11-BETA-HYDROXYSTEROID DEHYDROGENASE TYPE 1 EXPRESSION IN 2S FAZA HEPATOMA CELLS IS HORMONALLY REGULATED - A MODEL SYSTEM FOR THE STUDY OF HEPATIC GLUCOCORTICOID METABOLISM

摘要

11 beta-Hydroxysteroid dehydrogenase (11 beta-HSD) is a key enzyme in glucocorticoid metabolism, catalysing the conversion of active glucocorticoids into their inactive 11-keto metabolites, thus regulating glucocorticoid access to intracellular receptors. The type 1 isoform (11 beta-HSD 1) (EC 1.1.1.146) is widely distributed, with particularly high levels in liver, where accumulating evidence suggests that it acts as an 11 beta-reductase, regenerating active glucocorticoids. Investigation of the function and regulation of 11 beta-HSD 1 in liver has been hampered by the lack of hepatic cell lines which express 11 beta-HSD 1. Here, we describe 11 beta-HSD 1 mRNA expression and activity in 2S FAZA cells, a continuously cultured rat liver cell line. In intact 2S FAZA cells 11 beta-HSD 1 acts predominantly as a reductase, with very low dehydrogenase activity. In 2S FAZA cells 11 beta-HSD 1 activity and mRNA expression are regulated by hormones, with dexamethasone increasing activity and insulin, forskolin and insulin-like growth factor 1 decreasing it. Transfection of 2S FAZA cells with a luciferase reporter gene driven by the proximal promoter of the rat 11 beta-HSD 1 gene demonstrates that sequences which can mediate the responses to insulin, dexamethasone and forskolin all lie within 1800 bp of the transcription start site.