Nuclear localization of a glucocorticoid antagonist in cultured hepatoma cells

The binding characteristics of promegestone, a typical antagonist of glucocorticoid action, has been investigated. We localized 3H] promegestone in the nuclei purified from steroid-treated HTC cells but the radioactivity specifically bound to the nucleus was much lower for the antagonist than for an inducer steroid, for instance dexamethasone. We attempted to define the nature of the "nuclear" activity and found that promegestone does not bind to the perinuclear membrane but is associated with the chromatin fraction.