Signal-induced ubiquitination of IkappaBalpha by the F-box protein Slimb/beta-TrCP.
Signal-induced phosphorylation of IkappaBalpha targets this inhibitor of NF-kappaB for ubiquitination and subsequent degradation, thus allowing NF-kappaB to enter the nucleus to turn on its target genes. We report here the identification of an IkappaB-ubiquitin (Ub) ligase complex containing the F-box/WD40-repeat protein, beta-TrCP, a vertebrate homolog of Drosophila Slimb. beta-TrCP binds to IkappaBalpha only when the latter is specifically phosphorylated by an IkappaB kinase complex. Moreover, immunopurified beta-TrCP ubiquitinates phosphorylated IkappaBalpha at specific lysines in the presence of Ub-activating (E1) and -conjugating (Ubch5) enzymes. A beta-TrCP mutant lacking the F-box inhibits the signal-induced degradation of IkappaBalpha and subsequent activation of NF-kappaB-dependent transcription. Furthermore, Drosophila embryos deficient in slimb fail to activate twist and snail, two genes known to be regulated by the NF-kappaB homolog, Dorsal. These biochemical and genetic data strongly suggest that Slimb/beta-TrCP is the specificity determinant for the signal-induced ubiquitination of IkappaBalpha.
Spencer
E
E
Department of Molecular Biology and Oncology, University of Texas Southwestern Medical Center, Dallas, Texas 75235-9148 USA.
Jiang
J
J
Chen
Z J
ZJ
D000818:Animals; D001483:Base Sequence; D018797:Cell Cycle Proteins; D002461:Cell Line, Transformed; D018076:DNA, Complementary; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004330:Drosophila / Q000196:embryology; D029721:Drosophila Proteins; D005260:Female; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D020672:I-kappa B Proteins; D019476:Insect Proteins; D008025:Ligases / Q000378:metabolism; D008297:Male; D008969:Molecular Sequence Data; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism; D009687:Nuclear Proteins / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D015398:Signal Transduction; D000071250:Snail Family Transcription Factors; D014157:Transcription Factors / Q000378:metabolism; D051879:Twist-Related Protein 1; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*; D044844:beta-Transducin Repeat-Containing Proteins