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TNFR1:癌癥雙重作用分子,或可作為新型冠狀病毒(COVID-19)治療靶點(diǎn)

日期:2021-02-04 15:18:42

2021年1月7日,發(fā)表在Cancer Research雜志上的一項(xiàng)研究表明TNFR1介導(dǎo)的細(xì)胞凋亡和壞死與白血病相關(guān) [1]。作為一個(gè)熱門(mén)的生物靶點(diǎn),TNFR1具有雙重作用,大量研究證實(shí)TNFR1的表達(dá),能促進(jìn)或抑制腫瘤細(xì)胞的凋亡,同時(shí)參與自身免疫性疾病。更引人關(guān)注的是,有研究數(shù)據(jù)顯示,TNFR1抑制劑有望為成為治療COVID-19候選方案。但TNFR1復(fù)雜的生物學(xué)功能,使得TNFR1靶向藥物的研發(fā)面臨重重挑戰(zhàn)。去年2020年9月,全球頂級(jí)研究學(xué)者M(jìn)arc Feldmann和Michael Shepard發(fā)起了一個(gè)項(xiàng)目,研發(fā)TNFR1特效抑制劑,該抑制劑可阻斷TNFR1,用于急性炎癥和多種癌癥治療。那么TNFR1是什么?它介導(dǎo)的信號(hào)通路是怎樣的?TNFR1為何與COVID-19有關(guān)?靶向TNFR1藥物研發(fā)的潛在價(jià)值如何?


1. TNFR1結(jié)構(gòu)和功能

TNFR1屬于腫瘤壞死因子(TNF)受體超家族成員之一,又稱(chēng)TNFRSF1A,CD120a或p55,是分子量為55 ku的I型跨膜糖蛋白 [2]。TNFR1包含胞外區(qū)、跨膜區(qū)和胞內(nèi)區(qū)三個(gè)部分。胞外結(jié)構(gòu)域含182個(gè)氨基酸,由4個(gè)富含半胱氨酸的結(jié)構(gòu)域(CRD1-CRD2-CRD3-CRD4)組成??缒^(qū)位于細(xì)胞外結(jié)構(gòu)域和細(xì)胞內(nèi)結(jié)構(gòu)域之間,長(zhǎng)約22個(gè)氨基酸(殘基183-205個(gè))。胞內(nèi)結(jié)構(gòu)域長(zhǎng)約223個(gè)氨基酸。其中,在胞外結(jié)構(gòu)域有3個(gè)潛在的N-糖基化位點(diǎn),其功能主要是與三聚體形式的TNF結(jié)合。N末端殘基是亮氨酸。C末端含有80個(gè)保守氨基酸序列所構(gòu)成的死亡結(jié)構(gòu)域(Death domain,DD),是轉(zhuǎn)導(dǎo)細(xì)胞死亡信號(hào)所必需的,且TNFR1的很多功能都與此結(jié)構(gòu)域有關(guān)(圖1[3, 4]。

TNFR1的蛋白質(zhì)結(jié)構(gòu)

圖1. TNFR1的蛋白質(zhì)結(jié)構(gòu)

*本圖來(lái)源于ResearchGate 出版物[4]

TNFR1廣泛分布于正常細(xì)胞膜表面,也存在于多種腫瘤細(xì)胞表面 [5]。TNFR1主要介導(dǎo)凋亡信號(hào),引起細(xì)胞凋亡,在抗腫瘤和抗病毒感染中發(fā)揮重要作用,同時(shí)也參與自身免疫性疾病,是誘導(dǎo)類(lèi)風(fēng)濕關(guān)節(jié)炎 [6]和系統(tǒng)性紅斑性狼瘡(SLE)關(guān)鍵因子 [7]。由于TNFR1參與到復(fù)雜的生物學(xué)過(guò)程,使得TNFR1精確的功能意義尚不清楚。


2. TNFR1的配體TNF

TNF是三個(gè)相同的單體亞單位組成的致密三聚體 [8]。TNF包含TNF-α和TNF-β兩種,屬于Ⅱ型膜蛋白。巨噬細(xì)胞分泌出來(lái)的TNF,即TNF-α。T淋巴細(xì)胞分泌的淋巴毒素,即TNF-β [9]。TNF總活性中,TNF-α的占比為70%~95%,所以,平時(shí)所指的TNF基本為T(mén)NF-α [10]

TNFα在體內(nèi)又以?xún)煞N形式存在,分別是跨膜型TNF-α(tmTNF-α)和可溶型TNF-α(sTNF-α)。tmTNF-α為sTNF-α的前體形式,通過(guò)TNF轉(zhuǎn)化酶(TACE,又稱(chēng)ADAM17)的剪切,分泌到細(xì)胞外,形成可溶性sTNF-α(圖2[11]。

tmTNF-α轉(zhuǎn)化為sTNF-α過(guò)程

圖2. tmTNF-α轉(zhuǎn)化為sTNF-α過(guò)程

*本圖來(lái)源于Ochsner Journal 出版物[11]。

兩型TNFα與受體(TNFR1或TNFR2)相互作用而誘導(dǎo)生物效應(yīng),但因TNFR2缺乏死亡結(jié)構(gòu)域,TNFR1便成為介導(dǎo)TNF-α活動(dòng)的主要受體 [12, 13, 14]。TNFR1與TNF-α的胞外段結(jié)合后而引起胞內(nèi)段構(gòu)像的改變,使TNFR1激活 [15]。


3. TNFR1介導(dǎo)的信號(hào)通路

3.1 TNFR1-sTNF-α信號(hào)通路

TNFR1與sTNF-α結(jié)合,啟動(dòng)的下游信號(hào)通路已經(jīng)非常明確。TNFR1作為sTNF-α的主要受體,其胞內(nèi)段含有DD(death domain,死亡結(jié)構(gòu)域)。在無(wú)sTNF-α刺激時(shí),TNFR1的DD被死亡結(jié)構(gòu)域的沉默子蛋白(SODD)占據(jù),阻斷TNFR相關(guān)死亡結(jié)構(gòu)域蛋白(TRADD)與TNFR1的銜接,抑制TNFR1信號(hào)通路 [16]。當(dāng)sTNF-α刺激后,sTNF-α與TNFR1結(jié)合,SODD從TNFR1的DD結(jié)構(gòu)域脫落,TNFR1通過(guò)其暴露的DD結(jié)構(gòu)域募集TRADD,TNFR1信號(hào)通路激活(圖3[17]。

當(dāng)TNFR1/sTNF-α激活后,TRADD可以募集受體相關(guān)蛋白-1(RIP1)以及受體相關(guān)因子2(TRAF2),在胞膜上形成可激活NF-κB的信號(hào)復(fù)合物I(TNFR1-TRADD-RIP1-TRAF2),促進(jìn)靶基因轉(zhuǎn)錄,抵抗凋亡,促進(jìn)生存(圖3[4, 17]

此外,TNFR1通過(guò)網(wǎng)格蛋白(clathrin)發(fā)生內(nèi)化(internalization),內(nèi)化后的TNFR1通過(guò)TRADD的DD和FAS相關(guān)結(jié)構(gòu)死亡蛋白結(jié)構(gòu)域蛋白(FADD)的DD結(jié)合,F(xiàn)ADD可通過(guò)其死亡效應(yīng)DED結(jié)構(gòu)域與caspase-8的DED結(jié)合,在胞漿內(nèi)形成信號(hào)復(fù)合物II,即DISC(death-inducing signalling complex,死亡誘導(dǎo)信號(hào)復(fù)合體),激活caspase-8,導(dǎo)致細(xì)胞凋亡或程序化壞死(necroptosis)(圖3[4, 17]

TNFR1-sTNF-α信號(hào)通路

圖3. TNFR1-sTNF-α信號(hào)通路

*本圖來(lái)源于Cytokine 出版物[17]。

3.2 TNFR1-tmTNF-α信號(hào)通路

關(guān)于TNFR1-tmTNF-α的信號(hào)通路目前的研究機(jī)制尚不明確,有研究發(fā)現(xiàn),TNFR1-tmTNF-α信號(hào)通路不同于TNFR1-sTNF-α,后者可介導(dǎo)生存或凋亡兩種截然不同的信號(hào)途徑。而TNFR1-tmTNF-α僅能介導(dǎo)細(xì)胞的凋亡,并不能激活NF-κB。雖然TNFR1與兩型TNF結(jié)合都能引起凋亡,但兩者的信號(hào)轉(zhuǎn)導(dǎo)機(jī)制不同,細(xì)胞定位和影響因素也不同 [4]。


4. TNFR1在腫瘤疾病中的作用

近年來(lái),越來(lái)越多的研究者發(fā)現(xiàn),TNFR1廣泛參與各種疾病的病理生理過(guò)程,尤其是在腫瘤中,其調(diào)控作用引起人們的重視。大量的數(shù)據(jù)表明,TNFR1在不同癌細(xì)胞中可以決定細(xì)胞不同的命運(yùn)。雖然TNFR1包含死亡結(jié)構(gòu)域,但通過(guò)不同的信號(hào)傳導(dǎo)通路,TNFR1也可發(fā)揮促炎和致癌作用。所以TNFR1在癌癥中,不總是發(fā)揮其應(yīng)有的促凋亡生物學(xué)效應(yīng)。

在惡性星形膠質(zhì)瘤中,TNFR1和TNF結(jié)合,激活NF-κB通路,抑制腫瘤細(xì)胞的凋亡,研究提示TNFR1可能參與低度惡性星形細(xì)胞瘤的形成和惡性星形細(xì)胞瘤的發(fā)展 [18]。另有研究發(fā)現(xiàn),在胃癌細(xì)胞中,TNFR1的表達(dá)水平與胃癌細(xì)胞的分化程度有關(guān) [19];在大腸癌中,高表達(dá)TNFR1的病人存活率較高 [20]。最近一項(xiàng)研究發(fā)現(xiàn),在腎透明細(xì)胞癌中,TNFR1表達(dá),促進(jìn)腫瘤樣變,誘導(dǎo)耐藥 [21]。而在一項(xiàng)小鼠模型實(shí)驗(yàn)中,研究人員評(píng)估了TNFR1在肝癌中的作用,數(shù)據(jù)顯示TNFR1的缺失能顯著降低小鼠腫瘤發(fā)生率,說(shuō)明TNFR1介導(dǎo)的信號(hào)通路促進(jìn)肝癌發(fā)生 [22]

TNFR1參與到一個(gè)極其復(fù)雜的生物學(xué)過(guò)程,其對(duì)疾病的作用往往受到很多不可控因素(比如,患者個(gè)體化差異)的影響。目前對(duì)于TNFR1在人類(lèi)全身各系統(tǒng)腫瘤中的表達(dá)研究還不是很深入,在造血系統(tǒng)、神經(jīng)系統(tǒng)、泌尿生殖系統(tǒng)、消化系統(tǒng)以及頭頸部的惡性腫瘤中,TNFR1均表達(dá)增強(qiáng),其究竟是介導(dǎo)細(xì)胞增殖還是凋亡,需要更多的研究進(jìn)一步闡明。因此,TNFR1抗體或者抗TNFR1抗體在腫瘤治療中的意義重大。


5. TNFR1在COVID-19治療中的潛在價(jià)值

自從新型冠狀病毒(COVID-19)大流行開(kāi)始以來(lái),新型冠狀病毒(COVID-19)已在地球上幾乎每個(gè)國(guó)家被發(fā)現(xiàn),全球超過(guò)200萬(wàn)人死亡。值得注意的是,在COVID-19患者中,研究者們發(fā)現(xiàn)了高水平的炎癥和促炎性細(xì)胞因子,其中包括TNF,前面提到,TNF的功能主要通過(guò)TNFR1介導(dǎo),所以單獨(dú)阻斷TNFR1來(lái)保持免疫系統(tǒng)功能,成為研究者們最為理想的途徑。盡管目前市場(chǎng)上尚無(wú)抑制TNFR1的抗體藥物,但令人興奮的是,一項(xiàng)由葛蘭素史克(GSK)公司研發(fā)的抗TNFR1藥物(GSK-2862277)已進(jìn)入臨床二期,用于急性肺損傷。

事實(shí)上,制藥工業(yè)界和學(xué)術(shù)界為治療COVID-19正在做前所未有的努力中,強(qiáng)生、賽諾菲、輝瑞、默克等全球性公司正在開(kāi)發(fā)近200種治療藥物,世界各國(guó)政府正投入巨額資金用于藥物的研發(fā)。不斷出現(xiàn)的市場(chǎng)需求,加上有機(jī)會(huì)解決人類(lèi)最近記憶中最大的醫(yī)學(xué)挑戰(zhàn)之一-COVID-19,這讓全球的醫(yī)藥企業(yè)都斗志激昂。盡管要真正了解COVID-19,還有很長(zhǎng)的路要走,但是我們知道炎癥是其中的重要組成部分,因此TNFR1抑制劑有望成為治療冠狀病毒患者的候選藥物。


TNFR1蛋白

Recombinant Human Tumor necrosis factor receptor superfamily member 1A(TNFRSF1A),partial (Active) (Code: CSB-MP023977HU1)

High Purity Validated by SDS-PAGE
CSB-MP023977HU1 SDS-PAGE

(Tris-Glycine gel) Discontinuous SDS-PAGE (reduced) with 5% enrichment gel and 15% separation gel.

Excellent Bioactivity Validated by Functional ELISA
High Purity Validated of CSB-MP023977HU1

Immobilized TNF-α (CSB-YP023955HU) at 5 μg/ml can bind human TNFR1, the EC50 is 7.799-10.90 ng/ml.

Excellent Bioactivity Validated by Functional ELISA
High Purity Validated of CSB-MP023977HU1

Immobilized LTA (CSB-MP013218HU) at 5 μg/ml can bind human TNFR1, the EC50 is 4.409-6.797 ng/ml.


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