ACTIVATION OF NUCLEAR TRANSCRIPTION FACTOR NF-KAPPA-B BY INTERLEUKIN-1 IS ACCOMPANIED BY CASEIN KINASE II-MEDIATED PHOSPHORYLATION OF THE P65 SUBUNIT

In fibroblasts and hepatoma cells, interleukin-l (IL-1) treatment resu lts in the rapid nuclear accumulation of the transcription factor NF-k appa B, present largely as p65 (RelA)/p50 heterodimers. It is well est ablished that this process is dependent in large part upon the phospho rylation and subsequent degradation of the cytosolic inhibitor I kappa B. We looked for other IL-l-induced modifications of NF-kappa B compo nents and found that, in both cell types, IL-1 stimulation led, within minutes, to phosphorylation of both NF-kappa B p65 and p50. Phosphory lation of p65 was sustained for at least 30 min after addition of the cytokine and occurred principally upon serine residues. Immunoprecipit ates of NF-kappa B complexes contained an associated protein kinase, t he biochemical characteristics of which were indistinguishable from ca sein kinase II (CKII), Purified CKII efficiently phosphorylated p65 in vitro, apparently on the same major sites that became phosphorylated in intact IL-l-treated cells. Although IL-1 treatment caused little ap parent stimulation of total cellular CKII activity, the fraction that was specifically associated with NF-kappa B complexes was markedly ele vated by the cytokine. The association of CKII with NF-kappa B occurre d in the cytoplasm, suggesting that this phosphorylation might be invo lved either in control of translocation of the activated complex or in modulation of its DNA binding properties.