INDUCIBLE PHOSPHORYLATION OF I-KAPPA-B-ALPHA IS NOT SUFFICIENT FOR ITS DISSOCIATION FROM NF-KAPPA-B AND IS INHIBITED BY PROTEASE INHIBITORS

The ubiquitous transcription factor NF-kappa B is regulated by its cyt oplasmic inhibitor I kappa B. A variety of cellular stimuli cause the dissociation of NF-kappa B from I kappa B, allowing NF-kappa B to tran slocate to the nucleus and regulate gene expression. Although the acti vation of NF-kappa B in vivo is associated with the phosphorylation an d degradation of I kappa B alpha, it has remained unclear how each of these events contributes to this process. Recently, studies utilizing protease inhibitors have suggested that the proteolysis of I kappa B a lpha is a necessary event in the activation of NF-kappa B. We demonstr ate in this study that these and an additional protease inhibitor also completely repress inducible phosphorylation of I kappa B alpha. This surprising result suggests a more complex role of proteases in NF-kap pa B activation. In addition, data presented here indicate that many o f these inhibitors also directly modify NF-kappa B and inhibit its DNA binding activity. Due to the pleiotropic effects of these protease in hibitors, it is difficult to conclude from their use how I kappa B alp ha phosphorylation and degradation contribute to NF-kappa B activation . In the present study, a more direct approach demonstrates that phosp horylation of I kappa B alpha alone is not sufficient for NF-kappa B a ctivation.