趙帆, 楊澤

北京大學(xué)醫(yī)學(xué)部第五臨床醫(yī)學(xué)院, 衛(wèi)生部北京醫(yī)院老年醫(yī)學(xué)研究所, 北京 100730

前列腺癌的DNA甲基化及其臨床應(yīng)用

趙帆, 楊澤

北京大學(xué)醫(yī)學(xué)部第五臨床醫(yī)學(xué)院, 衛(wèi)生部北京醫(yī)院老年醫(yī)學(xué)研究所, 北京 100730

目前認(rèn)為惡性腫瘤的形成是遺傳和表觀遺傳機(jī)制共同作用的結(jié)果。表觀遺傳機(jī)制包括DNA甲基化、組蛋白修飾和 miRNA。DNA異常甲基化(高甲基化和低甲基化)是前列腺癌最具特征的表觀遺傳改變, 它能夠?qū)е禄蚪M不穩(wěn)定, 調(diào)控基因的異常表達(dá), 在前列腺癌的形成和發(fā)展中起到重要作用。同時(shí), DNA甲基化作為前列腺癌表觀遺傳研究的一個(gè)熱點(diǎn), 為臨床前列腺癌的早期診斷、預(yù)后評(píng)估及藥物治療提供新的方法和途徑。文章根據(jù)前列腺癌的 DNA高甲基化和低甲基化的最新研究成果闡述了前列腺癌形成的表觀遺傳學(xué)機(jī)制, 并且討論了它們?cè)谇傲邢侔┡R床轉(zhuǎn)化方面的最新研究進(jìn)展。

前列腺癌; DNA 高甲基化; DNA 低甲基化

前列腺癌是老年男性最常見(jiàn)的惡性腫瘤之一。目前, 前列腺癌已成為中老年男性癌癥發(fā)病的第 2大病因, 位居男性癌癥致死人數(shù)的第6位[1]。前列腺癌的發(fā)病機(jī)制較為復(fù)雜, 目前認(rèn)為遺傳和表觀遺傳機(jī)制共同作用導(dǎo)致前列腺癌的發(fā)生、發(fā)展, 其中表觀遺傳在前列腺癌的形成中起到重要的作用。表觀遺傳是指在染色體 DNA序列不發(fā)生改變的情況下產(chǎn)生的一種可穩(wěn)定遺傳的表型[2]。表觀遺傳機(jī)制包括DNA甲基化、組蛋白修飾和miRNA, 它們分別通過(guò)轉(zhuǎn)錄前和轉(zhuǎn)錄后控制基因表達(dá), 其中DNA甲基化在前列腺癌表觀遺傳機(jī)制研究中成果最多, 也最為引人注目。在哺乳動(dòng)物基因組中, DNA甲基化通常發(fā)生在 CpG雙核苷酸的胞嘧啶上, 由硫-腺苷-甲硫氨酸(S-adenosylmethionine, SAM)提供甲基供體,在DNA甲基轉(zhuǎn)移酶(DNA mthyltransferase, DNMT)的催化下, 將甲基轉(zhuǎn)移到CpG雙核苷酸胞嘧啶的第5個(gè)碳原子上。CpG不是隨機(jī)分布的, 它最常見(jiàn)于基因組CpG島的位置, 哺乳動(dòng)物中一半以上的基因都含有CpG島, 大部分CpG島位于基因啟動(dòng)子、非編碼區(qū)和第一外顯子, 且在正常細(xì)胞內(nèi)不發(fā)生甲基化[3,4]。前列腺癌中 DNA異常甲基化主要表現(xiàn)為基因組廣泛低甲基化和局部基因啟動(dòng)子區(qū)域的高甲基化。DNA異常甲基化發(fā)生在前列腺癌的形成過(guò)程中, 且DNA甲基化能夠通過(guò)藥物發(fā)生逆轉(zhuǎn), 因此, 前列腺癌 DNA甲基化的早期篩查及前列腺癌去甲基化藥物的臨床應(yīng)用, 可能會(huì)為臨床早期診斷和治療前列腺癌提供新的思路。

本文主要闡述了前列腺癌表觀遺傳機(jī)制中 DNA異常甲基化的最新研究成果以及前列腺癌 DNA異常甲基化在臨床轉(zhuǎn)化中的應(yīng)用及存在的問(wèn)題。

1 DNA高甲基化

基因組中 DNA高甲基化常發(fā)生于基因的啟動(dòng)子區(qū)域, 即富含CpG的CpG島區(qū)域。這些區(qū)域在正常細(xì)胞中通常是非甲基化的。這些基因主要參與激素應(yīng)答, 細(xì)胞增殖、遷移和侵襲, DNA修復(fù)及轉(zhuǎn)錄調(diào)控等(表1)。基因啟動(dòng)子DNA高甲基化致使相關(guān)基因表達(dá)沉默是前列腺腫瘤形成的一個(gè)重要原因。根據(jù)它們的功能和信號(hào)通路不同, 主要包括以下相關(guān)基因：

1.1 激素應(yīng)答相關(guān)基因

雄激素受體(Androgen receptor, AR)是類(lèi)固醇激素受體家族的一個(gè)成員, 與雄激素結(jié)合后與輔助蛋白分離進(jìn)入細(xì)胞核內(nèi), 刺激雄激素應(yīng)答基因的轉(zhuǎn)錄。5-氮脫氧胞苷(5-aza-CdR)可逆轉(zhuǎn)前列腺癌干細(xì)胞由AR基因啟動(dòng)子DNA高甲基化導(dǎo)致的表達(dá)沉默, AR表達(dá)上調(diào)可降低前列腺癌干細(xì)胞特性, 誘導(dǎo)癌細(xì)胞的增殖和分化[5]。視黃酸受體 β(Retinoic acid receptor beta, RARB)是甲狀腺類(lèi)固醇激素受體家族成員之一, 它與具有生物活性的維生素 A-視黃酸結(jié)合, 參與細(xì)胞生長(zhǎng)和分化及胚胎形成過(guò)程中的信號(hào)轉(zhuǎn)導(dǎo)。RARB基因啟動(dòng)子區(qū)域DNA高甲基化可發(fā)生在多個(gè)腫瘤的形成過(guò)程中, 如前列腺癌[6,7]、乳腺癌[8]、肺癌[9]、食管癌[10]、甲狀腺癌[11]、膀胱癌[12]、結(jié)直腸癌[13]、惡性膠質(zhì)瘤[14]、鼻咽癌[15]等。因此, 我們推斷該基因可能在多個(gè)腫瘤形成過(guò)程中參與調(diào)節(jié)腫瘤形成的共同傳導(dǎo)途徑。G蛋白偶聯(lián)受體(G protein coupling receptors, GPCRs)能夠刺激AR的雄激素非依賴(lài)性激活, 是導(dǎo)致激素難治性前列腺癌的發(fā)生的重要因素。G 蛋白信號(hào)調(diào)節(jié)因子 2 (Regulator of G-protein signaling 2, RGS2)是一種GTP酶激活蛋白,能夠抑制 GPCRs, 介導(dǎo)骨髓細(xì)胞分化, 可能參與白血病的形成。RGS2基因啟動(dòng)子DNA高甲基化異常能夠?qū)е滦奂に胤且蕾?lài)性前列腺癌細(xì)胞生長(zhǎng), 表明RGS2基因可能通過(guò)調(diào)控GPCRs參與AR反式激活通路[16]。ATP結(jié)合盒亞家族成員 1(ATP-binding cassette, sub-family A, member 1, ABCA1)是存在于細(xì)胞膜表面的外流性轉(zhuǎn)運(yùn)蛋白, 能夠轉(zhuǎn)運(yùn)細(xì)胞內(nèi)多余的膽固醇, 在維持細(xì)胞膽固醇穩(wěn)態(tài)方面起到重要作用。ABCA1基因啟動(dòng)子DNA高甲基化導(dǎo)致基因表達(dá)沉默, 它能使前列腺細(xì)胞內(nèi)的膽固醇升高, 雄激素合成增加, 后者通過(guò)AKT信號(hào)通路促進(jìn)前列腺癌的惡性進(jìn)展[17]。

1.2 抑癌基因

在前列腺癌DNA高甲基化研究中, 最常見(jiàn)的是抑癌基因啟動(dòng)子 DNA高甲基化。癌甲基化蛋白 1 (Hypermethylated in cancer 1, HIC1)基因表達(dá)一種轉(zhuǎn)錄阻抑蛋白, 在細(xì)胞中發(fā)揮生長(zhǎng)調(diào)控和抑癌基因的作用。前列腺癌細(xì)胞系、前列腺組織和血漿中均發(fā)現(xiàn)HIC1基因啟動(dòng)子DNA高甲基化, 在前列腺癌細(xì)胞異種移植的小鼠體內(nèi)誘導(dǎo)表達(dá)沉默的 HIC1基因激活, 可以觀察到它具有抑制前列腺腫瘤生長(zhǎng)、遷移和侵襲的作用[18,19]。結(jié)腸腺瘤性息肉 (Adeno-matous polyposis coli, APC) 基因表達(dá)一種WNT信號(hào)通路拮抗劑, 它參與細(xì)胞的遷移、侵襲、轉(zhuǎn)錄激活和細(xì)胞凋亡, 是一種常見(jiàn)的抑癌基因, 該基因突變常導(dǎo)致家族性結(jié)腸腺瘤性息肉病。APC基因啟動(dòng)子區(qū)域 DNA高甲基化在前列腺患者組織中常見(jiàn)[20],且甲基化程度與前列腺癌腫瘤分期和Glison評(píng)分呈正相關(guān)[21]。WNT抑制因子1(WNT inhibitory factor 1, WIF1) 基因編碼一種胞外信號(hào)分子, 能夠抑制WNT蛋白, 參與胚胎發(fā)育。該基因啟動(dòng)子DNA高甲基化發(fā)生在大多數(shù)前列腺癌細(xì)胞系中, 體外誘導(dǎo)PC-3細(xì)胞系表達(dá) WIF1, 可降低細(xì)胞遷移和侵襲能力, 上調(diào)E-鈣粘素(E-cadherin, CDH1)、角蛋白-8,18 (Keratin-8 and-18, KRT8,18)的表達(dá), 從而抑制上皮細(xì)胞向間充質(zhì)細(xì)胞轉(zhuǎn)化。在異種移植小鼠模型發(fā)現(xiàn)WIF1表達(dá)升高能夠抑制前列腺腫瘤生長(zhǎng)[22]。原鈣粘附蛋白10(Protocadherin 10, PCDH10)基因?qū)儆谠}黏蛋白家族成員, 為抑癌基因, 編碼鈣粘素相關(guān)蛋白受體, 參與腦內(nèi)特定細(xì)胞粘附及其功能聯(lián)系, 也參與前列腺癌的發(fā)生、發(fā)展[23]。

表1 前列腺癌中啟動(dòng)子區(qū)域發(fā)生DNA高甲基化的基因

1.3 信號(hào)轉(zhuǎn)導(dǎo)基因

WNT信號(hào)通路過(guò)度激活與腫瘤發(fā)生和腫瘤侵襲相關(guān), 分泌性卷曲相關(guān)蛋白 2(Secreted frizzledrelated protein 2, SFRP2)基因在WNT信號(hào)通路中能夠抑制該信號(hào)通路過(guò)度激活。SFRP2基因啟動(dòng)子DNA高甲基化在前列腺癌組織中的發(fā)生率明顯高于癌旁、高分級(jí)前列腺上皮內(nèi)瘤和前列腺增生組織[18,24]。Ras相關(guān)域家族蛋白 1(Ras association domain family member1, RASSF1)基因編碼一種與Ras效應(yīng)蛋白相似的蛋白, 該基因啟動(dòng)子DNA 高甲基化可在多個(gè)腫瘤組織中檢測(cè)到, 如前列腺癌[21]、乳腺癌[25]、膀胱癌[26]、肝癌[27]、非小細(xì)胞肺癌[28]、卵巢癌[29]等, 該基因同 RARB基因一樣, 在腫瘤形成過(guò)程中參與其共同通路的調(diào)節(jié)。配對(duì)樣同源域轉(zhuǎn)錄因子 2(Paired-like homeodomain 2, PITX2)基因表達(dá)一種轉(zhuǎn)錄因子, 調(diào)控原骨膠原賴(lài)氨酸羥化酶(Procollagenlysyl hydroxylase)基因的表達(dá), 在促生長(zhǎng)激素細(xì)胞和催乳素細(xì)胞的末端分化中發(fā)揮作用,同時(shí)也參與眼、牙齒和腹部器官的發(fā)育。在前列腺癌細(xì)胞系P69和M12中PITX2基因啟動(dòng)子區(qū)域均被甲基化, 它可能作為AR和IGF-1R基因上游的調(diào)節(jié)因子, 通過(guò)異常調(diào)節(jié)AR和IGF1-R通路, 影響前列腺細(xì)胞的正常生長(zhǎng)[30]。胰島素樣生長(zhǎng)因子蛋白7(Insulin-like growth factor binding protein 7, IGFBP7)能夠與胰島素生長(zhǎng)因子(Insulin-like growth factor, IGF)結(jié)合, 參與前列環(huán)素的合成及細(xì)胞粘附。IGFBP7基因啟動(dòng)子DNA高甲基化在多種前列腺癌細(xì)胞系和組織中檢測(cè)到[31], 但目前其作用機(jī)制尚不清楚。

1.4 DNA修復(fù)基因

谷胱甘肽 S-轉(zhuǎn)移酶 1(Glutathione S-transferase pi 1, GSTP1)基因, 屬于谷胱甘肽S-轉(zhuǎn)移酶基因家族成員, 它通過(guò)催化疏水性和親電性基團(tuán)與還原型谷胱甘肽結(jié)合發(fā)揮細(xì)胞解毒作用。在對(duì)25例行前列腺切除術(shù)的前列腺癌、癌旁基因甲基化水平評(píng)估后,發(fā)現(xiàn)GSTP1基因的甲基化水平在癌組織中明顯高于癌旁組織[20]。研究發(fā)現(xiàn)：前列腺癌細(xì)胞內(nèi)GSTP1基因啟動(dòng)子 DNA甲基化所致的表達(dá)沉默使胞內(nèi)活性氧物質(zhì)(ROS)聚集, DNA損傷標(biāo)記物——胞內(nèi)羥基脫氧鳥(niǎo)苷(8-oxo-2′-deoxogunosine, 8-OHdG)增加, GSTP1基因表達(dá)缺失可增加正常前列腺細(xì)胞對(duì)氧化應(yīng)激誘導(dǎo)的DNA損傷的敏感性, 從而導(dǎo)致前列腺癌形成[32]。

1.5 miRNA

miRNA是內(nèi)源性非編碼的 RNA, 能夠與靶mRNA3′-UTR(Untranslated region)部分互補(bǔ)結(jié)合抑制其翻譯或誘導(dǎo)特定的靶mRNA降解。前列腺癌中部分miRNA的異常調(diào)控也是因?yàn)楸磉_(dá)miRNA的基因啟動(dòng)子區(qū)域發(fā)生DNA高甲基化。在前列腺癌中啟動(dòng)子區(qū)域DNA高甲基化導(dǎo)致miR-31表達(dá)沉默, AR表達(dá)升高, 可能是前列腺癌的惡性進(jìn)展病因?qū)W機(jī)制之一[33]。miR-34b和miR-23b都具有抑制細(xì)胞增殖、遷移和侵襲, 以及 EMT(上皮間質(zhì)轉(zhuǎn)化)的作用, miR-34b和 miR-23b基因高甲基化導(dǎo)致其表達(dá)降低,原癌基因 Scr激酶表達(dá)升高, 前列腺腫瘤細(xì)胞惡性增殖, 導(dǎo)致患者復(fù)發(fā)生存期縮短[34,35]。此外, miR-205、miR-29a、miR-1256、miR-124、miR-26a、miR-132、miR-145基因高甲基化也參與前列腺癌形成[36～41]。

1.6 其他

互作蛋白1樣細(xì)絲蛋白A(Filamin A interacting protein 1-like, FILIP1L)基因表達(dá)一種細(xì)胞血管內(nèi)皮活性調(diào)控因子, FILIP1L基因啟動(dòng)子高甲基化在前列腺癌中常見(jiàn), 可能與前列腺癌形成過(guò)程中腫瘤血管的形成相關(guān)[42]。甲基胞嘧啶雙加氧酶 TET1(Tetmethylcytosinedioxygenase 1, TET1)基因表達(dá)參與胞嘧啶脫甲基的脫甲基酶。TET1基因啟動(dòng)子DNA高甲基化, 其 mRNA表達(dá)降低, 能夠下調(diào)金屬蛋白酶抑制劑1、2(Tissue inhibitor of metalloproteinase 1 and 2, TIMP1、TIMP2)表達(dá), 從而促進(jìn)前列腺癌轉(zhuǎn)移、侵襲[43]。死亡相關(guān)蛋白激酶1(Death-associated protein kinase1, DAPK1)基因參與γ干擾素(INF-γ)誘導(dǎo)的程序性細(xì)胞凋亡。DAPK1基因啟動(dòng)子區(qū)域DNA甲基化在前列腺癌組織中的發(fā)生率明顯高于正常前列腺組織[18]。泛素羧基末端水解酶L1(Ubiquitin carboxyl-terminal esterase L1, UCHL1)基因參與泛素化過(guò)程, 能夠水解泛素羧基末端的甘氨酸, 同時(shí)參與細(xì)胞增殖和分化。UCHL1基因啟動(dòng)子DNA甲基化在前列腺癌組織中的發(fā)生率為90%, 癌旁組織為15%,差異明顯[44]。此外, 激肽釋放酶 6、10(Kallikreinrelated peptidase 6,10, KLK6,10)、DNA結(jié)合蛋白抑制因子4(Inhibitor of DNA binding 4, ID4)、鋅指蛋白132(Zinc finger protein 132, ZNF132)、A型激酶鉚釘?shù)鞍?2(A-kinase anchor protein 12, AKAP12)、纖維蛋白樣表皮生長(zhǎng)因子細(xì)胞外基質(zhì)蛋白 1(EGF containing fibulin-like extracellular matrix protein 1, EFEMP1)等基因在前列腺癌細(xì)胞中也發(fā)生 DNA高甲基化, 可能通過(guò)其他途徑參與前列腺癌的發(fā)生、發(fā)展[45～47], 具體機(jī)制目前尚不清楚。

2 DNA低甲基化

盡管前列腺癌基因組中的部分基因啟動(dòng)子區(qū)域DNA常發(fā)生CpG高甲基化, 但是在前列腺癌基因組中, CpG 位點(diǎn)低甲基化卻占明顯優(yōu)勢(shì)[62], 在前列腺癌基因組內(nèi)呈現(xiàn)廣泛的低甲基化, 而且DNA低甲基化并非隨機(jī)的, 這些CpG位點(diǎn)在正常前列腺組織中為低甲基化, 它們常位于印記基因、逆轉(zhuǎn)錄轉(zhuǎn)座子、內(nèi)源性病毒序列、基因組的內(nèi)含子、基因間區(qū)以及基因組中散在分布的重復(fù)序列或端粒的重復(fù)序列內(nèi)[63]?；蚪M中該位置的CpG位點(diǎn)低甲基化會(huì)導(dǎo)致印記基因過(guò)表達(dá)、染色質(zhì)結(jié)構(gòu)改變、表觀遺傳重組及基因組不穩(wěn)定, 在前列腺癌的發(fā)病機(jī)制中同樣發(fā)揮重要作用。目前對(duì)前列腺癌DNA低甲基化的研究相對(duì)較少, 可能由于DNA低甲基化通常發(fā)生在重復(fù)元件內(nèi), 且DNA序列會(huì)有部分重疊, 因此較難在實(shí)驗(yàn)中研究。

長(zhǎng)散在核重復(fù)序列(Long interspersed nuclear element1, LINE1)為基因組內(nèi)散在分布的重復(fù)序列,在正常細(xì)胞基因組內(nèi)通常是高甲基化的。在前列腺癌樣本中發(fā)生低甲基化, 且更常見(jiàn)于轉(zhuǎn)移性前列腺癌[64]。此外, 胰島素樣生長(zhǎng)因子(Insulin-like growth factor 2, IGF2)基因?yàn)橛∮浕? 其父源等位基因表達(dá)相應(yīng)蛋白, 參與機(jī)體的生長(zhǎng)和發(fā)育。IGF2基因低甲基化導(dǎo)致兩個(gè)等位基因同時(shí)表達(dá), 前列腺癌中IGF2基因印記控制區(qū)尤其是CTCF結(jié)合域的甲基化水平與前列腺增生組織有顯著性差異[65,66]。三葉因子(Trefoil factor, TFF)基因在胃黏膜中表達(dá)一種穩(wěn)定的分泌性蛋白。前列腺癌細(xì)胞系中TFF1、3基因甲基化水平明顯低于正常前列腺細(xì)胞, 但它們?cè)谇傲邢倌[瘤的形成中的作用尚不清楚[67]。

3 DNA甲基化的前列腺癌早期診斷

表觀遺傳標(biāo)記物, 尤其是DNA甲基化, 可能會(huì)成為未來(lái)臨床檢測(cè)和診斷前列腺癌的新的方法和手段, 主要因?yàn)楸碛^遺傳改變?cè)谇傲邢侔┲衅毡榇嬖?而且在前列腺腫瘤形成前期就已經(jīng)發(fā)生, 有利于臨床早期篩查和檢測(cè)。其次, 相較于 RNA檢測(cè)來(lái)說(shuō),基因組DNA的檢測(cè)相對(duì)穩(wěn)定, 而且檢測(cè)方法多樣。再次, 隨著DNA甲基化檢測(cè)技術(shù)的不斷發(fā)展, 標(biāo)準(zhǔn)化的高通量檢測(cè)平臺(tái)的建立能夠用于多個(gè)樣本DNA 甲基化多個(gè)位點(diǎn)的檢測(cè), 有利于臨床開(kāi)展DNA甲基化檢測(cè)。另外, DNA甲基化作為標(biāo)志物檢測(cè)手段多樣, 不僅在腫瘤組織中檢測(cè), 還可以在體液(如尿液、血液)中檢測(cè)。

目前, 很多研究致力于相關(guān)基因啟動(dòng)子DNA高甲基化作為前列腺癌生物標(biāo)志物的臨床檢測(cè)。定量焦磷酸測(cè)序的方法對(duì)52例前列腺增生組織和97例前列腺癌組織中APC基因和GSTP1基因兩種DNA甲基化水平進(jìn)行分析, 發(fā)現(xiàn)區(qū)分前列腺癌和前列腺增生的敏感性為92.8%, 特異性為100%[68], 在對(duì)30多個(gè)前列腺癌GSTP1基因啟動(dòng)子DNA高甲基化研究進(jìn)行Meta分析, 發(fā)現(xiàn)GSTP1基因啟動(dòng)子DNA甲基化檢測(cè)能夠提高臨床前列腺癌診斷特異性[69]。APC基因 DNA甲基化檢測(cè)可以作為首次活檢陰性的前列腺癌高危人群再次活檢的指標(biāo)[70]。對(duì)34例早期前列腺癌的患者的尿沉渣進(jìn)行 DNA甲基化分析發(fā)現(xiàn), RARB和RASSF1基因啟動(dòng)子DNA高甲基化的檢出率分別為71%和44%[6]。此外, 聯(lián)合檢測(cè)EVX1和成纖維細(xì)胞生長(zhǎng)因子1(Fibroblast growth factor 1, FGF1)基因啟動(dòng)子DNA高甲基化可進(jìn)一步鑒別出前列腺穿刺活檢結(jié)果為陰性的前列腺癌患者, 減少檢查者不必要的痛苦, 也能夠降低檢測(cè)成本和穿刺后并發(fā)癥[71]。

基因 DNA甲基化檢測(cè)作為臨床前列腺癌的早期診斷, 可以提高前列腺癌診斷特異性, 為首次活檢陰性的前列腺癌患者是否二次活檢提供臨床診斷參考。但前列腺癌DNA甲基化檢測(cè)作為新的診斷方法也有需要待解決的問(wèn)題：一是如何選擇前列腺癌特異性的DNA異常甲基化基因, 有利于提高診斷特異性; 二是如何提高前列腺癌特異性的DNA異常甲基化基因檢測(cè)的敏感性。

4 DNA甲基化對(duì)前列腺癌治療

與常見(jiàn)的遺傳改變不同, 表觀遺傳學(xué)的改變不涉及到DNA序列中堿基的改變。這種表觀遺傳學(xué)的可行性使它們有望成為潛在的藥物治療靶。目前主要的DNMT抑制劑分為兩大類(lèi)：核苷類(lèi)似物和非核苷類(lèi)似物。它們通過(guò)抑制DNMT來(lái)恢復(fù)相關(guān)基因的表達(dá)功能, 從而達(dá)到治療前列腺癌的目的。前者主要有 5-氮雜胞苷、5-氮脫氧胞苷和 zebularine(Zeb,化學(xué)名 1-(β-D-呋喃核糖苷)-1,2-二氫嘧啶-2-酮), 前兩種藥物已經(jīng)被美國(guó)FDA批準(zhǔn)用于治療骨髓異常增生綜合征(MDS)。Zebularine能夠使LNCaP和DU145前列腺癌細(xì)胞系GSTP1基因發(fā)生去甲基化, 提高其他化療藥物的抗腫瘤活性[72]。

后者主要包括從植物中提取化學(xué)物質(zhì)如大豆異黃酮、姜黃素、茶多酚[73]、mahanine[74]、kazinol Q[75]、disulfiram[76]等, 最新合成的甲基化抑制劑RG108[77]及其他化學(xué)物質(zhì)如反式維甲酸等。大豆異黃酮能夠抑制前列腺癌細(xì)胞系中的 DNMT, 使多個(gè)基因啟動(dòng)子DNA發(fā)生去甲基化, 抑制前列腺癌細(xì)胞生長(zhǎng)和侵襲的作用[37,78,79]。在TRAMP小鼠前列腺癌表觀遺傳學(xué)的研究中發(fā)現(xiàn), 姜黃素可以使啟動(dòng)子高甲基化的Nrf2基因發(fā)生去甲基化[80]。全反式維甲酸能夠使R陰性的前列腺細(xì)胞系 DU145中表達(dá)沉默的HOXB13基因的甲基化水平降低, 從而抑制細(xì)胞增殖[81]。

上述DNMT抑制劑在前列腺癌甲基化的研究中主要應(yīng)用于細(xì)胞系, 之所以沒(méi)有應(yīng)用于臨床, 一是目前體外研究結(jié)果還未對(duì)DNMT抑制劑在抑制前列腺癌 DNA高甲基化方面提供一個(gè)可靠且公認(rèn)的生物學(xué)機(jī)制; 二是目前還沒(méi)有一種DNMT抑制劑為靶向治療, DNMT抑制劑的應(yīng)用可能會(huì)干擾正常組織及細(xì)胞功能, 這種長(zhǎng)期作用的結(jié)果是未知的; 三是在臨床前期實(shí)驗(yàn)中, 這些藥物對(duì)實(shí)體腫瘤細(xì)胞的細(xì)胞毒性較大及反應(yīng)率較低, 存在的藥物副作用遠(yuǎn)遠(yuǎn)大于藥物的治療作用, 因此限制了DNMT抑制劑在前列腺癌臨床治療中的應(yīng)用。

5 DNA甲基化對(duì)前列腺癌的預(yù)后評(píng)估

DNA甲基化檢測(cè)對(duì)前列腺癌經(jīng)臨床治療后疾病的預(yù)后預(yù)測(cè)也同樣重要。對(duì)267例根治性前列腺癌切除術(shù)患者和 111例前列腺癌保守治療患者組織APN基因啟動(dòng)子區(qū)域甲基化分析、免疫組化分析及隨訪研究發(fā)現(xiàn), APN基因啟動(dòng)子區(qū)域高甲基化明顯縮短前列腺癌患者的復(fù)發(fā)生存期和腫瘤生存期[57]。經(jīng)根治性前列腺癌切除術(shù)患者通過(guò)使用 RT-PCR方法檢測(cè)PIX2基因高甲基化, 能夠預(yù)測(cè)前列腺癌患者PSA 復(fù)發(fā), 是一個(gè)潛在的前列腺癌預(yù)后標(biāo)志物[82]。低Gleason評(píng)分患者中HSPB1基因甲基化可以作為不良預(yù)后的生物標(biāo)志物[61]。此外, 術(shù)前PSA水平低的前列腺癌患者 miR-205基因啟動(dòng)子高甲基化可能與PSA復(fù)發(fā)相關(guān)[36]。EVX1基因在前列腺癌中能夠預(yù)測(cè)PSA復(fù)發(fā)[55]。

6 結(jié)語(yǔ)與展望

表觀遺傳改變, 尤其是基因啟動(dòng)子區(qū)域的DNA高甲基化是前列腺癌的常見(jiàn)特征, 在前列腺癌的發(fā)生和發(fā)病機(jī)制的進(jìn)展中起到重要作用。但是, 前列腺癌 DNA異常甲基化研究還存在很多問(wèn)題。第一,大部分研究只是針對(duì)前列腺癌中某個(gè)特定基因啟動(dòng)子區(qū)域中的一個(gè)或幾個(gè) CpG位點(diǎn)進(jìn)行甲基化分析,整個(gè)基因啟動(dòng)子區(qū)域的甲基化水平研究不夠充分;第二, 現(xiàn)存的技術(shù)手段很難對(duì)前列腺癌DNA異常甲基化進(jìn)行精確的定量研究; 第三, 需要更多的前列腺癌組織樣本進(jìn)行大樣本的重復(fù)驗(yàn)證; 第四, 表觀遺傳中DNA甲基化、組蛋白修飾及miRNA三者在癌癥的發(fā)生、發(fā)展中是相互作用的, 因此需要更多更廣泛的研究全面的闡述前列腺癌表觀遺傳機(jī)制;此外, 遺傳和表觀遺傳共同作用導(dǎo)致前列腺癌的發(fā)生, 因此, 如何將遺傳和表觀遺傳結(jié)合起來(lái)共同解釋前列腺癌發(fā)病機(jī)制也是前列腺癌研究需解決的一個(gè)問(wèn)題。

隨著科學(xué)技術(shù)及研究水平的不斷提高, 我們相信通過(guò)獲得大量的前列腺腫瘤特異性的遺傳和表觀遺傳學(xué)改變, 尤其是前列腺癌DNA甲基化的改變, 從而對(duì)前列腺癌的發(fā)病機(jī)制進(jìn)行更全面的闡述, 并以此作為生物學(xué)標(biāo)志物, 可能會(huì)為前列腺癌的臨床早期檢測(cè)、診斷、預(yù)后評(píng)估及隨訪提供新的方法和手段。

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(責(zé)任編委: 朱衛(wèi)國(guó))

DNA methylation of prostate cancer and clinical application

Fan Zhao, Ze Yang

The 5th Medical College of Peking University, Institute of Geriatrics, Chinese Ministry of Health, Beijing Hospital, Beijing 100730, China

It is well-known that the interation of both genetic and epigenetic mechanisms results in the formation of malignant tumor. Epigenetic mechanism includes DNA methylation, histone modifications, and miRNA regulation. DNA aberrant methylation (hypermethylation and hypomethylation), which leads to genomic instability and inappropriate gene expression, is the best-characterized alteration in prostate cancer. It plays an important role in the initiation and development of prostate cancer. Meanwhile, DNA methylation, as a hotspot in researches of epigenetics, would provide a new methodology and approach for early clinical diagnosis, prognosis and medication treatment of prostate cancer. According to recent studies on DNA hypermethylation and DNA hypomethylation, this review highlights the potential epigenetic mechanism of prostate cancer and discusses the latest research progress in clinical translation.

prostate cancer; DNA hypermethylation; DNA hypomethylation

2013-12-09;

2014-01-14

國(guó)家自然科學(xué)基金項(xiàng)目(編號(hào)：30972709, 81061120527, 81241082), 北京醫(yī)院重大基金項(xiàng)目(編號(hào)：BJ-2010-30), 衛(wèi)生部部屬醫(yī)院臨床學(xué)科重點(diǎn)項(xiàng)目(編號(hào)：01020101), 衛(wèi)生部行業(yè)基金項(xiàng)目(編號(hào)：201302008)和科技部十二五支撐計(jì)劃項(xiàng)目(編號(hào)：2012BAI10B01)資助

趙帆, 碩士研究生, 專(zhuān)業(yè)方向：醫(yī)學(xué)遺傳學(xué)。E-mail: zhaofan1219@163.com

楊澤, 研究員, 博士生導(dǎo)師, 研究方向：醫(yī)學(xué)遺傳學(xué)。E-mail: yang_ze@sina.com

10.3724/SP.J.1005.2014.0420

時(shí)間: 2014-3-20 14:48:59

URL: http://www.cnki.net/kcms/detail/11.1913.R.20140320.1448.001.html