TRAIL 分子雙向訊息傳導在細胞活化與凋亡之研究

Bi-directional signaling of TRAIL on cell activation and apoptosis

周愛湘(Ai-Hsiang Chou)

指導教授 ： 許秉寧

國立臺灣大學/醫學院/免疫學研究所/博士(2004年)

https://doi.org/10.6342/NTU.2004.00279

摘要

TRAIL (又稱為Apo2 ligand) 屬於腫瘤壞死因子家族的一員，具有引發多種轉型細胞株進行細胞凋亡的能力，但是對於大部分的正常細胞則不具細胞毒殺性。TRAIL 表現在大部分的細胞上，尤其是在活化的T細胞，TRAIL的表現量會顯著增加。目前已知的TRAIL受體共有五個，顯示在TRAIL與其受體之間存在著複雜的相互作用關係。過去大部分的研究都著重在TRAIL對腫瘤細胞的毒殺作用，但是TRAIL及其受體的真正生物弁鄔|無法確知。
為了要研究TRAIL的生物弁遄A首先，我們探討TRAIL在T細胞傳遞的反向訊息之可能性。我們證實當TRAIL與其受體重組蛋白（recombinant DR4-Fc protein）結合，TRAIL本身可以傳遞一反向訊息，配合anti-CD3抗體所引發的T細胞受體訊息，將造成T細胞增生並引起細胞激素IFNg的分泌，而其所引起的細胞激素IFNg分泌可以被p38 MAPK抑制劑SB203580所抑制。這些結果顯示T細胞表面的TRAIL確實會傳遞一個反向訊息，並且透過p38 MAPK的訊息傳導進而促使細胞激素IFNg的分泌。我們的研究結果不只提供了另一個例證，證實在腫瘤壞死因子家族成員中會發生雙向訊息傳導的現象，更闡明TRAIL在真正生理弁鄐W的意義。
進一步去探討TRAIL受體的生物弁遄A以釐清TRAIL死亡受體所傳遞的死亡訊息及其調控機制，我們利用C型肝炎病毒的核心蛋白來研究TRAIL透過死亡受體所引起的死亡訊息傳導路徑是如何的被調控。C型肝炎病毒的核心蛋白是病毒的核甘酸鞘膜組成成分，根據之前的研究發現它會影響釵h胞內生理弁遄A包括細胞增生以及死亡。我們的結果發現C型肝炎病毒的核心蛋白會改變肝癌細胞株Huh7對TRAIL的抗性，但並不影響其對FasL的抗性。我們進而發現細胞對TRAIL敏感性的改變，是由於C型肝炎病毒的核心蛋白會促進caspase-8及其下游訊息分子的活化，這當中包括Bid活化、粒腺體膜電位的下降以及細胞色素c（cytochrome c）的釋放。所以C型肝炎病毒的核心蛋白透過活化caspase-8及粒腺體死亡訊息傳導路徑打開原本被阻斷的細胞凋亡路徑，使得原本對TRAIL具有抗性的Huh7細胞株變成對TRAIL有高度敏感性，輕易的被TRAIL引起大量的細胞凋亡。
總結來說，我們的研究明確的指出TRAIL與受體之間具有雙向的訊息傳導路徑，透過細胞表面的TRAIL可以傳遞一個共活化訊息，造成T細胞活化；另一方面，透過TRAIL死亡受體傳遞的死亡訊息，會受到病原蛋白的調控造成細胞凋亡。關於TRAIL與其受體的真正生物弁鄍H及他們在免疫相關疾病上的角色，我們的結果提供了一個全新的視野。

關鍵字

細胞活化 ； 訊息傳導 ； 細胞凋亡

並列摘要

TNF-related apoptosis-inducing ligand (TRAIL, also called Apo2L), a novel member of TNF superfamily, induces apoptosis in transformed cell lines of diverse origin but not in most of the primary cells. TRAIL is expressed in most of the cells, and the expression is upregulated in activated T cells. Five receptors for TRAIL have been identified, and there is complex interplay between TRAIL and TRAIL receptors in vivo. Role in tumor killing has been suggested based on in vitro study, however, the actual biological function of TRAIL/TRAIL receptor is still not clear.
In order to study the biological role of TRAIL, we first explored the possibility of reverse signaling of TRAIL in T cells. We demonstrated that cross-linking of TRAIL by plate-bound rTRAIL receptor, death receptor 4-Fc (DR4-Fc) fusion protein, enhanced T cell proliferation in conjunction with immobilized suboptimal anti-CD3 Ab stimulation. Engagement of TRAIL on anti-CD3 activated T cells also increased IFNg production and this effect could be blocked by SB203580, a p38 mitogen activated protein kinase (MAPK)-specific inhibitor. These results indicated the occurrence of reverse signaling through TRAIL on T cell and signal the augmentation of IFNg secretion via a p38-dependent pathway. Our results provide another example of reverse signaling by a member of TNF superfamily, suggesting that bi-directional signaling is a general phenomenon among TNF superfamily. These results also shed light on biological function of TRAIL.
To further explore the regulatory mechanism of TRAIL-mediated apoptosis, we studied TRAIL death receptor apoptosis signaling pathway and its regulation. We investigated the modulation of apoptosis signaling by hepatitis C virus (HCV) core protein to delineate the regulation of TRAIL-mediated apoptosis. The core protein of HCV is a viral nucleocapsid, which has been shown to affect various intracellular events including cell proliferation and apoptosis. We demonstrated that HCV core protein sensitizes human HCC cell line, Huh7, conferred sensitivity to TRAIL- but not FasL-mediated apoptosis. The induction of TRAIL sensitivity by HCV core protein was due to facilitating activation of caspase-8 and its downstream pathway, and enhancing Bid processing, breakdown of mitochondrial transmembrane potential as well as cytochrome c release. Therefore, the HCV core protein-induced TRAIL- mediated apoptosis via enhancing the activation of caspase-8 downstream pathway to convey death signal to mitochondria, leading to activation of mitochondrial signaling pathway and breaking apoptosis resistance.
Taken together, our results indicate a bi-directional signaling of TRAIL. Engagement of TRAIL with TRAIL receptor induces costimulation of T cells. On the other hand, engagement of TRAIL death receptor with TRAIL could also induce cell death via transducing apoptotic signal which could be modulated by pathogens or microorganisms. Our results add a new dimension of biological function of TRAIL and TRAIL receptors in immune mediated diseases.

並列關鍵字

TNF ； signal transduction ； TRAIL ； cell activation

參考文獻

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