王亞麗 陳凱 向曉輝 李嫚華 冀潤(rùn)利 夏時(shí)海

鋅指轉(zhuǎn)錄因子是人類基因組中最大的轉(zhuǎn)錄因子家族，迄今為止已經(jīng)報(bào)道了8種不同類別的鋅指基序，包括類C2H2型鋅指、塞結(jié)狀鋅指、高音譜號(hào)鋅指、帶狀鋅指、Zn2/Cys6型鋅指、類TAZ2型鋅指、鋅離子結(jié)合短環(huán)鋅指和金屬硫蛋白鋅指[1]。不同類型的鋅指基序顯示了生物功能的多樣性，除了與DNA結(jié)合，鋅指基序中的RNA、蛋白質(zhì)和脂質(zhì)可以與其他鋅指蛋白(zinc finger protein，ZFP)中的類似基團(tuán)相互作用[2-4]，因此，鋅指轉(zhuǎn)錄因子可以通過多個(gè)鋅指基序的不同組合大大擴(kuò)展它們?cè)诓煌?xì)胞環(huán)境或刺激下的多樣基因調(diào)控作用。在過去的幾十年里，越來越多的證據(jù)顯示了鋅指轉(zhuǎn)錄因子在癌癥進(jìn)程中的潛在作用，研究表明鋅指轉(zhuǎn)錄因子在胰腺癌中也發(fā)揮著重要作用。本文就鋅指轉(zhuǎn)錄因子在胰腺癌中作用的研究進(jìn)展進(jìn)行綜述。

一、ZFP91

ZFP91在1995年由Saotome等[5]發(fā)現(xiàn)，是一種具有轉(zhuǎn)錄因子特有結(jié)構(gòu)基序的保守核蛋白，含有5個(gè)鋅指結(jié)構(gòu)域，1個(gè)亮氨酸拉鏈模式，1個(gè)卷曲螺旋結(jié)構(gòu)和幾個(gè)核定位信號(hào)。據(jù)報(bào)道，ZFP91與腫瘤抑制因子ARF相互作用，后者可誘導(dǎo)p53依賴的細(xì)胞死亡或相應(yīng)癌基因激活后的生長(zhǎng)停滯[6]。Paschke等[7]發(fā)現(xiàn)ZFP91在前列腺癌組織中高表達(dá)，Ma等[8]研究發(fā)現(xiàn)，ZFP91可通過與NF-κB/p56相互作用激活HIF-1α啟動(dòng)子，從而促進(jìn)結(jié)腸癌細(xì)胞增殖并可在體內(nèi)促進(jìn)腫瘤的生長(zhǎng)。Huang等[9]研究報(bào)道，ZFP91在胰腺導(dǎo)管癌細(xì)胞中高表達(dá)，敲除ZFP91基因后胰腺導(dǎo)管癌細(xì)胞的遷移能力減弱，聯(lián)蛋白(catenin)表達(dá)上升而波形蛋白(vimentin)表達(dá)下降，表明敲除ZFP91可能是通過逆轉(zhuǎn)上皮細(xì)胞-間質(zhì)轉(zhuǎn)化(EMT)過程抑制胰腺導(dǎo)管癌細(xì)胞的生長(zhǎng)和遷移。

二、鋅指核酸結(jié)合蛋白

鋅指核酸結(jié)合蛋白(zinc finger RNA binding protein, ZFR)是一種古老的高度保守的染色體相關(guān)蛋白[10]，其編碼具有3個(gè)寬間隔C2H2鋅指的由1 052個(gè)氨基酸組成的蛋白質(zhì)[11]。鼠ZFR蛋白是在篩選精子發(fā)生期間表達(dá)的RNA結(jié)合蛋白時(shí)被發(fā)現(xiàn)，人ZFR則是在篩查與mRNA前體剪接活化劑RNPS1相互作用的遺傳因子時(shí)被確認(rèn)[12-13]。除骨骼肌外，轉(zhuǎn)錄水平ZFR在人體不同的組織中均可被檢測(cè)到。Zhao等[14]研究報(bào)道，ZFR在胰腺癌組織中表達(dá)明顯高于胰腺正常組織，沉默ZFR可顯著降低人胰腺癌PANC1細(xì)胞的存活率并可抑制細(xì)胞增殖和細(xì)胞活性，ZFR可以改變細(xì)胞周期調(diào)控分子導(dǎo)致細(xì)胞停滯于G0/G1期，通過調(diào)節(jié)某些癌癥相關(guān)基因抑制細(xì)胞的生長(zhǎng)和凋亡。沉默ZFR還可以抑制胰腺導(dǎo)管癌細(xì)胞的遷移和侵襲。

三、GLI

人GLI基因首先由Vofelestein等鑒定為在膠質(zhì)母細(xì)胞瘤中擴(kuò)增的癌基因。GLI基因不同于其他類型的癌基因，因?yàn)槠渚幋a包含5個(gè)重復(fù)鋅指基序的蛋白[15]。GLI家族包括GLI1、GLI2和GLI3，它們是hedgehog(Hh)信號(hào)轉(zhuǎn)導(dǎo)途徑中的關(guān)鍵轉(zhuǎn)錄因子[16]。Sheng等[17]研究發(fā)現(xiàn)，GLI1在胰腺癌組織中高表達(dá)，且與胰腺癌UICC期和T期密切相關(guān)，下調(diào)GLI1可以抑制PANC1細(xì)胞的遷移，使基質(zhì)金屬蛋白酶9(MMP9)的表達(dá)量下降，從而抑制胰腺癌的侵襲。GLI1在胰腺上皮內(nèi)瘤變(PanINs)中也高表達(dá)[18]，此外，激活的K-ras原癌基因與GLI2共同作用可誘導(dǎo)未分化的胰腺腫瘤，且GLI1基因可通過調(diào)節(jié)K-ras促進(jìn)胰腺導(dǎo)管腺癌細(xì)胞的生存和惡性細(xì)胞表型[19]。Jones等[20]研究發(fā)現(xiàn)，所有的胰腺導(dǎo)管癌細(xì)胞系均有Hh信號(hào)下游組分的突變，包括GLI1和GLI3，是胰腺癌發(fā)生發(fā)展的自主通路。GLI1的表達(dá)水平與胰腺癌浸潤(rùn)的深度及TNM分期相關(guān)，高表達(dá)GLI1的胰腺癌患者預(yù)后比GLI1正?；虻捅磉_(dá)患者差，是胰腺癌預(yù)后的獨(dú)立危險(xiǎn)因素[21]。Xu等[22]通過基因芯片技術(shù)在胰腺導(dǎo)管癌細(xì)胞系中篩選了高轉(zhuǎn)移靶基因EIF5A2，將GLI1綁定在EIF5A2基因的啟動(dòng)子后EIF5A2是GLI1的下游分子網(wǎng)絡(luò)節(jié)點(diǎn)，通過參與Hh信號(hào)通路促進(jìn)惡性腫瘤的發(fā)展。

四、ZIC2

ZIC2是小腦鋅指蛋白(zinc finger protein cerebellum, ZIC)家族中的成員，在篩選富含小鼠小腦的cDNA過程中被鑒定[23]。雞、小鼠和人中具有5個(gè)同源物，在斑馬魚中具有7個(gè)同源物，ZIC蛋白的特征是由5個(gè)串聯(lián)的Cys2His2型鋅指組成的高度保守的鋅指結(jié)構(gòu)域，并且與GLI、GLIS和NKL家族的鋅指結(jié)構(gòu)密切相關(guān)[24]。Inaguma等[25]研究發(fā)現(xiàn)ZIC2在胰腺癌組織中表達(dá)顯著升高，沉默ZIC2基因后可抑制癌細(xì)胞的增殖，減少G0/G1期細(xì)胞，增加亞G1期細(xì)胞。此外，沉默ZIC2可以使活化的DNA修復(fù)酶(PARP)表達(dá)升高。研究還發(fā)現(xiàn)ZIC2通過上調(diào)成纖維細(xì)胞生長(zhǎng)因子受體3(FGFR3)和膜聯(lián)蛋白A8(ANXA8)表達(dá)來調(diào)節(jié)胰腺癌細(xì)胞的增殖和凋亡。

五、KAISO

KAISO是在多種細(xì)胞類型中普遍表達(dá)POZ-ZF的蛋白，屬于BTB/POZ鋅指蛋白轉(zhuǎn)錄因子家族，最初被鑒定為細(xì)胞黏附連接素和Src激酶底物p120的結(jié)合配偶體，具有介導(dǎo)蛋白質(zhì)-蛋白質(zhì)相互作用的N末端POZ結(jié)構(gòu)域和3個(gè)C末端的C2H2鋅指結(jié)構(gòu)[26]。Jones等[27]研究發(fā)現(xiàn)，KAISO在惡性程度低的胰腺癌組織中于胞質(zhì)表達(dá)較高，于胞核表達(dá)較低；在惡性程度高的胰腺癌組織中，于胞質(zhì)和胞核的表達(dá)均較高，且與腫瘤的侵襲相關(guān)。另外，在男性惡性程度高的腫瘤中KAISO在胞質(zhì)的表達(dá)更高，確切原因尚不明確，可能與性激素水平不同相關(guān)。

六、鋅指E盒結(jié)合蛋白-1

鋅指E盒結(jié)合蛋白-1(zinc finger E-box-binding protein 1, ZEB1)屬于ZEB家族的轉(zhuǎn)錄因子，具有N端和C端2個(gè)DNA結(jié)合的鋅指簇及位于中心的同源結(jié)構(gòu)域[28]。有研究表明，miR-139-5p通過ZEB1抑制肝癌細(xì)胞的EMT和轉(zhuǎn)移過程[29]。Smigiel等[30]發(fā)現(xiàn)，抑瘤素M通過JAK/STAT3信號(hào)通路激活ZEB1的表達(dá)促進(jìn)胰腺導(dǎo)管癌細(xì)胞發(fā)生EMT，促使癌細(xì)胞從原發(fā)部位轉(zhuǎn)移到繼發(fā)部位，增強(qiáng)腫瘤細(xì)胞的致瘤性，還可以增強(qiáng)對(duì)治療藥物的耐藥性。Schickel等[31]報(bào)道，miR-200c可以通過下調(diào)fas相關(guān)磷酸酯酶-1(FAP-1)抑制ZEB1和波形蛋白的表達(dá)，增加E-Cad的表達(dá)，從而抑制EMT的發(fā)生。Burk等[32]研究發(fā)現(xiàn)，胰腺癌ZEB1的異常表達(dá)能夠抑制胰腺導(dǎo)管癌細(xì)胞miR-200c和miR-141的表達(dá)，ZEB1和miR-200相互抑制，達(dá)到平衡，在胰腺癌的發(fā)生發(fā)展中發(fā)揮重要作用。由此可見，ZEB1在胰腺癌中可以和多種miRNA相互作用，通過多種細(xì)胞信號(hào)通路影響腫瘤細(xì)胞EMT過程，從而影響腫瘤細(xì)胞的侵襲和轉(zhuǎn)移。

七、KLF

KLF家族作為重要的轉(zhuǎn)錄組件存在于酵母到脊椎動(dòng)物的真核細(xì)胞中，它們的結(jié)構(gòu)特征在于C端有3個(gè)高度保守的DNA結(jié)合鋅指結(jié)構(gòu)域和含有轉(zhuǎn)錄調(diào)節(jié)基序的N端結(jié)構(gòu)域[33]。迄今為止，在哺乳動(dòng)物中至少鑒定出了17種KLF因子[34]，它們參與細(xì)胞增殖、分化、凋亡和腫瘤轉(zhuǎn)化等許多生物過程。有研究表明[35]，KLF10啟動(dòng)子在胰腺導(dǎo)管癌細(xì)胞中具有顯著的活性。Chang等[36]研究發(fā)現(xiàn)，KLF10過表達(dá)可以誘導(dǎo)TGF-β1敏感的胰腺導(dǎo)管癌細(xì)胞凋亡，其預(yù)測(cè)胰腺癌患者無進(jìn)展生存期(PFS)和總存活期(OS)較血清CA19-9更具優(yōu)勢(shì)。Wei等[37]研究發(fā)現(xiàn)，KLF4通過調(diào)節(jié)p27的表達(dá)抑制胰腺導(dǎo)管癌細(xì)胞的細(xì)胞周期進(jìn)程，誘導(dǎo)癌細(xì)胞阻滯于G1期，抑制細(xì)胞增殖；裸鼠成瘤實(shí)驗(yàn)也表明KLF4在體內(nèi)抑制胰腺癌生長(zhǎng)和轉(zhuǎn)移。另外，Zhang等[38]發(fā)現(xiàn)KLF2在胰腺癌中表達(dá)下降，通過下調(diào)β-連環(huán)蛋白/TCF信號(hào)的表達(dá)抑制腫瘤細(xì)胞生長(zhǎng)和遷移，沉默KLF2后可以促進(jìn)胰腺導(dǎo)管癌細(xì)胞的侵襲。

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