CLK2-mediated IκBα-independent early-termination of NF-κB activation by phosphorylating nuclear-p65 for cytoplasmic redistribution and degradation

Abstract The NF-κB transcription factor families play significant roles in both the inflammatory and immune responses. The activation of the NF-κB pathway is subject to strict regulation to prevent excessive inflammatory and immune responses. While a widely accepted negative feedback model, IκBs-dependent NF-κB termination is observed as a lagged response pattern in the later stage of activation, the prompt termination mechanisms of active NF-κB remain not fully clarified. Here, we show an IκBs-independent prompt termination model of nuclear NF-κB that CLK2 negatively regulates active NF-κB by phosphorylating the p65 subunit of NF-κB at Ser-180 in the nucleus to limit the transcriptional activation through degradation and nuclear export. Depletion of CLK2 enhances the production of inflammatory and antiviral cytokines and reduces viral replication. Meanwhile, ablation of Clk2 in mice promotes antiviral effects and increases the survival of mice after virus infection. Mechanistically, CLK2 interacts with and phosphorylates p65 at Ser-180 in the nucleus, leading to the ubiquitin-proteasome-mediated degradation and cytoplasmic re-distribution. Importantly, the CLK2 inhibitor promotes the production of cytokines, reduces virus replication, and accelerates mouse psoriasis in vitro and in vivo . The study reveals a novel IκBs-independent NF-κB early-stage termination model wherein phosphorylated Ser-180 p65 turns off the post-translation modifications of transcriptional activation,ultimately resulting in the subsequent degradation and nuclear export of p65 to inhibit excessive inflammatory activation. Our findings show that Ser-180 phosphorylation of p65 in the nucleus serves as the main repression switch of early-stage NF-κB activation, thereby improving the recognition of the NF-κB negative regulation model in time and space.