Signal-induced site-specific phosphorylation targets I kappa B alpha to the ubiquitin-proteasome pathway.
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.
Chen
Z
Z
Myogenics, Inc., Cambridge, Massachusetts 02139, USA.
Hagler
J
J
Palombella
V J
VJ
Melandri
F
F
Scherer
D
D
Ballard
D
D
Maniatis
T
T
D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D020672:I-kappa B Proteins; D007700:Kinetics; D007976:Leupeptins / Q000494:pharmacology; D008387:Marine Toxins; D009097:Multienzyme Complexes / Q000378:metabolism*; D016297:Mutagenesis, Site-Directed; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D010080:Oxazoles / Q000494:pharmacology; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D014176:Protein Biosynthesis; D011994:Recombinant Proteins / Q000378:metabolism; D014452:Ubiquitins / Q000302:isolation & purification / Q000378:metabolism*
D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D007976:Leupeptins; D008387:Marine Toxins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D010080:Oxazoles; D011994:Recombinant Proteins; D014452:Ubiquitins; D000072000:NF-KappaB Inhibitor alpha; D010768:Phosphoserine; C059041:calyculin A; D010749:Phosphoprotein Phosphatases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde