Faisal Wasek, Symonds Peter, Panjwani Shiraj, Heng Yee, Murray John C
Wolfson Digestive Diseases Centre, University Hospital, University of Nottingham, Nottingham, UK.
Asian J Surg. 2007 Jan;30(1):13-22. doi: 10.1016/S1015-9584(09)60122-6.
The novel, proinflammatory cytokine endothelial-monocyte-activating-polypeptide-II (EMAP-II) was first found in tumour cell supernatants and is closely related or identical to the p43 component of the mammalian multisynthetase complex. In its secreted form, EMAP-II has multiple cytokine-like activities in vitro, including chemotactic, procoagulant and antiangiogenic properties. We recently showed that neoplastic but not normal hepatocytes expresses the 34-kDa molecule on the cell surface in vitro and the cell-surface expression is upregulated by treatment with tumour necrosis factor (TNF)-alpha/interferon (IFN)-gamma and/or hypoxia. We hypothesized an immune-regulatory role of EMAP-II within neoplastic tissues and investigated its effects on lymphocytes.
To study the role of EMAP-II in tumour cell-induced lymphocyte killing, Jurkat T-cells were co-cultured with a range of hepatocellular carcinoma (HCC) cell monolayers (HuH-7, HepG2 and Alexander cells), which were either untreated or treated with TNF-alpha/IFN-gamma under normoxic and hypoxic conditions over a period of 16-24 hours. Flow cytometric analysis of apoptosis in Jurkat cells was performed using the annexin-V-FITC/propidium iodide technique.
rEMAP-II caused a dose-dependent apoptosis in Jurkat T-cells. Co-culture of Jurkat cells with HCC cell monolayers induced significant apoptosis of the Jurkat cells. In general, under normoxic conditions, cytokine-treated HCC cell monolayer caused more apoptosis than untreated cells. This effect was enhanced by hypoxia. Critically, native EMAP-II expressed on the surface of the HCC cells also induced activation of caspase-8 and apoptosis in Jurkat cells, which was partially but significantly blocked by addition of polyclonal antibodies against EMAP-II to the incubation mixture.
Our data suggest that membrane-bound EMAP-II is cytotoxic to lymphocytes and, therefore, might constitute a component of a novel, immunosuppressive pathway by which HCC cells may eliminate attacking T-cells and evade the immune system. The mechanism by which it does so is currently under investigation.
新型促炎细胞因子内皮单核细胞激活多肽-II（EMAP-II）最初在肿瘤细胞上清液中被发现，与哺乳动物多合成酶复合体的p43成分密切相关或相同。以分泌形式存在时，EMAP-II在体外具有多种细胞因子样活性，包括趋化、促凝和抗血管生成特性。我们最近发现，肿瘤性而非正常肝细胞在体外细胞表面表达34 kDa分子，且肿瘤坏死因子（TNF）-α/干扰素（IFN）-γ处理和/或缺氧可上调该分子的细胞表面表达。我们推测EMAP-II在肿瘤组织中具有免疫调节作用，并研究了其对淋巴细胞的影响。
为研究EMAP-II在肿瘤细胞诱导的淋巴细胞杀伤中的作用，将Jurkat T细胞与一系列肝细胞癌（HCC）细胞单层（HuH-7、HepG2和Alexander细胞）共培养，这些细胞单层在常氧和缺氧条件下分别未经处理或用TNF-α/IFN-γ处理16 - 24小时。使用膜联蛋白-V-异硫氰酸荧光素/碘化丙啶技术对Jurkat细胞中的凋亡进行流式细胞术分析。
重组EMAP-II在Jurkat T细胞中引起剂量依赖性凋亡。Jurkat细胞与HCC细胞单层共培养可诱导Jurkat细胞显著凋亡。一般来说，在常氧条件下，细胞因子处理的HCC细胞单层比未处理细胞引起更多凋亡。缺氧可增强这种效应。至关重要的是，HCC细胞表面表达的天然EMAP-II也可诱导Jurkat细胞中半胱天冬酶-8的激活和凋亡，向孵育混合物中加入抗EMAP-II多克隆抗体可部分但显著地阻断这种作用。
我们的数据表明，膜结合EMAP-II对淋巴细胞具有细胞毒性，因此可能构成一种新的免疫抑制途径的组成部分，通过该途径HCC细胞可消除攻击的T细胞并逃避免疫系统。其具体机制目前正在研究中。
