부산대학교 도서관

Chromosomal translocations are considered as one of the major causes of lymphoid cancers. RAG complex, which is responsible for V(D)J recombination, can also cleave non-B DNA structures and cryptic RSSs in the genome leading to chromosomal translocations. The mechanism and factors regulating the illegitimate function of RAGs resulting in oncogenesis are largely unknown. Upon in silico analysis of 3760 chromosomal translocations from lymphoid cancer patients, we find that 93% of the translocation breakpoints possess adjacent cryptic nonamers (RAG binding sequences), of which 77% had CpGs at proximity. As a proof of principle, we show that RAGs can efficiently bind to cryptic nonamers present at multiple fragile regions and cleave at adjacent mismatches generated to mimic the deamination of CpGs. ChIP studies reveal that RAGs can indeed recognize these fragile sites on a chromatin context inside the cell. Finally, we show that AID, the cytidine deaminase, plays a significant role during the generation of mismatches at CpGs and reconstitute the process of RAG-dependent generation of DNA breaks both in vitro and inside the cells. Thus, we propose a novel mechanism for generation of chromosomal translocation, where RAGs bind to the cryptic nonamer sequences and direct cleavage at adjacent mismatch generated due to deamination of meCpGs or cytosines. Author summary: Chromosomal translocations are hallmark of lymphoid cancers. Recombination activating genes (RAGs) and activation induced cytidine deaminase (AID) are known to be responsible for chromosomal translocations. RAGs bind to DNA sequence called recombination signal sequence (RSS) consisting of heptamer, nonamer and spacer, and are involved in antigen receptor rearrangements. RAGs can also recognize and cleave other non-B DNA structures, thus causing DNA breaks. CpG dinucleotides are frequent in mammalian genome, which upon AID mediated deamination may form single nucleotide mismatches. In the present study, based on analysis of over 3500 chromosomal translocations seen in lymphoid cancer patients, we report that majority of breakpoints are seen when distance between CpG and nonamer like sequences (cryptic nonamer) is less than 80 bp. Using various biochemical and cellular assays, we show that mismatches generated due to deamination at CpGs or cytosines get cleaved by RAGs if cryptic nonamer is present at proximity. We propose a novel mechanism by which both AID and RAGs act together leading to generation of chromosomal translocation. [ABSTRACT FROM AUTHOR]