title: Regulation of the procine 1,25-dihydroxyvitamin D3-24-hydroxylase (CYP24) by 1,25-dihydroxyvitamin D3 and parathyroid hormone in AOK-B50 cells.
abstract: The 24-hydroxylase is the enzyme responsible for the first step in the catabolism of 1,25-dihydroxyvitamin D3, the active form of vitamin D. This enzyme was shown to be upregulated by 1,25-dihydroxyvitamin D3 itself and downregulated by parathyroid hormone (PTH). Upregulation of 24-hydroxylase by 1,25-dihydroxyvitamin D3 has been characterized; however, the mechanism by which PTH acts to downregulate 24-hydroxylase expression remains unknown. Here we report the cloning of the porcine 24-hydroxylase, and show that 1,25-dihydroxyvitamin D3-stimulated 24-hydroxylase mRNA and activity are repressed by PTH in AOK-B50 cells, a porcine kidney proximal tubule cell line with stably transfected opossum PTH receptors. Forskolin mimicked the effects of PTH consistent with in vivo data, and suppression by PTH was not due to changes in VDR levels. The first 1400 bp of the 24-hydroxylase promoter were not able to mediate the effects of PTH on a reporter gene. In view of the above findings we concluded that AOK-B50 cells are a suitable model for further studying the mechanism of action of PTH on 24-hydroxylase mRNA.
authors.affiliation: College of Agricultural and Life Sciences, Department of Biochemistry, University of Wisconsin-Madison, 53706, USA.
authors.forename: C
authors.initials: C
authors.lastname: Zierold
authors.forename: G G
authors.initials: GG
authors.lastname: Reinholz
authors.forename: J A
authors.initials: JA
authors.lastname: Mings
authors.forename: J M
authors.initials: JM
authors.lastname: Prahl
authors.forename: H F
authors.initials: HF
authors.lastname: DeLuca
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002117:Calcitriol / Q000494:pharmacology*; D002460:Cell Line; D003001:Cloning, Molecular; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics / Q000378:metabolism*; D017931:DNA Primers / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000201:enzymology; D008969:Molecular Sequence Data; D009893:Opossums; D010281:Parathyroid Hormone / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018167:Receptors, Calcitriol / Q000378:metabolism; D018016:Receptors, Parathyroid Hormone / Q000235:genetics / Q000378:metabolism; D013250:Steroid Hydroxylases / Q000235:genetics / Q000378:metabolism*; D013552:Swine; D014162:Transfection; D065668:Vitamin D3 24-Hydroxylase
chemical_list: D017931:DNA Primers; D018076:DNA, Complementary; D010281:Parathyroid Hormone; D012333:RNA, Messenger; D018167:Receptors, Calcitriol; D018016:Receptors, Parathyroid Hormone; D003577:Cytochrome P-450 Enzyme System; D013250:Steroid Hydroxylases; D065668:Vitamin D3 24-Hydroxylase; D002117:Calcitriol