Inducible nuclear expression of NF-κB in primary B cells stimulated through the surface Ig receptor

Constitutive expression of NF-κB has been associated with developmental maturity in B cells on the basis of studies using continuously growing cell lines and plasmacytomas; however, little is known about the behavior of NF-κB in primary, mature B cells. In the present work, the regulation of NF-κB expression was studied by analyzing subcellular fractions of adult murine splenic B cells with the electrophoretic mobility shift assay using a κB-containing oligonucleotide. Although nuclear extracts from resting B cells contained κB-binding activity, additional κB-binding activity was present in cytosolic fractions in a form that became apparent after treatment with detergent. Competition analysis indicated that the DNA binding activity detected by electrophoretic gel mobility shift assay was specific for the κB motif, and UV photo-cross-linking showed the molecular size of κB-binding protein to be similar to that of the DNA binding subunit of NF-κB. Nuclear expression of κB-binding activity was markedly induced by treatment of B cells with phorbol ester or with LPS. Most notably, κB-binding activity was induced after surface IgR cross-linking, and the mechanism of this induction involved PKC. Further, anti-Ig-induced activity was superinduced in the presence of cycloheximide. These results indicate that nuclear NF-κB is rapidly induced as a result of B cell stimulation, and further suggest that NF-κB may play a specific role in mature B cells after ligand binding to surface Ig distinct from its postulated developmental role as a stage-specific factor involved in κ-enhancer function.