Involvement of the vitamin D receptor in the regulation of NF-κB activity in fibroblasts

We have used mouse embryonic fibroblasts (MEFs) derived from VDR(+/-) and VDR(-/-) mice to determine whether the nuclear vitamin D receptor (VDR) is directly involved in the regulation of NF-kappa B activation. We found that the basal I kappa B alpha protein level was markedly decreased in VDR(-/-) MEFs compared to VDR(+/-) MEFs; however, degradation of I kappa B alpha and its phosphorylation were not altered in VDR(-/-) cells. neither were the levels of IKKa and IKK beta proteins. Consistently, p65 nuclear translocation was increased in unstimulated VDR(-/-) cells. The physical interaction between VDR and p65 was absent in VDR(-/-) MEFs, which may free p65 and increase its activity. Consequently, these alterations combined led to a marked increase in NF-kappa B transcriptional activity. Consistently, induction of IL-6 by TNF alpha or IL-1 beta was much more robust in VDR(-/-) than in VDR(+/-) cells, indicating that VDR(-/-) cells are more susceptible to inflammatory stimulation. Therefore, fibroblasts lacking VDR appear to be more pro-inflammatory due to the intrinsic high NF-kappa B activity. The reduction Of lKl3et in VDR(-/-) MEFs may be partially explained by the lack of VDR-mediated stabilization of I kappa B alpha by 1,25(OH)(2)D-3. These data suggest that VDR plays an inhibitory role in the regulation of NF-kappa B activation. (c) 2007 Elsevier Ltd. All rights reserved.