'Liver-type' 11 beta-hydroxysteroid dehydrogenase cDNA encodes reductase but not dehydrogenase activity in intact mammalian COS-7 cells.
11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) catalyses the metabolism of corticosterone to inert 11-dehydrocorticosterone, thus preventing glucocorticoid access to otherwise non-selective renal mineralocorticoid receptors (MRs), producing aldosterone selectivity in vivo. At least two isoforms of 11 beta-HSD exist. One isoform (11 beta-HSD1) has been purified from rat liver and an encoding cDNA cloned from a rat liver library. Transfection of rat 11 beta-HSD1 cDNA into amphibian cells with a mineralocorticoid phenotype encodes 11 beta-reductase activity (activation of inert 11-dehydrocorticosterone) suggesting that 11 beta-HSD1 does not have the necessary properties to protect renal MRs from exposure to glucocorticoids. This function is likely to reside in a second 11 beta-HSD isoform. 11 beta-HSD1 is co-localized with glucocorticoid receptors (GRs) and may modulate glucocorticoid access to this receptor type. To examine the predominant direction of 11 beta-HSD1 activity in intact mammalian cells, and the possible role of 11 beta-HSD in regulating glucocorticoid access to GRs, we transfected rat 11 beta-HSD1 cDNA into a mammalian kidney-derived cell system (COS-7) which has little endogenous 11 beta-HSD activity or mRNA expression. Homogenates of COS-7 cells transfected with increasing amounts of 11 beta-HSD cDNA exhibited a dose-related increase in 11 beta-dehydrogenase activity. In contrast, intact cells did not convert corticosterone to 11-dehydrocorticosterone over 24 h, but showed a clear dose-related 11 beta-reductase activity, apparent within 4 h of addition of 11-dehydrocorticosterone to the medium.(ABSTRACT TRUNCATED AT 250 WORDS)
University of Edinburgh Department of Medicine, Western General Hospital, UK.
S C
SC
Low
K E
KE
Chapman
C R
CR
Edwards
J R
JR
Seckl
D042842:11-beta-Hydroxysteroid Dehydrogenases; D000818:Animals; D002460:Cell Line; D003345:Corticosterone / Q000031:analogs & derivatives / Q000494:pharmacology; D018076:DNA, Complementary / Q000235:genetics*; D003907:Dexamethasone / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D017930:Genes, Reporter; D005822:Genetic Vectors; D006913:Hydroxysteroid Dehydrogenases / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D008156:Luciferases / Q000235:genetics; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics; D051381:Rats; D011965:Receptors, Glucocorticoid / Q000235:genetics; D014162:Transfection
D018076:DNA, Complementary; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D006913:Hydroxysteroid Dehydrogenases; D042842:11-beta-Hydroxysteroid Dehydrogenases; D008156:Luciferases; C003552:11-dehydrocorticosterone; D003345:Corticosterone