MULTIPLE STRUCTURAL DOMAINS WITHIN I-KAPPA-B-ALPHA ARE REQUIRED FOR ITS INDUCIBLE DEGRADATION BY BOTH CYTOKINES AND PHOSPHATASE INHIBITORS

Activation of the transcription factor NF-kappa B by various cellular stimuli involves phosphorylation and subsequent degradation of its inh ibitor 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 stim ulate similar although not identical pattern of I kappa B alpha phosph orylation, as demonstrated by phosphopeptide mapping. Interestingly, p hosphorylation of I kappa B alpha induced by both inducers involves se rine-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 o f the five ankyrin-like repeats of I kappa B alpha is critically requi red for the inducible degradation of this NF-kappa B inhibitor. Togeth er, these studies suggest that degradation of I kappa B alpha by both cytokines and phosphatase inhibitors is regulated by site-specific pho sphorylation and requires multiple structural domains. (C) 1996 Academ ic Press, Inc.