title: Glucocorticoid receptor regulates organic cation transporter 1 (OCT1, SLC22A1) expression via HNF4α upregulation in primary human hepatocytes.
abstract: BACKGROUND
  Organic cation transporter 1 (OCT1, SLC22A1) is a membrane transporter that is important for therapeutic effect of the antidiabetic drug metformin. Its liver-specific expression in hepatocytes is strongly controlled by hepatocyte nuclear factor-4α (HNF4α). HNF4α expression and transcriptional activity have been demonstrated to be augmented by glucocorticoid receptor (GR) in human hepatocytes and rodent livers.
  
  
  METHODS
  It was examined whether GR activation indirectly induces OCT1 gene expression via HNF4α up-regulation in primary human hepatocytes. We also examined which other transcription factors are involved in OCT1 gene expression and whether they are regulated by dexamethasone using qRT-PCR and gene reporter assays.
  
  
  RESULTS
  We found that dexamethasone significantly up-regulates OCT1 mRNA and protein in normal primary human hepatocytes, but not in hepatocyte-derived tumor cell lines HepG2 and MZ-Hep1. Consistently, we observed that HNF4α is induced by dexamethasone in primary human hepatocytes, but not in hepatocyte tumor-derived cell lines. Viral transduction of MZ-Hep1 cells with the expression constructs for HNF4α, CCAAT/enhancer binding proteins β (C/EBPβ) and peroxisome proliferator-activated receptor-γ coactivator 1α (PGC1α) demonstrated significant roles of the transcription factors in OCT1 gene regulation. We found that expression of OCT1 mRNA in human livers significantly correlates with C/EBPβ and HNF4α mRNAs expression and that C/EBPβ co-transfection stimulates OCT1 gene reporter construct in HepG2 cells. Nevertheless, neither C/EBPβ nor PGC1α were upregulated in human hepatocytes by dexamethasone.
  
  
  CONCLUSIONS
  We can conclude that GR-induced expression of HNF4α may contribute to indirect OCT1 gene up-regulation by dexamethasone in primary human hepatocytes, but not in hepatocyte-derived tumor cell lines.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho 1203, Hradec Kralove, CZ-500 05, Czech Republic. petr.pavek@faf.cuni.cz.
authors.forename: Alice
authors.initials: A
authors.lastname: Rulcova
authors.forename: Lucie
authors.initials: L
authors.lastname: Krausova
authors.forename: Tomas
authors.initials: T
authors.lastname: Smutny
authors.forename: Radim
authors.initials: R
authors.lastname: Vrzal
authors.forename: Zdenek
authors.initials: Z
authors.lastname: Dvorak
authors.forename: Ramiro
authors.initials: R
authors.lastname: Jover
authors.forename: Petr
authors.initials: P
authors.lastname: Pavek
mesh_terms: D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D005938:Glucocorticoids / Q000494:pharmacology*; D056945:Hep G2 Cells; D051557:Hepatocyte Nuclear Factor 4 / Q000235:genetics / Q000378:metabolism*; D022781:Hepatocytes / Q000187:drug effects* / Q000378:metabolism; D006801:Humans; D027702:Organic Cation Transporter 1 / Q000235:genetics / Q000378:metabolism*; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D061251:Primary Cell Culture; D012333:RNA, Messenger / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000819:agonists* / Q000378:metabolism; D013997:Time Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014161:Transduction, Genetic; D014162:Transfection; D015854:Up-Regulation
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; C545012:CEBPB protein, human; D005938:Glucocorticoids; C496592:HNF4A protein, human; D051557:Hepatocyte Nuclear Factor 4; C497713:NR3C1 protein, human; D027702:Organic Cation Transporter 1; C486497:PPARGC1A protein, human; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D012333:RNA, Messenger; D011965:Receptors, Glucocorticoid; D014157:Transcription Factors; D003907:Dexamethasone