Vitamin D regulates the phenotype of human breast cancer cells

1 alpha,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3), the most active vitamin D metabolite, regulates proliferation, survival, and differentiation in many cell types. 1,25(OH)(2)D-3 and several less calcemic analogs are in clinical trials against various neoplasias. We studied the effects of 1,25(OH)(2)D-3 on a panel of human breast cancer cells, which show similar vitamin D receptor (VDR) content but variable transcriptional and anti-proliferative responsiveness. In MDA-MB-453 cells, one of the responsive lines, 1,25(OH)(2)D-3 increased cell and nuclear size and induced a change from a rounded to a flattened morphology. By phase contrast, laser confocal and electron microscopy, we found that 1,25(OH)(2)D-3 changed the cytoarchitecture of actin filaments and microtubules and nuclear shape, induced filopodia and lamellipodia, and promoted cell-to-cell contacts via large cytoplasmic extensions. However, although claudin-7 and occludin content in the cells increased upon exposure to 1,25(OH)(2)D-3, these proteins were not located at the plasma membrane probably due to the absence of E-cadherin expression. Additionally, 1,25(OH)(2)D-3 induced the accumulation of alpha(v)-integrin, beta(5)-integrin, focal adhesion kinase (FAK), and paxillin in focal adhesion plaques, concomitant with the increased phosphorylation of the FAK. 1,25(OH)(2)D-3 enhanced MDA-MB-453 and MDA-MB-468 cell adhesion to plastic but decreased adhesion to laminin. The expression of the mesenchymal marker N-cadherin and of the myoepithelial marker P-cadherin was down-regulated by 1,25(OH)(2)D-3 in several breast cancer cell lines. Other myoepithelial proteins such as alpha(6)-integrin, beta(4)-integrin, and smooth muscle alpha-actin (SMA) were also repressed by 1,25(OH)(2)D-3 in MDA-MB-453 and MDA-MB-468 cells. Accordingly, mice lacking VDR (Vdr(-/-)) showed abnormally high levels of SMA and P-cadherin in their mammary gland. These findings show that 1,25(OH)(2)D-3 profoundly affects the phenotype of breast cancer cells, and suggest that it reverts the myoepithelial features associated with more aggressive forms and poor prognosis in human breast cancer.