Inducible phosphorylation of I kappa B alpha is not sufficient for its dissociation from NF-kappa B and is inhibited by protease inhibitors.

TLDR

NF‑κB activation normally involves phosphorylation and degradation of its inhibitor IκBα, but the relative importance of these events remains unclear, with protease inhibitors indicating that proteolysis may be required. The study shows that protease inhibitors block IκBα phosphorylation, directly inhibit NF‑κB DNA binding, and that phosphorylation alone does not trigger NF‑κB activation, revealing a more complex protease‑dependent regulation.

Abstract

The ubiquitous transcription factor NF-kappa B is regulated by its cytoplasmic 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 translocate to the nucleus and regulate gene expression. A variety of cellular stimuli cause the dissociation of NF-kappa B from I kappa B, allowing NF-kappa B to translocate to the nucleus and regulate gene expression. Although the activation of NF-kappa B in vivo is associated with the phosphorylation and 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 alpha is a necessary event in the activation of NF-kappa B. We demonstrate 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-kappa B activation. In addition, data presented here indicate that many of these inhibitors also directly modify NF-kappa B and inhibit its DNA binding activity. Due to the pleiotropic effects of these protease inhibitors, it is difficult to conclude from their use how I kappa B alpha phosphorylation and degradation contribute to NF-kappa B activation. In the present study, a more direct approach demonstrates that phosphorylation of I kappa B alpha alone is not sufficient for NF-kappa B activation.