Peroxisome proliferator-activated receptor (PPAR)-binding protein (PBP) but not PPAR-interacting protein (PRIP) is required for nuclear translocation of constitutive androstane receptor in mouse liver

Biochem Biophys Res Commun. 2006 Aug 25;347(2):485-95. doi: 10.1016/j.bbrc.2006.06.129. Epub 2006 Jun 30.

Abstract

The constitutive androstane receptor (CAR) regulates transcription of phenobarbital-inducible genes that encode xenobiotic-metabolizing enzymes in liver. CAR is localized to the hepatocyte cytoplasm but to be functional, it translocates into the nucleus in the presence of phenobarbital-like CAR ligands. We now demonstrate that adenovirally driven EGFP-CAR, as expected, translocates into the nucleus of normal wild-type hepatocytes following phenobarbital treatment under both in vivo and in vitro conditions. Using this approach we investigated the role of transcription coactivators PBP and PRIP in the translocation of EGFP-CAR into the nucleus of PBP and PRIP liver conditional null mouse hepatocytes. We show that coactivator PBP is essential for nuclear translocation of CAR but not PRIP. Adenoviral expression of both PBP and EGFP-CAR restored phenobarbital-mediated nuclear translocation of exogenously expressed CAR in PBP null livers in vivo and in PBP null primary hepatocytes in vitro. CAR translocation into the nucleus of PRIP null livers resulted in the induction of CAR target genes such as CYP2B10, necessary for the conversion of acetaminophen to its hepatotoxic intermediate metabolite, N-acetyl-p-benzoquinone imine. As a consequence, PRIP-deficiency in liver did not protect from acetaminophen-induced hepatic necrosis, unlike that exerted by PBP deficiency. These results establish that transcription coactivator PBP plays a pivotal role in nuclear localization of CAR, that it is likely that PBP either enhances nuclear import or nuclear retention of CAR in hepatocytes, and that PRIP is redundant for CAR function.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acetaminophen / toxicity
  • Active Transport, Cell Nucleus / drug effects
  • Adenoviridae / genetics
  • Animals
  • Blotting, Northern
  • Cell Nucleus / metabolism*
  • Cells, Cultured
  • Cytoplasm / metabolism
  • Gene Expression / drug effects
  • Genetic Vectors / genetics
  • Genotype
  • Green Fluorescent Proteins / genetics
  • Green Fluorescent Proteins / metabolism
  • Hepatocytes / cytology
  • Hepatocytes / drug effects
  • Hepatocytes / metabolism
  • Immunoblotting
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism*
  • Liver / drug effects
  • Liver / metabolism*
  • Liver / pathology
  • Mediator Complex Subunit 1
  • Mice
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Necrosis / chemically induced
  • Necrosis / genetics
  • Necrosis / metabolism
  • Nuclear Receptor Coactivators
  • Phenobarbital / pharmacology
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Recombinant Fusion Proteins / genetics
  • Recombinant Fusion Proteins / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*

Substances

  • Intracellular Signaling Peptides and Proteins
  • Med1 protein, mouse
  • Mediator Complex Subunit 1
  • Ncoa6 protein, mouse
  • Nuclear Receptor Coactivators
  • Receptors, Cytoplasmic and Nuclear
  • Recombinant Fusion Proteins
  • Transcription Factors
  • Green Fluorescent Proteins
  • Acetaminophen
  • constitutive androstane receptor
  • Phenobarbital