The activity of the transcription factor NF-kappa B is tightly regulated by the inhibitory molecule I kappa B alpha. Upon stimulation, I kappa B alpha is rapidly degraded and NF-kappa B translocates to the nucleus to induce gene expression. The I kappa B alpha degradation is preceded by phosphorylation, suggesting that this event plays a role in the activation of NF-kappa B. In this study, we have mutated three potential phosphorylation sites in porcine I kappa B alpha and found that expression of the Ser(32) mutant of I kappa B alpha (I-S32A), but not Tyr(42) or Ser(262) mutants or wild-type I kappa B alpha, blocked the activation of NF-kappa B by TNF-alpha. These results suggest that the Ser(32) residue, a potential casein kinase II phosphorylation site, is critical for NF-kappa B activation.
