1,25-Dihydroxyvitamin D (1,25(OH)2D3) is known to suppress NF-êB activity, but the underlying mechanism remains poorly understood. Here we show that the vitamin D receptor (VDR) physically interacts with IêB kinase â (IKKâ) to block NF-êB activation. 1,25(OH)2D3 rapidly attenuates TNFá-induced p65 nuclear translocation and NF-êB activity in a VDR-dependent manner. VDR overexpression inhibits IKKâ-induced NF-êB activity. GST pull-down assays and coimmunoprecipitation experiments demonstrated that VDR physically interacts with IKKâ and that this interaction is enhanced by 1,25(OH)2D3. Protein mapping reveals that VDR-IKKâ interaction occurs between the C-terminal portions of the VDR and IKKâ proteins. Reconstitution of VDR(-/-) cells with the VDR C terminus restores the ability to block TNFá-induced NF-êB activation and IL-6 up-regulation. VDR-IKKâ interaction disrupts the formation of the IKK complex and, thus, abrogates IKKâ phosphorylation at Ser-177 and abolishes IKK activity to phosphorylate IêBá. Consequently, stabilization of IêBá arrests p65/p50 nuclear translocation. Together, these data define a novel mechanism whereby 1,25(OH)2D3-VDR inhibits NF-êB activation.
Active Transport, Cell Nucleus Animals