Developing precursor (pré-) B lymphocytes initiate Ig: Locus expression and assembly at a stage that coincides with nuclear import of the transcription factor NFB. Subsequent stages of B lymphopoiesis constitutively express assembled IgK genes and possess high levels of nuclear NFB. To more precisely define the role of NFB in the regulation of endogenous IgK loci, we generated a panel of B lineage cell lines that express a dominant-negative form of iKBa, a major cytoplasmic inhibitor of NFtfB. We report that high ievel expression of this mutant I/tBa protein, termed ANI/cB, blocks lipopolysaccharide (LPS)-induced activation of NFB in pre-B cells as well as constitutive NFB activity in a mature B cell line. In pre-B cells that harbor unrearranged IgK loci, we demonstrate that NFrcB is required for LPS-mediated induction of germline IgK transcription and V to JK, recombination. In contrast, -yinterferon-induced expression of assembled Ig/c genes is largely unaffected. In mature B cells containing ANI/tB, constitutive expression of assembled IgK loci is preserved, despite dramatically reduced levels of nuclear NFB. We conclude that NFB plays a critical role in the initial activation of germline IgK loci, but may be dispensable for inducible or constitutive expression of assembled IgK alleles. Presently, we are using this panel of nuclear NFsB-deficient cell lines to dissect the roles of IgK enhancer elements in these development ally regulated processes.
|State||Published - Dec 1 1996|