Wnt-1或 Wnt/beta-catenin信號通路在惡性腫瘤中研究進(jìn)展

徐 東綜述 楊小龍審校

1 Wnt概述

1.1 起源

1973年,最初無翅基因(wingless,wg)產(chǎn)物是在果蠅中發(fā)現(xiàn)的[1]。1982年,在鼠乳腺癌病毒誘導(dǎo)的乳腺癌中,無翅有關(guān)的鼠乳腺腫瘤病毒整合位點(diǎn) 1(wingless-related MMTV int-egration site 1,Wnt-1)基因,也叫 int-1,首次作為原癌基因被發(fā)現(xiàn)的,位于(12q13),Wnt-1信號是在胚胎發(fā)育和腫瘤形成過程中起重要作用的分泌性糖蛋白[2]。1987年發(fā)現(xiàn) int-1和 wg是同源物,因此他們一起命名為 Wnt基因家族[3]。在兒童黏液瘤中發(fā)現(xiàn)int-1基因 t(12;16)(q13;p 11)易位,提示該基因可能參與了腫瘤形成。

1.2 通路與功能

Wnt糖蛋白通過結(jié)合到卷曲蛋白-低密度脂蛋白受體相關(guān)蛋白(Frizzled-low de-nsity lipop rotein recep tor-related protein,Frizzled-LRP)5/6復(fù)合物來調(diào)節(jié)內(nèi)穩(wěn)態(tài)和發(fā)育。經(jīng)典的 Wnt信號途徑:誘導(dǎo)參與細(xì)胞質(zhì) beta-catenin穩(wěn)定、核轉(zhuǎn)位和基因調(diào)節(jié)充當(dāng) T細(xì)胞因子(T-cell factor,TCF)輔助激活因子,經(jīng)典的Wnt信號靶基因包括如 FGF20,DK-K 1,WISP1,MYC,CCND 1,和 Glucagon(GCG)等,經(jīng)典的 Wnt信號決定細(xì)胞命運(yùn);而非經(jīng)典的Wnt信號途徑:激活 Rho、Rac、JNK、PKC或 Ca2+、編碼結(jié)合到LRP5/6的 Wnt信號分泌拮抗劑 DICKKOPF-1(DKK-1)并誘導(dǎo)其吞噬,導(dǎo)致經(jīng)典的Wnt信號途徑的抑制,與經(jīng)典的Wnt信號途徑形成負(fù)反饋環(huán)路,非經(jīng)典的 WNT信號控制細(xì)胞移動[4]。Wnt信號調(diào)節(jié)正常上皮干細(xì)胞更新,但其異常有助于腫瘤生長[5]。體外實(shí)驗(yàn)中,Wnt/beta-catenin和 Wnt/Ca(++)信號在內(nèi)皮細(xì)胞新生血管形成方面作用相反[6]。

1.3 Wnt在鼠乳腺癌中的作用機(jī)制

在 Wnt-1轉(zhuǎn)基因鼠的腫瘤模型中,減弱Wnt-1信號導(dǎo)致的乳腺原發(fā)癌和肺轉(zhuǎn)移灶消失,Wnt-1信號的激活與乳腺癌進(jìn)展密切相關(guān)。體內(nèi)實(shí)驗(yàn)中 Wnt-1小干擾RNA(small interfer-ence,siRNA)或抗 Wnt-1抗體誘導(dǎo)細(xì)胞凋亡,阻止其生長。因此,Wnt-1信號可作為癌癥治療的新的靶點(diǎn)[2]。體內(nèi)實(shí)驗(yàn)中,免疫抑制劑雷帕霉素具有直接抗 Wnt-1誘導(dǎo)的乳腺癌作用[7]。Dpr1穿梭蛋白在細(xì)胞質(zhì)和細(xì)胞核之間穿梭負(fù)性調(diào)節(jié)經(jīng)典的 Wnt/beta-catenin信號[8]。非甾類抗炎藥物和過氧化物酶增殖體活化受體r激動劑是經(jīng)典的 Wnt信號通路抑制劑,對癌癥有預(yù)防作用[4]。在Wnt-1/beta-catenin信號被激活的肉瘤細(xì)胞系 A-204,采用Wnt-1單克隆抗體或siRNA阻斷Wnt-1信號可導(dǎo)致下游因子beta-catenin表達(dá)水平下調(diào),細(xì)胞凋亡明顯增加。

果蠅翅細(xì)胞中,Wnt信號通過減輕 Notch的作用來促進(jìn) G1～S期進(jìn)展[9]。Wnt1和 Notch信號通路在乳腺癌形成過程中起協(xié)同作用[10]。在乳腺癌形成過程中,Wnt-1靶基因如 Axin-2 and Lef-1和 Notch如 Dll3 and Dll4表達(dá)同時(shí)上調(diào),Wnt和 Notch信號通路在這一過程中起協(xié)同作用[11],不知名的 hedgehog(Hh)信號通路在胚胎發(fā)育和腫瘤形成過程中起重要作用。已經(jīng)確定其在食管癌,胃癌,胰腺癌,胃癌中激活。該通路中Gli依賴分泌性卷曲相關(guān)蛋白 1(secreted frizzled-related proteinsFRP-1),其表達(dá)與癌癥發(fā)展有關(guān),在表達(dá) Gli1細(xì)胞系中,Wnt-1介導(dǎo)的 beta-catenin在細(xì)胞質(zhì)中聚集消失,而阻止 sFRP-1的表達(dá)則逆轉(zhuǎn)這一現(xiàn)象。表明 hedgehog和 Wnt信號通路之間存在交叉[12]。Gli1是 Hh信號通路的反式作用子,可阻止 Wnt信號和抑制人類結(jié)腸癌細(xì)胞增生[13]。轉(zhuǎn)化生長因子-β(Transforming grow th factor-beta,TGF-beta)和Wnt/beta-catenin信號通路在乳腺癌形成過程中起協(xié)同作用[14]。WNT,成纖維生長因子(fibroblastgrowth factor,FGF),Notch,Hh,和轉(zhuǎn)化生長因子 beta/骨形成蛋白信號網(wǎng)通過調(diào)節(jié)正常干細(xì)胞自我更新和前體細(xì)胞的增生和分化來維持內(nèi)穩(wěn)態(tài),如果破壞干細(xì)胞信號網(wǎng)則會導(dǎo)致腫瘤形成[4]。鼠乳腺癌病毒通過Wnt-1信號通路誘導(dǎo)干細(xì)胞形成乳腺癌[15]。siRNA沉默 Wnt-1基因誘導(dǎo)鼠乳腺癌細(xì)胞系 MCF-7凋亡[16]。

2 Wnt在各種人體腫瘤中的研究進(jìn)展

2.1 食管癌

Wnt信號通路的下游基因激活與食管鱗癌有關(guān)[17]。Wnt抑制因子-1(Wnt inhibitory factor-1,WIF1)是 Wnt信號通路的分泌性拮抗劑。在鼻咽癌和食管鱗癌中,因甲基化而失活,有助于Wnt通路的異常激活,促進(jìn)腫瘤形成[18]。垂體瘤轉(zhuǎn)化基因(pituitary tumor transforming gene,PTTG)在食管鱗癌形成過程中起重要作用,由于 beta-catenin/TCF通路激活引起其過表達(dá),促進(jìn)食管癌形成。寡核苷酸點(diǎn)陣表達(dá)數(shù)據(jù)分析方法得出:干擾素誘導(dǎo)跨膜蛋白 1(interferon induced transmembrane protein 1,IFITM 1)是 Wnt通路的關(guān)鍵基因,與對順鉑(cis-diamminedich loroplatinum,CDDP)的細(xì)胞敏感高度相關(guān),有助于食管癌根治術(shù)后,高效預(yù)測對CDDP敏感的無瘤生存期[19]。

2.2 胃癌

Wnt/beta-catenin信號,參與胃癌的形成[20]。Wnt/betacatenin信號通路在大多數(shù)胃癌中被激活。高遷移率組 A-1(high-mobility group A-1,HMGA-1)蛋白是致癌染色質(zhì)因子,不僅在未分化組織中而且在各種腫瘤組織中表達(dá)。HMGA-1是Wnt/beta-catenin下游基因,其活性是由 Wnt/beta-catenin信號誘導(dǎo)的并維持胃癌增殖。敲除 HMGA-1基因?qū)е录?xì)胞增殖顯著降低。beta-catenin及其下游基因 c-myc表達(dá)缺失導(dǎo)致 HMGA-1表達(dá)下降[21]。

2.3 結(jié)腸癌

最近,研究者經(jīng)常發(fā)現(xiàn)在結(jié)腸癌中,Wnt啟動子超甲基化導(dǎo)致分泌卷曲相關(guān)蛋白(secreted frizzled-related p rotein,sFRP)沉默,在結(jié)腸直腸癌演變過程中起重要作用,Wnt-1抗體、siRNA和多西紫杉醇在減弱 Wnt信號過程中起協(xié)調(diào)作用,結(jié)果癌細(xì)胞凋亡顯著增加。這一發(fā)現(xiàn)表明:在治療結(jié)腸直腸癌中,阻斷Wnt信號通路具有治療作用。在結(jié)腸癌中,DKK-1作為腫瘤抑制因子,誘導(dǎo) DKK-1表達(dá),Wnt/beta-catenin表達(dá)下調(diào)。Wnt1抑制因子 Sox17在腫瘤形成早期階段阻止胃和結(jié)腸良性腫瘤惡變,它表達(dá)下調(diào)促進(jìn)胃和結(jié)腸惡性腫瘤進(jìn)展[22]。

2.4 肝癌

丙型肝炎病毒核心蛋白刺激肝細(xì)胞增生與Wnt-1表達(dá)上調(diào)有關(guān)。Wnt-1可作為乙型與丙型肝炎相關(guān)性肝癌術(shù)后的預(yù)測復(fù)發(fā)的生物標(biāo)記[23]。

2.5 黑色素瘤與唾液腺癌

Wnt-1信號在鼠胚胎黑色素瘤分化和增長中發(fā)揮重要作用。Wnt-1信號在干擾口腔鱗狀細(xì)胞癌(oral squamous cell carcinoma,OSCC)分化和增生方面起重要作用。唾液腺癌形成過程中,Wntβ信號抑制因子 1(Wnt inhibitory factor 1,WIF1)表達(dá)下調(diào),Wnt信號激動劑 Wnt-1表達(dá)上調(diào),Wnt-1下游基因 beta-Catenin轉(zhuǎn)錄增加[24]。

2.6 其他

Wnt-1過表達(dá)與非小細(xì)胞肺癌增生、進(jìn)展和預(yù)后差有關(guān)[25,26]。Wnt1在卵巢癌中表達(dá)率較卵巢良性腫瘤或正常組織增加[27]。間質(zhì)金屬蛋白酶(matrix metallop roteinases,MMPs)在Wnt-1誘導(dǎo)的乳腺癌形成過程中起重要作用[28]。

綜上所述,Wnt-1或 Wnt/beta-catenin信號通路從鼠乳腺癌到在人類各種腫瘤的研究經(jīng)歷了漫長的過程,從發(fā)現(xiàn)該通路異常導(dǎo)致各種腫瘤到采用siRNA或抗Wnt-1抗體誘導(dǎo)細(xì)胞凋亡,阻止其生長;在體內(nèi)實(shí)驗(yàn)中,免疫抑制劑雷帕霉素具有直接抗Wnt-1誘導(dǎo)的乳癌作用;到 Dpr1穿梭蛋白在細(xì)胞質(zhì)和細(xì)胞核之間穿梭負(fù)性調(diào)節(jié)經(jīng)典的Wnt/beta-catenin信號;到非甾類抗炎藥物,在基礎(chǔ)實(shí)驗(yàn)研究中起到抑制各惡性腫瘤細(xì)胞增殖、促進(jìn)細(xì)胞凋亡等作用,顯示出抗腫瘤效應(yīng)。提示:Wnt-1或Wnt/beta-catenin信號異常具有致癌作用,以 Wnt-1或 Wnt/beta-catenin為靶向的抗腫瘤治療,值得進(jìn)一步研究。

但由于在特定的細(xì)胞類型、不同時(shí)間、不同空間和 Wnt-1或Wnt/beta-catenin有關(guān)的信號傳導(dǎo)途徑的復(fù)雜性以及腫瘤的發(fā)生發(fā)展的復(fù)雜病理生理過程,目前仍有許多問題有待闡明。相信隨著對該信號通路調(diào)節(jié)認(rèn)識的不斷深入,有效而副作用少的Wnt-1或 Wnt/beta-catenin靶向藥物開發(fā)和臨床應(yīng)用將揭開 1個(gè)新的篇章。

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