Dissertation
Dissertation > Medicine, health > Oncology > Gastrointestinal Cancer > Esophageal tumors

The Exploration of the Relationship between Gadd45α and Epigenetic Modification during the Process of Esophageal Carcinogenesis Induced by Nitrosamine in Mice

Author WuQiangQiang
Tutor ShuQing
School Fourth Military Medical University
Course Of Medical Genetics
Keywords nitrosamine esophageal cancer epigenetic modification Gadd45α
CLC R735.1
Type Master's thesis
Year 2008
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BACKGROUNDOne cause of esoghageal cancer is nitrosamine. The carcinogenic action of nitrosamines involved conversion of the nitrosamine to an alkylating intermediate, which alkylates the guanylic acid moieties of DNA. The alkylation of DNA may be relevant to the methylation of N7 guanylic acid. Usually the epigenetic modification pattern are changed in tumorigeness process. But it is uncertain whether the this change happened in the carcinogenesis induced by nitrosamine. It has been reported that the pattern of genomic DNA methylation was chaotic and one result were the demethylation of oncogene and supermethylation of anti-oncogene. DNA demethylation and ascending gene expression induced by nitrosamine were observed in our early research. So we want to know which pathway could induce gene expression between DNA methylation and histone acetylation. We also want to know whether Gadd45αis involved in the DNA demethylation in the process induced by nitrosamine. AIMTo explore the way of carcinogenic action between DNA methylation and histone acetylation;To explore whether Gadd45αis involved in the DNA demethylation in the carcinogenesis induced by nitrosamineMETHODS1. Mice were perosed with nitrosamine until the carcinogenesis was observed in esophagus. Analysis of pathological section and electron microscope to detect pathological changes of esophageal epithelium.2. cDNA microarray analysis of gene differential expression was performed at 4 weeks, 8 weeks and 20 weeks induction and properties of differentially expressed genes involved in epigenetic modification were examined.3. The expression of Gadd45αat early induction from 1 week to 4 weeks was analyzed by RT-PCR and immunohistochemistry for mRNA and protein levels.RESULTS1. Pathological changes of esophageal epithelium in animal model were confirmed. The results showed that paraplasm of epithelium was induced by nitrosamine and this lesion showed a property of time-dependence.2. From the result of cDNA microarray analysis, we did not find differentially expressed histone acetyltransferase genes, and there are seven histone deacetylase genes show ascending expression. At 8 weeks induction, Dnmt1 and Dnmt2 were upregulated 5.65、6.80 respectively, At 20 weeks they were upregulated 2.11、4.15 respectively; At 8 weeks and 20 weeks induction, demethyltransferase Mbd2 was upregulated 2.29、4.00, and Gadd45αwas upregulated 2.91、56.70、65.47 at 4 weeks, 8 weeks and 20 weeks respectively.3. We analyzed the expression of oncogene and anti-oncogene. In 136 oncogenes, there were 26 genes upregulated at 4 weeks and 97 genes upregulated at 8 weeks and 130 genes upregulated at 20 weeks. There were only 5 anti-oncogenes were upregulated at 8 weeks and 20 weeks.4. We detected Gadd45αmRNA and found Gadd45αmRNA expressed in two groups. From 1 week to 4 weeks, the treatment group showed ascending expression compared with the control group.5. Gadd45αprotein were mainly distributed in cell nucleus at the esophageal mucous layer. Our data showed that differential expression of Gadd45αwas first observed at 2 weeks, and the treatment group showed a high level than the control group.6. From 1 week to 4 weeks, the methylation of genomic DNA descended quickly; From 4 weeks gene expression was upregulated quickly; From 30 weeks pathological lesion was observed clearly.CONCLUSION1. Nitrosamine induction cause the upregulation of oncogene. 2. Histone acetyltransferases were not involved in the gene upregulation induced by nitrosamine, but may be DNA methylation induced ascending expression.3. From 1 week to 4 weeks, the minor upregulation of Gadd45αcould play a role in the genomic DNA demethylation, but the major upregulation of Gadd45αfrom 8 weeks to 20 weeks could be relative to DNA repair.4. We analyzed the methylation of Genomic DNA, gene differential expression level, pathological lesion level and Gadd45αexpression, the results showed an interesting temporal and spatial property. Their succession is that Gadd45αexpression ascending - Genomic DNA methylation descending - gene differential expression - pathological lesion formation.Nitrosamine induction show an temporal and spatial property of genomic DNA methylation descending→gene expression ascending→pathological lesion formation. The dynamic temporal and spatial property give more groundwork for an insight into the causality between epigenetic modification and tumorigeness, and it also provide new clues in the mechanism of epigenetic modification induced by nitrosamine and the regulation of carcinogenesis.

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