1α,25-Dihydroxyvitamin D₃ inhibits transcriptional potential of nuclear factor kappa B in breast cancer cells

1α,25-Dihydroxyvitamin D₃ (VD₃), the biologically active form of vitamin D, may have either pro- or anti-inflammatory activities because of its diverse actions on nuclear factor kappa B (NF-κB). Previous studies indicated that VD₃ can either activate or inhibit NF-κB via Akt-induced IκBα phosphorylation and increase in IκBα synthesis respectively. At present, the relevant contribution of each mechanism has not been fully explored. We observed a VD₃-mediated NF-κB inhibitory effect in vitamin D receptor (VDR)-positive MCF-7 breast cancer cells. We showed that VD₃ induced VDR-dependent IκBα expression but still able to lead on transient NF-κB p65 nuclear translocation through Akt-induced IκBα phosphorylation. Upon TNFα stimulation, VD₃ was not capable to inhibit IκBα degradation, p65 nuclear translocation and p65/p50-DNA binding. Here, we found that VD₃ strongly repressed p65 transactivation in MCF-7 cells using Gal4-p65 chimeras system. VDR was required for the VD₃-mediated transrepression and mutations in VDR affected its suppressive ability. We also demonstrated that neither inhibition of p65 phosphorylation nor acetylation was responsible for the transrepression. In fact, we found that treatment of MCF-7 cells with histone deacetylase inhibitors abrogated VD₃-induced p65 transrepression. In addition, knockdown of two nuclear corepressors HDAC3 and SMRT relieved p65 transactivation and particular TNFα-triggered gene expression. In conclusion, the reduction of gene activation by VD₃ in breast cancer cells was caused by the interference of the transactivation potential of NF-κB p65 subunit. Our studies provide a scientific background for rational use of vitamin D in the prevention and treatment of inflammatory diseases.