Multiple structural domains within I kappa B alpha are required for its inducible degradation by both cytokines and...

Activation of the transcription factor NF-kappa B by various cellular stimuli involves phosphorylation and subsequent degradation of its inhibitor I kappa B alpha. Both the cytokine tumor necrosis factor alpha (TNF-alpha) and the phosphatase inhibitor calyculin A have been shown to induce rapid phosphorylation and degradation of I kappa B alpha. In the present study, we demonstrate that TNF-alpha and calyculin A stimulate similar although not identical pattern of I kappa B alpha phosphorylation, as demonstrated by phosphopeptide mapping. Interestingly, phosphorylation of I kappa B alpha induced by both inducers involves serine-32 and serine-36 of I kappa B alpha. Furthermore, TNF-alpha- and calyculin A-induced degradation of I kappa B alpha appears to require the same structural domains within I kappa B alpha. In addition to the N-terminal phosphorylation sites and the C-terminal sequences, each of the five ankyrin-like repeats of I kappa B alpha is critically required for the inducible degradation of this NF-kappa B inhibitor. Together, these studies suggest that degradation of I kappa B alpha by both cytokines and phosphatase inhibitors is regulated by site-specific phosphorylation and requires multiple structural domains.