C99R mutation in IRF4 drives a novel gain of function binding and gene upregulation in classical Hodgkin lymphoma [ChIP-Seq]

Disease-causing mutations in genes encoding transcription factors (TF) are frequent in hematopoietic malignancies and might affect TF-interactions with respective DNA-binding motifs. Here, we report the characterization of a recurrent somatic mutation c.295T>C in the IRF4 gene in classic Hodgkin lymphoma (cHL) leading to a C99R exchange. IRF4-C99R is located in the center of the IRF4 alpha3-recognition helix contacting the DNA 5´-GAAA-3´ IRF consensus sequence. IRF4-C99R fundamentally alters IRF4 DNA-binding, combining loss-of-binding at canonical IRF motifs and neomorph gain-of-binding at canonical and non-canonical IRF composite elements (CEs), in particular AP-1-IRF-CEs (AICEs). In line, IRF4-C99R profoundly impairs IRF4-dependent plasma cell induction, and specifically up-regulates degenerate-AICE-dependent distinct cHL disease-characteristic genes. These data document an unprecedented mutation-induced shift of TF binding specificity and its impact for lymphoma pathogenesis and TF modulation. IRF4 and JunB ChIP-Seq from IRF4WT NHL and IRF4WT, IRF4C99R HL-derived cell lines