Abstract
Persistent infection by Helicobacter pylori causes chronic inflammation and consequent development of gastric lesions that may progress to intestinal type gastric cancer. The inflammatory response triggered by this pathogen is characterized by the induction of inflammatory cytokines expression, highlighting the tumor necrosis factor (TNF)-± as presenting tumor promoting function. TNF-± signaling can result in gene activation or cell death and depends on two main receptors: TNFR1 and TNFR2. The TNFR1 receptor can both activate apoptosis pathway and stimulate transcription of genes involved in cell survival. The control between these two pathways is regulated at various levels and changes in signaling triggered by TNFR1 can lead to the carcinogenic process. The apoptosis induction depends on the recruitment of the adapter protein TRADD and caspase 8, while the gene transcription is the result of NF-kB activation and involves the participation of TRAF2, TRAF1 and RIP. Studies indicate enhancer role of TNFR2 receptor in a cytotoxic effect of TNFR1, in addition to induction of apoptosis and cell survival independently of receptor 1. Dysregulation in the expression of genes involved in this pathway may be caused by microRNAs (miRNAs) in the post-transcriptional level and studies showed that they may regulate the inflammatory process induced by H. pylori, as well as gastric carcinogenesis. Furthermore, infection by this bacterium can alter the expression of these miRNAs and, thus, influence on multiple molecular mechanisms. Thus, the aim of this study is to evaluate in gastric cancer cell line, in the condition of inflammation induced by H. pylori extract, the occurrence of changes and interaction networks of genes and miRNAs involved in apoptosis pathway mediated by TNF-± and the performance of TNFR1 and TNFR2 receptors, as well as the consequences in cellular processes such as proliferation and apoptosis. Also investigate whether the expression of these genes and miRNAs are deregulated in lesions participating in gastric cancer progression cascade and whether is influenced by H. pylori infection. Therefore, the specific aims of this study are: a- To assess the mRNA quantitative expression of mediators and receptors of the apoptosis extrinsic pathway mediated by TNF-± (TNFA, TNFR1, TNFR2, TRADD, TRAF2, cFLIP, IL1B, IL6, CASP3 and CASP8) and of miRNAs targeting TNFA or mediators of its signaling pathway (hsa-miR-19a-3p, hsa-miR-34a-3p, hsa-miR-103-3p, hsa-miR-181c-5p, hsa-miR-370-3p) in gastric adenocarcinoma cell lines (AGS and MKN-45), after induction with H. pylori extract, with and without silencing of TNFR1 and TNFR2 receptors, besides the effect of these treatments on parameters such as cell proliferation and apoptosis; b- Evaluate the expression of the same mRNA of mediators and receptors and miRNA in the lesions of gastric cancer progression cascade (chronic gastritis, intestinal metaplasia and cancer) with and without H. pylori infection; c- Search in public databases to gene prediction-targets of miRNAs, build the network of miRNA-mRNA interactions, as well as functional validation. The results can reveal changes in cellular processes resulting in changes in expression of genes and miRNAs involved in TNF-± signaling pathway in gastric carcinogenesis and which receptor (TNFR1 and/or TNFR2) contribute more effectively to changes in this signaling pathway triggered by inflammation induced by H. pylori. Therefore, may contribute to a better understanding of the pathway and the role of TNFR1 and TNFR2 receptors and indicate molecular targets and therapeutic strategies in inflammation and gastric cancer.
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