α-黑素细胞刺激素对恶性黑色素瘤细胞Fas/FasL表达的影响及其与凋亡的关系

目的:研究α黑素细胞刺激素(αMSH)对恶性黑色素瘤细胞凋亡特性的影响。方法:采用流式细胞检测分析、DNA琼脂糖凝胶电泳方法检测α黑素细胞刺激素作用后恶性黑色素瘤细胞的凋亡情况,应用RT PCR检测恶性黑色素瘤细胞Fas/FasLmRNA的表达情况。结果:α黑素细胞刺激素作用1、3、24小时恶性黑色素瘤细胞凋亡率分别为14.9%、33.7%、46.7%,α黑素细胞刺激素能明显上调恶性黑色素瘤细胞Fas/FasL的表达,各处理组间差异比较均具有显著性(P<0.05);α黑素细胞刺激素作用24小时组细胞的DNA琼脂糖凝胶电泳显示明显“梯状(ladder)”条带。结论:α黑素细胞刺激素能上调恶性黑色素瘤细胞Fas/FasL的表达并诱导恶性黑色素瘤细胞的凋亡。     

凋亡抑制基因c-FLIPs对人肺腺癌细胞增殖和凋亡的作用

目的:探讨过表达凋亡抑制基因c-FLIPs重组腺病毒对人肺腺癌细胞增殖和凋亡的作用。方法:构建过表达凋亡抑制c-FLIPs的重组腺病毒Ad5 c-FLIPs,感染人肺腺癌细胞Calu-3。Real-time PCR检测感染前后c-FLIPs、Caspase-8,Caspase-10和Bcl-2的表达。MTT法检测细胞增殖。流式细胞仪检测感染Ad5 c-FLIPs后人肺腺癌细胞的凋亡情况。结果:成功构建过表达c-FLIPs重组腺病毒Ad5 c-FLIPs,real-time PCR检测凋亡抑制基因c-FLIPs在Calu-3细胞株高表达,过表达c-FLIPs基因,凋亡相关基因Caspase-8、Caspase-10和Bcl-2的表达明显降低。MTT法检测感染前后细胞增殖情况发现,过表达c-FLIPs基因可诱导细胞增殖,流式细胞仪分析经PI染色后的Calu-3细胞株,对照组和腺病毒感染组细胞的凋亡率分别为（55.17±9.68）%和（10.97±1.66）%,差异具有统计学意义（P<0.05）。结论:凋亡抑制基因c-FLIPs可明显诱导人肺腺癌细胞增殖并抑制凋亡。     

基因转移FasL治疗人黑素瘤的实验研究

目的探讨体内外基因转移F as配体(F as-ligand,F asL)对恶性人黑素瘤细胞凋亡的影响。方法用携带人F asL cDNA的缺陷型重组腺病毒(A d-F asL),在体外转导两株黑素瘤细胞,并使其表达;通过流式细胞仪、RT-PCR法进行F as/F asL表达检测,TUNEL法及荧光显微镜相关凋亡检测、分析。建立人黑素瘤裸鼠模型,并对其进行体内疗效观察及病理学检查。结果流式细胞仪和RT-PCR检测两株黑素瘤细胞表面均表达F as,不表达F asL,而A d-F asL转导的两株黑素瘤细胞均能表达F asL;A d-F asL能显著诱导两株黑素瘤细胞在体外凋亡或抑制其生长。体内疗效观察黑素瘤荷瘤鼠模型治疗组瘤重(0.48±0.16)g与对照组瘤重(1.02±0.19)g相比,差异有显著性(P<0.05)。肿瘤组织形态学检查,治疗组可见肿瘤细胞凋亡坏死区及炎性细胞浸润。结论F asL基因重组腺病毒在体内外均具有显著诱导人黑素瘤细胞凋亡的效果。     

重组复制缺陷型腺病毒Ad p53AIP1的抗肿瘤效应及其作用机制

目的:探讨外源性p53AIP1（p53regulated apoptosisinducing protein 1）基因抗肿瘤效应及其作用机制，以评估p53AIP1基因在肿瘤基因治疗中应用的可行性。方法：构建携带p53AIP1基因的重组复制缺陷型腺病毒Adp53AIP1，感染人肝癌细胞HepG2，应用MTT比色法、Western blotting、流式细胞术、罗丹明染色以及电镜等观察外源性p53AIP1基因表达对肿瘤细胞的作用及其相关机制。小鼠皮下接种感染Adp53AIP1的小鼠乳腺癌4T1细胞，观察Adp53AIP1对肿瘤细胞体内成瘤性的影响;建立4T1细胞皮下移植瘤小鼠模型, 直接瘤内多点注射重组腺病毒，观察Adp53AIP1的抗肿瘤疗效。结果：感染Adp53AIP1的HepG2细胞能够高效表达P53AIP1蛋白。MTT检测显示Adp53AIP1对人肝癌细胞HepG2的生长抑制率达50％以上；流式细胞术分析证实p53AIP1使肿瘤细胞周期阻滞于G2/M期；罗丹明染色、电镜观察以及凋亡相关蛋白PARP表达的检测均证实p53AIP1 能诱导肿瘤细胞发生明显凋亡。感染Adp53AIP1的肿瘤细胞体内成瘤受到非常明显的抑制（P<001）, Adp53AIP1瘤体注射对移植瘤生长也有明显的抑制作用（P<0.05）。Western blotting以及RTPCR检测证实Adp53AIP1对p53mRNA表达无影响，能下调mdm2 基因的表达；p53AIP1能上调P53蛋白的表达、下调MDM2蛋白的表达水平，同时还影响P21等细胞周期相关蛋白和凋亡相关蛋白的表达。结论：p53AIP1有明显的体内外抗肿瘤作用，其作用机制与其反向调控P53蛋白、调控多种细胞周期和细胞凋亡相关蛋白、诱导细胞周期阻滞和细胞凋亡有关，该基因在肿瘤基因治疗中具有潜在的应用前景。     

受体依赖性TRAIL重组腺病毒对人肺癌细胞凋亡的诱导作用

目的：观察重组TRAIL腺病毒（Ad5TRAIL及Ad5F35TRAIL）对人非小细胞肺癌（nonsmallcell lung cancer,NSCLC）原代培养细胞和细胞株的凋亡诱导作用,探讨两种AdTRAIL用于肺癌基因治疗的价值。方法：采用流式细胞术检测人肺癌细胞系A549、Z793、QG56和NCIH520及10例原代培养肺癌细胞中CAR和CD46的表达水平;分别以Ad5TRAIL及Ad5F35TRAIL重组腺病毒按MOI 10和50感染上述细胞,48 h后Annexin VFITC双标法流式细胞术检测细胞的早期凋亡。结果：A549、Z793、QG56和NCIH520 4株肺癌细胞中,CD46的表达均明显高于CAR表达。Z793、QG56细胞对Ad5TRAIL和Ad5F35TRAIL的作用较敏感, MOI=10感染后凋亡率分别为（11.76±2.10）%、（15.96±2.89）%和（6.05±158）%、（10.11±1.26）%,显著高于对照组\[（2.33±0.37）%和(5.95±1.89）%,P<0.05\];MOI=50感染时NCIH520细胞凋亡率分别为（12.89±3.2）%和（9.08±1.35）%,与对照组（7.04±2.17）%相比差异无统计学意义（P>0.05）;Ad5TRAIL和Ad5F35TRAIL均不能诱导A549细胞凋亡。10例原代肺癌细胞CD46表达也明显较CAR高;Ad5TRAIL或Ad5F35TRAIL 感染后,5例的原代肺癌细胞检测到凋亡;与Ad5TRAIL相比,Ad5F35TRAIL诱导的凋亡率更高。结论：两种TRAIL重组腺病毒对非小细胞肺癌细胞均有凋亡诱导作用,Ad5F35TRAIL的作用强于Ad5TRAIL,更适合于非小细胞肺癌的基因治疗。     

TRAIL真核表达治疗肝细胞癌作用的研究

目的：构建鼠源TRAIL（mTRAIL）真核表达质粒。研究其体内、外表达对肝癌细胞的诱导凋亡作用，抑制肝癌生长作用及与重组人FN多肽真核表达质粒pCH510协同抑制肝癌生长作用。方法：采用RTPCR及重组DNA技术构建mTRAIL真核表达质粒；体内、外进行基因转染；用流式细胞仪检测肝癌细胞凋亡率，用TdTmediated dUTP nick end labeling (TUNEL)法及免疫组织化学技术检测肝癌细胞凋亡；小鼠实体瘤块模型研究基因转染抑制肝癌生长作用。结果：用RTPCR方法自小鼠脾细胞RNA扩增出TRAIL基因的全长cDNA，并克隆至真核表达载体pcDNA3.1中获重组质粒pX1；以pX1转染BHK细胞株后攻击肝癌细胞株H22细胞，可检测到肝癌细胞凋亡；肌肉内注射转染质粒DNA pX1，通过诱导肿瘤细胞凋亡抑制肝癌生长；pX1与FN多肽真核表达质粒pCH510有协同抑制肝癌生长作用。结论：质粒pX1可在细胞及小鼠体内表达；体内、外表达可诱导肝癌细胞凋亡并可通过该机制抑制肝癌生长；与FN多肽真核表达质粒pCH510有协同抑制肝癌生长作用。     

重组反义c-myc腺病毒抑制K562细胞生长、诱导凋亡的作用

目的：研究重组反义cmyc腺病毒（Ad—AS-c-myc）对人慢性粒细胞K562细胞系抑制生长，诱导凋亡作用及分子机制，探讨Ad-As-c—myc用于慢性粒细胞白血病基因治疗的可能性。方法：采用重组腺病毒Lac—Z（Ad—LacZ）及Ad—AS-c—myc联合多聚季胺转染K562细胞，Xgal染色判断转染效率。采用形态学、MTT试验、RT—PCR、DNA凝胶电泳、流式细胞仪及免疫细胞化学等方法进行研究。结果：多聚阳离子可提高腺病毒载体对K562细胞的转染，Ad—LacZ＋多聚季胺转染率达86％。AdAS—c—myc能抑制K562细胞c—myc基因在转录水平的表达，K562细胞生长受抑（抑制率38％）；Ad—AS-c—myc可使K562细胞G2、G2期阻滞，增殖相关基因PCNA表达降低，Apo2．7蛋白阳性细胞率增高，DNA电泳出现DNA梯形条带。结论：Ad—AS-c-myc对K562细胞具有抑制生长及诱导凋亡作用，其生物学作用与K562细胞c-myc及PCNA的表达降低有关。Ad-AS-c-myc在慢性粒细胞白血病基因治疗中具有潜在的临床价值。     

MMC诱导EJ细胞凋亡和Fas/FasL、Caspase-3基因表达

目的；研究丝裂霉素（MMC）在体外诱导膀胱癌细胞EJ凋亡和凋亡相关基因Fas/FasL,Caspas-3表达的关系。方法：以低剂量MMC（0.100mg/ml)诱导EJ细胞凋亡；以TUNEL法和FCM研究EJ细胞凋亡，细胞周期分布及Caspase-3抗体对抗MMC诱导凋亡；以免疫组化检测Fas/FasL,Caspas-3蛋白表达。结果：低剂量MMC处理的EJ细胞出现明显的凋亡形态特征，凋亡峰和细胞生长阻滞均发生于G0／G1期，Fas/FasL,Caspas-3蛋白呈上调表达，Caspase-3抗体能特异性阻断MMC诱导EJ细胞凋亡。结论；低剂量MMC能够诱导EJ细胞凋亡和增加Fas/FasL,Caspas-3基因表达，且与启动Caspase凋亡信号传导有关。     

caspase-6基因诱导成骨肉瘤细胞凋亡

目的：探讨caspase6对成骨肉瘤细胞株的凋亡诱导作用。方法：应用RTPCR方法检测成骨肉瘤细胞株SOSP9607中caspase6基因的表达水平。以腺病毒adv5作载体，构建含caspase6基因的转基因载体，用脂质体包裹法转染SOSP9607细胞株， 用RTPCR方法检测转染后SOSP9607细胞中caspase6基因的表达。用MTT法检测转染caspase6对SOSP9607细胞株生长的影响。结果：成骨肉瘤细胞株SOSP9607中未检出caspase6表达。RTPCR法证实转染caspase6后SOSP9607中caspase6表达显著增强，MTT检测显示对SOSP9607细胞的生长有抑制作用，形态学观察及DNA电泳证实转染后的细胞株存在细胞凋亡特征。结论：caspase6对成骨肉瘤细胞的生长有抑制作用，并可诱导成骨肉瘤细胞凋亡。     

腺病毒介导人VEGF-siRNA对裸鼠移植骨肉瘤的抑制作用

目的: 研究腺病毒介导人VEGFsiRNA对裸鼠移植骨肉瘤的治疗作用。方法：利用腺病毒重组技术将VEGFsiRNA基因克隆入增殖缺陷型腺病毒基因组中，构建重组腺病毒AdVEGFsiRNA，重组腺病毒体外感染骨肉瘤MG63细胞，RT-PCR检测MG63细胞VEGF的表达水平。建立荷人骨肉瘤MG63裸小鼠动物模型，以Ad-VEGFsiRNA瘤组织注射治疗，检测移植瘤组织中VEGF的表达情况及Ad-VEGFsiRNA对肿瘤生长和肺转移的抑制作用。结果：成功构建了表达VEGFsiRNA的重组腺病毒载体AdVEGFsiRNA；体外与体内实验检测Ad-VEGFsiRNA转染骨肉瘤细胞MG63后显著抑制VEGF表达。荷人骨肉瘤裸鼠经Ad-VEGFsiRNA治疗后，显示其对移植骨肉瘤生长有明显抑制作用（P<0.05），并且对骨肉瘤的肺转移有显著的抑制作用（P<0.05）。结论：所构建的Ad-VEGFsiRNA可以有效抑制骨肉瘤中VEGF表达，使裸鼠移植骨肉瘤生长减慢，并且显著抑制荷瘤裸小鼠肺转移的发生。     

THP-1 monocytic leukemia cells express Fas ligand constitutively and kill Fas-positive Jurkat cells

Normal human monocytes express Fas and are susceptible to Fas ligand (FasL)-induced apoptosis. Because the myeloid leukemia cell lines HL-60 and THP-1 can be differentiated into functional monocytes and macrophages, we studied their expression of Fas and Fas ligand (FasL) to determine whether there were differentiation-associated changes in these proteins. THP-1, HL-60 and HCW-2, both before and after treatment with PMA, expressed high levels of Fas ligand (FasL), but did not express Fas. The FasL expressed by THP-1 cells was functional as measured by their ability to kill Jurkat T-cells by apoptosis. The THP-1 Fas gene appears to be silent, because bacterial lipopolysaccharide (LPS) induced Fas expression in fully differentiated THP-1 cells. Our results suggest that FasL expression by leukemia cells may account in part for the pathophysiology of myeloid leukemia, and that PMA-differentiated THP-1 cells, while possessing many of the functional properties of normal macrophages, are abnormal with respect to a major apoptotic pathway.     

Frequent downregulation of Fas (CD95) expression and function in melanoma

Membrane-bound Fas ligand (FasL, Apo-1L, CD95L) induces rapid apoptosis of Fas (CD95)-sensitive cells on interaction with Fas, and is an important effector molecule of cytolytic T lymphocytes (CTLs). Melanomas are immunogenic and induce the production of specific CTLs, but are usually able to escape immune destruction. We investigated Fas expression and function in 53 cutaneous melanocytic lesions and 13 melanoma cell lines grown in vitro. Immunohistochemical analysis of Fas expression in cutaneous melanocytic lesions showed moderate to high levels of Fas in common benign melanocytic naevi, but low to undetectable levels in atypical naevi, primary (superficial spreading melanoma, nodular melanoma) and cutaneous melanoma metastases. Fluorescence-activated cell sorting (FACS) analysis of Fas expression in melanoma cell lines revealed undetectable or low levels of cell surface Fas expression in five of the 13 melanoma cell lines. Analysis of Fas signalling by quantification of cell death following exposure to recombinant FasL showed that a reduction in Fas expression results in resistance to FasL-mediated cell death. Furthermore, two of the 13 melanoma cell lines were found to be resistant to FasL-mediated cell death despite conserved Fas expression. Thus seven of the 13 melanoma cell lines were found to have impaired Fas signalling. Taken together, our results indicate that downregulation of Fas expression and resistance to Fas-mediated apoptosis are frequent in melanoma.     

Fas/FasL与肿瘤局部及全身性免疫抑制

Ｆａｓ（ＣＤ９５）及其配体（ＦａｓＬ）属ＴＮＦ和ＮＧＦ受体家族,Ｆａｓ在多种质细胞表面均有表达。Ｆａｓ与ＦａｓＬ结合可引起多种细胞产生凋亡。近年来研究发现ＦａｓＬ在多种种瘤细胞的表面和细胞质中表达,同时已证实肿瘤周围激活的淋巴细胞表面有Ｆａｓ的表达,而这些淋巴细胞的凋亡异常增加,因此推测表达ＦｓａＬ的肿瘤细胞能诱发淋巴细胞的异常凋亡或抑制其功能,肿瘤细胞表面表达的ＦａｓＬ可能在局部免疫抑制中起着重     

Fas and Fas ligand expression in tumor cells and in vascular smooth-muscle cells of colonic and renal carcinomas.

CD95/APO-1 ligand (FasL) is implicated in the maintenance of immune privileged sites by inducing apoptosis of activated infiltrating T lymphocytes. Therefore, progressive tumors might express high levels of FasL and develop as immune privileged sites. In this study, we investigated the expression of FasL and CD95/APO-1 (Fas, the FasL-receptor) in vitro in rat adenocarcinoma cell lines and the localization in situ in normal human kidney and colon and in their adenocarcinomas. The rat cell line PROb (a progressive tumor in vivo) expressed a higher level of FasL than the sister cell line REGb (a regressive tumor in vivo), as detected by flow cytometry. The 2 cell lines expressed the same level of Fas, but were resistant to FasL-induced apoptosis. In human tissue, both kidney and colon extracts expressed FasL by Western blot. Further investigations, using immunohistochemical staining of paraffin sections, showed that normal colon mucosa expressed Fas and FasL in crypt epithelial cells in the subnuclear compartment. Normal kidney showed Fas and FasL labeling mostly restricted to epithelial cells of proximal tubules and Henlé's loop, showing that this expression is not uniform throughout the organ. Smooth-muscle cells of muscularis propria and blood vessels in and around the tumors were also intensely but more uniformly labeled. In colon-cancer cells, FasL expression remained strong, whereas Fas expression was significantly reduced. A similar reduction in Fas expression was noted in renal-cancer cells. Tumor-infiltrating immune cells of the macrophage lineage do not express FasL. Our results show that smooth-muscle cells of muscularis propria and blood vessels are able to express FasL and to a slight extent Fas. In normal epithelial cells of colon and kidney, Fas and FasL are often co-expressed. The reduced expression of Fas in corresponding cancer cells in combination with the ability to express FasL might facilitate immune escape.     

Tamoxifen induces apoptosis in Fas<Superscript>+</Superscript> tumor cells by upregulating the expression of Fas ligand

PURPOSE: Tamoxifen (TAM), a nonsteroidal anticancer agent, is used in the treatment of breast cancer. In the current study, we investigated whether TAM induces apoptosis in tumor cells by altering the expression of Fas and Fas ligand (FasL). METHODS: Several tumor cell lines were used to test the ability of TAM to induce apoptosis, which was studied using the TUNEL assay. The effect of TAM on the expression of Fas and FasL was analyzed using a flow cytometer. RESULTS: TAM was found to suppress the growth of an estrogen receptor-positive human mammary tumor cell line (T-47D) by inducing apoptosis. Interestingly, TAM also induced apoptosis in an estrogen receptor-negative murine T cell lymphoma cell line, EL-4. The ability of TAM to induce apoptosis in T-47D and EL-4 tumor cells correlated with the increased expression of FasL but not Fas on the tumor cells. Similar to TAM, a metalloproteinase (MP) inhibitor, which is known to increase the expression of membrane-bound FasL, was found to induce apoptosis in both T-47D and EL-4 tumor cells by increasing the expression of FasL but not Fas. Furthermore, both TAM and the MP inhibitor failed to induce apoptosis in L1210 tumor cell lines that failed to express FasL. CONCLUSIONS: The current study demonstrates that TAM can induce apoptosis in Fas(+) tumor cells by upregulating FasL.     

Analysis of Fas and Fas ligand expression and function in lung cancer cell lines

The aim of this study was to investigate the expression of Fas and Fas ligand (FasL) and to determine the significance of these molecules in lung cancer cell lines. Immunoblotting, RT-PCR and flow cytometric analyses were carried out to measure the expression of Fas and FasL and to examine their interactions and effects on cell growth and apoptosis. Fas and FasL were co-expressed in most of the cell lines but to varying degrees. Apoptosis induced by the agonistic anti-Fas antibody was significantly correlated with Fas expression (P=0.0075), whereas cisplatin-induced apoptosis was not. Upregulation of Fas and FasL expression by the administration of cisplatin was found in 7 of 11 (64%) and 9 of 11 (82%) cell lines, respectively. However, cisplatin-induced apoptosis was not suppressed by antagonistic anti-FasL antibody. Thus, our data indicated that Fas and FasL were co-expressed in lung cancer cell lines, and that Fas ligation induced by agonistic anti-Fas antibody is functional and induced apoptosis that was dependent on the levels of Fas expression. In contrast, Fas-FasL interactions appeared to be non-functional. Furthermore, our results suggest that cisplatin-induced apoptosis in lung cancer cells was independent of the Fas-FasL interaction.     

RNA干扰肺癌细胞H460 FasL表达对T细胞凋亡的影响

背景与目的已有的研究表明肺癌细胞可通过上调Fas配体（FasL）表达、借助FasL/Fas凋亡途径反杀伤Fas阳性肿瘤浸润淋巴细胞（TIL）,主动逃避免疫监视,导致肿瘤局部抗肿瘤免疫下降。本研究旨在探讨遗传修饰调节肺癌细胞FasL基因表达对T细胞凋亡的影响。方法通过质粒载体,将体外化学合成的靶向FasL的小干扰RNA（siRNA）直接转染人大细胞肺癌细胞株H460,采用RT-PCR和Westernblot技术观察肺癌细胞FasLmRNA及蛋白表达的变化及其诱导T细胞凋亡的改变。结果化学合成的靶向FasL基因的siRNA能够显著下调肺癌细胞H460FasLmRNA和蛋白表达水平,产生序列特异性干扰效果。RNA干扰（RNAi）抑制H460细胞FasL表达后可以降低和逆转肺癌细胞诱导的T细胞凋亡,恢复T细胞增殖能力。结论FasL是一新的具有发展前途的肺癌基因治疗靶位。     

In vitro apoptotic induction of human glioblastoma cells by Fas ligand plus etoposide and in vivo antitumour activity of combined drugs in xenografted nude rats

Human glioblastomas that express Fas/CD95 receptor are highly resistant to conventional brain tumour therapies. The aim of this study is to evaluate anti-tumour properties of a combination of Fas ligand (FasL) plus etoposide with or without dexamethasone on intracerebral experimental glioblastomas. The human Fas-expressing glioblastoma cell line, U-87 MG, was firstly studied in vitro for apoptosis and proliferation assays in the presence of FasL and etoposide, separately or associated, in order to detect a supra-additive effect on FasL or etoposide-induced apoptosis. The tumourigenicity of the U-87 MG cell line and therapeutic effects of FasL-etoposide alone or combined with dexamethasone were next studied on U-87 MG cells xenografted to nude-rat brain and tumour size was hence examined by histological and immunohistochemical stainings. We demonstrated in vitro that the combination of both molecules strongly inhibited the proliferation rate and increased the sensitivity of glioblastoma cells to Fas or etoposide-mediated apoptosis. Moreover, analysis of rat brains was performed 30 days after xenograft of glioblastoma cells. These data show that the combination of FasL and etoposide could reduce significantly the tumour size and that the addition of dexamethasone enhanced the inhibiting effect of FasL and etoposide on tumour growth in vivo.     

Serial in vivo loss and in vitro gain of Fas expression and function in human cancerous pancreatic duct cells

Recent studies have shown the involvement of the Fas system (Fas receptor and its ligand FasL) in cancerous processes. The absence or downregulation of Fas, reported in the majority of human tumors, conflicts with its presence in cancerous cells from the same tumors but maintained in vitro. Recently, the eventual role of environmental factors in the loss of Fas expression, or in the in vivo selection of a Fas-negative cell population has been suggested. We determined the Fas expression and function in the Capan-1 human cancerous pancreatic duct cells over 2 successive passages in vivo separated by a period of 10-20 passages in vitro. We showed that Capan-1 cells express Fas and are sensitive to Fas-mediated apoptosis when maintained in vitro. When these cells were xenografted into nude mice the expression of Fas was lost in the majority of the tumors. Culture of tumor-derived cells exhibited that they became Fas-positive and sensitive to Fas-mediated apoptosis after a short period in vitro. The loss/gain of Fas was reproduced after re-explantation and re-culture of these Fas-expressing cells. Furthermore, RT-PCR evidenced a strong inhibition of Fas, FLICE and FADD mRNAs expression in the xenografts. Our observations indicate that the expression of Fas and its function could depend to factors in the tumoral environment. The in vivo loss of Fas may thus play an important role in the tumor formation and in the evasion of tumor cells from immune surveillance.