A proteasome inhibitor prevents activation of NF‐kappa B and stabilizes a newly phosphorylated form of I kappa B‐alpha that is still bound to NF‐kappa B
Activation of the inducible transcription factor NF‐kappa B involves removal of the inhibitory subunit I kappa B‐alpha from a latent cytoplasmic complex. It has been reported that I kappa B‐alpha is subject to both phosphorylation and proteolysis in the process of NF‐kappa B activation. In this stud...
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Veröffentlicht in: | The EMBO journal 1994-11, Vol.13 (22), p.5433-5441 |
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Sprache: | eng |
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Zusammenfassung: | Activation of the inducible transcription factor NF‐kappa B involves removal of the inhibitory subunit I kappa B‐alpha from a latent cytoplasmic complex. It has been reported that I kappa B‐alpha is subject to both phosphorylation and proteolysis in the process of NF‐kappa B activation. In this study, we present evidence that the multicatalytic cytosolic protease (proteasome) is involved in the degradation of I kappa B‐alpha. Micromolar amounts of the peptide Cbz‐Ile‐Glu(O‐t‐Bu)‐Ala‐leucinal (PSI), a specific inhibitor of the chymotrypsin‐like activity of the proteasome, prevented activation of NF‐kappa B in response to tumor necrosis factor‐alpha (TNF) and okadaic acid (OA) through inhibition of I kappa B‐alpha degradation. The m‐calpain inhibitor Cbz‐Leu‐leucinal was ineffective. In the presence of PSI, a newly phosphorylated form of I kappa B‐alpha accumulated in TNF‐ and OA‐stimulated cells. However, the covalent modification of I kappa B‐alpha was not sufficient for activation of NF‐kappa B: no substantial NF‐kappa B DNA binding activity appeared in cells because the newly phosphorylated form of I kappa B‐alpha was still tightly bound to p65 NF‐kappa B. Pyrrolidinedithiocarbamate, an antioxidant inhibitor of NF‐kappa B activation which did not interfere with proteasome activities, prevented de novo phosphorylation of I kappa B‐alpha as well as its subsequent degradation. This suggests that phosphorylation of I kappa B‐alpha is equally necessary for the activation of NF‐kappa B. |
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ISSN: | 0261-4189 1460-2075 |
DOI: | 10.1002/j.1460-2075.1994.tb06878.x |