CUE Domain Containing 2 (CUEDC2) Negative Regulation Of NF-κB Activity Through Inhibition Of IκBα Kinase Phosphorylation

CUEDC2 is revealed by bioinformatics analysis as a CUE domain-contained protein, whose function is unknown. Identified as ubiquitin binding motifs, the CUE domains are small, moderately-conserved domains of about 40 amino acid residues that are found in a variety of eukaryotic proteins. CUE domains interact with both mono- and poly-ubiquitin, and have a dual role in mono- and poly-ubiquitin recognition as well as in facilitating intramolecular monoubiquitination. Recently, we demonstrate that CUEDC2 interacts with progesterone receptor and promotes progesterone-induced PR degradation by the ubiquitin-proteasome pathway. These provide an important insight into the function of CUEDC2 in breast cancer proliferation. In this study, we performed yeast two-hybrid screens to identify CUEDC2-interacting proteins and preliminary analysis on its biological function in NF-κB signaling, to help us understand its mechanisms.Here, we demonstrate that CUE domain containing 2 (CUEDC2), whose function was previously unknown, interacts with IKKα/βand represses NF-κB signaling by reducing IKK phosphorylation. Cytokine-induced activation of the IκB kinases IKKαand IKKβis a key step in the activation of the NF-κB pathway. Thus, precise control of IKK phosphorylation is a crucial component of NF-κB signaling. Specific knockdown of CUEDC2 by siRNA results in increased TNF-induced NF-κB activation, while enforced expression of CUEDC2 sensitizes cells to apoptotic stimuli such as TNF. Interestingly, we also found that CUEDC2 interacts with GADD34, a regulatory subunit of protein phosphatase 1 (PP1). Moreover, we demonstrated that inhibition of NF-κB activation by CUEDC2 is mediated, at least in part, by an IKK-CUEDC2-PP1 complex that exists endogenously. siRNA silencing of CUEDC2 revealed that it is required for formation of this complex, indicating CUEDC2 acts as an adaptor protein that targets IKK for dephosphorylation. Therefore, we have uncovered a potent inhibitor of NF-κB signaling that controls IKK activity, providing important insight into the function of CUEDC2 in NF-κB signaling.