Coordinate transcription and V(D)J recombination of the kappa immunoglobulin light-chain locus: NF-κB-dependent and -independent pathways of activation

To further elucidate the potential role of mitogens and cytokines in regulation of the kappa immunoglobulin light-chain locus, we have characterized the activation of transcription factor binding, kappa germ line transcription, DNase I hypersensitivity, and Vκ-to-Jκ recombination upon induction of model pre-B-cell lines. We find that both lipopolysaccharide (LPS) and gamma interferon (IFN-γ) are capable of activating germ line transcription, DNase I hypersensitivity, and recombination of the kappa locus. We also find that transforming growth factor β is capable of completely inhibiting LPS activation of transcription and recombination but has no apparent effect on activation of transcription factor binding, including activation of NF-κB. To address the functional role of NF-κB in LPS and IFN-γ induction of these events, we blocked the nuclear translocation of NF-κB by overexpression of a dominant negative mutant of IκB-α (IκBΔN). Overexpression of the IκBΔN protein results in an inhibition of LPS but not IFN-γ activation of germ line transcription, DNase I hypersensitivity, and Vκ-to-Jκ recombination. Our results demonstrate that activation of NF-κB is necessary but not sufficient for LPS activation of transcription and recombination at kappa. These results also suggest that NF-κB is not required for IFN-γ activation of transcription or recombination. These results are important in establishing that there are multiple independent pathways of activation of both transcription and recombination.