鄭亞,孫紅
·綜述·
溶血磷脂酸在卵巢癌進(jìn)展中的機(jī)制研究
鄭亞,孫紅△
在卵巢癌的發(fā)生發(fā)展中,脂代謝發(fā)揮重要作用,溶血磷脂酸(LPA)作為一種生物活性磷脂分子,通過(guò)與多種G蛋白偶聯(lián)受體結(jié)合,參與卵巢癌的增殖、轉(zhuǎn)移和侵襲活動(dòng)。一方面,LPA可通過(guò)促進(jìn)腫瘤血管新生、調(diào)節(jié)細(xì)胞周期、抑制凋亡、促進(jìn)糖代謝及維持腫瘤干細(xì)胞(CSC)的特性來(lái)促進(jìn)卵巢癌細(xì)胞增殖;另一方面,LPA可增加基質(zhì)金屬蛋白酶(MMP)及尿激酶型纖溶酶原激活物(uPA)的表達(dá)、干預(yù)細(xì)胞間連接和骨架蛋白、促進(jìn)上皮-間質(zhì)轉(zhuǎn)化(EMT),進(jìn)而促進(jìn)卵巢癌的轉(zhuǎn)移和侵襲。此外,卵巢癌患者血漿中高水平的LPA單獨(dú)或與卵巢癌的其他腫瘤標(biāo)記物聯(lián)合檢測(cè)具有更高的敏感度和特異度。綜述LPA在卵巢癌增殖、轉(zhuǎn)移和侵襲中的作用機(jī)制以及潛在的診斷、治療靶點(diǎn)方面的研究進(jìn)展。
卵巢腫瘤;溶血磷脂酸;信號(hào)通路;治療靶點(diǎn);診斷
卵巢癌是女性生殖系統(tǒng)腫瘤中死亡率最高的惡性腫瘤[1]。因?yàn)槁殉舶┖茈y被早期發(fā)現(xiàn),就診時(shí)往往已發(fā)展成晚期,所以患者預(yù)后較差,對(duì)于晚期卵巢癌患者,目前治療措施為手術(shù)加鉑類、紫杉醇類的化療。但是絕大多數(shù)患者在數(shù)月內(nèi)復(fù)發(fā),并產(chǎn)生耐藥,這部分患者再應(yīng)用其他化療藥也僅起到微弱的效果[2]。因此,研發(fā)新的分子靶向治療藥物迫在眉睫。近年有關(guān)卵巢癌與脂代謝間關(guān)系的研究較為一致的結(jié)論為,腫瘤細(xì)胞依靠脂肪的從頭合成途徑產(chǎn)生大量脂肪酸為腫瘤的生長(zhǎng)提供能量,并伴隨脂代謝的改變。研究已證實(shí)溶血磷脂酸(LPA)在卵巢癌的增殖、轉(zhuǎn)移和侵襲中起到重要作用[3-4]。本文對(duì)LPA在卵巢癌進(jìn)展中的相關(guān)信號(hào)通路以及潛在的生物靶點(diǎn)進(jìn)行綜述。
在人體內(nèi),LPA的來(lái)源主要包括兩種途徑:循環(huán)中的LPA由溶血磷脂酶D/自分泌運(yùn)動(dòng)因子(ATX)分解溶血磷脂類(LPLs)而來(lái),另一種主要來(lái)源是磷脂酸類(PAs),由磷脂酶A1(PLA1)和PLA2水解所得,這種LPA主要位于細(xì)胞內(nèi)或者細(xì)胞膜上。
卵巢癌患者的血清和腹水中存在較高水平的LPA,LPA作為一種磷脂類信號(hào)分子,通過(guò)與G蛋白偶聯(lián)受體結(jié)合發(fā)揮多種生物學(xué)功能,LPA的受體包括6種,分別為L(zhǎng)PA1~LPA6,其中LPA1、LPA2、LPA3屬于內(nèi)皮細(xì)胞分化基因(EDG)家族,LPA1、LPA2、LPA3按照EDG方式命名時(shí)分別稱作EDG2、EDG4、EDG7,LPA1在肺組織高表達(dá),介導(dǎo)肺炎性損傷[5],LPA2及LPA3參與紅細(xì)胞的生成和分化[6],其中LPA2及LPA3在卵巢癌中的表達(dá)水平遠(yuǎn)高于良性卵巢腫瘤或正常卵巢組織[7]。而LPA4、LPA5和LPA6屬于非EDG家族受體,非EDG家族受體目前研究較少。
2.1 LPA在卵巢癌增殖中的作用新生血管對(duì)于腫瘤的生長(zhǎng)和增殖是必需的,而血管新生需要血管生長(zhǎng)因子的刺激,血管內(nèi)皮生長(zhǎng)因子(VEGF)是比較強(qiáng)而有效的一種血管生長(zhǎng)因子。Song等[8]發(fā)現(xiàn)阻斷轉(zhuǎn)錄因子(Rho)、Rho相關(guān)蛋白激酶(ROCK)或細(xì)胞型骨髓細(xì)胞瘤原癌基因(c-Myc)后,LPA依賴的VEGF水平顯著降低,說(shuō)明在LPA誘導(dǎo)卵巢癌患者高表達(dá)VEGF中,G12/13-Rho-ROCK-c-Myc信號(hào)通路發(fā)揮作用。然而,一些卵巢癌細(xì)胞系(如Hey-A8、OCC-1)并不表達(dá)VEGF,但也對(duì)LPA有反應(yīng)[9],說(shuō)明存在其他促進(jìn)癌細(xì)胞增殖的機(jī)制。叉頭框蛋白M1(FOXM1)是一種增殖特異性轉(zhuǎn)錄因子,在調(diào)控細(xì)胞周期基因表達(dá)及促進(jìn)腫瘤進(jìn)展中起重要作用[10],LPA能夠誘導(dǎo)FOXM1的表達(dá)[11],因此LPA能以這種直接的方式促進(jìn)腫瘤增殖。
除了對(duì)血管新生方面的作用外,LPA還可以間接抑制凋亡[12]以及上調(diào)端粒酶的表達(dá)和活性,進(jìn)而促進(jìn)卵巢癌增殖[13]。此外,最近研究發(fā)現(xiàn),LPA能上調(diào)己糖激酶Ⅱ(HKⅡ)的表達(dá),進(jìn)而使糖酵解加強(qiáng),為腫瘤提供更多能量,促進(jìn)了癌細(xì)胞的增殖,并證實(shí)LPA2為主要受體,這也是首次發(fā)現(xiàn)LPA能夠通過(guò)干預(yù)腫瘤的糖代謝發(fā)揮促腫瘤作用[14]。
腫瘤干細(xì)胞(CSC)是維持惡性腫瘤生物特性的重要成分,有學(xué)者從卵巢癌細(xì)胞系A(chǔ)2780、SKOV3和OVCAR3以及卵巢癌組織中分離CSC,應(yīng)用酶聯(lián)免疫吸附法(ELISA)發(fā)現(xiàn)CSC的培養(yǎng)基中LPA和ATX的水平遠(yuǎn)高于無(wú)CSC培養(yǎng)基中二者的水平,用外源性LPA處理后,其耐藥性、異種移植的成瘤能力等都顯著增強(qiáng),抑制ATX后,CSC的特性被抑制,表明ATX-LPA的自分泌環(huán)路參與維持CSC的特性[15],因此針對(duì)打破這一分泌環(huán)路的藥物或許能為卵巢癌的治療帶來(lái)新的靶點(diǎn)。
綜上,LPA可以通過(guò)促進(jìn)腫瘤血管新生、調(diào)節(jié)細(xì)胞周期、抑制凋亡、干擾腫瘤糖代謝以及維持CSC特性來(lái)促進(jìn)卵巢癌細(xì)胞的增殖。
2.2 LPA在卵巢癌轉(zhuǎn)移和侵襲中的作用LPA主要從促進(jìn)基質(zhì)金屬蛋白酶(MMP)和尿激酶型纖溶酶原激活物(uPA)的表達(dá)、干預(yù)細(xì)胞間連接和細(xì)胞骨架蛋白、促進(jìn)EMT及促進(jìn)腫瘤血管生成等方面來(lái)增強(qiáng)卵巢癌的轉(zhuǎn)移和侵襲。
MMP和uPA分解細(xì)胞外基質(zhì),從而易化癌細(xì)胞的轉(zhuǎn)移。LPA誘導(dǎo)VEGF的表達(dá),VEGF與VEGF-R2結(jié)合促進(jìn)MMP-2和uPA的分泌[16],LPA還可以通過(guò)G(i)-Ras/Rho/ROCK-核因子κB(NF-κB)信號(hào)通路介導(dǎo)MMP-9、uPA的表達(dá)[17-18]。2015年Lizalek等[19]發(fā)現(xiàn),LPA還能促使uPA受體在卵巢癌細(xì)胞表面聚集且表達(dá)增加,uPA與其受體結(jié)合增多,這為L(zhǎng)PA促進(jìn)卵巢癌轉(zhuǎn)移和侵襲的機(jī)制做了補(bǔ)充。
另外,LPA還可以通過(guò)干預(yù)腫瘤細(xì)胞間連接及細(xì)胞骨架蛋白,進(jìn)而促進(jìn)癌細(xì)胞的轉(zhuǎn)移。一方面,LPA可以增加N-鈣黏蛋白和β鏈蛋白的內(nèi)化導(dǎo)致細(xì)胞間黏著小帶崩解,使細(xì)胞間連接分散[20],2015年,Burkhalter等[21]發(fā)現(xiàn),LPA激活Wnt/β-鏈蛋白通路而刺激β1整合素的集簇,啟動(dòng)了EMT。另一方面,LPA能夠使連接蛋白-1表達(dá)增加[22]。
EMT是惡性腫瘤獲得轉(zhuǎn)移和侵襲能力的重要機(jī)制之一,缺氧誘導(dǎo)因子1-α(HIF1-α)在EMT中起著重要作用[23],LPA可以通過(guò)原癌基因酪氨酸激酶家族之一Gαi2(G蛋白)-Src激酶途徑刺激HIF1-α的表達(dá),進(jìn)而使N-鈣黏蛋白和介導(dǎo)EMT的轉(zhuǎn)錄因子Slug/Snail2的水平增加[24],促進(jìn)卵巢癌的EMT。
最后,LPA也可通過(guò)促進(jìn)血管生成促進(jìn)腫瘤發(fā)展,除上述提及的LPA促進(jìn)VEGF表達(dá)外,LPA與LPA2結(jié)合后刺激生長(zhǎng)調(diào)節(jié)癌基因蛋白α(GROα)的表達(dá),而GROα能夠促進(jìn)血管生成,進(jìn)而促進(jìn)腫瘤的發(fā)展[25]。
關(guān)于LPA在卵巢癌中的診斷價(jià)值,Zhang等[26]開展了一項(xiàng)病例對(duì)照研究,納入了123例卵巢癌患者和101例卵巢良性腫瘤患者,檢測(cè)他們血漿中LPA和CA-125的水平,發(fā)現(xiàn)在卵巢癌的診斷中,LPA具有更高的敏感度、特異度、陽(yáng)性預(yù)測(cè)值和陰性預(yù)測(cè)值,LPA和CA-125的受試者工作特征(ROC)曲線下面積分別為0.983、0.910,差異有統(tǒng)計(jì)學(xué)意義。也有學(xué)者收集108例卵巢癌、43例卵巢良性腫瘤和50例正常健康女性,檢測(cè)血清中LPA、惡性腫瘤特異性生長(zhǎng)因子(TSGF)和CA-125的水平,發(fā)現(xiàn)三者聯(lián)合檢測(cè)對(duì)卵巢癌診斷的敏感度和特異度顯著高于單項(xiàng)和兩兩聯(lián)合檢測(cè)[27]。另外,也有Meta分析,應(yīng)用隨機(jī)效應(yīng)模型等方法評(píng)估了血漿LPA水平診斷卵巢癌的可靠性[28-29]。為此,已有研究對(duì)LPA的檢測(cè)方法進(jìn)行了探討,主要包括放射線酵素法、比色法、免疫酶法、氣相色譜法等[30],為L(zhǎng)PA將來(lái)在臨床應(yīng)用打下基礎(chǔ),因此LPA可能成為卵巢癌的診斷標(biāo)記,從而有助于早期發(fā)現(xiàn)卵巢癌,改善預(yù)后。
前已提及,Rho因子參與LPA介導(dǎo)的卵巢癌侵襲的信號(hào)通路,阿倫磷酸鹽是一種治療骨質(zhì)疏松的藥物,其能阻止包括Rho在內(nèi)的小GTP酶的失活,用阿倫磷酸鹽處理卵巢癌細(xì)胞系后,LPA介導(dǎo)的癌細(xì)胞轉(zhuǎn)移被明顯抑制[31],而白藜蘆醇則能夠在表皮生長(zhǎng)因子受體(EGFR)-Rho/ROCK-NF-κB通路的開始抑制EGFR磷酸化使LPA介導(dǎo)的MMP-9和uPA表達(dá)降低[32]。此外,法舒地爾是一種抑制血管痙攣的藥物,其也是ROCK的特異性抑制劑,用法舒地爾處理卵巢癌細(xì)胞系后,導(dǎo)致細(xì)胞內(nèi)骨架蛋白重組的丟失,顯著抑制癌細(xì)胞的侵襲[33]。由于LPA介導(dǎo)卵巢癌的增殖和侵襲時(shí)涉及到較多的分子,因此對(duì)于其中潛在的有診斷和治療價(jià)值的靶點(diǎn)值得進(jìn)一步研究,以提高卵巢癌患者的生存率。
在女性生殖系統(tǒng)腫瘤中,卵巢癌發(fā)病率雖是位于宮頸癌、子宮內(nèi)膜癌之后的第3位惡性腫瘤,但死亡率卻遠(yuǎn)高于前兩者。LPA作為一種生物活性的磷脂類分子,在卵巢癌的增殖、轉(zhuǎn)移和侵襲中起重要的介導(dǎo)作用,其通過(guò)對(duì)細(xì)胞周期、血管新生、腫瘤干細(xì)胞及糖代謝的影響介導(dǎo)卵巢癌的增殖,通過(guò)促進(jìn)EMT、干擾細(xì)胞間連接和細(xì)胞骨架及增強(qiáng)MMP、uPA的表達(dá)刺激卵巢癌的轉(zhuǎn)移和侵襲。在診斷價(jià)值方面,卵巢癌患者血漿中高水平的LPA較CA-125具有更高的敏感度和特異度,但是相關(guān)研究納入的病例數(shù)較少,并且未按照卵巢癌的期別和惡性程度進(jìn)行分層研究。因此,將來(lái)需要更大樣本量的數(shù)據(jù)支持LPA的診斷價(jià)值。進(jìn)一步闡明LPA作用的分子機(jī)制,有望開發(fā)出針對(duì)LPA靶向抑制的新型藥物,或許能夠?yàn)閺?fù)發(fā)性、耐藥性卵巢癌的治療提供新的生物靶點(diǎn),從而有望降低卵巢癌的死亡率。
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Mechanisms of Lysophosphatidic Acid Involved in the Progression of Ovarian Cancer
ZHENG Ya,SUN Hong.Obstetrics and Gynecology Hospital,Fudan University,Shanghai 200011,China(ZHENG Ya,SUN Hong);Shanghai Key Laboratory of Reproductive Endocrine Related Disease,Shanghai 200011,China(ZHENG Ya)
SUN Hong,E-mail:hongsun57@hotmail.com
In the development of ovarian cancer,the aberrant lipid metabolism plays a critical role.Lysophosphatidic acid(LPA),a bioactive molecular,can bind to different G protein-coupled receptors and stimulate the proliferation,metastasis and invasion of ovarian cancer.On one hand,LPA could stimulate proliferation by promoting angiogenesis,regulating cell cycle, inhibiting apoptosis,promoting glucose metabolism and maintaining cancer stem cell(CSC)characteristics.On the other hand, LPA could stimulate the metastasis and invasion by enhancing the expression of matrix metalloproteinases(MMPs)and urokinase-type plasminogen activator(uPA),interfering intercellular junctions and cytoskeletons and inducing epithelialmesenchymal transition(EMT).Besides,testing plasma level of LPA alone or combining with other tumor biomarkers is more sensitive and specific.In this article,we review the latest knowledge on the molecular mechanism of LPA in the proliferation, migration and invasion of ovarian cancer as well as potential biological targets.
Ovarian neoplasms;Lysophosphatidic acid;Signal path;Therapeutic targets;Diagnosis(J Int Obstet Gynecol,2016,43:673-676)
2016-06-13)
[本文編輯秦娟]
上海市科學(xué)技術(shù)委員會(huì)科研計(jì)劃(14ZR1404100)
200011上海,復(fù)旦大學(xué)附屬婦產(chǎn)科醫(yī)院(鄭亞,孫紅);上海市女性生殖內(nèi)分泌相關(guān)疾病重點(diǎn)實(shí)驗(yàn)室(鄭亞)
孫紅,E-mail:hongsun57@hotmail.com
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