Association of the Adaptor TANK with the IκB Kinase (IKK) Regulator NEMO Connects IKK Complexes with IKKε and TBK1 Kinases*

Canonical activation of NF-κB is mediated via phosphorylation of the inhibitory IκB proteins by the IκB kinase complex (IKK). IKK is composed of a heterodimer of the catalytic IKKα and IKKβ subunits and a presumed regulatory protein termed NEMO (NF-κB essential modulator) or IKKγ. NEMO/IKKγ is indispensable for activation of the IKKs in response to many signals, but its mechanism of action remains unclear. Here we identify TANK (TRAF family member-associated NF-κB activator) as a NEMO/IKKγ-interacting protein via yeast two-hybrid analyses. This interaction is confirmed in mammalian cells, and the domains required are mapped. TANK was previously shown to assist NF-κB activation in a complex with TANK-binding kinase 1 (TBK1) or IKKε, two kinases distantly related to IKKα/β, but the underlying mechanisms remained unknown. Here we show that TBK1 and IKKε synergize with TANK to promote interaction with the IKKs. The TANK binding domain within NEMO/IKKγ is required for proper functioning of this IKK subunit. These results indicate that TANK can synergize with IKKε or TBK1 to link them to IKK complexes, where the two kinases may modulate aspects of NF-κB activation.