Skin cancer remains the most prevalent form of cancer in the United States, with about 1 in 5 Americans contracting basal and squamous skin cancers in their lifetime. Mutation hotspots in tumor suppressor genes in these cancers are C to T and CC to TT mutations that occur mainly at methylated CpG sites that are also hotspots for cyclobutane pyrimidine dimer (CPD) formation. These mutations appear to arise from the deamination of the C's and 5-methylC's (mC) in the CPDs followed by error-free bypass by the DNA damage bypass polymerase eta. What is not well understood, or appreciated, however, is how chromatin structure modulates the rate of deamination and hence the mutagenic potential of mC-containing CPDs, or the epigenetic consequences of CPD formation at methylated CpG sites. Furthermore, the photochemistry of telomeres is largely unknown, in spite of their importance in maintaining genome stability. The major focus of this grant will therefore be to elucidate the structure-activity relationships of photoproduct formation and deamination in nucleosomes and telomeres with regard to their mutagenic and epigenetic consequences. Specifically we propose: (1) To test the hypothesis that chromatin structure can greatly affect the deamination rate and hence the mutagenicity of C/mC containing CPDs, by determining their rate of formation, deamination and repair as a function of rotational and translational position in nucleosome core particles, nucleosomal arrays, and in human cells. We will also determine the physical basis for the modulation of CPD deamination rate by nucleosomes, and the stability and dynamics of nucleosomes containing singly and doubly deaminated CPDs as a function of rotational and translational position in relation to DNA excision repair. (2) To test the hypothesis that error-free bypass of undeaminated mC-containing CPDs contributes to the progression to skin cancer through demethylation of CpG sites, by determining the ability of CPDs to inhibit DNMT1 catalyzed methylation of a complementary strand in vitro, in cell-free extracts, and in human cells. We will also investigate the ability of methyC-binding proteins to enhance the formation of methylC-containing CPDs and prevent their demethylation, thereby promoting the demethylation pathway in preference to the deamination- bypass mutational pathway. (3) To test the hypothesis that photoproduct formation in telomeres may be unusual and could contribute to skin cancer induction, by determining the structure of the photoproducts that are induced by UVB light in telomeric DNA in human cells and compare with those formed in the presence of telomere DNA binding proteins. We will also determine the rates of deamination of C-containing CPDs that would be predicted to lead to telomere mutagenesis and destabilization.

Public Health Relevance

Knowledge gained through this research will provide a better understanding of the mechanisms by which skin cancer arises, and may led to better risk assessment and preventative strategies, as well as diagnostic methods, prognosis, and therapeutic strategies.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
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Synthetic and Biological Chemistry A Study Section (SBCA)
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Okano, Paul
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Washington University
Schools of Arts and Sciences
Saint Louis
United States
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Taylor, John-Stephen (2015) Design, synthesis, and characterization of nucleosomes containing site-specific DNA damage. DNA Repair (Amst) 36:59-67
Cannistraro, Vincent J; Pondugula, Santhi; Song, Qian et al. (2015) Rapid deamination of cyclobutane pyrimidine dimer photoproducts at TCG sites in a translationally and rotationally positioned nucleosome in vivo. J Biol Chem 290:26597-609
Smith, Jillian E; Lu, Chen; Taylor, John-Stephen (2014) Effect of sequence and metal ions on UVB-induced anti cyclobutane pyrimidine dimer formation in human telomeric DNA sequences. Nucleic Acids Res 42:5007-19
Song, Qian; Cannistraro, Vincent J; Taylor, John-Stephen (2014) Synergistic modulation of cyclobutane pyrimidine dimer photoproduct formation and deamination at a TmCG site over a full helical DNA turn in a nucleosome core particle. Nucleic Acids Res 42:13122-33
Taggart, David J; Camerlengo, Terry L; Harrison, Jason K et al. (2013) A high-throughput and quantitative method to assess the mutagenic potential of translesion DNA synthesis. Nucleic Acids Res 41:e96
Song, Qian; Sherrer, Shanen M; Suo, Zucai et al. (2012) Preparation of site-specific T=mCG cis-syn cyclobutane dimer-containing template and its error-free bypass by yeast and human polymerase ?. J Biol Chem 287:8021-8
Song, Qian; Cannistraro, Vincent J; Taylor, John-Stephen (2011) Rotational position of a 5-methylcytosine-containing cyclobutane pyrimidine dimer in a nucleosome greatly affects its deamination rate. J Biol Chem 286:6329-35
Asagoshi, Kenjiro; Liu, Yuan; Masaoka, Aya et al. (2010) DNA polymerase beta-dependent long patch base excision repair in living cells. DNA Repair (Amst) 9:109-19
Brown, Jessica A; Pack, Lindsey R; Sherrer, Shanen M et al. (2010) Identification of critical residues for the tight binding of both correct and incorrect nucleotides to human DNA polymerase ?. J Mol Biol 403:505-15
Cannistraro, Vincent J; Taylor, John-Stephen A (2010) Methyl CpG binding protein 2 (MeCP2) enhances photodimer formation at methyl-CpG sites but suppresses dimer deamination. Nucleic Acids Res 38:6943-55

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