Reductions in IκBε and Changes in NF-κB Activity during B Lymphocyte Differentiation

Abstract

The levels and stability of IκBε have been examined in unstimulated and stimulated splenic B cells and compared with that of IκBα and IκBβ. Primary murine splenic B cells but not T cells were found to contain high levels of IκBε protein, equivalent to levels of the abundant IκBα. Most agents that activate IκBα and IκBβ degradation do not induce rapid degradation of IκBε. Interestingly, however, the levels of IκBε, but not of IκBα or IκBβ, are dramatically reduced upon the stimulation of B cells both in vivo and in vitro. Since IκBε exhibits substrate specificity for NF-κB Rel homodimers, this suggested the possibility that changes in NF-κB-responsive genes might also occur during this transition. Consistent with this hypothesis, we found that a NF-κB reporter construct sensitive to p65/RelA homodimers is activated at the time that IκBε levels decline following B cell stimulation. In IgG+ B cell lines, which contain low levels of IκBε, this same reporter construct was inactive, suggesting that the increases in Rel homodimer activity that accompany B cell stimulation are transient. However, there are differences in the level of expression of NF-κB-responsive genes in these IgG+ B cell lines compared with their IgM+ counterparts. From these data, we conclude that there are transient changes in NF-κB activity due to reductions in IκBε, which might contribute to long-term, persistent changes that accompany B cell differentiation. We propose an important role for IκBε in the differential regulation of nuclear NF-κB activity in stimulated B cells.

Lipopolysaccharide fromSalmonella entericaActivates NF-κB through both Classical and Alternative Pathways in Primary B Lymphocytes

“…IBε levels decreased more rapidly and more significantly than IB␤. Our data are consistent with previous results showing that IBε levels are reduced much more dramatically than IB␣ levels after B-cell stimulation with LPS for 24 h. However, it must be stressed that, in interleukin-4-activated B cells, IBε does not degrade as rapidly as IB␣ after LPS stimulation, thus suggesting that the stimulation of degradation of the different IB proteins not only depends on the stimulus but also exhibits cell activation stage specificity (11). It appears that the canonical and noncanonical NF-B pathways can be distinguished by their dependence on kinases that regulate the stimulus degradation of IB proteins IKK␤ and IKK␣, respectively (20,21).…”

Multiple roles of the NF‐?B signaling pathway regulated by coupled negative feedback circuits

“…NF-B is intimately involved in CSR by binding to the promoter of the immunoglobulin C␥1 gene (34) as well as by stimulating the expression of genes involved in CSR (35). The exact involvement of different NF-B and IB isoforms in CSR is still unknown (33). Our results can give some hints regarding this interesting phenomenon.…”

NF-κB, the first quarter-century: remarkable progress and outstanding questions

“…More recently, it has been observed that B cells lacking IkBe have augmented basal and B-cell receptor (BCR)-induced nuclear c-Rel (Clark et al 2011). IkBe is differentially expressed during B-cell development and has been proposed to regulate both p65-and c-Rel-containing NF-kB complexes in B cells (Doerre and Corley 1999;Doerre et al 2005). The temporal and cell type-specific degradation and expression of IkBe support the hypothesis that different IkBs play unique functions in NF-kB responses and indicate that a more detailed analysis of IkBe function in vivo is needed.…”