The hallmark of Burkitt’s lymphoma is t(8;14) translocations resulting in overexpression of the c-myc gene, however, the mechanism(s) with which the DNA breakages occur remains unclear. Interestingly, one of the breakpoint hotspots in the c-myc gene occurs at a region capable of adopting a specific non-B-DNA structure, H-DNA. Thus, we hypothesize that DNA secondary structure plays an important role in chromosomal breakage and translocation. We found that a sequence capable of adopting H-DNA near the breakpoint in the c-myc gene induces DNA double strand-breaks (DSBs) in mammalian cells and induces a mutation frequency ∼20-fold above background. Thus, our initial findings provide a plausible mechanism for the translocation in human lymphoma. To gain a better understanding of the mechanism of H-DNA-induced mutagenesis, we explored possible impacting factors such as DNA replication and repair. We observed that the H-DNA-induced mutagenesis is orientation dependent, suggesting the involvement of DNA replication and/or transcription. Interestingly, we show the existence of replication-independent H-DNA-induced cleavage and mutagenesis in HeLa cell free extracts. Additionally, we tested the role of DNA repair in H-DNA-induced mutagenesis and found that the human mismatch repair (MMR) protein, hMSH2, contributes to the instability. Taken together, our results indicate that the H-DNA-induced DSBs and mutagenesis require multiple DNA metabolic processes such as replication and repair. Thus, environmental stresses that activate these processes might result in increased risk of H-DNA-induced genomic instability.
[Proc Amer Assoc Cancer Res, Volume 46, 2005]