This application is a continuation of an ongoing investigation of the mechanisms by which analogs of 1,25-dihydroxyvitamin D3 (1,25D) modulate the transcriptional responses of the vitamin D receptor (VDR). The working hypothesis is that the contact points used by the hormone and analogs in the ligand-binding pocket are different and thereby are able to affect differentially the functional surface of the VDR. Because the surface of the ligand-binding domain of VDR provides an interface for interaction with dimerization partners, transcription coactivators, and corepressors, any subtle change in these interactions may alter the level and spectrum of VDR-mediated gene expression.
In Specific Aim 1, Dr. Peleg and her laboratory will complete the analysis of the ligand-binding pocket of the VDR by site-directed mutagenesis. They will define the site of hormone interaction through its 1-alpha-hydroxyl and 25-hydroxyl groups by comparing contact points used by the natural hormone and three types of ligands: 20-epi analogs, analogs with modified A ring and analogs with substitution of their 25-hydroxyl group.
In Specific Aim 2, they will determine the effect of differential ligand interaction on the functional surface of the VDR. Again, the use of the natural hormone and two groups of analogs will provide information on the differences and similarities of functional surfaces generated by superagonists (20-epi analogs) and by cell-specific noncalcemic agonists (the A ring-modified analogs). The three types of ligand-receptor complexes will be examined for their potency and efficacy to induce interaction with dimerization partners, coactivators, and corepressors. Using site-directed mutagenesis, the composition of surfaces created by each of these ligands will also be examined.
In Specific Aim 3, Dr. Peleg's laboratory will focus on the molecular and cellular mechanism of action of cell-specific analogs. They have identified A ring-modified analogs that have low calcemic activity in vivo, and a profound cell-segregated transcriptional profile in culture. VDR complexes with these analogs will be used as probes to isolate factors that augment or restrict receptor action in a given cellular environment. They will examine whether cell-specific action is due to loss of function by recruitment of a common corepressor, a gain of function due to overexpression of a common coactivator or recruitment of cell-specific factors. These studies will facilitate the development of selective vitamin D receptor modulators that may be useful for treatment of various clinical conditions, including osteoporosis, secondary hyperparathyroidism, and cancer.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Research Project (R01)
Project #
2R01DK050583-04
Application #
6130998
Study Section
General Medicine B Study Section (GMB)
Program Officer
Margolis, Ronald N
Project Start
1997-05-01
Project End
2004-04-30
Budget Start
2000-05-01
Budget End
2001-04-30
Support Year
4
Fiscal Year
2000
Total Cost
$240,660
Indirect Cost
Name
University of Texas MD Anderson Cancer Center
Department
Internal Medicine/Medicine
Type
Other Domestic Higher Education
DUNS #
001910777
City
Houston
State
TX
Country
United States
Zip Code
77030
Peleg, Sara; Nguyen, Cuong V (2010) The importance of nuclear import in protection of the vitamin D receptor from polyubiquitination and proteasome-mediated degradation. J Cell Biochem 110:926-34
Klopot, Anna; Hance, Kenneth W; Peleg, Sara et al. (2007) Nucleo-cytoplasmic cycling of the vitamin D receptor in the enterocyte-like cell line, Caco-2. J Cell Biochem 100:617-28
Marks, Hilary D; Fleet, James C; Peleg, Sara (2007) Transgenic expression of the human Vitamin D receptor (hVDR) in the duodenum of VDR-null mice attenuates the age-dependent decline in calcium absorption. J Steroid Biochem Mol Biol 103:513-6
Peleg, Sara; Khan, Farhana; Navone, Nora M et al. (2005) Inhibition of prostate cancer-meditated osteoblastic bone lesions by the low-calcemic analog 1alpha-hydroxymethyl-16-ene-26,27-bishomo-25-hydroxy vitamin D3. J Steroid Biochem Mol Biol 97:203-11
Phokela, Sarabjit S; Peleg, Sara; Moya, Fernando R et al. (2005) Regulation of human pulmonary surfactant protein gene expression by 1alpha,25-dihydroxyvitamin D3. Am J Physiol Lung Cell Mol Physiol 289:L617-26
Fizazi, Karim; Sikes, Charles R; Kim, Jeri et al. (2004) High efficacy of docetaxel with and without androgen deprivation and estramustine in preclinical models of advanced prostate cancer. Anticancer Res 24:2897-903
Kahraman, Mehmet; Sinishtaj, Sandra; Dolan, Patrick M et al. (2004) Potent, selective and low-calcemic inhibitors of CYP24 hydroxylase: 24-sulfoximine analogues of the hormone 1alpha,25-dihydroxyvitamin D(3). J Med Chem 47:6854-63
Posner, Gary H; Crawford, Kenneth R; Yang, Hong Woon et al. (2004) Potent, low-calcemic, selective inhibitors of CYP24 hydroxylase: 24-sulfone analogs of the hormone 1alpha,25-dihydroxyvitamin D3. J Steroid Biochem Mol Biol 89-90:5-12
Ismail, Ayesha; Nguyen, Cuong V; Ahene, Ago et al. (2004) Effect of cellular environment on the selective activation of the vitamin D receptor by 1alpha,25-dihydroxyvitamin D3 and its analog 1alpha-fluoro-16-ene-20-epi-23-ene-26,27-bishomo-25-hydroxyvitamin D3 (Ro-26-9228). Mol Endocrinol 18:874-87
Swamy, Narasimha; Chen, Tai C; Peleg, Sara et al. (2004) Inhibition of proliferation and induction of apoptosis by 25-hydroxyvitamin D3-3beta-(2)-Bromoacetate, a nontoxic and vitamin D receptor-alkylating analog of 25-hydroxyvitamin D3 in prostate cancer cells. Clin Cancer Res 10:8018-27

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