title: Regulation of 1,25-dihydroxyvitamin d synthesis by intracellular vitamin d binding protein-1.
abstract: Control of 125-dihydroxyvitamin D (1,25-(OH)2D) synthesis is believed to be primarily at the level of expression of the vitamin D-1-hydroxylase (CYP1alpha; CYP1alpha) gene. Once transcribed, generation of product, as catalyzed by 1-hydroxylase, depends upon the availability of various co-factors, molecular oxygen, electrons as well as substrate to the enzyme. Here we provide evidence that the quantity of product 1,25-(OH)2D generated also relies on the presence and level of expression of the intracellular vitamin D binding protein-1 (IDBP-1) and its capacity to promote 24-hydroxylase (CYP24) gene expression. Stable transfection of the IDBP-1 cDNA increased 1,25-(OH)2D synthesis up to 700% (p < 0.001) in cells devoid of 24-hydroxylating potential but only 70% (p = 0.018) in cells in which the CYP24 gene is expressed. IDBP-1-mediated increase in 1,25-(OH)2D production was independent of any change in CYP1alpha expression but highly dependent on the ability of exogenously-added or endogenously-synthesized 1,25-(OH)2D to stimulate CYP24 gene expression. These data suggest that IDBP-1 is capable of controlling 1,25-(OH)2D production by modulating the delivery of 1) substrate 25-OHD to in the mitochondrial CYP1alpha gene product and 2) CYP1alpha product 1,25-(OH)2D to the vitamin D receptor for upregulation of expression of the catabolic CYP24 gene.
authors.affiliation: Division of Endocrinology, Diabetes and Metabolism, Department of Medicine, Cedars-Sinai Medical Center, UCLA School of Medicine, 90048, USA.
authors.forename: Shaoxing
authors.initials: S
authors.lastname: Wu
authors.forename: Rene
authors.initials: R
authors.lastname: Chun
authors.forename: Mercedes A
authors.initials: MA
authors.lastname: Gacad
authors.forename: Songyang
authors.initials: S
authors.lastname: Ren
authors.forename: Hong
authors.initials: H
authors.lastname: Chen
authors.forename: John S
authors.initials: JS
authors.lastname: Adams
mesh_terms: D000818:Animals; D019556:COS Cells; D002352:Carrier Proteins / Q000502:physiology*; D006900:Hydroxylation / Q000187:drug effects; D007425:Intracellular Membranes / Q000378:metabolism*; D013250:Steroid Hydroxylases / Q000378:metabolism / Q000494:pharmacology; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000096:biosynthesis* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D002352:Carrier Proteins; C417526:vitamin D binding protein 1, primate; D014807:Vitamin D; C097949:1,25-dihydroxyvitamin D; D013250:Steroid Hydroxylases; C406322:vitamin D 1-alpha hydroxylase