朱明明 李占全 崔森
摘要:乳腺癌是發(fā)生在乳腺腺上皮組織的惡性腫瘤,早期癥狀多不明顯,晚期可發(fā)生癌細(xì)胞遠(yuǎn)處轉(zhuǎn)移,出現(xiàn)全身多器官病變,增加臨床治療難度,嚴(yán)重影響患者生活質(zhì)量和生命安全。目前,乳腺癌的發(fā)病機(jī)制尚不明確,研究乳腺癌的發(fā)生、發(fā)展,尤其是轉(zhuǎn)移相關(guān)的調(diào)控機(jī)制對(duì)乳腺癌的治療具有重要意義。近年來(lái)研究表明MMP-9相關(guān)信號(hào)通路與乳腺癌的發(fā)生發(fā)展密切相關(guān)。本文就MMP-9的結(jié)構(gòu)與生物學(xué)功能及其介導(dǎo)的乳腺癌侵襲及轉(zhuǎn)移機(jī)制與預(yù)后作一綜述,以期為臨床治療提供參考。
關(guān)鍵詞:MMP-9;乳腺癌;信號(hào)通路
中圖分類(lèi)號(hào):R737.9? ? ? ? ? ? ? ? ? ? ? ? ? ? ?文獻(xiàn)標(biāo)識(shí)碼:A? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? DOI:10.3969/j.issn.1006-1959.2020.13.007
文章編號(hào):1006-1959(2020)13-0022-04
Mechanism of MMP-9 Signaling Pathway Regulating Breast Cancer Development
ZHU Ming-ming1,2,LI Zhan-quan1,2,CUI Sen1,2
(1.Plateau Medical Research Center,Medical College of Qinghai University,Xining 810001,Qinghai,China;
2.Department of Hematology,the Affiliated Hospital of Qinghai University,Xining 810001,Qinghai,China)
Abstract:Breast cancer is a malignant tumor that occurs in the epithelial tissue of the breast gland. The early symptoms are mostly insignificant. In the late stage, cancer cells can metastasize to a distant location, and there are multiple organ lesions throughout the body. This increases the difficulty of clinical treatment and seriously affects the quality of life and safety of patients. At present, the pathogenesis of breast cancer is not yet clear. It is of great significance to study the occurrence and development of breast cancer, especially the metabolic regulation mechanism for the treatment of breast cancer. Recent studies have shown that MMP-9-related signaling pathways are closely related to the occurrence and development of breast cancer. This article reviews the structure and biological function of MMP-9 and the mechanisms and prognosis of breast cancer invasion and metastasis mediated by it, in order to provide a reference for clinical treatment.
Key words:MMP-9;Breast cancer;Signaling pathway
乳腺癌(breast cancer)作為目前全球發(fā)病率最高的腫瘤之一,其發(fā)病率逐年增高,嚴(yán)重威脅女性健康及生活質(zhì)量。乳腺癌晚期易發(fā)生侵襲或轉(zhuǎn)移,是乳腺癌治療的難題[1]。目前,關(guān)于乳腺癌轉(zhuǎn)移機(jī)制的尚未達(dá)成統(tǒng)一共識(shí),近年來(lái)研究表明,腫瘤細(xì)胞周?chē)腅CM降解是癌細(xì)胞發(fā)生浸潤(rùn)的必要步驟,而MMPs是導(dǎo)致細(xì)胞外基質(zhì)(extracellular matrix,ECM)包括基底膜降解的重要酶類(lèi)之一。有研究表明[1-3],MMP-9的多信號(hào)通路與乳腺癌侵襲和轉(zhuǎn)移密切相關(guān),其可通過(guò)降解ECM,破壞細(xì)胞粘附分子的正常組織結(jié)構(gòu),聯(lián)合其它相關(guān)的酶降解血管周?chē)幕|(zhì),誘導(dǎo)腫瘤轉(zhuǎn)移。本文就MMP-9的結(jié)構(gòu)與生物學(xué)功能及其與乳腺癌侵襲與轉(zhuǎn)移機(jī)制作一綜述,以期為我國(guó)乳腺癌的研究提供借鑒和參考,為其進(jìn)一步干預(yù)治療提供理論依據(jù)。
1 MMP-9的結(jié)構(gòu)與生物學(xué)功能
基質(zhì)金屬蛋白酶(matrix metal proteinases,MMPs)是一組具有許多共同生化性質(zhì)的可降解細(xì)胞外基質(zhì)的鋅依賴蛋白內(nèi)切酶家族,近年來(lái)研究較多的是MMP-9。MMP-9屬于明膠酶類(lèi)B,又稱(chēng)Ⅳ型膠原酶,是基質(zhì)金屬蛋白酶家族中的重要成員,其分子質(zhì)量是92 kDa,分別由催化區(qū)、前肽區(qū)和C-結(jié)構(gòu)域組成。同時(shí),MMPs也是一組含有Zn2+能夠降解絕大多數(shù)ECM的肽鏈內(nèi)切酶,通常在中性條件下發(fā)揮活性,有Ca2+參與時(shí),其活性最大。MMP-9激活后可能夠特異地水解ECM和基底膜(basal membrane,BM)的化學(xué)成分Ⅳ型膠原、Ⅴ型膠原、黏連蛋白等,可由中性粒細(xì)胞、血管內(nèi)皮細(xì)胞、單核巨噬細(xì)胞、平滑肌細(xì)胞、成纖維細(xì)胞等分泌[4,5]。MMP-9主要作用是在生理pH值下,在金屬鋅離子作用下,結(jié)合基底膜的大分子物質(zhì)并破壞明膠,從而參與細(xì)胞外基質(zhì)的降解與重建。在正常生理情況下,其能夠切斷細(xì)胞外基質(zhì)成分,調(diào)節(jié)細(xì)胞間粘附并作用于細(xì)胞外成分或其它蛋白成分而啟動(dòng)潛在生物學(xué)功能,直接或間接參與胚胎發(fā)育、組織重塑、創(chuàng)傷愈合和血管增生等生理學(xué)過(guò)程。同時(shí),MMP-9激活后可降解基底膜的Ⅳ型膠原蛋白,刺激腫瘤內(nèi)部新生血管形成,增加腫瘤的營(yíng)養(yǎng)供給;同時(shí),其可增加腫瘤細(xì)胞間及與宿主細(xì)胞間的黏附方便轉(zhuǎn)移,導(dǎo)致乳腺癌的進(jìn)一步演變進(jìn)化,發(fā)生侵襲和轉(zhuǎn)移[4-7]。
2 MMP-9介導(dǎo)的乳腺癌侵襲及轉(zhuǎn)移機(jī)制
有研究表明[11],MMP-9對(duì)于乳腺癌進(jìn)展是至關(guān)重要的,該因子從多方面、多層次參與乳腺癌進(jìn)展的機(jī)制及通路調(diào)控,主要由其生物學(xué)特性決定:一方面,由于Ⅳ型膠原蛋白是血管基底膜的主要成分,MMP-9可通過(guò)降解Ⅳ型膠原蛋白,造成血管基底膜結(jié)構(gòu)破壞,進(jìn)而破壞腫瘤周?chē)M織,以增加腫瘤侵犯的風(fēng)險(xiǎn),這通常是入侵和轉(zhuǎn)移的初步步驟;另一方面,該因子另一生物學(xué)功能是促進(jìn)血管生成,進(jìn)一步加重乳腺癌的血行轉(zhuǎn)移,從而導(dǎo)致腫瘤的進(jìn)展[8-10]。
2.1 Ets-1? Ets轉(zhuǎn)錄因子家族含有一個(gè)高度保守的DNA結(jié)合結(jié)構(gòu)域,可以識(shí)別特異性的螺旋-轉(zhuǎn)角-螺旋基序DNA結(jié)合元件,而Ets-1作為Ets轉(zhuǎn)錄因子家族的重要成員,又稱(chēng)為Ets結(jié)合位點(diǎn),以GGAA/T共有序列為核心模體,定位于人類(lèi)11號(hào)染色體,主要表現(xiàn)為轉(zhuǎn)錄激活因子或阻遏,并在腫瘤發(fā)生過(guò)程中起著至關(guān)重要的作用[12,13]。此外,Ets-1參與腫瘤細(xì)胞的分化、增殖、遷移和凋亡等不同的生理過(guò)程,研究發(fā)現(xiàn)[14,15],Ets-1與乳腺癌腫瘤進(jìn)展密切相關(guān),其通過(guò)調(diào)控下游靶基因基質(zhì)金屬蛋白酶(MMPs)的過(guò)表達(dá),從而引起癌癥的多種侵襲性病理改變。也有研究表明[16],Ets-1轉(zhuǎn)錄因子直接結(jié)合MMP-9啟動(dòng)子發(fā)揮致癌作用,在乳腺癌細(xì)胞系中轉(zhuǎn)染Ets-1 siRNA可導(dǎo)致Ets-1和MMP-9下調(diào),Ets-1被敲除后反而增加了乳腺癌細(xì)胞侵襲性。此外,該研究也指出MMP-9基因依賴Ets-1調(diào)控,主要是由于MMP-9基因啟動(dòng)子具有一個(gè)與Ets-1轉(zhuǎn)錄因子結(jié)合的位點(diǎn),該位點(diǎn)可能與EMT標(biāo)記一起直接反激活Ets-1,進(jìn)而導(dǎo)致癌細(xì)胞侵襲性和轉(zhuǎn)移性增強(qiáng),最終參與了乳腺癌的侵襲和轉(zhuǎn)移有關(guān)??傊@些發(fā)現(xiàn)提示了Ets-1依賴于MMP-9基因的調(diào)控作用,對(duì)乳腺癌的發(fā)生發(fā)展有重要影響,且其與MMP-9的生物學(xué)功能有關(guān),通過(guò)促進(jìn)血管生成及基膜降解,進(jìn)一步加重腫瘤的侵襲。
2.2 TGF-β/SMAD信號(hào)通路? 轉(zhuǎn)化生長(zhǎng)因子β(transforming growth factor,TGF-β)作為一種多功能的細(xì)胞因子超家族,TGF-β的活化為其發(fā)揮作用的首要前提,該因子的激活由許多元素誘導(dǎo),包括pH、活性氧、血小板反應(yīng)蛋白-1、蛋白酶和金屬蛋白酶。已知MMP-9和MMP-2可通過(guò)裂解潛在的TGF-β的結(jié)構(gòu),進(jìn)而促進(jìn)TGF-β活化,而活化的TGF-β與其他因子形成絲氨酸/蘇氨酸激酶復(fù)合物,該復(fù)合物與TGF-β受體結(jié)合,進(jìn)一步激活下游底物和蛋白的表達(dá),誘導(dǎo)轉(zhuǎn)錄各種靶基因參與細(xì)胞分化、增殖,該調(diào)控過(guò)程與SMAD和DAXX途徑的密切相關(guān)[17]。有研究表明[18],由于TGF-β/SMAD信號(hào)傳導(dǎo)的激活,引起TGF-β以及SMAD4,SMAD2/3和磷酸化SMAD2的水平均明顯增加,進(jìn)一步激活MMP-9過(guò)表達(dá),其表達(dá)水平與乳腺惡性腫瘤細(xì)胞的惡性程度呈正比;且在乳腺癌組織中發(fā)現(xiàn)MMP-9和TGF-β強(qiáng)信號(hào),并顯著增加癌細(xì)胞惡性程度,包括癌細(xì)胞集落形成和遷移。Dong H等[19]研究表明,在應(yīng)用MMP-9和TGF-β特異性抑制劑后,可明顯抑制SMAD信號(hào)的激活及MMP-9的過(guò)表達(dá),顯著降低了乳腺癌細(xì)胞系的侵襲性??傊橄侔┘?xì)胞的轉(zhuǎn)移和侵襲與MMP-9的表達(dá)密切相關(guān),推測(cè)其主要與MMP-9的生物學(xué)功能密切相關(guān),一方面MMP-9過(guò)表達(dá)促進(jìn)血管生成,導(dǎo)致乳腺癌的血行播散增加,另一方面,MMP-9過(guò)表達(dá)直接導(dǎo)致基膜的降解增加,進(jìn)一步加重癌細(xì)胞向周?chē)M織的破壞和侵犯。
2.3 PI3K/AKT/NFKB/MMP-9信號(hào)通路? PI3K/AKT是腫瘤侵襲的主要途徑[20]。在乳腺癌中,PI3K/AKT通路發(fā)生磷酸化后通過(guò)核易位和亞基轉(zhuǎn)錄兩種形式激活NFκB的表達(dá),NFκB進(jìn)一步促進(jìn)介導(dǎo)MMP-9的激活,促進(jìn)癌細(xì)胞粘附、分化和生長(zhǎng),最終導(dǎo)致腫瘤細(xì)胞侵襲、轉(zhuǎn)移[21,22]。此外,MMP-9啟動(dòng)子區(qū)域具有順式調(diào)節(jié)元件,該位點(diǎn)可以與NFκB結(jié)合,負(fù)反饋調(diào)控NFκB的激活,因此,NFκB介導(dǎo)MMP-9與乳腺癌發(fā)展密切相關(guān)。有研究表明[22],經(jīng)抑制PI3K/AKT磷酸化處理后,NFκB活化受抑,其介導(dǎo)的MMP-9表達(dá)下降,最終抑制MMP-9介導(dǎo)的MDA-MB-231人乳腺癌細(xì)胞侵襲性增強(qiáng),最終增加乳腺癌的侵襲和轉(zhuǎn)移。目前研究認(rèn)為,MMP-9經(jīng)PI3K/AKT/NFκB信號(hào)通路調(diào)控高表達(dá)與增加乳腺癌細(xì)胞的轉(zhuǎn)移和侵襲。
2.4 EGFR/STAT3/Akt/MMP-9信號(hào)通路? 表皮生長(zhǎng)因子受體(epidermal growth factor receptor,EGFR),是一種跨膜糖蛋白,通過(guò)與表皮生長(zhǎng)因子(EGF)形成激酶活性同源二聚體或異二聚體,進(jìn)一步促進(jìn)EGFR磷酸化,誘導(dǎo)下游信號(hào)轉(zhuǎn)導(dǎo)和轉(zhuǎn)錄激活子(signal transducer and activator of transcription3,STAT3)發(fā)生磷酸化,進(jìn)一步激活A(yù)KT磷酸化,激發(fā)的下游靶基因MMP-9呈高表達(dá),導(dǎo)致促進(jìn)細(xì)胞增殖,從而加速侵襲和血管生成[23]。有研究表明[24],阻斷EGFR磷酸化后,STAT3磷酸化受到抑制,磷酸化的AKT水平下降,其下游MMP-9表達(dá)降低,導(dǎo)致乳腺癌細(xì)胞侵襲性及轉(zhuǎn)移受抑。由此可見(jiàn),EGFR/STAT3/AKT/MMP-9信號(hào)通路參與了乳腺癌進(jìn)展的過(guò)程。
3 MMP-9 與乳腺癌預(yù)后
MMP-9在腫瘤中起發(fā)揮重要作用,其過(guò)度表達(dá)促進(jìn)腫瘤進(jìn)展和轉(zhuǎn)移,與乳腺癌的預(yù)后密切相關(guān)[25]。有研究表明[26,27],MMP-9的高表達(dá)與具有侵襲性和轉(zhuǎn)移性乳腺癌發(fā)生發(fā)展密切相關(guān),是乳腺癌預(yù)后不良基因之一,并通過(guò)入侵、誘導(dǎo)血管生成和免疫調(diào)節(jié)與腫瘤相關(guān)的微環(huán)境,以增加乳腺癌的侵襲性、轉(zhuǎn)移和預(yù)后不良[28]。此外,血清和尿液中MMP-9高表達(dá)與其在乳腺癌轉(zhuǎn)移和預(yù)后中的關(guān)聯(lián)極為密切[29]。研究提出[30,31],MMP-9通過(guò)破壞基底結(jié)構(gòu)的能力膜,脫離原發(fā)腫瘤,侵入局部組織,進(jìn)而參與乳腺癌的發(fā)生發(fā)展;且其與淋巴結(jié)轉(zhuǎn)移、組織學(xué)分級(jí)和遠(yuǎn)處轉(zhuǎn)移密切相關(guān),在淋巴結(jié)陰性的乳腺癌患者中具有重要的預(yù)后價(jià)值。
4總結(jié)
MMP-9作為乳腺癌重要基質(zhì)金屬蛋白酶,可通過(guò)參與并調(diào)控多信號(hào)通路增加乳腺癌的侵襲與轉(zhuǎn)移。在腫瘤局部缺氧條件下,MMP-9參與并促進(jìn)血管生成,增加腫瘤的血行播散及轉(zhuǎn)移;在低氧腫瘤細(xì)胞培養(yǎng)過(guò)程中,該因子的分泌增加引起微血管增生,進(jìn)一步促進(jìn)腫瘤的侵襲。目前對(duì)于MMP-9在乳腺癌侵襲與轉(zhuǎn)移的機(jī)制研究有限,尚未形成統(tǒng)一定論,而了解MMP-9在乳腺癌中具體調(diào)控機(jī)制,有利于對(duì)乳腺癌臨床預(yù)后評(píng)估指標(biāo),并有助乳腺癌患者的靶向治療和生存率提高帶來(lái)希望。
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收稿日期:2020-04-09;修回日期:2020-04-24
編輯/王海靜
基金項(xiàng)目:1.青海省衛(wèi)生計(jì)生委一般指導(dǎo)性課題項(xiàng)目(編號(hào):2018-wjzdx-121);2.青海省科技廳應(yīng)用基礎(chǔ)研究項(xiàng)目(編號(hào):2019-ZJ-7081)
作者簡(jiǎn)介:朱明明(1989.7-),女,河南禹州人,博士研究生,住院醫(yī)師,主要從事血液病、腫瘤性疾病的相關(guān)研究
通訊作者:李占全(1962.6-),男,青海西寧人,碩士,博士生導(dǎo)師,主任醫(yī)師,主要從事高原病、血液腫瘤病的相關(guān)研究