Journal of Biological Chemistry
Volume 280, Issue 52, 30 December 2005, Pages 43272-43279
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Mechanisms of Signal Transduction
Site-specific Monoubiquitination of IκB Kinase IKKβ Regulates Its Phosphorylation and Persistent Activation*

https://doi.org/10.1074/jbc.M508656200Get rights and content
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Transcription factor NF-κB governs the expression of multiple genes involved in cell growth, immunity, and inflammation. Nuclear translocation of NF-κB is regulated from the cytoplasm by IκB kinase-β (IKKβ), which earmarks inhibitors of NF-κB for polyubiquination and proteasome-mediated degradation. Activation of IKKβ is contingent upon signal-induced phosphorylation of its T loop at Ser-177/Ser-181. T loop phosphorylation also renders IKKβ a substrate for monoubiquitination in cells exposed to chronic activating cues, such as the Tax oncoprotein or sustained signaling through proinflammatory cytokine receptors. Here we provide evidence that the T loop-proximal residue Lys-163 in IKKβ serves as a major site for signal-induced monoubiquitination with significant regulatory potential. Conservative replacement of Lys-163 with Arg yielded a monoubiquitination-defective mutant of IKKβ that retains kinase activity in Tax-expressing cells but is impaired for activation mediated by chronic signaling from the type 1 receptor for tumor necrosis factor-α. Phosphopeptide mapping experiments revealed that the Lys-163 → Arg mutation also interferes with proper in vivo but not in vitro phosphorylation of cytokine-responsive serine residues located in the distal C-terminal region of IKKβ. Taken together, these data indicate that chronic phosphorylation of IKKβ at Ser-177/Ser-181 leads to monoubiquitin attachment at nearby Lys-163, which in turn modulates the phosphorylation status of IKKβ at select C-terminal serines. This mechanism for post-translational cross-talk may play an important role in the control of IKKβ signaling during chronic inflammation.

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*

This work was supported in part by Grants CA082556, AI052379, HL068744, and HL069452 from the National Institutes of Health. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. 1 and 2.

1

Present address: Math & Science Division, Volunteer State Community College, Gallatin, TN 37066.

2

Supported by National Research Service Award T32 HL069765.