Chemistry and Biology of DNA Carboxyalkylation

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ABSTRACT The integrity of human genome is frequently challenged by endogenous and exogenous sources of agents. Endogenously produced byproducts of glycolysis or N-nitroso compounds present in the gastrointestinal tract can both lead to the carboxyalkylation of nucleobases in DNA. Previous studies carried out in this and other laboratories revealed that some of the carboxyalkylated nucleosides are present at significant levels in cells and tissues of humans and laboratory animals. The long-term goal of this project is to understand, at the molecular level, the biological consequences of the carboxyalkylated DNA adducts. In the present application, we propose experiments according to the following four specific aims: Aim 1, to assess the chemistry of DNA modifications induced by diazoacetate, which is a reactive intermediate arising from endogenously induced N-nitroso compounds. Aim 2, to quantify the carboxyalkylated DNA adducts in cultured human cells and in diabetic animal models by using LC-MS/MS with the standard isotope dilution method. Aim 3, to synthesize oligodeoxyribonucleotides harboring a carboxyalkylated lesion at a specific site. Aim 4, to employ shuttle vector technology and investigate how the carboxyalkylated DNA lesions are replicated in E. coli and human cells. In this respect, the roles of various translesion synthesis DNA polymerases will be delineated by using polymerase-deficient bacterial strains or, for replication studies using mammalian cells, by knocking down the expression of these polymerases with the siRNA technique. The outcome of the proposed research will provide significant new knowledge about the cytotoxic and mutagenic properties of this group of DNA adducts. The proposed research will also reveal the implications of hyperglycemia and exposure to N-nitroso compounds in the etiology of diabetic complications and gastrointestinal tumors. Furthermore, the proposed study may lead to the discovery of novel molecular biomarkers and risk factors for developing these pathological conditions.