VDR/RXR and TCF4/β-Catenin Cistromes in Colonic Cells of Colorectal Tumor Origin: Impact on c-FOS and c-MYC Gene Expression

Abstract

Many of the transcriptional and growth regulating activities of 1α,25-dihydroxyvitamin D3 [1,25-(OH)2D3] in the intestine and colon are recapitulated in the human colorectal cancer cell LS180. We therefore used this line together with chromatin immunoprecipitation-seq and gene expression analyses to identify the vitamin D receptor (VDR)/retinoid X receptor (RXR) and transcription factor 7-like 2 (TCF7L2/TCF4)/β-catenin cistromes and the genes that they regulate. VDR and RXR colocalized to predominantly promoter distal, vitamin D response element-containing sites in a largely ligand-dependent manner. These regulatory sites control the expression of both known as well as novel 1,25-(OH)2D3 target genes. TCF4 and β-catenin cistromes partially overlapped, contained TCF/lymphoid enhancer-binding factor consensus elements, and were only modestly influenced by 1,25-(OH)2D3. However, the two heterodimer complexes colocalized at sites near a limited set of genes that included c-FOS and c-MYC; the expression of both genes was modulated by 1,25-(OH)2D3. At the c-FOS gene, both VDR/RXR and TCF4/β-catenin bound to a single distal enhancer located 24 kb upstream of the transcriptional start site. At the c-MYC locus, however, binding was noted at a cluster of sites between −139 and −165 kb and at a site located −335 kb upstream. Examined as isolated enhancer fragments, these regions exhibited basal and 1,25-(OH)2D3-inducible activities that were interlinked to both VDR and β-catenin activation. These data reveal additional complexity in the regulation of target genes by 1,25-(OH)2D3 and support a direct action of both VDR and the TCF4/β-catenin regulatory complex at c-FOS and c-MYC.