Examination of Glucocorticoid Receptor α-Mediated Transcriptional Regulation of P-glycoprotein, CYP3A4, and CYP2C9 Genes in Placental Trophoblast Cell Lines

The placental trophoblast at different stages of pregnancy contains some drug transporters and xenobiotic-metabolising enzymes, as well as ligand-activated nuclear receptors, which control their inducible transcriptional regulation. Glucocorticoid receptor α (GRα) is expressed in both placental syncytiotrophoblast and cytotrophoblast. GRα was shown to control inducible expression of several enzymes of the cytochrome P-450 family (CYP) and the drug transporter P-glycoprotein in the liver. However, GRα-mediated transcriptional regulation of drug transporters and CYPs has not been studied in the placental trophoblast. In this study, we examined the expression and activity of GRα in the transcriptional regulation of P-glycoprotein, CYP3A4, and CYP2C9 in placental trophoblast cell lines. Employing RT–PCR, Western blotting, and luciferase gene reporter assay, we detected the expression and activity of GRα in JEG3 and BeWo cell lines. However, we observed that only MDR1 mRNA was up-regulated after treatment of placental cells with dexamethasone. Accordingly, only the promoter of the MDR1 gene was activated by dexamethasone in gene reporter assays in placental cells and the activation was abolished by RU486, an antagonist of GRα. CYP3A4 and CYP2C9 promoters were activated in placental cells only after co-transfection with hepatocyte nuclear factor 4α (HNF4α), which indicates the hepatocyte-specific character of GRα-mediated regulation of the genes. On the other hand, coexpression of HNF4α had no effect on the activation of the MDR1 gene promoter, suggesting HNF4α-independent regulation via GRα. We conclude that GRα may be involved in the transcriptional regulation of P-glycoprotein in the placental trophoblast. We also indicate that the CYP3A4 and CYP2C9 genes are not inducible through GRα in placental cell lines, due to the lack of HNF4α expression and possibly some additional hepatocyte-specific transcriptional factors.