BARD1 is necessary for ubiquitylation of nucleosomal histone H2A and for transcriptional regulation of estrogen metabolism genes

Proc Natl Acad Sci U S A. 2018 Feb 6;115(6):1316-1321. doi: 10.1073/pnas.1715467115. Epub 2018 Jan 24.


Missense mutations that disrupt the RING domain of the tumor suppressor gene BRCA1 lead to increased risk of breast and ovarian cancer. The BRCA1 RING domain is a ubiquitin ligase, whose structure and function rely critically on forming a heterodimer with BARD1, which also harbors a RING domain. The function of the BARD1 RING domain is unknown. In families severely affected with breast cancer, we identified inherited BARD1 missense mutations Cys53Trp, Cys71Tyr, and Cys83Arg that alter three zinc-binding residues of the BARD1 RING domain. Each of these mutant BARD1 proteins retained the ability to form heterodimeric complexes with BRCA1 to make an active ubiquitin ligase, but the mutant BRCA1/BARD1 complexes were deficient in binding to nucleosomes and in ubiquitylating histone H2A. The BARD1 mutations also caused loss of transcriptional repression of BRCA1-regulated estrogen metabolism genes CYP1A1 and CYP3A4; breast epithelial cells edited to create heterozygous loss of BARD1 showed significantly higher expression of CYP1A1 and CYP3A4 Reintroduction of wild-type BARD1 into these cells restored CYP1A1 and CYP3A4 transcription to normal levels, but introduction of the cancer-predisposing BARD1 RING mutants failed to do so. These results indicate that an intact BARD1 RING domain is critical to BRCA1/BARD1 binding to nucleosomes and hence to ubiquitylation of histone H2A and also critical to transcriptional repression of BRCA1-regulated genes active in estrogen metabolism.

Keywords: BARD1; BRCA1; breast cancer; transcriptional repression; ubiquitin.

Publication types

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

MeSH terms

  • BRCA1 Protein / genetics
  • BRCA1 Protein / metabolism
  • Breast Neoplasms / genetics
  • Cytochrome P-450 CYP1A1 / genetics
  • Cytochrome P-450 CYP1A1 / metabolism
  • Cytochrome P-450 CYP3A / genetics
  • Cytochrome P-450 CYP3A / metabolism
  • Estrogens / genetics
  • Estrogens / metabolism*
  • Female
  • Gene Expression Regulation
  • Histones / genetics
  • Histones / metabolism*
  • Humans
  • Male
  • Mutation, Missense
  • Nucleosomes / metabolism
  • Protein Domains
  • Tumor Suppressor Proteins / chemistry
  • Tumor Suppressor Proteins / genetics*
  • Tumor Suppressor Proteins / metabolism*
  • Ubiquitin-Protein Ligases / chemistry
  • Ubiquitin-Protein Ligases / genetics*
  • Ubiquitin-Protein Ligases / metabolism*
  • Ubiquitination


  • BRCA1 Protein
  • BRCA1 protein, human
  • Estrogens
  • Histones
  • Nucleosomes
  • Tumor Suppressor Proteins
  • CYP1A1 protein, human
  • Cytochrome P-450 CYP1A1
  • Cytochrome P-450 CYP3A
  • CYP3A4 protein, human
  • BARD1 protein, human
  • Ubiquitin-Protein Ligases