E2A and IRF-4/Pip promote chromatin modification and transcription of the immunoglobulin κ locus in pre-B cells

The immunoglobulin kappa light chain (Ig kappa) locus is regulated in a lineage- and stage-specific manner during B-cell development. The highly restricted timing of V to J gene recombination at the pre-B-cell stage is under the control of two enhancers, the intronic enhancer (kappa Ei) and the 3' enhancer (KEY), flanking the constant exon. E2A transcription factors have been indicated to be directly involved in the regulation of Ig kappa locus activation. In this study, we utilize E2A-deficient pre-B cells to directly investigate the mechanism of E2A-mediated IgK activation. We demonstrate that IgK germ line transcription is severely impaired and recombination is blocked in the absence of E2A. Reconstitution of E2A(-/-) pre-B cells with inducible human E2A (E47R) is sufficient to promote chromatin modification Of IgK and rescue Ig kappa germ line transcription and J kappa gene recombinase accessibility. Furthermore, we show that increased E2A recruitment to kappa Ei and kappa E3' correlates with activation Of IgK in pre-B cells and that recruitment of E2A to kappa E3' is in part dependent on the transcription factor IRF-4. Inhibition of IRF-4 expression in pre-B cells leads to a significant reduction Of Ig kappa germ line transcription and enhancer acetylation. In the absence of E2A, increased IRF-4 expression is not sufficient to promote IgK enhancer chromatin modification or transcription, suggesting that the sequential involvement of IRF-4 and E2A is necessary for the activation of the IgK locus. Finally, we provide genetic evidence in the mouse that E2A gene dosage can influence the development of pre-B cells during the phase of IgK gene activation.