G-quadruplex stabilization induces DNA breaks in pericentromericrepetitive DNA sequences in B lymphocytes

DNA secondary G-quadruplex (G4) structures can impair and even obstruct the DNA replication. Defects in processing G4 structures are associated with replication stress, a common property of both B cell cancers and hyperproliferative premalignant cells. Genome instability arising from replication stress is a hallmark of cancer and strongly contributes to the chromosome rearrangements in B cell cancers. Here, we define the impact of G4-stabilizing ligands on generating genome instability in primary and malignant B cells. Treatment with the G4-stabilizing compound pyridostatin (PDS) causes breaks and chromosome rearrangements at ribosomal DNA and pericentromeric major satellite regions in both mouse primary B cell culture and CH12 lymphoma cells. PDS also causes extensive pericentromeric DNA damage in immortalized human B cell lines. Remarkably, PDS causes high level of tetraploid metaphase cells correlated with high level of dicentric chromosomes specifically in primary but not in CH12 B cells. Unlike primary B cells, CH12 cells undergo checkpoint activation and strong G2/M arrest in response to PDS treatment thus preventing tetraploid appearance. Altogether, these results highlight the difference between primary and malignant B cells in response to PDS, revealing the therapeutic potential of G4-stabilizing drugs to selectively suppress tumor cell growth and proliferation. Significance StatementG-quadruplexes are guanine-rich DNA secondary structures, abundantly found in most eukaryotic genomes. Stabilization of G-quadruplexes creates an obstacle for DNA replication, particularly in DNA repair-deficient cells. We show that G-quadruplex stabilization by the small molecule pyridostatin leads to recurrent DNA breaks and aberrant chromosomal fusions in the repetitive DNA sequences found at major satellite pericentromeric repeats and ribosomal DNA arrays in mouse primary B cells. Pyridostatin also causes extensive pericentromeric DNA damage and pathogenic rearrangements in mouse and human B cell lymphoma cell lines. Thus we have found a role for G-quadruplexes in inciting damage driving the formation of recurrent rearrangements observed in lymphoid cancers.