAR 和 CYP3A4 的 mRNA 和蛋白水平。此外，与空白对照或用 10-80 μM 的 PXT 处理的正常 HepG2 细胞相比，hCAR 沉默 HepG2 细胞中 PXR 和 CYP3A4 的表达明显升高。综上所述，CAR 通过抑制 PXR 的激活，显著减弱了 PXT 诱导 CYP3A4 表达的能力。在 PXT 存在的情况下，PXR 和 CAR 可能存在调节 CYP3A4 的交叉对话机制。此外，高浓度的 PXT(80 μM)通过 CAR 调节途径诱导 CYP3A4。
