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Mol. Cell. Biol., 05 1995, 2413-2419, Vol 15, No. 5
MS Rodriguez, I Michalopoulos, F Arenzana-Seisdedos and RT Hay
After exposure of cells to tumor necrosis factor (TNF), I kappa B alpha is
rapidly degraded by a proteolytic activity that is required for nuclear
localization and activation of transcription factor NF-kappa B. To
investigate this problem, we have developed a cell-free system to study the
degradation of I kappa B alpha initiated in vivo. In this in vitro system,
characteristics of endogenous I kappa B alpha degradation were comparable
to those observed in vivo. Recombinant I kappa B alpha, when added to
lysates from cells exposed to TNF, was specifically degraded by a cellular
proteolytic activity; however, it was stable in extracts from unstimulated
cells. Inhibition characteristics of the proteolytic activity responsible
for I kappa B alpha degradation suggest the involvement of a serine
protease. Analysis of mutated forms of I kappa B alpha in the in vitro
system demonstrated that an I kappa B alpha species which was unable to
interact with NF-kappa B was still efficiently degraded. In contrast,
deletion of the C-terminal 61 amino acids from I kappa B alpha rendered the
protein resistant to proteolytic degradation. Expression of I kappa B alpha
mutated forms in COS-7 cells confirmed the importance of the C-terminal
domain for the degradation of the protein in vivo following cell
activation. Thus, it is likely that the acidic, negatively charged region
represented by the C-terminal 61 amino acids of the protein contains
residues critical for TNF-inducible degradation of I kappa B alpha.
Copyright © 1995, American Society for Microbiology
Inducible degradation of I kappa B alpha in vitro and in vivo requires the acidic C-terminal domain of the protein
Unite d'Immunologie Virale, Institut Pasteur, Paris, France.
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