RSK2 mediates NF-κB activity through the phosphorylation of IκBα in the TNF-R1 pathway

The ribosomal S6 kinase 2 (RSK2) is a well-known serine/threonine kinase and a member of the p90 ribosomal S6 kinase (p90RSK) family of proteins. It is activated downstream of the MEK/ERKs cascade by mitogenic stimuli such as EGF or TPA. Here, we show that RSK2 is activated by treatment with tumor necrosis factor-α (TNF-α) and directly phosphorylates IκBα at Ser-32, leading to IκBα degradation. The phosphorylation of IκBα promotes the activation and translocation of the nuclear factor-κB (NF-κB) subunits p65 and p50 to the nucleus. The net result is an increased NF-κB activity, which serves as a mechanism for RSK2 blockade of TNF-α-induced apoptosis and enhanced cell survival.