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The Human Transient Receptor Potential Vanilloid Type 6 Distal Promoter Contains Multiple Vitamin D Receptor Binding Sites that Mediate Activation by 1,25-Dihydroxyvitamin D₃ in Intestinal Cells

Department of Biochemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706

Address all correspondence and requests for reprints to: J. Wesley Pike, Department of Biochemistry, University of Wisconsin-Madison, 433 Babcock Drive, Madison, Wisconsin 53706. E-mail: pike{at}biochem.wisc.edu.

Transient receptor potential vanilloid type 6 (TRPV6) (ECAC2, CaT1) is the major ion channel in intestinal epithelial cell membranes responsible for calcium entry. Its expression is actively regulated at the transcriptional level by 1,25-dihydroxyvitamin D₃ [1,25-(OH)₂D₃]. In this report, we identify mechanisms integral to the regulation of TRPV6 by 1,25-(OH)₂D₃. Based upon the hormonal responsiveness of a 7-kb TRPV6 promoter fragment in intestinal cell lines, we used a chromatin immunoprecipitation (ChIP) scanning method to search for possible vitamin D receptor (VDR) and retinoid X receptor (RXR) regulatory regions within the TRPV6 locus. VDR/RXR binding was broad, ranging from –1.2 to –5.5 kb relative to the start site of TRPV6 transcription. These results were consistent with an in silico analysis that revealed putative regulatory elements (VDREs) located at –1.2, –2.1, –3.5, –4.3, and –5.5 kb. Despite the ChIP analyses, only regions of the TRPV6 gene that contained putative elements at –2.1 and –4.3 kb transferred 1,25-(OH)₂D₃ response to a heterologous promoter. Further study revealed that each of these two active regions contained composite VDREs comprised of two separate regulatory elements. Mutagenesis of the VDREs within the –2.1- and –4.3-kb region and the VDRE at –1.2 kb abrogated all response to 1,25-(OH)₂D₃ when examined within the natural TRPV6 promoter. A final ChIP assay revealed that VDR/RXR heterodimer binding to the TRPV6 gene was accompanied by both the recruitment of steroid receptor coactivator 1 as well as a broad change in histone 4 acetylation. These studies identify a mechanism by which 1,25-(OH)₂D₃ regulates the expression of TRPV6 in human intestinal cells.

NURSA Molecule Pages Link:

Nuclear Receptors:   VDR  |  RXRα

Coregulators:   SRC-1  |  GRIP1  |  AIB1

Ligands:   Calcitriol