Epigenetic dynamics of Helicobacter pylori-induced COX-2 activation.
[Tesi di dottorato]
Background and Aims: Cyclooxigenase (COX)-2 is over expressed in gastrointestinal neoplasia and Helicobacter pylori (H. pylori) infection is casually linked to gastric cancer. We undertook this study to investigate the mechanism mediating H. pylori-induced COX-2 expression in human gastric epithelial cell line MKN28. Methods: MKN28 cells were infected with wild-type H. pylori 60190 strain for different time points, and the levels of COX-2 messenger RNA (mRNA) and protein expression were evaluated using real-time polymerase chain reaction (PCR) and Western blotting, respectively. Chromatin immunoprecipitation assays were performed to evaluate the level of histone modifications and the recruitment of histone deacetylases (HDACs) 1, and 2, nuclear transcription factor (NF-κB) and RNA polymerse II (PolII) to the COX-2 promoter. The technique of MALDI-TOF MS was used to determine the methylation analysis of CpG islands of the COX-2 promoter. Results: H. pylori induced a time-dependent increase of mRNA and protein expression of COX-2 in MKN28 cells. Furthermore, H. pylori-infected gastric epithelial cells showed dynamic changes of methylation and acetylation pattern of histone H3 at the promoter of COX-2 gene. Preventing histone deacetylation by the histone deacetylase inhibitor trichostatin A (TSA) augumented the H. pylori-induced COX-2 response. After exposure to H. pylori, we found a decreased in global histone deacetylase expression and activity. The hyperacetylation of histone H3 correlate with the release of HDAC 1, which first decreased and later reappeared at the COX-2 promoter. Moroever after H. pylori infection, NF-κB and RNA polymerase II were time-dependently recruited to the COX-2 promoter. In addition we show a dynamic changes in the methylaion status of promoter CpGs. Conclusions: These results show for the first time that H. pylori-induced activation of COX-2 gene transcription was caused by interference with epigenetic mechanisms regulating COX-2 gene accessibility. These patways may contribute to the host response in H. pylori-associated gastric inflammation and carcinogenesis.
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