Mutations in CHD2 cause defective association with active chromatin in chronic lymphocytic leukemia

Great progress has recently been achieved in the understanding of the genomic alterations driving chronic lymphocytic leukemia (CLL). Nevertheless, the specific molecular mechanisms governing chromatin remodeling in CLL are unknown. Here we report the genetic and functional characterization of somatic mutations affecting the chromatin remodeler CHD2, one of the most frequently mutated genes in CLL (5.3%) and in monoclonal B lymphocytosis (MBL, 7%), a B-cell expansion that can evolve to CLL. Most of the mutations affecting CHD2, identified by whole-exome sequencing of 456 CLL and 43 MBL patients, are either truncating or affect conserved residues in functional domains, thus supporting a putative role for CHD2 as a tumor suppressor gene. CHD2 mutants show altered nuclear distribution, and a chromodomain helicase DNA binding protein 2 (CHD2) mutant affected in its DNA-binding domain exhibits defective association with active chromatin. Clinicobiological analyses show that most CLL patients carrying CHD2 mutations also present mutated immunoglobulin heavy chain variable region genes (IGHVs), being the most frequently mutated gene in this prognostic subgroup. This is the first study providing functional evidence supporting CHD2 as a cancer driver and opens the way to further studies of the role of this chromatin remodeler in CLL.