Nuclear nf-κb is essential for b-cell specific demethylation of the igκ locus

DNA methylation plays a role in the regulation of eukaryotic gene expression by acting in cis to modulate protein-DNA interactions. We have recently identified a cis acting regulatory element located in the immunoglobulin κ chain gene that directs demethylation in a B-cell specific manner. This element, which induces bidirectional demodification in a distance, orientation and position-independent manner, is localized on a single, complex 1.5 kb cis acting fragment containing the intronic κ-chain transcriptional enhancer, a matrix attachment region (MAR) and a novel element located 3′ to Jκ5. The demodification reaction is both tissue- and stage-specific. While any MAR sequence (including evolutionarily distant) is sufficient for this reaction, mutation analysis indicates that tissue specificity is mediated by κB binding sequences within the κ intronic enhancer. The plasmacytoma cell line S107 lacks κB binding activity and fails to demethylate the κ locus. However, B-cell specific demethylation is restored by the introduction of an active RelB gene. This represents the first demonstration of a transacting factor which confers cell-type-specific demethylation.