Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P62988 (Ubiquitin)
 4,326 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Stimulation-dependent I kappa B alpha phosphorylation marks the NF-kappa B inhibitor for degradation via the ubiquitin-proteasome pathway. 747 48

Activation of NF-kappaB is regulated via numerous ubiquitin- and proteasome-mediated steps; an important one is processing of the precursor p105 to the p50 active subunit. The mechanisms involved are largely unknown, because this is an exceptional case where the ubiquitin system does not destroy its substrate completely. Here, we demonstrate that proteasomal processing of p105 requires ubiquitin but not generation of polyubiquitin chains. In vitro, ubiquitin species that cannot polymerize mediate processing. In yeasts that express nonpolymerizable ubiquitins, processing proceeds normally, whereas degradation of substrates that are dependent on polyubiquitination is inhibited. Similar results were obtained in mammalian cells. Interestingly, processing requires multiple monoubiquitinations, because progressive elimination of lysines in p105 is accompanied by gradual inhibition of p50 generation. Finally, the proteasome recognizes the multiply monoubiquitinated p105. These findings suggest that a proteolytic signal can be composed of a cluster of single ubiquitins, not necessarily a chain.
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PMID:Modification by single ubiquitin moieties rather than polyubiquitination is sufficient for proteasomal processing of the p105 NF-kappaB precursor. 1925 Sep 10