Vitamin D Receptor Inhibits Nuclear Factor κB Activation by Interacting with IκB Kinase β Protein

Abstract

1,25-Dihydroxyvitamin D (1,25(OH) 2 D 3 ) is known to suppress NF-κB activity, but the underlying mechanism remains poorly understood. Here we show that the vitamin D receptor (VDR) physically interacts with IκB kinase β (IKKβ) to block NF-κB activation. 1,25(OH) 2 D 3 rapidly attenuates TNFα-induced p65 nuclear translocation and NF-κB activity in a VDR-dependent manner. VDR overexpression inhibits IKKβ-induced NF-κB activity. GST pull-down assays and coimmunoprecipitation experiments demonstrated that VDR physically interacts with IKKβ and that this interaction is enhanced by 1,25(OH) 2 D 3 . Protein mapping reveals that VDR-IKKβ interaction occurs between the C-terminal portions of the VDR and IKKβ proteins. Reconstitution of VDR −/− cells with the VDR C terminus restores the ability to block TNFα-induced NF-κB activation and IL-6 up-regulation. VDR-IKKβ interaction disrupts the formation of the IKK complex and, thus, abrogates IKKβ phosphorylation at Ser-177 and abolishes IKK activity to phosphorylate IκBα. Consequently, stabilization of IκBα arrests p65/p50 nuclear translocation. Together, these data define a novel mechanism whereby 1,25(OH) 2 D 3 -VDR inhibits NF-κB activation. Background: 1,25(OH) 2 D 3 inhibits NF-κB activation by an undefined mechanism. Results: Vitamin D receptor protein binds to IKKβ protein, blocking TNFα-induced IKK complex formation and NF-κB activity. Conclusion: The vitamin D receptor suppresses NF-κB activation by directly interacting with IKKβ. Significance: This is a novel mechanism whereby 1,25(OH) 2 D 3 -VDR inhibits NF-κB.