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Open Access Publications from the University of California

Characterizing Previously Unknown Levels of Genotoxicity Found in Lymphocyte-Mediated Pathogeneses

  • Author(s): Malkin, Daniel
  • Advisor(s): Schiestl, Robert H
  • et al.

The genome is constantly subjected to DNA damaging events from the environment in the form of radiation, chemicals, and pollution. Endogenous production of reactive oxygen species also contributes to DNA damage. Conversely, programmed DNA breaks are essential for healthy lymphocyte development during V(D)J and class switch recombination. Dysregulation or mutation of genes involved in the DNA damage and repair pathways can exacerbate environmental insults, impede proper lymphocyte development, and promote cellular transformation. Interleukin-13 (IL-13), Activation-induced cytidine deaminase (AID), Myocyte-specific enhancer factor 2c (Mef2c), and Tumor protein p53 (p53) are all necessary for proper immune function in lymphocytes. There is evidence that these genes are implicated in either establishing or repairing DNA breaks and therefore dysregulation of these genes could lead to increased levels of oncogenic mutations. IL-13 may increase levels of DNA damage indirectly by inducing inflammation and increasing levels of reactive oxygen species. AID is known to elicit mutations by deamination of cytosine which in turn promotes DNA breaks. Mef2c enhances DNA repair machinery in developing B cells and p53 promotes DNA repair through cell cycle arrest. Using several transgenic mouse models, we have altered the expression of these genes to better establish the solitary role each one has on genomic stability. We found that overexpression of IL-13 in the lungs of CC10-rtTA-IL13 transgenic mice is sufficient to induce genotoxicity in not only the lungs but also circulating blood cells. In a genome-wide translocation sequencing study, we have exposed mechanisms which promote AID -dependent translocation mutations occurring in stimulated B cells. In a third study we have found that Mef2c is an important regulator for the repair of DNA double strand breaks occurring during V(D)J recombination in B cells. Finally, we found that conditional knockout of p53 in mature B cells induces clonal but non-recurrent translocations. Our findings highlight the influence of these genes on genomic stability and the risk of developing oncogenic malignancies.

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