哈獸研發現逆轉錄病毒拮抗HIV限制性因子的新機制

導 讀

近日，中國農業科學院哈爾濱獸醫研究所重要人獸共患病與烈性外來病研究團隊鄭永輝研究員在鼠白血病病毒附屬蛋白glycoGag拮抗艾滋病病毒宿主限制因子SERINC5的研究中取得新進展，相關研究成果以「Murine leukemia virus glycosylated Gag reduces murine SERINC5 protein expression at steady-state levels via endosome/lysosome pathway tocounteract the SERINC5 antiretroviral activity」為題，發表在病毒學專業期刊Journal of Virology上。

研究背景

絲氨酸整合蛋白5（SERINC5，Ser5）是最新發現的可以抑制逆轉錄病毒如艾滋病病毒（HIV-1）、鼠白血病病毒（MLV）等複製的天然免疫分子。MLV編碼的附屬蛋白glycoGag可以拮抗SERINC5對MLV和HIV感染性的限制作用。然而，涉及到的分子機制目前仍不清楚。

研究結果

研究發現單獨表達Ser5時，Ser5主要在細胞膜表面表達；在glycoGag和Ser5共表達的情況下，glycoGag在接頭蛋白複合物AP-2σ的幫助下將Ser5從細胞膜表面內化到細胞漿裡面，並通過早期內吞體、晚期內吞體及溶酶體降解泛素化的Ser5，進而拮抗Ser5的抗病毒活性。進一步研究發現P31、Y36、 L39以及 R63四個關鍵氨基酸位點在glycoGag降解Ser5的過程中發揮重要作用。除了Ser5之外，glycoGag也能降解SERINC家族的其他成員Ser1、Ser2、Ser3。這一研究結果表明glycoGag蛋白通過內體/溶酶體通路降解Ser5，並且這一作用在SERINC家族中高度保守。

鄭永輝研究員近年來致力於針對艾滋病病毒宿主與天然免疫分子之間的相互拮抗機制的研究，這是自該研究小組今年報道了HIV-1 Nef蛋白拮抗Ser5的分子機制以後，在天然免疫分子Ser5的研究中取得的又一突破性進展。

博士後李蘇楠、博士研究生Iqbal Ahmad為本文共同第一作者。

ABSTRACT

GlycosylatedGag(glycoGag) is an accessoryproteinexpressed by most gamma-retroviruses includingmurineleukemiavirus(MLV). MLV glycoGagnot only enhances MLV replication and disease progression but also increases human immunodeficiencyvirustype 1 (HIV-1) infectivity as Nef does. Recently,SERINC5(Ser5) was identified asthetarget for Nef, andtheglycoGagNef-likeactivityhas beenattributedtotheSer5 antagonism. Here, we investigated how glycoGagantagonizes Ser5 using MLV glycoMA andmurineSer5proteins. We confirm previous observations thatglycoMA re-localizes Ser5 from plasma membranetoperinuclear punctated compartments andtheimportant role of its YXXL motif in this process. We find thatglycoMA decreases Ser5expressionatsteady-statelevels, and identify two other glycoGagcrucial residues P31 and R63 fortheSer5 downregulation.TheglycoMA and Ser5 interaction is detected in live cells using a bimolecular fluorescence complementation (BiFC) assay. Ser5 is internalizedviareceptor-mediated endocytosis, and re-localizedtoRab5 early, Rab7 late, and Rab11 recycling endosomes by glycoMA. Although glycoMA is not polyubiquitinated,theSer5 downregulation requires Ser5 polyubiquitinationviatheK48- and K63-linkage, resulting in Ser5 destruction in lysosomes. Although P31, Y36, L39, and R63 are not required for glycoMA interaction with Ser5,they are required for Ser5 re-localizationtolysosomes for destruction. In addition, althoughmurineSer1, Ser2, and Ser3 exhibit very poor antiviralactivity,they are also targeted by glycoMA for lysosomal destruction. We conclude thatglycoGaghas a broadactivitytodownregulate SERINCproteinsviathecellularendosome/lysosomepathway, which promotes viral replication. MLV glycoGagnot only enhances MLV replication but also increases HIV-1 infectivity similarly as Nef. Recent studies have discovered thatboth glycoGagand Nef antagonize a novel host restriction factor Ser5 and promote viral replication. ComparedtoNef,theglycoGagantagonism of Ser5 is still poorly understood. MLV glycoGagis a transmembrane version ofthestructuralGagproteinwith an extra 88-amino-acid leader region thatdetermines itsactivity. We now show thatglycoGaginteracts with Ser5 in live cells, and internalizes Ser5viareceptor-mediated endocytosis. Ser5 is polyubiquitinated and re-localizedtoendosomes and lysosomes for massive destruction. In additiontothepreviously identified tyrosine-based sorting signal, we find two more important residues for Ser5 re-localization and downregulation. We also find thattheSer5-sensitivitytoglycoGagis conserved in SERINC family.Together, our findings highlighttheimportant role ofendosome/lysosomepathwayintheenhancement of viral replication by viralproteins.

1.Murine leukemiavirus glycosylated Gag reduces murine SERINC5 protein expression atsteady-state levels via endosome/lysosome pathway to counteract the SERINC5antiretroviral activity.J. Virol. 2018 Oct 24; DOI：10.1128/JVI.01651-18

2.哈獸研官網：哈獸研發現逆轉錄病毒拮抗HIV限制性因子的新機制

本期編輯：Annabella

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