Rapid proteolysis of I kappa B-alpha is necessary for activation of transcription factor NF-kappa B

Nature. 1993 Sep 9;365(6442):182-5. doi: 10.1038/365182a0.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • B-Lymphocytes / metabolism
  • Blotting, Western
  • Cell Line
  • Cycloheximide / pharmacology
  • DNA / metabolism
  • DNA-Binding Proteins / metabolism*
  • Endopeptidases / metabolism
  • HeLa Cells
  • Humans
  • Hydrolysis
  • I-kappa B Proteins*
  • Interleukin-1 / pharmacology
  • Lipopolysaccharides / pharmacology
  • NF-KappaB Inhibitor alpha
  • NF-kappa B / metabolism*
  • Protease Inhibitors / pharmacology
  • Protein Binding / drug effects
  • Reactive Oxygen Species / metabolism
  • Tetradecanoylphorbol Acetate / pharmacology
  • Tosylphenylalanyl Chloromethyl Ketone / pharmacology
  • Tumor Necrosis Factor-alpha / pharmacology


  • DNA-Binding Proteins
  • I-kappa B Proteins
  • Interleukin-1
  • Lipopolysaccharides
  • NF-kappa B
  • NFKBIA protein, human
  • Protease Inhibitors
  • Reactive Oxygen Species
  • Tumor Necrosis Factor-alpha
  • NF-KappaB Inhibitor alpha
  • Tosylphenylalanyl Chloromethyl Ketone
  • DNA
  • Cycloheximide
  • Endopeptidases
  • Tetradecanoylphorbol Acetate