ABIN-1 binds to NEMO/IKKγ and co-operates with A20 in inhibiting NF-κB

Nuclear factor kappa B (NF-kappa B) plays a pivotal role in inflammation, immunity, stress responses, and protection from apoptosis. Canonical activation of NF-kappa B is dependent on the phosphorylation of the inhibitory subunit I kappa B alpha that is mediated by a multimeric, high molecular weight complex, called I kappa B kinase (IKK) complex. This is composed of two catalytic subunits, IKK alpha and IKK beta, and a regulatory subunit, NEMO/IKK gamma. The latter protein is essential for the activation of IKKs and NF-kappa B, but its mechanism of action is not well understood. Here we identified ABIN-1 (A20 binding inhibitor of NF-kappa B) as a NEMO/IKK gamma-interacting protein. ABIN-1 has been previously identified as an A20-binding protein and it has been proposed to mediate the NF-kappa B inhibiting effects of A20. We find that both ABIN-1 and A20 inhibit NF-kappa B at the level of the IKK complex and that A20 inhibits activation of NF-kappa B by de-ubiquitination of NEMO/IKK gamma. Importantly, small interfering RNA targeting ABIN-1 abrogates A20-dependent de-ubiquitination of NEMO/IKK gamma and RNA interference of A20 impairs the ability of ABIN-1 to inhibit NF-kappa B activation. Altogether our data indicate that ABIN-1 physically links A20 to NEMO/IKK gamma and facilitates A20-mediated de-ubiquitination of NEMO/IKK gamma, thus resulting in inhibition of NF-kappa B.