Department of Biomedical Sciences, Center for Pharmacogenomics and Molecular Therapy, University of Rhode Island, 41 Lower College Road, Kingston, RI 02881, USA.
Biochem Pharmacol. 2010 Oct 15;80(8):1274-83. doi: 10.1016/j.bcp.2010.06.043. Epub 2010 Jul 1.
The pregnane X receptor (PXR) is recognized as a key regulator for the induction of a large number of genes in drug metabolism and transport. The transactivation of PXR is enhanced by the glucocorticoid dexamethasone and the enhancement is linked to the induction of PXR in humans and rats. The present study was undertaken to determine the mechanism for the induction and ascertain the synergistic effect on the expression of CYP3A23, a rat PXR target. In primary hepatocytes, significant induction of PXR was detected as early as 2h after the treatment and the maximal induction occurred at 1 microM dexamethasone. Similar induction kinetics was observed in the hepatoma line H4-II-E-C3. The induction was abolished by actinomycin D and dexamethasone efficaciously stimulated the rat PXR promoter. In addition, dexamethasone synergized esfenvalerate (an insecticide and a PXR activator) in inducing CYP3A23 and stimulating the CYP3A23 promoter. The full promoter of CYP3A23 (-1445/+74) was activated in a similar pattern as the changes in PXR mRNA in response to dexamethasone, esfenvalerate and co-treatment. In contrast, different responding patterns were detected on the stimulation of the CYP3A23 proximal promoter. Synergistic stimulation was also observed on the CYP3A4-DP-Luc reporter, the human counterpart of CYP3A23. These findings establish that transactivation is responsible for the induction of rat PXR and the induction presents potential interactions with insecticides in a species-conserved manner. The different responding patterns among CYP3A23 reporters point to an involvement of multiple transcriptional events in the regulation of CYP3A23 expression by dexamethasone, esfenvalerate and both.
孕激素相关受体（PXR）被认为是调节药物代谢和转运的大量基因表达的关键调控因子。糖皮质激素地塞米松增强 PXR 的转录激活，这种增强与人和大鼠中 PXR 的诱导有关。本研究旨在确定诱导 PXR 的机制，并确定其对大鼠 PXR 靶标 CYP3A23 表达的协同作用。在原代肝细胞中，在处理后 2 小时即可检测到 PXR 的显著诱导，在 1 μM 地塞米松时诱导作用最大。在肝癌细胞系 H4-II-E-C3 中也观察到类似的诱导动力学。诱导作用被放线菌素 D 消除，地塞米松有效地刺激大鼠 PXR 启动子。此外，地塞米松与 esfenvalerate（一种杀虫剂和 PXR 激活剂）协同诱导 CYP3A23 并刺激 CYP3A23 启动子。CYP3A23 的全长启动子（-1445/+74）的激活模式与 PXR mRNA 对地塞米松、esfenvalerate 和联合处理的反应变化相似。相比之下，在刺激 CYP3A23 近端启动子时检测到不同的反应模式。在 CYP3A4-DP-Luc 报告基因上也观察到协同刺激作用，该报告基因是 CYP3A23 的人对应物。这些发现表明，转录激活是大鼠 PXR 诱导的原因，并且这种诱导以种属保守的方式与杀虫剂存在潜在的相互作用。CYP3A23 报告基因之间不同的反应模式表明，地塞米松、esfenvalerate 及其两者在调节 CYP3A23 表达中涉及多个转录事件。
