HUMAN 11-BETA-HYDROXYSTEROID DEHYDROGENASE - STUDIES ON THE STABLY TRANSFECTED ISOFORMS AND LOCALIZATION OF THE TYPE-2 ISOZYME WITHIN RENALTISSUE

The type 1 and type 2 isoforms of human 11 beta-hydroxysteroid dehydro genase (11 beta;HSD) play a crucial role, respectively, in modulating glucocorticoid and mineralocorticoid hormone action. Deficiency of the 11 beta-HSD2 isoform, as described in the syndrome of apparent minera locorticoid excess and following liquorice (glycyrrhetinic acid) or ca rbenoxolone ingestion, results in hypertension in which cortisol acts as a potent mineralocorticoid. Several studies have addressed the effe cts of progesterone, glycyrrhetinic acid, and their derivatives on 11 beta-HSD activity, but these were largely undertaken before the charac terization of the 11 beta-HSD isoforms. The aim of this study was to e valuate the localization of 11 beta-HSD2 in human kidney and to study the effects of progesterone, glycyrrhetinic acid, and their related co mpounds on stable transfectants of the human 11 beta-HSD isoforms. Usi ng an in-house sheep antibody against human 11 beta-HSD2, immunoperoxi dase studies localized 11 beta-HSD2 to renal cortical and medullary co llecting ducts. Glomeruli, vascular structures, loops of Henle, and pr oximal tubules were all negative. Confocal laser microscopy studies in dicated both a cytoplasmic and nuclear localization for the enzyme wit hin renal collecting ducts. The nuclear staining, which was intranucle ar and was not associated with the nuclear membrane, accounted for 40% of the total cellular 11 beta-HSD2 immunoreactivity. Kinetic analysis of 11 beta-HSD activity in fetal kidney 293 cells stably transfected with h11 beta-HSD1/pcDNA3 or 11 beta-HSD2/pCR3, indicated, respectivel y, low-affinity dehydrogenase/oxoreductase activity (K-m for F, 1.8 mu M; K-m for E, 270 nM) and high-affinity dehydrogenase activity (K-m f or F, 190 nM). The reductase activity of 11 beta-HSD1 was inhibited by 11 alpha-hydroxyprogesterone > carbenoxolone = glycyrrhetinic acid = progesterone > 11 beta-hydroxyprogesterone. The dehydrogenase activity of 11 beta-HSD2 was inhibited 11 alpha-hydroxyprogesterone = 11 beta- hydroxyprogesterone > glycyrrhetinic acid > carbenoxolone = progestero ne. 11 beta-HSD2, expressed in the renal collecting duct, serves to pr otect the mineralocorticoid receptor (MR) in an autocrine fashion. The demonstration of a nuclear localization for what was thought to be pr incipally a microsomal enzyme suggests that interaction between the MR and its ligand (either aldosterone or cortisol) may be a nuclear rath er than a cytoplasmic event. The inhibitory effects of progesterone, g lycyrrhetinic acid, and related compounds on 11 beta-HSD1 and 2 were s imilar, and it remains to be seen what implication these findings have for 11 beta-HSD1 action in tissues such as the liver and gonad and re nal 11 beta-HSD2 activity in relation to sodium homeostasis and blood pressure control. (C) 1997 by Elsevier Science Inc.