title: MicroRNA-122 down-regulation is involved in phenobarbital-mediated activation of the constitutive androstane receptor.
abstract: Constitutive androstane receptor (CAR) is a nuclear receptor that regulates the transcription of target genes, including CYP2B and 3A. Phenobarbital activates CAR, at least in part, in an AMP-activated protein kinase (AMPK)-dependent manner. However, the precise mechanisms underlying phenobarbital activation of AMPK are still unclear. In the present study, it was demonstrated that phenobarbital administration to mice decreases hepatic miR-122, a liver-enriched microRNA involved in both hepatic differentiation and function. The time-course change in the phenobarbital-mediated down-regulation of miR-122 was inversely correlated with AMPK activation. Phenobarbital decreased primary miR-122 to approximately 25% of the basal level as early as 1 h and suppressed transactivity of mir-122 promoter in HuH-7 cells, suggesting that the down-regulation occurred at the transcriptional level. AMPK activation by metformin or 5-aminoimidazole-4-carboxamide 1-β-D-ribonucleoside had no evident effect on miR-122 levels. An inhibitory RNA specific for miR-122 increased activated AMPK and CAR-mediated trancactivation of the phenobarbital-responsive enhancer module in HepG2 cells. Conversely, the reporter activity induced by the ectopic CAR was almost completely suppressed by co-transfection with the miR-122 mimic RNA. GFP-tagged CAR was expressed in the cytoplasm in addition to the nucleus in the majority of HuH-7 cells in which miR-122 was highly expressed. Co-transfection of the mimic or the inhibitor RNA for miR-122 further increased or decreased, respectively, the number of cells that expressed GFP-CAR in the cytoplasm. Taken together, these results suggest that phenobarbital-mediated down-regulation of miR-122 is an early and important event in the AMPK-dependent CAR activation and transactivation of its target genes.
authors: Department of Biochemical Toxicology, Showa University School of Pharmacy, Tokyo, Japan.
authors: Ryota
authors: R
authors: Shizu
authors: Sawako
authors: S
authors: Shindo
authors: Takemi
authors: T
authors: Yoshida
authors: Satoshi
authors: S
authors: Numazawa
mesh_terms: D000263:Adenylate Kinase / Q000378:metabolism; D000818:Animals; D000090702:Constitutive Androstane Receptor; D015536:Down-Regulation; D056945:Hep G2 Cells; D006801:Humans; D008099:Liver / Q000378:metabolism; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D035683:MicroRNAs / Q000096:biosynthesis*; D010634:Phenobarbital / Q000494:pharmacology*; D010957:Plasmids / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation
chemical_list: D000090702:Constitutive Androstane Receptor; C531907:MIRN122 microRNA, human; D035683:MicroRNAs; C544354:Mirn122 microRNA, mouse; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; D000263:Adenylate Kinase; D010634:Phenobarbital