Nuclear receptor coactivator SRC-1 interacts with the Q-rich subdomain of the AhR and modulates its transactivation potential

Gene Expr. 1999;8(5-6):273-86.


The aryl hydrocarbon receptor (AhR), a soluble cytosolic protein, mediates many of the toxic effects of TCDD and related chemicals. The toxic effects are largely cell, tissue, and promoter context dependent. Although many details of the overall dioxin signal transduction have been elucidated, the transcriptional regulation of dioxin-induced genes like cyp1A1 is not yet completely understood. Previously, we have shown that the co-regulator RIP140 is a potential AhR coactivator. In this report, the role of coactivator, SRC-1, in AhR-mediated transcriptional regulation was examined. SRC-1 increased AhR-mediated, TCDD-dependent reporter gene activity three-fold in Hepa-1 and COS-1 cells. In in vitro interaction assays, SRC-1 was found to interact with AhR but not with ARNT. SRC-1 interacted weakly with AhR in the absence of TCDD and the addition of ligand further increased SRC-1 binding to AhR. Deletional mapping studies of the AhR revealed that SRC-1 binds to the AhR transactivation domain. Finer mapping of the SRC-1-interacting subdomains in the AhR transactivation domain suggested that the Q-rich subdomain was necessary and sufficient for interaction, similar to that seen with RIP140. Using GFP-tagged constructs, SRC-1 was shown to interact with AhR in cells. Unlike RIP140, LXXLL motifs in SRC-1 were necessary for interaction with AhR in vitro and for coactivation in Hepa-1 cells. The recruitment of certain coactivators by a variety of receptors suggests possible common coactivator pools and competition among receptors for limiting coactivators. Examination of the role of SRC-1 in AhR/ARNT transactivation in ARNT-deficient mutant Hepa-1 c4 cells demonstrates that the AhR transactivation domain is sufficient for enhanced coactivation mediated by SRC-1 in the presence of a transactivation domain deleted ARNT protein.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Adaptor Proteins, Signal Transducing
  • Amino Acid Motifs
  • Animals
  • Aryl Hydrocarbon Receptor Nuclear Translocator
  • Binding Sites
  • COS Cells / drug effects
  • Cell Line / drug effects
  • DNA-Binding Proteins*
  • Green Fluorescent Proteins
  • Histone Acetyltransferases
  • Humans
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Mutation
  • Nuclear Proteins / metabolism
  • Nuclear Receptor Coactivator 1
  • Nuclear Receptor Interacting Protein 1
  • Polychlorinated Dibenzodioxins / pharmacology
  • Receptors, Aryl Hydrocarbon / drug effects
  • Receptors, Aryl Hydrocarbon / genetics
  • Receptors, Aryl Hydrocarbon / metabolism*
  • Recombinant Proteins / genetics
  • Recombinant Proteins / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*
  • Transcriptional Activation*


  • ARNT protein, human
  • Adaptor Proteins, Signal Transducing
  • DNA-Binding Proteins
  • Luminescent Proteins
  • NRIP1 protein, human
  • Nuclear Proteins
  • Nuclear Receptor Interacting Protein 1
  • Polychlorinated Dibenzodioxins
  • Receptors, Aryl Hydrocarbon
  • Recombinant Proteins
  • Transcription Factors
  • Aryl Hydrocarbon Receptor Nuclear Translocator
  • Green Fluorescent Proteins
  • Histone Acetyltransferases
  • NCOA1 protein, human
  • Nuclear Receptor Coactivator 1