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NEMO oligomerization in the dynamic assembly of the IκB kinase core complex
Author(s) -
Fontan Elisabeth,
Traincard François,
Levy Samuel G.,
Yamaoka Shoji,
Véron Michel,
Agou Fabrice
Publication year - 2007
Publication title -
the febs journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.981
H-Index - 204
eISSN - 1742-4658
pISSN - 1742-464X
DOI - 10.1111/j.1742-4658.2007.05788.x
Subject(s) - kinase , iκb kinase , chemistry , protein kinase domain , phosphorylation , microbiology and biotechnology , biophysics , biochemistry , biology , signal transduction , nf κb , mutant , gene
NF‐κB essential modulator (NEMO) plays an essential role in the nuclear factor κB (NF‐κB) pathway as a modulator of the two other subunits of the IκB kinase (IKK) complex, i.e. the protein kinases, IKKα and IKKβ. Previous reports all envision the IKK complex to be a static entity. Using glycerol‐gradient ultracentrifugation, we observed stimulus‐dependent dynamic IKK complex assembly. In wild‐type fibroblasts, the kinases and a portion of cellular NEMO associate in a 350‐kDa high‐molecular‐mass complex. In response to constitutive NF‐κB stimulation by Tax, we observed NEMO recruitment and oligomerization to a shifted high‐molecular‐mass complex of 440 kDa which displayed increased IKK activity. This stimulus‐dependent oligomerization of NEMO was also observed using fluorescence resonance energy transfer after a transient pulse with interleukin‐1β. In addition, fully activated, dimeric kinases not bound to NEMO were detected in these Tax‐activated fibroblasts. By glycerol gradient ultracentrifugation, we also showed that: (a) in fibroblasts deficient in IKKα and IKKβ, NEMO predominantly exists as a monomer; (b) in NEMO‐deficient fibroblasts, IKKβ dimers are present that are less stable than IKKα dimers. Intriguingly, in resting Rat‐1 fibroblasts, 160‐kDa IKKα–NEMO and IKKβ–NEMO heterocomplexes were observed as well as a significant proportion of NEMO monomer. These results suggest that most NEMO molecules do not form a tripartite IKK complex with an IKKα–IKKβ heterodimer as previously reported in the literature but, instead, NEMO is able to form a complex with the monomeric forms of IKKα and IKKβ.