20β-hydroxysteroid dehydrogenase gene promoter: Potential role for cyclic AMP and xenobiotic responsive elements

Teleostean 20 beta-hydroxysteroid dehydrogenase (20 beta-HSD) is involved in final oocyte maturation and steroid hormone metabolism. It has structural and functional similarities to mammalian carbonyl reductases that are involved in the metabolism of endogenous carbonyl and xenobiotic compounds. To understand the transcriptional regulation of 20 beta-HSD, here we report the cloning of 20 beta-HSD promoter from two fish species, rainbow trout and air-breathing catfish. Analysis of the promoter motifs, in silico identified the presence of several sites for transcription factor binding including cAMP, xenobiotic and steroid hormone responsive elements. Luciferase reporter assays with progressive deletion constructs demonstrated that 20 beta-HSD type B of trout has no promoter activity while 20 beta-HSD type A of trout and catfish 20 beta-HSD promoters showed basal promoter activity. A TATA box flanked by a CAAT box is important for basal transcription. Deletion of cAMP responsive element in the promoter decreased basal promoter activity significantly. Reporter assays with forskolin and IBMX, drugs that increase intracellular cAMP induced the promoter activity over the basal level. Intriguingly, beta-nafthoflavone, an arylhydrocarbon receptor ligand, induced the 20 beta-HSD promoter activity and is further evidenced by the induction of 20 beta-HSD expression in the livers of catfish, in vivo. These results demonstrate for the first time that 20 beta-HSD expression is not only modulated by cAMP but also by xenobiotics and further studies may provide significance to the ubiquitous distribution and broad substrate specificity of this enzyme. (C) 2012 Elsevier B.V. All rights reserved.