Vitamin D and Myofibroblasts in Fibrosis and Cancer: At Cross-purposes with TGF-β/SMAD Signaling

The multifaceted involvement of the active vitamin D metabolite 1,25-dihydroxyvitamin D-3 (henceforth referred to by the synonyms 1,25(OH)(2)D-3, calcitriol or vitamin D) in blunting the growth of cancer cells is amply recognized. In this review we focused our attention on the cross-talk between 1,25 (OH)(2)D-3 and the tumor microenvironment (TME), signaling out stromal cancer-associated fibroblasts (CAFs), the most abundant TME population, as a target for calcitriol anticancer action. In view of the commonality of the phenotypic signature in myofibroblasts, resident in the cancer stroma and in non-neoplastic fibrotic loci, we examined modes of action of vitamin D in non-neoplastic chronic diseases and in cancer to assess mechanistic similarities and divergences. A constant observation was that 1,25(OH)(2)D-3 or synthetic ligands via the active vitamin D receptor (VDR) impede transforming growth factor (TGF)-beta/mothers against decapentaplegic homologs (SMADs) signaling in myofibroblasts regardless of the initiating insult. The translational impact of 1,25(OH)(2)D-3 in targetting stromal CAFs is discussed.