Xenobiotic induction of cytochrome P450 2B1 (CYP2B1) is mediated by the orphan nuclear receptor constitutive androstane receptor (CAR) and requires steroid co-activator 1 (SRC-1) and the transcription factor Sp1

Biochem J. 2001 Apr 1;355(Pt 1):71-8. doi: 10.1042/0264-6021:3550071.


The constitutive androstane receptor (CAR) activates the expression of a reporter gene attached to the phenobarbital-response element (PBRE) of the cytochrome P450 2B1 (CYP2B1) gene in response to the barbiturate phenobarbital and the plant product picrotoxin. The xenobiotic-mediated increase in transactivation occurs in transfected primary hepatocytes and in liver transfected by biolistic-particle-mediated DNA transfer, but not in the transformed cell lines HepG2, CV-1 and HeLa, which support only constitutive activation of gene expression by CAR. Steroid co-activator 1 (SRC-1) enhances both constitutive and xenobiotic-induced CAR-mediated transactivation via the CYP2B1 PBRE in transfected primary hepatocytes. The nuclear receptor 1 (NR1) site of the PBRE is sufficient for CAR-mediated transactivation, but additional sequences within the PBRE, and hence the proteins that bind to them, are required for the interaction of CAR with SRC-1. The NR2 site of the PBRE binds proteins other than CAR, including an unidentified nuclear receptor heterodimerized with retinoid X receptor alpha. By binding to the proximal promoter of CYP2B1, the transcription factor Sp1 increases both basal transcription and xenobiotic-induced expression via the PBRE. Thus induction of CYP2B1 expression by xenobiotics is mediated by the nuclear receptor CAR and, for optimal expression, requires SRC-1 and Sp1.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Base Sequence
  • Cell Line, Transformed
  • Cells, Cultured
  • Constitutive Androstane Receptor
  • Cytochrome P-450 CYP2B1 / biosynthesis*
  • Cytochrome P-450 CYP2B1 / genetics
  • DNA Primers
  • Enzyme Induction / drug effects
  • Enzyme Induction / physiology
  • Hepatocytes / drug effects
  • Hepatocytes / enzymology
  • Histone Acetyltransferases
  • Nuclear Receptor Coactivator 1
  • Rats
  • Receptors, Cytoplasmic and Nuclear / physiology*
  • Sp1 Transcription Factor / physiology*
  • Transcription Factors / physiology*
  • Transcriptional Activation / drug effects
  • Xenobiotics / pharmacology*


  • Constitutive Androstane Receptor
  • DNA Primers
  • Receptors, Cytoplasmic and Nuclear
  • Sp1 Transcription Factor
  • Transcription Factors
  • Xenobiotics
  • Cytochrome P-450 CYP2B1
  • Histone Acetyltransferases
  • Nuclear Receptor Coactivator 1