GβL regulates TNFα-induced NF-кB signaling by directly inhibiting the activation of IкB kinase

The transcriptional activation of NF-кB, a critical player in both physiological and pathological cellular responses to diverse cytokines, is dependent on IKK activation. Although molecular mechanisms underlying IKK activation have been well elucidated, the processes that negatively regulate IKK activity are still largely unknown. Using yeast two-hybrid screening, we have identified GβL as an interacting partner of IKKβ. In this study, we demonstrate that GβL interacts with IKKα and IKKβ in vitro and in vivo. The C-terminal WD domains of GβL are required for the interaction with both the kinase domain and leucine zipper domain of IKKβ. Overexpression of GβL inhibits TNFα-induced activation of NF-кB signaling, while down-regulation of GβL expression by small interfering RNA enhances NF-кB activity. GβL constitutively interacts with IKKβ, and this interaction is enhanced by TNFα treatment. GβL also inhibits TNFα-induced phosphorylation of IKKs. Taken together, these data suggest that GβL is involved in the negative regulation of TNFα-stimulated NF-кB signaling through a direct interaction with IKK.