Direct phosphorylation of IkappaB by IKKalpha and IKKbeta: discrimination between free and NF-kappaB-bound substrate.
A large protein complex mediates the phosphorylation of the inhibitor of kappaB (IkappaB), which results in the activation of nuclear factor kappaB (NF-kappaB). Two subunits of this complex, IkappaB kinase alpha (IKKalpha) and IkappaB kinase beta (IKKbeta), are required for NF-kappaB activation. Purified recombinant IKKalpha and IKKbeta expressed in insect cells were used to demonstrate that each protein can directly phosphorylate IkappaB proteins. IKKalpha and IKKbeta were found to form both homodimers and heterodimers. Both IKKalpha and IKKbeta phosphorylated IkappaB bound to NF-kappaB more efficiently than they phosphorylated free IkappaB. This result explains how free IkappaB can accumulate in cells in which IKK is still active and thus can contribute to the termination of NF-kappaB activation.
Laboratory of Gene Regulation and Signal Transduction, Department of Pharmacology, University of California at San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA.
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E
Zandi
Y
Y
Chen
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M
Karin
D000818:Animals; D002460:Cell Line; D019281:Dimerization; D004789:Enzyme Activation; D006367:HeLa Cells; D018257:Helix-Loop-Helix Motifs; D006801:Humans; D051550:I-kappa B Kinase; D016350:Leucine Zippers; D009154:Mutation; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D018411:Spodoptera; D051841:Transcription Factor RelB; D014157:Transcription Factors
D016328:NF-kappa B; D011518:Proto-Oncogene Proteins; C497593:RELB protein, human; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D051841:Transcription Factor RelB; D017346:Protein Serine-Threonine Kinases; C496559:CHUK protein, human; D051550:I-kappa B Kinase; C496560:IKBKB protein, human; C496565:IKBKE protein, human