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標題: | 胃幽門桿菌誘發TRAIL引起細胞凋亡中Bid調節訊息傳遞的角色 The Role of Bid in Regulation of Helicobacter pylori-induced TRAIL Apoptosis Signaling |
作者: | Chiu-Hsuan Lu 呂秋璇 |
指導教授: | 許秉寧 |
關鍵字: | 胃幽門桿菌, Helicobacter pylori,TRAIL,Bid, |
出版年 : | 2006 |
學位: | 碩士 |
摘要: | TRAIL全名TNF-related apoptosis-inducing ligand,是TNF superfamily的一員。在體外測試中,TRAIL具有誘導許多腫瘤細胞株凋亡之能力。在我們實驗室之前的研究發現,胃幽門桿菌(Helicobacter pylori,簡稱H. pylori),一種會引起胃潰瘍、胃炎更甚者胃癌的人類病源,可以使人類胃上皮細胞株從原本對TRAIL具有抗性轉而敏感化。在胃幽門桿菌存在下加入TRAIL會使細胞進行凋亡。我們同時發現胃幽門桿菌活化caspase-8進而傳遞死亡訊息到粒線體,活化粒線體凋亡訊息途徑並打破對TRAIL的抗性。Bid,Bcl-2 family的一員,在結構上只具有BH-3 domain。在胃幽門桿菌引起的訊息傳遞中Bid會被活化並進而活化粒線體凋亡途徑。在我們之前的研究也顯示,在TRAIL的作用下,胃幽門桿菌可以引起Bid的切除和活化,暗示Bid的活化在胃幽門桿菌誘導TRAIL的凋亡訊息傳導中可能連結caspase-8和粒線體間的訊息傳遞。然而,在胃幽門桿菌誘導的TRAIL凋亡訊息中Bid的角色和調節機制仍不清楚。
為了進一步研究Bid在調節胃幽門桿菌誘導的TRAIL凋亡訊息傳遞中的角色,我們使用siRNA去降低Bid的表現量並觀察這對胃幽門桿菌誘導的TRAIL凋亡訊息傳遞的影響。我們發現降低Bid的表現量可以抑制胃幽門桿菌誘導的TRAIL凋亡現象,這意味著Bid對於胃幽門桿菌誘導的TRAIL凋亡現象非常重要。再者,最近的研究顯示,除了caspase-8,當TRAIL的受體和TRAIL作用之後,caspase-10也會進入TRAIL DISC。然而,caspase-10在調節TRAIL凋亡訊息傳遞中的角色仍不清楚。我們的研究結果顯示,在TRAIL與其受體作用後,胃幽門桿菌誘導caspase-10活化。再者,caspase-10特定的抑制劑,Z-AEVD-FMK,可以抑制Bid的切除和活化,進而抑制胃上皮細胞株中胃幽門桿菌誘導的TRAIL凋亡現象。以上結果意味著caspase-10對胃幽門桿菌誘導的TRAIL凋亡現象也非常重要。更甚者,caspase-10特定的抑制劑能抑制caspase-2的活化;同樣地,caspase-2特定的抑制劑也能抑制caspase-10的活化。這個結果似乎顯示caspase-10和caspase-2在TRAIL DISC的聚集和活化中位在相同的階級。所以,按照我們的結果,我們假設胃幽門桿菌打破人類胃上皮細胞對TRAIL的抗性是經由加強TRAIL DISC的形成,進而產生足夠且活化的caspase-8,使其切除Bid,導致粒線體凋亡途徑的活化並使細胞凋亡。 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. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/32842 |
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