Signal-induced site-specific phosphorylation targets I kappa B alpha to the ubiquitin-proteasome pathway

Genes Dev. 1995 Jul 1;9(13):1586-97. doi: 10.1101/gad.9.13.1586.

Abstract

The transcription factor NF-kappa B is sequestered in the cytoplasm by the inhibitor protein I kappa B alpha. Extracellular inducers of NF-kappa B activate signal transduction pathways that result in the phosphorylation and subsequent degradation of I kappa B alpha. At present, the link between phosphorylation of I kappa B alpha and its degradation is not understood. In this report we provide evidence that phosphorylation of serine residues 32 and 36 of I kappa B alpha targets the protein to the ubiquitin-proteasome pathway. I kappa B alpha is ubiquitinated in vivo and in vitro following phosphorylation, and mutations that abolish phosphorylation and degradation of I kappa B alpha in vivo prevent ubiquitination in vitro. Ubiquitinated I kappa B alpha remains associated with NF-kappa B, and the bound I kappa B alpha is degraded by the 26S proteasome. Thus, ubiquitination provides a mechanistic link between phosphorylation and degradation of I kappa B alpha.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Cysteine Endopeptidases / metabolism*
  • DNA-Binding Proteins / isolation & purification
  • DNA-Binding Proteins / metabolism*
  • HeLa Cells
  • Humans
  • I-kappa B Proteins*
  • Kinetics
  • Leupeptins / pharmacology
  • Marine Toxins
  • Multienzyme Complexes / metabolism*
  • Mutagenesis, Site-Directed
  • NF-KappaB Inhibitor alpha
  • NF-kappa B / antagonists & inhibitors*
  • Oxazoles / pharmacology
  • Phosphoprotein Phosphatases / antagonists & inhibitors
  • Phosphorylation
  • Phosphoserine / metabolism
  • Proteasome Endopeptidase Complex
  • Protein Biosynthesis
  • Recombinant Proteins / metabolism
  • Ubiquitins / isolation & purification
  • Ubiquitins / metabolism*

Substances

  • DNA-Binding Proteins
  • I-kappa B Proteins
  • Leupeptins
  • Marine Toxins
  • Multienzyme Complexes
  • NF-kappa B
  • NFKBIA protein, human
  • Oxazoles
  • Recombinant Proteins
  • Ubiquitins
  • NF-KappaB Inhibitor alpha
  • Phosphoserine
  • calyculin A
  • Phosphoprotein Phosphatases
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • benzyloxycarbonylleucyl-leucyl-leucine aldehyde