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 D3 (henceforth referred to by the synonyms 1,25(OH)2D3, 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)2D3 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)2D3 or synthetic ligands via the active vitamin D receptor (VDR) impede transforming growth factor (TGF)-β/mothers against decapentaplegic homologs (SMADs) signaling in myofibroblasts regardless of the initiating insult. The translational impact of 1,25(OH)2D3 in targetting stromal CAFs is discussed.