Transactivation of a DR-1 PPRE by a human constitutive androstane receptor variant expressed from internal protein translation start sites

Nucleic Acids Res. 2007;35(7):2177-90. doi: 10.1093/nar/gkm090. Epub 2007 Mar 13.

Abstract

Downstream in-frame start codons produce amino-terminal-truncated human constitutive androstane receptor protein isoforms (DeltaNCARs). The DeltaNCARs are expressed in liver and in vitro cell systems following translation from in-frame methionine AUG start codons at positions 76, 80, 125, 128, 168 and 265 within the full-length CAR mRNA. The resulting CAR proteins lack the N-terminal DNA-binding domain (DBD) of the receptor, yielding DeltaNCAR variants with unique biological function. Although the DeltaNCARs maintain full retinoid X receptor alpha (RXRalpha) heterodimerization capacity, the DeltaNCARs are inactive on classical CAR-inducible direct repeat (DR)-4 elements, yet efficiently transactivate a DR-1 element derived from the endogenous PPAR-inducible acyl-CoA oxidase gene promoter. RXRalpha heterodimerization with CAR1, CAR76 and CAR80 isoforms is necessary for the DR-1 PPRE activation, a function that exhibits absolute dependence on both the respective RXRalpha DBD and CAR activation (AF)-2 domains, but not the AF-1 or AF-2 domain of RXRalpha, nor CAR's DBD. A new model of CAR DBD-independent transactivation is proposed, such that in the context of a DR-1 peroxisome proliferator-activated response element, only the RXRalpha portion of the CAR-RXRalpha heterodimer binds directly to DNA, with the AF-2 domain of tethered CAR mediating transcriptional activation of the receptor complex.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • COS Cells
  • Cells, Cultured
  • Chlorocebus aethiops
  • Codon, Initiator
  • Hepatocytes / metabolism
  • Humans
  • Ligands
  • Molecular Sequence Data
  • Peroxisome Proliferator-Activated Receptors / metabolism
  • Protein Isoforms / chemistry
  • Protein Isoforms / genetics
  • Protein Isoforms / metabolism
  • Protein Structure, Tertiary
  • RNA, Messenger / chemistry
  • Receptors, Cytoplasmic and Nuclear / chemistry
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Response Elements*
  • Retinoid X Receptors / metabolism
  • Sequence Alignment
  • Sequence Deletion
  • Transcription Factors / chemistry
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation*

Substances

  • Codon, Initiator
  • Ligands
  • Peroxisome Proliferator-Activated Receptors
  • Protein Isoforms
  • RNA, Messenger
  • Receptors, Cytoplasmic and Nuclear
  • Retinoid X Receptors
  • Transcription Factors
  • constitutive androstane receptor