title: Novel regulation of 25-hydroxyvitamin D3 24-hydroxylase (24(OH)ase) transcription by glucocorticoids: cooperative effects of the glucocorticoid receptor, C/EBP beta, and the Vitamin D receptor in 24(OH)ase transcription.
abstract: Glucocorticoid-induced bone loss has been proposed to involve direct effects on bone cells as well as alterations in calcium absorption and excretion. Since vitamin D is important for the maintenance of calcium homeostasis, in the present study the effects of glucocorticoids on vitamin D metabolism through the expression of 24(OH)ase, an enzyme involved in the catabolism of 1,25(OH)(2)D(3), were examined. Injection of vitamin D replete mice with dexamethasone (dex) resulted in a significant induction in 24(OH)ase mRNA in kidney, indicating a regulatory effect of glucocorticoids on vitamin D metabolism. Whether glucocorticoids can affect 24(OH)ase transcription is not known. Here we demonstrate for the first time a glucocorticoid receptor (GR) dependent enhancement of 1,25(OH)(2)D(3)-induced 24(OH)ase transcription. Dex treatment of GR and vitamin D receptor (VDR) transfected COS-7 cells and dex treatment of osteoblastic cells (in which VDR and GR are present endogenously) potentiated 1,25(OH)(2)D(3)-induced 24(OH)ase transcription. In addition, GR was found to cooperate with C/EBP beta to enhance VDR-mediated 24(OH)ase transcription. Using the rat 24(OH)ase promoter with the C/EBP site mutated, GR-mediated potentiation of 1,25(OH)(2)D(3)-induced 24(OH)ase transcription was inhibited. Immunoprecipitation indicated that that GR can interact with C/EBP beta and ChIP/re-ChIP analysis showed that C/EBP beta and GR bind simultaneously to the 24(OH)ase promoter. These findings indicate a novel mechanism whereby glucocorticoids can alter VDR-mediated 24(OH)ase transcription through functional cooperation between C/EBP beta and GR that results in an enhanced ability of C/EBP beta to cooperate with VDR in the regulation of 24(OH)ase.
authors.affiliation: Department of Biochemistry and Molecular Biology, UMDNJ-New Jersey Medical School, Newark, New Jersey 07103, USA.
authors.forename: Puneet
authors.initials: P
authors.lastname: Dhawan
authors.forename: Sylvia
authors.initials: S
authors.lastname: Christakos
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015152:Blotting, Northern; D015153:Blotting, Western; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism; D019556:COS Cells; D045744:Cell Line, Tumor; D002522:Chlorocebus aethiops; D003907:Dexamethasone / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects*; D005938:Glucocorticoids / Q000494:pharmacology*; D007668:Kidney / Q000187:drug effects / Q000378:metabolism; D051379:Mice; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D018167:Receptors, Calcitriol / Q000235:genetics / Q000378:metabolism; D011965:Receptors, Glucocorticoid / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013250:Steroid Hydroxylases / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects*; D014162:Transfection; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D022782:CCAAT-Enhancer-Binding Protein-beta; D005938:Glucocorticoids; D018167:Receptors, Calcitriol; D011965:Receptors, Glucocorticoid; D003907:Dexamethasone; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase