E2A and IRF-4/Pip Promote Chromatin Modification and Transcription of the Immunoglobulin κ Locus in Pre-B Cells

Abstract

The immunoglobulin kappa light chain (Igκ) 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 (κEi) and the 3′ enhancer (κE3′), flanking the constant exon. E2A transcription factors have been indicated to be directly involved in the regulation of Igκ locus activation. In this study, we utilize E2A-deficient pre-B cells to directly investigate the mechanism of E2A-mediated Igκ activation. We demonstrate that Igκ 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 Igκ and rescue Igκ germ line transcription and Jκ gene recombinase accessibility. Furthermore, we show that increased E2A recruitment to κEi and κE3′ correlates with activation of Igκ in pre-B cells and that recruitment of E2A to κE3′ 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 Igκ germ line transcription and enhancer acetylation. In the absence of E2A, increased IRF-4 expression is not sufficient to promote Igκ enhancer chromatin modification or transcription, suggesting that the sequential involvement of IRF-4 and E2A is necessary for the activation of the Igκ 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 Igκ gene activation.

We thank Mike Krangel and Annette Jackson for providing helpful discussions and technical support for the histone acetylation studies and Mary Elizabeth Jones and Jason Wojciechowski for critical reading of the manuscript.

This work was supported by National Institutes of Health grants CA072433 to Y. Zhuang and HL48702 and AI40227 to M. Schlissel.

We have no conflicting financial interests.