Dexamethasone‐Mediated Regulation of CYP3A4 and UGTs in Human Hepatoma HuH‐7 Cells

BACKGROUND: The application of human hepatic cell lines to early drug discovery and development instead of human primary hepatocytes (HPHs) has been limited because of the low level of drug-metabolizing enzymes (DMEs). OBJECTIVE: The study aimed to evaluate the effects of dexamethasone (DEX) treatment on DME expression, activities, and regulation in HuH-7 hepatoma cells. METHODS: Expression and transcriptional regulation of major CYPs and UGTs in HuH-7 cells was evaluated by immunoblotting, probe substrate assays, and treatments with nuclear receptor agonists, including DEX, and antagonists. RESULTS: DEX increased the expression and activity of cytochrome P450 (CYP) 3A4, uridine 5'-diphospho-glucuronosyltransferase (UGT) 1A1, and UGT2B7 but had minimal effects on CYP1A2, CYP2B6, or CYP2C9. These augmented activities of CYP3A4, UGT1A1, and UGT2B7 were concentration-dependently inhibited by their corresponding selective inhibitors. DEX-induced upregulation of CYP3A4 protein expression was abolished by co-treatment with the glucocorticoid receptor (GR) inhibitor, but not by co-treatment with the pregnane X receptor (PXR) inhibitor. However, treatment with PXR or constitutive androstane receptor (CAR) agonist did not lead to transcriptional activation of CYP3A4 and 2B6. Only CYP1A1 was transactivated by an aryl hydrocarbon receptor (AhR) ligand. CONCLUSION: Our results suggest that the activities of some major DMEs (CYP3A4, UGT1A1, and UGT2B7) in HuH-7 cells are promoted by DEX treatment possibly through GR activation. However, unlike HPHs, HuH-7 cells fail to show transcriptional regulation of DMEs by PXR or CAR, which limits their suitability for evaluating DME induction potential of investigational drugs.