Metal inhibition of the base excision repair enzymes

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DESCRIPTION (provided by applicant): Metals are known to cause cancer in humans and the general population is unavoidably exposed to various metals, such as Cd2+, Ni2+ and Pb2+. However the molecular mechanisms of metal carcinogenesis are still unknown. Recent data suggest that inhibition of DNA repair may be an important contributing factor to carcinogenesis and mutagenesis. The long-term goal of this research is to identify molecular mechanisms of metal toxicity through the inhibition of DNA repair. Metal toxicity represents a novel mechanism, by which various environmental mutagens and carcinogens can destabilize DNA integrity leading to mutagenic and carcinogenic events in the cell. Research in this area has focused on the subset of repair enzymes that utilize a metal-dependent catalytic mechanism or require a metal ions for maintaining structural integrity. The goal of this application is to identify potential inhibition targets among the base excision repair (BER) enzymes which do not require metals for their function and/or structure. The central hypothesis is that metal ions, such as Cd2+, Ni2+ and Pb2+ can interfere with the catalytic activity of non-metal requiring repair enzymes through binding to key active site residues or changing the chemical nature of the catalytic reaction. Exposure to these metals leads to the inhibition of enzyme activity towards its toxic/mutagenic DNA substrates. Inhibition of key DNA damage repair pathways may actually be even more important than direct DNA damage by carcinogens and/or mutagens. The hypothesis has been formulated based on our recently obtained data showing that one of the BER enzymes, human N-methylpurine-DNA glycosylase (MPG), is inhibited by several toxic metal ions. We also observed inhibition of the Uracil-DNA glycosylase (UNG) activity in cell-free extracts suggesting that another non-metal requiring enzyme is a target for metal inhibition. This hypothesis will be tested by two specific aims: 1) Use computational approaches (QM/MM) to uncover the mechanisms of metal ion interactions with BER repair enzymes, 2) Identify new targets for metal ion inhibition among BER glycosylases that do not require metal ions for their structure or function using biochemical assays. The proposed research is significant, because it will lead to the identification of new targets for metal ion inhibition among DNA repair proteins. It will also lead to new structural and mechanistic details on molecular interactions among these metals and the repair proteins. Ultimately, the mechanisms uncovered through this effort will aid future studies to develop potential prevention and/or treatment approaches to block or remove these toxic metal interactions with biologically important molecules. In addition the proposed research will increase the competiveness and productivity of the PI allowing him to develop into an independent investigator and achieve the following developmental objectives: (a) establish an independent research group, (b) enhance mentoring skills, and (c) improve the quality of research and professional advancement. PUBLIC HEALTH RELEVANCE: The proposed research is relevant to public health because it will examine the toxic effects of metal ions on reducing the capacity of DNA repair, which will lead to an increase in carcinogenic and mutagenic events in the cell. The general population is exposed to toxic metals through occupational exposure, food, water, air and a variety of consumer products. Understanding the mechanisms, by which toxic metals interfere with DNA repair, is relevant to developing fundamental knowledge that will aid in cancer prevention and treatment.