The broad objective of the proposed continuing research is to elucidate the molecular functions of the nuclear vitamin D receptor (VDR), which is known to cooperate with the retinoid X receptor (RXR) in order to mediate the actions of the vitamin D hormone (1,25(OH)2D3) to prevent rickets and osteopenia by effecting normal calcium and phosphate homeostasis. Effort for the requested renewal period will be concentrated on characterizing new roles for VDR that are postulated to be relevant to suppressing the promotion of colon cancer, and to facilitating normal hair cycling and skin cell integrity. Actions of VDR in colon and keratinocyte cells are hypothesized to be executed by novel VDR ligands that are structurally divergent from 1,25(OH)2D3. One of these, lithocholic acid, likely relevant in colon, is identified in preliminary data. The proposed hair follicle VDR ligand will be detected utilizing a cell-based reporter gene assay and characterized by HPLC purification and negative-ion nanoelectrospray mass spectrometry. Furthermore, the central hypothesis being tested is that several of the extraosseous (non-calcemic) functions of VDR are analogous to those of SXR (the human steroid and xenobiotic receptor, also referred to as PXR), and involve the sensing of xenobiotic lipids and their detoxification via the induction of cytochrome P450s (CYPs). Specifically, intestinal CYP3A4, as well as renal CYP24 and CYP3A23 gene expression will be investigated as VDR targets in cotransfected cultured cells.
A second Aim will be to extend the concepts of extraosseous VDR ligands and gene targets to the identification of unique VDR-interacting proteins (VIPs) at these sites, with candidates such as the hairless (Hr) gene product in skin. The characterization of VIPs will enhance our understanding of the biochemical mechanisms whereby VDR represses or induces the transcription of target genes in skin, and those encoding enzymes for the metabolism of xenobiotics. Cell- and CYP promoter-specific VIPs will be screened by employing the yeast two-hybrid system and CYP vitamin D responsive element-VDR-RXR differential affinity chromatography, respectively, with functional relevance verified by mammalian two-hybrid and chromatin immunoprecipitation (CHIP) assays.
The final Aim i s to probe the functional impact of common polymorphisms in the 5' and 3' regions of the human VDR gene on CYP induction and the non-calcemic actions of VDR. It is conceivable that VDR gene polymorphisms could influence the sensitivity of VDR to xenobiotic ligands that induce CYPs, as is the case for SXR/PXR. Therefore, by investigating novel VDR ligands, cell- and promoter-specific VIPs, and the role of common human VDR gene polymorphisms in terms of the affect of genotype on transcriptional activation phenotype, it should be possible to clarify the participation of this nuclear receptor in xenobiotic detoxification, as well as in the pathophysiology and treatment of abnormal hair cycling, and hyperproliferative diseases of epithelial cells.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
9R01DK063930-32
Application #
6572893
Study Section
Orthopedics and Musculoskeletal Study Section (ORTH)
Program Officer
Malozowski, Saul N
Project Start
1975-01-01
Project End
2007-12-31
Budget Start
2003-01-01
Budget End
2003-12-31
Support Year
32
Fiscal Year
2003
Total Cost
$378,750
Indirect Cost
Name
University of Arizona
Department
Biochemistry
Type
Schools of Medicine
DUNS #
806345617
City
Tucson
State
AZ
Country
United States
Zip Code
85721
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Haussler, Mark R; Haussler, Carol A; Whitfield, G Kerr et al. (2010) The nuclear vitamin D receptor controls the expression of genes encoding factors which feed the ""Fountain of Youth"" to mediate healthful aging. J Steroid Biochem Mol Biol 121:88-97
Hsieh, Jui-Cheng; Slater, Stephanie A; Whitfield, G Kerr et al. (2010) Analysis of hairless corepressor mutants to characterize molecular cooperation with the vitamin D receptor in promoting the mammalian hair cycle. J Cell Biochem 110:671-86
Haussler, Mark R; Haussler, Carol A; Bartik, Leonid et al. (2008) Vitamin D receptor: molecular signaling and actions of nutritional ligands in disease prevention. Nutr Rev 66:S98-112
Jurutka, Peter W; Bartik, Leonid; Whitfield, G Kerr et al. (2007) Vitamin D receptor: key roles in bone mineral pathophysiology, molecular mechanism of action, and novel nutritional ligands. J Bone Miner Res 22 Suppl 2:V2-10
Barthel, Thomas K; Mathern, Douglas R; Whitfield, G Kerr et al. (2007) 1,25-Dihydroxyvitamin D3/VDR-mediated induction of FGF23 as well as transcriptional control of other bone anabolic and catabolic genes that orchestrate the regulation of phosphate and calcium mineral metabolism. J Steroid Biochem Mol Biol 103:381-8
Jurutka, Peter W; Thompson, Paul D; Whitfield, G Kerr et al. (2005) Molecular and functional comparison of 1,25-dihydroxyvitamin D(3) and the novel vitamin D receptor ligand, lithocholic acid, in activating transcription of cytochrome P450 3A4. J Cell Biochem 94:917-43
Hsieh, Jui-Cheng; Whitfield, G Kerr; Jurutka, Peter W et al. (2003) Two basic amino acids C-terminal of the proximal box specify functional binding of the vitamin D receptor to its rat osteocalcin deoxyribonucleic acid-responsive element. Endocrinology 144:5065-80
Hsieh, Jui-Cheng; Sisk, Jeanne M; Jurutka, Peter W et al. (2003) Physical and functional interaction between the vitamin D receptor and hairless corepressor, two proteins required for hair cycling. J Biol Chem 278:38665-74