Rapid proteolysis of I kappa B-alpha is necessary for activation of transcription factor NF-kappa B.
Inducible gene expression in eukaryotes is mainly controlled by the activity of transcriptional activator proteins, such as NF-kappa B (refs 1-3), a factor activated upon treatment of cells with phorbol esters, lipopolysaccharide, interleukin-1 and tumour necrosis factor-alpha. Activation of NF-kappa B involves release of the inhibitory subunit I kappa B from a cytoplasmic complex with the DNA-binding subunits Rel-A (formerly p65) and p50 (refs 6, 7). Cell-free experiments have suggested that protein kinase C and other kinases transfer phosphoryl groups onto I kappa B causing release of I kappa B and subsequent activation of NF-kappa B. Here we report that I kappa B-alpha (formerly MAD-3) is degraded in cells after stimulation with phorbol ester, interleukin-1, lipopolysaccharide and tumour necrosis factor-alpha, an event coincident with the appearance of active NF-kappa B. Treatment of cells with various protease inhibitors or an antioxidant completely prevented the inducible decay of I kappa B-alpha as well as the activation of NF-kappa B. Our findings suggest that the activation of NF-kappa B relies on an inducible degradation of I kappa B-alpha through a cytoplasmic, chymotrypsin-like protease. In intact cells, phosphorylation of I kappa B-alpha is apparently not sufficient for activation of NF-kappa B.
Laboratory for Molecular Biology, Gene Center, Martinsried, Germany.
T
T
Henkel
T
T
Machleidt
I
I
Alkalay
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M
Krönke
Y
Y
Ben-Neriah
P A
PA
Baeuerle
D001402:B-Lymphocytes / Q000378:metabolism; D015153:Blotting, Western; D002460:Cell Line; D003513:Cycloheximide / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D010450:Endopeptidases / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D006868:Hydrolysis; D020672:I-kappa B Proteins; D007375:Interleukin-1 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000378:metabolism*; D011480:Protease Inhibitors / Q000494:pharmacology; D011485:Protein Binding / Q000187:drug effects; D017382:Reactive Oxygen Species / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014108:Tosylphenylalanyl Chloromethyl Ketone / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D007375:Interleukin-1; D008070:Lipopolysaccharides; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D011480:Protease Inhibitors; D017382:Reactive Oxygen Species; D014409:Tumor Necrosis Factor-alpha; D000072000:NF-KappaB Inhibitor alpha; D014108:Tosylphenylalanyl Chloromethyl Ketone; D004247:DNA; D003513:Cycloheximide; D010450:Endopeptidases; D013755:Tetradecanoylphorbol Acetate