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NCOA6 differentially regulates the expression of the CYP2C9 and CYP3A4 genes

Sailesh Surapureddi1, Ritu Rana, Joyce A Goldstein

  • 1Laboratory of Toxicology and Pharmacology, National Institute of Environmental Health Sciences, P.O. Box 12233, Research Triangle Park, NC 27709, United States.

Pharmacological Research
|February 5, 2011
PubMed

Insights

Nuclear receptors pregnane X receptor (PXR) and hepatocyte nuclear factor 4 alpha (HNF4α) synergistically regulate drug-metabolizing enzymes. NCOA6 acts as a bridge, mediating this interaction for CYP2C9 but not CYP3A4.

Area of Science:

  • Pharmacology
  • Molecular Biology
  • Biochemistry

Background:

  • Cytochrome P450 enzymes, specifically CYP2C and CYP3A subfamilies, are crucial for metabolizing prescribed medications.
  • The expression of these enzymes is regulated by nuclear receptors, including hepatocyte nuclear factor 4 alpha (HNF4α) and rifampicin-activated pregnane X receptor (PXR).

Purpose of the Study:

  • To elucidate the mechanism of ligand-dependent synergistic cross-talk between PXR and HNF4α.
  • To investigate the role of NCOA6 in mediating the interaction between PXR and HNF4α in regulating CYP gene expression.

Main Methods:

  • Two-hybrid screening to identify interacting proteins.
  • GST pull-down and mammalian two-hybrid assays to confirm protein interactions.
  • Reporter assays to assess promoter activity.
  • NCOA6 silencing to evaluate its functional role.
  • Chromatin immunoprecipitation (ChIP) analysis to determine promoter binding.

Main Results:

  • NCOA6 was identified as an interacting protein for HNF4α and also interacts with PXR.
  • NCOA6 enhances the synergistic activation of CYP2C9 and CYP3A4 promoter activity by PXR and HNF4α.
  • Silencing NCOA6 abrogated the synergistic activation and induction of CYP2C9, but not CYP3A4, by PXR-HNF4α.
  • ChIP analysis showed NCOA6 bridges PXR and HNF4α binding sites on the CYP2C9 promoter.

Conclusions:

  • NCOA6 is essential for the synergistic activation of CYP2C9 gene expression by HNF4α and PXR.
  • NCOA6 differentially regulates CYP2C9 and CYP3A4 gene expression, despite both being regulated by the same nuclear receptors.

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