Antiprogestin-receptor complexes: Differences in the interaction of the antiprogestin RU38,486 and the progestin R5020 with the progesterone receptor of human breast cancer cells

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In order to understand the molecular basis for antiprogestin action, we have compared the interaction of the antiprogestin [3H]RU38,486 (RU486) and the progestin [3H]R5020 with the progesterone receptor (PR). In both MCF-7 and T47D human breast cancer cells, we have observed marked differences in the sedimentation properties of the PR on high salt sucrose gradients: while the R5020-receptor complexes sediment at approximately 4 S (4.4±0.1 S), the RU486-receptor sediments as a prominent 6 S species as well as a 4 S species. This binding is abolished by excess unlabelled R5020, RU486 or progesterone, but is unaffected by excess unlabelled hydrocortisone or dexamethasone, indicating that both the 4 S and 6 S species represent the PR and not glucocorticoid receptor. Although the relative distribution of 4 S and 6 S forms is not altered by treatment with DNAse or RNAse, exposure to 10 mM thioglycerol or to 3 M urea results in conversion of the 6 S to the 4 S form, suggesting that disulfide bonds and hydrophobic interactions are important in maintaining the integrity of the 6 S form. These findings suggest that the 6 S antiprogestin complex is formed as a result of the interaction of PR units with each other or with a different protein. This change in receptor association state may be an important aspect of the antiprogestin activity of RU486.

Original languageEnglish (US)
Pages (from-to)90-97
Number of pages8
JournalBiochemical and Biophysical Research Communications
Issue number1
StatePublished - Feb 26 1986


ASJC Scopus subject areas

  • Biophysics
  • Biochemistry
  • Molecular Biology
  • Cell Biology

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