miR-21與結(jié)直腸癌的相關(guān)性研究進(jìn)展

伍怡穎, 張仲林(成都醫(yī)學(xué)院藥理學(xué)教研室,成都 610083)

·綜 述·

miR-21與結(jié)直腸癌的相關(guān)性研究進(jìn)展

伍怡穎, 張仲林*
(成都醫(yī)學(xué)院藥理學(xué)教研室,成都 610083)

miR-21；結(jié)直腸癌；相關(guān)性

結(jié)直腸癌是嚴(yán)重危害人類健康的消化道惡性腫瘤,其發(fā)病率及病死率在癌癥中排前3位。全球每年約有100多萬(wàn)人新發(fā)結(jié)直腸癌,約有50萬(wàn)人死于結(jié)直腸癌。近年來(lái),隨著經(jīng)濟(jì)發(fā)展,居民生活方式和飲食結(jié)構(gòu)改變,我國(guó)結(jié)直腸癌發(fā)病率和病死率均呈上升趨勢(shì),現(xiàn)已高于世界平均水平。結(jié)直腸癌早期診斷率低、復(fù)發(fā)轉(zhuǎn)移率高及缺乏有效治療手段是導(dǎo)致患者高病死率的主要原因[1-3]。而尋找結(jié)直腸癌發(fā)病機(jī)制中的關(guān)鍵調(diào)控分子,是提高其臨床診治水平的關(guān)鍵。MicroRNAs(miRNAs)是新發(fā)現(xiàn)的一類內(nèi)源性表達(dá)的小分子非編碼單鏈RNA,通過(guò)與靶mRNA 3'UTR互補(bǔ)結(jié)合,在轉(zhuǎn)錄后水平調(diào)控蛋白編碼基因,是腫瘤形成和轉(zhuǎn)移的重要調(diào)節(jié)因子[4]。其中位于染色體脆性區(qū)域17q23.2的miR-21是人類基因組中最早發(fā)現(xiàn)的miRNAs之一,也是唯一在幾乎所有人類惡性腫瘤中均表達(dá)上調(diào)的miRNAs[5,6]。研究[7]顯示,miR-21在結(jié)直腸癌的發(fā)生、發(fā)展、轉(zhuǎn)移、耐藥等多種生物學(xué)行為中發(fā)揮著重要作用,提示miR-21很可能在結(jié)直腸癌早期診斷、臨床治療及預(yù)后評(píng)估中具有廣闊的應(yīng)用前景。本文通過(guò)檢索近年來(lái)國(guó)內(nèi)外miR-21與結(jié)直腸癌的相關(guān)研究文獻(xiàn),對(duì)miR-21在結(jié)直腸癌的發(fā)生、轉(zhuǎn)移、預(yù)后、治療及耐藥等環(huán)節(jié)中的作用進(jìn)行綜述。

1 miR-21在結(jié)直腸癌中具有異常表達(dá)特性

近年來(lái),隨著分子生物學(xué)實(shí)驗(yàn)技術(shù)的發(fā)展,研究者們通過(guò)基因芯片、定量PCR及Northern雜交等方法進(jìn)行研究,結(jié)果顯示,miR-21在結(jié)直腸腫瘤中異常高表達(dá),且發(fā)現(xiàn)在結(jié)直腸癌細(xì)胞系中miR-21的表達(dá)也較高。Schetter等[8]先后從美國(guó)及中國(guó)香港分別收集了84例及113例結(jié)直腸癌組織樣本,利用基因芯片檢測(cè)了兩組腫瘤樣本的miRNAs表達(dá)譜,發(fā)現(xiàn)miR-21在結(jié)直腸癌組織中高表達(dá)。近來(lái)Schee K等[9]利用qRT-PCR方法檢測(cè)193例結(jié)直腸癌腫瘤組織中miR-21、miR-31、miR-92a、miR-101、miR-106a 及 miR-145等6種miRNAs的表達(dá)水平,結(jié)果發(fā)現(xiàn)miR-21在結(jié)直腸癌中表達(dá)升高最明顯。同時(shí)隨著循環(huán)miRNAs的發(fā)現(xiàn)及其在臨床非創(chuàng)傷性檢查中的應(yīng)用,結(jié)直腸癌患者體液中miR-21的表達(dá)也受到研究者廣泛關(guān)注。Toiyama等[10]分別檢測(cè)了186例結(jié)直腸癌患者血清及腫瘤組織的miR-21表達(dá)量,包括64例切除術(shù)后患者以及43例晚期結(jié)直腸腺瘤患者,結(jié)果發(fā)現(xiàn)miR-21在結(jié)直腸癌及腺瘤患者血清中的高表達(dá)狀態(tài)與腫瘤組織一致,且與腫瘤大小、遠(yuǎn)端轉(zhuǎn)移及不良預(yù)后均呈正相關(guān),在腫瘤切除術(shù)后其表達(dá)水平有所下降。Kanaan等[11]從結(jié)直腸癌組織中篩選出表達(dá)明顯異常的miRNAs,再經(jīng)血漿檢測(cè)后發(fā)現(xiàn)miR-21是唯一在結(jié)直腸癌患者血漿中仍呈現(xiàn)出高度特異性及敏感性的miRNAs。另外,Wu等[12]發(fā)現(xiàn)在結(jié)直腸癌患者糞便中也存在miR-21的異常高表達(dá),在腫瘤切除術(shù)后其表達(dá)有所降低,而在結(jié)直腸息肉患者糞便中miR-21表達(dá)并無(wú)異常。miR-21在結(jié)直腸癌的異常表達(dá)情況(見表1)提示,miR-21可作為結(jié)直腸癌臨床診斷的生物標(biāo)志分子,具有很好的應(yīng)用前景。

2 miR-21與結(jié)直腸癌的發(fā)生、轉(zhuǎn)移及預(yù)后的關(guān)系

結(jié)直腸癌是從結(jié)直腸腺瘤性息肉逐步發(fā)展起來(lái)的,然而并不是所有的息肉都會(huì)發(fā)展成癌。防止息肉發(fā)展為惡性腫瘤最好的方法就是準(zhǔn)確判斷出可能癌變的息肉,及早切除并給予治療。Hogan等[13]發(fā)現(xiàn)miR-21、miR-31、miR-96、 miR-221、miR-191、miR-19a及miR-135b在結(jié)直腸腺瘤中表達(dá)明顯升高。Yamamichi等[14]證實(shí)miR-21在結(jié)直腸癌前腺瘤就開始出現(xiàn)高表達(dá),而在非致瘤性息肉中表達(dá)并無(wú)異常,提示在早期腺瘤中miR-21的表達(dá)升高預(yù)示癌癥進(jìn)程的開始,miR-21的表達(dá)隨著腫瘤病程演進(jìn)持續(xù)升高。伍怡穎等[15]以105例結(jié)直腸癌組織標(biāo)本為對(duì)象,證實(shí)miR-21在腫瘤組織中的高表達(dá)與腫瘤的臨床分期、分化、局部浸潤(rùn)、淋巴結(jié)轉(zhuǎn)移及CEA水平高低呈正相關(guān)。另外發(fā)現(xiàn),miR-21在血清中的高表達(dá)與結(jié)直腸腫瘤的遠(yuǎn)處臟器轉(zhuǎn)移呈正相關(guān)[16]。由此可見,miR-21對(duì)癌基因的調(diào)控作用覆蓋了結(jié)直腸癌發(fā)生、發(fā)展以及轉(zhuǎn)移等病理過(guò)程。研究也發(fā)現(xiàn),miR-21與腫瘤的臨床分期、轉(zhuǎn)移情況及結(jié)直腸癌患者的預(yù)后密切相關(guān)。Nugent等[17]發(fā)現(xiàn),miR-21、miR-320、miR-498、miR-106a及miR-200c的異常表達(dá)均與結(jié)直腸癌患者無(wú)病存活率及總生存期有關(guān)。Faltejskova等[18]在結(jié)直腸癌組織中同樣發(fā)現(xiàn)miR-21高表達(dá)與腫瘤惡性程度及患者較短存活期呈正相關(guān)。Schetter等[8]在結(jié)直腸癌異常表達(dá)的miRNAs中篩選發(fā)現(xiàn),miR-21是唯一與較差存活率及不良治療效果有關(guān)的miRNAs。Xia等[19]收集近年來(lái)關(guān)于miR-21的高表達(dá)與結(jié)直腸癌預(yù)后相關(guān)性的文獻(xiàn),篩選出1 174個(gè)病例數(shù)據(jù),通過(guò)Meta分析發(fā)現(xiàn)miR-21的高表達(dá)與結(jié)直腸癌患者的不良預(yù)后有關(guān)。miR-21異常表達(dá)與結(jié)直腸癌發(fā)生發(fā)展的相關(guān)性(見表1)。綜合上述研究數(shù)據(jù)提示,miR-21可作為結(jié)直腸癌臨床診斷及預(yù)后評(píng)估的標(biāo)志物。

表1 miR-21異常表達(dá)與結(jié)直腸癌臨床的相關(guān)性

3 miR-21與結(jié)直腸癌的治療及耐藥

目前結(jié)直腸癌的治療主要采用以手術(shù)切除為主,放化療為輔的綜合治療模式；而術(shù)后高復(fù)發(fā)和轉(zhuǎn)移率以及傳統(tǒng)放化療的巨大毒副作用都是導(dǎo)致患者死亡的主要原因。因此,現(xiàn)急需尋找針對(duì)性更強(qiáng)、敏感性更高的有效治療靶點(diǎn)。miR-21很可能是其臨床治療的重要靶點(diǎn),在基因治療及新藥開發(fā)中具有潛在價(jià)值。多項(xiàng)研究[21-23]顯示,通過(guò)轉(zhuǎn)染反義miR-21,降低結(jié)直腸癌細(xì)胞內(nèi)miR-21表達(dá),可明顯抑制腫瘤細(xì)胞的增殖、遷移、侵襲以及血管生成等惡性生物學(xué)行為。同樣,在以miR-21為靶點(diǎn)的藥物研究[24,25]中發(fā)現(xiàn),姜黃素可通過(guò)結(jié)合AP-1轉(zhuǎn)錄因子,抑制結(jié)直腸癌細(xì)胞內(nèi)miR-21表達(dá),升高抑癌基因PTEN、PDCD4表達(dá)水平,從而抑制腫瘤的生長(zhǎng)、侵襲及轉(zhuǎn)移,還可增強(qiáng)化療藥物的抗癌作用。此外,結(jié)直腸癌中miR-21的表達(dá)與腫瘤的化療敏感性有關(guān)。Liu等[26]檢測(cè)了42例術(shù)前接受FOLFOX4方案(奧沙利鉑+氟尿嘧啶+甲酰四氫葉酸鈣)輔助化療的結(jié)直腸癌患者腫瘤組織中miR-21的表達(dá),并通過(guò)組織病理學(xué)方法比較化療前后改變,結(jié)果發(fā)現(xiàn),化療敏感的患者腫瘤組織中miR-21的表達(dá)水平明顯低于不敏感的患者。Yu等[27]通過(guò)體外細(xì)胞實(shí)驗(yàn)發(fā)現(xiàn),miR-21在化療耐藥的結(jié)直腸癌細(xì)胞中表達(dá)明顯升高,且抑制miR-21表達(dá)后能有效增加耐藥細(xì)胞對(duì)5-氟尿嘧啶(5-FU)等化療藥物的敏感性。上述研究表明,miR-21不僅是監(jiān)測(cè)和預(yù)測(cè)臨床治療效果的理想標(biāo)準(zhǔn)物,也是結(jié)直腸癌治療的有效靶點(diǎn)。

4 miR-21調(diào)控靶基因及其對(duì)結(jié)直腸癌細(xì)胞的調(diào)控作用

為進(jìn)一步認(rèn)識(shí)miR-21在結(jié)直腸癌發(fā)生發(fā)展中的調(diào)控作用及機(jī)制,研究者將研究重點(diǎn)擴(kuò)展到對(duì)其下游靶點(diǎn)以及信號(hào)通路的研究。Asangani等[22]利用熒光素酶報(bào)告檢測(cè)系統(tǒng)在結(jié)直腸癌細(xì)胞中首次發(fā)現(xiàn)PDCD4為miR-21的靶基因。研究者將RKO細(xì)胞轉(zhuǎn)染反義miR-21后,PDCD4蛋白表達(dá)升高,細(xì)胞侵襲性降低,雞胚尿囊膜轉(zhuǎn)移實(shí)驗(yàn)結(jié)果顯示的血管浸潤(rùn)及肺轉(zhuǎn)移減少,表明miR-21可能通過(guò)抑制PDCD4蛋白表達(dá)從而誘導(dǎo)結(jié)直腸癌腫瘤的侵襲轉(zhuǎn)移。隨后,Chang等[28]也在結(jié)直腸癌組織標(biāo)本上證實(shí)了miR-21與PDCD4蛋白表達(dá)的負(fù)相關(guān)性。另外,有研究[29]證實(shí),miR-21的表達(dá)升高伴隨PDCD4的表達(dá)降低與炎性腸道疾病的癌變有關(guān)。Ferraro等[30]發(fā)現(xiàn)miR-21的高表達(dá)與結(jié)直腸癌細(xì)胞的上皮間質(zhì)轉(zhuǎn)化(EMT)有關(guān)。miR-21可通過(guò)調(diào)節(jié)Integrin-β4表達(dá),影響結(jié)直腸癌細(xì)胞的遷移能力,且發(fā)現(xiàn)在結(jié)直腸癌腫瘤組織中, miR-21的表達(dá)升高伴Integrin-β4的表達(dá)降低與腫瘤轉(zhuǎn)移有關(guān)。同樣,Xiong等[23]在結(jié)直腸癌組織及細(xì)胞系中發(fā)現(xiàn),miR-21與PTEN蛋白表達(dá)呈負(fù)相關(guān),miR-21可通過(guò)抑制PTEN,誘導(dǎo)結(jié)直腸癌細(xì)胞凋亡,抑制細(xì)胞的增殖、周期轉(zhuǎn)化、遷移及侵襲力。此外,研究[31,32]證實(shí)CCL20及RhoB均為miR-21在結(jié)直腸癌細(xì)胞中的調(diào)控靶點(diǎn),與細(xì)胞的增殖、凋亡及侵襲力調(diào)節(jié)有關(guān)。由此可見,miR-21通過(guò)調(diào)控多靶點(diǎn),調(diào)節(jié)結(jié)直腸癌細(xì)胞增殖、周期轉(zhuǎn)化、凋亡及侵襲力,影響腫瘤的生長(zhǎng)及轉(zhuǎn)移。

綜上,miR-21通過(guò)對(duì)靶基因的調(diào)控參與調(diào)節(jié)結(jié)直腸癌細(xì)胞的增殖、侵襲、轉(zhuǎn)移和耐藥。miR-21對(duì)結(jié)直腸癌的臨床診斷、治療及預(yù)后監(jiān)測(cè)都有著非常重要的潛在價(jià)值。目前,對(duì)miR-21的生物學(xué)功能方面研究很多,但對(duì)其作用機(jī)制及治療方面的應(yīng)用研究仍較少。隨著分子生物學(xué)深入研究,miR-21作為重要的調(diào)控因子必將在結(jié)直腸癌的診斷、治療及預(yù)后評(píng)估中發(fā)揮重要作用,具有廣闊的應(yīng)用前景。

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成都醫(yī)學(xué)院?；?NO：CYZ13-005)

張仲林,E-mail：zhlzhang2007@163.com

http://www.cnki.net/kcms/detail/51.1705.R.20140415.1048.005.html

10.3969/j.issn.1674-2257.2014.02.033

R735.3

A