The goal of this project is to characterize the molecular mechanism of action of the renal vitamin D hormone, 1,25-dihydroxyvitamin D3 (1,25(OH)2D3), in regulating bone mineral ions to prevent diseases such as rickets/osteomalacia and osteoporosis. The hypothesis to be tested is that 1,25(OH)2D3 exerts its actions to support the mineralized skeleton via liganding of the nuclear vitamin D receptor (VDR), which in turn recruits its retinoid X receptor (RXR)heterodimeric partner to recognize vitamin D responsive elements (VDREs) in bone relevant target gene promoters, with 1,25(OH)2D3-VDR-RXR attracting comodulator protein/enzyme complexes that either repress or induce DNA transcription by chromatin remodeling and linkage to RNA polymerase II. Cultured 1,25(OH)2D3target cells will be used as model systems for Specific Aims designed to elucidate the VDR-mediated events in signaling by 1,25(OH)2D3.
Aim 1 will determine if 1,25(OH)2D3-VDR modulates osteoblast development/bone formation by impacting the Wnt/LRP5/p-catenin and BMP/SMAD/Runx2 signal cascades, and possibly limits bone overmineralization by controlling a newly recognized phosphate regulatory system, FGF23 and PHEX, in osteoblasts.
Aim 2 will probe the role of 1,25(OH)2D3-VDR to stimulate calcium and phosphate translocation in small intestine and kidney through the enhanced expression of epithelial calcium transporter 1 (TRPV6) and sodium-phosphate cotransporter 2c (Npt2c), respectively. Methodology will include genomics and chromatin immunoprecipitation (ChIP) assays to scan for candidate VDREs, plus DNA gel mobility shift, real time PCR and promoter dissection to identify VDR-controlled genes. Comparing 1,25(OH)2D3 to its superactive analogs, ChIP assays will assess intact cell VDR-RXR-VDRE binding and characterize the sequential recruitment of transcriptional comodulators that differentially control the expression of bone mineral target genes. Finally, in Aim 3 ChIP display will be used to reveal novel upstream VDR-controlled genes should any of the proposed VDR targets emerge as secondarily or tertiarily induced/repressed via mediating transfactors. The significance of the proposed studies is that the precise molecular mechanisms whereby 1,25(OH)2D3 maintains proper bone mineralization, as well as the relative importance of novel vitamin D-regulated genes expressed in bone (Aim 1) and small intestine and kidney (Aim 2), are not understood; comprehending these pathways should enhance our ability to develop vitamin D mimetics to prevent and treat osteopenic disorders. Thus, despite the recognized relevance of vitamin D in promoting calcium absorption and bone remodeling to preclude the development of osteoporosis and resulting fractures of the spine, hip and wrist, the manner through which the vitamin D hormone accomplishes this beneficial effect has not been fully elucidated. Defining the molecular pathway of vitamin D action to enhance and preserve the mineralized skeleton may not only reveal new therapeutic strategies to prevent and treat osteoporosis with bone anabolic 1,25(OH)2D3 analogs, but could also shed light on the novel anticancer effects of vitamin D at sites such as the colon, skin, breast and

National Institute of Health (NIH)
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Research Project (R01)
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Skeletal Biology Structure and Regeneration Study Section (SBSR)
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Malozowski, Saul N
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University of Arizona
Other Basic Sciences
Schools of Medicine
United States
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Sabir, Marya S; Haussler, Mark R; Mallick, Sanchita et al. (2018) Optimal vitamin D spurs serotonin: 1,25-dihydroxyvitamin D represses serotonin reuptake transport (SERT) and degradation (MAO-A) gene expression in cultured rat serotonergic neuronal cell lines. Genes Nutr 13:19
Karrys, Amitis; Rady, Islam; Chamcheu, Roxane-Cherille N et al. (2018) Bioactive Dietary VDR Ligands Regulate Genes Encoding Biomarkers of Skin Repair That Are Associated with Risk for Psoriasis. Nutrients 10:
Sabir, Marya S; Khan, Zainab; Hu, Chengcheng et al. (2017) SIRT1 enzymatically potentiates 1,25-dihydroxyvitamin D3 signaling via vitamin D receptor deacetylation. J Steroid Biochem Mol Biol 172:117-129
Haussler, Mark R; Whitfield, G Kerr; Haussler, Carol A et al. (2016) 1,25-Dihydroxyvitamin D and Klotho: A Tale of Two Renal Hormones Coming of Age. Vitam Horm 100:165-230
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Hsieh, Jui-Cheng; Estess, Rudolf C; Kaneko, Ichiro et al. (2014) Vitamin D receptor-mediated control of Soggy, Wise, and Hairless gene expression in keratinocytes. J Endocrinol 220:165-78
Austin, Heather R; Hoss, Elika; Batie, Shane F et al. (2014) Regulation of late cornified envelope genes relevant to psoriasis risk by plant-derived cyanidin. Biochem Biophys Res Commun 443:1275-9
Saini, Rimpi K; Kaneko, Ichiro; Jurutka, Peter W et al. (2013) 1,25-dihydroxyvitamin D(3) regulation of fibroblast growth factor-23 expression in bone cells: evidence for primary and secondary mechanisms modulated by leptin and interleukin-6. Calcif Tissue Int 92:339-53
Hoss, Elika; Austin, Heather R; Batie, Shane F et al. (2013) Control of late cornified envelope genes relevant to psoriasis risk: upregulation by 1,25-dihydroxyvitamin D3 and plant-derived delphinidin. Arch Dermatol Res 305:867-78

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