1alpha,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.