Specific nuclear localization of 11-dehydrocorticosterone in rat colon: evidence for a novel corticosteroid receptor

When colonic crypt cells isolated from intact rats are incubated with [3H]corticosterone specific nuclear binding is displaced by neither aldosterone nor the antiglucocorticoid RU38486, suggesting that [3H]corticosterone is binding to a site distinct from classical mineralocorticoid and glucocorticoid receptors. TLC revealed that the predominant nuclear [3H]steroid in the nucleus of [3H]corticosterone-incubated colonic crypt cells is [3H]11-dehydrocorticosterone. Where the enzyme 11 beta-hydroxysteroid dehydrogenase converting corticosterone to 11-dehydrocorticosterone is absent (cytosol preparations), [3H]corticosterone binds to classical glucocorticoid and mineralocorticoid receptors; in whole cells when 11 beta-hydroxysteroid dehydrogenase is blocked by carbenoxolone, cytoplasmic and nuclear binding of authentic [3H]corticosterone rises. Saturation and Scatchard analyses of nuclear [3H]11-dehydrocorticosterone binding demonstrate a single saturable binding site with a dissociation constant of < or = 10 nM at 22 C. We interpret these studies as evidence for a novel 11-dehydrocorticosterone-preferring receptor that may mediate glucocorticoid effects in tissues with high level of 11 beta-hydroxysteroid dehydrogenase activity.