The regulation of transcriptional activity of vitamin D receptor in Caco-2 cells
Abstract
Intestinal calcium absorption is regulated by 1,25(OH)2D 3 through a vitamin D receptor-dependent genomic mechanism. Additional evidence indicates that VDR abundance does not always predict responsiveness of intestinal epithelium to 1,25(OH)2D3. Our study showed that compared to post-proliferating Caco-2 cultures proliferating cells have blunted transcriptional responsiveness to 1,25(OH)2D3 and that this is not associated with decreased VDR protein levels. Therefore, we used the spontaneous differentiation of Caco-2 cells as a natural condition to examine what factors may account for changes in efficiency of 1,25(OH) 2D3-stimulated VDR-mediated gene transcription in intestine epithelium. We hypothesized that transcriptional activity of VDR in intestine epithelium cells may be affected by cellular mobility of this transcription factor, as well as abundance and activity of various coregulatory proteins involved in this process. Our data showing the correlation between the ability of two VDR ligands: 1,25(OH)2D3 and 1-alpha-fluoro-16-ene-20-epi-23-ene-26,27-bishomo-25-hydroxyvitamin D3 (Ro-26-9228) to stimulate nuclear translocation of GFP-VDR and to induce CYP24A1 gene expression supports the hypothesis that VDR translocation is a critical component of VDR-mediated gene expression in intestine epithelium cells. However, we showed using confocal imaging that impaired 1,25(OH) 2D3-transcriptional activity is not due to a defect in nuclear translocation of VDR. Interestingly, we found that proliferating Caco-2 cells have impaired 1,25(OH)2D3-stimulated binding of VDR to the chromatin and lower levels of chromatin-associated RXRa compared to post-proliferating Caco-2 cells. Our data supports the hypothesis that blunted 1,25(OH)2D3-stimulated transcription in proliferating Caco-2 cells is due to impaired binding of VDR and RXR to DNA. Our additional analysis revealed that impaired 1,25(OH)2D3-transcription) activity in proliferating Caco-2 cells is not associated with either increased expression of corepressor or decreased expression of coactivators.
Degree
Ph.D.
Advisors
Fleet, Purdue University.
Subject Area
Nutrition
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