李華英，黃守國(guó)

(中南大學(xué)湘雅醫(yī)學(xué)院附屬?？卺t(yī)院婦產(chǎn)科，海南海口570208)

Gal3ST-2基因表達(dá)與惡性腫瘤細(xì)胞轉(zhuǎn)移關(guān)系的研究進(jìn)展

李華英，黃守國(guó)

(中南大學(xué)湘雅醫(yī)學(xué)院附屬?？卺t(yī)院婦產(chǎn)科，海南?？?70208)

惡性腫瘤轉(zhuǎn)移是一個(gè)多步驟、多因素綜合參與的極其復(fù)雜的過(guò)程，而惡性腫瘤細(xì)胞轉(zhuǎn)移也是惡性腫瘤致死性的主要原因。研究表明，惡性腫瘤細(xì)胞的轉(zhuǎn)移與轉(zhuǎn)移基因的分布及表達(dá)密切相關(guān)。半乳糖：3-O-磺?；D(zhuǎn)移酶-2(Gal3ST-2)是1989年發(fā)現(xiàn)的磺?；D(zhuǎn)移基因，其特定的結(jié)構(gòu)與廣泛的組織分布以及明顯的促惡性腫瘤轉(zhuǎn)移作用尤為引人注目。

磺?；D(zhuǎn)移酶；腫瘤；惡性；轉(zhuǎn)移；基因；表達(dá)

隨著長(zhǎng)期以來(lái)對(duì)惡性腫瘤細(xì)胞轉(zhuǎn)移機(jī)制的深入研究發(fā)現(xiàn)，惡性腫瘤的轉(zhuǎn)移是轉(zhuǎn)移基因與抑制轉(zhuǎn)移基因參與調(diào)節(jié)的復(fù)雜過(guò)程，通過(guò)腫瘤轉(zhuǎn)移相關(guān)基因表達(dá)的改變，以及一系列相關(guān)因子的參與，對(duì)腫瘤轉(zhuǎn)移整個(gè)過(guò)程進(jìn)行調(diào)控。轉(zhuǎn)移基因是指直接促進(jìn)轉(zhuǎn)移發(fā)生的關(guān)鍵基因，其存在或表達(dá)增強(qiáng)會(huì)引起侵襲轉(zhuǎn)移的發(fā)生。半乳糖：3-O-磺?；D(zhuǎn)移酶-2(Gal3ST-2)基因是近年來(lái)研究較熱的腫瘤轉(zhuǎn)移基因，是半乳糖：3-O-磺?；D(zhuǎn)移酶基因家族(Gal3STs)中的一員，此基因家族已克隆出有四個(gè)成員，分別為腦苷脂磺酰基轉(zhuǎn)移酶基因Gal3ST-1(CST)、Gal3ST-2(GP3ST)、Gal3ST-3、Gal3ST-4，它們?cè)谌梭w的分布具有組織特異性。Gal3ST-2(GP3ST)分布廣泛，在心臟、胃、結(jié)腸、肝臟和脾臟中表達(dá)相對(duì)較高[1]。Gal3ST-3主要表達(dá)在甲狀腺、腎臟和腦中[2]；Gal3ST-4主要表達(dá)在胎盤(pán)、胸腺、睪丸、卵巢、脊髓、氣管、腎上腺中[3]。在國(guó)內(nèi)外近年來(lái)的研究發(fā)現(xiàn)Gal3ST-2在多種腫瘤組織中表達(dá)具有差異性，以及催化所形成的磺?；擎溑c腫瘤轉(zhuǎn)移潛能密切相關(guān)[4-7]。

1 Gal3 ST-2 的結(jié)構(gòu)與功能

半乳糖：3-O-磺?；D(zhuǎn)移酶-2(Gal：3-O-Sulfotransferase-2，Gal3ST-2或GP3ST)是一個(gè)磺?；D(zhuǎn)移酶，于1989年首先在甲狀腺微粒體中發(fā)現(xiàn)[8]。Gal3ST-2于2001年成功克隆，該基因位于人類(lèi)染色體的2q37.3位點(diǎn)，編碼由398個(gè)氨基酸殘基組成的Ⅱ型跨膜蛋白[1]?；酋；D(zhuǎn)移酶的主要作用是使糖復(fù)合物磺?；?，其中磺基可附著在半乳糖(Gal)的3號(hào)和6號(hào)位置，n-乙酰葡糖胺(GalNAc)的3號(hào)和6號(hào)位置，以及GlcNAc的4號(hào)位置[9]。Gal3ST-2基因是3-O-磺?；D(zhuǎn)移酶基因家族中的一員，家族中各個(gè)基因的氨基酸序列的一致性為30%～40%[10]。

磺?；亩嗵菂⑴c多個(gè)生物過(guò)程，其中包括細(xì)胞附著和腫瘤的轉(zhuǎn)移[10]。Gal3ST-2通常使用3'-磷酸腺苷-5'-磷酰硫酸(PAPS)作為供體，將PAPS上的磺?；D(zhuǎn)移到多種糖聚合物的半乳糖殘基的C-3位置[11]。包含3'-磺基-β-半乳糖連接的糖鏈結(jié)構(gòu)存在于糖蛋白中的N-聚糖和O-聚糖，在對(duì)Gal3ST-2酶在不同物種之間的研究發(fā)現(xiàn)，Gal3ST-2在不同物種之間底物的特異性具有差異，其中以人類(lèi)的Gal3ST-2的作用范圍最廣，可以分別作用于Galβ 1-3GlcNAc-R(typeⅠ)、Gal β 1-4GlcNAc-R(typeⅡ)和Galβ 1→3GalNAc(Core I)結(jié)構(gòu)[12]。另外，值得注意的是，除了β半乳糖殘基，Gal3ST-2還能作用于Gal-alpha-o-pNP,其中Galβ 1→3GlcNAcβ 1→3Galβ 1→4Glc(LNT)只能被Gal3ST-2催化[11]。

2 al3 ST-2 與腫瘤細(xì)胞轉(zhuǎn)移的關(guān)系

腫瘤細(xì)胞的轉(zhuǎn)移分為多個(gè)階段[13-14]，目前的研究表明，Gal3ST-2至少參與其中兩個(gè)重要的階段，即腫瘤細(xì)胞從實(shí)體瘤的脫離以及在目標(biāo)組織的種植。

2.1 Gal3ST-2參與腫瘤細(xì)胞從實(shí)體瘤的脫離單個(gè)腫瘤細(xì)胞脫離與實(shí)體瘤的黏連，從實(shí)體瘤中分離出來(lái)，標(biāo)志著腫瘤轉(zhuǎn)移的開(kāi)始[13]。細(xì)胞間的黏附主要由E-鈣黏蛋白/連環(huán)蛋白混合物構(gòu)成[15]，細(xì)胞黏附分子是細(xì)胞表面的一類(lèi)蛋白，主要分為三類(lèi)：免疫球蛋白超家族(Ig)、整合素以及選凝蛋白，細(xì)胞間的黏附主要由E-鈣黏蛋白負(fù)責(zé)，E-鈣黏蛋白是由700～750個(gè)氨基酸殘基組成的橫跨膜糖蛋白，主要負(fù)責(zé)細(xì)胞間親同種抗原的細(xì)胞間黏附[13]。E-鈣連蛋白的減少能夠促進(jìn)腫瘤細(xì)胞的分化和轉(zhuǎn)移，被認(rèn)為是導(dǎo)致膀胱癌、胰腺癌以及胃癌細(xì)胞轉(zhuǎn)移及病灶?lèi)盒赃M(jìn)展的重要因素[16-18]。整合素連接激酶(ILK)是一種胞內(nèi)蛋白，能夠通過(guò)調(diào)節(jié)E-鈣黏蛋白的激活子的活性調(diào)節(jié)E-鈣黏蛋白的表達(dá)[19]。研究表明，Gal3ST-2的表達(dá)被干擾后，ILK的表達(dá)也下降，但是E-鈣黏蛋白的表達(dá)卻升高了。另外，整合素蛋白亞基alpha-v的表達(dá)能夠促進(jìn)腫瘤細(xì)胞在裸鼠中的種植轉(zhuǎn)移，隨后也有相關(guān)文獻(xiàn)報(bào)道[20]，alpha-v的在高轉(zhuǎn)移潛能的腫瘤細(xì)胞中表達(dá)更明顯，通過(guò)RNAi/ Gal3ST-2質(zhì)粒轉(zhuǎn)染肝癌細(xì)胞株SMMC7721，發(fā)現(xiàn)整合素蛋白亞基alpha-v的表達(dá)受到了抑制，這表明Gal3ST-2可以通過(guò)調(diào)節(jié)E-鈣黏蛋白和整合素蛋白亞基alpha-v的表達(dá)促進(jìn)腫瘤細(xì)胞從實(shí)體瘤的脫離及向遠(yuǎn)處的轉(zhuǎn)移。

2.2 Gal3ST-2參與腫瘤細(xì)胞在目標(biāo)組織中的種植腫瘤細(xì)胞轉(zhuǎn)移到目標(biāo)組織，并與目標(biāo)組織的內(nèi)皮細(xì)胞黏附，這標(biāo)志著腫瘤實(shí)現(xiàn)了到目標(biāo)組織的遠(yuǎn)處轉(zhuǎn)移[13]。眾多研究表明，在血液中傳播的腫瘤細(xì)胞與血小板，白細(xì)胞相互作用形成的微栓能夠促進(jìn)腫瘤細(xì)胞在血管壁的黏附[11]。參與腫瘤細(xì)胞與血管壁相互作用的選凝蛋白(Selectin)是哺乳類(lèi)血管中一類(lèi)細(xì)胞粘附分子，包含E-選凝蛋白、P-選凝蛋白和L-選凝蛋白，能夠介導(dǎo)補(bǔ)充血液中白細(xì)胞的凝集素[21]。實(shí)驗(yàn)證明，E-選凝蛋白配體表達(dá)的腫瘤細(xì)胞株表現(xiàn)出了高轉(zhuǎn)移的能力[22]。而P-選凝蛋白和L-選凝蛋白也能夠通過(guò)協(xié)同的方式促進(jìn)腫瘤轉(zhuǎn)移[11]。選凝蛋白具有識(shí)別含有唾液酸化Lewisx/a的糖蛋白的白細(xì)胞或血小板細(xì)胞的能力[4]，因此若腫瘤細(xì)胞表面包含唾液酸化的Lewisx/a也將被識(shí)別，這為腫瘤細(xì)胞在遠(yuǎn)處轉(zhuǎn)移種植提供了可能。Gal3ST-2催化后的產(chǎn)物能夠能夠進(jìn)一步被巖藻基轉(zhuǎn)移酶催化，合成3'-磺?；?Lewis抗原。有學(xué)者于2001發(fā)現(xiàn)Gal3ST-2與巖藻糖基轉(zhuǎn)移酶Ⅲ共同合成3'-磺?；?Lex抗原，而Gal3ST-2與巖藻糖基轉(zhuǎn)移酶Ⅲ、Ⅳ、Ⅴ、Ⅵ、Ⅶ和Ⅺ參與了3-磺酰基-Lea的合成[9，23]。與唾液酸基-LeX和唾液酸基-Lea比較，磺酰基-LeX和磺?；?Lea能夠與E-選凝蛋白和L-選凝蛋白更好地結(jié)合[6，24-26]，這與腫瘤細(xì)胞的轉(zhuǎn)移潛能密切相關(guān)。

3 Gal3 ST-2 在不同腫瘤中的表達(dá)

Gal3ST-2在人體組織中分布十分廣泛，其中在心臟、胃、結(jié)腸、肺以及脾組織中均有較高表達(dá)水平[1]。用反轉(zhuǎn)錄RT-PCR的方法對(duì)直腸腺癌和正常直腸黏膜中的Gal3ST-2基因的轉(zhuǎn)錄水平進(jìn)行量化，發(fā)現(xiàn)Gal3ST-2在非黏膜腺癌中的轉(zhuǎn)錄水平明顯低于在正常黏膜組織的轉(zhuǎn)錄水平[11，27]。在肺癌、喉癌及肝癌中Gal3ST-2在轉(zhuǎn)移性的腫瘤組織中表達(dá)比在非轉(zhuǎn)移性的腫瘤組織中的表達(dá)更為強(qiáng)烈[28]。為了評(píng)估DNA甲基化對(duì)早期胃癌組織亞型的意義，在38例早期胃癌(18例腸性，12例混合型，8例彌散性)進(jìn)行焦磷酸測(cè)序?qū)嶒?yàn)后發(fā)現(xiàn)，Gal3ST-2與混合型早期胃癌相關(guān)(P=0.015 8)[29]。

乳房的上皮乳腺細(xì)胞能夠產(chǎn)生Gal3ST-2酶[5]。在前體脂肪細(xì)胞株3T3-L1的實(shí)驗(yàn)顯示，Gal3ST-2能夠通過(guò)抑制脂肪細(xì)胞轉(zhuǎn)錄時(shí)的調(diào)控因子，如C/EBPβ和FABP4等基因的表達(dá)，以此干擾前體脂肪細(xì)胞3T3-L1的分化，因此Gal3ST-2被認(rèn)為可能干擾前體脂肪細(xì)胞的正常分化[5]。前體脂肪細(xì)胞能夠分化為脂肪細(xì)胞，而脂肪細(xì)胞的去分化被認(rèn)為是腫瘤產(chǎn)生的一個(gè)重要因素[30]。以往的實(shí)驗(yàn)證實(shí)了成脂特定基的轉(zhuǎn)錄因子(C/EBPs和PPARr)具有調(diào)控甘油三酯在細(xì)胞中含量的功能[31]，且C/EBPB和PPAR的表達(dá)受到TgIF(甘油三酯抑制因子)的抑制。有文獻(xiàn)報(bào)道用MALDI-tof證實(shí)了Gal3ST-2的表達(dá)與TgIF呈正相關(guān)，且在NMMMG培養(yǎng)基中檢測(cè)到了小鼠前脂肪細(xì)胞(3T3-1L)中的甘油三酯的含量減少了70%。Gal3ST-2通過(guò)減少乳腺前脂肪細(xì)胞中甘油三酯的積累，干擾乳腺成脂細(xì)胞的分化過(guò)程。此外，Gal3ST-2在轉(zhuǎn)移性乳腺乳腺癌上皮細(xì)胞系中比在非轉(zhuǎn)移性乳腺癌上皮細(xì)胞系中表達(dá)更為強(qiáng)烈[7]。

總之，腫瘤是全球疾病致死的重要元兇之一。據(jù)世界衛(wèi)生組織統(tǒng)計(jì)：惡性腫瘤早期發(fā)現(xiàn)和早期治療，可降低大約三分之一的腫瘤負(fù)擔(dān)。隨著分子生物學(xué)的不斷發(fā)展，腫瘤的發(fā)生發(fā)展的分子學(xué)機(jī)制也逐步被闡明，為腫瘤的早期實(shí)驗(yàn)室診斷提供了重要的基礎(chǔ)。腫瘤細(xì)胞的轉(zhuǎn)移與轉(zhuǎn)移基因的分布及表達(dá)密切相關(guān)。

Gal3ST-2是一個(gè)新近研究的腫瘤轉(zhuǎn)移基因，由于其在轉(zhuǎn)移性腫瘤中的普遍存在和高表達(dá)，有望成為這些腫瘤的診斷標(biāo)志及臨床靶向治療的新靶點(diǎn)。在腫瘤的早期診斷和臨床的實(shí)踐應(yīng)用中具有一定的前景。

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Research progress on the relationship between Gal3ST-2 gene expression and malignant tumor metastasis.

LI Hua-ying,HUANG Shou-guo.Department of Obstetrics and Gynaecology,Haikou People's Hospital Affiliated to Xiangya Medical School of Central South University,Haikou 570208,Hainan,CHINA

Tumor metastasis is an extremely complex process which involves multi-steps and multi-factors,and it is also the primary cause of death.Previous researches show that tumor metastasis is closely correlated to the distribution and expression of metastasis genes.And Gal:3-O-sulfotransferase-2(Gal3ST-2),a sulfo-transferase gene first discovered in 1989,is especially noteworthy for its special structure,broad distribution in tissues and obvious effect on promoting tumor metastasis.

Sulfo-transferase;Tumor;Malignant;Matastasis;Gene;Expression

R73-37

A

1003—6350（2016）01—0088—03

10.3969/j.issn.1003-6350.2016.01.031

2015-01-28)

黃守國(guó)。E-mail：shouguohuang@126.com