Generation of Genomic Alteration from Cytidine Deamination

The sources of genome instability can be attributed to many extra- and exo- cellular factors accompanying various biological processes. In leukemia and lymphomas, the collateral effect of programmed DNA alterations during immune diversification is the major source of genome instability. Cytidine deamination from cytidine (C) to uridine (U) at immunoglobulin (Ig) gene loci is required for initiation of antibody diversification, while the same process also contributes to recurrent translocation or mutations outside of Ig loci in lymphocyte-origin tumors. Furthermore, genome sequencing of cancer cells from many tissue origins revealed a significant enrichment of cytidine deaminase mutagenesis signature in human cancers. Thus, cytidine deamination, which can intensively happen in an enzyme-dependent fashion at specific genomic regions, is a widespread genome instability source across many tumor types. AID/APOBEC superfamily proteins are the main single-stranded DNA deaminases in eukaryotes, which play vital roles in adaptive and innate immunity. Their deamination products can be channeled into mutations, insertions and deletions (indels), clusters of mutations called kaetagis, or chromosomal rearrangements/translocations. Here, we review the generation of genome instability from AID/APOBEC-dependent cytidine deamination with emphasis on the most studied enzyme, AID.