Steroid specificity of the putative DHB receptor: evidence that the receptor is not 11betaHSD

Recently, we identified a novel putative nuclear receptor in colonic crypt cells distinct from both mineralocorticoid receptor and glucocorticoid receptor, with high affinity for 11-dehydrocorticosterone (11-DHB) (33). In the present study, competitive nuclear binding assays demonstrated that this site has a unique steroid binding specificity that distinguishes it from other steroid receptors. Western blot analysis showed the presence of 11beta-hydroxysteroid dehydrogenase-2 (11betaHSD2) but not 11betaHSD1 in colonic crypt cells and showed that 11betaHSD2 was present in the nuclear pellet. Differences in steroid specificity between the putative DHB receptor and inhibition of 11betaHSD activity indicate that binding is not to the enzyme. Furthermore, modified Chinese hamster ovary cells transfected with the 11betaHSD2 gene express nuclear 11betaHSD2 but not a nuclear DHB binding site. In conclusion, these data support the existence of a novel nuclear DHB receptor in rat colon that is distinct from the classic steroid receptors and from both 11betaHSD1 and 11betaHSD2.