WIF-1与肿瘤.pdf

中国癌症杂志2010年第20卷第4期 CHINA ONCOLOGY 2010 Vol.20 No.4299WIF-1与肿瘤关系的研究进展江黎珠 综述陈鸿雁 审校重庆医科大学附属第一医院耳鼻咽喉科，重庆 400016 摘要WIF-1是Wnt/-catenin信号通路的重要拮抗物之一。WIF-1作为一种抑癌基因，被发现在大多数肿瘤中表达降低，这与其启动子甲基化密切相关，而经去甲基化剂作用可恢复其表达。启动子甲基化导致的WIF-1抑癌作用的丧失可能主要通过异常激活Wnt/-catenin信号通路而促进了肿瘤的发生。在不同肿瘤中，WIF-1表达降低与临床病理参数之间的关系有差异性。检测WIF-1表达及启动子甲基化水平可能为肿瘤早期诊断、治疗及判断预后提供帮助。关键词WIF-1；抑癌基因；甲基化；Wnt；肿瘤中图分类号：R730.231文献标识码：A文章编号：1007-3639(2010)04-0299-04Research progresses on relationship between Wnt inhibitory factor-1 and tumorJIANG Li-zhu,CHEN Hong-yan(Department of Otorhinolaryngology,the First Affiliated Hospital of Chongqing Medical University,Chongqing 400016,China)Correspondence to：CHEN Hong-yanE-mail：Abstract WIF-1 is an important antagonist in the Wnt/-catenin pathway.As a tumor suppressor,WIF-1 is down-regulated in majority cancers but when it is correlated with WIF-1 promoter hypermethylation and treated with demethylation drugits expression can be restored.Functional loss of WIF-1 due to promoter hypermethylation plays an important role in a tumors pathogenesis,possibly mainly through aberrant canonical Wnt/-catenin signal activation.The correlation of the expression of WIF-1 with clinicopathological features in different cancers is not identical.Detecting WIF-1 and promoter hypermethylation may offer help for early diagnosis,therapy and predicting prognoses.Key wordsWIF-1;tumor suppressor;methylation;Wnt;tumor通讯作者：陈鸿雁E-mail:Wnt（Wingless-type）信号通路具有传递生长刺激信号的作用，该通路的异常激活可引起细胞异常增殖、分化而导致肿瘤的发生。WIF-1（Wnt inhibitory factor-1）是新近发现的Wnt信号通路的重要拮抗物之一，并因其为抑癌基因，与肿瘤发生、发展有着密切联系。近来WIF-1与各系统肿瘤发生、发展之间的关系研究成为了研究热点。本文就目前国内外针对WIF-1与肿瘤关系的研究进展作一综述。1WIF-1 基因定位及其结构WIF-1基因位于染色体12q14.3上，全长约200 kb，其中包含10个外显子，cDNA序列约2 014 bp。WIF-1作为WIF-1基因的编码产物，是一种分泌性糖蛋白，具有高度保守性，最早发现表达于人视网膜上1，而后发现在前列腺、乳腺、肺、胃肠道和膀胱等都有高度表达。检测WIF-1蛋白结构，发现其中有一个140个氨基酸组成的信号区域WD（WIF domain），5个表皮生长因子样（EGF-Like repeats）重复序列以及由45个亲水性氨基酸组成的羧基末端1。其中WD在WIF-1的拮抗作用中占主导地位。核磁共振图像研究发现WD的三维结构是由8个片层形成的免疫球蛋白折叠体2。2WIF-1 与 Wnt信号通路Wnt信号通路可分为经典通路和非经典通路，该通路的异常激活与肿瘤的发生密切相关，而通过阻断其异常激活可以抑制肿瘤的发生。WNTS（Wnt pro-WNTS（Wnt pro-（Wnt pro-Wnt pro-teins）作为Wnt信号通路中重要的分子群，是一种细胞间分泌蛋白，通过与细胞膜上卷曲蛋白（Frizzled，Fz）受体家族的成员作用，将信号传至细胞内。WIF-1 通过直接与WNTS结合而阻断WNTS与受体蛋白复合物相连，使细胞质中的-catenin 因为磷酸化而不能积累，从而阻断了经典和非经典通路3。研究发现WD信号域参与组成了酪氨酸激酶受体Ryk（related-to-tryosine-kinase）的细胞外主要结构4。Ryk受300体被证实是促进轴索生长的Wnt的复合受体结构，与Wnts结合参与Wnt信号通路的传递5。Hsieh等1在将编码WIF-1的RNA注射入非洲爪蟾早期胚胎实验中，发现人WIF-1 阻断了爪蟾 Wnt8的活性，WD信号区域发挥着如同整个WIF-1的功能而参与抑制作用。所以WD主要介导了WIF-1的功能，与Wnts配体竞争与卷曲蛋白受体（frizzled recepter，FzR）的结合，从而阻断Wnt信号转导，因而WIF-1被认为是Wnt信号通路的下游区负反馈调节基因。近来研究发现Wnt信号通路参与干细胞 6-9 和肿瘤干细胞10-12自我更新和增殖。而WIF-1也在干细胞增殖更新中发挥着调节作用13，并维持其内环境的稳定14。但是WIF-1在肿瘤干细胞形成、增殖中的作用以及具体机制尚不清楚。3WIF-1与各系统肿瘤3.1呼吸系统肿瘤研究发现75%83%的肺癌组织和肺癌细胞株中WIF-1蛋白表达降低与WIF-1启动子CpG岛高甲基化密切相关，而经5-氮-2-脱氧胞苷去甲基化后，WIF-1恢复表达15-17。另有研究发现WIF-1蛋白表达的降低与病理分级及临床分期无关，指出其表达降低可能是肺癌发生的早期事件16-17。还有研究指出WIF-1作为IA期非小细胞肺癌（non-small cell lung carcinoma，NSCLC）患者预后判断的生物指标的可能18。有学者检测NMCLC患者的恶性胸腔积液中WIF-1的甲基化水平，结果69.4%呈阳性，而良性胸腔积液中无一例阳性，指出检测WIF-1启动子甲基化水平可能将成为NMCLC患者恶性胸腔积液细胞学检测的又一辅助手段19。近期有研究发现中药成分表没食子儿茶素能逆转肺癌细胞中WIF-1启动子甲基化，这也为肺癌的治疗提供了新的依据20。在恶性胸膜间皮瘤细胞株和组织中也出现WIF-1表达缺失或降低，且与其启动子甲基化密切相关，特别指出在个别案例中，WIF-1表达缺失也在正常组织细胞中出现，提示应考虑癌前病变的可能21。3.2消化系统肿瘤在食管癌细胞株和27%35%食管癌组织中发现WIF-1表达下降，与其启动子甲基化相关，经去甲基化剂作用后WIF-1恢复表达，并发现WIF-1通过抑制-catenin积累来抑制Wnt信号通路而发挥作抑癌基因作用22-23。有学者指出启动子甲基化造成的WIF-1表达降低是barrett食管发生肿瘤化的早期常见事件，恢复其表达可成为治疗靶点24。也有研究表明WIF-1基因重排或丢失是导致唾液腺瘤中WIF-1蛋白表达下降的原因，而表达下降是促使唾液腺瘤发生的原因之一25-26。研究发现在胃组织和胃癌组织中都无WIF-1表达，而在结肠组织和结肠癌组织中都有显著表达，表明虽然在其他肿瘤中WIF-1表达缺失或下降有大量报道，但是在该研究中并未发现WIF-1的表达与胃、结肠癌相关27。也有学者发现72.7%的结直肠腺瘤和78.2%的早期黏膜和黏膜下结直肠癌组织中WIF-1表达降低，同样与WIF-1启动子甲基化相关28，近来更有学者指出WIF-1的异常甲基化可能成为结肠癌早期检测的生物指标29。有学者研究WIF-1在肝癌细胞中的抗肿瘤机制，发现WIF-1通过降低E2F1、cyclin D1、C-MYC表达而促进肝癌细胞的凋亡，并且减少血管内皮生长因子和间质细胞衍生因子-1的生成，抑制了血管形成，发挥了抗肿瘤作用30。3.3泌尿系统肿瘤64%前列腺癌组织中WIF-1表达降低，与临床分期分型无关，表明 WIF-1表达缺失或下降是前列腺癌发生的早期事件16。研究发现膀胱癌组织中WIF-1的表达水平与其启动子甲基化呈负相关，并且启动子甲基化水平与临床分期分型有相关，分期越高或恶性程度越高，则甲基化水平越高31。而检测WIF-1甲基化可作为膀胱癌早期诊断和预测复发的指标32。还有学者发现WIF-1甲基化膀胱癌患者的5年总生存率低于未甲基化膀胱癌患者，分别为60.6和91.7%（P0.05），指出 WIF-1甲基化水平可作为膀胱癌患者预后判断的分子标志物33。启动子甲基化使WIF-1蛋白表达降低，使胞质内-catenin增加，其进入细胞核内，导致靶物C-MYC和cyclin D1 增加，从而激活Wnt信号通路，诱导膀胱癌的发生31。也有研究指出WIF-1通过降低SKP2表达而使得P27/KIP1积累，通过增加C-MYC表达而使P21/WAF1得以转录，从而使侵袭性膀胱癌细胞发生G1期阻滞而抑制其增殖34。在肾细胞癌中，WIF-1表达同样也降低，与其启动子甲基化相关；转染WIF-1基因后抑制了肾癌细胞增殖，并促进癌细胞凋亡和抑制肿瘤生长；机制研究发现，WIF-1在期中主要通过减少-catenin表达、抑制Wnt信号通路而发挥作用35。江黎珠，等.WIF-1与肿瘤关系的研究进展中国癌症杂志2010年第20卷第4期3013.4血液系统肿瘤研究发现急性淋巴细胞性白血病（acute lymphocytic leukemia，ALL）细胞株和261例ALL中WIF-1表达降低与其启动子甲基化相关，并证实启动子甲基化与ALL Wnt信号通路的持续激活相关，抑制Wnt 信号通路可以诱导ALL细胞程序性死亡，而无甲基化ALL其复发率比甲基化ALL相对低，分别为29%和59%，死亡率也相对较低，分别为36%和59%，而10年无病生存率分别为25%和66%36。在43例慢性淋巴细胞性白血病（chronic lymphocytic leukemia，CLL）患者中，发现只有11.6%CLL骨髓细胞的WIF-1启动子甲基化，说明甲基化在CLL不常发生，而发现WIF-1甲基化在老年患者是常见事件，并且WIF-1启动子甲基化与患者性别、淋巴细胞计数以及临床分期无相关性37。3.5其他系统肿瘤研究发现60%的乳腺癌中WIF-1蛋白表达降低，并且DNA甲基转移酶DNMT1和DNMT3B 共同作用促使WIF-1启动子甲基化，且甲基化水平与患者年龄、肿瘤大小、肿瘤组织学分期分型、淋巴结转移、雌激素孕激素受体以及预后无关16，38-40。WIF-1在鼻咽癌和垂体瘤中也表达降低，并都与启动子甲基化密切相关，WIF-1在抑制垂体瘤、黑色素瘤细胞、脉络丛癌细胞增殖中起着重要作用，且WIF-1可能成为治疗视网膜母细胞瘤的新靶点22，41-43。4结论与前景展望综上所述，WIF-1是一种抑癌基因，被发现在大多数肿瘤中表达降低，其在肿瘤的发生、发展中起着重要作用。而其启动子异常甲基化是导致WIF-1表达降低的主要原因，并且经去甲基化剂5-氮杂胞苷、5-氮杂-2脱氧胞苷酸等作用可恢复其表达。WIF-1表达降低可能主要通过异常激活Wnt/-catenin信号通路而促进了肿瘤的发生。在不同肿瘤中WIF-1表达降低与临床病理参数之间的关系具有差异性，通过检测WIF-1表达及启动子甲基化水平可能为肿瘤早期诊断、治疗及判断预后提供帮助。随着WIF-1在Wnt/-catenin信号通路中的地位逐渐受到重视，其与肿瘤发生、发展之间的关系也越来越受到研究者的关注，但目前还有许多方面需要我们去进一步深入研究。首先，作为抑癌基因，WIF-1参与抑制肿瘤细胞增殖，促进肿瘤细胞凋亡，抑制肿瘤发生的具体机制需要更加深入。其次，研究发现WIF-1所在的Wnt/-catenin信号通路在肿瘤干细胞形成中具有重要作用，但是WIF-1在其中又起着怎样的作用？这也必将成为一大研究热点。此外，几乎在各系统肿瘤中都发现WIF-1表达降低，且表达降低均与其启动子甲基化密切相关。而DNA甲基化是一种可逆过程，应用DNA甲基化抑制剂5-氮杂胞苷、5-氮杂-2脱氧胞苷酸可以逆转WIF-1启动子甲基化，并恢复WIF-1的表达水平，这就给肿瘤治疗展示了广泛的应用前景。但是仍存在着许多局限，比如非特异的激活多种靶基因，必将产生潜在的诱导性和致癌性。同时，尽管通过药物可以暂时修正DNA甲基化模式，但是由于其可逆性的特征，同样有可能恢复到原始的甲基化状态，所以还存在很大的临床风险。另外，这类药物在水溶液中不稳定且有毒性，导致在临床应用中存在局限性，因此提高药物稳定性及减少毒性必将是以后要去攻克的难题。参考文献1 Hsieh JC,Kodjabachian L,Rebbert ML,et al.A new secreted 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Wnt/wingless signaling in choroid plexus tumorsJ.Pediatr Blood Cancer,2009,53:1152-1155.收稿日期：2010-01-04 修回日期：2010-03-05）江黎珠，等.WIF-1与肿瘤关系的研究进展