ABIN-1 Binds to NEMO/IKKγ and Co-operates with A20 in Inhibiting NF-κB

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