Fas ligand expression in colon cancer： A possible mechanism of tumor immune privilege

AIM: To detect the expression of Fas ligand (FasL) in colon cancer tissues and cell lines and analyze the function of FasL-expressing colon cancer cells in inducing Fas-sensitive T lymphocyte apoptosis. METHODS: Ninety surgically resected colon cancer tissues and 15 hepatic metastasis specimens were investigated by immunohistochemical method with normal colon mucosa and colon adenoma as control. The relationship between FasL expression and pathologic features was also analyzed. FasL expression of 4 colon cancer cell lines, SW620, Lovo, LS-174T and SW1116, were detected by Western blotting assay. The function of FasL expressed on colon cancer cells was determined by coculture assay with Jurkat T lymphocytes, the apoptotic rate of which was detected by flow cytometry assay. RESULTS: Fifty-six (62.22%) cases of all the 90 colon cancer tissues and all (100%) the liver metastasis specimens expressed FasL, significantly higher than normal colon mucosa and colonic adenoma. Higher expression of FasL was found in more advanced stage of colon cancer and in cancer tissues with lymphatic or hepatic metastasis. All the colon cancer cell lines were found to express FasL. After coculture with the SW1116 cells for 24 h with an effector: target ratio 10:1, the rate of apoptosis of Jurkat cells rose from 1.9% to 21.0%. CONCLUSION: The expression of FasL is upregulated in colon cancer and the functionally expressed FasL can induce apoptosis of Fas-expressing T lymphocytes.     

Fas/Fas配体在大肠癌发生和免疫逃逸及反击中的作用

目的　探讨Fas、Fas配体 (FasL)在大肠癌发生和免疫逃逸及反击中的作用。方法　应用免疫组织化学染色的方法 ,对 5 2例大肠癌、2 7例大肠腺瘤、2 8例溃疡性结肠炎、30例正常大肠组织及 2 3例大肠癌淋巴结转移癌组织进行Fas和FasL的检测。对 5 2例大肠癌用TUNEL法 ,检测不同FasL表达区肿瘤细胞的凋亡情况。结果　 (1)Fas在不同大肠组织中的表达规律是 :大肠癌中表达最低 ,其次是大肠腺瘤、溃疡性结肠炎 ,表达水平最高的是正常大肠组织。FasL在不同大肠组织中的表达规律与Fas正好相反 ,大肠癌组织中表达最高 ,其次是大肠腺瘤、溃疡性结肠炎 ,正常大肠组织中几乎不表达FasL。 (2 )Fas、FasL的表达与大肠癌的组织学类型无关 (P >0 0 5 ) ,与Dukes分期、分化程度、有无淋巴结转移有关 (P <0 0 5 )。 (3)在同一大肠癌组织切片中 ,FasL的表达不均匀 ;FasL表达阳性区(n =2 5 )肿瘤细胞的凋亡率 (81 2 % )比FasL阴性区 (n =2 5 ) (47 4 % )高 (P <0 0 1)。 (4)在 2 3例大肠癌淋巴结转移癌组织中 ,发现 2 3例转移癌FasL均强阳性表达 ,阳性细胞率均大于 75 %。结论　Fas、FasL在大肠癌发生和免疫逃逸及反击中起重要的作用     

Resistance to Fas (APO-1/CD95)-mediated apoptosis and expression of Fas ligand in esophageal cancer: the Fas counterattack

The mechanisms by which esophageal tumors escape immunologic recognition and clearance are only partly understood at the molecular level. Esophageal cancers have been shown to evade host recognition by down-regulation of antigen presentation and production of immunosuppressive factors. Recently, two independent reports have shown that esophageal tumor cells abundantly express Fas ligand (FasL) in vivo. As the triggering agonist for Fas receptor (Fas or APO-1/CD95)-mediated apoptosis of lymphocytes, FasL normally plays immune down-regulatory roles, including activation-induced cell death of T and B cells, as well as maintaining immune privilege in certain organs. Fas ligand expressed by esophageal cell lines has been shown to induce apoptosis of cocultured Fas-sensitive lymphoid cells in vitro. FasL expression by esophageal carcinomas in vivo has been associated with significantly reduced tumor-infiltrating lymphocytes (TILs) in FasL-positive tumor nests, concomitant with significantly increased TIL apoptosis in these nests. These studies support a 'Fas counterattack' mechanism of immune escape in esophageal cancer. By expressing functional Fas ligand, esophageal cancer cells can deplete antitumor lymphocytes by inducing apoptosis. To express functional FasL, esophageal carcinomas also acquire molecular mechanisms to resist autocrine Fas-mediated apoptosis of tumor cells.     

Role of cytokines in promoting immune escape of FasL-expressing human colon cancer cells

AIM: To investigate the potential role of cytokines in promoting Fas ligand (FasL)-expressing colon cancer cells. METHODS: Immunohistochemical SABC method was used to observe the expression of Fas receptor and ligand in SW620 colon cancer cell line and Jurkat T cells in order to provide the morphological evidence for the functions of Fas receptor and ligand. To examine the cytotoxicity of effector cells, CytoTox96 non-radioactive cytotoxicity assay was adopted to measure the lactate dehydrogenase-releasing value after SW620 cells were co-cultured with Jurkat T lymphocytes. RESULTS: The FasL of colon cancer SW620 cells was positive. The positive substances were distributed in the cell membrane and cytoplasm. The Fas receptor of colon cancer SW620 cells was negative. The Fas receptor and ligand of Jurkat T lymphocytes turned out to be positive. The positive substances were distributed in the cell membrane. After phytohemagglutinin (PHA)-stimulated Jurkat T lymphocytes were co-cultured with phorbol 12-myristate 13-acetate (PMA)-plus-ionomycin-stimulated (for 48 h) SW620 cells or tumor necrosis factor-alpha (TNF-α)-stimulated (for 48 h) SW620 cells or unstimulated SW620 cells for 4 h, the cytotoxicity of SW620 cells to PHA-stimulated Jurkat cells at effector-to-target ratios of 10:1, 5:1, 2.5:1, and 1.25:1 was 74.6%, 40.8%, 32.4%, and 10.9% (F= 8.19, P<0.05); or 54.9%, 35.3%, 22.0%, and 10.3% (F= 11.12, P<0.05); or 14.9%, 10.5%, 6.9%, and 5.8% (F = 3.45, P<0.05). After PHA-stimulated Jurkat T lymphocytes were co-cultured with unstimulated SW620 cells for 8 h, the cytotoxicity of SW620 cells to PHA-stimulated Jurkat cells at effector-to-target ratios of 5:1, 2.5:1, and 1.25:1 from the experiment was 83.9%, 74.1%, and 28.5% (F=137.04, P<0.05) respectively. Non-radioactive cytotoxicity assay showed that the apoptotic rate of Jurkat cells remarkably increased with the increase of planting concentration of SW620 cells and co-culture time after the SW620 cells were co-cultured with the Jurkat T lymphocytes. The cytotoxicity was significantly enhanced by PMA+ionomycin or TNF-α. CONCLUSION: The FasL expressed in human colon cancer cells may be regulated by endogenous factors in the microenvironment of the host and facilitate the escape of tumor cells from the host immune system.     

Fas通路的激活促进结肠癌细胞迁移侵袭

目的探讨Fas通路激活对结肠癌细胞SW480和DLD1产生的非凋亡效应。方法流式细胞学检测结肠癌SW480及DLD1细胞系的Fas、FasL、抗凋亡蛋白c-FLIP、Bcl-2、Bcl-xl、XIAP等在细胞膜上的表达水平;对结肠癌SW480及DLD1细胞系予以梯度浓度（0ng/ml、12.5ng/ml、25ng/ml、50ng/ml）的FasL刺激,计数并比较各组细胞的增殖速率变化;对结肠癌SW480及DLD1细胞系予以低剂量FasL处理,分别对实验组和对照组进行细胞增殖速率及迁移侵袭能力测试,探讨低剂量FasL刺激对结肠癌细胞活力的影响;稳定敲除SW480和DLD1细胞的Fas基因表达,重复上述实验,以明确低剂量FasL刺激对结肠癌细胞活力的影响是否依赖于Fas通路的激活。结果 SW480及DLD1细胞系中均可检测到中等程度的Fas表达及抗凋亡蛋白FLIP、Bcl-2的表达,未检测到FasL表达,在SW480中可测到Bcl-xl表达;低剂量FasL不影响结肠癌SW480和DLD1细胞的增殖速率,但可促进两种细胞的迁移侵袭能力;稳定敲除Fas基因后,低剂量FasL对结肠癌细胞迁移侵袭能力的促进作用受到抑制。结论低剂量FasL可激活Fas通路的非凋亡途径从而增强结肠癌SW480和DLD1细胞的迁移侵袭能力。     

Fas ligand expression in thyroid carcinomas: a potential mechanism of immune evasion.

Fas ligand (FasL) induces apoptosis by cross-linking the Fas receptor and is expressed by cells of the immune system. Recently, FasL was found in malignant tumors, suggesting that it helps them escape immune surveillance by eliminating infiltrating lymphocytes. We investigated the presence of FasL immunohistochemically in 48 thyroid carcinomas and by Western blotting and RT-PCR in 5 thyroid carcinoma cell lines. We found that in contrast to normal thyroid tissue, FasL was highly expressed in all papillary, follicular, and Huerthle carcinomas. Medullary carcinomas lacked or had minimal FasL expression. In papillary carcinomas, high levels of expression correlated independently with aggressive histology and unfavorable clinical presentation. FasL was also present in all thyroid cell lines. Thyroid carcinoma cells killed Fas-sensitive targets in a FasL-dependent manner in a coculture experiment. Cross-linking of Fas induced apoptosis in thyroid carcinoma cells only in the presence of cycloheximide. We conclude that FasL is specifically expressed in thyroid carcinomas of follicular epithelial origin, may help them evade the immune system, and may have prognostic implications in papillary carcinoma, as it is associated with a more aggressive phenotype. Thyroid carcinoma cells avoid Fas-mediated suicide possibly by expressing an inhibitor of the Fas apoptotic pathway.     

Suppression of FasL expression in tumor cells and preventing TNF-induced apoptosis was better for immune cells survival

OBJECTIVE: To elucidate if Fas/FasL signal pathway participates in the immune escape of tumor cells, and if contemporarily preventing Fas/FasL and TNF-induced apoptosis is better for immune cells survival than just blocking Fas/FasL-induced apoptotic signal. METHODS: Suppression of FasL expression in mouse H22 hepatocellular cancer cells by siRNA technique. Wild-type Ad5 14.7K gene was amplified by PCR and transduced into Jurkat T cells. Detecting apoptosis of target Jurkat cells by Flow Cytometry. Detection of TNF-alpha in the culture supernatant of H22 cells by ELISA. FasL and 14.7K gene expression in stably transfected or transduced clones were determined by western blotting. RESULTS: FasL expression in H22 cells was down-regulated following stable transfection with a plasmid encoding antisense FasL cDNA. Down-regulation of FasL expression in H22 cells had no effect on tumor growth in vitro. There was an apparent decrease in the number of apoptotic Jurkat T cells following coculture with transfected H22 cells, relative to coculture with FasL-expressing untransfected cells. Compared with untransduced Jurkat cells, apoptotic rates in 14.7K transduced Jurkat cells were significantly reduced in three different E/T ratios (P < 0.01), respectively. CONCLUSIONS: Fas/FasL signal pathway participated in the immune escape of tumor cells by inducing immune cells apoptosis. Reducing the expression of FasL in tumor cells can decrease the apoptotic rate of immune cells. Further blocking of apoptotic signal pathway of immune cells by preventing TNF-induced apoptosis can increase the survival of immune cells.     

Expression of Fas ligand by human gastric adenocarcinomas: a potential mechanism of immune escape in stomach cancer

Background—Despitebeing immunogenic, gastric cancers overcome antitumour immune responsesby mechanisms that have yet to be fully elucidated. Fas ligand (FasL)is a molecule that induces Fas receptor mediated apoptosis of activatedimmunocytes, thereby mediating normal immune downregulatory rolesincluding immune response termination, tolerance acquisition, andimmune privilege. Colon cancer cell lines have previously been shown toexpress FasL and kill lymphoid cells by Fas mediated apoptosis invitro. Many diverse tumours have since been found to express FasLsuggesting that a "Fas counterattack" against antitumour immuneeffector cells may contribute to tumour immune escape.
Aim—To ascertain ifhuman gastric tumours express FasL in vivo, as a potential mediator ofimmune escape in stomach cancer.
Specimens—Thirtyparaffin wax embedded human gastric adenocarcinomas.
Methods—FasL proteinwas detected in gastric tumours using immunohistochemistry; FasL mRNAwas detected in the tumours using in situ hybridisation. Cell death wasdetected in situ in tumour infiltrating lymphocytes using terminaldeoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL).
Results—Prevalentexpression of FasL was detected in all 30 resected gastricadenocarcinomas examined. In the tumours, FasL protein and mRNA wereco-localised to neoplastic gastric epithelial cells, confirmingexpression by the tumour cells. FasL expression was independent oftumour stage, suggesting that it may be expressed throughout gastriccancer progression. TUNEL staining disclosed a high level of cell deathamong lymphocytes infiltrating FasL positive areas of tumour.
Conclusions—Humangastric adenocarcinomas express the immune downregulatory molecule,FasL. The results suggest that FasL is a prevalent mediator of immuneprivilege in stomach cancer.

Keywords:Fas ligand; gastric cancer; immune escape; apoptosis; tumour; mRNA

     

Cholangiocarcinomas express Fas ligand and disable the Fas receptor

Cholangiocarcinoma is a highly-malignant adenocarcinoma originating from cholangiocytes. Current concepts support escape from immune surveillance using aberrant expression of Fas ligand (FasL) and dysregulation of receptor (FasR) signaling as a potential mechanism for tumor progression. Our aims were to determine if altered expression of FasR and FasL or changes in expression of FLICE inhibitor (I-FLICE) allow cholangiocarcinoma cells to escape immune surveillance. Human cholangiocarcinoma cell lines were evaluated for the functional expression of FasR and FasL by (1) quantitating apoptosis after incubation of cells with agonistic antibodies and (2) an in vitro cell death assay involving coculture of cholangiocarcinoma cells with Fas-sensitive thymocytes. I-FLICE antisense treatment was performed by stable transfection with complementary DNA (cDNA) for I-FLICE in the reverse orientation. We found that normal cholangiocytes in vivo express FasL. Human cholangiocarcinoma cell lines express both FasL and FasR and I-FLICE. FasL expressed by cholangiocarcinomas in vitro induced lymphocyte cell death (70% after 24 hours). Despite the expression of FasR, exposure of the cells to agonistic antibodies (500 ng/mL) induced only minimal apoptosis in the Jurkat cells. Antisense treatment of cholangiocarcinomas in vitro with I-FLICE reduced protein expression of I-FLICE by 90% to 95% and increased Fas-mediated apoptosis 2-fold. We concluded that cholangiocarcinomas escape immune surveillance either by disabling FasR signaling through the expression of I-FLICE and/or increased FasL expression to induce apoptosis of invading T cells. Reduction of I-FLICE expression in cholangiocarcinoma cells restored Fas-mediated apoptosis. Therapeutic maneuvers to inhibit expression of I-FLICE may aid in the treatment of cholangiocarcinoma.     

姜黄素对结肠癌细胞SW480 FasL基因表达和侵袭能力的影响

目的研究姜黄素对人结肠癌SW480细胞FasL mRNA表达及对其侵袭能力的影响,为中药抗肿瘤提供实验依据。方法根据MTT法得到姜黄素对SW480细胞的半数有效抑制浓度（IC50）,确定药物作用浓度。SW480细胞分别经姜黄素不同浓度（0．5 IC50、IC50）作用后,应用逆转录-聚合酶链反应（RT-PCR）法检测姜黄素作用前后人结肠癌SW480细胞FasL mRNA的变化;应用Transwell细胞侵袭试验检测姜黄素对SW480细胞侵袭能力的影响。结果姜黄素处理后SW480细胞FasL mRNA表达水平均明显高于对照组（P〈0．01）;而且FasL mRNA表达水平随姜黄素作用浓度增加显著上调,姜黄素不同浓度组比较均有显著性差异（P〈0．01）;随姜黄素作用浓度升高,SW480细胞侵袭能力明显增强,不同浓度组比较均有显著性差异（P〈0．01）。结论姜黄素在一定时间内均可上调人结肠癌SW480细胞FasL mRNA的表达,而且这种上调作用在一定范围内呈剂量依赖性,可使结肠癌细胞的侵袭能力增强。     

Fas receptor counterattack against tumor-infiltrating lymphocytes in vivo as a mechanism of immune escape in gastric carcinoma

We investigated the presence and functional status of surface expression of the Fas receptor (FasR) and its ligand (FasL) in tumor and tumor-infiltrating lymphocytes (TIL) in gastric carcinoma (n=36) from the primary locus, metastatic gastric carcinoma (n=30) from malignant ascites, and benign gastric mucosa (n=30) for the control. The quantitative analysis was based on the percentage of positive cells by a flow cytometry. The results showed that the membrane-bound FasL molecule was constitutively expressed in primary and metastatic gastric carcinomas as well as normal gastric epithelium in nearly all the patients. In particular, metastatic carcinoma proved to aberrantly express the FasL molecule. On the other hand, FasR expression ranged from minimal or absent in primary and metastatic gastric carcinomas, suggesting that the carcinoma might be rendered less sensitive toward FasR-induced killing. Apoptotic tumor cells detected by terminal deoxynucleotidyl transferase (TdT)-mediated dUTP nick and labeling (TUNEL) were barely identified in primary and metastatic carcinomas. In the analysis of TIL, the expression of FasR and FasL, and apoptotic TIL could not usually be observed in primary gastric carcinoma. In metastatic carcinoma, however, there was significant overexpression of FasR and FasL in immune TIL associated with a higher frequency of apoptotic cell death detected by TUNEL. The results suggest that metastatic carcinoma expressing FasL, but not FasL⁺ primary carcinoma, might evade the immune attack by apoptotic depletion of activated TIL through the FasR/FasL systems. These results provide the direct and quantitative evidence of FasR counterattacks and/or paracrine fratricides as a mechanism of tumor-immune escape in vivo in human cancer. Received: 29 March 2000 / Accepted: 30 June 2000     

Alpha-fetoprotein triggers hepatoma cells escaping from immune surveillance through altering the expression of Fas／FasL and tumor necrosis factor related apoptosis-inducing ligand and its receptor of lymphocytes and liver cancer cells

AIM: To investigate the mechanism ofα-fetoprotein (AFP) in escaping from the host immune surveillance of hepatoc-ellular carcinoma. METHODS: AFP purified from human umbilical blood was administrated into the cultured human lymphoma Jurkat T cell line or hepatoma cell line, Bel7402 in vitro. The expression of tumor necrosis factor related apoptosis-inducing ligand (TRAIL) and its receptor (TRAILR) mRNA were analyzed by Northern blot and Western blot was used to detect the expression of Fas and Fas ligand (FasL) protein. RESULTS: AFP (20 mg/L) could promote the expression of FasL and TRAIL, and inhibit the expression of Fas and TRAILR of Bel7402 cells. For Jurkat cell line, AFP could suppress the expression of FasL and TRAIL, and stimulate the expression of Fas and TRAILR. AFP also could synergize with Bel7402 cells to inhibit the expression of FasL protein and TRAIL mRNA in Jurkat cells. The monoclonal antibody against AFP (anti-AFP) could abolish these functions of AFP. CONCLUSION: AFP is able to promote the expression of FasL and TRAIL in hepatoma cells and enhance the expression of Fas and TRAILR in lymphocytes. These could elicit the escape of hepatocellular carcinoma cells from the host's lymphocytes immune surveillance.     

幽门螺杆菌感染对Fas/FasL表达的影响在胃癌发生中的作用

目的：观察幽门螺杆菌（Hp）及其不同毒力株（cagA阳性与cagA阴性株）感染对胃黏膜上皮细胞Fas/FasL表达的影响，进而探讨胃癌的发生机制。方法：胃镜下取胃窦黏膜标本，将研究对象按病理结果分为黏膜萎缩组，黏膜萎缩伴轻度不典型增生组，黏膜萎缩伴中度不典型增生组，胃腺癌组，黏膜大致正常组为对照组，再根据Hp感染情况为分Hp阳性组与阴性组，并将Hp阳性组进一步成cagA阳性组及阴性组，共9组80例。以快速尿素酶试验，PCR及组织学第三种方法检测Hp，用PCR方法对Hp进行分型。用免疫组化法检测Fas、FasL等表达情况。结果Hp感染率为60．0％，cagA阳性率为90．47％，非腺癌病人Hp阳性组Fas/FasL表达明显高于Hp阴性组（P＜0．05），腺癌组Fas/FasL表达明显高于大致正常组及黏膜萎缩，黏膜萎缩伴轻度不典型增生，黏萎缩伴中度不典型增生组（P＜0．01）。cagA阳性组Fas/FasL表达与cagA阴性组差异无显著性（P＞0．05）。结论：幽门螺杆菌感染后早期即黏 萎缩阶段已出现Fas、FasL等的表达增加，随细胞凋亡的增加，黏膜上皮细胞萎缩加重，细胞DNA不稳定性增加，并出现不典型增生加重， Fas、FasL的表达随之增强，一旦肿瘤细胞形成，Fas/FasL表达进一步增加，形成局部免疫豁免区，导致肿瘤的浸润生长。cagA阳性的菌株在促成肿瘤的发生过程中无明显作用。     

Fas/Fas ligand expression and characteristics of primed CD45RO+ T cells in the inflamed mucosa of ulcerative colitis

BACKGROUND: Chronic immune activation in the colon is characteristic of ulcerative colitis (UC). Fas/Fas ligand (FasL) system is a mechanism responsible for activation-induced cell death (AICD), which maintains homeostasis within the immune system. Thus, Fas/FasL expression on activated colonic T cells of UC patients, as well as the susceptibility of such T cells to AICD was investigated in order to determine the role of activated colonic T cells in the long lasting inflammation in UC. METHODS: Fas, FasL, and CD45RO expression on peripheral blood and colonic T cells of UC patients were assayed by flow cytometry. Apoptosis of colonic T cells induced by anti Fas antibody was assessed using the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling (TUNEL) assay. RESULTS: The majority of colonic T cells expressed both CD45RO and Fas in the colonic mucosa, a situation that was quite different from that in the peripheral blood. The number of CD45RO+CD8+ and Fas+CD8+ T cells was significantly lower in UC patients than the controls, unlike the number of Fas+CD4+ T cells. In contrast, the number of both CD45RO+CD4+ and CD45RO+CD8+ T cells in UC mucosa expressing FasL was significantly higher than in the controls. While Fas mediated apoptosis of CD45RO+CD8+ T cells was higher in UC patients than the controls, the number of apoptotic CD45RO+CD4+ T cells from UC mucosa was not. CONCLUSIONS: In UC patients, CD45RO+CD4+ T cells are less sensitive to apoptotic signals mediated by Fas. These phenomena may contribute to the pathogenesis of UC.     

FasL的表达在结直肠癌免疫逃逸中的意义

目的研究结直肠癌中Fas配体（FasL）的表达及其在结直肠癌免疫逃逸中的意义。方法采用免疫组织化学染色法，检测80例结直肠癌组织中FasL表达及肿瘤浸润淋巴细胞（TIL）的数量。应用原位杂交法，检测80例结直肠癌组织连续切片的FasL的。RNA的表达。采用脱氧核糖核酸末端转移酶介导的缺口末端标记技术（TUNEL），对80例结直肠癌组织中凋亡的TIL及肿瘤细胞进行观察。结果80例结直肠癌组织FasL表达程度不等，不论是在同一组织切片不同部位或两组织切片间相比，FasL表达程度和范围都不均匀。FasL的mRNA的表达部位与FasL蛋白的表达部位相对应。FasL表达程度高的组织的TIL计数低于FasL表达低的组织（P〈0．05），同时其TIL凋亡指数高于FasL表达低的组织，而结直肠癌细胞的凋亡指数低于FasL表达程度低的组织（P〈0．01），TIL凋亡指数与胃癌细胞的凋亡指数呈负相关（r=-0．631，P〈0．01）。结论全占直肠癌细胞可通过表达FasL，诱导TIL发生凋亡，反击机体免疫系统，这可能是结直肠癌免疫逃避的重要机制之一。