Tumor necrosis factor alpha-induced phosphorylation of RelA/p65 on Ser(529) is controlled by casein kinase II

Nuclear factor kappaB (NF-kappaB)/Rel transcription factors are key regulat ors of a variety of genes involved in immune and inflammatory responses, gr owth, differentiation, apoptosis, and development. In unstimulated cells, N F-kappaB/Rel proteins are sequestered in the cytoplasm by I kappaB inhibito r proteins. Many extracellular stimuli, such as tumor necrosis factor alpha (TNF alpha), cause rapid phosphorylation of I kappaB at N-terminal serine residues leading to ubiquitination and degradation of the inhibitor. Subseq uently, NF-kappaB proteins translocate to the nucleus and activate gene exp ression through KB response elements. TNF alpha, as well as certain other s timuli, also induces the phosphorylation of the NP-kappaB proteins. Previou sly, we have shown that TNF alpha induces RelA/p65 phosphorylation at serin e 529 and that this inducible phosphorylation increases NF-kappaB transcrip tional activity on an exogenously supplied reporter (1). In this report, we demonstrate that casein kinase II (CKII) interacts with p65 in vivo and ca n phosphorylate p65 at serine 529 in vitro. A CKII inhibitor (PD144795) inh ibited TNF alpha -induced p65 phosphorylation in vivo. Furthermore, our res ults indicate that the association between I kappaB alpha and p65 inhibits p65 phosphorylation by CKII and that degradation of I kappaB alpha allows C KII to phosphorylate p65 to increase NF-kappaB transactivation potential. T hese data may explain the ability of CKII to modulate cell growth and demon strate a mechanism whereby CKII can function in an inducible manner.