Regulation of I kappa B beta in WEHI 231 mature B cells

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