INHIBITION OF NF-KAPPA-B ACTIVATION BY A DOMINANT-NEGATIVE MUTANT OF I-KAPPA-B-ALPHA

The activity of the transcription factor NF-kappa B is tightly regulat ed by the inhibitory molecule I kappa B alpha. Upon stimulation, I kap pa B alpha is rapidly degraded and NF-kappa B translocates to the nucl eus to induce gene expression. The I kappa B alpha degradation is prec eded by phosphorylation, suggesting that this event plays a role in th e activation of NF-kappa B. In this study, we have mutated three poten tial phosphorylation sites in porcine I kappa B alpha and found that e xpression of the Ser(32) mutant of I kappa B alpha (I-S32A), but not T yr(42) or Ser(262) mutants or wild-type I kappa B alpha, blocked the a ctivation of NF-kappa B by TNF-alpha. These results suggest that the S er(32) residue, a potential casein kinase II phosphorylation site, is critical for NF-kappa B activation.