Vitamin D-dependent chromatin association of CTCF in human monocytes

• The cistrome of CTCF in THP-1 human monocytes contains 40,078 binding sites.
• At 2,130 loci CTCF binding is significantly (p < 0.05) modulated by 1,25(OH)2D3.
• Vitamin D-sensitive CTCF sites mark the anchors of 587 TADs containing at least VDR binding site and 1,25(OH)2D3 target gene.
• These TADs can explain the regulatory scenarios of up to 70% of all 1,25(OH)2D3 target genes.
• Vitamin D-sensitive CTCF sites provide further mechanistic details to the understanding of gene regulation by 1,25(OH)2D3.

CCCTC-binding factor (CTCF) is a transcription factor being involved in 3D chromatin organization and displays a highly conserved genome-wide binding pattern. In this study, we report the cistrome of CTCF in THP-1 human monocytes and confirm that from the 40,078 CTCF binding sites nearly 85% are identical with those found in K562 monocytes. Quadruplicate chromatin immunoprecipitation sequencing (ChIP-seq) demonstrated that at 2130 loci the association strenght of CTCF with genomic DNA was significantly (p < 0.05) modulated by stimulation with the natural vitamin D receptor (VDR) ligand 1α,25-dihydroxyvitamin D3 (1,25(OH)2D3). Some 55% of these CTCF sites contribute to DNA looping and mark the anchors of 587 putative topologically associating domains (TADs) containing at least one VDR binding site and one 1,25(OH)2D3 target gene. These TADs can explain the regulatory scenarios of up to 70% of all 1,25(OH)2D3 target genes. A self-organizing map approach subdivided the vitamin D-sensitive CTCF sites into seven classes that can be distinguished by participation in DNA loop formation, binding to open chromatin, carrying binding motifs for CTCF or its relative BORIS, overlap with transcription start site (TSS) regions and binding of VDR. These variant molecular profiles suggest different mechanisms of the 1,25(OH)2D3-dependent action of CTCF. The co-location of VDR and 1,25(OH)2D3-dependent CTCF sites increases in the context of accessible chromatin and TSS regions but does not show any significant correlation with classical DNA binding mechanisms of CTCF. In conclusion, vitamin D-sensitive CTCF sites provide further mechanistic details to the epigenome-wide understanding of 1,25(OH)2D3-mediated gene regulation.