Molecular Mechanism of Chromium GenotoxicityEPA Grant Number: F5D40840
Title: Molecular Mechanism of Chromium Genotoxicity
Investigators: Kirpnick, Zhanna
Institution: University of California - Los Angeles
EPA Project Officer: Jones, Brandon
Project Period: September 1, 2005 through August 1, 2007
Project Amount: $104,096
RFA: STAR Graduate Fellowships (2005) RFA Text | Recipients Lists
Research Category: Academic Fellowships
Chromium(VI) [Cr(VI)] is a widespread environmental contaminant. Although the carcinogenic effect of Cr(VI) to the respiratory tract is well established, the carcinogenic potential of Cr(VI) via the oral route has yet to be determined. In order to understand the carcinogenic potential of Cr(VI) in drinking water, it is necessary to determine the mechanism by which Cr causes DNA damage. The objective of this study is to determine the molecular mechanism of Cr(VI) genotoxicity utilizing the frequency of DNA deletions as a genotoxic endpoint. Researchers have previously shown that intracellular reduction of Cr(VI) can produce reactive oxygen species or result in Cr(III)-DNA interactions. The first aim of this study is to determine whether oxidative DNA damage or the Cr(III)-DNA interactions are primarily responsible for inducing DNA deletions. The second aim of this study is to characterize how Cr(III)-DNA interactions lead to the formation of DNA deletions.
This proposal outlines a study that will determine how Chromium induces DNA damage. The DNA damaging mechanism provides a clue about how chromium causes cancer. The knowledge gained from this study will help researchers and regulatory agencies evaluate the health risk from drinking Chromium-contaminated water.
I will address the specific aims of this proposal by utilizing the well-established DEL (deletion) assay in the yeast Saccharomyces cerevisiae as a measure of DNA deletions. The DEL assay measures an intrachromosomal homologous recombination event that results in a deletion of the intervening DNA sequence. An elevated frequency of homologous recombination is associated with genomic instability and increased cancer risk. The DEL assay has correctly identified many carcinogens and detected a wide range of DNA damaging activity. Thus, the use of the DEL assay provides a measure of a genotoxic endpoint that is relevant to the process of carcinogenesis and is sensitive to diverse types of DNA damage.
Experiments in our laboratory have shown that both Cr(VI) and Cr(III) induce DNA deletions. I will accomplish the first aim of this proposal by performing the following three experiments. First, I will measure the frequency of 8-oxo-guanine lesions and correlate it with DNA deletion frequency after exposure to Cr(VI) and Cr(III). Second, I will expose cells under aerobic and anaerobic conditions and calculate the difference in DNA deletion frequency between the two conditions. Third, I will measure the difference in sensitivity between the wild type strain and a number of oxidative-DNA-damage-repair mutants in their response to Cr(VI) and Cr(III). I will accomplish the second aim of this proposal by measuring Cr(III)-DNA interactions and calculating the correlation between these interactions and DNA deletion frequency.
Exposure to Cr(VI) has previously been linked with oxidative DNA damage and Cr(III)-mediated DNA interactions. This study will clarify the uncertainty about the relative contribution of these lesions to Cr(VI) genotoxicity. The results of this study will guide the design of animal and epidemiological research.