| Summary: | 碩士 === 國立臺灣大學 === 免疫學研究所 === 94 === TNF-related apoptosis-inducing ligand (TRAIL), a new member of TNF superfamily, induces apoptosis in many tumor cell lines in vitro. Previous studies in our laboratory demonstrated that Helicobacter pylori (H. pylori), a common human pathogen causing gastritis, peptic ulcer and gastric adenocarcinoma, could sensitize human gastric epithelial cell line, conferring susceptibility to TRAIL-induced apoptosis. The H. pylori-induced TRAIL sensitivity is dependent on the activation of caspase-8 to convey the death signal to mitochondria, leading to activation of mitochondrial apoptosis signaling pathway and breaking the resistance to TRAIL-induced apoptosis. Bid, a BH3-domain only protein belonging to Bcl-2 family, could be cleaved by caspase-8 and further active mitochondrial pathway. Our preliminary results indicated H. pylori could induce cleavage and activation of Bid after engagement with TRAIL, indicating Bid activation may connect the apoptosis signaling between caspase-8 and mitochondria in H. pylori-induced TRAIL apoptosis signaling. However, role of Bid in H. pylori-induced TRAIL apoptosis and its regulation is still unclear.
In order to further study the role of Bid in regulation of H. pylori-induced TRAIL apoptosis signaling, we use siRNA approach to knock down the expression of Bid and to investigate H. pylori-induced TRAIL apoptosis signaling. We demonstrated that silencing of Bid expression could inhibit H. pylori-induced TRAIL apoptosis, indicating Bid is crucial for H. pylori-induced TRAIL apoptosis signaling. Moreover, it has been shown recently that in addition to caspase-8, caspase-10 is also recruited to the TRAIL DISC when the TRAIL death receptor is aggregated, however, role of caspase-10 in regulation of TRAIL apoptosis remains unclear. Our results demonstrated that H. pylori induced caspase-10 activation after TRAIL engagement. Furthermore, caspase-10 specific inhibitor, Z-AEVD-FMK, could inhibit Bid cleavage and its activation to completely abolish H. pylori-induced TRAIL apoptosis in AGS cells, indicating caspase-10 is also essential in H. pylori-induced TRAIL apoptosis signaling. Moreover, caspase-10 specific inhibitor could suppress activation of caspase-2; instead, caspase-2 inhibition also could inhibit caspase-10 cleavage. This suggests that caspase-10 and caspase-2 may act at the same level in the TRAIL DISC assemble and activation. Therefore, our results hypothesize that H. pylori sensitize human gastric epithelial cells via enhancing formation of TRAIL DISC to further generate sufficient active caspase-8, and to cleave Bid, leading to mitochondrial pathway activation and apoptosis.
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