AID induces double-strand breaks at immunoglobulin switch regions and c-MYC causing chromosomal translocations in yeast THO mutants

• Published in: PLoS genetics Vol. 7; no. 2; p. e1002009
• Main Authors: Ruiz, José F, Gómez-González, Belén, Aguilera, Andrés
• Format: Journal Article
• Language: English
• Published: United States Public Library of Science 01.02.2011; Public Library of Science (PLoS)
• Subjects: Animals; Base Sequence; Biology; Chromosomes, Fungal; Cytidine Deaminase - genetics; Cytidine Deaminase - metabolism; Deoxyribonucleic acid; DNA; DNA Breaks, Double-Stranded; DNA repair; Genetic aspects; Genetic transcription; Genomics; Humans; Immunoglobulin Switch Region; Immunoglobulins; Mice; Molecular Sequence Data; Mutation; Physiological aspects; Proto-Oncogene Proteins c-myc - genetics; Rearrangements (Chemistry); Recombination, Genetic; Saccharomyces cerevisiae - enzymology; Saccharomyces cerevisiae - genetics; Sequence Alignment; Translocation, Genetic; Yeast; Yeast fungi
• ISSN: 1553-7404; 1553-7390; 1553-7404
• DOI: 10.1371/journal.pgen.1002009

Transcription of the switch (S) regions of immunoglobulin genes in B cells generates stable R-loops that are targeted by Activation Induced Cytidine Deaminase (AID), triggering class switch recombination (CSR), as well as translocations with c-MYC responsible for Burkitt's lymphomas. In Saccharomyces cerevisiae, stable R-loops are formed co-transcriptionally in mutants of THO, a conserved nuclear complex involved in mRNP biogenesis. Such R-loops trigger genome instability and facilitate deamination by human AID. To understand the mechanisms that generate genome instability mediated by mRNP biogenesis impairment and by AID, we devised a yeast chromosomal system based on different segments of mammalian S regions and c-MYC for the analysis of chromosomal rearrangements in both wild-type and THO mutants. We demonstrate that AID acts in yeast at heterologous S and c-MYC transcribed sequences leading to double-strand breaks (DSBs) which in turn cause chromosomal translocations via Non-Homologous End Joining (NHEJ). AID-induced translocations were strongly enhanced in yeast THO null mutants, consistent with the idea that AID-mediated DSBs depend on R-loop formation. Our study not only provides new clues to understand the role of mRNP biogenesis in preventing genome rearrangements and the mechanism of AID-mediated genome instability, but also shows that, once uracil residues are produced by AID-mediated deamination, these are processed into DSBs and chromosomal rearrangements by the general and conserved DNA repair functions present from yeast to human cells.