The subunit composition of NF-kappa B complexes changes during B-cell development.

The transcription factor NF-kappa B, shown to be essential for expression of the immunoglobulin C kappa gene, is a key regulatory component in pre-B to B-cell differentiation. While previous studies have used lymphoid cell line models, here we examine the expression and subunit composition of rel/NF-kappa B complexes in normal murine pre-B and B lymphocytes. Two major NF-kappa B complexes are detected in pre-B and B cells. A high mobility complex, found in pre-B (Cb) and B cells (C beta) is a homodimer of the NF-kappa B subunit p50. In pre-B cells, the slower migrating complex (Ca), which is predominantly cytoplasmic, is largely comprised of p50 and p65, whereas in B cells, a nuclear and cytoplasmic complex (C alpha) of identical mobility to Ca mainly consists of p50 and p75c-rel. While p50 and p65 levels do not change during pre-B to B-cell differentiation, p75c-rel is 5- to 6-fold more abundant in B cells compared to pre-B cells, a finding consistent with the switch in NF-kappa B subunit usage. During lipopolysaccharide-induced B-cell proliferation, transient up-regulation of both the nuclear p50 homodimer and p75c-rel containing complex is mirrored by a concurrent increase in c-rel and p105 but not p65 mRNA expression, a finding consistent with rel-NF-kappa B expression in B cells being controlled by an autoregulatory mechanism.