Dexamethasone enhances constitutive androstane receptor expression in human hepatocytes: consequences on cytochrome P450 gene regulation.

The barbiturate phenobarbital induces the transcription of cytochromes P450 (CYPs) 2B through the constitutive androstane receptor (CAR; NR1I3). CAR is a member of the nuclear receptor family (NR1) mostly expressed in the liver, which heterodimerizes with retinoid X receptor (RXR) and was shown to transactivate both the phenobarbital responsive element module of the human CYP2B6 gene and the CYP3A4 xenobiotic response element. Because previous studies in rodent hepatocyte cultures have shown that the phenobarbital-mediated induction of CYP2B genes is potentiated by glucocorticoids, we examined the role of activated glucocorticoid receptor in this process. We show that submicromolar concentrations of dexamethasone enhance phenobarbital-mediated induction of CYP3A4, CYP2B6, and CYP2C8 mRNA in cultured human hepatocytes. In parallel, we observed that glucocorticoid agonists, such as dexamethasone, prednisolone, or hydrocortisone, specifically increase human car (hCAR) mRNA expression. Accumulation of hCAR mRNA parallels that of tyrosine aminotransferase: both mRNAs reach a maximum at a concentration of 100 nM dexamethasone and are down-regulated by concomitant treatment with the glucocorticoid antagonist RU486. Moreover, the effect of dexamethasone on hCAR mRNA accumulation appears to be of transcriptional origin because the addition of protein synthesis inhibitor cycloheximide has no effect, and dexamethasone does not affect the degradation of hCAR mRNA. Furthermore, dexamethasone increases both basal and phenobarbital-mediated nuclear translocation of CAR immunoreactive protein in human hepatocytes. The up-regulation of CAR mRNA and protein in response to dexamethasone explains the synergistic effect of this glucocorticoid on phenobarbital-mediated induction of CYP2B genes and the controversial role of the glucocorticoid receptor on phenobarbital-mediated CYP gene inductions.

[1]  J. Pascussi,et al.  Dexamethasone induces pregnane X receptor and retinoid X receptor-alpha expression in human hepatocytes: synergistic increase of CYP3A4 induction by pregnane X receptor activators. , 2000, Molecular pharmacology.

[2]  L. Moore,et al.  Orphan Nuclear Receptors Constitutive Androstane Receptor and Pregnane X Receptor Share Xenobiotic and Steroid Ligands* , 2000, The Journal of Biological Chemistry.

[3]  E. Schuetz,et al.  The glucocorticoid receptor is essential for induction of cytochrome P-4502B by steroids but not for drug or steroid induction of CYP3A or P-450 reductase in mouse liver. , 2000, Drug metabolism and disposition: the biological fate of chemicals.

[4]  B. Goodwin,et al.  The orphan human pregnane X receptor mediates the transcriptional activation of CYP3A4 by rifampicin through a distal enhancer module. , 1999, Molecular pharmacology.

[5]  K. Griffin,et al.  Molecular mechanisms of cytochrome P-450 induction by xenobiotics: An expanded role for nuclear hormone receptors. , 1999, Molecular pharmacology.

[6]  D. Waxman,et al.  P450 gene induction by structurally diverse xenochemicals: central role of nuclear receptors CAR, PXR, and PPAR. , 1999, Archives of biochemistry and biophysics.

[7]  T. Kawamoto,et al.  Phenobarbital-Responsive Nuclear Translocation of the Receptor CAR in Induction of the CYP2B Gene , 1999, Molecular and Cellular Biology.

[8]  J. Pascussi,et al.  Evidence for the presence of a functional pregnane X receptor response element in the CYP3A7 promoter gene. , 1999, Biochemical and biophysical research communications.

[9]  Paavo Honkakoski,et al.  The Repressed Nuclear Receptor CAR Responds to Phenobarbital in Activating the Human CYP2B6 Gene* , 1999, The Journal of Biological Chemistry.

[10]  T. Nagaya,et al.  Glucocorticoids increase retinoid-X receptor alpha (RXRalpha) expression and enhance thyroid hormone action in primary cultured rat hepatocytes. , 1999, Journal of molecular endocrinology.

[11]  E. Schuetz,et al.  Environmental xenobiotics and the antihormones cyproterone acetate and spironolactone use the nuclear hormone pregnenolone X receptor to activate the CYP3A23 hormone response element. , 1998, Molecular pharmacology.

[12]  W. Sabbagh,et al.  SXR, a novel steroid and xenobiotic-sensing nuclear receptor. , 1998, Genes & development.

[13]  R Ohlsson,et al.  Identification of a human nuclear receptor defines a new signaling pathway for CYP3A induction. , 1998, Proceedings of the National Academy of Sciences of the United States of America.

[14]  David D. Moore,et al.  Androstane metabolites bind to and deactivate the nuclear receptor CAR-β , 1998, Nature.

[15]  T. Sueyoshi,et al.  The Nuclear Orphan Receptor CAR-Retinoid X Receptor Heterodimer Activates the Phenobarbital-Responsive Enhancer Module of the CYP2B Gene , 1998, Molecular and Cellular Biology.

[16]  J. Lehmann,et al.  The human orphan nuclear receptor PXR is activated by compounds that regulate CYP3A4 gene expression and cause drug interactions. , 1998, The Journal of clinical investigation.

[17]  B. Kemper,et al.  Nuclear factor-1 motif and redundant regulatory elements comprise phenobarbital-responsive enhancer in CYP2B1/2. , 1998, DNA and cell biology.

[18]  S. Dubois,et al.  The CYP2B2 Phenobarbital Response Unit Contains an Accessory Factor Element and a Putative Glucocorticoid Response Element Essential for Conferring Maximal Phenobarbital Responsiveness* , 1998, The Journal of Biological Chemistry.

[19]  M. Negishi,et al.  Protein serine/threonine phosphatase inhibitors suppress phenobarbital-induced Cyp2b10 gene transcription in mouse primary hepatocytes. , 1998, The Biochemical journal.

[20]  J. Lehmann,et al.  An Orphan Nuclear Receptor Activated by Pregnanes Defines a Novel Steroid Signaling Pathway , 1998, Cell.

[21]  M. Negishi,et al.  Regulatory DNA elements of phenobarbital‐responsive cytochrome P450 CYP2B genes , 1998, Journal of biochemical and molecular toxicology.

[22]  J. Gustafsson,et al.  Identification of a functional glucocorticoid response element in the CYP3A1/IGC2 gene. , 1998, DNA and cell biology.

[23]  D. Moore,et al.  Differential Transactivation by Two Isoforms of the Orphan Nuclear Hormone Receptor CAR* , 1997, The Journal of Biological Chemistry.

[24]  C. Bonfils,et al.  Effect of cell density and epidermal growth factor on the inducible expression of CYP3A and CYP1A genes in human hepatocytes in primary culture , 1997, Hepatology.

[25]  M. Lechner,et al.  Glucocorticoid receptor-independent transcriptional induction of cytochrome P450 3A1 by metyrapone and its potentiation by glucocorticoid. , 1996, Molecular pharmacology.

[26]  Youngkyu Park,et al.  Phenobarbital Induction Mediated by a Distal CYP2B2 Sequence in Rat Liver Transiently Transfected in Situ * , 1996, The Journal of Biological Chemistry.

[27]  S. Strom,et al.  Use of human hepatocytes to study P450 gene induction. , 1996, Methods in enzymology.

[28]  P. Guzelian,et al.  A Novel cis-Acting Element in a Liver Cytochrome P450 3A Gene Confers Synergistic Induction by Glucocorticoids plus Antiglucocorticoids * , 1995, The Journal of Biological Chemistry.

[29]  J. S. Sidhu,et al.  cAMP-associated Inhibition of Phenobarbital-inducible Cytochrome P450 Gene Expression in Primary Rat Hepatocyte Cultures (*) , 1995, The Journal of Biological Chemistry.

[30]  J. S. Sidhu,et al.  Modulation of xenobiotic-inducible cytochrome P450 gene expression by dexamethasone in primary rat hepatocytes. , 1995, Pharmacogenetics.

[31]  C. Bonfils,et al.  Oxidative metabolism of lansoprazole by human liver cytochromes P450. , 1995, Molecular pharmacology.

[32]  Wolfgang Schmid,et al.  Molecular genetic analysis of glucocorticoid signaling during mouse development , 1995, Steroids.

[33]  O. MacDougald,et al.  Transcriptional regulation of gene expression during adipocyte differentiation. , 1995, Annual review of biochemistry.

[34]  J. Auwerx,et al.  Regulation of the peroxisome proliferator-activated receptor alpha gene by glucocorticoids. , 1994, The Journal of biological chemistry.

[35]  O. MacDougald,et al.  Glucocorticoids reciprocally regulate expression of the CCAAT/enhancer-binding protein alpha and delta genes in 3T3-L1 adipocytes and white adipose tissue. , 1994, The Journal of biological chemistry.

[36]  D. Moore,et al.  A new orphan member of the nuclear hormone receptor superfamily that interacts with a subset of retinoic acid response elements , 1994, Molecular and cellular biology.

[37]  L. Corcos,et al.  The phenobarbital-induced transcriptional activation of cytochrome P-450 genes is blocked by the glucocorticoid-progesterone antagonist RU486. , 1993, Molecular pharmacology.

[38]  E. Schuetz,et al.  Expression of multiple forms of cytochrome P450 mRNAs in primary cultures of rat hepatocytes maintained on matrigel. , 1993, Molecular pharmacology.

[39]  W. Fan,et al.  Cloning of a mu-class glutathione S-transferase gene and identification of the glucocorticoid regulatory domains in its 5' flanking sequence. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[40]  P. Maurel,et al.  Effect of corticosteroids on the expression of cytochromes P450 and on cyclosporin A oxidase activity in primary cultures of human hepatocytes. , 1992, Molecular pharmacology.

[41]  E. Schuetz,et al.  Paradoxical transcriptional activation of rat liver cytochrome P-450 3A1 by dexamethasone and the antiglucocorticoid pregnenolone 16 alpha-carbonitrile: analysis by transient transfection into primary monolayer cultures of adult rat hepatocytes. , 1992, Proceedings of the National Academy of Sciences of the United States of America.

[42]  L. Azároff,et al.  Phenobarbital induction of cytochrome P-450 gene expression. , 1992, The Biochemical journal.

[43]  P. Luc,et al.  Glucocorticoid regulation of a phenobarbital-inducible cytochrome P-450 gene: the presence of a functional glucocorticoid response element in the 5'-flanking region of the CYP2B2 gene. , 1990, Nucleic Acids Research.

[44]  S. Morris,et al.  Induction of mRNA for phosphoenolpyruvate carboxykinase (GTP) by dexamethasone in cultured rat hepatocytes requires on-going protein synthesis. , 1987, The Biochemical journal.

[45]  A. Conney,et al.  Induction of microsomal enzymes by foreign chemicals and carcinogenesis by polycyclic aromatic hydrocarbons: G. H. A. Clowes Memorial Lecture. , 1982, Cancer research.