NF-κB/p50 and NF-κB/c-Rel differentially regulate the activity of the 3′αE-hsl,2 enhancer in normal murine B cells in an activation-dependent manner

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Abstract
The enhancer complex located 3′ to the CHα gene in the IgH locus (3αE) may regulate B cell function through its ability to act as a locus control region. Multiple, functionally relevant NF-κB binding sites are located within the 3′αE. NF-κB subunits, especially p50 and c-Rel, have also been shown to play critical and differential roles in regulating B cell proliferation, Ig secretion, germline CH transcription and Ig class switching. Thus, NF-κB could regulate B cell function in part through modulation of 3′αE activity. In this study we determined whether p50 and/or c-Rel regulate 3′αE activity in normal murine B cells and whether this depends on the nature of the B cell activator. For this purpose, we crossed p50- and c-Rel-deficient mice with mice that are transgenic for a 3′αE-hsl,2-human β-globin reporter gene, and established p50–/– or c-Rel–/– mice homozygous for the enhancer transgene. We show, using optimal stimulating conditions, that p50 selectively augments 3′α E-hsl,2 activity in lipopolysaccharide-activated B cells, whereas c-Rel is required for optimal 3′αE-hs1,2 induction in B cells activated through CD40.