Characterization of 25-hydroxyvitamin D binding protein from intestinal cells.
We have previously purified a cytosolic vitamin D metabolite binding protein (cDBP) from rat enterocytes, which has characteristics distinct from other vitamin D binding proteins. In these studies, we demonstrate that cDBP in a semi-purified fraction from human intestinal cells (Caco-2 cells) binds 25-hydroxyvitamin D (25OHD) with at least a 1000-fold greater affinity than 1, 25-dihydroxyvitamin D (1,25(OH)(2)D) or 24,25-dihydroxyvitamin D. Treatment of cells with 1,25(OH)(2)D reduced 25OHD binding to approximately one third that of the untreated cells (0.42 CPM/mg total protein vs 1.34 CPM/mg total protein, respectively). Finally, the cDBP is not immunoreactive to antibodies prepared against the C-terminus of the nuclear vitamin D receptor (VDR). In summary, cDBP bound 25OHD with greater affinity than either 1,25(OH)(2)D or 24,25 dihydroxyvitamin D, the cytosolic binding activity was down-regulated by 1,25(OH)(2)D and cBDP is distinct from the nuclear VDR.
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Department of Foods and Nutrition, Purdue University, West Lafayette, Indiana 47907, USA. Teegarden@CFS.purdue.edu
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D015650:24,25-Dihydroxyvitamin D 3 / Q000378:metabolism; D000906:Antibodies / Q000276:immunology; D018938:Caco-2 Cells; D003600:Cytosol / Q000737:chemistry; D015536:Down-Regulation / Q000187:drug effects; D006801:Humans; D009687:Nuclear Proteins / Q000276:immunology; D011485:Protein Binding / Q000187:drug effects; D018167:Receptors, Calcitriol / Q000276:immunology; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000378:metabolism* / Q000494:pharmacology; D014809:Vitamin D-Binding Protein / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*
D000906:Antibodies; D009687:Nuclear Proteins; D018167:Receptors, Calcitriol; D014809:Vitamin D-Binding Protein; D014807:Vitamin D; D015650:24,25-Dihydroxyvitamin D 3; C097949:1,25-dihydroxyvitamin D; C104450:25-hydroxyvitamin D