CCAR1, a key regulator of mediator complex recruitment to nuclear receptor transcription complexes

Mol Cell. 2008 Aug 22;31(4):510-519. doi: 10.1016/j.molcel.2008.08.001.


DNA-bound transcription factors recruit many coactivator proteins to remodel chromatin and activate transcription. The Mediator complex is believed to recruit RNA polymerase II to most protein-encoding genes. It is generally assumed that interaction of Mediator subunits with DNA-binding transcription factors is responsible for Mediator recruitment to promoters. However, we report here that Mediator recruitment by nuclear receptors (NR) requires a coactivator protein, CCAR1 (cell-cycle and apoptosis regulator 1). CCAR1 associates with components of the Mediator and p160 coactivator complexes and is recruited to endogenous NR target genes in response to the appropriate hormone. Reduction of endogenous CCAR1 levels inhibited hormone-induced expression of endogenous NR target genes, hormone-induced recruitment of Mediator components and RNA polymerase II to target gene promoters, and estrogen-dependent growth of breast cancer cells. Thus, CCAR1 regulates expression of key proliferation-inducing genes. CCAR1 also functions as a p53 coactivator, suggesting a broader role in transcriptional regulation.

Publication types

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

MeSH terms

  • Animals
  • Apoptosis Regulatory Proteins / metabolism*
  • COS Cells
  • Cell Cycle Proteins / metabolism*
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Chlorocebus aethiops
  • Estrogens / pharmacology
  • Gene Expression Regulation, Neoplastic / drug effects
  • Humans
  • Promoter Regions, Genetic / genetics
  • Protein Binding / drug effects
  • Protein Structure, Tertiary
  • Receptors, Cytoplasmic and Nuclear / metabolism*
  • Receptors, Estrogen / metabolism
  • Receptors, Glucocorticoid / metabolism
  • Trans-Activators / metabolism*
  • Transcription, Genetic* / drug effects
  • Tumor Suppressor Protein p53 / metabolism


  • Apoptosis Regulatory Proteins
  • CCAR1 protein, human
  • Cell Cycle Proteins
  • Estrogens
  • Receptors, Cytoplasmic and Nuclear
  • Receptors, Estrogen
  • Receptors, Glucocorticoid
  • Trans-Activators
  • Tumor Suppressor Protein p53