Perspectives on mechanisms of gene regulation by 1,25-dihydroxyvitamin D3 and its receptor

Abstract

1, (1,25(OH) 2 D 3 ) functions as a systemic signal in vertebrate organisms to control the expression of genes whose products are vital to the maintenance of calcium and phosphorus homeostasis. This regulatory capability is mediated by the vitamin D receptor (VDR) which localizes at DNA sites adjacent to the promoter regions of target genes and initiates the complex events necessary for transcriptional modulation. Recent investigations using chromatin immunoprecipitation techniques combined with various gene scanning methodologies have revealed new insights into the location, structure and function of these regulatory regions. In the studies reported here, we utilized the above techniques to identify key enhancer regions that mediate the actions of vitamin D on the calcium ion channel gene TRPV6, the catabolic calcium-mobilizing factor gene RankL and the anabolic Wnt signaling pathway co-receptor gene LRP5. We also resolve the mechanism whereby 1,25(OH) 2 D 3 autoregulates the expression of its own receptor. The results identify new features of vitamin D-regulated enhancers, including their locations at gene loci, the structure of the VDR binding sites located within, their modular nature and their functional activity. Our studies suggest that vitamin D enhancers regulate the expression of key target genes by facilitating the recruitment of both the basal transcriptional machinery as well as the protein complexes necessary for altered gene expression. KeywordsChIP scanning; ChIP-chip scanning; enhancer modules; VDR/RXR DNA binding; distal transcriptional regulation; chromatin looping; histone acetylation; RNA polymerase II recruitment Introductory backgroundTwo sequential hydroxylations of vitamin D 3 in the liver and kidney lead to the formation of 1,25-dihydroxyvitamin D 3 (1,25(OH) 2 D 3 ), a hormone whose primary function is to control mineral homeostasis in higher organisms [1]. Like other hormones in this class, the biological effects of 1,25(OH) 2 D 3 are achieved through the regulation of gene expression [2]. These activities are mediated by the vitamin D receptor (VDR), a member of the steroid receptor family of genes that control the diverse biological actions of numerous small molecule hormones [3]. The DNA targets of the VDR can be found in a number of induced genes including those for osteocalcin, osteopontin, several p450-containing genes and p21 as well as *To whom correspondence should be addressed: Department of Biochemistry, University of 433 Babcock Drive, Madison, WI 53706. Tel: (608) 262-8229; fax: (608) 263-7609; email: pike@biochem.wisc.edu.. Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and a...

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