title: Chrysin, baicalein and galangin are indirect activators of the human constitutive androstane receptor (CAR).
abstract: The constitutive androstane receptor (CAR) is a crucial transcriptional regulator of key xenobiotic-metabolizing enzymes such as cytochrome P450 CYP3A4, CYP2C9 and CYP2B6. The flavonoids chrysin, baicalein and galangin have been reported to activate CAR and interfere with EGFR signaling. Nevertheless, it is not known if these flavonoids are direct CAR ligands or indirect phenobarbital-like CAR activators via the inhibition of epidermal growth factor receptor (EGFR) signaling. We analyze the interactions of chrysin, galangin and baicalein and its glycoside baicalin with human CAR. We have employed and validated methods that can study direct interaction with the CAR ligand binding pocket. Secondly, we determined if the compounds affect human EGFR signaling and interact with EGFR. Employing a TR-FRET coactivator assay with recombinant CAR or CAR assembly assay, a consistent activation of CAR with flavonoids and phenobarbital was not observed. It was determined, however, that galangin, chrysin, and baicalein may slightly repress EGFR-Tyr1068 autophosphorylation after EGF treatment, phosphorylation of downstream transcription factor ELK1 and stimulate EGFP-CAR nuclear translocation in primary human hepatocytes. These data suggest that flavonoids chrysin, galangin and baicalein are indirect human CAR activators. This study also demonstrates new approach how to test the direct CAR interaction with its ligands.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy, Charles University in Prague, Heyrovského 1203, Hradec Kralove CZ500 05, Czech Republic.
authors.forename: Alejandro
authors.initials: A
authors.lastname: Carazo Fernández
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy, Charles University in Prague, Heyrovského 1203, Hradec Kralove CZ500 05, Czech Republic.
authors.forename: Tomas
authors.initials: T
authors.lastname: Smutny
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy, Charles University in Prague, Heyrovského 1203, Hradec Kralove CZ500 05, Czech Republic.
authors.forename: Lucie
authors.initials: L
authors.lastname: Hyrsová
authors.affiliation: Regional Centre of Advanced Technologies and Materials, Department of Physical Chemistry Palacky University in Olomouc, 17. listopadu 1131, Olomouc CZ779 00, Czech Republic.
authors.forename: Karel
authors.initials: K
authors.lastname: Berka
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy, Charles University in Prague, Heyrovského 1203, Hradec Kralove CZ500 05, Czech Republic. Electronic address: petr.pavek@faf.cuni.cz.
authors.forename: Petr
authors.initials: P
authors.lastname: Pavek
mesh_terms: D001665:Binding Sites / Q000187:drug effects; D002460:Cell Line; D000090702:Constitutive Androstane Receptor; D065702:Cytochrome P-450 CYP2B6 / Q000378:metabolism; D066246:ErbB Receptors / Q000187:drug effects; D044950:Flavanones / Q000494:pharmacology*; D005419:Flavonoids / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D010634:Phenobarbital / Q000494:pharmacology; D021381:Protein Transport / Q000187:drug effects; D018160:Receptors, Cytoplasmic and Nuclear / Q000819:agonists*; D050807:ets-Domain Protein Elk-1 / Q000187:drug effects / Q000235:genetics
chemical_list: D000090702:Constitutive Androstane Receptor; C494112:ELK1 protein, human; D044950:Flavanones; D005419:Flavonoids; D018160:Receptors, Cytoplasmic and Nuclear; D050807:ets-Domain Protein Elk-1; C037032:galangin; C043561:chrysin; C006680:baicalein; D065702:Cytochrome P-450 CYP2B6; D066246:ErbB Receptors; D010634:Phenobarbital
keywords: Constitutive androstane receptor; Cytochrome P450; Flavonoids; Gene regulation; Nuclear receptors