IκB kinase α-mediated derepression of SMRT potentiates acetylation of RelA/p65 by p300

Over the last several years, significant progress has been made in identifying chromatin-regulated events that govern NF-kappa B transcription. Using either laminin attachment or tumor necrosis factor alpha as a physiological stimulus of NF-kappa B activation, we demonstrate that I kappa B kinase of (IKK alpha) is recruited to chromatin in distinct phases. In the initial phase, IKK alpha is responsible for derepressing the silencing mediator for retinoic acid and thyroid hormone receptor (SMRT)-histone deacetylase 3 (HDAC3) corepressor complex from the p50 homodimer. However, in the latter phase, chromatin-bound IKK alpha coordinates the simultaneous phosphorylation of RelA/p65(S536) and SMRT(S2410) as detected by chromatin immunoprecipitation (ChIP) assays. Although phosphorylated SMRT remains bound to the active p50-ReIAp65 heterodimer of NF-kappa B, derepression of SMRT is evidenced by the loss of chromatin-associated HDAC3 activity. ChIP and re-ChIP analysis demonstrates that phosphorylation of ReWp65(S536) and SMRT(S2410) occurs prior to acetylation of ReIA/p65 at K310. Moreover, IKK alpha-induced phosphorylation of ReWp65(S536) displaces corepressor activity, allowing p300-mediated acetylation of RelAp65. Introduction of nonphosphorylatable mutants of ReIA/p65 and SMRT proteins or the inhibition of IKK activity results in active repression of NF-kappa B promoters by tethering the SMRT-HDAC3 complex. Similar to phosphorylation within the Rel homology domain of RelA/p65, which governs an exchange of HDAC1 for CBP/p300 acetyltransferases, we demonstrate that phosphorylation within the transactivation domain of ReIA/p65(S536) displaces SMRT-HDAC3 repressor activity, allowing p300 to acetylate RelA/p65.