11-BETA-HYDROXYSTEROID DEHYDROGENASES OF THE CHORIOCARCINOMA CELL-LINE JEG-3 AND THEIR INHIBITION BY GLYCYRRHETINIC ACID AND OTHER NATURAL SUBSTANCES

Mineralocorticoid receptor (MR) selectivity for aldosterone is thought to be exerted by enzymes which inactivate competing glucocorticoids b efore they bind the receptor. Two different 11 beta-hydroxysteroid deh ydrogenases (11 beta-HSD) have been described. 11 beta-HSD-1 is NADP()-dependent and has a K-m in the micromolar range and bidirectional ac tivity. 11 beta-HSD-2 is NAD(+)-dependent, has a K-m in the nanomolar range, exhibits only oxidase activity, and colocalizes with the MR in the kidney, so is likely to serve as the gatekeeper for the MR. We hav e further characterized 11 beta-HSD activity in JEG-3 cells, a cell li ne derived from a human choriocarcinoma which was reported to have onl y the high affinity, NAD(+)-dependent 11 beta-HSB-2. we found that the K-m for the conversion of corticosterone to Il-dehydrocorticosterone in intact cells and homogenates was about 16 nM. NAD(+)-dependent cort icosterone conversion was equal in the nuclear and mitochondrial fract ions and less, but significant, in the microsomal fraction. A high aff inity K-m = 40 nM, NADP(+)-dependent enzyme was also found in homogena tes. The subcellular distribution of this high affinity activity was g reatest in the mitochondria, less in the nuclei, and even less, but st ill significant, in microsomes. Because of its cofactor dependency, hi gh affinity, and different subcellular distribution, we suggest that t his enzyme is neither the 11 beta-HSD-1 nor the 11 beta-HSD-2 and have named it 11 beta-HSD-3. Conversion of II-dehydrocorticosterone to cor ticosterone did not occur in intact cells or in homogenates incubated with NADH or NADPH. Enzyme activity in intact cells was inhibited by g lycyrrhetinic acid, carbenoxolone, progesterone, 5 beta-dihydroprogest erone, and 5 alpha-dihydroprogesterone, but not bile acids.