Regulation of IκBβ in WEHI 231 Mature B Cells

Abstract

Constitutive activation of NF-κB in WEHI 231 early mature B cells resembles the persistent activation of NF-κB that is observed upon prolonged stimulation of other cells. In both cases, NF-κB DNA binding complexes are found in the nucleus, despite the abundance of cytosolic IκBα. Recently, we have shown that prolonged activation of 70Z/3 cells with lipopolysaccharide results in the degradation of IκB β, followed by its subsequent resynthesis as a hypophosphorylated protein. This protein was shown to facilitate transport of a portion of NF-κB to the nucleus in a manner that protects it from cytosolic IκBα. We now demonstrate that the most abundant form of IκB β in WEHI 231 cells is a hypophosphorylated protein. This hypophosphorylated IκB β is found in a stable complex with NF-κB in the cytosol and is also detected in NF-κB DNA binding complexes in the nucleus. It is likely that hypophosphorylated IκB β in WEHI 231 cells also protects NF-κB from IκBα, thus leading to the continuous nuclear import of this transcription factor.