Résumé
IKKα regulates many chromatin events in the nuclear phase of the NF-κB program, including phosphorylation of histone H3 and removal of co-repressors from NF-κB-dependent promoters. However, all of the nuclear functions of IKKα are not understood. In this study, using mouse embryonic fibroblasts IKKα knock-out and reexpressing IKKα after retroviral transduction, we demonstrate that IKKα contributes to NF-κB/p65 DNA binding activity on an exogenous κB element and on some, but not all, endogenous NF-κB-target promoters. Indeed, p65 chromatin immunoprecipitation assays revealed that IKKα is crucial for p65 binding on κB sites of icam-1 and mcp-1 promoters but not on iκbα promoter. The mutation of IKKα putative nuclear localization sequence, which prevents its nuclear translocation, or of crucial serines in the IKKα activation loop completely inhibits p65 binding on icam-1 and mcp-1 promoters and rather enhances p65 binding on the iκbα promoter. Further molecular studies demonstrated that the removal of chromatin-bound HDAC3, a histone deacetylase inhibiting p65 DNA binding, is differentially regulated by IKKα in a promoter-specific manner. Indeed, whereas the absence of IKKα induces HDAC3 recruitment and repression on the icam-1 promoter, it has an opposite effect on the iκbα promoter, where a better p65 binding occurs. We conclude that nuclear IKKα is required for p65 DNA binding in a gene-specific manner.