Cross-linking of the B-cell receptor (BCR) induces transcriptional activation of immediate early genes (IEGs) including EGR1 and DUSP2 in chronic lymphocytic leukaemia (CLL). Here, we have shown that this transcriptional activation correlated with histone H3 threonine 6 and 11 phosphorylation.Both transcription and histone post-translational modifications are repressed by ibrutinib, a small molecule inhibitor used in CLL treatment. Moreover, we have identified the death-associated protein kinase 3 (DAPK3), as the kinase mediating these histone phosphorylation marks in response to activation of the BCR signalling pathway with this kinase being recruited to RNA polymerase II in an anti-IgM-dependent manner. DAPK inhibition mimics ibrutinib-induced repression of both IEG mRNA and histone H3 phosphorylation and has anti-proliferative effect comparable to ibrutinib in CLL in vitro. DAPK inhibitor does not repress transcription itself but impacts on mRNA processing and has a broader anti-tumour effect than ibrutinib, by repressing both anti-IgMand CD40L-dependent activation.Abbreviations (U/M)-CLL, (unmutated/mutated)-chronic lymphocytic leukaemia; BCR, B-cell receptor; BTK, Bruton's tyrosine kinase; Co-IP, coimmunoprecipitation; CpG ODN, CpG oligodeoxynucleotides; DAPK1, death-associated protein kinase 1; DAPK3, death-associated protein kinase 3; DAPKi, DAPK inhibitor; DLBCL, diffuse large B-cell lymphoma; DUSP2, dual-specificity phosphatase 2; EGR1, early growth response 1; GAIT, interferon-gamma-activated inhibitor of translation; GAPDH, glyceraldehyde 3-phosphate dehydrogenase; H3T11-P, histone H3 threonine 11 phosphorylation; H3T6-P, histone H3 threonine 6 phosphorylation; IEG, immediate early gene; IFNc, interferongamma; IgHV, immunoglobulin heavy chain variable (region); Kb, kilobase; MYD88, myeloid differentiation primary response 88; NF-jB, nuclear factor-kappa B; NLC, nurse-like cell; PLCc2, phospholipase Cc2; PPP6C, protein phosphatase 6 catalytic subunit; PTM, posttranslational modification; qPCR, quantitative polymerase chain reaction; RNA pol II S2-P, RNA polymerase II serine 2 phosphorylation; RPMI, Roswell Park Memorial Institute (media); siRNA, small interfering ribonucleic acid; TBP, TATA-box binding protein; TLR, Toll-like receptor; TSS, transcription start site; ZIPK, zipper-interacting protein kinase.
