鄭 航，孫英杰，張 頻，丁 鏟

（1.吉林農(nóng)業(yè)大學(xué)動(dòng)物科學(xué)技術(shù)學(xué)院，長(zhǎng)春 130118；2.中國(guó)農(nóng)業(yè)科學(xué)院上海獸醫(yī)研究所，上海 200241；3. 山東農(nóng)業(yè)大學(xué)動(dòng)物科技學(xué)院，泰安 271018）

MAVS介導(dǎo)的抗病毒天然免疫信號(hào)通路的調(diào)控

鄭 航1，孫英杰2，張 頻1，丁 鏟2

（1.吉林農(nóng)業(yè)大學(xué)動(dòng)物科學(xué)技術(shù)學(xué)院，長(zhǎng)春 130118；2.中國(guó)農(nóng)業(yè)科學(xué)院上海獸醫(yī)研究所，上海 200241；3. 山東農(nóng)業(yè)大學(xué)動(dòng)物科技學(xué)院，泰安 271018）

先天性免疫通路作為抵御入侵的病原微生物第一道屏障，在宿主抗病毒反應(yīng)中發(fā)揮重要的作用。細(xì)胞質(zhì)中最重要的識(shí)別病毒RNA的模式識(shí)別受體是維甲酸誘導(dǎo)基因蛋白I和黑色素瘤分化相關(guān)基因5，它們有著相同的下游信號(hào)接頭分子線粒體抗病毒信號(hào)蛋白（mitochondrial antiviral-signaling protein, MAVS），MAVS在介導(dǎo)的先天性免疫中起中樞作用。MAVS介導(dǎo)的信號(hào)通路的激活是重要的抗病毒反應(yīng)，但在長(zhǎng)期的共存過(guò)程中，病毒進(jìn)化出一系列拮抗MAVS的機(jī)制。同時(shí)，在靜息狀態(tài)下，為了防止過(guò)度免疫反應(yīng)，細(xì)胞還具備一系列調(diào)控MAVS的機(jī)制。MAVS的精細(xì)調(diào)控對(duì)于行使細(xì)胞功能和發(fā)揮抗病毒反應(yīng)至關(guān)重要。本文簡(jiǎn)單介紹了MAVS的結(jié)構(gòu)和功能，總結(jié)了細(xì)胞對(duì)MAVS的轉(zhuǎn)錄和翻譯后調(diào)控，最后闡述了病毒如何通過(guò)調(diào)控MAVS拮抗宿主先天性免疫，為細(xì)胞的免疫調(diào)節(jié)和控制病毒感染提供新的思路。

天然免疫；線粒體抗病毒信號(hào)蛋白；病原體；宿主

病毒感染細(xì)胞能夠激活一系列先天性抗病毒反應(yīng)，其中最重要的一種先天性抗病毒機(jī)制是通過(guò)模式識(shí)別受體（pattern recognition recetproreceptor，PRRs）識(shí)別病毒從而誘導(dǎo)產(chǎn)生干擾素（interferon，IFN）和促炎性因子（proinflammatory cytokines），抑制病毒復(fù)制。而在所有保守的模式識(shí)別受體中，維甲酸誘導(dǎo)基因蛋白I（retinoic acid-inducible gene 1，RIG-I）和黑色素瘤分化相關(guān)基因5（melanoma differentiation-associated protein 5，MDA5）是最重要的細(xì)胞質(zhì)模式識(shí)別受體，在病毒感染時(shí)識(shí)別病毒RNA，激活下游一系列抗病毒信號(hào)通路，誘導(dǎo)表達(dá)I型干擾素和其他的促炎因子[1,2]。RIG-I和MDA5是相似的兩種受體，識(shí)別不同種類的病毒RNA，它們有著相同的下游信號(hào)接頭分子線粒體抗病毒信號(hào)蛋白（Mitochondrial antiviral-signaling protein，MAVS,又稱IPS-1、VISA、CARDIF）[3,4]。RIG-I、MDA5通過(guò)N端串聯(lián)的caspase招募結(jié)構(gòu)域（amino-terminal caspase recruitment domain，CARD）與MAVS的N端 CARD結(jié)構(gòu)域互作，激活下游NF-кB（nuclear factor κB）和IRF3/7（interferon regulatory factors 3/7）相關(guān)信號(hào)通路，并誘導(dǎo)干擾素的表達(dá)，參與先天性抗病毒反應(yīng)[5,6]。MAVS在介導(dǎo)的先天性免疫中起中樞作用，因此MAVS介導(dǎo)的信號(hào)通路的激活是重要的抗病毒反應(yīng)，但在長(zhǎng)期的共存過(guò)程中，病毒有了一系列拮抗MAVS的機(jī)制。同時(shí)，在靜息狀態(tài)下，為了防止過(guò)度免疫反應(yīng)，細(xì)胞還具備一系列調(diào)控MAVS的機(jī)制。MAVS的精細(xì)調(diào)控對(duì)于行使細(xì)胞功能和發(fā)揮抗病毒反應(yīng)至關(guān)重要[7]。

1 MAVS的結(jié)構(gòu)和功能

M A V S是由細(xì)胞核基因組編碼的，并在不同組織和細(xì)胞中均有表達(dá)的蛋白[5]。MAVS由N端的C A R D結(jié)構(gòu)域，富含脯氨酸結(jié)構(gòu)域（proline-rich domain，PRD）和C端的跨膜結(jié)構(gòu)域 （transmembrane domain，TM）組成[8]。MAVS在所介導(dǎo)的先天性抗病毒反應(yīng)中起中樞性的作用，以RIG-I信號(hào)通路為例，E3泛素連接酶Riplet和TRIM25在其識(shí)別RNA和激活的過(guò)程中發(fā)揮關(guān)鍵作用，RIG-I被Riplet和TRIM25（tripartite motifcontaining protein 25）介導(dǎo)的K63泛素化修飾后發(fā)生活化，RIG-I多聚化后和TRIM25及分子伴侶14-3-3ε形成復(fù)合物，這種復(fù)合物被稱之為“轉(zhuǎn)位子（translocon）”，轉(zhuǎn)位子從細(xì)胞質(zhì)轉(zhuǎn)運(yùn)至細(xì)胞內(nèi)膜，例如線粒體相關(guān)膜（mitochondrion-associated membrane, MAM）和MAVS結(jié)合[9]。MAVS的N端的CARD區(qū)域與胞質(zhì)中與RIG-I的2CARD結(jié)構(gòu)域結(jié)合，隨后激活下游的兩種細(xì)胞質(zhì)蛋白激酶復(fù)合物，一種包括“非經(jīng)典”IKK-相關(guān)激酶TBK1（TANK-binding kinase 1）或IKK-i/ε（inducible I B kinase）和一系列接頭蛋白例如TANK（TRAF family member associated NF- B activator）、NAP1（NAK-associated protein 1）和NEMO（NF- B Essential Modulator）。這種TBK1復(fù)合物負(fù)責(zé)激活轉(zhuǎn)錄因子IRF3和IRF7的磷酸化和二聚化，IRF3和IRF7轉(zhuǎn)位至細(xì)胞核中，與干擾素刺激反應(yīng)元件（IFN-stimulated response elements，ISREs）結(jié)合，誘導(dǎo)I型IFN基因和一系列干擾素誘導(dǎo)基因（ISG）的表達(dá)。另一種激酶復(fù)合物包括IKKa、IKKb和NEMO，這種IKK復(fù)合物激活NF-κB，促進(jìn)下游促炎性細(xì)胞因子的表達(dá)，參與先天性抗病毒反應(yīng)[5,10]。

MAVS是經(jīng)典的“尾部錨定”膜蛋白，其C端的跨膜結(jié)構(gòu)域（TM）使MAVS錨定在許多細(xì)胞器膜表面，例如線粒體、過(guò)氧化物酶體以及內(nèi)質(zhì)網(wǎng)的亞結(jié)構(gòu)域（MAM）[6]。MAVS不同亞細(xì)胞定位的具體機(jī)制還未知，據(jù)推測(cè)MAVS可能通過(guò)識(shí)別膜上特定的脂質(zhì)或蛋白而錨定在不同的細(xì)胞器膜上，發(fā)揮其抗病毒功能。MAVS的這種膜定位特性對(duì)其發(fā)揮抗病毒活性是必須的，去除MAVS跨膜結(jié)構(gòu)域使其喪失抗病毒活性[6]。在表達(dá)只含有CARD結(jié)構(gòu)域和TM結(jié)構(gòu)域的MAVS突變體（miniMAVS），仍然可以引起MAVS介導(dǎo)的信號(hào)傳導(dǎo)，miniMAVS仍可以保持MAVS線粒體定位、寡聚化、CARD結(jié)構(gòu)域的吸附的功能特性，這種MAVS的解螺旋酶域和C末端結(jié)合域（CTD）是識(shí)別病毒RNA，激活下游信號(hào)通路的必需結(jié)構(gòu)[5]。

2 MAVS的轉(zhuǎn)錄和翻譯后調(diào)控

2.1 MAVS的轉(zhuǎn)錄和轉(zhuǎn)錄后調(diào)控 MAVS不屬于干擾素刺激基因，其表達(dá)不直接受干擾素（IFN）調(diào)控，因此與RIG-I等基因不同，MAVS的表達(dá)和功能更多受到轉(zhuǎn)錄、轉(zhuǎn)錄后和翻譯后的調(diào)控。在轉(zhuǎn)錄水平，MAVS mRNA水平受到活性氧（reactive oxygen species，ROS）介導(dǎo)的負(fù)反饋環(huán)的調(diào)控[6,11]。MAVS基因還編碼一系列不同的剪切體發(fā)揮負(fù)調(diào)控MAVS介導(dǎo)的信號(hào)通路[12]。而在轉(zhuǎn)錄后水平，MAVS的翻譯能夠在兩個(gè)不同的轉(zhuǎn)錄起始位點(diǎn)，包括用序列中部的甲硫氨酸起始翻譯[13]。這種MAVS的選擇性翻譯可能由上游開(kāi)放性讀碼框跳躍介導(dǎo)，導(dǎo)致398個(gè)氨基酸的缺失CARD結(jié)構(gòu)域的MAVS的短異構(gòu)體，這種短異構(gòu)體被稱之為短MAVS（short-MAVS，sMAVS）。盡管有報(bào)道認(rèn)為sMAVS發(fā)揮負(fù)調(diào)控抗病毒先天性免疫的作用，但也有報(bào)道顯示sMAVS發(fā)揮正向調(diào)控抗病毒信號(hào)通路[13]。最近的兩篇報(bào)道顯示RNA病毒感染后，全長(zhǎng)MAVS（FL-MAVS）逐漸降解，但sMAVS量則保持恒定[13,14]。FL-MAVS降解的具體機(jī)制是由于其在RNA病毒感染后第7和第10位氨基酸發(fā)生K48多泛素化介導(dǎo)的蛋白酶體降解，但是由于sMAVS缺失FL-MAVS的N端序列，因此不發(fā)生K48泛素化降解。介導(dǎo)MAVS降解的E3連接酶是TRIM25，巧合的是，TRIM25正是介導(dǎo)RIG-I的K63活化的E3連接酶，因此推測(cè)RNA病毒感染后，MAVS的位置上與RIG-I轉(zhuǎn)位子成分TRIM25接近而被泛素化。值得注意的是，由于FL-MAVS的降解先于IRF3的磷酸化，說(shuō)明這種降解正向調(diào)控抗病毒信號(hào)[14]。

2.2 MAVS的蛋白水平調(diào)控

2.2.1 MAVS翻譯后負(fù)調(diào)控 MAVS通過(guò)翻譯后調(diào)控先天性抗病毒反應(yīng)，其中最重要的負(fù)調(diào)控機(jī)制是對(duì)MAVS的賴氨酸位點(diǎn)進(jìn)行K48泛素化修飾，通過(guò)蛋白酶體途徑降解MAVS。例如在病毒感染時(shí)，E3泛素連接酶RNF5（ring finger protein 5）與線粒體上的MAVS的C末端的跨膜結(jié)構(gòu)域相結(jié)合，RNF5在MAVS的氨基酸K362和K461位點(diǎn)進(jìn)行K48泛素化修飾，降解MAVS，負(fù)調(diào)控MAVS介導(dǎo)的I型干擾素生成與細(xì)胞抗病毒應(yīng)答[15]；另一種E3泛素連接酶MARCH5的RING結(jié)構(gòu)域與MAVS的CARD域結(jié)合，阻止MAVS聚集，促進(jìn)其通過(guò)蛋白酶體途徑降解；MAVS的Lys7和Lys500氨基酸位點(diǎn)是E3連接酶MARCH5泛素化關(guān)鍵位點(diǎn)，MARCH5負(fù)調(diào)控MAVS介導(dǎo)的抗病毒信號(hào)通路，防止過(guò)度的免疫反應(yīng)[16]。除此之外，還有許多其他E3泛素連接酶介導(dǎo)了MAVS的K48泛素化降解，例如AIP4[17]、Smurf1[18]等。

除了泛素化降解之外，另一種重要的負(fù)調(diào)控機(jī)制是通過(guò)與MAVS互作阻斷其介導(dǎo)的抗病毒信號(hào)通路，例如TSPAN6（Tetraspanin-6）在病毒感染時(shí)自身發(fā)生賴氨酸K63的泛素化修飾，促進(jìn)了其與MAVS的結(jié)合，TSPAN6 和MAVS的互作干擾了RLR下游分子TRAF3, STING（stimulator of interferon genes）和IRF3招募至MAVS，阻斷了信號(hào)轉(zhuǎn)導(dǎo)分子的裝配[19]；E3泛素連接酶RNF125通過(guò)泛素調(diào)控MDA-5和MAVS的結(jié)合，來(lái)抑制其下游的信號(hào)通路傳導(dǎo)；E3泛素連接酶Triad3A與MAVS的TRAF相互作用結(jié)構(gòu)域（TIM）（氨基酸第143-147位）互作，競(jìng)爭(zhēng)性結(jié)合TRAF3位點(diǎn)，負(fù)調(diào)控機(jī)體天然抗病毒反應(yīng)[20]；MUL1（Mitochondrial E3 ubiquitin protein ligase 1）定位在線粒體外膜上，與MAVS相互作用，并催化RIG-I的SUMO化修飾，抑制RIG-I介導(dǎo)的細(xì)胞信號(hào)傳導(dǎo)[21]。NOD樣受體NLRX1也位于線粒體上，能夠通過(guò)扣留MAVS使其遠(yuǎn)離RIG-I來(lái)發(fā)揮負(fù)調(diào)控作用[22]。自噬相關(guān)蛋白ATG12-ATG5復(fù)合物能通過(guò)影響MAVS與RIG-I的結(jié)合，來(lái)負(fù)調(diào)控I型干擾素信號(hào)通路[23]。而COX5B（Cytochrome c oxidase subunit 5B）也能通過(guò)與ATG5的互作負(fù)調(diào)控MAVS介導(dǎo)的信號(hào)通路[24]。

除了以上兩種最重要的負(fù)調(diào)控途徑之外，還有其他一些其他的非經(jīng)典的負(fù)調(diào)控機(jī)制，例如蛋白酶體PSMA7（α4）亞基與細(xì)胞內(nèi)的MAVS相互作用介導(dǎo)MAVS被蛋白酶體降解[25]。胰島素受體酪氨酸激酶底物（IRTKS）在細(xì)胞核中募集E2連接酶UBC9，它在病毒感染期間易位到細(xì)胞質(zhì)，引起SUMO化的PCBP2蛋白介導(dǎo)MAVS降解[26]。蛋白磷酸激酶PLK1（polo-like kinase 1）磷酸化修飾MAVS，從而抑制MAVS招募信號(hào)分子。線粒體蛋白也能調(diào)控RLR信號(hào)通路[27]。兩個(gè)協(xié)同的線粒體蛋白MFN1和MFN2（mitofusin 1 and 2）都可與MAVS相互作用，但是其作用不同。MFN2負(fù)調(diào)控MAVS介導(dǎo)的通路，MFN1通過(guò)影響線粒體動(dòng)態(tài)變化正調(diào)控RLR介導(dǎo)的抗病毒信號(hào)通路[28]。除了細(xì)胞蛋白之外，miRNA也被報(bào)道影響MAVS介導(dǎo)的抗病毒反應(yīng)，水泡性口炎病毒感染后，內(nèi)源性的miR-576-3p 通過(guò)和STING、MAVS和TRAF3結(jié)合，抑制IRF3入核，干擾素水平下降[29]。

2.2.2 MAVS翻譯后正調(diào)控 有很多蛋白被發(fā)現(xiàn)通過(guò)對(duì)MAVS的翻譯后修飾正調(diào)控MAVS介導(dǎo)信號(hào)傳導(dǎo)通路[30]。其中最重要的正調(diào)控機(jī)制是對(duì)MAVS的賴氨酸位點(diǎn)進(jìn)行K63泛素化修飾，活化MAVS。例如線粒體接頭蛋白TRIM14與MAVS相互作用，促進(jìn)了MAVS信號(hào)小體（signalosome）組裝。當(dāng)病毒感染時(shí)，TRIM14的賴氨酸Lys365位點(diǎn)發(fā)生K63多聚泛素化修飾，招募NEMO到MAVS信號(hào)小體，促使IRF3和NF-κB信號(hào)通路激活，正調(diào)控RIG-I介導(dǎo)的抗病毒免疫。I型干擾素能促進(jìn)TRIM14的表達(dá)，從而增強(qiáng)先天免疫反應(yīng)，對(duì)抗病毒感染[31]。E3泛素連接酶MIB2（mindbomb2）與MAVS上高度保守的DLAIS基序結(jié)合，促使TBK1的K63連接的泛素化修飾，并磷酸化激活I(lǐng)RF3/7，激活下游轉(zhuǎn)錄因子和誘導(dǎo)更多的IFN-β的生成[32]；E3泛素連接酶RNF135，能促進(jìn)RIG-I的C端結(jié)構(gòu)域K63聚泛素化，從而增強(qiáng)病毒感染早期I型干擾素的生成[33]。E3泛素連接酶TRIM25能K63泛素化修飾RIG-I、MDA5與MAVS的復(fù)合物，并正調(diào)控抗病毒信號(hào)通路，RIG-I第172位賴氨酸是TRIM25介導(dǎo)的K63泛素化的關(guān)鍵位點(diǎn)，增強(qiáng)RIG-I與MAVS相互結(jié)合[34]。有趣的是，TRIM25還對(duì)全長(zhǎng)MAVS的在第7和第10位賴氨酸位點(diǎn)發(fā)生K48泛素化介導(dǎo)的蛋白酶體降解，而這種降解正向調(diào)控抗病毒信號(hào)[14]。

除了對(duì)MAVS的泛素化修飾之外，磷酸化修飾也是MAVS正調(diào)控的主要方式。例如MAVS的酪氨酸Tyr9位點(diǎn)磷酸化激活下游IFN-β的信號(hào)傳導(dǎo)[35]；酪氨酸激酶c-Abl直接與MAVS相互作用磷酸化MAVS，正調(diào)控MAVS介導(dǎo)的信號(hào)通路[36]（圖1）。

圖1 MAVS介導(dǎo)的先天性免疫的調(diào)控Fig.1 The regulation of MAVS-mediated innate immunity

3 病毒感染調(diào)控MAVS信號(hào)通路

3.1 病毒蛋白裂解MAVS 許多病毒的蛋白具有蛋白酶功能，能夠通過(guò)切割MAVS來(lái)負(fù)調(diào)控MAVS介導(dǎo)的信號(hào)通路。例如丙肝病毒NS3-NS4A蛋白酶特異性識(shí)別位于MAVS的跨膜結(jié)構(gòu)域半胱氨酸C508位點(diǎn)來(lái)切割MAVS，MAVS從線粒體膜上釋放，從而抑制下游I型干擾素和III型干擾素抗病毒信號(hào)通路[37]。與NS3/NS4A同源的犬肝炎病毒NS3、GB病毒B型NS3/4A，也能裂解MAVS，促使病毒免疫逃避[38,39]。除此以外，甲肝病毒的半胱氨酸蛋白酶的前體3C、乙肝病毒的HBX蛋白和腸道病毒71型的蛋白酶2A前體均可以裂解MAVS，從而阻斷下游信號(hào)轉(zhuǎn)導(dǎo)[40,41]?？滤_奇病毒B3半胱氨酸蛋白酶前體3C介導(dǎo)MAVS，在富含脯氨酸的區(qū)域的谷氨酰胺Q148位點(diǎn)裂解，導(dǎo)致了MAVS在線粒體膜的重新定位并抑制下游信號(hào)通路[42]。豬繁殖與呼吸綜合征病毒的3C樣蛋白酶通過(guò)在蛋白酶體和獨(dú)立的含半胱氨酸的天冬氨酸蛋白水解酶（caspase）方式在谷氨酸Glu268位點(diǎn)切割MAVS，抑制病毒誘導(dǎo)IFN-β的產(chǎn)生[43]。

3.2 蛋白酶體降解MAVS 除了直接裂解MAVS之外，有些病毒能利用蛋白酶體降解MAVS途徑直接抑制MAVS。冠狀病毒編碼的開(kāi)放閱讀框9B（ORF-9B）通過(guò)PCBP2介導(dǎo)的E3泛素連接酶AIP4降解MAVS、TRAF3和TRAF6的復(fù)合物。冠狀病毒SARS的ORF-9B能操縱宿主細(xì)胞的線粒體功能，以幫助其逃避宿主天然免疫[44]。輪狀病毒非結(jié)構(gòu)蛋白1（NSP1）在感染后，介導(dǎo)MAVS通過(guò)蛋白酶體途徑被泛素化降解，抑制線粒體外膜上MAVS聚集體的形成，從而抑制了抗病毒信號(hào)級(jí)聯(lián)反應(yīng)[45]。乙型肝炎病毒X蛋白對(duì)MAVS的賴氨酸Lys136位點(diǎn)進(jìn)行泛素化修飾后，被蛋白酶體降解[46]。鯉春病毒血癥病毒（SVCV）的N蛋白可以通過(guò)經(jīng)由泛素-蛋白酶體途徑降解斑馬魚(yú)的MAVS[47]。腸道病毒（CVB）感染細(xì)胞后，E3泛素連接酶Gp78通過(guò)蛋白酶體途徑和內(nèi)質(zhì)網(wǎng)關(guān)聯(lián)降解通路（ER-associated degradation）直接降解MAVS，Gp78也能與MAVS的N端、C端的結(jié)構(gòu)域相結(jié)合，負(fù)調(diào)控MAVS介導(dǎo)的抗病毒信號(hào)轉(zhuǎn)導(dǎo)[48]。

3.3 與MAVS互作影響調(diào)控 病毒感染后，細(xì)胞內(nèi)某些蛋白能夠與MAVS直接相互作用，阻礙下游接頭分子與MAVS結(jié)合。例如UBXN1（domaincontaining protein 1）能負(fù)調(diào)控RNA病毒誘導(dǎo)的I型干擾素反應(yīng)。水泡口炎病毒、仙臺(tái)病毒、西尼羅河病毒、登革熱病毒等RNA病毒感染時(shí)，誘導(dǎo)生成的N端具有UBA結(jié)構(gòu)域的泛素結(jié)合蛋白UBXN1特異性與MAVS結(jié)合，競(jìng)爭(zhēng)TRAF3/6的結(jié)合位點(diǎn)（氨基酸第455-460位），阻礙MAVS招募TRAF3/6（TNF receptor-associated factor 3/6），干擾胞內(nèi)的MAVS寡聚化，負(fù)調(diào)控MAVS下游信號(hào)通路[49]。

病毒蛋白與MAVS的互作也會(huì)通過(guò)影響線粒體上MAVS的集聚或改變MAVS的空間定位和構(gòu)象，從而調(diào)控MAVS介導(dǎo)的通路。呼吸道合胞病毒（RSV）感染細(xì)胞后，非結(jié)構(gòu)蛋白NS1與MAVS相結(jié)合，阻礙招募RIG-I的下游干擾素活化因子，如TRAF3、TRAF6和RIP1（receptor interacting protein-1）[50]。人類偏肺病毒（hMPV）的毒力因子M2-2蛋白通過(guò)與MAVS的互作抑制MAVS介導(dǎo)的細(xì)胞抗病毒反應(yīng)，幫助偏肺病毒逃避先天性免疫[51]。甲型禽流感病毒（IAVAIV）H5N1的RNA聚合酶復(fù)合體PB2亞基通過(guò)直接相互作用于MAVS第1-37位氨基酸位點(diǎn)，阻礙MAVS的寡聚化和分子間構(gòu)象變化，導(dǎo)致MAVS復(fù)合物的失活[52]。禽甲型流感病毒H5N1 RNA編碼的開(kāi)放閱讀框（ORF）變化形成的毒力因子PB1-F2蛋白和PB2Δ蛋白都能用與MAVS在線粒體的相互作用，PB1-F2蛋白抑制宿主的先天免疫應(yīng)答，PB2Δ蛋白增加甲型流感病毒誘導(dǎo)的I型干擾素表達(dá)，降低病毒復(fù)制水平[53,54]。Caspase募集域和膜相關(guān)鳥(niǎo)苷酸激酶樣結(jié)構(gòu)域蛋白（CARD recruited membrane associated protein 3，CARMA3）作為宿主因子，在RNA病毒感染后，能抑制線粒體上MAVS的集聚，負(fù)調(diào)控RIG-I與MAVS介導(dǎo)的TBK1和IRF3激活[55]。

3.4 病毒感染后正調(diào)控 抗病毒反應(yīng)與正調(diào)控MAVS介導(dǎo)的信號(hào)通路并不矛盾，病毒感染也可以正調(diào)控MAVS介導(dǎo)的信號(hào)通路。流感病毒感染時(shí)，鴨的TRIM27.1基因和TRIM27-L基因表達(dá)上調(diào)。TRIM家族蛋白是常見(jiàn)的E3泛素連接酶， TRIM27-L基因表達(dá)能強(qiáng)烈激活RIG介導(dǎo)的MAVS先天免疫信號(hào)，誘導(dǎo)抗病毒基因MX1和IFN-β的轉(zhuǎn)錄水平上調(diào)[56]。豬干擾素誘導(dǎo)蛋白三十四肽重復(fù)3（poIFIT3）是豬流感病毒（SIV）誘導(dǎo)出的基因之一，poIFIT3通過(guò)靶向MAVS ,誘導(dǎo)IFN-β水平上調(diào)，而且poIFIT3的過(guò)度表達(dá)可有效抑制SIV的復(fù)制[57]。腺病毒能共價(jià)結(jié)合補(bǔ)體C3進(jìn)入細(xì)胞內(nèi)，在細(xì)胞質(zhì)內(nèi)C3能增強(qiáng)激活線粒體抗病毒信號(hào)（MAVS）依賴的信號(hào)級(jí)聯(lián)和誘導(dǎo)促炎細(xì)胞因子的分泌[58]（圖1）。

4 展望

先天性抗病毒信號(hào)通路，作為第一道屏障消滅入侵的病原微生物，還避免了過(guò)度炎癥細(xì)胞損傷。作為先天性免疫的中樞蛋白，MAVS的精細(xì)調(diào)控，對(duì)于MAVS發(fā)揮功能和防止過(guò)度免疫反應(yīng)至關(guān)重要。如上所述，細(xì)胞和病毒使用許多不同的機(jī)制來(lái)調(diào)控MAVS信號(hào)通路，包括轉(zhuǎn)錄和翻譯后修飾，與MAVS關(guān)聯(lián)的蛋白質(zhì)-蛋白質(zhì)相互作用。作為先天性免疫反應(yīng)的中樞分子，越來(lái)越多的研究結(jié)果顯示：MAVS除了參與先天性免疫之外還參與了很多其他重要的細(xì)胞通路，例如細(xì)胞凋亡、細(xì)胞自噬等。反之其他通路的成分也被發(fā)現(xiàn)能夠通過(guò)調(diào)控MAVS來(lái)影響先天性免疫，例如自噬相關(guān)蛋白ATG5-ATG12等[7]。MAVS作為RLR信號(hào)通路中保守的接頭蛋白，在I型干擾素通路中起重要作用。動(dòng)物病毒通過(guò)干擾MAVS，影響宿主干擾素反應(yīng)，來(lái)逃避機(jī)體的抗病毒天然免疫。盡管近年來(lái)研究進(jìn)展顯著，目前關(guān)于動(dòng)物病毒抑制MAVS介導(dǎo)的干擾素表達(dá)機(jī)制的研究很少，尤其是禽類和水生動(dòng)物類，大部分動(dòng)物體內(nèi)MAVS介導(dǎo)的抗病毒信號(hào)通路的調(diào)控機(jī)制不明確。通過(guò)對(duì)動(dòng)物的MAVS介導(dǎo)的抗病毒天然免疫信號(hào)通路的調(diào)控機(jī)制還有待探索，有希望從該通路入手尋找到新的治療靶點(diǎn)來(lái)防治動(dòng)物傳染病。

[1]Kawai T, Akira S. Signaling to NF-kappaB by Toll-like receptors[J]. Trends Mol Med, 2007, 13(11): 460-469.

[2]Loo Y M, Gale M Jr. Immune signaling by RIG-I-like receptors[J]. Immunity, 2011, 34(5): 680-692.

[3]Kato H, Takeuchi O, Sato S,et al. Differential roles of MDA5 and RIG-I helicases in the recognition of RNA viruses[J]. Nature, 2006, 441(7089): 101-105.

[4]Loo Y-M, Fornek J, Crochet N,et al. Distinct RIG-I and MDA5 signaling by RNA viruses in innate immunity[J]. J Virol, 2008, 82(1): 335-345.

[5]Seth R B, Sun L, Ea C-K,et al. Identification and characterization of MAVS, a mitochondrial antiviral signaling protein that activates NF-κB and IRF3[J].Cell, 2005, 122(5): 669-682.

[6]Vazquez C, Horner S M. MAVS Coordination of Antiviral Innate Immunity[J]. J Virol, 2015, 89(14): 6974-6977.

[7]Belgnaoui S M, Paz S, Hiscott J. Orchestrating the interferon antiviral response through the mitochondrial antiviral signaling (MAVS) adapter[J]. Curr Opin Immunol, 2011, 23(5): 564-572.

[8]Ye J, Maniatis T. A prion-like trigger of antiviral signaling[J]. Cell, 2011, 146(3): 348-350.

[9]Liu H M, Loo Y M, Horner S M,et al. The mitochondrial targeting chaperone 14-3-3epsilon regulates a RIG-I translocon that mediates membrane association and innate antiviral immunity[J]. Cell Host Microbe, 2012, 11(5):528-537.

[10]Takeuchi O, Akira S. Pattern recognition receptors and inflammation[J]. Cell, 2010, 140(6): 805-820.

[11]Koshiba T. Mitochondrial-mediated antiviral immunity[J]. Biochim Biophys Acta, 2013, 1833(1): 225-232.

[12]Lad S P, Yang G, Scott D A,et al. Identification of MAVS splicing variants that interfere with RIGI/MAVS pathway signaling[J]. Mol Immunol, 2008, 45(8): 2277-2287.

[13]Brubaker S W, Gauthier A E, Mills E W,et al. A bicistronic MAVS transcript highlights a class of truncated variants in antiviral immunity[J]. Cell, 2014,156(4): 800-811.

[14]Castanier C, Zemirli N, Portier A,et al. MAVS ubiquitination by the E3 ligase TRIM25 and degradation by the proteasome is involved in type I interferon production after activation of the antiviral RIG-I-like receptors[J]. BMC Biol, 2012, 10: 44.

[15]Zhong B, Zhang Y, Tan B,et al. The E3 ubiquitin ligase RNF5 targets virus-induced signaling adaptor for ubiquitination and degradation[J]. J Immunol, 2010,184(11): 6249-6255.

[16]Yoo Y S, Park Y Y, Kim J H,et al. The mitochondrial ubiquitin ligase MARCH5 resolves MAVS aggregates during antiviral signalling[J]. Nat Commun, 2015, 6:7910.

[17]You F, Sun H, Zhou X,et al. PCBP2 mediates degradation of the adaptor MAVS via the HECT ubiquitin ligase AIP4[J]. Nat Immunol, 2009, 10(12): 1300-1308.

[18]Wang Y, Tong X, Ye X. Ndfip1 negatively regulates RIG-I-dependent immune signaling by enhancing E3 ligase Smurf1-mediated MAVS degradation[J]. J Immunol, 2012, 189(11): 5304-5313.

[19]Wang Y, Tong X, Omoregie E S,et al. Tetraspanin 6(TSPAN6) negatively regulates retinoic acid-inducible gene I-like receptor-mediated immune signaling in a ubiquitination-dependent manner[J]. J Biol Chem, 2012,287(41): 34626-3434.

[20]Nakhaei P, Mesplede T, Solis M,et al. The E3 ubiquitin ligase Triad3A negatively regulates the RIG-I/MAVS signaling pathway by targeting TRAF3 for degradation[J].PLoS Pathog, 2009, 5(11): e1000650.

[21]Jenkins K, Khoo J J, Sadler A,et al. Mitochondrially localised MUL1 is a novel modulator of antiviral signaling[J]. Immunol Cell Biol, 2013, 91(4): 321-330.

[22]Moore C B, Bergstralh D T, Duncan J A,et al. NLRX1 is a regulator of mitochondrial antiviral immunity[J].Nature, 2008, 451(7178): 573-577.

[23]Huang X, Yue Y, Li D,et al. Antibody-dependent enhancement of dengue virus infection inhibits RLR-mediated Type-I IFN-independent signalling through upregulation of cellular autophagy[J]. Sci Rep, 2016, 6:22303.

[24]Zhao Y, Sun X, Nie X,et al. COX5B regulates MAVS-mediated antiviral signaling through interaction with ATG5 and repressing ROS production[J]. PLoS Pathog,2012, 8(12): e1003086.

[25]Jia Y, Song T, Wei C,et al. Negative regulation of MAVS-mediated innate immune response by PSMA7[J].J Immunol, 2009, 183(7): 4241-4248.

[26]Xia P, Wang S, Xiong Z,et al. IRTKS negatively regulates antiviral immunity through PCBP2 sumoylation-mediated MAVS degradation[J]. Nat Commun, 2015, 6: 8132.

[27]Vitour D, Dabo S, Ahmadi Pour M,et al. Polo-like kinase 1 (PLK1) regulates interferon (IFN) induction by MAVS[J]. J Biol Chem, 2009, 284(33): 21797-21809.

[28]Arnoult D, Soares F, Tattoli I,et al. Mitochondria in innate immunity[J]. EMBO Rep, 2011, 12(9): 901-910.

[29]Yarbrough M L, Zhang K, Sakthivel R,et al. Primatespecific miR-576-3p sets host defense signalling threshold[J]. Nat Commun, 2014, 5: 4963.

[30]Eisenacher K, Krug A. Regulation of RLR-mediated innate immune signaling--it is all about keeping the balance[J]. Eur J Cell Biol, 2012, 91(1): 36-47.

[31]Zhou Z, Jia X, Xue Q,et al. TRIM14 is a mitochondrial adaptor that facilitates retinoic acid-inducible gene-I-like receptor-mediated innate immune response[J]. Proc Natl Acad Sci U S A, 2014, 111(2): E245-254.

[32]Ye J S, Kim N, Lee K J,et al. Lysine 63-linked TANK-binding kinase 1 ubiquitination by mindbomb E3 ubiquitin protein ligase 2 is mediated by the mitochondrial antiviral signaling protein[J]. J Virol, 2014, 88(21): 12765-12776.

[33]Oshiumi H, Matsumoto M, Hatakeyama S,et al. Riplet/RNF135, a RING finger protein, ubiquitinates RIG-I to promote interferon-beta induction during the early phase of viral infection[J]. J Biol Chem, 2009, 284(2): 807-817.

[34]Gack M U, Shin Y C, Joo C H,et al. TRIM25 RING-finger E3 ubiquitin ligase is essential for RIG-I-mediated antiviral activity[J]. Nature, 2007, 446(7138): 916-920.

[35]Wen C, Yan Z, Yang X,et al. Identification of tyrosine-9 of MAVS as critical target for inducible phosphorylation that determines activation[J]. PLoS One, 2012, 7(7):e41687.

[36]Song T, Wei C, Zheng Z,et al. c-Abl tyrosine kinase interacts with MAVS and regulates innate immune response[J]. FEBS Lett, 2010, 584(1): 33-38.

[37]Ferreira A R, Magalhaes A C, Camoes F,et al. Hepatitis C virus NS3-4A inhibits the peroxisomal MAVS-dependent antiviral signalling response[J]. J Cell Mol Med, 2016, 20(4): 750-757.

[38]Chen Z, Benureau Y, Rijnbrand R,et al. GB virus B disrupts RIG-I signaling by NS3/4A-mediated cleavage of the adaptor protein MAVS[J]. J Virol, 2007, 81(2):964-976.

[39]Parera M, Martrus G, Franco S,et al. Canine hepacivirus NS3 serine protease can cleave the human adaptor proteins MAVS and TRIF[J]. PLoS One, 2012, 7(8):e42481.

[40]Paulmann D, Magulski T, Schwarz R,et al. Hepatitis A virus protein 2B suppresses beta interferon (IFN) gene transcription by interfering with IFN regulatory factor 3 activation[J]. J Gen Virol, 2008, 89(Pt 7): 1593-1604.

[41]Wang B, Xi X, Lei X,et al. Enterovirus 71 protease 2Apro targets MAVS to inhibit anti-viral type I interferon responses[J]. PLoS Pathog, 2013, 9(3): e1003231.

[42]Mukherjee A, Morosky S A, Delorme-Axford E,et al.The coxsackievirus B 3C protease cleaves MAVS and TRIF to attenuate host type I interferon and apoptotic signaling[J]. PLoS Pathog, 2011, 7(3): e1001311.

[43]Dong J, Xu S, Wang J,et al. Porcine reproductive and respiratory syndrome virus 3C protease cleaves the mitochondrial antiviral signalling complex to antagonize IFN-beta expression[J]. J Gen Virol, 2015, 96(10): 3049-3058.

[44]Shi C S, Qi H Y, Boularan C,et al. SARS-coronavirus open reading frame-9b suppresses innate immunity by targeting mitochondria and the MAVS/TRAF3/TRAF6 signalosome[J]. J Immunol, 2014, 193(6): 3080-3089.

[45]Nandi S, Chanda S, Bagchi P,et al. MAVS protein is attenuated by rotavirus nonstructural protein 1[J]. PLoS One, 2014, 9(3): e92126.

[46]Wei C, Ni C, Song T,et al. The hepatitis B virus X protein disrupts innate immunity by downregulating mitochondrial antiviral signaling protein[J]. J Immunol,2010, 185(2): 1158-1168.

[47]Lu L F, Li S, Lu X B,et al. Spring Viremia of Carp Virus N Protein Suppresses Fish IFNphi1 Production by Targeting the Mitochondrial Antiviral Signaling Protein[J]. J Immunol, 2016, 196(9): 3744-3753.

[48]Jacobs J L, Zhu J, Sarkar S N,et al. Regulation of mitochondrial antiviral signaling (MAVS) expression and signaling by the mitochondria-associated endoplasmic reticulum membrane (MAM) protein Gp78[J]. J Biol Chem, 2014, 289(3): 1604-1616.

[49]Wang P, Yang L, Cheng G,et al. UBXN1 interferes with Rig-I-like receptor-mediated antiviral immune response by targeting MAVS[J]. Cell Rep, 2013, 3(4): 1057-1070.

[50]Webster Marketon J I, Corry J, Teng M N. The respiratory syncytial virus (RSV) nonstructural proteins mediate RSV suppression of glucocorticoid receptor transactivation[J].Virology, 2014, 449: 62-69.

[51]Ren J, Wang Q, Kolli D,et al. Human metapneumovirus M2-2 protein inhibits innate cellular signaling by targeting MAVS[J]. J Virol, 2012, 86(23): 13049-13061.

[52]Patel D, Schultz L W, Umland T C. Influenza A polymerase subunit PB2 possesses overlapping binding sites for polymerase subunit PB1 and human MAVS proteins[J]. Virus Res, 2013, 172(1-2): 75-80.

[53]Varga Z T, Grant A, Manicassamy B,et al. Influenza virus protein PB1-F2 inhibits the induction of type I interferon by binding to MAVS and decreasing mitochondrial membrane potential[J]. J Virol, 2012, 86(16): 8359-8366.

[54]Boergeling Y, Rozhdestvensky T S, Schmolke M,et al.Evidence for a Novel Mechanism of Influenza Virus-Induced Type I Interferon Expression by a Defective RNA-Encoded Protein[J]. PLoS Pathog, 2015, 11(5):e1004924.

[55]Jiang C, Zhou Z, Quan Y,et al. CARMA3 Is a Host Factor Regulating the Balance of Inflammatory and Antiviral Responses against Viral Infection[J]. Cell Rep,2016, 14(10): 2389-2401.

[56]Blaine A H, Miranzo-Navarro D, Campbell L K,et al.Duck TRIM27-L enhances MAVS signaling and is absent in chickens and turkeys[J]. Mol Immunol, 2015, 67(2 Pt B): 607-615.

[57]Li Y, Wen Z, Zhou H,et al. Porcine interferon-induced protein with tetratricopeptide repeats 3, poIFIT3, inhibits swine influenza virus replication and potentiates IFN-beta production[J]. Dev Comp Immunol, 2015, 50(1): 49-57.

[58]Tam J C, Bidgood S R, Mcewan W A,et al. Intracellular sensing of complement C3 activates cell autonomous immunity[J]. Science, 2014, 345(6201): 1256070.

THE REGULATION OF MAVS-MEDIATED ANTIVIRAL INNATE IMMUNITY

ZHENG Hang1, SUN Ying-jie2, ZHANG Pin3, DING Chan2

(1. College of Animal Science and Technology, Jilin Agricultural University, Changchun 130118, China; 2. Shanghai Veterinary Research Institute, CAAS, Shanghai 200241, China; 3. College of Animal Science and Technology, Shandong Agricultural University, Taian 271018,China)

As the fi rst barrier of immune defense towards invading pathogens, the signaling pathway of the innate immunity plays an important role in antiviral response. The most important cytoplasmic pathogen recognition receptors are retinoic acid-inducible gene 1 and differentiation-associated protein 5. They possess the same downstream adaptor mitochondrial antiviral-signaling protein (MAVS).MAVS functions as the central molecular tool in innate immunity signaling pathway. MAVS-mediated signaling pathway is the important antiviral mechanism. However, viruses obtain a series of anti-MAVS mechanisms in the long-term coexistence status. Furthermore, cells in the resting state possess a number of MAVS regulation mechanisms to avoid excessive immune response. The delicate regulation of MAVS is critical for cell function and antiviral response. This review brie fl y introduces the structure and function as well as transcriptional and translational regulation mechanisms of MAVS. Furthermore, the mechanisms how viruses “fight back” MAVS-mediate innate immunity are elaborated. Understanding the regulation mechanism of MAVS may provide new insights into therapeutic strategies for the immunity regulation and virus infection.

Innate immunity; mitochondrial antiviral-signaling protein; pathogen; host

S852.42

A

1674-6422（2018）01-0081-08

2016-08-29

國(guó)家自然科學(xué)基金重點(diǎn)項(xiàng)目（31530074）；國(guó)家自然科學(xué)基金面上項(xiàng)目（31372421）；國(guó)家自然科學(xué)基金青年基金（31400144）

鄭航，男，碩士研究生，預(yù)防獸醫(yī)學(xué)專業(yè)

丁鏟，E-mail: shoveldeen @ shvri.ac.cn