Archives of Toxicology

, Volume 88, Issue 12, pp 2243–2259 | Cite as

U0126, a mitogen-activated protein kinase kinase 1 and 2 (MEK1 and 2) inhibitor, selectively up-regulates main isoforms of CYP3A subfamily via a pregnane X receptor (PXR) in HepG2 cells

  • Tomas Smutny
  • Michal Bitman
  • Michal Urban
  • Michaela Dubecka
  • Radim Vrzal
  • Zdeněk Dvorak
  • Petr PavekEmail author
Molecular Toxicology


Hepatocyte tumor cell lines lack the expression or induction properties of major cytochrome P450 (CYP) enzymes compared to primary human hepatocytes. The Ras/Raf/MEK/ERK signaling cascade contributes to hepatocarcinogenesis, dedifferentiation and loss of hepatocyte drug metabolism in hepatocyte tumors. In the present study, we examined whether MEK1/2 inhibitors can restore the expression of CYP genes in hepatocarcinoma HepG2 cells. We found that U0126, a prototype dual MEK1/2 inhibitor, is a potent inducer of CYP3A4, CYP3A5 and CYP3A7 mRNA expression (>100-fold) in HepG2 cells and CYP3A4 mRNA expression in primary human hepatocytes. This U0126-mediated induction is sensitive to the transcriptional inhibitor actinomycin D and was not detected for CYP2B6 or MDR1 mRNA expression. In gene reporter assays, U0126 activates a CYP3A4 promoter luciferase reporter construct containing PXR response elements (PXREs), but not a construct containing mutated PXREs. Based on a ligand binding assay and the examination of a PXR mutant expressing an obstructed ligand binding pocket, we found that U0126 is a ligand of PXR. We also found that U0126 up-regulates the mRNA expression of the nuclear receptors HNF4α, CAR, VDR and PXR but abolishes small heterodimer partner (SHP) corepressor expression in HepG2 cells. The MEK1/2 inhibitors PD0325901 and PD184352, as well as dominant-negative MEK1 expression, also down-regulate SHP mRNA expression. In contrast, dominant-negative MEK1 expression does not significantly induce CYP3A4 gene in HepG2 cells. In conclusion, we found that U0126 is an atypical PXR ligand that via direct (binding and activation of PXR) and indirect (SHP dowregulation) mechanisms selectively restores CYP3A genes in HepG2 cells.


Cytochrome P450 CYP3A4 Gene regulation Pregnane X receptor ERK cascade 



Constitutive androstane receptor


Chenodeoxycholic acid


Cyclin-dependent kinase


Cytochrome P450


Drug-metabolizing enzymes


Dominant negative


Extracellular signal-regulated kinases 1/2


Farnesoid X receptor


Hepatocyte nuclear factor-4 alpha


Ligand binding domain


Mitogen-activated protein kinase


Multi-drug resistance 1; ABCB1 gen; P-glycoprotein


Mitogen-activated/extracellular signal-regulated kinase kinases 1/2


Nuclear receptor


Cyclic AMP-dependent protein kinase


Protein kinase C


Pregnane X receptor


Pregnane X receptor response element


Short/small heterodimer partner (N0B2)


Steroid receptor coactivator-1


Untranslated region



This research has been supported by the Czech Scientific Agency GACR303/12/0472 (to P.P.) and by SVV 170/50/33904-3 Project.

Conflict of interest



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Copyright information

© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  • Tomas Smutny
    • 1
  • Michal Bitman
    • 1
  • Michal Urban
    • 1
  • Michaela Dubecka
    • 1
  • Radim Vrzal
    • 2
  • Zdeněk Dvorak
    • 2
  • Petr Pavek
    • 1
    Email author
  1. 1.Department of Pharmacology and Toxicology, Faculty of Pharmacy in Hradec KraloveCharles University in PragueHradec KraloveCzech Republic
  2. 2.Department of Cell Biology and Genetics, Regional Centre of Advanced Technologies and Materials, Faculty of SciencePalacky University in OlomoucOlomoucCzech Republic

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