Role of AID/APOBEC cytidine deaminases in genome destabilization in cancer: insights from a yeast test system

   Uncontrolled expression of AID/APOBEC family cytidine deaminases is an important factor in genome destabilization during carcinogenesis. In normal cells, these enzymes deaminate cytosine to uracil in RNA or DNA during mRNA editing, defense against viruses, and immunoglobulin affinity maturation. Misregulation of AID/APOBEC gene expression results in non-specific deamination of genomic DNA and, consequently, increased mutagenesis. Somatic mutations induced by AID/APOBEC can trigger the process of carcinogenesis and contribute to the development of cancer cell resistance to therapy and increased tumor aggressiveness. A convenient approach to studying the mechanisms of AID/APOBEC cytidine deaminase-dependent mutagenesis is using of a heterologous expression system in yeast strains Saccharomyces cerevisiae carrying human cytidine deaminase genes. In this work, we constructed S. cerevisiae strains expressing the human APOBEC3A, APOBEC3B, and AID genes and the PmCDA gene from the sea lamprey Petromyzon marinus as a positive control. Using these strains, we identified specific amino acid substitutions that enhance or attenuate deaminase activity and demonstrated that recombination repair and base excision repair significantly affect the mutagenic activity of cytosine deaminases in the heterologous expression system. Our results confirm the efficiency of the developed model and open the way to study factors that can modify the activity of AID/APOBEC, which is of great importance for finding therapeutic and diagnostic methods for treating cancer and infectious diseases.

1. Alexandrov L..B, Kim J., Haradhvala N.J., et al., The repertoire of mutational signatures in human cancer. Nature, 2020; 578(7793):94-101. doi: 10.1038/s41586-020-1943-3.

2. Stepchenkova E.I., Zadorsky S.P., Shumega A.R., Aksenova A.Y. Practical Approaches for the Yeast Saccharomyces cerevisiae Genome Modification. Int J Mol Sci. 2023; 24(15):11960. doi: 10.3390/ijms241511960.

3. Lada A.G., Stepchenkova E.I., Waisertreiger I.S., et al., Genome-wide mutation avalanches induced in diploid yeast cells by a base analog or an APOBEC deaminase. PLoS Genet. 2013; 9(9):e1003736. doi: 10.1371/journal.pgen.1003736.

4. Zhuk A.S., Shiriaeva A.A., Andreychuk Y.V., et al., Detection of primary dna lesions by transient changes in mating behavior in yeast Saccharomyces cerevisiae using the alpha-test. Int. J. Mol. Sci. 2023; 24: 12163. doi: 10.3390/ijms241512163