Glucocorticoid-mediated induction of CYP3A4 is decreased by disruption of a protein: DNA interaction distinct from the pregnane X receptor response element.
CYP3A4 is the most abundant cytochrome P450 (P450) in human liver, comprising approximately 30% of the total liver P450 content. This enzyme has an important role in steroid catabolism and metabolism of foreign compounds, with the majority of pharmaceutical compounds being substrates for CYP3A4. The molecular mechanisms that underlie transcriptional activation of CYP3A4 are complex with many steroid hormone nuclear receptors, including glucocorticoid receptor, pregnane X receptor (PXR), vitamin D receptor, and constitutive androstane receptor, playing roles. Nowhere is this more evident than in the induction of CYP3A4 gene expression by glucocorticoids. CYP3A genes lack a consensus glucocorticoid receptor response element and yet are highly induced by classical glucocorticoids such as hydrocortisone and dexamethasone. Recent evidence has demonstrated that glucocorticoids are ligands for the orphan nuclear receptor PXR, and induction of CYP3A genes by glucocorticoids may occur primarily through PXR interactions. In this paper, we present a mutant that disrupts a hepatocyte-nuclear-factor-3/CCAAT-enhancer binding protein alpha binding site in the CYP3A4 proximal promoter. This mutation disrupts induction of a reporter gene construct by the glucocorticoids dexamethasone and hydrocortisone; yet induction by the potent PXR ligand rifampicin is unaffected. Such data provides strong evidence that glucocorticoids induce CYP3A4 gene expression both through the established PXR-dependent pathway but also through a PXR-independent pathway.
El-Sankary
Wafaa
W
Molecular Toxicology Group, School of Biomedical and Life Sciences, University of Surrey, Guildford, United Kingdom.
Bombail
Vincent
V
Gibson
G Gordon
GG
Plant
Nick
N
D001665:Binding Sites; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D004247:DNA / Q000378:metabolism*; D018983:DNA Footprinting; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D003850:Deoxyribonuclease I; D003907:Dexamethasone / Q000494:pharmacology; D024202:Electrophoretic Mobility Shift Assay; D004790:Enzyme Induction; D005938:Glucocorticoids / Q000494:pharmacology*; D051541:Hepatocyte Nuclear Factor 3-alpha; D006801:Humans; D006854:Hydrocortisone / Q000494:pharmacology; D008024:Ligands; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics* / Q000378:metabolism; D011987:Receptors, Steroid / Q000235:genetics* / Q000378:metabolism; D020218:Response Elements; D012293:Rifampin / Q000494:pharmacology; D014157:Transcription Factors; D014407:Tumor Cells, Cultured
D022763:CCAAT-Enhancer-Binding Protein-alpha; D004268:DNA-Binding Proteins; C496499:FOXA1 protein, human; D005938:Glucocorticoids; D051541:Hepatocyte Nuclear Factor 3-alpha; D008024:Ligands; D009687:Nuclear Proteins; D000077297:Pregnane X Receptor; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D014157:Transcription Factors; D003907:Dexamethasone; D004247:DNA; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D003850:Deoxyribonuclease I; D012293:Rifampin; D006854:Hydrocortisone