黃羽，胡斯奇，郭斐

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應(yīng)激顆粒與病毒的相互制約

黃羽，胡斯奇，郭斐

中國醫(yī)學(xué)科學(xué)院/北京協(xié)和醫(yī)學(xué)院病原生物學(xué)研究所，國家衛(wèi)生健康委員會(huì)病原系統(tǒng)生物學(xué)重點(diǎn)實(shí)驗(yàn)室，北京 100730

哺乳動(dòng)物細(xì)胞受到熱休克、氧化應(yīng)激、營養(yǎng)缺乏或者病毒感染等環(huán)境壓力時(shí)，能夠迅速啟動(dòng)細(xì)胞的壓力應(yīng)答機(jī)制，終止細(xì)胞內(nèi)的蛋白翻譯，形成應(yīng)激顆粒(stress granules, SGs)。SGs作為胞漿中翻譯起始復(fù)合物的聚集產(chǎn)物，在細(xì)胞的基因表達(dá)和穩(wěn)態(tài)中發(fā)揮著重要的作用，與細(xì)胞凋亡以及核功能具有密切聯(lián)系。尤其是當(dāng)病毒感染細(xì)胞時(shí)，SGs的形成可以使細(xì)胞內(nèi)病毒蛋白翻譯水平大大降低，從而抑制入侵病毒的復(fù)制。然而，病毒在長期進(jìn)化過程中也衍生出了對(duì)抗細(xì)胞壓力應(yīng)答的相應(yīng)機(jī)制，如與SGs關(guān)鍵組分相互作用，甚至切割等方式。本文對(duì)SGs的組成及誘發(fā)機(jī)制，特別是多種病毒誘導(dǎo)eIF2α磷酸化促成SGs組裝的機(jī)制，以及病毒進(jìn)化過程中形成的應(yīng)對(duì)措施等方面進(jìn)行了綜述，旨在進(jìn)一步闡釋病毒感染與應(yīng)激顆粒形成之間的相互影響和調(diào)控，為人們深入理解人體先天性免疫防御提供參考。

應(yīng)激顆粒；翻譯阻滯；病毒；先天性免疫

當(dāng)哺乳動(dòng)物細(xì)胞遇到壓力環(huán)境(如熱刺激、電離輻射、低氧、內(nèi)質(zhì)網(wǎng)壓力和病毒感染等)時(shí)，細(xì)胞內(nèi)會(huì)發(fā)生一系列的應(yīng)激反應(yīng)，其中細(xì)胞質(zhì)中會(huì)形成一種可逆性動(dòng)態(tài)結(jié)構(gòu)，被稱為應(yīng)激顆粒(stress granules, SGs)。SGs是一種核糖核蛋白(ribonucleoprotein, RNP)聚集物，包括翻譯起始需要的mRNAs、40S核糖體亞基、翻譯起始因子以及一些RNA結(jié)合蛋白[1]。病毒感染宿主細(xì)胞后在其體內(nèi)復(fù)制，對(duì)于宿主而言，無疑是一種強(qiáng)烈的刺激，可促進(jìn)SGs的聚集；而SGs的形成又能夠干擾病毒在宿主細(xì)胞內(nèi)的復(fù)制，這是因?yàn)樗胁《镜膹?fù)制都無一例外的需要宿主翻譯系統(tǒng)的幫助和參與。因此，病毒感染與SGs的形成兩者間的相互作用關(guān)系對(duì)于先天性免疫的調(diào)節(jié)存在重要意義。本文通過對(duì)病毒感染誘導(dǎo)SGs的形成的機(jī)制及其相互作用作以總結(jié)，以期為人們深入理解先天性免疫調(diào)節(jié)在宿主抗病毒免疫系統(tǒng)中的作用提供參考。

1 SGs的形成及調(diào)節(jié)機(jī)制

SGs最早是在植物細(xì)胞中被發(fā)現(xiàn)，當(dāng)植物細(xì)胞受到熱刺激后，會(huì)出現(xiàn)包含RNA結(jié)合蛋白的TIA-1、TIAR以及poly (A)-RNA的細(xì)胞質(zhì)內(nèi)顆粒物質(zhì)，被稱作為SGs。在20世紀(jì)末期，研究發(fā)現(xiàn)在真核細(xì)胞內(nèi)，當(dāng)翻譯起始因子elF2α磷酸化后，會(huì)導(dǎo)致胞質(zhì)內(nèi)出現(xiàn)TIA-1/TIAR陽性的SGs的出現(xiàn)，將未翻譯的mRNA隔離，并且這種變化是可逆的[2]。

在真核細(xì)胞內(nèi)，SGs形成的明顯特征為mRNA翻譯起始的暫時(shí)停滯。所形成的SGs主要包含以下組分：(1)靶向mRNA的翻譯起始因子(elF4G、elF3、PABPC1、p-elF2α和elF5a)[3,4]；(2)調(diào)控翻譯和保護(hù)mRNA穩(wěn)定性的mRNA結(jié)合蛋白(TIA-1、TIAR、HuR/ ELAVL1、FMRP和Pum1)[3,5]；(3) mRNA代謝有關(guān)的蛋白質(zhì)(G3BP1、G3BP2、p54/rck/DDX6、PMR1、SMN、Staufen1、DHX36、Caprin1、ZBP1、HDAC6和ADAR)[6~11]；(4)信號(hào)傳遞蛋白(mTOR、RACK1和TRAF2)[12]；(5)干擾素誘導(dǎo)基因的表達(dá)產(chǎn)物(interferon- stimulated gene, ISG)，如PKR、ADAR1、RNA-sensing RIG-I-like receptors (RIG-I、MDA5和LGP2)、RNase L和OAS；(6)對(duì)SGs的形成有調(diào)控作用的蛋白(APOB-EC3G、Ago2、BRF1、DDX3、FAST和TTP等)[13,14]。

目前研究表明，引發(fā)真核細(xì)胞SGs生成的機(jī)制主要有3種，分別為：elF2α的磷酸化、mTOR的失活以及干擾elF4F復(fù)合物的生成。這其中研究最多的是elF2α的可逆性磷酸化作用。磷酸化狀態(tài)下的elF2α可與elF2B穩(wěn)定結(jié)合，這種結(jié)合作用使elF2B不能催化GDP再生成GTP，也就阻礙了翻譯起始過程中eIF2–GTP–Met–tRNAMet三元復(fù)合物的形成，誘導(dǎo)SGs的形成[2]。在哺乳動(dòng)物細(xì)胞中，目前共發(fā)現(xiàn)了4種能夠使elF2α磷酸化的激酶，分別可被不同種類的刺激反應(yīng)激活。HRI (heme-regulated inhibitor)可被氧化損傷和熱刺激激活[15,16]；GCN2 (general co-ntrol non-derepressible 2)的激活可由于氨基酸的缺乏[17]和紫外輻射損傷[18]所引起；PKR可被特殊的dsRNA所激活[19]，如病毒RNA復(fù)制中間產(chǎn)物等；PERK (PKR-like endoplasmic reticulum (ER) kinase)可被內(nèi)質(zhì)網(wǎng)刺激作用激活[20]。另外，由于eIF2–GTP– Met–tRNAMet三元復(fù)合物的缺乏，使翻譯起始區(qū)域不能被識(shí)別，也影響了核糖體大亞基的招募，結(jié)果造成了mRNP的累積和聚集[2]。這也是病毒感染引發(fā)細(xì)胞內(nèi)SGs聚集的主要因素。

哺乳動(dòng)物mTORC1是一種調(diào)控細(xì)胞代謝、營養(yǎng)分配和促進(jìn)生長的激酶[21]。mTORC可對(duì)許多底物蛋白產(chǎn)生磷酸化作用，包括elF4E-binding proteins (4EBPs)。亞硒酸鈉(sodium selenite, Se)和雷帕霉素(rapamycin)等藥物和饑餓誘導(dǎo)等可明顯抑制mTORC的活性。去磷酸化狀態(tài)下的4EBPs可與elF4E結(jié)合，阻止elF4E與elF4G的相互作用[22]，也抑制了翻譯的起始，從而導(dǎo)致SGs的聚集。另外，pateamine A和hippuristanol等化合物可抑制RNA解旋酶elF4E的活性，使其不能與elF4G相互作用，干擾了elF4F 復(fù)合物的形成阻礙了翻譯的起始，也是誘發(fā)SGs的重要機(jī)制。

壓力刺激引起的翻譯抑制可快速下調(diào)大量帽子結(jié)構(gòu)依賴的翻譯起始的蛋白質(zhì)合成，不過，也有一些mRNA可被選擇性翻譯增強(qiáng)。例如熱休克蛋白可被熱刺激所誘導(dǎo)，并且其mRNA可在高水平的磷酸化elF2α存在下被翻譯[23,24]。當(dāng)elF2α磷酸化導(dǎo)致eIF2–GTP–Met–tRNAMet三元復(fù)合物的再生延遲時(shí)，位于uORF下游區(qū)的ATF4 (activating transcription factor 4)則被翻譯合成。ATF4又可激活GADD34 (growth arrest and DNA damage-inducible protein 34)，與蛋白磷酸酶1 (protein phosphatase 1, PP1)一起，催化elF2α去磷酸化，進(jìn)而緩解翻譯的抑制作用[25]。

在實(shí)驗(yàn)過程中，研究人員通常需要誘導(dǎo)哺乳動(dòng)物細(xì)胞產(chǎn)生SGs的聚集，進(jìn)而探究外界條件對(duì)其影響。比較常見的亞砷酸鈉就是通過HRI磷酸化elF2α，進(jìn)而誘導(dǎo)SGs的生成[15]；另外，pateamine A和hippuristanol作為elF4A解旋酶的干擾物質(zhì)，在48S復(fù)合物形成后，使mRNA二級(jí)結(jié)構(gòu)不能打開，影 響核糖體小亞基通過mRNA 5￠UTR，進(jìn)而阻滯翻 譯[26,27]。過氧化氫以及亞硒酸鈉可通過抑制mTOR使4EBP去磷酸化誘導(dǎo)非經(jīng)典SGs，但不導(dǎo)致elF2α的磷酸化[28,29]。這種非經(jīng)典的SGs較經(jīng)典SGs相比缺少elF3等分子，其形成機(jī)制目前還有待研究。此外，TIA-1/TIAR和G3BP1等SG標(biāo)志蛋白的過表達(dá)也可導(dǎo)致SGs的產(chǎn)生。

許多SGs的組成蛋白可通過翻譯后修飾來調(diào)節(jié)SGs的形成，主要包括泛素化[30]、多聚ADP核糖基化(poly (ADP)-ribosylation)[31]、O連接的N乙酰氨基葡糖基化(-linked-acetylglucosamination)[32]、精氨酸脫甲基作用[33]、類泛素化修飾[34]、磷酸化及去磷酸化的修飾作用[8]。結(jié)果就導(dǎo)致了一些酶通過這些修飾作用來調(diào)節(jié)SGs的形成，并被招募至SGs，成為了其組成成分。還有一些酶在免疫信號(hào)途徑中起了至關(guān)重要的作用如RIG-I、MDA5和LGP2等解旋酶，被招募至SGs，也印證了SGs作為調(diào)節(jié)抗病毒反應(yīng)的平臺(tái)，介導(dǎo)下游信號(hào)傳遞存在的生物學(xué)意義[35]。

SGs也是相分離(phase separation)的一種存在形式。相分離概念提出主要針對(duì)于一些細(xì)胞內(nèi)存在的無膜結(jié)構(gòu)，他們多數(shù)由蛋白質(zhì)或RNA蛋白復(fù)合物聚集物的方式相對(duì)獨(dú)立的存在于細(xì)胞中，主要包括信號(hào)復(fù)合物(signaling complexes)，突觸后聚集物，P小體(P bodies)，細(xì)胞核內(nèi)斑點(diǎn)，應(yīng)激顆粒等[36]。在細(xì)胞承受外界刺激條件下所形成的SGs為無膜聚集結(jié)構(gòu)，其中包括mRNAs和與之結(jié)合的多種翻譯起始因子，以及RNA結(jié)合蛋白。細(xì)胞通過這種相對(duì)的隔離方式，將這些重要的翻譯原件儲(chǔ)存起來，待到刺激因素解除，細(xì)胞從這種應(yīng)激狀態(tài)恢復(fù)后，被SGs所隔離的這些翻譯起始因子及RNA可恢復(fù)工作，從而幫助細(xì)胞渡過難關(guān)[37]。另外SGs可在空間上將某些毒性蛋白和致病成分與細(xì)胞內(nèi)環(huán)境相對(duì)分離，隨后通過p62介導(dǎo)的自噬溶酶體途徑將其降解，來維持細(xì)胞內(nèi)環(huán)境的穩(wěn)定[38,39]。

2 病毒與SGs的相互作用

從最開始有關(guān)SGs的形成可抑制病毒復(fù)制的報(bào)道至今，10余年的時(shí)間里[40]，研究人員將病毒感染與SGs形成及其相互作用的關(guān)系的研究，已經(jīng)遍及多種病毒：從簡單的正向單鏈RNA病毒，到較復(fù)雜的逆轉(zhuǎn)錄病毒。許多病毒在復(fù)制的不同階段抑制SGs的形成。很多時(shí)候病毒抑制SGs的生成，目的在于適應(yīng)病毒自身的復(fù)制反應(yīng)，這也提示SGs形成所導(dǎo)致的蛋白質(zhì)翻譯的抑制作用，擁有一定的抗病毒功能。另外一些報(bào)道稱，SGs形成為病毒的模式識(shí)別分子提供一個(gè)平臺(tái)，募集天然免疫中的重要分子[14]，進(jìn)而為下游的抗病毒反應(yīng)傳遞信號(hào)。病毒的感染作為一種強(qiáng)烈的外源刺激，可誘導(dǎo)哺乳動(dòng)物細(xì)胞產(chǎn)生SGs。下文通過不同病毒家族討論了其與SGs的相互作用關(guān)系(表1)。

2.1 雙鏈DNA病毒

許多皰疹病毒科()及痘病毒科()都屬于具有包膜的dsDNA病毒。單純性皰疹病毒(herpes simplex virus type 1, HSV1)可通過自身的vhs (virionhostshutoff)蛋白[41]、US11[42]、ICP34.5[43]和gB (glycoprotein B )[44]影響elF2激酶的激活作用，從而影響宿主蛋白質(zhì)的合成。當(dāng)HSV-1感染時(shí)，宿主細(xì)胞TIA-1、TIAR和TTP水平上調(diào)，但不形成明顯的SGs，主要原因?yàn)椴《綬NA莖環(huán)結(jié)構(gòu)可捕獲TIA-1/TIAR來協(xié)助自身的復(fù)制[45]；vhs缺失的HSV-1感染細(xì)胞后，則可通過激活PKR引起SGs的聚集[46,47]。Finnen及其同事報(bào)道，感染HSV-2可下調(diào)亞砷酸鹽誘導(dǎo)的SGs，而對(duì)于pateamine A誘導(dǎo)的SGs則沒有作用[48]。這種抑制亞砷酸鹽誘導(dǎo)的SGs作用也依賴于vhs，感染vhs缺失的HSV-2突變體則可在感染后期誘導(dǎo)SGs的形成[49]。

表1 病毒與應(yīng)激顆粒的相互作用

續(xù)表1

痘苗病毒(vaccinia virus, VV)，是痘病毒科()家族的一員，其在宿主細(xì)胞復(fù)制過程中在胞質(zhì)內(nèi)形成大顆粒，被稱作病毒DNA工廠，其中招募了許多SG蛋白質(zhì)，如G3BP1、Caprin1、eIF4E、PABP (poly (A)-binding protein)以及eIF4G[50,51]。VV將這些蛋白利用在自身復(fù)制的不同階段，如G3BP1/ Caprin1復(fù)合物可增強(qiáng)VV的轉(zhuǎn)錄[50]；病毒翻譯的起始依賴eIF4E/eIF4G/PABP；另外，病毒蛋白I3可與elF4G相互作用，從而招募病毒ssDNA[52]，這都說明了SG的組分對(duì)于VV的轉(zhuǎn)錄和翻譯都有協(xié)助作用。然而，TIA-1并沒有出現(xiàn)在這個(gè)病毒DNA工廠中[53]；當(dāng)利用缺失E3L的突變體VV感染宿主細(xì)胞時(shí)，則可激活PKR，導(dǎo)致形成含有TIA-1、eIF3b、G3BP1和USP10的大顆粒，由于其具有抑制病毒復(fù)制的功能，所以稱之為抗病毒顆粒(antiviral stress granules, avSGs)[54]。

2.2 雙鏈RNA病毒

呼吸孤病毒科()為包含9~12條dsRNA基因組的無包膜病毒。典型的代表為輪狀病毒(rotavirus)，其感染宿主細(xì)胞同樣可引起宿主蛋白質(zhì)合成的抑制。由于大量病毒dsRNA在宿主細(xì)胞內(nèi)生成，激活了PKR引起elF2α的磷酸化，但由于SGs的核心成分PABP從胞質(zhì)向細(xì)胞核發(fā)生了轉(zhuǎn)移，胞質(zhì)內(nèi)SG聚集受阻[55,56]。相反，哺乳動(dòng)物正呼腸孤病毒(mammalian orthoreovirus, MRV)可在感染早期(脫殼后和mRNA轉(zhuǎn)錄之間)能夠誘導(dǎo)SG的形成，這種SG的形成依賴于elF2α的磷酸化，對(duì)病毒的復(fù)制也有促進(jìn)作用[57]。而到了MRV感染的晚期，盡管elF2α的磷酸化水平還很高，但SG的形成水平則有所降低[58]。還有研究報(bào)道SGs可招募病毒非結(jié)構(gòu)蛋白μN(yùn)S與G3BP1產(chǎn)生相互作用，進(jìn)而干擾SGs的聚集形成，在G3BP1敲除的細(xì)胞中，MRV的復(fù)制效率明顯提升[59]。

2.3 單股正鏈RNA病毒

小RNA病毒科()的所有成員都是無包膜病毒顆粒。骨髓灰質(zhì)炎病毒(poliovirus, PV)蛋白酶2A可在感染早期誘導(dǎo)SGs生成[60]，而到了感染晚期，PV 3C蛋白酶切割G3BP1[61]，則可能導(dǎo)致了此類SG的解聚。但在PV感染的晚期，還有一種細(xì)胞質(zhì)顆粒穩(wěn)定存在，其組成不是典型的SGs，包含病毒RNA和TIA-1，但不包括elF4G和PABP[62]。腦心肌炎病毒(encephalomyocarditis virus, EMCV)、柯薩奇病毒(coxsackievirus B3, CVB3)也通過切割G3BP1來干擾SGs的形成[63,64]。小鼠腦脊髓炎病毒(Theiler’s murine encephalomyelitis virus, TMEV)則通過表達(dá)leader (L)蛋白與G3BP1產(chǎn)生穩(wěn)定的相互作用，來干擾SG的合成[65]。門戈病毒(mengovirus) L蛋白的鋅指結(jié)構(gòu)域突變后，則導(dǎo)致了PKR依賴的G3BP1聚集，說明G3BP1-Caprin1-PKR復(fù)合物在門戈病毒感染相關(guān)的抗病毒免疫反應(yīng)中有重要的作用[66]。手足口病病毒(foot-and-mouth disease virus, FMDV)則通過L蛋白來切割G3BP1和G3BP2抑制SGs的生成[67]；而EV71可通過蛋白酶2A來切割elF4GI來誘導(dǎo)非經(jīng)典的SGs生成，卻抑制了經(jīng)典的SGs的生成[68]。

黃病毒科()是一類包膜病毒，西尼羅河病毒(West Nile virus, WNV)為此類病毒家族中首次報(bào)道的具有抑制SG聚集的成員，其病毒基因組3￠莖環(huán)結(jié)構(gòu)可與TIA-1和TIAR相互作用，抑制SG的形成[69]，而嵌和WNV W956IC則通過激活PKR，在感染早期引起大量的SGs的形成[70]。不過，在WSN感染后期，可通過激活mTOR來解除對(duì)翻譯的抑制，有利于病毒的復(fù)制[71]。另外，Xia等[72]報(bào)道登革病毒(dengue virus, DENV)感染的A549細(xì)胞可誘導(dǎo)非TIA-1依賴的G3BP1的聚集。蛋白組學(xué)分析顯示，G3BP1、G3BP2、Caprin1和USP10與DENV 2 sfRNA (subgenomic flavivirus RNAs, sfRNA)相互作用，并且G3BP1、G3BP2和Caprin1通過調(diào)控ISG mRNA的轉(zhuǎn)錄，有利于DENV的復(fù)制[73,74]。森林腦炎病毒(tick-borne encephalitis virus，TBEV)感染宿主細(xì)胞后將TIA-1和TIAR招募至其復(fù)制的位點(diǎn)，形成包含G3BP1、elF3和elF4B的SGs[75]。另一方面，日本腦炎病毒(Japanese encephalitis virus, JEV)核心蛋白可通過與Caprin 1相互作用，從而隔離G3BP1和USP10，導(dǎo)致SG形成受阻[76]。

與上述黃病毒的作用方式略有不同，HCV是通過控制elF2α的磷酸化來實(shí)現(xiàn)其對(duì)于SGs形成的調(diào)控。Garaigorta等[77]的研究表明HCV感染宿主細(xì)胞可引起PKR依賴的SGs聚集，且TIA-1，TIAR和G3BP1對(duì)于HCV的復(fù)制周期具有重要調(diào)控作用。另外，Ruggieri等[78]研究表明，HCV感染宿主細(xì)胞，早期可以迅速誘導(dǎo)SGs的產(chǎn)生，在感染的后期又出現(xiàn)SGs解聚的現(xiàn)象，這一系列的變化依賴于elF2α磷酸化水平的變化。HCV感染前期的SGs聚集是由于細(xì)胞內(nèi)病毒dsRNA激活了PKR，促進(jìn)了elF2α的磷酸化水平；而SGs的解聚則是由于elF2α的去磷酸化，這種變化是通過蛋白磷酸酶1 (PP1)和GADD34的作用[77]。還有報(bào)道稱，SGs的另一種成分DDX3可與HCV 3￠UTR和IKKα相結(jié)合，并激活I(lǐng)KKα，誘導(dǎo)LD產(chǎn)生基因表達(dá)[79]，從而達(dá)到抗病毒的作用。這些發(fā)現(xiàn)解釋了在HCV感染過程中SGs產(chǎn)生水平波動(dòng)的現(xiàn)象。寨卡病毒(Zika virus, ZIKV)作為近幾年的新發(fā)病毒廣受關(guān)注，ZIKV感染宿主細(xì)胞，可引起elF2α磷酸化水平的增高，整體翻譯水平的抑制，但并沒有明顯SGs聚集。病毒蛋白NS3和NS4A與細(xì)胞整體的翻譯抑制有關(guān)，而病毒capsid protein、NS3/NS2B-3和NS4A干擾SG的聚集，而G3BP1、TIAR、Caprin-1與ZIKV在宿主細(xì)胞內(nèi)的復(fù)制有關(guān)，且G3BP1與病毒基因組RNA和Capsid相互作用。這些表明ZIKV利用多種病毒組分來抑制SG的形成，從而促進(jìn)自身的復(fù)制[80]。另外一篇報(bào)道顯示，ZIKV可通過elF2α的去磷酸化來抑制亞砷酸鈉引起的SGs聚集；而對(duì)于亞硒酸鈉和PatA誘導(dǎo)的SGs沒有抑制作用[81]。

冠狀病毒家族是一類有包膜的病毒。已有報(bào)道顯示，鼠肝炎冠狀病毒(mouse hepatitis coronavirus, MHV)和豬傳染性胃腸炎病毒(transmissible gastro-enteritis virus, TGEV)引起TIA-1/TIAR的聚集和elF2α的磷酸化[82,83]。MHV在感染早期SGs的聚集，而TGEV則是感染的晚期引起SG聚集。在TGEV感染時(shí)，多聚嘧啶區(qū)結(jié)合蛋白(polypyrimidine tract-bind-ing protein, PTB)被重新分配于細(xì)胞質(zhì)中，與病毒的基因組RNA和亞基因組RNA共同聚集于包含有TIA-1/TIAR的聚集體中。中東呼吸綜合征(Middle East respiratory syndrome, MERS)病毒(MERS-CoV)可通過結(jié)合dsRNA，抑制PKR介導(dǎo)的elF2α的磷酸化來抑制SGs的形成，但缺乏4a和4b的MERS-CoV (MERS-CoV-Δp4)則可誘導(dǎo)SGs的生成[84]。

甲病毒屬的基孔肯雅病毒(Chikungunya virus, CHIKV)非結(jié)構(gòu)蛋白nsP3可同nsP1、dsRNA一起穩(wěn)定定位于包含有G3BP1/2的SGs內(nèi)，并靠近核膜和核孔蛋白Nup98，限制了病毒的復(fù)制[85]。

2.4 單股負(fù)鏈RNA病毒

正粘病毒科()家族為一類包含反向ssRNA基因組的包膜病毒。流感病毒A (in-fluenza A virus, IAV)通過表達(dá)非結(jié)構(gòu)蛋白NS1來抑制PKR的活性，進(jìn)而抑制SGs的聚集，如感染NS1缺失或突變的IAV，則可誘導(dǎo)形成SGs[86]。NS1介導(dǎo)的SGs的抑制作用，依賴于NS1于RNA相關(guān)蛋白55 (RNA associated protein 55, RAP55)的相互作用[87]。除了NS1、IAV的NP和PA-X都能通過非elF2α磷酸化依賴的方式來抵抗SGs的聚集[88]。此外，當(dāng)感染IAV后，DDX3可與NP相互作用，并調(diào)節(jié)IFN的產(chǎn)生及SGs的聚集；當(dāng)感染宿主的IAV缺失NS1，DDX3還能夠與產(chǎn)生的SGs共定位[89]；DDX6也可結(jié)合病毒RNA，促進(jìn)RIG-I介導(dǎo)的干擾素應(yīng)答反應(yīng)，起到抗病毒作用[90]。

水泡性口炎病毒(vesicular stomatitis virus, VSV)屬于彈狀病毒科()，感染宿主細(xì)胞可誘導(dǎo)elF2α磷酸化，并促進(jìn)SG樣顆粒形成聚集。這種SG樣顆粒包含TIA-1、TIAR、PCBP2、病毒復(fù)制蛋白和RNA，但缺少elF3和elF4A[91]。

副黏病毒科()家族由一類包膜病毒組成。呼吸道合胞體病毒(Respiratory syncytial virus, RSV)的感染可以引起PKR介導(dǎo)的SGs聚集，而這種變化又能夠促進(jìn)RSV的復(fù)制[92]。RSV感染人上皮細(xì)胞可產(chǎn)生一種細(xì)胞質(zhì)包涵體(cytoplasmic inclusion bodies, IBs)其中包含多種病毒蛋白，RSV利用這種結(jié)構(gòu)來調(diào)節(jié)病毒的復(fù)制[93]。這種IBs中包含了SGs的組成成分HuR、MDA5和MAVS，病毒通過這種方式，抑制了IFN的產(chǎn)生[94]。另有報(bào)道稱，RSV的感染可利用形成IBs隔離磷酸化的p38和O-linked N-acetylglucosamine transferase (OGT)，從而抑制了MAPK-activated protein kinase 2 (MK2)途徑，也就抑制亞砷酸鈉誘導(dǎo)的SGs聚集[95]。麻疹病毒(Measles virus, MeV)可通過病毒蛋白C和V來影響宿主的先天性免疫和適應(yīng)性免疫[96]。并且，當(dāng)?shù)鞍證缺失的MeV感染宿主細(xì)胞時(shí)，可誘導(dǎo)PKR依賴的SGs聚集，而野生型的MeV則不能。但是，野生型MeV感染ADAR1敲除細(xì)胞則可誘導(dǎo)SGs的產(chǎn)生[13]。仙臺(tái)病毒(sendai virus, SeV)感染可以引起輕微的SGs的聚集，而病毒3￠末端反向基因組RNA的轉(zhuǎn)錄產(chǎn)物，可與TIAR相互作用，而下調(diào)SGs的生成[97]。另外，還有研究報(bào)道仙臺(tái)病毒C蛋白在影響SGs聚集和IFN長生上有重要作用，當(dāng)用缺失C蛋白的SeV感染宿主細(xì)胞，會(huì)產(chǎn)生包含RIG-I和病毒RNA片段的SG樣結(jié)構(gòu)[98]。

布尼亞病毒家族由許多基因組為(-)ssRNA的包膜病毒組成。這類病毒的特點(diǎn)是需要一種“帽子”結(jié)構(gòu)來協(xié)助起始mRNA合成，這個(gè)“帽子”是從宿主mRNA上獲取來的。首先，病毒N蛋白與“帽子”結(jié)合，由RNA依賴的RNA聚合酶(RNA-dependent RNA polymerase, RdRp)的核酸內(nèi)切酶domain將宿主mRNA“帽子”切下，作為引物來進(jìn)行病毒mRNA的合成[99]。裂谷熱病毒(rift valley fever virus, RVFV)可下調(diào)Akt/mTOR信號(hào)途徑，從而增加4EBP1/2蛋白的活性來抑制翻譯過程，可引起短暫的SGs聚集，而這種SGs的聚集也可能為病毒獲取“帽子”結(jié)構(gòu)提供便利[100]。另外，布雅病毒家族病毒蛋白也像其他病毒一樣，進(jìn)化出了下調(diào)PKR活性和抑制IFN產(chǎn)生的機(jī)制。Hantaviruses和Phleboviruses中S片段的非結(jié)構(gòu)蛋白可抑制IFN反應(yīng)[101,102]；漢坦病毒(Andes Hantavirus, ANDV)的衣殼N蛋白可抑制PKR的二聚化，并影響其激活[103]。

另外，絲狀病毒科()家族的埃博拉病毒(Ebola viruse, EBOV)是一種包膜病毒，當(dāng)其感染宿主，SGs成分Staufen1可與病毒基因組RNA的3'和5'外顯子區(qū)域結(jié)合，并與結(jié)構(gòu)蛋白NP、VP30和VP35等產(chǎn)生結(jié)合作用，從而促進(jìn)病毒基因組RNA的合成[104]。

2.5 逆轉(zhuǎn)錄病毒

逆轉(zhuǎn)錄病毒都是含有正向ssRNA的包膜病毒，通過逆轉(zhuǎn)錄合成cDNA并整合到宿主基因組DNA上。人T細(xì)胞白血病病毒(human T-cell leukemia virus, HTLV-1)是一種致癌的反轉(zhuǎn)錄病毒，可通過病毒蛋白Tax與組蛋白脫乙酰酶6 (histone deacetylase 6, HDAC6)的相互作用抑制SGs的形成，HDAC6是SGs的組成成分[105]。另有報(bào)道稱，Tax可與USP10相互作用來抑制SGs的生成[106]。另外，人免疫缺陷病毒1 (human immunodeficiency virus type 1, HIV-1)感染宿主細(xì)胞可通過形成包含Staufen1的HIV-1依賴的核糖核蛋白(staufen1-containing HIV-1-depen-dent ribonucleoproteins, SHRNP )來明顯的抑制SGs的形成[107]。核定位信號(hào)(nuclear localization signal, NLS)突變的Sam68能夠誘導(dǎo)應(yīng)激顆粒的形成，在HIV-1感染過程中，Sam68 突變體特異的與HIV- 1nef mRNA發(fā)生相互作用，將nef mRNA募集到應(yīng)激顆粒中，抑制了nef蛋白表達(dá)，最終導(dǎo)致HIV-1復(fù)制受阻[108]。并且，HIV-1 Gag可通過非elF2α磷酸化依賴的方式來抑制SGs的聚集。HIV-1 capsid的N末端可通過與eEF2的相互作用來行使抵抗SGs形成的作用，若eEF2缺失，不僅SGs的形成受到抑制，HIV-1的在宿主細(xì)胞內(nèi)的產(chǎn)生及感染性也會(huì)受到影響；HIV-1 Gag也可與G3BP1相互作用，來干擾SGs的生成[109]，且G3BP1可與巨噬細(xì)胞內(nèi)HIV-1未剪切的mRNA (gRNA)形成相互作用，來抑制病毒的復(fù)制[110]。HIV-1 Gag對(duì)于不同類型刺激產(chǎn)生的SGs的作用機(jī)理是有差異的。亞硒酸鈉(Se)誘導(dǎo)宿主細(xì)胞可4EBP1介導(dǎo)產(chǎn)生的翻譯抑制，形成非經(jīng)典的SGs[28]。Cinti及其同事有報(bào)道顯示，當(dāng)HIV-1感染Se誘導(dǎo)的宿主細(xì)胞時(shí)，HIV-1 Gag可通過與elF4E相互作用，來降低4EBP1的去磷酸化，進(jìn)而促進(jìn)SGs的解聚[111]。另有最新報(bào)道表示，HIV-1 NC (nucleocapsid)蛋白過表達(dá)可引起細(xì)胞內(nèi)mRNA聚集進(jìn)而激活PKR，并與G3BP1和TIAR1的相互作用來誘導(dǎo)含有elF3的一型經(jīng)典的SGs，并不會(huì)被前文所述的Capsid蛋白以及Gag全長蛋白所解聚；而宿主因子Staufen 1可與NC產(chǎn)生相互作用，來調(diào)節(jié)PKR的反應(yīng)，抑制NC誘導(dǎo)的SGs的產(chǎn)生[112]。與HIV-1相反，HIV-2則通過gRNA招募TIAR來誘導(dǎo)SGs的生成[113]。

綜上所述，多種病毒在感染早期，可引起PKR的激活，進(jìn)而形成elF2α的磷酸化作用，如MRV、PV、HCV和MHV等；另外，RVFV也可通過下調(diào)Akt/mTOR通路，來引起SGs的快速聚集。而在病毒與宿主間千萬年的作用中，也進(jìn)化出了多種措施來調(diào)節(jié)這種翻譯抑制的限制作用，其中一些可與SGs核心成分相互作用，比較有代表性的包括HSV-1和WNV的RNA莖環(huán)結(jié)構(gòu)可與TIA-1相互做用；MRV、IIKV和HIV-1 Gag等多種病毒可結(jié)合G3BP1；VV與elF4G的相互結(jié)合；EBOV、HIV-1等與Staufen1的相互作用等都可引起SGs的解聚或抑制其聚集；另外，MERS和ANDV等還可通過抑制PKR二聚化的方式來影響SGs的聚集；PV和TMEV等則進(jìn)化出了切割G3BP1的酶活性來阻止SGs對(duì)病毒復(fù)制的限制作用。通過對(duì)多種病毒的研究，研究人員也發(fā)現(xiàn)，當(dāng)對(duì)病毒進(jìn)行適當(dāng)改造后，如vhs缺失的HSV-1，E3L缺失的VV等，則恢復(fù)了誘導(dǎo)SGs生成的特性，這些研究也為人們?nèi)蘸髴?yīng)對(duì)病毒感染提供了更多的提示和研究靶點(diǎn)。

3 應(yīng)激顆粒與抗病毒先天性免疫

許多研究都指出，病毒感染引起的SGs的形成與抗病毒先天性免疫存在著千絲萬縷的聯(lián)系。宿主抗壓力應(yīng)答的過程中，或多或少都會(huì)有先天性免疫相關(guān)蛋白成分的參與，有些蛋白成分還起到至關(guān)重要的作用。病毒感染誘導(dǎo)SGs與天然免疫概況如圖1所示。

PKR是一個(gè)典型的干擾素應(yīng)答蛋白分子，它能夠識(shí)別病毒的dsRNA及5'ppp RNA，感知細(xì)胞內(nèi)病毒核酸的存在情況，介導(dǎo)下游的干擾素反應(yīng)。與此同時(shí)，PKR的活化誘導(dǎo)了eIF2α的磷酸化，阻滯了細(xì)胞內(nèi)的翻譯進(jìn)程，引起應(yīng)激顆粒的產(chǎn)生。此外，PKR在細(xì)菌和雙鏈RNA病毒感染時(shí)，還可以激活炎性小體和巨噬細(xì)胞的應(yīng)答作用，引起細(xì)胞因子IL-1b和HMGB1的釋放[114]。在先天性免疫的轉(zhuǎn)錄應(yīng)答中，PKR也發(fā)揮著重要作用[115]。

胞質(zhì)內(nèi)的dsRNA及5′ppp-RNA還可被模式識(shí)別分子MDA5及RIG-I所識(shí)別，這些都是SGs的組成成分[116]。病毒RNA經(jīng)MDA5，RIG-I或LGP2識(shí)別后，將信號(hào)傳遞至線粒體外膜上的MAVS (mitochon-drial antiviral signaling protein)，而后將信號(hào)傳遞至IKK和TBK-1，導(dǎo)致轉(zhuǎn)錄因子NF-kB和IRF3的激活，從而導(dǎo)致抗病毒的IFN及其他炎癥因子的轉(zhuǎn)錄，而后激活I(lǐng)SGs表達(dá)，行使抗病毒免疫的功能。這表明，病毒誘導(dǎo)的SGs在細(xì)胞內(nèi)提供了一個(gè)模式識(shí)別分子的平臺(tái)，調(diào)控著下游信號(hào)的傳導(dǎo)[117]。

IFN的誘導(dǎo)表達(dá)在先天性免疫應(yīng)答中有著舉足輕重的地位，而由ISG編碼的誘導(dǎo)IFN信號(hào)途徑的相關(guān)蛋白，很多都被招募至SGs中，并調(diào)控著SG的形成，SGs也為宿主的抗病毒反應(yīng)搭建起了一個(gè)平臺(tái)[118]。除了上文提到的PKR、RIG-I和MDA5，還有經(jīng)IFN誘導(dǎo)產(chǎn)生的OASs，可識(shí)別dsRNA，而后催化ATP產(chǎn)生2-5A，從而激活SG組成成分RNase L對(duì)于dsRNA的降解。ADAR1也可被IFN誘導(dǎo)，并包含于SGs中，可將dsRNA的A轉(zhuǎn)化為I，從而改變病毒dsRNA，干擾病毒的復(fù)制[119]。

圖1 病毒感染誘導(dǎo)SGs形成及誘發(fā)先天性免疫反應(yīng)機(jī)制圖

病毒感染細(xì)胞后，病毒基因組RNA激活PKR，使elF2α磷酸化，抑制翻譯的起始，從而抑制了病毒蛋白質(zhì)的合成，也誘發(fā)SGs的形成。SGs的組成成分多樣，包含病毒RNA、RNA結(jié)合蛋白和翻譯起始因子等，尤其還包括許多先天性免疫模式識(shí)別分子(MDA5/ RIG-I/LDP2等)；這些模式識(shí)別分子可結(jié)合病毒RNA，進(jìn)而將信號(hào)傳遞至線粒體外膜上的MAVS，激活TBK1/IKK的磷酸化，從而使轉(zhuǎn)錄因子IRF3/7以及NF-κB入核，激活Ⅰ型干擾素和一些炎性因子的表達(dá)和分泌；干擾素經(jīng)自分泌或旁分泌與細(xì)胞膜干擾素受體結(jié)合后，激活胞內(nèi)的STAT1/2磷酸化，而后同IRF9一起入核，識(shí)別IRSE區(qū)域，激活表達(dá)多種ISGs，產(chǎn)生抗病毒作用。另外，OAS/RNase L也是SGs的組成成分，可切割病毒RNA，被切割后的病毒RNA也可被模式識(shí)別分子識(shí)別，進(jìn)一步活化抗病毒免疫通路。病毒也通過多種方式來拮抗這種抗病毒作用，如ANCV可抑制PKR的二聚化，HCV可通過PP1來去除eIF2α的磷酸化，PV/TMEV/ZIKV等可切割G3BP1，以及多種病毒可通過與SGs的成分結(jié)合的方式來拮抗SGs的形成。OAS: 2￠,5￠-oligoadenlate synthetase; IRSE: interferon stimulated respnonse element; IRF: interferon regulatory factor; RIG-I: retinoic acid inducible gene I; STAT: signal transducer and activator of transcription; IFNR: interferon receptor; IRF: interferon regulatory factor; ISG: interferon-stimulated gene; MDA5: melanoma differentiation-associated protein 5; NF-κB: nuclear factor kappa-light-chain-enhancer of activated B cells; TRIM25: tripartite motif-containing protein 25; TIA1: T cell restricted intracellular antigen-1; TIAR: TIA1-related protein；PABP: poly(A)-binding protein; G3BP1: Ras-GTPase-activating protein SH3-domain-binding protein 1.

綜上所述不難發(fā)現(xiàn)，細(xì)胞的壓力應(yīng)答，在各種方面都與先天性免疫有著千絲萬縷的聯(lián)系，而這其中的機(jī)制目前仍不甚明朗，有待于后期的研究來揭示細(xì)胞中各類先天性免疫信號(hào)通路與細(xì)胞壓力應(yīng)答之間的聯(lián)系及其在功能上的相互影響。

4 結(jié)語與展望

在病毒感染引起的細(xì)胞各類應(yīng)答反應(yīng)中，壓力應(yīng)答仍舊是一類相對(duì)較新的領(lǐng)域。雖然目前已經(jīng)有大量的關(guān)于各類病毒對(duì)應(yīng)激顆粒操縱的報(bào)道，但是目前人們對(duì)這其中分子水平作用機(jī)制仍然知之甚少。宿主感染病毒引發(fā)SGs生成，限制病毒的復(fù)制，而病毒在與宿主上萬年的博弈中，也進(jìn)化出來克制這種限制，甚至將其利用于自身復(fù)制的相關(guān)機(jī)制；人們在逐漸清楚了病毒通過SGs與宿主之間的相互作用關(guān)系的過程中，可揚(yáng)長避短的尋找抗病毒治療的異性藥物靶點(diǎn)為后期臨床應(yīng)用提供更多信息。

目前已知SGs在許多層面上都與先天性免疫相互關(guān)聯(lián)，因此，在對(duì)于應(yīng)激顆粒的研究中可能會(huì)發(fā)現(xiàn)一些在抗病毒治療中具有價(jià)值的廣譜的作用位點(diǎn)。由藥物誘發(fā)的，經(jīng)PKR或elF2α磷酸化生成的SGs，有望控制病毒感染。體外實(shí)驗(yàn)已經(jīng)證明，elF4A解旋酶抑制劑hippuristanol可抑制卡里色病毒(calici-viruses)[120]；pateamine A可抑制流感病毒A (influ-enza A virus)的復(fù)制[88]。不過，這些藥物對(duì)于未感染細(xì)胞的毒性影響限制了其發(fā)展。

在過去的十幾年中，相關(guān)研究多圍繞于病毒與SGs之間的相互影響，主要著重于其對(duì)于IFNs和ISGs的影響來確定SGs的抗病毒作用。而對(duì)于病毒引起的翻譯起始的抑制和隨后SGs的形成對(duì)于獲得性免疫的激活的影響幾乎還是空白。有意思的是，向樹突狀細(xì)胞中轉(zhuǎn)染poly (I:C)并不會(huì)引起整個(gè)細(xì)胞翻譯水平的下降，這與其他細(xì)胞有很大的區(qū)別[121]?？乖岢始?xì)胞或淋巴細(xì)胞這類免疫細(xì)胞與非免疫細(xì)胞在誘導(dǎo)和調(diào)控翻譯存在著什么不同？TIA1 (T cell-restricted intracellular antigen 1)是T細(xì)胞毒性顆粒的組成部分，也參與細(xì)胞凋亡的過程，這是不是暗示著SGs的形成與獲得性免疫通路有著某種聯(lián)系，許多未知還等待著人們?nèi)ヌ剿鳌?/p>

[1] Buchan JR, Parker R. Eukaryotic stress granules: the ins and out of translation.,2009, 36(6): 932–941.

[2] Kedersha NL. Gupta M, Li W, Miller I, Anderson P. RNA-binding proteins TIA-1 and TIAR link the phosphorylation of eIF-2α to the assembly of mammalian stress granules.,1999, 147(7): 1431–1442.

[3] Jackson RJ, Hellen CU, Pestova TV. The mechanism of eukaryotic translation initiation and principles of its regulation.,2010, 11(2): 113– 127.

[4] Anderson P, Kedersha N. Stressful initiations.,2002, 115(Pt 16): 3227–3234.

[5] Anderson P, Kedersha N. RNA granules.,2006, 172(6): 803–808.

[6] Hua Y, Zhou J. Modulation of SMN nuclear foci and cytoplasmic localization by its C-terminus.,2004, 61(19–20): 2658–2663.

[7] Thomas MG, Martinez Tosar LJ, Desbats MA, Leishman CC, Boccaccio GL. Mammalian staufen 1 is recruited to stress granules and impairs their assembly.,2009, 122(Pt 4): 563–573.

[8] Tourrière H, Chebli K, Zekri L, Courselaud B, Blanchard JM, Bertrand E, Tazi J. The RasGAP-associated endori-bonuclease G3BP assembles stress granules.,2003, 160(6): 823–831.

[9] Wilczynska A, Aigueperse C, Kress M, Dautry F, Weil D. The translational regulator CPEB1 provides a link between dcp1 bodies and stress granules.,2005, 118(Pt 5): 981–992.

[10] Yang F, Peng Y, Murray EL, Otsuka Y, Kedersha N, Schoenberg DR. Polysome-bound endonuclease PMR1 is targeted to stress granules via stress-specific binding to TIA-1.,2006, 26(23): 8803–8813.

[11] Chalupníková K, Lattmann S, Selak N, Iwamoto F, Fujiki Y, Nagamine Y. Recruitment of the RNA helicase RHAU to stress granules via a unique RNA-binding domain.,2008, 283(50): 35186–35198.

[12] Wippich F, Bodenmiller B, Trajkovska MG, Wanka S, Aebersold R, Pelkmans L. Dual specificity kinase DYRK3 couples stress granule condensation/dissolution to mTORC1 signaling.,2013, 152(4): 791–805.

[13] Okonski KM, Samuel CE. Stress granule formation induced by measles virus is protein kinase PKR dependent and impaired by RNA adenosine deaminase ADAR1.,2012, 87(2): 756–766.

[14] Onomoto K, Jogi M, Yoo JS, Narita R, Morimoto S, Takemura A, Sambhara S, Kawaguchi A, Osari S, Nagata K, Matsumiya T, Namiki H, Yoneyama M, Fujita T. Critical role of an antiviral stress granule containing RIG-I and PKR in viral detection and innate immunity.,2012, 7(8): e43031.

[15] McEwen E, Kedersha N, Song B, Scheuner D, Gilks N, Han A, Chen JJ, Anderson P, Kaufman RJ. Heme- regulated inhibitor kinase-mediated phosphorylation of eukaryotic translation initiation factor 2 inhibits translation, induces stress granule formation, and mediates survival upon arsenite exposure.,2005, 280(17): 16925–16933.

[16] Lu L, Han AP, Chen JJ. Translation initiation control by heme-regulated eukaryotic initiation factor 2alpha kinase in erythroid cells under cytoplasmic stresses.,2001, 21(23): 7971–7980.

[17] Sheree A. Wek SZ, Wek RC. The histidyl-tRNA synthetase-related sequence in the elf-2α protein kinase GCN2 interacts with tRNA and is required for activation in response to starvation for different amino acids., 1995, 15(8): 4497–4506.

[18] Jing D HPH, Brian R. Activation of GCN2 in UV-irradiated cells inhibits translation.,2002, 12(15): 1279–1286.

[19] García MA, Meurs EF, Esteban M. The dsRNA protein kinase PKR: virus and cell control.,2007, 89(6–7): 799–811.

[20] Harding HP, Zhang Y, Bertolotti A, Zeng H, Ron D. Perk is essential for translational regulation and cell survival during the unfolded protein response.,2000, 5(5): 897–904.

[21] Zoncu R, Efeyan A, Sabatini DM. MTOR: from growth signal integration to cancer, diabetes and ageing.,2011, 12(1): 21–35.

[22] von der Haar T, Gross JD, Wagner G, McCarthy JE. The mRNA cap-binding protein eIF4E in post-transcriptional gene expression.,2004, 11(6): 503–511.

[23] Panniers R. Translational control during heat shock.,1994, 76: 737–747.

[24] Thomas MG, Loschi M, Desbats MA, Boccaccio GL. RNA granules: the good, the bad and the ugly.,2011, 23(2): 324–334.

[25] Novoa I, Zhang Y, Zeng H, Jungreis R, Harding HP, Ron D. Stress-induced gene expression requires programmed recovery from translational repression.,2003, 22(5): 1180–1187.

[26] Dang Y, Kedersha N, Low WK, Romo D, Gorospe M, Kaufman R, Anderson P, Liu JO. Eukaryotic initiation factor 2alpha-independent pathway of stress granule induction by the natural product pateamine A.,2006, 281(43): 32870–32878.

[27] Mazroui R, Sukarieh R, Bordeleau ME, Kaufman RJ, Northcote P, Tanaka J, Gallouzi I, Pelletier J. Inhibition of ribosome recruitment induces stress granule formation independently of eukaryotic initiation factor 2alpha phosphorylation.,2006, 17(10): 4212– 4219.

[28] Fujimura K, Sasaki AT, Anderson P. Selenite targets eIF4E-binding protein-1 to inhibit translation initiation and induce the assembly of non-canonical stress granules.,2012, 40(16): 8099–8110.

[29] Emara MM, Fujimura K, Sciaranghella D, Ivanova V, Ivanov P, Anderson P. Hydrogen peroxide induces stress granule formation independent of eIF2α phosphorylation.,2012, 423(4): 763–769.

[30] Kwon S, Zhang Y, Matthias P. The deacetylase HDAC6 is a novel critical component of stress granules involved in the stress response.,2007, 21(24): 3381– 3394.

[31] Leung AK, Vyas S, Rood JE, Bhutkar A, Sharp PA, Chang P. Poly(ADP-ribose) regulates stress responses and microRNA activity in the cytoplasm.,2011, 42(4): 489–499.

[32] Ohn T, Kedersha N, Hickman T, Tisdale S, Anderson P. A functional RNAi screen links O-GlcNAc modification of ribosomal proteins to stress granule and processing body assembly.,2008, 10(10): 1224–1231.

[33] Tsai WC, Gayatri S, Reineke LC, Sbardella G, Bedford MT, Lloyd RE. Arginine demethylation of G3BP1 promotes stress granule assembly.,2016, 291(43): 22671–22685.

[34] Jayabalan AK, Sanchez A, Park RY, Yoon SP, Kang GY, Baek JH, Anderson P, Kee Y, Ohn T. NEDDylation promotes stress granule assembly.,2016, 7: 12125.

[35] Kedersha N, Ivanov P, Anderson P. Stress granules and cell signaling: more than just a passing phase?,2013, 38(10): 494–506.

[36] Boeynaems S, Alberti S, Fawzi NL, Mittag T, Polymenidou M, Rousseau F, Schymkowitz J, Shorter J, Wolozin B, Van Den Bosch L, Tompa P, Fuxreiter M. Protein phase separation: a new phase in cell biology., 2018, 28(6): 420–435.

[37] Takahara T, Maeda T. Transient sequestration of TORC1 into stress granules during heat stress., 2012, 47(2): 242–252.

[38] Buchan R, Kolaitis RM, Taylor JP, Parker R. Eukaryotic stress granules are cleared by autophagy and Cdc48VCP function., 2013, 153(7): 1461–1474.

[39] Chitiprolu M, Jagow C, Tremblay V, Bondy-Chorney E, Paris G, Savard A, Palidwor G, Barry FA, Zinman L, Keith J, Rogaeva E, Robertson J, Lavallée-Adam M, Woulfe J, Couture JF, C?té J, Gibbings D. A complex of C9ORF72 and p62 uses arginine methylation to eliminate stress granules by autophagy., 2018, 9(1): 2794.

[40] McInerney GM, Kedersha NL, Kaufman RJ, Anderson P, Liljestr?m P. Importance of eIF2alpha phosphorylation and stress granule assembly in alphavirus translation regulation.,2005, 16(8): 3753–3763.

[41] Sciortino MT, Parisi T, Siracusano G, Mastino A, Taddeo B, Roizman B. The virion host shutoff RNase plays a key role in blocking the activation of protein kinase R in cells infected with herpes simplex virus 1.,2013, 87(6): 3271–3276.

[42] Cassady KA, Gross M. The Herpes Simplex virus type 1 U(S)11 protein interacts with protein kinase R in infected cells and requires a 30-amino-acid sequence adjacent to a kinase substrate domain.,2002, 76(5): 2029–2035.

[43] He B, Gross M, Roizman B. The γ134.5 protein of herpes simplex virus 1 complexes with protein phosphatase 1α to dephosphorylate the α subunit of the eukaryotic translation initiation factor 2 and preclude the shutoff of protein synthesis by double-stranded RNA- activated protein kinase.,1996, 94(3): 843–848.

[44] Mulvey M, Arias C, Mohr I. Maintenance of endoplasmic reticulum (ER) homeostasis in herpes simplex virus type 1-infected cells through the association of a viral glycoprotein with PERK, a cellular ER stress sensor.,2007, 81(7): 3377–3390.

[45] Esclatine A, Taddeo B, Roizman B. Herpes simplex virus 1 induces cytoplasmic accumulation of TIA-1/TIAR and both synthesis and cytoplasmic accumulation of tristetraprolin, two cellular proteins that bind and destabilize AU-rich RNAs.,2004, 78(16): 8582– 8592.

[46] Dauber B, Poon D, Dos Santos T, Duguay BA, Mehta N, Saffran HA, Smiley JR. The herpes simplex virus virion host shutoff protein enhances translation of viral true late mRNAs independently of suppressing protein kinase R and stress granule formation.,2016, 90(13): 6049–6057.

[47] Burgess HM, Mohr I. Defining the role of stress granules in innate immune suppression by the herpes simplex virus 1 endoribonuclease VHS.,2018, 92(15): e00829–18.

[48] Finnen RL, Pangka KR, Banfield BW. Herpes simplex virus 2 infection impacts stress granule accumulation.,2012, 86(15): 8119–8130.

[49] Finnen RL, Hay TJ, Dauber B, Smiley JR, Banfield BW. The herpes simplex virus 2 virion-associated ribonuclease vhs interferes with stress granule formation.,2014, 88(21): 12727–12739.

[50] Katsafanas GC, Moss B. Vaccinia virus intermediate stage transcription is complemented by Ras-GTPase- activating protein SH3 domain-binding protein (G3BP) and cytoplasmic activation/proliferation-associated protein (p137) individually or as a heterodimer.,2004, 279(50): 52210–52217.

[51] Katsafanas GC, Moss B. Linkage of transcription and translation within cytoplasmic poxvirus DNA factories provides a mechanism to coordinate viral and usurp host functions.,2007, 2(4): 221–228.

[52] Zaborowska I, Kellner K, Henry M, Meleady P, Walsh D. Recruitment of host translation initiation factor eIF4G by the Vaccinia Virus ssDNA-binding protein I3.,2012, 425(1): 11–22.

[53] Walsh D, Arias C, Perez C, Halladin D, Escandon M, Ueda T, Watanabe-Fukunaga R, Fukunaga R, Mohr I. Eukaryotic translation initiation factor 4F architectural alterations accompany translation initiation factor redistribution in poxvirus-infected cells.,2008, 28(8): 2648–2658.

[54] Simpson-Holley M, Kedersha N, Dower K, Rubins KH, Anderson P, Hensley LE, Connor JH. Formation of antiviral cytoplasmic granules during orthopoxvirus infection.,2011, 85(4): 1581–1593.

[55] Montero H, Rojas M, Arias CF, López S. Rotavirus infection induces the phosphorylation of eIF2alpha but prevents the formation of stress granules.,2008, 82(3): 1496–1504.

[56] Rojas M, Arias CF, López S. Protein kinase R is responsible for the phosphorylation of eIF2α in rotavirus infection.,2010, 84(20): 10457–10466.

[57] Qin Q, Hastings C, Miller CL. Mammalian orthoreovirus particles induce and are recruited into stress granules at early times postinfection.,2009, 83(21): 11090– 11101.

[58] Qin Q, Carroll K, Hastings C, Miller CL. Mammalian orthoreovirus escape from host translational shutoff correlates with stress granule disruption and is independent of eIF2alpha phosphorylation and PKR.,2011, 85(17): 8798–8810.

[59] Carroll K, Hastings C, Miller CL. Amino acids 78 and 79 of mammalian orthoreovirus protein μN(yùn)S are necessary for stress granule localization, core proteinλ2 interaction, and de novo virus replication.,2014, 448: 133–145.

[60] Dougherty JD, Tsai WC, Lloyd RE. Multiple poliovirus proteins repress cytoplasmic RNA granules.,2015, 7(12): 6127–6140.

[61] White JP, Cardenas AM, Marissen WE, Lloyd RE. Inhibition of cytoplasmic mRNA stress granule formation by a viral proteinase.,2007, 2(5): 295–305.

[62] Piotrowska J, Hansen SJ, Park N, Jamka K, Sarnow P, Gustin KE. Stable formation of compositionally unique stress granules in virus-infected cells.,2010, 84(7): 3654–3665.

[63] Ng CS, Jogi M, Yoo JS, Onomoto K, Koike S, Iwasaki T, Yoneyama M, Kato H, Fujita T. Encephalomyocarditis virus disrupts stress granules, the critical platform for triggering antiviral innate immune responses.,2013, 87(17): 9511–9522.

[64] Fung G, Ng CS, Zhang J, Shi J, Wong J, Piesik P, Han L, Chu F, Jagdeo J, Jan E, Fujita T, Luo H. Production of a dominant-negative fragment due to G3BP1 cleavage contributes to the disruption of mitochondria-associated protective stress granules during CVB3 infection.,2013, 8(11): e79546.

[65] Borghese F, Michiels T. The leader protein of cardi-oviruses inhibits stress granule assembly.,2011, 85(18): 9614–9622.

[66] Reineke LC, Kedersha N, Langereis MA, van Kuppeveld FJ, Lloyd RE. Stress granules regulate double-stranded RNA-dependent protein kinase activation through a complex containing G3BP1 and Caprin1.,2015, 6(2): e02486.

[67] Visser LG, Medina GN, Rabouw HH, de Groot RG, Langereis MA, de los Santos T, van Kuppeveld FJM. Foot-and-Mouth disease leader protease cleaves G3BP1 and G3BP2 and inhibits stress granule formation.,2019, 93(2): e00922–18.

[68] Yang X, Hu Z, Fan S, Zhang Q, Zhong Y, Guo D, Qin Y, Chen M. Picornavirus 2A protease regulates stress granule formation to facilitate viral translation.,2018, 14(2): e1006901.

[69] Li W, Li Y, Kedersha N, Anderson P, Emara M, Swiderek KM, Moreno GT, Brinton MA. Cell proteins TIA-1 and TIAR interact with the 3' Stem-Loop of the West nile virus complementary minus-strand RNA and facilitate virus replication.,2002, 76(23): 11989– 12000.

[70] Courtney SC, Scherbik SV, Stockman BM, Brinton MA. West nile virus infections suppress early viral RNA synthesis and avoid inducing the cell stress granule response.,2012, 86(7): 3647–3657.

[71] Shives KD, Beatman EL, Chamanian M, O'Brien C, Hobson-Peters J, Beckham JD. West nile virus-induced activation of mammalian target of rapamycin complex 1 supports viral growth and viral protein expression.,2014, 88(16): 9458–9471.

[72] Xia J, Chen X, Xu F, Wang Y, Shi Y, Li Y, He J, Zhang P. Dengue virus infection induces formation of G3BP1 granules in human lung epithelial cells.,2015, 160(12): 2991–2999.

[73] Bidet K, Dadlani D, Garcia-Blanco MA. G3BP1, G3BP2 and CAPRIN1 are required for translation of interferon stimulated mRNAs and are targeted by a dengue virus non-coding RNA.,2014, 10(7): e1004242.

[74] Zhang HW, Meng XY, Li LF, Yang YY, Qiu HJ. Long non-coding RNAs: Emerging regulators of antiviral innate immune responses., 2018, 40(7): 525–533張華偉, 孟星宇, 李連峰, 楊玉瑩, 仇華吉. 長鏈非編碼RNA——抗病毒天然免疫應(yīng)答的新興調(diào)控因子. 遺傳, 2018, 40(7): 525–533.

[75] Albornoz A, Carletti T, Corazza G, Marcello A. The stress granule component TIA-1 binds tick-borne encephalitis virus RNA and is recruited to perinuclear sites of viral replication to inhibit viral translation.,2014, 88(12): 6611–6622.

[76] Katoh H, Okamoto T, Fukuhara T, Kambara H, Morita E, Mori Y, Kamitani W, Matsuura Y. Japanese encephalitis virus core protein inhibits stress granule formation through an interaction with Caprin-1 and facilitates viral propagation.,2013, 87(1): 489–502.

[77] Garaigorta U, Heim MH, Boyd B, Wieland S, Chisari FV. Hepatitis C virus (HCV) induces formation of stress granules whose proteins regulate HCV RNA replication and virus assembly and egress.,2012, 86(20): 11043–11056.

[78] Ruggieri A, Dazert E, Metz P, Hofmann S, Bergeest JP, Mazur J, Bankhead P, Hiet MS, Kallis S, Alvisi G, Samuel CE, Lohmann V, Kaderali L, Rohr K, Frese M, Stoecklin G, Bartenschlager R. Dynamic oscillation of translation and stress granule formation mark the cellular response to virus infection.,2012, 12(1): 71–85.

[79] Li Q, Pène V, Krishnamurthy S, Cha H, Liang TJ. Hepatitis C virus infection activates an innate pathway involving IKK-αin lipogenesis and viral assembly,,2013, 19(6): 722–729.

[80] Hou S, Kumar A, Xu Z, Airo AM, Stryapunina I, Wong CP, Branton W, Tchesnokov E, G?tte M, Power C, Hobman TC. Zika virus hijacks stress granule proteins and modulates the host stress response.,2017, 91(16): e00474–17.

[81] Amorim R, Temzi A, Griffin BD, Mouland AJ. Zika virus inhibits eIF2α-dependent stress granule assembly.,2017, 11(7): e0005775.

[82] Raaben M, Groot Koerkamp MJ, Rottier PJ, de Haan CA. Mouse hepatitis coronavirus replication induces host translational shutoff and mRNA decay, with concomitant formation of stress granules and processing bodies.,2007, 9(9): 2218–2229.

[83] Sola I, Galán C, Mateos-Gómez PA, Palacio L, Zú?iga S, Cruz JL, Almazán F, Enjuanes L. The polypyrimidine tract-binding protein affects coronavirus RNA accum-ulation levels and relocalizes viral RNAs to novel cytoplasmic domains different from replication-transcription sites.,2011, 85(10): 5136–5149.

[84] Nakagawa K, Narayanan K, Wada M, Makino S. Inhibition of stress granule formation by middle east respiratory syndrome coronavirus 4a accessory protein facilitates viral translation, leading to efficient virus replication.,2018, 92(20): e00902–18.

[85] Utt A, Das PK, Varjak M, Lulla V, Lulla A, Merits A. Mutations conferring a noncytotoxic phenotype on chikungunya virus replicons compromise enzymatic properties of nonstructural protein 2.,2014, 89(6): 3145–3162.

[86] Khaperskyy DA, Hatchette TF, McCormick C. Influenza a virus inhibits cytoplasmic stress granule formation.,2011, 26(4): 1629–1639.

[87] Mok BWY, Song W, Wang P, Tai H, Chen Y, Zheng M, Wen X, Lau SY, Wu WL, Matsumoto K, Yuen KY, Chen H. The NS1 protein of influenza a virus interacts with cellular processing bodies and stress granules through RNA-associated protein 55 (RAP55) during virus infection.,2012, 86(23): 12695–12707.

[88] Khaperskyy DA, Emara MM, Johnston BP, Anderson P, Hatchette TF, McCormick C. Influenza a virus host shutoff disables antiviral stress-induced translation arrest.,2014, 10(7): e1004217.

[89] Thulasi Raman SN, Liu G, Pyo HM, Cui YC, Xu F, Ayalew LE, Tikoo SK, Zhou Y. DDX3 Interacts with influenza a virus NS1 and NP proteins and exerts antiviral function through regulation of stress granule formation.,2016, 90(7): 3661–3675.

[90] Nú?ez RD, Budt M, Saenger S, Paki K, Arnold U, Sadewasser A, Wolff T. The RNA helicase DDX6 associates with RIG-I to augment induction of antiviral signaling.,2018, 19(7). DOI:10.3390/ ijms19071877.

[91] Dinh PX, Beura LK, Das PB, Panda D, Das A, Pattnaik AK. Induction of stress granule-like structures in vesicular stomatitis virus-infected cells.,2013, 87(1): 372–383.

[92] Lindquist ME, Mainou BA, Dermody TS, Crowe JE Jr. Activation of protein kinase R is required for induction of stress granules by respiratory syncytial virus but dispensable for viral replication.,2011, 413(1): 103–110.

[93] Lindquist ME, Lifland AW, Utley TJ, Santangelo PJ, Crowe JE Jr. Respiratory syncytial virus induces host RNA stress granules to facilitate viral replication.,2010, 84(23): 12274–12284.

[94] Lifland AW, Jung J, Alonas E, Zurla C, Crowe JE Jr, Santangelo PJ. Human respiratory syncytial virus nucleoprotein and inclusion bodies antagonize the innate immune response mediated by MDA5 and MAVS.,2012, 86(15): 8245–8258.

[95] Fricke J, Koo LY, Brown CR, Collins PL. P38 and OGT sequestration into viral inclusion bodies in cells infected with human respiratory syncytial virus suppresses MK2 activities and stress granule assembly.,2012, 87(3): 1333–1347.

[96] Randall RE, Goodbourn S. Interferons and viruses: an interplay between induction, signalling, antiviral responses and virus countermeasures.,2008, 89(Pt 1): 1–47.

[97] Iseni F, Garcin D, Nishio M, Kedersha N, Anderson P, Kolakofsky D. Sendai virus trailer RNA binds TIAR, a cellular protein involved in virus-induced apoptosis.,2002, 21(19): 5141–5150.

[98] Valiente-Echeverría F, Hermoso MA, Soto-Rifo R. RNA helicase DDX3: at the crossroad of viral replication and antiviral immunity.,2015, 25(5): 286– 299.

[99] Mir MA, Duran WA, Hjelle BL, Ye C, Panganiban AT. Storage of cellular 5′ mRNA caps in P bodies for viral cap-snatching.,2008, 105(49): 19294–19299.

[100] Hopkins KC, Tartell MA, Herrmann C, Hackett BA, Taschuk F, Panda D, Menghani SV, Sabin LR, Cherry S. Virus-induced translational arrest through 4EBP1/2- dependent decay of 5'-TOP mRNAs restricts viral infection.,2015, 112(22): E2920– E2929.

[101] Cimica V, Dalrymple NA, Roth E, Nasonov A, Mackow ER. An innate immunity-regulating virulence determinant is uniquely encoded by the Andes virus nucleocapsid protein.,2014, 5(1): e01088–13.

[102] Matthys VS, Cimica V, Dalrymple NA, Glennon NB, Bianco C, Mackow ER. Hantavirus GnT elements mediate TRAF3 binding and inhibit RIG-I/TBK1-directed beta interferon transcription by blocking IRF3 phosphorylation.,2014, 88(4): 2246–2259.

[103] Wang Z, Mir MA. Andes virus nucleocapsid protein interrupts protein kinase R dimerization to counteract host interference in viral protein synthesis.,2015, 89(3): 1628–1639.

[104] Fang J, Pietzsch C, Ramanathan P, Santos RI, Ilinykh PA, Garcia-Blanco MA, Bukreyev A, Bradrick SS. Staufen1 interacts with multiple components of the ebola virus ribonucleoprotein and enhances viral RNA synthesis.,2018, 9(5): e01771–18.

[105] Legros S, Boxus M, Gatot JS, Van Lint C, Kruys V, Kettmann R, Twizere JC, Dequiedt F. The HTLV-1 tax protein inhibits formation of stress granules by interacting with histone deacetylase 6.,2011, 30(38): 4050–4062.

[106] Takahashi M, Higuchi M, Makokha GN, Matsuki H, Yoshita M, Tanaka Y, Fujii M. HTLV-1 tax oncoprotein stimulates ROS production and apoptosis in T cells by interacting with USP10.,2013, 122(5): 715–725.

[107] Abrahamyan LG, Chatel-Chaix L, Ajamian L, Milev MP, Monette A, Clément JF, Song R, Lehmann M, DesGroseillers L, Laughrea M, Boccaccio G, Mouland AJ. Novel Staufen1 ribonucleoproteins prevent formation of stress granules but favour encapsidation of HIV-1 genomic RNA.,2010, 123(Pt 3): 369–383.

[108] Henao-Mejia J, Liu Y, Park IW, Zhang J, Sanford J, He JJ. Suppression of HIV-1 Nef translation by Sam68 mutant-induced stress granules and nef mRNA sequestration.,2009, 33(1): 87–96.

[109] Valiente-Echeverría F, Melnychuk L, Vyboh K, Ajamian L, Gallouzi IE, Bernard N, Mouland AJ. EEF2 and Ras- GAP SH3 domain-binding protein (G3BP1) modulate stress granule assembly during HIV-1 infection.,2014, 5: 4819.

[110] Jiménez VC, Martinez FO, Booiman T, van Dort KA, van de Klundert MAA, Gordon S, Geijtenbeek TB, Kootstra NA. G3BP1 restricts HIV-1 replication in macrophages and T-cells by sequestering viral RNA.,2015, 486: 94–104.

[111] Cinti A, Le Sage V, Ghanem M, Mouland AJ. HIV-1 gag blocks selenite-induced stress granule assembly by altering the mRNA Cap-Binding complex.,2016, 7(2): e00329.

[112] Rao S, Temzi A, Amorim R, You JC, Mouland AJ. HIV-1 NC-induced stress granule assembly and translation arrest are inhibited by the dsRNA binding protein Staufen1., 2018, 24(2): 219–236.

[113] Nelson EV, Schmidt KM, Deflubé LR, Do?anay S, Banadyga L, Olejnik J, Hume AJ, Ryabchikova E, Ebihara H, Kedersha N, Ha T, Mühlberger E. Ebola virus does not induce stress granule formation during infection and sequesters stress granule proteins within viral inclusions.,2016, 90(16): 7268–7284.

[114] Lu B, Nakamura T, Inouye K, Li J, Tang Y, Lundb?ck P, Valdes-Ferrer SI, Olofsson PS, Kalb T, Roth J, Zou Y, Erlandsson-Harris H, Yang H, Ting JP, Wang H, Andersson U, Antoine DJ, Chavan SS, Hotamisligil GS, Tracey KJ. Novel role of PKR in inflammasome activation and HMGB1 release.,2012, 488 (7413): 670–674.

[115] Taghavi N, Samuel CE. Protein kinase PKR catalytic activity is required for the PKR-dependent activation of mitogen-activated protein kinases and amplification of interferon beta induction following virus infection.,2012, 427(2): 208–216.

[116] Reikine S, Nguyen JB, Modis Y. Pattern recognition and signaling mechanisms of RIG-I and MDA5.,2014, 5: 342.

[117] Wu B, Hur S. How RIG-I like receptors activate MAVS.,2015, 12: 91–98.

[118] George CX, Ramaswami G, Li JB, Samuel CE. Editing of cellular self-RNAs by adenosine deaminase ADAR1 suppresses innate immune stress responses.,2016, 291(12): 6158–6168.

[119] Silverman RH. Viral encounters with 2￠,5￠-oligoadenylate synthetase and RNase L during the interferon antiviral response.,2007, 81(23): 12720–12729.

[120] Chaudhry Y, Nayak A, Bordeleau ME, Tanaka J, Pelletier J, Belsham GJ, Roberts LO, Goodfellow IG. Caliciviruses differ in their functional requirements for eIF4F components.,2006, 281(35): 25315– 25325.

[121] Clavarino G, Cláudio N, Dalet A, Terawaki S, Couderc T, Chasson L, Ceppi M, Schmidt EK, Wenger T, Lecuit M, Gatti E, Pierre P. Protein phosphatase 1 subunit Ppp1r15a/ GADD34 regulates cytokine production in polyinosinic: polycytidylic acid-stimulated dendritic cells.,2012, 109(8): 3006–3011.

Interaction between stress granules and viruses

Yu Huang, Siqi Hu, Fei Guo

Stress granule (SG) formation is a primary mechanism through which gene expression is rapidly modulated when the eukaryotic cells undergo cellular stresses (including heat shock, oxidative stress, starvation, viral infection). SGs have been proposed to affect mRNA translation and stability,as well as being linked to apoptosis and nuclear processes. Formation of SGs after viral infection result in blockade of viral protein synthesis and viral replication. Not surprisingly, viruses from diverse families have been found to modulate SG formation in infected cells by associating with important SG effector proteins. Here we provide a summary of the current understanding of the mechanism of SG formation, describe the current knowledge on viruses induce and/or modulate SGs in infected cells via phosphorylation of eIF2α, and regulation of SGs in virus systems. Further, we summarize recent progresses in understanding the relationship between viruses and stress granules in mammalian cells, and suggest that SG formation is an important aspect of the antiviral innate immune response.

stress granules; translation arrest; virus; innate immunity

2019-03-07;

2019-05-15

國家重點(diǎn)研發(fā)計(jì)劃項(xiàng)目(編號(hào)：2016YFD0500307FF09)資助[Supported by the National Key Plan for Scientific Research and Development of China (No. 2016YFD0500307FF09)]

黃羽，博士研究生，專業(yè)方向：病毒與宿主限制因子相互作用。E-mail: huangyu910730@163.com

郭斐，博士，研究員，研究方向：分子病毒學(xué)。E-mail: guoafei@ipbcams.ac.cn

10.16288/j.yczz.19-020

2019/5/17 10:48:01

URI: http://kns.cnki.net/kcms/detail/11.1913.R.20190517.1047.001.html

(責(zé)任編委: 張?zhí)煊?