8-hydroxyguanosine and Cell-Transformation--Neoplastic

Reactive oxygen species (ROS) are produced through normal cellular metabolism, and their formation is further enhanced by exposure to ionizing radiation and various chemicals. ROS attack DNA, and the resulting oxidative DNA damage is considered to contribute to aging, carcinogenesis and neurodegeneration. Among various types of oxidative DNA damage, 8-oxo-7,8-dihydroguanine (8-oxoguanine or 8-oxoG) is the most abundant, and plays significant roles in mutagenesis because of its ability to pair with adenine as well as cytosine. Enzymatic activities that may be responsible for preventing 8-oxoG-evoked mutations were identified in mammalian cells. We have focused on the following three enzymes: MTH1, OGG1 and MUTYH. MTH1 is a mammalian ortholog of Escherichia coli MutT, which hydrolyzes 8-oxo-dGTP to its monophosphate form in nucleotide pools, thereby preventing incorporation of the mutagenic substrate into DNA. OGG1, a functional counterpart of E. coli MutM, has an 8-oxoG DNA glycosylase activity. MUTYH, a mammalian ortholog of E. coli MutY, excises an adenine paired with 8-oxoG. These three enzymes are thought to prevent mutagenesis caused by 8-oxoG in mammals. To analyze the functions of mammalian MTH1 (Mth1), OGG1 (Ogg1) and MUTYH (Mutyh) in vivo, we established mutant mice for these three enzymes by targeted mutagenesis, and investigated spontaneous tumorigenesis as well as mutagenesis. Here we discuss our recent investigation of mutagenesis and carcinogenesis in these mutant mice.

Topics: Amino Acid Sequence; Animals; Cell Transformation, Neoplastic; DNA Damage; DNA Glycosylases; Guanosine; Mice; Mice, Mutant Strains; Molecular Sequence Data; Mutagenesis; Neoplasms; Phosphoric Monoester Hydrolases; Reactive Oxygen Species

The objective of this study was to assess the dynamics of oxidative damage to cellular macromolecules such as proteins, lipids, and DNA under conditions of oxidative stress triggering early stages of estrogen-dependent carcinogenesis. A rodent model of carcinogenesis was used. Syrian hamsters were sacrificed after 1, 3, 5 h and 1 month from the initial implantation of 17beta-estradiol (E2). Matching control groups were used. Kidneys as target organs for E2-mediated oxidative stress were excised and homogenized for biochemical assays. Subcellular fractions were isolated. Carbonyl groups (as a marker of protein oxidation) and lipid hydroxyperoxides were assessed. DNA was isolated and 8-oxodGuo was assessed. Electron paramagnetic resonance spectroscopy was used to confirm the results for lipid peroxidation. Exposition to E2 in rodent model leads to a damage of macromolecules of the cell, including proteins and DNA, but not lipids. Proteins appear to be primary target of the damage but are shortly followed by DNA. It has previously been speculated that protein peroxides can increase DNA modifications. This time sequence was observed in our study. Nevertheless, direct relation between protein and DNA damage still remains unsolved.

Topics: Animals; Cell Transformation, Neoplastic; Cricetinae; DNA Damage; Electron Spin Resonance Spectroscopy; Estradiol; Estrogens; Guanosine; Kidney; Lipid Peroxidation; Male; Mesocricetus; Oxidants; Oxidation-Reduction; Oxidative Stress; Protein Carbonylation; Subcellular Fractions

Oxidative damage can lead to a highly mutagenic 8-oxoguanine lesion, which mispairs with adenosine residues, leading to G:C-->T:A transversions. In mammalian cells 8-oxoguanine glycosylase initiates the DNA base excision repair pathway to repair the 8-oxoguanine lesion. To date, there is no information regarding oxidative DNA damage and repair pathways in esophageal cancer. Therefore we designed the current study to demonstrate the DNA damage and repair pathways in esophageal cancer by expression of 8-oxoguanine glycosylase in reflux-induced and mutagen (methyl-n-amyl nitrosamine)-induced DNA damage and apoptosis in esophageal tumors.. Gastroduodenal reflux was surgically created in male Sprague Dawley rats (n = 120). Half of the animals received methyl-n-amyl nitrosamine. Animals not undergoing operations served as control animals (n = 10). The experiment concluded 30 weeks postoperatively. Immunohistochemistry for 8-oxoguanine and 8-oxoguanine glycosylase was assessed by 2 independent observers. Protein expression was assessed by using the Western blot method.. There was significantly more DNA damage in both adenocarcinoma (n = 15) and squamous cell carcinoma (n = 19), as exemplified by positive 8-oxoguanine expression compared with that seen in control animals (P < .05). 8-Oxoguanine glycosylase was several folds upregulated in adenocarcinoma (P < .05), but there was significantly decreased expression in squamous cell carcinoma (P < .01). The apoptosis was assessed as caspase-dependent and caspase-independent pathways, and both were active and correlated well with 8-oxoguanine expression.. These results demonstrate the selective decrease in the DNA base excision repair pathway in combined reflux and methyl-n-amyl nitrosamine-induced squamous cell cancer of the esophagus.

Topics: Adenocarcinoma; Animals; Apoptosis Inducing Factor; Barrett Esophagus; Carcinogens; Carcinoma, Squamous Cell; Caspase 3; Cell Transformation, Neoplastic; DNA Damage; DNA Glycosylases; DNA Repair; Esophageal Neoplasms; Esophagitis; Esophagus; Gastroesophageal Reflux; Guanosine; Immunohistochemistry; Male; Nitrosamines; Papilloma; Rats; Rats, Sprague-Dawley

Phototherapy with narrow-band UVB (NB-UVB), with a peak exclusively at 311 nm wavelength, has been found to be more effective in treating a variety of skin diseases than conventional broad-band UVB (BB-UVB). To assess the difference in carcinogenic activity between NB-UVB and BB-UVB, we investigated skin tumor formation by irradiating albino hairless, Ogg1 knockout mice and C57BL/6J wild counterparts with these two UV sources. We found that the ratio of malignant skin tumors induced by NB-UVB was significantly higher than that induced by BB-UVB. There was no significant difference in carcinogenicity of skin tumor induced by NB-UVB between Ogg1 knockout and wild-type mice. To investigate the possible cause of different carcinogenic activity by the different UV sources, we examined three types of DNA damage: cyclobutane pyrimidine dimer (CPD), (6-4) photoproduct, and 8-oxoguanine (8-oxoG) induced by each UV source. We found that CPD formation following a minimum erythema dose (MED) by NB-UVB was significantly higher than that following 1 MED by BB-UVB, whereas the formation of (6-4) photoproducts and 8-oxoG following BB-UVB was significantly higher than those following NB-UVB exposure. These results suggest that CPD formation is closely related to the higher carcinogenic characteristics of NB-UVB. JID JOURNAL CLUB ARTICLE: For questions, answers and open discussion about this article please go to http://network.nature.com/.

Topics: Animals; Cell Transformation, Neoplastic; Cyclobutanes; DNA Glycosylases; Epidermis; Guanosine; Humans; Immunohistochemistry; Mice; Mice, Inbred BALB C; Mice, Inbred C57BL; Mice, Knockout; Photochemistry; Pyrimidine Dimers; Skin Neoplasms; Ultraviolet Rays