LOXL2
——具有潛在臨床應(yīng)用價(jià)值的新標(biāo)志物

魏楓林

(三門峽市中心醫(yī)院心胸外科，河南 三門峽 472000)

LOXL2
——具有潛在臨床應(yīng)用價(jià)值的新標(biāo)志物

魏楓林

(三門峽市中心醫(yī)院心胸外科，河南 三門峽 472000)

賴氨酰氧化酶樣蛋白2(Lysyl oxidase-like 2，LOXL2)是賴氨酰氧化酶家族成員之一，其在細(xì)胞外主要參與基質(zhì)膠原蛋白和彈性蛋白的交聯(lián)產(chǎn)物的形成，在細(xì)胞內(nèi)主要通過Snail途徑調(diào)節(jié)上皮細(xì)胞-間葉樣細(xì)胞轉(zhuǎn)化(Epithelial-mesenchymal transition，EMT)過程，LOXL2正在作為一種新的治療方法的靶點(diǎn)研究。但是在不同腫瘤中或不同腫瘤亞型中的表達(dá)情況差異明顯，需要進(jìn)一步研究。

賴氨酰氧化酶樣蛋白2；侵襲；轉(zhuǎn)移

賴氨酰氧化酶樣蛋白2是近年來逐漸受到重視的一種胺氧化酶。它與組織纖維化和腫瘤的侵襲、轉(zhuǎn)移都有密切的關(guān)系，但是在不同類型的腫瘤中，發(fā)揮的作用是不同的，甚至是矛盾的。需要我們進(jìn)一步的深入研究，以了解其中的分子生物學(xué)機(jī)制，為臨床治療或預(yù)測(cè)提供一種新的途徑或指標(biāo)。

1 賴氨酰氧化酶家族

賴氨酰氧化酶樣蛋白2(Lysyl oxidase-like 2，LOXL2)是賴氨酰氧化酶家族成員之一，這個(gè)家族具有代表性成員，分別是LOX、LOXL1、LOXL2、LOXL3、LOXL4。它們的-COOH端具有高度保守的序列，這決定了它們的同源性和相似性[1]。然而，LOX家族各亞型的N-端具有更大的差異性，這可能決定了這一組同工酶各自不同的功能角色和組織分布[2]。賴氨酸-酪氨酸輔酶因子和四組氨酸銅結(jié)合域是賴氨酰氧化酶家族成員獨(dú)有的[3-4]，也是LOX、LOXL2、LOXL4發(fā)揮胺氧化酶活性的必要結(jié)構(gòu)[5-8]。賴氨酰氧化酶家族中最具代表性的LOX和LOXL一直被看做是與基質(zhì)膠原蛋白和彈性蛋白的交聯(lián)產(chǎn)物形成密切相關(guān)的細(xì)胞核外酶[4，9]。然而，Hayashi等[9]和Csiszar等[10]的研究發(fā)現(xiàn)，在正常壯年小鼠的各種組織的不同區(qū)域細(xì)胞的核內(nèi)和核外都有LOX和LOXL存在，發(fā)揮各種對(duì)腫瘤的發(fā)生和進(jìn)展密切相關(guān)的生物學(xué)功能，包括：細(xì)胞生長(zhǎng)調(diào)控[11]、粘附、細(xì)胞運(yùn)動(dòng)和侵襲[3，12]。

2 LOXL2與腫瘤

1997年，Saito等[13]首次研究發(fā)現(xiàn)，相對(duì)于粘附性腫瘤細(xì)胞株，在各種非粘附腫瘤細(xì)胞株中LOXL2表達(dá)均下調(diào)。在RAS轉(zhuǎn)化小鼠的纖維母細(xì)胞中LOXL2 mRNA的表達(dá)減少近60%[14]。還有報(bào)道，在頭頸部鱗狀細(xì)胞癌(HNSCC)和漿液性卵巢癌中發(fā)現(xiàn)LOXL2表達(dá)的下調(diào)[15-17]。Saux等[18]在1998年將LOXL2基因定位于8p21.2-p21.3，這個(gè)區(qū)域的染色體丟失現(xiàn)象在多種惡性腫瘤中被發(fā)現(xiàn)，包括卵巢癌[19]、頭頸部鱗狀細(xì)癌[20]、腸癌[21-22]、食管癌[23-24]和乳腺癌[25-26]。

但是，在新近的研究中卻發(fā)現(xiàn)LOXL2的高表達(dá)和腫瘤的侵襲行為有關(guān)。首先在高致瘤性、轉(zhuǎn)移性鼠鱗狀細(xì)胞癌和梭狀細(xì)胞癌中發(fā)現(xiàn)LOXL2 mRNA的表達(dá)，而同時(shí)在無致瘤性的角質(zhì)細(xì)胞株中未發(fā)現(xiàn)LOXL2 mRNA的表達(dá)[27]。而且同樣的情況也出現(xiàn)在高侵襲性、轉(zhuǎn)移性乳腺癌細(xì)胞株與低侵襲性、轉(zhuǎn)移性乳腺癌細(xì)胞株的對(duì)比研究中[3]。有關(guān)LOXL2的表達(dá)與乳腺癌的臨床腫瘤分級(jí)的研究資料也支持上述結(jié)果[29]。而且進(jìn)一步研究發(fā)現(xiàn)，原本無侵襲性的MCF-7乳腺癌細(xì)胞株被轉(zhuǎn)染了LOXL2基因后即出現(xiàn)了侵襲性[29]，支持了LOXL2是一種致癌基因的觀點(diǎn)。隨后，有多家分別報(bào)道在乳腺癌、腸癌、食管癌、膽管癌、胰腺癌和胃癌細(xì)胞和組織中LOXL2的表達(dá)升高，而且這種高表達(dá)與更差的分化、更高的N分期和臨床TNM分期以及較差的生存期有關(guān)[29-33]。

在RAS轉(zhuǎn)化小鼠的纖維母細(xì)胞、頭頸部鱗狀細(xì)胞癌、肺腺癌和漿液性卵巢癌中發(fā)現(xiàn)LOXL2表達(dá)的下調(diào)。但是，在乳腺癌、腸癌、食管癌、膽管癌、胰腺癌和胃癌中LOXL2的表達(dá)上調(diào)，這說明了LOXL2在腫瘤發(fā)展過程中的角色是復(fù)雜的。而且在Zhan等[34]的報(bào)道中，在NSCLC中LOXL2表達(dá)的顯著下調(diào)，而且和更高的N分期和臨床TNM分期有密切聯(lián)系，但這種現(xiàn)象僅僅出現(xiàn)在肺腺癌患者，而在肺鱗癌患者中卻沒有觀察到這種聯(lián)系。這更進(jìn)一步說明了LOXL2的復(fù)雜性。

3 LOXL2與EMT

進(jìn)一步研究發(fā)現(xiàn)，在上皮細(xì)胞-間葉樣細(xì)胞轉(zhuǎn)化(Epithelial-mesenchymal transition，EMT)過 程 中LOXL2的表達(dá)上調(diào)，其中包括上皮表型的丟失和間葉細(xì)胞的活動(dòng)性表型的獲得[35]。SNAIL是EMT過程中至關(guān)重要的一種轉(zhuǎn)錄因子[27]。Fong等[29]研究顯示LOXL2能夠與SNAIL相互作用并提高SNAIL蛋白的穩(wěn)定性，誘導(dǎo)EMT。當(dāng)SNAIL表達(dá)的轉(zhuǎn)移性癌細(xì)胞中LOXL2下調(diào)，引起E-cadherin的合成，減少了間葉細(xì)胞轉(zhuǎn)化和促血管生成物質(zhì)的生成，減低了侵襲性。雖然目前還不確定LOXL2是否通過抑制SNAIL活性的促進(jìn)侵襲、轉(zhuǎn)移，但重要的是發(fā)現(xiàn)了在EMT過程中LOXL2與NAIL相互作用的重要性，這對(duì)于腫瘤的進(jìn)展，特別是侵襲性和遠(yuǎn)處轉(zhuǎn)移非常重要[29]。LOXL2抗體可以明顯抑制腫瘤的生長(zhǎng)和轉(zhuǎn)移[32]。在上皮細(xì)胞株T47D、MCF-7、HCT-116、HCT-15和DLD-1中，LOXL2的表達(dá)缺失，而在高侵襲性和轉(zhuǎn)移性的乳腺癌細(xì)胞株MDAMB-231和Hs578T中表達(dá)[29]，MDAMB-231和Hs578T具有間葉細(xì)胞表型[3]，這與前面的結(jié)果是一致的。在一些組織中，例如乳腺和卵巢，早期可能出現(xiàn)LOXL2的表達(dá)缺失，但在腫瘤的演化過程中出現(xiàn)LOXL2的再表達(dá)，這種現(xiàn)象可能與微環(huán)境的變化誘因有關(guān)。事實(shí)上，MCF-7細(xì)胞與纖維母細(xì)胞在特定的培養(yǎng)基中共同培養(yǎng)，能夠被促發(fā)LOXL2的表達(dá)[2]。這和家族中的另一個(gè)成員LOX是相近的。LOX已經(jīng)被證明，根據(jù)細(xì)胞類型和轉(zhuǎn)化狀態(tài)的不同，可以表現(xiàn)出腫瘤抑制或促腫瘤兩種截然不同的功能[3，36-37]。此外，Peng等[32]研究顯示分泌的LOXL2能夠同時(shí)激活Snail/E-cadherin and Src kinase/Focal adhesion kinase(Src/FAK)途徑。然而，LOXL2誘導(dǎo)胃癌細(xì)胞侵襲和遠(yuǎn)處轉(zhuǎn)移僅僅通過Src/ FAK途徑。

4 LOXL2的調(diào)節(jié)

Kaneda等[38]提出，是否象LOX一樣，LOXL2表達(dá)調(diào)節(jié)存在一種外在轉(zhuǎn)錄調(diào)節(jié)機(jī)制。Fong等[29]用脫甲基因子處理腸癌細(xì)胞株，結(jié)果發(fā)現(xiàn)LOXL2表達(dá)的增加。Lind等[39]報(bào)道，在腸癌細(xì)胞株與原位癌細(xì)胞中，LOXL2表達(dá)和甲基化率是相同的。然而，但在隨后的腸癌細(xì)胞的進(jìn)展演化中，隨著啟動(dòng)子的去甲基化，獲得了LOXL2的表達(dá)。表達(dá)的調(diào)控也可能通過腫瘤演化和EMT過程中的轉(zhuǎn)錄因子完成，如AP1、NFjB和WT1[40-42]。這意味著遺傳和外在環(huán)境因素都可能參與了癌癥進(jìn)展過程中LOXL2基因表達(dá)的調(diào)節(jié)。

綜上所述，LOXL2可能會(huì)成為一種預(yù)測(cè)腫瘤侵襲性和遠(yuǎn)處轉(zhuǎn)移風(fēng)險(xiǎn)的指標(biāo)，或者成為一種新的治療方法的靶點(diǎn)，但仍需要進(jìn)一步的研究來證明在體內(nèi)腫瘤轉(zhuǎn)移過程中LOXL2的功能作用，探索如何把LOXL2阻斷發(fā)展成為一個(gè)新的、具有發(fā)展?jié)摿Φ闹委煵呗浴?/p>

[1]Csiszar K.Lysyl oxidases:A novel multifunctional amine oxidase family[J].Prog NucleicAcid Res Mol Biol,2001,70:1-32.

[2]Molnar J,Fong KS,He QP,et al.Structural and functional diversity of lysyl oxidase and the LOX-like proteins[J].Biochim Biophys Acta,2003,1647(1-2):220-224.

[3]Kirschmann DA,Seftor EA,Fong SFT,et al.A molecular role for lysyl oxidase in breast cancer invasion[J].Cancer Res,2002,62: 4478-4483.

[4]Wang SX,Mure M,Medzihradszky KF,et al.A crosslinked co-factor in lysyl oxidase:Redox function for amino acid side chains[J]. Science,1996,273:1078-1084.

[5]Borel A,Eichenberger D,Farjanel J,et al.Lysyl oxidase-like protein from bovine aorta:Isolation and maturation to an active form by bone morphogenetic protein-1[J].J Biol Chem,2001,276: 48944-48949.

[6]Vadasz Z,Kessler O,Akiri G,et al.Abnormal deposition of collagen around hepatocytes in Wilson's disease is associated with hepatocyte specific expression of lysyl oxidase and lysyl oxidase like protein-2[J].J Hepatol,2005,43(3):499-507.

[7]Ito H,Akiyama H,Iguchi H,et al.Molecular cloning and biological activity of a novel lysyl oxidase-related gene expressed in cartilage [J].J Biol Chem,2001,276:24023-24029.

[8]Kim MS,Kim SS,Jung ST,et al.Expression and purification of enzymatically active forms of the human lysyl oxidase-like protein 4 [J].J Biol Chem,2003,278:52071-52074.

[9]Hayashi K,Fong KS,Mercier F,et al.Comparative immunocytochemical localization of lysyl oxidase(LOX)and the lysyl oxidase-like(LOXL)proteins:changes in the expression of LOXL during development and growth of mouse tissues[J].J Mol Histol, 2004,35(8-9):845-855.

[10]Csiszar K.Lysyl oxidases:A novel multifunctional amine oxidase family[J].Prog NucleicAcid Res Mol Biol,2001,70:1-32.

[11]Butler E,Hardin J,Benson S.The role of lysyl oxidase and collagen crosslinking during sea urchin development[J].Exp Cell Res,1987, 173:174-182.

[12]Payne SL,Fogelgren B,Hess AR,et al.Lysyl oxidase regulates breast cancer cell migration and adhesion through a hydrogen peroxide-mediated mechanism[J].Cancer Res,2005,65:11426-11429.

[13]Saito H,Papaconstantinou H,Sato H,et al.Regulation of a novel gene encoding a lysyl oxidase-related protein in cellular adhesion and senescence[J].J Biol Chem,1997,272:8157-8160.

[14]Zuber J,Tchernitsa OI,Hinzmann B,et al.A genome-wide survey of RAS transformation targets[J].Nat Genet,2000,24:144-152.

[15]Hough CD,Sherman-Baust CA,Pizer ES,et al.Large-scale serialanalysis of gene expression reveals genes differentially expressed in ovarian cancer[J].Cancer Res,2000,60:6281-6287.

[16]Ono K,Tanaka T,Tsunoda T,et al.Identification by cDNA microarray of genes involved in ovarian carcinogenesis[J].Cancer Res, 2000,60:5007-5011.

[17]Rost T,Pyritz V,Rathcke IO,et al.Reduction of LOX-and LOXL2-mRNA expression in head and neck squamous cell carcinomas[J].Anticancer Res,2003,23:1565-1574.

[18]Jourdan-Le Saux C,Le Saux O,Donlon T,et al.The human lysyl oxidase related gene(LOXL2)maps between markers D8S280 and D8S278 on chromosome 8p 21.2-21.3[J].Genomics,1998,51: 301-307.

[19]Lassus H,Laitinen MP,Anttonen M,et al.Comparison of serous and mucinous ovarian carcinomas:Distinct pattern of allelic loss at distal 8p and expression of transcription factor GATA-4[J].Lab Invest,2001,81:517-526.

[20]Bockmuhl U,Schluns K,Kuchler I,et al.Genetic imbalances with impact on survival in head and neck cancer patients[J].Am J Pathol,2000,157:369-375.

[21]Arai T,Akiyama Y,Yamamura A,et al.Allelotype analysis of early colorectal cancers with lymph node metastasis[J].Int J Cancer, 1998,79:418-423.

[22]Lerebours F,Olschwang S,Thuille B,et al.Deletion mapping of the tumor suppressor locus involved in colorectal cancer on chromosome band 8p21[J].Genes Chromosomes Cancer,1999,25: 147-153.

[23]Du Plessis L,Dietzsch E,Van Gele M,et al.Mapping of novel regions of DNA gain and loss by comparative genomic hybridization in esophageal carcinoma in the Black and Colored populations of SouthAfrica[J].Cancer Res,1999,59:1877-1883.

[24]Hu N,Roth MJ,Polymeropolous M,et al.Identification of novel regions of allelic loss from a genomewide scan of esophageal squamous-cell carcinoma in a high-risk Chinese population[J].Genes Chromosomes Cancer,2000,27:217-228.

[25]Yaremko ML,Kutza C,Lyzak J,et al.Loss of heterozygosity from the short arm of chromosome 8 is associated with invasive behavior in breast cancer[J].Genes Chromosomes Cancer,1996,16: 189-195.

[26]Anbazhagan R,Fujii H,Gabrielson E.Allelic loss of chromosomal arm 8p in breast cancer progression[J].Am J Pathol,1998,152: 815-819.

[27]Peinado H,Del Carmen Iglesias-de la Cruz M,Olmeda D,et al.A molec-Genes,Chromosomes&Cancer DOI 10.1002/gccular role for lysyl oxidase-like 2 enzyme in Snail regulation and tumor progression[J].EMBO J,2005,24:3446-3458.

[28]Akiri G,Sabo E,Dafni H,Vadasz Z,et al.Lysyl oxidase-related protein-1 promotes tumor fibrosis and tumor progression in vivo[J]. Cancer Res,2003,63:1657-1666.

[29]Fong SF,Dietzsch E,Fong KS,et al.Lysyl oxidase-like 2 expression is increased in colon and esophageal tumors and associated with less differentiated colon tumors[J].Genes Chromosomes Cancer,2007,46(7):644-655.

[30]Barker HE,Chang J,Cox TR,et al.LOXL2-Mediated Matrix Remodeling in Metastasis and Mammary Gland Involution[J].Cancer Res,2011,71(5):1561-1572.

[31]Ru¨ckert F,Joensson P,Saeger HD,et al.Functional analysis of LOXL2 in pancreatic carcinoma[J].Int J Colorectal Dis,2010,25 (3):303-311.

[32]Peng L,Ran YL,Hu H,et al.Secreted LOXL2 is a novel therapeutic target that promotes gastric cancer metastasis via the Src/FAK pathway[J].Carcinogenesis,2009,30(10):1660-1669.

[33]高應(yīng)鴻,李天宇,高占峰,等.膽管癌組織中賴氨酰氧化酶樣蛋白-2的表達(dá)及其與EMT的關(guān)系[J].中華普通外科雜志,2008,23 (10):784-787.

[34]Zhan P,Shen XK,Qian Q,et al.Down-regulation of lysyl oxidase-like 2(LOXL2)is associated with disease progression in lung adenocarcinomas[J].Med Oncol,2012,29:648-655

[35]Kiemer AK,Takeuchi K,Quinlan MP.Identification of genes involved in epithelial mesenchymal transition and tumor progression [J].Oncogene,2001,20:6679-6688.

[36]Erler JT,Bennewith KL,Nicolau M,et al.Lysyl oxidase is essential for hypoxia-induced metastasis[J].Nature,2006,440:1222-1226.

[37]Lucero HA,Kagan HM.Lysyl oxidase:And oxidative enzyme and effector of cell function[J].Cell Mol Life Sci,2006,63:2304-2316. [38]Kaneda A,Kaminishi M,Yanagihara K,et al.Identification of silencing of nine genes in gastic cancers[J].Cancer Res,2002,62: 6645-6650.

[39]Lind GE,Thorstensen L,Lovig T,et al.A CpG island hypermethylation profile of primary colorectal carcinomas and colon cancer cell lines[J].Mol Cancer,2004,3:28-39.

[40]Perez-Pomares JM,PhelpsA,Sedmerova M,et al.Experimental studies on the spatiotemporal expression of WT1 and RALDH2 in the embryonic avian heart:A model for the regulation of myocardial and valvuloseptal development by epicardially derived cells(EPDCs)[J]. Dev Biol,2002,247:307-326.

[41]Eferl R,Wagner EF.AP-1:A double edged sword in tumorigenesis [J].Nat Rev Cancer,2003,3:859-868.

[42]Huber MA,Azoitei N,Baumann B,et al.NF-jB is essential for epithelial-mesenchymal transition and metastasis in a model of breast cancer progression[J].J Clin Invest,2004,114:569-581.

R33

A

1003—6350(2014)15—2258—03

10.3969/j.issn.1003-6350.2014.15.0877

2014-01-08)

魏楓林。E-mail：hhyywfl@163.com