KLHL21 does not interfere with the interaction between IKKβ and TRAF2, TAK1, or IκBα. A, 293T cells were cotransfected with vector expressing IKKβ-EE, TBK1-EE, TRAF2-EE, TRAF6-EE, and KLHL21-3F as indicated. Lysates were immunoprecipitated with anti-FLAG and then analyzed by immunoblotting with anti-EE and anti-FLAG, respectively. B–D, IKKβ and KLHL21 were coexpressed with TRAF2 (B), TAK1 (C), or undegradable IκBα mutant (D), respectively. The interactions between IKKβ and TRAF2, TAK1, or IκBα were analyzed by coimmunoprecipitation. WCL, whole cell lysates; IP, immunoprecipitation; IB, immunoblotting. Error bars, S.E.