title: Stimulation-dependent I kappa B alpha phosphorylation marks the NF-kappa B inhibitor for degradation via the ubiquitin-proteasome pathway.
abstract: The nuclear translocation of NF-kappa B follows the degradation of its inhibitor, I kappa B alpha, an event coupled with stimulation-dependent inhibitor phosphorylation. Prevention of the stimulation-dependent phosphorylation of I kappa B alpha, either by treating cells with various reagents or by mutagenesis of certain putative I kappa B alpha phosphorylation sites, abolishes the inducible degradation of I kappa B alpha. Yet, the mechanism coupling the stimulation-induced phosphorylation with the degradation has not been resolved. Recent reports suggest a role for the proteasome in I kappa B alpha degradation, but the mode of substrate recognition and the involvement of ubiquitin conjugation as a targeting signal have not been addressed. We show that of the two forms of I kappa B alpha recovered from stimulated cells in a complex with RelA and p50, only the newly phosphorylated form, pI kappa B alpha, is a substrate for an in vitro reconstituted ubiquitin-proteasome system. Proteolysis requires ATP, ubiquitin, a specific ubiquitin-conjugating enzyme, and other ubiquitin-proteasome components. In vivo, inducible I kappa B alpha degradation requires a functional ubiquitin-activating enzyme and is associated with the appearance of high molecular weight adducts of I kappa B alpha. Ubiquitin-mediated protein degradation may, therefore, constitute an integral step of a signal transduction process.
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D002478:Cells, Cultured; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000378:metabolism*; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004789:Enzyme Activation; D006801:Humans; D020672:I-kappa B Proteins; D008025:Ligases / Q000378:metabolism; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000187:drug effects / Q000378:metabolism*; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D044764:Ubiquitin-Activating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D020672:I-kappa B Proteins; D009097:Multienzyme Complexes; D016328:NF-kappa B; C000606204:NFKBIA protein, human; D014452:Ubiquitins; D000072000:NF-KappaB Inhibitor alpha; D000255:Adenosine Triphosphate; D044767:Ubiquitin-Protein Ligases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D008025:Ligases; D044764:Ubiquitin-Activating Enzymes