The active metabolite of vitamin D modulates the expression of a wide variety
of genes in a developmentally-specific manner. This secosteroid hormone
can up- or downregulate the expression of genes involved in a diverse array
of responses such as proliferation, differentiation and calcium homeostasis.
1,25-(OH)2-vitamin D3 exerts its effects through interaction with the vitamin D
receptor (VDR), a member of the superfamily of hormone-activated nuclear
receptors. In its ligand-bound state, the VDR forms heterodimers with the 9-
cis retinoic acid receptor, RXR, and affects gene expression by binding specific
DNA sequences known as hormone response elements, or HREs. In addition
to regulating the above-mentioned cellular responses, 1,25-(OH)2-vitamin D3
exhibits antiproliferative properties in osteosarcoma, melanoma, colon carcinoma
and breast carcinoma cells.