Cross-linking of estrogen receptor to chromatin in intact MFC-7 human breast cancer cells: Optimization and effect of ligand

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To investigate the effect of ligand (be it hormone, antihormone, or no hormone) on the interaction between estrogen receptor (ER) and chromatin, we have used formaldehyde as a cross-linking agent in intact MCF-7 human breast cancer cells. After a 1-to 2-h hormone treatment, the cells are exposed for 8 min to formaldehyde, which is added directly to their culture medium to minimize environmental perturbation. Nuclei are prepared from formaldehyde-treated cells and their contents are fractionated on CsCI density gradients to separate DNA-protein complexes from free protein. Peak gradient fractions are assayed for the presence of specific proteins by immunoblot of sodium dodecyl sulfate-polyacrylamide gel patterns. Using this approach, we find that 0.15% formaldehyde is optimal for cross-linking ER to chromatin. We detect ER and the large subunit of RNA polymerase II with DNA from formaldehyde-treated, but not from untreated cells. On the other hand, actin (a cytoplasmic protein) and small nuclear ribonucleoprotein particle proteins (nuclear RNA binding proteins) are not cross-linked to DNA. Therefore, cross-linking appears to be selective and fractionation is efficient. Interestingly, we detect similar levels of ER (as well as RNA polymerase II) with DNA from formaldehyde-treated cells, regardless of whether the cells are preexposed to estrogen (17β-estradiol at 10-8 m), antiestrogen (IC1164,384 at 10-7 or 10-6 m), or no hormone. These results, using covalent cross-linking in intact cells, indicate that both ligand-occupied and unoccupied ER are associated with chromatin.

Original languageEnglish (US)
Pages (from-to)1647-1654
Number of pages8
JournalMolecular Endocrinology
Issue number11
StatePublished - Nov 1990

ASJC Scopus subject areas

  • Molecular Biology
  • Endocrinology


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