Compositions and methods for modulating the activation of nuclear factor .kappa.B (NF-.kappa.B) are provided. The compositions comprise one or more agents that modulate ubiquitination of phosphorylated I.kappa.B.alpha. and/or I.kappa.B.beta.. Such compositions may be used for treating diseases associated with NF-.kappa.B activation. Modulating agents include human E3 ubiquitin ligases, antibodies thereto and variants thereof, as well as related proteins.