Regulation of 25-hydroxyvitamin D3-24-hydroxylase mRNA by 1,25-dihydroxyvitamin D3 and parathyroid hormone

• Published in: Journal of cellular biochemistry Vol. 88; no. 2; pp. 234 - 237
• Main Authors: Zierold, Claudia, Mings, Jamie A., DeLuca, Hector F.
• Format: Journal Article
• Language: English
• Published: New York Wiley Subscription Services, Inc., A Wiley Company 01.02.2003
• Subjects: actinomycin D; Animals; AOK-B50; cycloheximide; Cytochrome P-450 Enzyme System - genetics; Cytochrome P-450 Enzyme System - metabolism; Gene Expression Regulation, Enzymologic; Half-Life; Humans; Parathyroid Hormone - genetics; Parathyroid Hormone - metabolism; Parathyroid Hormone - pharmacology; RNA, Messenger - metabolism; Steroid Hydroxylases - genetics; Steroid Hydroxylases - metabolism; Transcription Factors - genetics; Transcription, Genetic; Vitamin D - analogs & derivatives; Vitamin D - genetics; Vitamin D - metabolism; Vitamin D - pharmacology; vitamin D receptor; Vitamin D3 24-Hydroxylase
• ISSN: 0730-2312; 1097-4644
• DOI: 10.1002/jcb.10341

The 25‐hydroxyvitamin D3‐24‐hydroxylase mRNA is tightly and reciprocally regulated by 1,25‐dihydroxyvitamin D3 (1,25(OH)2D3) and parathyroid hormone (PTH). The upregulation of the 24‐hydroxylase by 1,25(OH)2D3 is well established and occurs at the transcriptional level through two vitamin D response elements in the promoter of the gene. However, this induction is blocked by the protein synthesis inhibitor cycloheximide (CHX) indicating a protein component in the regulation pathway. CHX treatment reduced total vitamin D receptor (VDR) protein levels in cells, but reintroduction of VDR and/or retinoid X receptor protein into cells by transfection did not reduce the inhibition by CHX. This indicates that production of another transcription factor or mRNA‐stabilizing protein synthesized in response to 1,25(OH)2D3 is required for optimal accumulation of 24‐hydroxylase mRNA. PTH downregulates the 24‐hydroxylase mRNA by affecting its stability. The half‐life of 24‐hydroxylase mRNA is reduced 4.2‐fold in AOK‐B50 cells by PTH. Untranslated regions of the 24‐hydroxylase mRNA in reporter gene assays did not confer PTH responsiveness. Further analysis of the coding region of the rat 24‐hydroxylase may reveal sites of action of PTH. J. Cell. Biochem. 88: 234–237, 2003. © 2002 Wiley‐Liss, Inc.