Abstract
Antibody gene expression is primarily controlled by transcription factors including the B-cell specific factor Oct2. Gene expression is also controlled through epigenetics: heritable, reversible changes, such as histone modifications which alter the ability of other proteins to interact with the DNA rather than to mutations in DNA sequence itself. Brd4 binds to acetylated lysine, including those on histones and helps to activate transcription.
We therefore investigated the role of Brd4 in IgG production and the mechanisms involved.
We treated the human B cell line CLNH11.4 with the Brd4 inhibitor JQ1(+) and its negative enantiomer JQ1(-) and measured cell viability, proliferation and IgG production. Whilst cell viability was unaffected by JQ1 both proliferation and IgG production were reduced by JQ1(+) but not (-) in a concentration-dependent manner.
Transcription of IGKC (light chain) and IGH1G (heavy chain), measured by RT-qPCR, was significantly reduced by JQ1(+) treatment. JQ1(+) did not reduce the protein levels of Brd4 or Oct2 per se but reduced the ability of Brd4 and Oct2 to co-immunoprecipitate. The interaction was due to the presence of acetylated lysine residues on Oct2. Finally we used Chromatin Immunoprecipitation to confirm that JQ1 affected Brd4 and Oct2 binding to Ig gene promoters.
Our results indicate that Oct2 contains acetylated lysine residues, which is bound by Brd4. Brd4 in turn is bound to acetylated histones in the immunoglobulin promoter regions and is critical for Oct2 binding. Therefore, Brd4 plays a crucial role regulation B cell specific gene expression and immunoglobulin production.
- © 2014 ERS