黃艷霞　張　靖　王　歌　朱金水

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長鏈非編碼RNA與胃癌相關(guān)性的研究進(jìn)展

黃艷霞張靖王歌朱金水

200233上海交通大學(xué)附屬第六人民醫(yī)院消化內(nèi)科

摘要：長鏈非編碼RNA(lncRNA)因其長度大于200個核苷酸，缺乏編碼蛋白能力而得名。在表觀遺傳學(xué)控制、轉(zhuǎn)錄和轉(zhuǎn)錄后調(diào)控等多個層面，lncRNA參與了機(jī)體多種生理及病理過程的調(diào)節(jié)。研究已經(jīng)證明，lncRNA在胃癌生物學(xué)的調(diào)節(jié)過程中起關(guān)鍵的作用，lncRNA與胃癌的發(fā)生、發(fā)展、侵襲、轉(zhuǎn)移及預(yù)后密切相關(guān)。該文對lncRNA在胃癌中的研究進(jìn)展作一綜述。

關(guān)鍵詞：lncRNA；胃癌；轉(zhuǎn)移

長鏈非編碼RNA(lncRNA)因其長度大于200個核苷酸,缺乏編碼蛋白能力而得名。lncRNA Xist 為哺乳動物中首先被發(fā)現(xiàn)的lncRNA，可導(dǎo)致染色質(zhì)結(jié)構(gòu)與組成的重塑。盡管lncRNA發(fā)揮了重要的生物學(xué)功能，但多數(shù)情況下仍被認(rèn)為是轉(zhuǎn)錄中的“噪音”。其后發(fā)現(xiàn)lncRNA HOTAIR可與多梳蛋白復(fù)合體相互作用，參與機(jī)體生長、發(fā)育過程的調(diào)節(jié)。隨著高通量測序等生物信息學(xué)技術(shù)的快速發(fā)展，已發(fā)現(xiàn)lncRNA在表觀遺傳學(xué)控制、轉(zhuǎn)錄和轉(zhuǎn)錄后調(diào)控等多個層面參與了機(jī)體多種生理及病理過程的調(diào)節(jié)。

1lncRNA的結(jié)構(gòu)、分類及功能

lncRNA可位于細(xì)胞核和細(xì)胞質(zhì)中，多由RNA聚合酶Ⅱ轉(zhuǎn)錄。其長度變異性較大，部分可延長至100 kb。人類基因組約有15 000種lncRNA，其轉(zhuǎn)錄水平遠(yuǎn)低于蛋白編碼基因，且具有組織特異性。目前分子結(jié)構(gòu)明確的lncRNA所占比例甚少，Niazi等[1]對204種功能性lncRNA進(jìn)行分析后發(fā)現(xiàn)，內(nèi)含子數(shù)量少、鳥嘌呤(G)和胞嘧啶(C)含量低、起始密碼子和開放閱讀框架的缺乏可能是lncRNA的一些結(jié)構(gòu)特征。根據(jù)lncRNA基因與編碼基因間的位置關(guān)系，可以將其分為正義lncRNA、反義lncRNA、雙向lncRNA、內(nèi)含子lncRNA和基因間lncRNA五類[2]。lncRNA的異常表達(dá)與人類疾病密切相關(guān)，如老化相關(guān)的阿爾茨海默病及認(rèn)知障礙相關(guān)疾病都被認(rèn)為與lncRNA的異常表達(dá)有關(guān)；其在心血管疾病、內(nèi)分泌疾病(如糖尿病)中亦發(fā)揮了作用[3]。值得關(guān)注的是，lncRNA與腫瘤的發(fā)生發(fā)展密切相關(guān)，lncRNA在前列腺癌、結(jié)直腸癌、乳腺癌、膀胱癌、肝細(xì)胞癌及胃癌等多種惡性腫瘤中均有異常表達(dá)，可作為致癌或抑癌因子參與腫瘤細(xì)胞轉(zhuǎn)錄、染色質(zhì)重塑、微血管侵襲等過程的調(diào)控。

2lncRNA與胃癌

lncRNA AC096655首先被發(fā)現(xiàn)與胃癌相關(guān)，并被命名為GACAT1[4]。2012年Yang等[5]發(fā)現(xiàn)lncRNA H19表達(dá)上調(diào)可促進(jìn)胃癌細(xì)胞增殖。其后lncRNA在胃癌中的重要性得到越來越多的關(guān)注，它們幾乎參與胃癌發(fā)生發(fā)展的全過程，包括腫瘤細(xì)胞增殖、凋亡、侵襲、轉(zhuǎn)移、預(yù)后及耐藥性等多個方面。此外，lncRNA對胃癌的診斷也有幫助，可能是胃癌診斷的潛在分子標(biāo)志物。

2.1lncRNA在胃癌中的生物學(xué)功能

lncRNA在胃癌的發(fā)生發(fā)展中具有促癌或抑癌雙重作用。如lncRNA H19、HULC、Linc00152、HOTAIR、PVT1、HIF1A-AS2、LINC00982、MALAT1及SPRY4-IT1等具有促進(jìn)腫瘤細(xì)胞增殖、入侵及轉(zhuǎn)移的作用[6-14]，而lncRNA MEG3、GAS5、FENDRR、LEIGC、FER1L4及WT1-AS等具有抑制腫瘤細(xì)胞增殖、促進(jìn)腫瘤細(xì)胞凋亡的作用[15-20]。此外，lncRNA在胃癌組織中的表達(dá)水平也不一致，lncRNA的表達(dá)水平與胃癌臨床病理特征的關(guān)系見表1。

2.2lncRNA在胃癌耐藥中的作用

腫瘤細(xì)胞耐藥是化學(xué)治療失敗的重要原因之一，越來越多的研究發(fā)現(xiàn)lncRNA參與腫瘤細(xì)胞耐藥的調(diào)節(jié)，如Zhang等[29]的研究發(fā)現(xiàn)lncRNA PVT1在對順鉑耐藥患者的胃癌組織及胃癌細(xì)胞中高表達(dá)，過表達(dá)lncRNA PVT1促進(jìn)了胃癌細(xì)胞耐藥。Ding等[30]亦證實(shí)lncRNA PVT1表達(dá)升高能促進(jìn)胃癌細(xì)胞對紫杉醇的耐藥。此外，癌細(xì)胞中高表達(dá)的lncRNA MRUL促進(jìn)了胃癌耐藥細(xì)胞中ABCB1的表達(dá)，從而促進(jìn)了胃癌細(xì)胞對藥物的耐藥性[31]。然而，一些lncRNA卻具有提高腫瘤細(xì)胞對化學(xué)治療藥物敏感性的作用，如Han等[32]發(fā)現(xiàn)lncRNA LEIGC可增加胃癌細(xì)胞對5-氟尿嘧啶的敏感性。

表1　lncRNA的表達(dá)與胃癌臨床病理特征的關(guān)系

2.3lncRNA在胃癌侵襲轉(zhuǎn)移中的作用

侵襲和轉(zhuǎn)移是惡性腫瘤的重要特征之一。越來越多的證據(jù)表明，上皮-間質(zhì)轉(zhuǎn)化(EMT)及腫瘤細(xì)胞間的黏附能力下降，可能參與了腫瘤轉(zhuǎn)移的重要環(huán)節(jié)。Zhao等[8]的研究發(fā)現(xiàn)，lncRNA Linc00152能抑制胃癌細(xì)胞中EMT的進(jìn)程。Han等[32]研究了lncRNA LEIGC在胃癌細(xì)胞中的作用，敲低其表達(dá)水平后，胃癌細(xì)胞發(fā)生了EMT。該研究進(jìn)一步檢測了與EMT相關(guān)的一些蛋白，研究結(jié)果與此一致，因此可以認(rèn)為lncRNA LEIGC在胃癌細(xì)胞中是一個潛在的EMT抑制劑。Zhao等[7]的研究發(fā)現(xiàn)，lncRNA HULC可抑制胃癌細(xì)胞凋亡、促進(jìn)胃癌細(xì)胞增殖，其作用機(jī)制可能與誘導(dǎo)細(xì)胞自噬，促進(jìn)EMT有關(guān)。轉(zhuǎn)化生長因子-β(TGF-β)信號通過miR-200家族和ZEB1/2之間的雙負(fù)反饋循環(huán)調(diào)節(jié)腫瘤EMT[33]，Saito等[34]的研究發(fā)現(xiàn)，lncRNA ATB通過TGF-β誘導(dǎo)胃癌EMT變化以促進(jìn)轉(zhuǎn)移發(fā)生。Xu等[17]發(fā)現(xiàn)過表達(dá)lncRNA FENDRR能誘導(dǎo)胃癌肺轉(zhuǎn)移結(jié)節(jié)增多，并使腫瘤細(xì)胞間的黏附分子FN1表達(dá)下降，證明了lncRNA FENDRR可能通過影響FN1來調(diào)節(jié)胃癌細(xì)胞的轉(zhuǎn)移。

2.4lncRNA與胃癌的診斷

lncRNA可存在于血漿、胃液及組織中，目前部分血漿中的lncRNA已被作為潛在的腫瘤標(biāo)志物。Zhou等[35]的研究發(fā)現(xiàn)血漿中l(wèi)ncRNA H19能為早期胃癌的診斷提供可靠依據(jù)。胃液中l(wèi)ncRNA的獲得相對容易，并能夠?yàn)槲赴┨峁┯行У脑\斷。Zheng等[36]收集了49份胃液標(biāo)本(26份胃癌患者標(biāo)本和23份健康者標(biāo)本)，發(fā)現(xiàn)胃癌標(biāo)本中l(wèi)ncRNA UCA1的水平高于健康標(biāo)本。Yang等[37]研究了130份胃液標(biāo)本(包括胃良性病變、胃不典型增生、胃癌癌前病變和胃癌患者)，發(fā)現(xiàn)胃癌患者的胃液中l(wèi)ncRNA ABHD11-AS1水平顯著高于正常胃、萎縮性胃炎、胃潰瘍，并與胃癌患者的性別、腫瘤大小、分期、勞倫分型及血清中癌胚蛋白(CEA)水平相關(guān)。值得注意的是，胃液中l(wèi)ncRNA ABHD11-AS1作為診斷胃癌的標(biāo)志物時，早期胃癌的診斷率提高到71.4%。

2.5lncRNA可能的作用機(jī)制

lncRNA的調(diào)節(jié)機(jī)制復(fù)雜且多樣化：可調(diào)控下游基因轉(zhuǎn)錄或作為分子阻斷劑阻斷該分子發(fā)生作用；亦可通過與蛋白結(jié)合，定位到特定的DNA序列上；也可與多個相關(guān)轉(zhuǎn)錄因子結(jié)合發(fā)揮作用；還可競爭性結(jié)合miRNA以調(diào)控基因表達(dá)。Cai等[22]發(fā)現(xiàn)lncRNA FRLnc1可通過調(diào)節(jié)FOXM1參與腫瘤生長及血管生成。Wang等[13]研究了lncRNA MALAT1的功能，發(fā)現(xiàn)其可能通過調(diào)節(jié)SF2/ASF來促進(jìn)胃癌細(xì)胞增殖。有研究表明，lncRNA GAS5通過下調(diào)E2F1和p21的表達(dá)來誘導(dǎo)胃癌細(xì)胞增殖[16]，而lncRNA WT1-AS則通過抑制細(xì)胞外信號調(diào)節(jié)激酶(ERK)蛋白磷酸化水平來阻止胃癌發(fā)生[20]。

競爭性內(nèi)源RNA(ceRNA)在轉(zhuǎn)錄后調(diào)節(jié)及腫瘤的發(fā)生發(fā)展中具有重要的作用[38]。ceRNA通過競爭性結(jié)合miRNA以調(diào)節(jié)基因表達(dá)，是RNA之間相互作用的一種新機(jī)制。如Liu等[39]發(fā)現(xiàn)胃癌中l(wèi)ncRNA HOTAIR可通過競爭性抑制miR-331-3p來調(diào)節(jié)表皮生長因子受體2(HER2)的表達(dá)，增加了轉(zhuǎn)錄后調(diào)控的水平。lncRNA H19可通過調(diào)控miR-675抑制RUNX1而促進(jìn)腫瘤細(xì)胞增殖[40]。lncRNA H1F1A-AS2在胃癌發(fā)展中發(fā)揮了重要的作用，通過調(diào)節(jié)與腫瘤相關(guān)的缺氧誘導(dǎo)因子-1α(HIF-1α)途徑促進(jìn)腫瘤發(fā)展。lncRNA ANRIL在胃癌組織中表達(dá)上調(diào)，通過表觀沉默miR-99a/miR-449a促進(jìn)腫瘤生長[11]。

3問題與展望

lncRNA在組織生理及病理過程中發(fā)揮了重要的調(diào)節(jié)作用，其作用機(jī)制仍有待進(jìn)一步探索。lncRNA在疾病發(fā)生發(fā)展中的作用是錯綜復(fù)雜的，一方面可能是由于lncRNA在物種間的低保守性，使得物種中l(wèi)ncRNA的功能不確定[41]；另一方面由于缺乏相關(guān)的研究工具，lncRNA的數(shù)據(jù)庫還不夠充足，很難全面揭示lncRNA的生物學(xué)功能；此外，lncRNA與腫瘤轉(zhuǎn)移或耐藥的機(jī)制研究尚不成熟[42-43]。無論當(dāng)前研究顯示lncRNA是抑癌基因或是促癌基因，可以確定的是lncRNA與胃癌有著密切的聯(lián)系，以lncRNA為靶點(diǎn)的藥物有望在胃癌的臨床治療中起到重要的作用。因此，明確lncRNA在胃癌及其他疾病中的具體作用尤為重要，有助于全面深入地認(rèn)識胃癌的發(fā)生發(fā)展機(jī)制，并為臨床治療胃癌提供更多的途徑。

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(本文編輯：林磊)

基金項(xiàng)目：國家自然科學(xué)基金(81573747，81302093，81272752)

通信作者：朱金水，Email: zhujs1803@163.com

DOI:10.3969/j.issn.1673-534X.2016.03.005

(收稿日期：2015-12-20)