CLONING OF CDNA-ENCODING AN NAD(-DEPENDENT ISOFORM OF 11-BETA-HYDROXYSTEROID DEHYDROGENASE IN SHEEP KIDNEY())

11 beta-Hydroxysteroid dehydrogenase (11-HSD) catalyzes the conversion of cortisol to cortisone and corticosterone to 11-dehydrocorticostero ne. This activity may be required to confer normal ligand specificity upon the mineralocorticoid receptor. Although an isozyme of 11-HSD was previously isolated from rat liver, a different isozyme is apparently expressed in mineralocorticoid target tissues. We isolated a sheep ki dney cDNA clone encoding this isozyme by expression screening using Xe nopus oocytes. The cDNA is 1.8 kb in length and encodes a protein of 4 27 amino acid residues with a predicted M(r) of 46,700. When expressed in oocytes, this enzyme functions as an NAD(+)-dependent 11 beta-dehy drogenase with very high affinity for steroids, but it has no detectab le reductase activity. It is 37% identical in amino acid sequence to a n NAD(+)-dependent isozyme of 17 beta-hydroxysteroid dehydrogenase, bu t only 20% identical to the NADP(+)-dependent liver isozyme of 11-HSD. It is expressed at high levels in the kidney and adrenal and at lower levels in the colon. The corresponding gene is present in a single co py in the sheep genome. In humans, this gene is a candidate locus for the syndrome of apparent mineralocorticoid excess, a form of hypertens ion postulated to result from 11-HSD deficiency in mineralocorticoid t arget tissues.