Vitamin D Receptor Binding with DNA in Duodenal Crypt, Duodenal Villi, and Colonic Epithelial Cells of Mice

Vitamin D receptor (VDR) is a transcription factor that mediates calcium absorption by intestinal epithelial cells. Although calcium absorption is ca-nonically thought to occur only in the small intestine, recent studies have shown that VDR activity in the co-lon alone is sufficient to prevent calcium deficiency in mice. Here, we further investigate VDR activity in the colon. We assess VDR-DNA binding in mouse duodenal crypt, duodenal villi, and colonic epithelial cells using Chromatin Immunoprecipitation se-quencing (ChIP-seq). We find that most VDR-respon-sive elements are common to all intestinal epithelial cells, though some VDR-responsive elements are re-gionally-enriched and exhibit greater VDR-binding affinity in either duodenal epithelial cells or colonic epithelial cells. We also assess chromatin accessibil-ity in the same three cell types using Assay for Trans-posase-Accessible Chromatin sequencing (ATAC-seq). By integrating the VDR ChIP-seq and ATAC-seq data, we find that regionally-enriched VDR-re-sponsive elements exhibit greater chromatin acces-sibility in the region of their enrichment. Finally, we assess the transcription factor motifs present in VDR-responsive elements. We find that duodenum- and colon-enriched VDR-responsive elements exhibit different sets of transcription factor motifs other than VDR, suggesting that VDR may act together with dif-ferent partner transcription factors in the two re-gions. Our work is the first investigation of VDR-DNA binding in the colon and provides a basis for further investigations of VDR activity in the colon.