The vitamin D receptor in cancer.

Over the last 25 years roles have been established for vitamin D receptor (VDR) in influencing cell proliferation and differentiation. For example, murine knock-out approaches have revealed a role for the VDR in controlling mammary gland growth and function. These actions appear widespread, as the enzymes responsible for 1alpha,25-dihydroxycholecalciferol generation and degradation, and the VDR itself, are all functionally present in a wide range of epithelial and haematopoietic cell types. These findings, combined with epidemiological and functional data, support the concept that local, autocrine and paracrine VDR signalling exerts control over cell-fate decisions in multiple cell types. Furthermore, the recent identification of bile acid lithocholic acid as a VDR ligand underscores the environmental sensing role for the VDR. In vitro and in vivo dissection of VDR signalling in cancers (e.g. breast, prostate and colon) supports a role for targeting the VDR in either chemoprevention or chemotherapy settings. As with other potential therapeutics, it has become clear that cancer cells display de novo and acquired genetic and epigenetic mechanisms of resistance to these actions. Consequently, a range of experimental and clinical options are being developed to bring about more targeted actions, overcome resistance and enhance the efficacy of VDR-centred therapeutics.