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 11β-hydroxysteroid dehydrogenase-2 (11βHSD2) but not 11βHSD1 in colonic crypt cells and showed that 11βHSD2 was present in the nuclear pellet. Differences in steroid specificity between the putative DHB receptor and inhibition of 11βHSD activity indicate that binding is not to the enzyme. Furthermore, modified Chinese hamster ovary cells transfected with the 11βHSD2 gene express nuclear 11βHSD2 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 11βHSD1 and 11βHSD2.
ISOLATION OF APICAL MEMBRANES FROM HORMONE-SENSITIVE RAT COLONIC CRYPT CELLS
