DAPK3 participates in the mRNA processing of immediate early genes in chronic lymphocytic leukaemia

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‐IgM‐ and CD40L‐dependent activation.