RIP1 modification with Lys-63 polyubiquitin chains was shown to be essential for TNF-induced activation of NF-kB (Ea et al. 2006). It is thought that TRAF family members mediate this Lys63-linked ubiquitination of RIP1 (Wertz et al. 2004, Tada et al 2001, Vallabhapurapu and Karin 2009), which may facilitate recruitment of the TAK1 complex and thus activation of NF-kB. Binding of NEMO to Lys63-linked polyubiquitinated RIP1 is also required in the signaling cascade from the activated receptor to the IKK-mediated NF-kB activation (Wu et al. 2006)."^^ . "Reviewed: D'Eustachio, P, 2011-12-07"^^ . "Reviewed: Upton, JW, Mocarski, ES, 2012--0-2-"^^ . "In humans, the IKKs - IkB kinase (IKK) complex serves as the master regulator for the activation of NF-kB by various stimuli. It contains two catalytic subunits, IKK alpha and IKK beta, and a regulatory subunit, IKKgamma/NEMO. The activation of the IKK complex and the NFkB mediated antiviral response are dependent on the phosphorylation of IKK alpha/beta at its activation loop and the ubiquitination of NEMO [Solt et al 2009; Li et al 2002]. NEMO ubiquitination by TRAF6 is required for optimal activation of IKKalpha/beta; it is unclear if NEMO subunit undergoes K63-linked or linear ubiquitination.

This basic trimolecular complex is referred to as the IKK complex. Each catalytic IKK subunit has a N-term kinase domain and leucine zipper (LZ) motifs, a helix-loop-helix (HLH) and a C-ter NEMO binding domain (NBD). IKK catalytic subunits are dimerized through their LZ motifs.

IKK beta is the major IKK catalytic subunit for NF-kB activation. Phosphorylation in the activation loop of IKK beta requires Ser177 and Ser181 and thus activates the IKK kinase activity, leading to the IkB alpha phosphorylation and NF-kB activation."^^ . . . . . . . . . . . . . "RIP1 facilitates IKK complex phosphorylation"^^ . . . . .