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Abstract

Protein kinase C increases 11β-hydroxysteroid dehydrogenase oxidation and inhibits reduction in rat Leydig cells (PDF) (HTML) 
Ge,Renshan; Hardy,Matthew P.
Journal of Andrology 23(1): 135-143
Publication date: 2002

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Glucocorticoid hormone controls Leydig cell steroidogenic function througha receptor-mediated mechanism. The enzyme 11beta-hydroxysteroiddehydrogenase (11betaHSD) plays an important role in Leydig cells bymetabolizing glucocorticoids, and catalyzing the interconversion ofcorticosterone (the active form in rodents) and 11-dehydrocorticosterone(the biologically inert form). The net direction of this interconversiondetermines the amount of biologically active ligand, corticosterone,available for glucocorticoid receptor binding. We hypothesize that11betaHSD oxidative and reductive activities are controlled separately inLeydig cells, and that shifts in the favored direction of 11betaHSDcatalysis provide a mechanism for the control of intracellularcorticosterone levels. Therefore, in the present study, we tested thedependency of 11betaHSD oxidative and reductive activities on proteinkinase C (PKC) and calcium-dependent signaling pathways. 11betaHSDoxidative and reductive activities were measured in freshly isolated intactrat Leydig cells using 25 nM radiolabeled substrates after treatment withprotein kinase modulators. We found that PKC and calcium-dependentsignaling had opposing effects on 11betaHSD oxidative and reductiveactivities. Stimulation of PKC using the PKC activator,6-[N-decylamino]-4-hydroxymethylinole (DHI), increased 11betaHSD oxidativeactivity from a conversion rate of 5.08% to 48.23% with an EC50 of 1.70 +/-0.44 microM (mean +/- SEM), and inhibited reductive activity from 26.90% to3.66% conversion with an IC50 of 0.22 +/- 0.05 microM. This indicated thatPKC activation in Leydig cells favors 11betaHSD oxidation and lower levelsof corticosterone. The action of DHI was abolished by the PKC inhibitorbisindolylmaleimide I. In contrast, addition of calcium to Leydig cellsincreased 11betaHSD reductive activity while decreasing oxidative activity,thereby favoring reduction and conversion of inert 11-dehydrocorticosteroneinto active corticosterone. The opposite effect was seen after eliminationof calcium-dependent signaling, including removal of calcium by EGTA oraddition of the calmodulin (calcium binding protein) inhibitor SKF7171A, orthe calcium/calmodulin-dependent protein kinase I (CaMK II) inhibitor,KN62. We conclude that 11betaHSD oxidative and reductive activities areseparately regulated and that, in contrast to calcium-dependent signaling,PKC stimulates 11betaHSD oxidation while inhibiting 11betaHSD reduction.Maintenance of a predominantly oxidative 11betaHSD could serve to eliminateadverse glucocorticoid-induced action in Leydig cells.

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