1,25-dihyroxyvitamin D3 enhances the activity of the FOXP3 gene in human CD4+ T cells through directly binding to putative VDRE sites in the FOXP3 gene (49.2)

Abstract

Abstract 1,25-dihyroxyvitamin D3 (1,25(OH)2VD3) is known to have immune regulatory effects on T cells. However, it is unknown whether 1,25(OH)2VD3 can directly regulate the expression of the FOXP3 gene in human CD4+ T cells. We thus searched and found putative response elements for vitamin D receptor (VDR) in a highly conserved non-coding sequence (CNS) region of the human FOXP3 gene that encompassed +1,722 to +2,562 using NUBIscan algorithm. The presence of VDR and retinoid X receptor (RXR), which heterodimerizes with VDR, in the nucleus of human CD4+ T cells was detected by co-immunoprecipitation using biotinylated fragments of the CNS region that contained the putative vitamin D response elements (VDRE) sites. We next performed a chromatin immunoprecipitation (ChiP) assay to determine whether VDR directly bound to the sites. The results of this assay showed the binding of VDR to the putative VDREs of the CNS but not to the promoter of the FOXP3 gene. To test whether 1,25(OH)2VD3 could directly enhance the FOXP3 promoter activity, we conducted a reporter assay using a PGL3 vector containing the FOXP3 gene promoter with or without VDREs in the CNS of the FOXP3 gene. Indeed, 1,25(OH)2VD3 enhanced the promoter activity of the FOXP3 gene in the presence of VDREs. Our findings indicate that 1,25(OH)2VD3 up-regulate the FOXP3 gene expression in human CD4+ T cells through directly binding to VDREs in the CNS region of the FOXP3 gene that encompasses +1,722 to +2,562.