Interleukin-1 receptor-associated kinase (IRAK)-1 plays an essential role in Toll-like receptor/interleukin-1 receptor (TLR/IL-1R) -associated NF-κB activation through its involvement in IKK activation, which then leads to subsequent IκB degradation and NF-κB nuclear translocation. In the present studies, we demonstrate a novel pathway in which IRAK-1 present in the nucleus participates in NF-κB-dependent gene expression. Nuclear localization of IRAK-1 is increased on cellular stimulation with IL-1 and LPS, or CRM-1-dependent nuclear export blockade. Induction of IRAK-1 produces enhanced NF-κB transcriptional activity that precedes IκB-α degradation and nuclear translocation of NF-κB. IRAK-1 binds to the promoter of NF-κB-regulated gene, IκB-α, and enhances binding of the NF-κB p65 subunit to NF-κB responsive elements within the IκB-α promoter. IRAK-1 phosphorylates histone H3 in vitro and is required for IL-1-induced phosphorylation of histone H3 at serine 10 in vivo. These data indicate that both cytosolic and nuclear actions of IRAK-1 participate in the activation of NF-κB-dependent transcriptional events. © FASEB.