Low nuclear levels of nuclear factor-kappa B are essential for KC self-induction in astrocytes: requirements for shuttling and phosphorylation.

Stimulation with the chemokine KC induces an autocrine response in mouse astrocytes. A requirement for NF-kappa B was established for KC self-induction. NF-kappa B inhibitors, p65 antisense oligonucleotides, or dominant-negative Ikappa Balpha inhibited this autocrine response. Mutation of a specific kappa B site in the KC promoter also blocked KC self-induction. Chromatin immunoprecipitation and in vivo footprinting confirmed the direct binding of NF-kappa B to the KC promoter. However, neither NF-kappa B nuclear translocation, increased Ikappa B degradation, nor upregulation of NF-kappa B DNA binding activity was observed after KC stimulation. Reporter gene assays demonstrated KC-upregulated NF-kappa B transcriptional activity, and this effect was inhibited by dominant-negative IkappaBalpha. Accumulation of NF-kappaB was noted within the nucleus in the presence of nuclear export inhibitor leptomycin B, demonstrating constitutive shuttling of NF-kappa B between the cytoplasm and nucleus. Blocking NF-kappa B shuttling inhibited KC transcription. KC induced p65 phosphorylation, which was critical for NF-kappa B activation as determined with the Gal-4-p65 fusion protein and mutation of p65 phosphorylation sites. In conclusion, low-level nuclear NF-kappa B is essential for KC self-induction, and this effect is mediated by shuttling and phosphorylation of NF-kappa B. The results outline a novel mechanism for NF-kappa B participation in transcription regulation.