Regulatory subunit NEMO promotes polyubiquitin-dependent induction of NF-κB through a targetable second interaction with upstream activator IKK2

J Biol Chem. 2022 May;298(5):101864. doi: 10.1016/j.jbc.2022.101864. Epub 2022 Mar 24.

Abstract

Canonical NF-κB signaling through the inhibitor of κB kinase (IKK) complex requires induction of IKK2/IKKβ subunit catalytic activity via specific phosphorylation within its activation loop. This process is known to be dependent upon the accessory ubiquitin (Ub)-binding subunit NF-κB essential modulator (NEMO)/IKKγ as well as poly-Ub chains. However, the mechanism through which poly-Ub binding serves to promote IKK catalytic activity is unclear. Here, we show that binding of NEMO/IKKγ to linear poly-Ub promotes a second interaction between NEMO/IKKγ and IKK2/IKKβ, distinct from the well-characterized interaction of the NEMO/IKKγ N terminus to the "NEMO-binding domain" at the C terminus of IKK2/IKKβ. We mapped the location of this second interaction to a stretch of roughly six amino acids immediately N-terminal to the zinc finger domain in human NEMO/IKKγ. We also showed that amino acid residues within this region of NEMO/IKKγ are necessary for binding to IKK2/IKKβ through this secondary interaction in vitro and for full activation of IKK2/IKKβ in cultured cells. Furthermore, we identified a docking site for this segment of NEMO/IKKγ on IKK2/IKKβ within its scaffold-dimerization domain proximal to the kinase domain-Ub-like domain. Finally, we showed that a peptide derived from this region of NEMO/IKKγ is capable of interfering specifically with canonical NF-κB signaling in transfected cells. These in vitro biochemical and cell culture-based experiments suggest that, as a consequence of its association with linear poly-Ub, NEMO/IKKγ plays a direct role in priming IKK2/IKKβ for phosphorylation and that this process can be inhibited to specifically disrupt canonical NF-κB signaling.

Keywords: NF-κB; enzyme inactivation; peptide interaction; polyubiquitin chain; protein kinase.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Humans
  • I-kappa B Kinase* / metabolism
  • NF-kappa B* / metabolism
  • Polyubiquitin* / metabolism
  • Protein Binding

Substances

  • IKBKG protein, human
  • NF-kappa B
  • Polyubiquitin
  • I-kappa B Kinase
  • IKBKB protein, human